James A. McEwen

Occlusion of arterial flow in the extremities at subsystolic pressures through the use of wide tourniquet cuffs

Tourniquet-induced peripheral neuropathy is at least partially attributable to excessive forces applied to the nerves beneath cuffs inflated to high pressures. Lowering the inflation pressure to the minimum necessary to obtain an effective arrest of blood flow distal to the tourniquet cuff should increase the safety of these systems. Tourniquet cuffs with widths varying from 4.5 cm to 80 cm were applied to the upper and lower extremities of 34 healthy, normotensive volunteers. Occlusion pressure for the arterial system under study was estimated by determining that level of cuff inflation at which the distal pulse became detectable by ultrasonic flowmetry. The occlusion pressure was inversely proportional to the ratio of tourniquet cuff width to limb circumference and was in the subsystolic range at a cuff width to limb circumference ratio above 0.5. Wide tourniquet cuffs can achieve an effective arrest of the regional arterial circulation at subsystolic pressures of inflation. Wide cuffs may reduce the risk of tourniquet-induced injury to underlying soft tissues by lowering the inflation pressure required to secure a bloodless field.

Wide contoured thigh cuffs and automated limb occlusion measurement allow lower tourniquet pressures.

We examined the amount of thigh tourniquet pressure that can be reduced from the typical 300 to 350 mm Hg by using a new automated plethysmographic limb occlusion pressure measurement technique. We also examined how much pressure could be reduced by using a wide contoured cuff compared with a standard cuff and if limb occlusion and systolic blood pressures were well correlated. Patients having surgery with a thigh tourniquet were randomized into two groups, one group having surgery with a standard cuff and the other with a wide cuff. Pressure was set at the automatically measured limb occlusion pressure plus a safety margin. Systolic blood pressure and quality of the bloodless field were recorded. The standard cuff maintained an acceptable bloodless field for 18 of 20 patients at an average pressure of 242 mm Hg, and the wide cuff was acceptable for 19 of 20 patients at an average of 202 mm Hg. One patient in each group had a poor bloodless surgical field at the initial pressure, and one patient in each group had a poor bloodless surgical field after a sharp rise in blood pressure during surgery. Systolic blood pressure was not correlated well enough to limb occlusion pressure to be used alone to set the optimum cuff pressure. The automated limb occlusion pressure technique and the wide contoured cuff reduced average pressure by 33–42% from typical pressures.

An Adaptive Tourniquet for Improved Safety in Surgery

The increasingly recognized inability of the current generation of pneumatic tourniquets to control pressure with adequate accuracy, reliability, and stability has been associated with continuing reports of tourniquet-related injuries, incidents, and hazards. Moreover, the labor-intensiveness and operating costs associated with the use of current types of pneumatic tourniquets have significant cost implications for hospitals. To a large extent, the recent development of a microprocessor-based tourniquet capable of safely and accurately maintaining a desired pressure, and capable of simultaneously performing other functions such as detection of alarm conditions, has reduced these hazards and operating-cost implications. Furthermore, the availability of a microprocessor-based tourniquet has facilitated the development of the adaptive tourniquet described in this paper, in which the pressure in a tourniquet cuff is changed throughout a surgical procedure as a function of the patients changing intraoperative systolic pressure, thus approximating the minimum safe pressure necessary to maintain a bloodless field for surgery. While the use of an adaptive tourniquet, rather than just a microprocessor-based tourniquet set at a constant pressure may not be necessary in most cases, it promises to have significant value in certain surgical procedures and for patients who may be at greater risk of tourniquet-induced complications. Also, the lower average pressures possible through the use of an adaptive tourniquet may permit the evolution of surgical techniques of longer duration without a concomitant increase in the risk of tourniquet-induced complications.

