Technical development of
common anesthesiology techniques
Ruben A. Lee
Technical development of common anesthesiology techniques
Neuraxial anesthesia & laryngoscopy for
endotracheal intubation
Technical development of
common anesthesiology techniques
Neuraxial anesthesia & laryngoscopy for
endotracheal intubation
Technical development of
common anesthesiology techniques
Neuraxial anesthesia & laryngoscopy for
endotracheal intubation
Proefschrift
ter verkrijging van de graad van doctor aan de Technische Universiteit Delft,
op gezag van de Rector Magnificus prof. ir. K.C.A.M. Luyben, voorzitter van het College voor Promoties,
in het openbaar te verdedigen op woensdag 11 september 2013 om 12.30 uur, door
Ruben Armstrong LEE
Bachelor of Engineering with First Class Honors and Bachelor of Commerce, both from the University of Canterbury, Christchurch, New Zealand.
Dit proefschrift is goedgekeurd door de promotoren:
Prof. dr. ir. P.A. Wieringa Prof. dr. A.A.J. van Zundert
Samenstelling promotiecommissie:
Rector Magnificus Voorzitter
Prof. dr. ir. P.A. Wieringa (Promotor) Technische Universiteit Delft
Prof. dr. A.A.J. van Zundert (Promotor) Universiteit van Maastricht, Universiteit van
Ghent (België) and University of Queensland
(Australia)
Prof. dr. ir. P. Breedveld Technische Universiteit Delft
Prof. dr. S.P. Gatt University of New South Wales (Australia)
Prof. dr. ir. R.H.M. Goossens Technische Universiteit Delft
Prof. dr. M.A.E. Marcus Universiteit van Maastricht
Prof. dr. R.-J. Stolker Erasmus Universiteit
Prof. dr. J. Dankelman (Reserve) Technische Universiteit Delft
Colofon
Design and layout:
Rachel van Esschoten (www.divingduck.nl) Cover artwork:
Yves Brandsma
‘Jacob Kevorkian’, 2012 – oil on canvas, 58 x 53 cm Cover design:
Rachel van Esschoten Cover photography:
Colin Hill (www.colinhillimagery.com) Printing:
Wöhrmann Print Service (www.cpibooks.com/nl) ISBN:
978-94-6203-391-7
All rights reserved. No part of this publication may be reproduced, translated, stored in a retrieval system of any nature, or transmitted, in any form or by any means, electronically, mechanically, by photocopying, microfilming, recording, or otherwise, without the prior written permission from the author. August, 2013
Contents
Chapter 1 Introduction . . . .6
Chapter 2 Thoracic combined spinal-epidural anesthesia . . . .24
Chapter 3 The anatomy of the thoracic spinal canal investigated with magnetic resonance imaging (MRI). . . .48
Chapter 4 The anatomy of the thoracic spinal canal in different postures. . . .58
Chapter 5 Technical review of epidural needle insertion training simulators. . . .72
Chapter 6 Evaluation of the Mediseus® Epidural Simulator. . . .88
Chapter 7 Factors affecting simulated epidural needle insertion. . . .104
Chapter 8 In vivo force measurement and task analysis during epidural needle insertion. . . .124
Chapter 9 Forces applied to the maxillary incisors during video-assisted intubation . . . .140
Chapter 10 Forces applied to the maxillary incisors by video-laryngoscopes and the Macintosh laryngoscope . . . .154
Chapter 11 Stylet use in patients with normal airways during video- laryngoscopy . . . .166
Chapter 12 Comparison of three video-laryngoscopes. . . .184
Chapter 13 Conclusion . . . .198
Chapter 1
1.1
Summary
Modern anesthesia forms a cornerstone of medical practice, supporting virtually all medical specializations and the clinicians forming an integral component of each operating room medical team. The domain of anesthesia is broad, including intensive care, perioperative care, emergency and trauma medicine, pain, and gene-ral and regional anesthesia for diagnostic and therapeutic procedures, of which a large amount of diverse surgery, orthopedics, and obstetrics and gynecology. Ever increasing technological advancement and research in medicine necessitates greater specialization in all medical fields. However, the anesthesiologist remains somewhat of a generalist. While the required skill-set for (resident) anesthesiologists continues to expand, there remain some basic techniques that are continually practiced and applied.
Laryngoscopy for intubation (during general anesthesia) and neuraxial anesthesia (often for obstetrics, surgery of the lower extremities and postoperative thoracic and abdominal pain relief) are some of the most ubiquitous of anesthesia techniques, carried out thousands of times every day around the world. The tech-niques are both basic components of the anesthesiology tool set, yet there are no universal guidelines for carrying them out and unclear performance metrics by which to judge the anesthesiologist’s competency with the techniques.
At first glance, both laryngoscopy and neuraxial techniques seem relatively basic and straightforward procedures. The sequelae of either incorrect neuraxial an-esthesia or laryngoscopy are usually not very serious. However, there are persistent problems for both techniques, even for experienced anesthesiologists, and occasional errors can have very serious consequences – for example, neurological damage fol-lowing neuraxial anesthesia and failure to intubate a patient in an emergency situation that can result in death during laryngoscopy. Considering the ubiquity of the techni-ques, even small advances, either in training or instrumentation, may have significant merit – which is the key motivation for this thesis.
There have been comparatively many technological advances in other as-pects of anesthesiology; and in that sense both laryngoscopy and neuraxial anes-thesia are somewhat neglected techniques, with relatively minor modification of the tools or training since the techniques’ respective inception. Furthermore, it remains unclear what bottlenecks remain in the techniques and how the persistent error in-cidence may be overcome. Clearly, all anesthesiologists are, and will remain, fallible – but improved training and instrumentation may help improve patient safety.
Both laryngoscopy and neuraxial anesthesia techniques rely significantly on the haptic (pertaining to the tactile and kinesthetic) senses. Laryngoscopy also has an (increasingly) important visual component that is used in successfully intubating 8
the patient. These characteristics are shared by many fellow medial fields, in which haptic research has resulted in improved training, advanced instruments and new procedures.
This chapter firstly presents background information around develop-ments in neuraxial anesthesia and fellow percutaneous therapies. Secondly, there is a description of developments in laryngoscopy. Finally, the problem and objectives of the thesis, and approach to the respective cases (neuraxial anesthesia and laryngo-scopy) are described.
1.2
Developments in percutaneous therapy
Percutaneous therapies, or more simply therapies performed through the skin, are some of the most practiced in modern medicine. Needles fulfill the demand for de-livery of both solids and fluids to and from the body, for applications as diverse as biopsy, brachytherapy and insulin injection. The advantages are obvious, relative mi-nor trauma and general simplicity of administration to areas of the body otherwise inaccessible without surgery.
The cannulated needle is a basic instrument in any modern medical kit. There has been considerable technological innovation around quality control in needle production, reduction in needle diameters, and modification of the needle-point. However, a key bottleneck to the development of new percutaneous applica-tions and improvement of existing therapies is the administering clinician’s profici-ency in handling the needle. The demanded dexterity for percutaneous procedures is evident in the long learning trajectories and persistent failures, even by experienced clinical personnel.
