A Randomised Trial of the Effectiveness of Different in vitro Models in Teaching Ultrasound Guided Regional Anaesthesia

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BACKGROUND Ultrasound guided regional anaesthesia (UGRA) is a complex component of anaesthesia practice to learn. UGRA has evidence of improved safety, efficacy and is considered standard of care for peripheral nerve blocks. To safely practice UGRA, procedural accuracy is required when introducing the nerve block needle into the patient and guiding that needle to the target nerve structure under real time ultrasound guidance. This procedural task encompasses several domains of knowledge and manual dexterity skills: 1. Ability to manipulate the ultrasound transducer to visualise and optimise the nerve and surrounding tissue sonoanatomy 2. Ability to plan a needle path trajectory that maintains an in-plane visualisation of the needle shaft and tip from skin surface to deeper structures 3. Motor skill ability to guide the needle under real time visualisation to inject local anaesthesia at positions around the nerve to create a circumferential deposition of injectate (local anaesthesia) 4. Ability to recognise an optimal spread of injectate and to correct the needle position appropriately Successful performance of UGRA thus requires hand-eye coordination and needle guidance techniques to maximise efficacy while minimising potential complications. Learning curve patterns of novices performing UGRA in patients has revealed an initial high rate of errors, from a mean of 12.6 errors per block during the first 10 attempts, decreasing to 4.6 errors per block by the end of the 39th attempt. In a study using cadavers, 28 UGRA attempts were required to reach competency as defined by needle visualisation under ultrasound and transducer steadiness. Both studies revealed wide variability in novices' error and success rates. This suggests that UGRA skills are difficult to master and individuals reach proficiency at different times, due to innate psychomotor abilities. For ethical reasons, initial teaching of these procedural skills has thus focused on in vitro models. It allows repeated practice of high stakes procedural skills without risk of patient harm. It concentrates trainees and trainers in a single learning environment. A curriculum can be devised without distractions of clinical duties as occurs in hospital-based teaching. The ideal in vitro model should be inexpensive, has similar properties to human tissue both under ultrasound (echogenicity, fascial planes, muscle texture, hyperechoic peripheral nerves, arterial and venous blood vessels that collapse appropriately under pressure, spread of injectate along fascial planes and around nerves, swelling of the nerve sheath if an intraneural injection was performed), as well as tactile feedback of resistance and fascial plane pops when a facet tipped nerve block needle is used. Commonly used in vitro models include the gelatin model, meat model, and fresh frozen human cadaveric model. None of these satisfy as an ideal model, and all have advantages and disadvantages. Inexpensive and easily procured models such as gelatin and meat based models are commonly used in teaching, but offer a low fidelity experience of what a trainee would expect when performing UGRA in patients. Anatomical relationships, tactile feedback, appearance of human tissues and fascial planes under ultrasound, and nerve block needle echogenicity are not realistic. In our experience, these models are useful in introducing novices to UGRA but create overconfidence in performance as they do not reflect the clinical reality. The meat model, usually constructed out of turkey, beef or pork, is relatively inexpensive, easy to construct, and has more similar properties to human tissue in terms of echogenicity and texture. Hydrodissection by injections of simulated local anaesthetic can also be performed. However, meat models do not have realistic human anatomical relationships. Unlike traditional formalin based cadaveric dissections, fresh frozen human cadavers retain all of the in vivo anatomical relationships and currently represents the highest fidelity model for UGRA training. Nerves, fascial planes, and muscle textures are similar to live patients. Tactile feedback is retained when performing needling manoeuvres. Injection spreads patterns are similar to live patients. Limitation to access include financial cost and scarcity of centres accredited to handle fresh cadavers. This study will compare the effectiveness of two in vitro models commonly used to teach UGRA: pork meat model, and fresh frozen cadavers. Effectiveness is measured using objective assessment of proficiency in procedural skills before and after exposure to different in vitro models. RATIONALE FOR PERFORMING THE STUDY The traditional apprenticeship model of teaching medicine has emphasised clinical exposure and supervised tutelage of procedural skills in our patients. Due to multiple factors including ethical concerns of relatively unskilled trainees performing invasive procedures on patients, reduction in caseload due to safe working hours directives, and reduction of available teaching staff, this apprenticeship model may be inappropriate. In UGRA, poor needle visualisation and suboptimal sonoanatomical imaging have been identified as the two most common mistakes in novices, which may contribute to patient complications during nerve blocks. Educators are still uncertain as to the best methods of teaching UGRA, including what are the best in vitro models. In this study, we will compare the effectiveness of 2 commonly used in vitro models. The models range from low fidelity (but low cost, easily accessible) to high fidelity (but high cost, not easily accessible). Each model has been used and reported in literature, but no previous study has compared each model's effectiveness in teaching procedural skills to trainees. The results of this study will inform us of the value of fresh frozen cadavers in UGRA teaching. We will compare the relative skills of trainees taught with different models using an objective assessment tool. If the hypothesis is confirmed, we would recommend that fresh frozen cadavers be incorporated into regular UGRA teaching. HYPOTHESIS That fresh frozen human cadavers, representing a high fidelity simulator of human anatomy, is the most effective in vitro model to teach UGRA technical skills to doctors training in anaesthesia when measured against time taken, error rates, and success rates. STUDY OBJECTIVES Primary objective is time taken from insertion of the needle using an in-plane technique (maintaining visualisation of needle shaft and tip) to the 6 o’clock and 12 o’clock positions of the target, and injecting 0.5mls of saline at each position. Secondary outcomes were selected based on common problems exhibited by novices in UGRA. 1. Number of needle passes 2. Number of errors during performance of task 3. Image quality score of best sonoanatomical image

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