Pain and Efficacy Rating of a Microprocessor-Controlled Metered Injection System for Local Anaesthesia in Minor Hand Surgery

Pain and Efficacy Rating of a Microprocessor-Controlled Metered Injection System for Local Anaesthesia in Minor Hand Surgery André S. Nimigan1,2 and Bing Siang Gan1,2,3,4,5 1The Hand and Upper Limb Centre, St. Joseph's Health Centre, The University of Western Ontario, London, ON, Canada N6A 4L6 2Division of Plastic Surgery, University of Western Ontario, London, Ontario, Canada N6A 4L6 3Division of Orthopedic Surgery, University of Western Ontario, London, ON, Canada N6A 4L6 4Department of Physiology and Pharmacology, University of Western Ontario, London, ON, Canada N6A 5C1 5Department of Medical Biophysics, University of Western Ontario, London, ON, Canada N6A 5C1 Received 23 October 2010; Accepted 21 March 2011 Academic Editor: Michael G. Irwin Copyright © 2011 André S. Nimigan and Bing Siang Gan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Purpose. Little attention has been given to syringe design and local anaesthetic administration methods. A microprocessor-controlled anaesthetic delivery device has become available that may minimize discomfort during injection. The purpose of this study was to document the pain experience associated with the use of this system and to compare it with use of a conventional syringe. Methods. A prospective, randomized clinical trial was designed. 40 patients undergoing carpal tunnel release were block randomized according to sex into a two groups: a traditional syringe group and a microprocessor-controlled device group. The primary outcome measure was surgical pain and local anaesthetic administration pain. Secondary outcomes included volume of anaesthetic used and injection time. Results. Analysis showed that equivalent anaesthesia was achieved in the microprocessor-controlled group despite using a significantly lower volume of local anaesthetic ( ). This same group, however, has significantly longer injection times ( ). Pain during the injection process or during surgery was not different between the two groups. Conclusions. This RCT comparing traditional and microprocessor controlled methods of administering local anaesthetic showed similar levels of discomfort in both groups. While the microprocessor-controlled group used less volume, the total time for the administration was significantly greater. 1. Introduction The use of local anaesthesia allows surgeons to perform minor surgery procedures in a variety of settings, including the emergency rooms and clinics. The first recorded nerve block was achieved by Halstead, who used cocaine to accomplish an inferior alveolar block on himself in 1884. Hollow tip hypodermic syringes were introduced not long after by Pravaz and Wood. Unfortunately, the administration of local anaesthesia in itself causes pain, despite attempts to diminish this anaesthesia-associated pain, such as by chemically modifying anaesthetic agents, adding buffering agents, or changing the anaesthetic temperature during administration. Very little attention has been given to the current syringe design and the administration methods, and effectively, syringe systems have changed a little since their introduction over a century ago [1]. A new development in the attempt to give greater operator control and minimize patient discomfort and distress is a product known as the Midwest Comfort Control System. This anaesthetic delivery device eliminates the variability of a thumb-operated plunger, allowing for maintenance of an ideal flow rate of anaesthetic [2]. The infusion rate is precisely regulated by a computer processor which immediately compensates for varying tissue resistance encountered in a single injection. In previous studies examining the effectiveness of pressure-regulated injection, it was found that when the flow rate and pressure of an injected anaesthetic were precisely controlled by a microprocessor, the injections were two to three times less painful than the manual injection ( ) [3]. Significant reductions in postoperative discomfort for an inferior alveolar nerve block have been demonstrated, and both users of the device as well as patients stated a preference for the microprocessor-controlled system [3]. The computerized anaesthesia delivery system has also been shown to provide significantly lower pain ratings for dental restorations [4] and reduce anxiety as well as pain and pain perception in the pediatric population [5, 6]. One study showed no difference in the pain behavior of children during the administration of local anaesthesia with a conventional injection or a computerized device when the operator was an experienced pediatric dentist [7]. The majority of these studies have come from the dental literature, but the device has also been studied and shown to be beneficial in minor anal surgery, toe surgery, and hair transplantation [8, 9]. The purpose of this study was to examine the benefits of this new injection system in minor hand surgery. 2. Methods This single-centre, prospective randomized study was conducted at the Hand and Upper Limb Centre in London, Ontario, Canada. Approval was obtained from the institutional ethics review board prior to the beginning of the study. The objective of this study was to compare the pain, discomfort, and effectiveness of the traditional syringe method and a microprocessor-controlled delivery device for achieving local anaesthesia for carpal tunnel release surgery. A permuted block design was used to randomize 40 adult patients undergoing open carpal tunnel release according to sex into two groups. One group was designated to receive local anaesthesia using traditional needle and syringe method, while patients in the second group received their anaesthesia using the microprocessor-controlled syringe system. The initial sample size calculation was based on the highest standard deviation in reported VAS pain scores from a recent study looking at pain from open carpal tunnel release under local anaesthesia [10]. The alpha error in the study was set at 0.05, and the sample calculated to achieve a statistical power of 0.80 was 15.7 patients per group. The primary outcome measure was defined as the difference between the traditional needle and syringe group and the microprocessor-controlled system group measured by the validated visual analog scale (VAS) score for both perioperative surgical pain and pain related to the delivery of the local anaesthetic. This was accomplished with seven questions (Table 1). Table 1: Primary outcome measure questions asked to elicit scores on the visual analog scale (VAS) for patients undergoing carpal tunnel release. Secondary outcomes of this study included the total volume of anaesthetic used, injection time, and the level of training of the practitioner administering the local anaesthetic. 2.1. Recruitment Consecutive subj (...truncated)