1.2.1 Developments in spinal and epidural anesthesia
Neuraxial anesthesia, including spinal (the bolus delivery of local anesthetic solu-tion into the cerebrospinal fluid, generally below the terminasolu-tion of the spinal cord) and epidural (most commonly introduction of a catheter into the epidural space for intra- and post-operative pain relief) anesthesia are some of the best recognized and ubiquitous of regional anesthesia techniques. The incidence of complications associated with neuraxial anesthesia is low but persistent.1-7 Complications include
post-dural puncture headache (PDPH), trauma to spinal blood vessels and neural tissue, incorrect delivery site of the anesthetic (with subsequently toxic reactions or unexpected levels of (sensory) neural blockade), and neurological complications.
9 Introduction
PDPH is the most commonly occurring complication of neuraxial anes-thesia. For spinal anesthesia this has been addressed with the development of finer needles and refined tip geometries for spinal needles.8 Clinically, a trade-off is often
made between gauge of the spinal needle and tip geometry. Finer needles are bene-ficial to patient recovery;9 but are often more difficult to use, with often higher
com-plication and failure rates.10 Similarly, needles with a pencil-pointed (e.g. Whitacre,
Spottre) tip offer better recovery,11 and puncture of the dura (‘spinal-click’) is more
readily felt.12 However, some anesthesiologists find the insertion more difficult and
many still prefer a cutting tip (e.g. Quincke) design.13
Epidural anesthesia is commonly administered at all levels from cervical to sacral. The most common administration methods are the ‘loss-of-resistance’ (to air or saline solution) and ‘hanging-drop’. The loss-of-resistance technique makes use of lower tissue densities in the epidural space to inject a fluid, at once halting the needle advance and identifying the epidural location. ‘Hanging-drop’ techniques methods utilize (transient14) negative pressure gradients upon breach of the flavum. Almost
all techniques developed for epidural detection work on these two principles.1 There
are a wide variety of needle tip geometries, handle designs and locking mechanisms, stylets and catheter designs (also for spinal catheters) available for epidural adminis-tration.
An increasingly popular technique in neuraxial anesthesia is combined spinal-epidural (CSE) anesthesia.3 CSE anesthesia offers the superior block
charac-teristics of a spinal bolus, with the flexibility and post-operative performance of an epidural catheter.3 CSE anesthesia can be administered with both single segment
(SST) and double segment (DST) techniques. The DST is essentially the sequential administration of epidural catheter, followed by spinal injection. The SST options employ needle-through-needle delivery of the spinal bolus. Various options exist for the epidural tip design to facilitate spinal needle insertion (e.g. the BBraun®
Espo-can™ incorporates a separate ‘back-eye’ opening for the spinal needle – while most CSE systems have a curved Tuohy tip through which the epidural catheter and the spinal needle both pass).
Research has indicated that material choice affects outcome (e.g. catheter nozzle design influences epidural sensory neural blockade15,16), but there are no
una-nimously preferred combinations for given patient and surgical characteristics. Perso-nal preferences of the administering clinician dominate both the material choice and administration technique in neuraxial anesthesia. This section only glances across the subtleties of the various techniques and intricacies of the research and design effort. Despite this brevity, it should be noted that there are shortcomings to the techniques (e.g. fallible information of epidural placement) and apparatus (e.g. deflection of a needle from the intended insertion path).
10 Chapter 1
1.2.2 Developments in fellow percutaneous therapies
There are overlaps in the requirements for most needle therapies. The most obvi-ous requirement is accurate guidance of the needle to the intended location for the therapy. For anesthesia, this is towards the nerve or blood vessel, in biopsy to the lo-cation of the tumor. Secondly, percutaneous therapies are often performed without imaging or other stimuli, so rely largely on the tactile perception of the clinician to correctly identify landmark anatomical structures (i.e. puncture of blood vessel wall in venal injections, loss of resistance for epidural). There are three major research fields for the improvement of percutaneous therapies that are directly applicable to this thesis: 1) haptics; 2) training simulators; and, 3) tissue mechanics and device development. This section briefly describes the research in these disciplines and ap-plication to neuraxial anesthesia.
Figure 1.1: Spinal needle (top), epidural needle (middle) and spinal needle inserted through canula of epidural needle (bottom). CSEcure® Combined Spinal Epidural System,
Portex™ (reproduced with courtesy of Smiths Medical, Ashford, Kent, United King-dom)
11 Introduction
1.2.3 Haptics devices
Haptic teleoperators (whereby the forces of the remote manipulator are communi-cated to the operator of the master device) are used in a variety of applications (e.g. nuclear industry, deep-sea robotics, ‘drive-by-wire systems’ for aircraft and cars).17,18
It has been shown that haptic feedback to the operator can improve the task perfor-mance in certain teleoperation tasks (e.g. tissue identification).19 Operator perception
of teleoperation is similar to the concept of extended physiological proprioception developed for prostheses in some tasks.20
It is often suggested that haptic feedback would help to improve patient safety and to reduce the clinician’s mental workload.21,22 However, it is still unknown
how good this feedback must be to actually help the operator. By using information about the human sensor system, it could be possible to reformulate the requirements for the teleoperator, especially for the master device, to allow better information transfer to the operator.23-26 For example, for many stimuli we cannot distinguish
dif-ferences below 10 percent of the current stimulus level (sometimes called the Weber fraction).27
In performing needle insertion tasks, the haptic perception of the inter-action of the needle with the patient’s tissues, and a cognitive model of the proce-dure are paramount. Yet it is known that human haptic perception is limited, human cognitive processing fallible, and there exists a lower bound to the needle sizes and associated contact forces perceivable - this limits what is accomplishable without supporting the haptic information available during the procedure. It is possible to measure forces and deformations far more accurately than our hands can register.
There have been numerous attempts to develop haptic equipped devices for the training of percutaneous therapy, including devices for catheter insertion, lumbar puncture, and laparoscopic surgeries.28-30 There has been limited
develop-ment towards force and friction models employed in real-time robotically assisted procedures.31 Of the limited devices that use reality-based modeling, there is a
hand-held device used for the determination of tissue type in lumbar puncture for epidural blockade.32 There has also been published in vivo testing of an instrument for
bra-chytherapy of canine cadavers.33
1.2.4 Training simulators
Traditionally, training in anesthesia, similar to other operating room specializations, has followed the apprenticeship model whereby young anesthesiologists are trained on actual patients under the careful supervision of an experienced anesthesiologist. However, the costs and ethical questionability of current training has resulted in a groundswell for improvement through simulation in fellow medical fields (e.g. la-12
paroscopic surgery)34-37. Additionally, the time available for training of residents is
increasingly limited.38
In anesthesiology, the ‘learning-curve’ is usually defined as the decline in necessary time for a given procedure and errors made in performing the procedure. Simulators, it is proposed, can improve the efficacy of training schemes with better task-orientation, objective performance metrics, and better instructional feedback enabling unambiguous assessment of progress, competencies and shortcomings of the trainee.30,39 Drawing parallels with the airline industry with its reputation for
safe-ty and lifetime learning, virtual realisafe-ty (VR) simulation for anesthesiology has gained increasing popularity. VR simulators are widely tested and validated for common anesthesiology techniques (e.g. general anesthesia, laryngoscopy). There are also a number of commercially available training simulators for epidural simulation.
To ensure effective use in training curricula the design, tasks and per-formance metrics used by these trainers have to be evaluated. Furthermore, this research might offer insight into improvement of next generation simulators, and possibly even the difficulties of the actual procedure.
1.2.5 Tissue mechanics and device development
The complexity of tissue fracture in puncture (as with a needle) makes instrument optimization for a given therapy challenging. For example, the initial premise that pencil-pointed spinal needles were less traumatic is incorrect, although some studies have shown it reduces morbidity from PDPH.8,40-42 Research on needle-tissue
me-chanics is leading to novel therapies such as needle-less designs.43,44 There has been
research into the distribution of forces acting on the needle in vivo on bovine liver and canine prostate.33,45 Recently a model was also presented for the viscoelastic
na-ture of the dura mater.46 Validation of such models, either for instrument design or
simulation, remains a bottleneck. Ideally, model validation should be done in vivo,47
however this brings the additional complexity that estimations made for any given real tissue are intractable,48 given the variability between patients and inhomogeneity
of the tissue itself. As such, the use of phantom materials has been popular.49
The physiological variation between patients makes qualification of tissue boundaries impossible by considering absolute values of penetration force. There has been development of devices that use force transients in puncture for identi-fication of tissue boundaries.32 The same authors also integrate laser spectroscopy
techniques for the differentiation of tissue boundaries in the needle tip. Unfortuna-tely, this has the drawback that connective tissue between tissue layers shows rapid degradation. For neuraxial anesthesia the most common physiological phenomenon used for identification is the low density of the epidural fat.50,51 There is a
commer-13 Introduction
cially available device that translates the measured pressures in the syringe barrel to acoustic signals.52-54 This device has now been tested in a multicenter trial. Other
devices for neuraxial anesthesia have used electrical resistance as means of differen-tiating between the tissue layers.55
1.3
Developments in laryngoscopy
The advent of general anesthesia for surgery necessitated development of artificial respiration and airway management techniques for patients. In the 20th century, the
safety and efficacy of general anesthesia was greatly improved through the routine use of endotracheal intubation and other advanced airway management techniques. In 1913, Jackson was the first to report a high rate of success for using direct laryn-goscopy to intubate the trachea.56 He also introduced the first laryngoscope design
with light source at the distal tip and design for passage of an endotracheal tube.57
Also in 1913, Janeway introduced a laryngoscope with a slight curve to the distal end of the blade to better guide the endotracheal tube through the glottis.58 The success
of this blade design let to its subsequent use in other surgeries and popularized di-rect laryngoscopy and tracheal intubation in the practice of anesthesiology. In 1943, Macintosh introduced his curved laryngoscopy blade, which remains the most widely used blade design for orotracheal intubation.59
Presently, general anesthesia is of course administered daily in hospitals around the world for a variety of surgical interventions and is a cornerstone of mo-dern medical practice (in the UK alone there are approximately three million general anesthetics administered every year).60 The art and science of airway management
thus holds a prominent position in anesthesiology practice and research. Airway ma-nagement can be generally defined as prevention and treatment of hypoxia of the patient.61
The laryngoscope is essentially a curved blade with handle that the anes-thesiologist can use to manipulate the tongue and other soft-tissues of the mouth and palate to facilitate a direct view of the larynx and glottic arch. The respiratory endotracheal tube would then be introduced through the mouth and correctly positi-oned by the anesthesiologist using their direct view of the tube insertion.
Unfortunately, it is not always easy to gain such a direct view of the rele-vant anatomy and the procedure was often performed ‘blind’ as such.62 There are a
number of reasons for difficultly in ascertaining a direct view of the relevant ana-tomy including trauma to the patient, limited mobility of the mouth opening or neck, irregular anatomy of the mouth and larynx, tumor, or, most commonly amongst modern patient populations, obesity.63 The incidence of difficult intubation where
there is only partial or no direct view of the glottic arch is between 1-4%.64 14
There is a small but persistent risk of patient death or severe brain da-mage during anesthetic induction.65 Due to the severity of the threat from hypoxia, a
tracheotomy may be performed to secure the patient’s airway (i.e. a surgical incision made through the anterior neck of the patient to the trachea; may also be perfor-med percutaneously). This carries with it significant morbidity for the patient with longer recovery times, pain and scarring. Therefore, even where absolute impact of developments in airway management techniques may be modest, the sheer number of patients receiving anesthesia will mean there is a huge potential increase in patient safety.66
The clear and present danger to the patient of failure to quickly and easily intubate has driven science and clinical research in difficult airway management. This has led to the development of a variety of adjuncts and tools for helping attain cor-rect placement of the endotracheal tube, as well as clinical protocol for the identifica-tion of patients with potentially difficult airways and methodologies for successfully managing the difficult airway. The tools and adjuncts include stylets, gum elastic bougie and fiber optic devices. The concept of using a fiber optic endoscope for tracheal intubation was introduced by Murphy in 1967.67 By the mid-80’s the flexible
fiber optic scope was a common addition to difficult airway management trolleys for anesthesiology departments. The fiber optic scope provides the anesthesiologist with an indirect view of the larynx usually superior to the direct view. However, this indirect view complicates the dexterous task of inserting the endotracheal tube.
Recently, there has been a significant paradigm shift for laryngoscope de-sign with the development of the video-laryngoscope.68-70 These devices
approxi-mately retain the traditional shape of classic laryngoscopes, but include optics at the distal end of the blade to provide a closer view of the relevant anatomy. Usually, this means that the anesthesiologist performs the intubation using the direct line of sight augmented by the indirect view from the optics in the blade tip. In more difficult cases, the indirect view is sufficient to perform the intubation in itself. This has significant advantages for successfully performing intubation and mitigating the incidence of ‘difficult’ or failed intubation.71
Despite the many new devices that enter the market for airway manage-ment every year there are no requiremanage-ments on manufacturers to prove clinical ef-ficacy before marketing.72-74 It is similarly unclear what exactly the metrics are for
determining clinical efficacy of medical devices. For video-laryngoscope designs this is certainly true. Because the incidence of a difficult airway or failed intubation is relatively rare, large numbers of patients need to be enrolled in trials. Additionally, it is highly desirable to investigate the performance of devices in the most challenging of patient groups and to use objective metrics for considering the ease of use of the devices.
15 Introduction
1.4
Problem statement and objectives
Laryngoscopy, for endotracheal intubation, and neuraxial anesthesia are frequently used techniques in anesthesiology. Although the rate and seriousness of sequelae from error are both relatively low, there are persistent problems associated with both techniques. Furthermore, the learning trajectories are relatively long (especially for advanced neuraxial techniques), and there is no consensus on techniques or materi-als.
For neuraxial anesthesia, the main bottlenecks are poorly understood for reducing the complication rate and required training time. It has been clinically shown that there can be novel application of the CSE technique at thoracic level. Besides understanding the cause of errors for standard neuraxial techniques, there must be better information on the patient anatomy for practice of this technique.
Laryngoscopy, for endotracheal intubation, has undergone a minor re-volution in recent years with the production of video-laryngoscopes that integrate optics in the distal tip for improved viewing of the glottic arch. It remains to be fully qualified what the benefits are of VLS compared to classic direct laryngoscopy. Ad-ditionally, the comparative merit of the various VLSs has not been determined.
There are essentially three main objectives of the first part of this thesis: • Evaluation of thoracic CSE anesthesia and description of relevant
thora-cic spinal anatomy for neuraxial anesthesia
• Qualification of the training ability of existing VR simulators for epidural anesthesia
• Determination of the bottlenecks for application of epidural anesthesia For the second part of the thesis the objective is the following:
• Quantify the clinical performance of common commercial video-laryngo-scopes for endotracheal intubation
1.5
Approach
This thesis examines laryngoscopy and neuraxial anesthesia techniques from somew-hat different perspectives. Part I on neuraxial anesthesia takes a broad perspective in examining the potential for new applications of the technique particularly at thoracic levels, possibilities for improved training of the procedure and current limitations that can result in clinical errors. Part II on laryngoscopy is a comprehensive study of the performance of new video-assisted laryngoscopes in different patient popu-lations.
16 Chapter 1
1.5.1 Part I – Developing thoracic combined spinal-epidural anesthesia
Part I begins with a description of a new application of neuraxial anesthesia in de-livering combined spinal-epidural anesthesia at thoracic level. This technique may prove advantageous for difficult patients, which could otherwise not be operated un-der general anesthesia, due to the ability to create a deep and highly specific blockade with good flexibility. Additionally, the technique may have hemodynamic advanta-ges since the lower extremities experience no venal dilation. Chapter 2 details the relevant anatomy of neuraxial anesthesia and current understanding of combined spinal-epidural techniques, besides presenting first results of the technique applied at thoracic levels.
In Chapters 3 and 4 we consider the patient anatomy in two studies that investigate the relative position of the anatomical structures of the thoracic spine. The patient anatomy may provide possibilities for new applications of neuraxial techniques, such as thoracic application of spinal anesthesia. Additionally, the study in Chapter 4 provides information on the relative displacement of the structures of the spinal canal in different patient postures.
Chapter 5 focuses on existing training simulators for the epidural techni-que. The features of the devices are reviewed, as well as evidence of their respec-tive training efficacy. By considering the actual procedure we derive some boundary conditions necessary for simulation of the procedure, and make recommendations regarding the specification of hardware for new simulators. Chapter 6 is a validation study of the training ability of the Mediseus® Epidural Simulator. The validation
study considers the content, face and construct validation of the simulator purely for the dexterous epidural needle insertion task.
Chapter 7 examines subject performance in a simulated epidural needle insertion task, similar to the validation of the Mediseus® Simulator. The custom-built
simulator used for the study in Chapter 7 provides additional information on the task being performed by the subjects and quantifies the respective performance of stra-tegies for epidural needle insertion. By quantifying this performance, it is possible to draw conclusions regarding the techniques that should be taught to resident anesthe-siologists. Furthermore, this study provides information on the relative importance of human reflexes influencing ‘over-shoot’ of the needle through the epidural space. Part I concludes with a study of the forces, torques and stiffnesses encountered in an epidural needle insertion in vivo in a porcine model. The study presented in Chapter 8 provides information on the haptic information that is used by the anesthesiologist during needle insertion, and the magnitude of forces that are encountered.
17 Introduction
1.5.2 Part II – Evaluation of developments in video-assisted laryngoscopy
The second part of the book focuses on assessment of new laryngoscopes that integrate optics in the distal end of the blade for video imaging of the throat and glottis of the patient – the video-laryngoscope (VLS). The video-laryngoscope pro-vides improved view of the glottic arch, especially in problematic cases,68,75 and this
part of the thesis examines how this translates to improved intubation conditions for the clinic. Chapter 9 evaluates the forces applied to the maxillary incisors of patients during intubation with a classic Macintosh style blade and Storz® V-MAC™
video-laryngoscope (both Karl Storz, Tuttlingen, Germany). Force measurements may provide a more objective assessment of the intubation ease.
In Chapter 10 this work is further extended to include two more VLS, the GlideScope® (Ranger™, Verathon Inc, Bothell, WA, USA), and McGrath® ( McGrath
Series 5™, Aircraft Medical, Edinburgh, United Kingdom). The study examines if there are respective difference in the ease of intubation between the VLS again using force measurement. Chapter 11 is a large study including 450 patients that examines the necessity of using an adjunct (stylet) for the insertion of the endotracheal tube during intubation between the same video-laryngoscopes in a population of normal, elective surgery patients. In Chapter 12 this work is extended further to consider an obese patient population. There is an increasing prevalence of obesity in society and these patients are often more challenging to intubate, the time pressure is also grea-ter, as desaturation develops more quickly than in non-obese patients.24,25
The thesis concludes with Chapter 13 summarizing the conclusions from the respective studies, examines the approach taken in this thesis, and directions for future work. This thesis is a compilation of published articles and work submitted for publication – as such, each chapter is a ‘stand-alone’ piece of work, and there are some overlaps between the chapters.
18 Chapter 1
1.6
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19 Introduction
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31. Okamura AM, Simone C, O’Leary MD: Force modeling for needle insertion into soft tissue. IEEE Trans Biomed Eng 2004; 51: 1707-16
32. Brett PN, Harrison AJ, Thomas TA: Schemes for the identification of tissue types and boundaries at the tool point for surgical needles. IEEE Trans Inf Technol Biomed 2000; 4: 30-6
20 Chapter 1
33. Simone C, Okamura AM: Modelling of the needle insertion forces for robot-assisted percutaneous therapy, IEEE International Conference on Robotics and Automation - ICRA. Washington D.C., USA, 2002, pp 2085-91
34. Dankelman J, Di Lorenzo N: Surgical training and simulation. Minim Invasive Ther Allied Technol 2005; 14: 211-3
35. Haluck RS: Computer-based surgical simulation is too expensive. Or is it? Surg Endosc 2005; 19: 159-60
36. Haluck RS, Krummel TM: Simulation and Virtual Reality for Surgical Educa-tion. Surg Technol Int 2000; VIII: 59-63
37. Schijven M, Jakimowicz J: Virtual reality surgical laparoscopic simulators. Surg Endosc 2003; 17: 1943-50
38. ACGME ACfGME: The ACGME’s Approach to Limit Resident Duty Hours:
The Common Standards and Activities to Promote Adherence. www.acgme. org 2003
39. Haluck RS, Krummel TM: Computers and virtual reality for surgical educa-tion in the 21st century. Arch Surg 2000; 135: 786-92
40. Reina MA, de Leon-Casasola OA, Lopez A, De Andres J, Martin S, Mora M: An in vitro study of dural lesions produced by 25-gauge Quincke and Whita-cre needles evaluated by scanning electron microscopy. Reg Anesth Pain Med 2000; 25: 393-402
41. Kokki H, Heikkinen M, Turunen M, Vanamo K, Hendolin H: Needle design does not affect the success rate of spinal anaesthesia or the incidence of post-puncture complications in children. Acta Anaesthesiol Scand 2000; 44: 210-3 42. Lybecker H, Djernes M, Schmidt JF: Postdural puncture headache (PDPH):
onset, duration, severity, and associated symptoms. An analysis of 75 conse-cutive patients with PDPH. Acta Anaesthesiol Scand 1995; 39: 605-12 43. Shergold OA, Fleck NA: Experimental investigation into the deep
penetra-tion of soft solids by sharp and blunt punches, with applicapenetra-tion to the piercing of skin. J Biomech Eng 2005; 127: 838-48
44. Shergold OA, Fleck NA, King TS: The penetration of a soft solid by a liquid jet, with application to the administration of a needle-free injection. J Bio-mech 2006; 39: 2593-602
45. Kataoka H, Washio T, Chinzei K, Mizuhara K, Simone C, Okamura AM: Measurement of the tip and friction forces acting on a needle during punc-ture, Medical Image Computing and Computer Assisted Intervention - MIC-CAI. Edited by Dohi T, Kikinis R. Tokyo, Japan, Springer, 2002, pp 253-61 46. Wilcox RK, Bilston LE, Barton DC, Hall RM: Mathematical model for the
viscoelastic properties of dura mater. J Orthop Sci 2003; 8: 432-4
21 Introduction
47. Ottensmeyer MP: In vivo measurement of solid organ visco-elastic proper-ties. Stud Health Technol Inform 2002; 85: 328-33
48. DiMaio SP, Salcudean SE: Needle insertion modeling and simulation. Ieee Transactions on Robotics and Automation 2003; 19: 864-875
49. Kerdok AE, Cotin SM, Ottensmeyer MP, Galea AM, Howe RD, Dawson SL:
Truth cube: establishing physical standards for soft tissue simulation. Med Image Anal 2003; 7: 283-91
50. Visser WA, Gielen MJ, Giele JL, Scheffer GJ: A comparison of epidural pres-sures and incidence of true subatmospheric epidural pressure between the mid-thoracic and low-thoracic epidural space. Anesthesia and Analgesia 2006; 103: 1318-21
51. Okutomi T, Watanabe S, Goto F: Time course in thoracic epidural pressure measurement. Can J Anaesth 1993; 40: 1044-8
52. Lechner TJ, van Wijk MG, Maas AJ, van Dorsten FR: Thoracic epidural punc-ture guided by an acoustic signal: clinical results. Eur J Anaesthesiol 2004; 21: 694-9
53. Lechner TJ, van Wijk MG, Maas AJ, van Dorsten FR, Drost RA, Langenberg CJ, Teunissen LJ, Cornelissen PH, van Niekerk J: Clinical results with the acoustic puncture assist device, a new acoustic device to identify the epidural space. Anesth Analg 2003; 96: 1183-7, table of contents
54. Lechner TJ, van Wijk MG, Jongenelis AA, Rybak M, van Niekerk J, Langen-berg CJ: The use of a sound-enabled device to measure pressure during inser-tion of an epidural catheter in women in labour. Anaesthesia 2011; 66: 568-73 55. Young ST, Chan KH, Chen CF: An instrument using variation of resistance
to aid in needle tip insertion in epidural block in monkeys. Med Instrum 1987; 21: 266-8
56. Jackson C: The technique of insertion of intratracheal insufflation tubes. Sur-gery, gynecology & obstetrics 1913; 17: 507-9
57. Zeitels SM: Chevalier Jackson’s contributions to direct laryngoscopy. Journal of voice : official journal of the Voice Foundation 1998; 12: 1-6
58. Janeway HH: Intra-tracheal anesthesia from the standpoint of the nose, thro-at and oral surgeon with a description of a new instrument for cthro-atheterizing the trachea. The Laryngoscope 1913; 23: 1082-90
59. Scott J, Baker PA: How did the Macintosh laryngoscope become so popular? Paediatric anaesthesia 2009; 19 Suppl 1: 24-9
60. Woodall NM, Cook TM: National census of airway management techniques used for anaesthesia in the UK: first phase of the Fourth National Audit Pro-ject at the Royal College of Anaesthetists. Br J Anaesth 2011; 106: 266-71
22 Chapter 1
61. Pandit JJ, Cook TM: Guest editors’ commentary: ‘State of the art’ in airway management in 2011. Anaesthesia 2011; 66 Suppl 2: 1-2
62. Van Zundert A, Stessel B, De Ruiter F, Giebelen D, Weber E: Video-assisted laryngoscopy: a useful adjunct in endotracheal intubation. Acta Anaesthesiol Belg 2007; 58: 129-31
63. Juvin P, Lavaut E, Dupont H, Lefevre P, Demetriou M, Dumoulin JL, Des-monts JM: Difficult tracheal intubation is more common in obese than in lean patients. Anesth Analg 2003; 97: 595-600, table of contents
64. Seo SH, Lee JG, Yu SB, Kim DS, Ryu SJ, Kim KH: Predictors of difficult intubation defined by the intubation difficulty scale (IDS): predictive value of 7 airway assessment factors. Korean journal of anesthesiology 2012; 63: 491-7
65. Peterson GN, Domino KB, Caplan RA, Posner KL, Lee LA, Cheney FW:
Management of the difficult airway: a closed claims analysis. Anesthesiology 2005; 103: 33-9
66. Isono S, Greif R, Mort TC: Airway research: the current status and future directions. Anaesthesia 2011; 66 Suppl 2: 3-10
67. Murphy P: A fibre-optic endoscope used for nasal intubation. Anaesthesia 1967; 22: 489-91
68. Cooper RM: Use of a new video-laryngoscope (GlideScope) in the manage-ment of a difficult airway. Can J Anaesth 2003; 50: 611-3
69. Cooper RM, Pacey JA, Bishop MJ, McCluskey SA: Early clinical experience with a new video-laryngoscope (GlideScope) in 728 patients. Can J Anaesth 2005; 52: 191-8
70. Van Zundert AA, Maassen RL, Hermans B, Lee RA:
Videolaryngoscopy--making intubation more successful. Acta Anaesthesiol Belg 2008; 59: 177-8
71. van Zundert A, Maassen R, Lee R, Willems R, Timmerman M, Siemonsma
M, Buise M, Wiepking M: A Macintosh laryngoscope blade for videolaryngo-scopy reduces stylet use in patients with normal airways. Anesth Analg 2009; 109: 825-31
72. Wilmshurst P: The regulation of medical devices. BMJ 2011; 342: d2822 73. Pandit JJ: Initiative in anaesthesia. BMJ 2011; 342: d3849
74. Pandit JJ, Popat MT, Cook TM, Wilkes AR, Groom P, Cooke H, Kapila A, O’Sullivan E: The Difficult Airway Society ‘ADEPT’ guidance on selecting airway devices: the basis of a strategy for equipment evaluation. Anaesthesia 2011; 66: 726-37
75. Shippey B, Ray D, McKeown D: Use of the McGrath video-laryngoscope in the management of difficult and failed tracheal intubation. Br J Anaesth 2008; 100: 116-9
23 Introduction
Chapter 2
Thoracic combined
spinal-epidural anesthesia
SAJAA 2008; 14:63-69 Anesth Analg 2008; 107:708-21
2.1
Summary
The delivery of spinal anesthetics to the desired location in the body, even above the termination of the spinal cord (thoracic level), is potentially very valuable. Since the-re is no blockade of the lower extthe-remities (little caudal spthe-read) a significantly larger portion of the body experiences no venal dilation. This may offer a compensatory buffer to adverse changes in blood pressure intra-operatively. Further, the dosing of the anesthetic is exceedingly low, because of the highly specific block to only certain nerve function along a section of the cord. Thirdly, the degree of muscle relaxation achievable without central or peripheral respiratory or circulatory depression is su-perior to that with general anesthesia.
Results from MRI studies indicate that the spinal cord lies anteriorly wit-hin its thecal boundaries in the apex of the thoracic curve. Intrathecal injections, therefore, at thoracic levels may have a greater absolute margin of error before need-le contact with neural tissue - although the consequences of inadvertent contact are possibly more disastrous.
In the study reported here, the thoracic CSE technique has been applied in the anesthetic care of twelve patients with cardiovascular and/or pulmonary pro-blems.* Despite bad hemodynamic situations and/or severe end-stage lung problems,
abdominal surgery (i.e. cholecystectomy, bowel, and vascular surgery) was performed successfully with the thoracic CSE method with low impact on the patient. Anes-thetic care of the patients would have been more difficult, with consequently larger impacts on hemodynamic and pulmonary function, should these surgeries have oc-curred under general anesthesia - the usual anesthetic technique of choice.
CSE techniques can be used in the thoracic region in patients who other-wise would receive general anesthesia. High-risk patients, with limited cardio-respi-ratory reserves, present challenges to the anesthesiologist. Using the thoracic CSE technique in the thoracic space is extending the boundaries of regional anesthesia.
2.2
Introduction
It is often undesirable to use general anesthesia for surgery, and many indications exist for regional techniques. Negative side effects of the drugs, relatively longer re-covery times, contraindications for certain patients (elderly or those with heart
con-* Subsequent to publication of these results the procedure has been successfully carried out with tens of at-risk patients otherwise poorly treatable with general anesthetic techniques
26 Chapter 2
ditions), safety and cost all limit the usefulness of general anesthesia.1-4 Indeed, some
recent studies indicate that, besides pre-existing medical complications, time under anesthetic-induced sleep and the degree of intra-operative hypotension may be im-portant indicators of postoperative mortality.5 Not surprisingly, there is significant
and renewed interest in the use of regional anesthesia techniques for a number of common surgeries.6-8 Some of the most versatile and well-known regional techniques
for surgery are spinal and epidural anesthesia, although recent innovation of their employment in the operating room has been limited.
Anesthesiologists are unwilling to perform spinal anesthesia above the termination of the spinal cord, largely due to direct threats to the spinal cord from the needlepoint. Nevertheless, in the past, neurologists performed subarachnoid my-elographic injections at thoracic and cervical levels.9 Even high spinal anesthesia has
been employed for craniotomies.10 MRI and other imaging techniques have since
rendered these myelographic procedures largely obsolete, although it is clearly pos-sible to inject radiopaque or anesthetic agents into the subarachnoid space at the tho-racic level. The experimental delivery of spinal anesthetics to the desired levels in the body, even above the termination of the spinal cord (thoracic level), has been shown to be potentially very valuable.11,12 Benefits to the patient include that common
surge-ries of the abdomen may be performed with the lowest possible drug dosing, and the advantage of leaving the lower extremities un-anesthetized. The last point enables compensatory reactions to adverse changes in blood pressure inter-operatively, one of the major risks identified in surgery. Safe administration of thoracic CSE anes-thesia may facilitate the option that common surgeries, usually requiring prolonged hospital stays, may be performed on an outpatient basis – or that at-risk patients can be more safely anesthetized.12
2.3
Anatomy
Recent investigations into the anatomy of the spinal canal have uncovered new in-sights into the anatomy pertinent to neuraxial anesthesia.13-18 The information
garne-red by new methods such as cryomicrotome sectioning, epiduroscopy and magnetic resonance imaging (MRI) reveals more about the mechanism of neuraxial blockade and enables the development of new techniques. With regard to the CSE techniques at thoracic level, it is relevant to consider the margins that are available to the clini-cian administering the spinal bolus. To this end, the anatomy of the spinal cord and surrounding tissues is revisited.
27 Thoracic combined spinal-epidural anesthesia
2.3.1 Boundaries and contents of the epidural space
The posterior longitudinal ligament binds the epidural space anteriorly. The ligamen-ta flava and the periosteum of the lamina encompass the space posteriorly, whilst the periosteum of the pedicles and the intervertebral foramina encompass it laterally.19
Figure 2.1: Medial sagittal preparation of a part of the human thoracic spinal canal, with dura held slightly away from the spinal cord
28 Chapter 2
Figure 2.1 is an excellent preparation in the medial sagittal plane, showing the relevant anatomy. The epidural space communicates freely with the paravertebral space by way of the intervertebral foramina. Loose areolar connective tissue, semi-liquid fat, lymphatics, arteries, an extensive plexus of veins, sensory ganglia, and the spinal nerve roots as they exit the dural sac passing through the intervertebral fora-mina, are all contained within the epidural space. The epidural contents are arranged in a series of metamerically and circumferentially discontinuous units, separated by zones where the dura contacts the canal wall, as shown in Figure 2.2. However, the posterior epidural space becomes more continuous in the thoracic region.
2.3.2 Posterior epidural space
The posterior epidural space is enclosed by two steeply arched ligamenta flava that may not completely merge at the midline.17 The ligaments extend laterally as far as
the articular facets, and their thickness increases with distance down the column. Claims of a midline fibrous septum to the homogenous low viscosity fat of the pos-terior epidural space are not necessarily confirmed by cryomicrotome or histological examinations.17 In fact, the epidural fat is unique in the body in having no fibrous
content.17 Traditional techniques have shown that the anterior-posterior depth of the
Figure 2.2: A drawing of the compartments of the lumbar epidural space (stippled). Adapted from Hogan, 1991
29 Thoracic combined spinal-epidural anesthesia
posterior epidural space varies with the vertebral level, ranging from 1–1.5 mm at C5, to 2.5–3 mm at T6, to its widest point of 5–6 mm at the L2 level.20,21 When examined
by cryomicrotome sectioning, there has been no evidence of cervical posterior epi-dural content above C7.22
2.3.3 Lateral epidural space
The lateral epidural space communicates freely with the paravertebral space through the intervertebral foramina. The pia and arachnoid membranes are contiguous with the spinal nerve roots as they leave the spinal cord and exit through the intervertebral foramina, where they blend with the perineurium of the spinal nerves. The dura ma-ter also extends over the nerve roots lama-terally, but becomes much thinner and blends with the connective tissue of the epineurium.
2.3.4 Dural barrier
The spinal dura mater extends from the foramen magnum to the second segment of the sacrum. The dura itself constitutes a dense collection of collagen and elastic fibers. The traditional description of collagen fibers running in a longitudinal direc-tion23 has been disputed by a number of studies of the dura using scanning electron
microscopy that indicate that fibers of the dura run in neither a longitudinal direction nor parallel to each other.24
There is a large amount of variation in the cerebrospinal fluid (CSF) vo-lume of patients. In addition, it has been shown that the vovo-lume of CSF in the lumbosacral region varies significantly in obese patients, presumably due to compres-sion of the dura due to inward movement of soft tissue through the intervertebral foramina.25 The same study shows that there is a reduction in CSF volume with
abdominal compression. This is an important consideration for pharmacological in-teractions of drug delivery in the parturient and obese patients. There is a possibility of greater than intended effects of drug delivery without anticipated dilution of the anesthetic from an expected CSF volume. Indeed, the variability of CSF volume is estimated to account for 80% of the variability of peak of block height and regres-sion of sensory and motor block.26
2.3.5 Relative geometry of spinal cord and surrounding thecal tissue
Results from MRI studies indicate that the spinal cord lies anteriorly within its thecal boundaries in the apex of the thoracic curve.27 Essentially, the spinal cord follows 30
the straightest line through the imposed geometry of the vertebrae (see Chapters 3 & 4 for a more complete description). Specifically, within the lumbar curve the cord is relatively posterior to its thecal boundaries. Therefore, intrathecal injections at tho-racic levels may have a greater absolute margin of error before needle contact with neural tissue. The consequences of inadvertent contact are possibly more disastrous. It is well known that the geometry of the processes dictates the angle of entry of the needle for mid-line neuraxial blockade, and this contributes to extra space between the dura and spinal cord posterior at thoracic levels.
2.3.6 Spread of injected solutions through the epidural space
Using in vivo CT myelography immediately after epidural injection, large pools or accumulations of contrast are seen near the injection site that compress and distort the dural sac.28 Hydrodynamic studies of fluids injected into the epidural space have
yielded conflicting results: Some researchers have concluded that the epidural space acts as a Starling resistor.29 Others have found that fluid leaves a porcine epidural
space via channels that are open and functional at low epidural pressure, and that there was no evidence for recruitment of additional pathways.30 In the latter study,
the authors suggest that after epidural injection, pressure does not immediately rise to a plateau value because the structures within the spinal canal are somewhat com-pressible. When epidural pressure exceeds epidural vein pressure, blood is displaced into the central venous circulation. In addition, a small volume of cerebrospinal fluid is displaced rostrally. This phenomenon has been demonstrated in clinical practice: Cephalad spread of sensory blockade after intrathecal injection of local anesthetic (LA) is increased when LA or saline is injected into the epidural space soon after the intrathecal injection.31-34
Cryomicrotome sectioning after epidural injection of ink, which by nature allows further distribution of injectate compared to myelography, has shown that solution injected into the epidural space spreads through numerous small channels between fat lobules, rather than a unified advancing front.35 Therefore, the pattern
of spread varies between the area close to the injection site and the margin of distri-bution, where fluid pressure is at its lowest. Furthermore, cryomicrotome sectioning has demonstrated that the lateral extension of the posterior longitudinal ligament (sometimes referred to as the fascia of the posterior longitudinal ligament) forms a barrier to injectate.35 The fascia funnels injectate to the nerves in the intervertebral
foramina, where it spreads along the spinal nerve sleeve and dorsal root ganglia. Indeed, it is possible that an important component of epidural block is due to the action of LA at these sites.
31 Thoracic combined spinal-epidural anesthesia
Sensory
Sympa-thetic Motor Notes PATIENT CHARACTERISTICS
Age + ++ +++ Conflicting results between the various studies. 3-8 segments more, dose requirement 40% less when > 60 yrs. Correlation stronger in TEA than in LEA, and stronger for autonomic and motor block than for sensory block
Height 0/+ ? ? No or small correlations
Pregnancy ++ ++ ++ Generally higher block levels
Dural surface area + ? ? Inverse correlation between dural surface area and peak sensory block
Posterior epidural fat
volume ? ? + Inverse correlation between posterior epidural fat volume and degree of motor block ANESTHESIOLOGIST DETERMINED
Epidural insertion site High-thoracic Caudal
Spread ? ? Does not have effect on number of segments blocked, but does influence direction of spread Mid-thoracic Even distribution ? ? Low-thoracic Cephalad Spread ? ? Patient positioning Sitting or laterally recumbent versus supine
+ ? + Quicker onset and blockade 1-2 segments greater than supine
Head down + ? ? Quicker onset times, slightly higher block levels Local anesthetics
Total mass of local
anesthetic ++++ ++++ ++++ Non-linear relationship between total mass of local anesthetic and number of segments blocked, linear relationship between segmental dose requirements and dose already injected Volume/concentration
relationship 0/+ 0 0
Additives (bicarbonate, α2 agonists, opioids)
0 0 + Quicker onset of blockade, no change in segments blocked; more pronounced motor block with bicarbonate
Method of injection Needle versus
catheter 0/+ ? ? Possibly higher block level after injection through catheter compared to needle Speed of injection 0/+ ? ? Quicker onset of blockade; possibly higher block
levels after rapid injection Fractional injection
versus single bolus + ? ? Fractional injection resembles single shot injection when intervals are shorter Needle direction and
catheter position +/0 ? ? No or only minor effects Threading of catheter
to side ++ + ? Preferential distribution of sensory and motor block with threading of catheter to one side
Table 2.1: Summary of factors affecting the spread of epidural neural block
32 Chapter 2
Fluids injected in the epidural space are evacuated through several me-chanisms. As described above, a significant volume is lost through the intervertebral foramina. Furthermore, drainage by lymphatics, diffusion across the dura and uptake in epidural veins contribute to the removal of epidurally injected agents.36-38
The spread of sensory blockade after epidural injection of a specific dose of local anesthetic differs considerably between individuals and the factors affecting this distribution remain the subject of debate. Based on the results of recent inves-tigations regarding the distribution of neural blockade following thoracic epidural anesthesia, it is noted that the total mass of local anesthetic appears to be most im-portant factor in determining the extent of sensory, sympathetic, and motor neural blockade, while the site of epidural needle/catheter placement governs the pattern of distribution of relative blockade. Age may be positively correlated with the spread of sensory blockade, although the evidence is somewhat stronger for thoracic than for lumbar epidural anesthesia. Other patient characteristics and technical details such as patient position and mode and speed of injection exert only a small effect on the distribution of sensory blockade, or their effects are equivocal. However, combi-nations of several patient and technical factors may aid in predicting local anesthetic dose requirements. Table 2.1 indicates the influence that various factors associated with the epidural injection may have on the distribution of sensory blockade.
2.4
Central neuraxial techniques
Spinal anesthesia (commonly, the bolus delivery of anesthetic intrathecally below the termination of the spinal cord) and epidural anesthesia at any vertebral in-terspace, most often with the accompanied insertion of a catheter for intra-operative and postoperative pain management, are used frequently by most anesthesiologists. Both are considered safe techniques with many indications to relieve pre-operative and postoperative pain, acute pain (trauma and obstetric patients) and chronic pain relief (e.g. in cancer patients). Despite the maturity of both techniques, there has been, in a mechanical sense, relatively minor innovation since their inception in the 19th century.39
There are limitations to the suitability of neuraxial techniques for anes-thesia and pain management. Table 2.2 indicates the biochemical merits and possible restrictions of the respective anesthesia techniques. The main difference between the techniques is the diffusion distance to the nerves, with epidural anesthetics having to diffuse first through the meningeal barrier. A relatively modern technique that ideally combines the best features of both the above-mentioned methods, without including their weaknesses, is combined spinal-epidural (CSE) anesthesia.40-42 CSE 33 Thoracic combined spinal-epidural anesthesia
Advantages Disadvantages Spinal
Anesthesia •Rapid onset of the neural blockade - quick time to anesthetize the patient •Profound block
•Low drug dosing
•Single-bolus (injection) nature means that there is only a single opportunity to ensure correct anesthesia
•Unpredictable level of the blockade Epidural
Anesthesia •Titratable (adjustable concentration) levels for pain management • Ability to prolong indefinitely • Good for postoperative pain
management
•Missed nerve segments (inconsistent block)
• Incomplete motor blockade
• Poor sacral (towards the tailbone) spread of the anesthetic
• Local anesthetic toxicity to the (neural) tissue
anesthesia generally involves the sequential delivery of spinal anesthetic, followed by the placement of an epidural catheter – providing both the profound block of spinal, and adaptability of epidural techniques.
2.4.1 Applications of CSE technique in the lumbar region
The CSE technique (as shown in Figure 2.3 with the Epidural Tuohy needle in situ, acting as a guide for the long spinal needle, which is positioned in the subarachnoid space) attained widespread popularity in obstetric anesthesia worldwide, due to the rapid and reliable onset of analgesia, produced by the spinal component, resulting in high maternal satisfaction scores.43,44 The epidural catheter provides the traditional
back-up, with either top-ups or a continuous infusion system, either to improve an insufficient spinal block or to restore an expired block.
Depending on the LA solution used, including opioids or other additi-ons, a fast reliable spinal block develops, similar to a single shot spinal anesthesia. However the CSE allows for dose reduction in order to obtain a limited regional an-esthesia block (limited extent of sensory blockade, often avoiding motor blockade) with minimal side effects for both mother and baby. Disadvantages of the CSE technique are that it is a technically more demanding, more expensive and more time-consuming technique compared to each of the techniques alone, and that only those with an advanced experience in spinal and epidural techniques should be allowed to use the technique.
CSE is not only feasible in obstetrics (vaginal and Caesarean deliveries), but is also a suitable technique in ambulatory surgery, vascular, orthopedic and gene-ral surgery, and urology. The sequential technique can be used in virtually all patients (excluding anticoagulated patients) who are operated on below the umbilicus, even if Table 2.2: Advantages and possible disadvantages of spinal and epidural anesthesia techniques
respectively
34 Chapter 2
high-risk patients are involved. Postoperative pain relief using the epidural catheter further contributes to a fast rehabilitation with fewer complications.
2.4.2 Complications of CSE anesthesia
Encountered problems in CSE techniques are similar to those of the components, including misalignment of the needles, incorrect delivery site of the anesthetic (with subsequently toxic reactions or unexpected levels of (sensory) neural blockade), trauma to spinal blood vessels, Post-Dural Puncture Headache (PDPH), and
paraly-sis.23,40,45-47 Despite a relatively low incidence of complications, the problems result in
higher costs of care, increased morbidity for the patient, and restricted application of the techniques. The CSE technique complicates positioning of the needles in that it is not suitable to use loss of resistance to saline injection, the fluid of choice, for positioning of the epidural needle. This is because the saline may be wrongly identi-fied as cerebrospinal fluid when inserting the spinal needle. In reviews of common regional anesthesia techniques (excluding CSE), it has been noted that the epidural technique is the hardest to master: The anesthesiologist often learns to successfully perform a lumbar epidural anesthesia only after 40 to 70 procedures.48 The CSE
technique is even more difficult due to its added complexity. Figure 2.3: The combined spinal-epidural technique in situ.
35 Thoracic combined spinal-epidural anesthesia
Single epidurals are, contrary to single spinal injections, also performed above the lumbar region, often with the use of 16G or 18G Tuohy needles. It is well established that approximately 1% of epidural attempts accidentally perforate the dura mater.49 The incidence of serious neurological complications in epidural
pro-cedures is, however, far below that of the incidence of inadvertent dural tap.45 This
auspicious fact gives rise to the question of what safety margin might be associated with introduction of a spinal needle through the cannula of a correctly positioned epidural needle for perforation of the dura and delivery of anesthetic bolus spinally. When performing CSE techniques, the practicing anesthesiologist often has better recognition of the dural ‘click’, and can faithfully halt the spinal needle in the sub-arachnoid space, whilst avoiding contact with the delicate nerve fibers. Danger of nerve trauma from inadvertent contact with the needle and higher risks of paralysis preclude most anesthesiologists from considering puncture of the dura above the termination of the cord. Once again, this is despite studies that indicate that the incidence of accidental dural tap far exceeds that of neurological damage.
2.4.3 Thoracic CSE anesthesia
A pioneering application of CSE anesthesia is the practicing of the technique at thoracic levels. There are a number of advantages to delivering the (spinal) anesthetic directly to the required locations in the body. Firstly, one of the most obvious ad-vantages is that there is no blockade of the lower extremities, i.e. little caudal spread. This means that a significantly larger portion of the body experiences no venal di-lation, and may offer a compensatory buffer to adverse changes in blood pressure intra-operatively. This is one of the major risks identified in surgery.5 Secondly, the
dosing of the anesthetic is exceedingly low, given the highly specific block to only certain nerve functions along a section of the cord. Thirdly, the degree of muscle relaxation achievable without central or peripheral respiratory or circulatory
depres-Indications Contraindications
•Abdominal surgery: bowel, cholecystectomy, gastric operations, vascular operations •Caesarean sections
•Difficult patients with contraindication for general anesthesia
•Surgeries requiring a conscious and/or ambulatory patient
•Experienced anesthesiologist with CSE techniques
•Major bleeding is expected
•Abdominal surgery includes the pelvic region (e.g. prostate resection)
•Operations below the inguinal groin (i.e. urological or orthopedic surgery) •Not suitable for patient to be conscious •Inexperienced anesthesiologist
•No contraindication for general anesthesia
Table 2.3: Indications and contraindications of thoracic CSE anesthesia
36 Chapter 2