Advances in surgical tourniquets

James A McEwen G F Auchinleck E very year in North America, an estimated 10,000 surgical tourniquets are used in approximately one million procedures. Despite the almost universal use of such tourniquets for surgery of the extremities, recent studies show every use results in some injury to the patient. The nature, extent, and duration of such injuries are largely a result of characteristics of the tourniquets used.1 Increased awareness of tourniquet-related injuries and hazards may lead to the development of new standards for surgical tourniquets.2 The history of nonpneumatic and pneumatic tourniquets in surgery has been reviewed extensively.3 it is recorded that Roman surgeons used constricting devices for amputation. In 1718, the French surgeon Jean Louis Petit developed a screw device for hemostasis. Because of its turning action, Petit called the device a tourniquet. Tourniquets were fIrst used in surgical procedures other tban amputations in 1864. Figure 1 shows a nineteenth century tourniquet from an amputating and general surgery set. Since that time, three technical advances have facilitated the development of bloodless-field· surgery: . • the introduction by Esmarch of an elastic-wrap bandage for exsanguination of a limb before tourniquet application • the introduction of a pneumatic tourniquet by Cushing in 1904 • the development of an automated, microprocessor-based tourniquet in 1982. The use of tourniquets in surgery has been acompanied by reports of limb

Detection of interruptions in the breathing gas of ventilated anaesthetized patients

Interruption of the breathing gas to a ventilated anaesthetized patient due to accidental disconnection or anaesthesia system malfunction may have serious consequences if not detected quickly. A series of tests which covers the range of foreseeable mechanical problems was developed and used to test the performance of three breathing gas interruption monitors, two commercially available and one developed at Vancouver General Hospital. The tests were designed to evaluate the performance of monitors as installed on anaesthesia systems under a variety of failure conditions, including endotracheal tube disconnection with and without occlusion of the opening, kinks in the inspiratory and fresh gas hoses, disconnection of the fresh gas hose, leaks in the breathing circuit, excessive high or low pressure in the scavenging circuit, continuing high breathing circuit pressure, and kinks in the circuit pressure sensing hose. Ability to detect both significant changes in ventilation variables and faults existing at initiation of ventilation were also tested over a representative range of ventilator and patient variables using circle, coaxial and paediatric circuits.Only complete endotracheal tube disconnections with no obstruction of the opening were reliably detected by all three monitors. A commercial monitor with a single fixed-threshold alarm level also detected fresh gas interruptions in circle and adult coaxial circuits, but failed to alarm in response to any other fault condition. A monitor with selectable pressure thresholds and high, low, and continuing pressure limits detected just under half of the fault conditions. A microprocessorbased monitor developed at Vancouver General Hospital detected and correctly identified roughly 80 per cent of the faults.The series of tests forms the basis for a Canadian Standards Association Preliminary Standard (Z168.10) and will allow hospitals to test the performance of breathing gas interruption monitors in use in their institutions. Comments on the test series are solicited.RésuméChez un patient ventilé ľinterruption de ľapport des gaz par déconnection accidentelle ou un malfonctionnement du circuit anesthésique peut avoir des conséquences sérieuses si elle n’est pas détectée rapidement. Une série de lests qui couvre les problèmes mécaniques possibles a été développée et utilisée afin ďétudier la performance de trois moniteurs de détection de débit de gaz dont deux sont commercialement disponibles et un développé à ľHôpital Général de Vancouver. Les lests ont été planifiés afin ďévaluer la performance de ces moniteurs installés sur les machines ďanesthésie dans différentes conditions de bris de circuits incluant la déconnection du tube endotracheal avec ou sans occlusion de ľouverture, une coudure des tubulures de gaz frais et inspiré, une déconnection de la tubulure de gas frais, une fuite dans le circuit, une pression excessivement haute ou basse dans le circuit de scavenging, une pression élevée dans le circuit inspiratoire, et une coudure dans le tuyau détectant les variations de pression du circuit. La possibilité de détecter des changements significatifs dans les paramètres de ventilation et des erreurs à ľinitiation de la ventilation était aussi étudiée utilisant des circuits pédiatriques, coaxiaux et systèmes circulaires.Seulement une déconnection du tube endotrachéal sans obstruction de ľouverture était détectée avec fiabilité par tous les moniteurs. Un moniteur commercial avec un seuil fixe du niveau ďalarme à détecté ľinterruption du débit de gaz frais dans le circuii circulaire et coaxial adulte, mais n’a pu déclencher ľalarme en réponse à ďautres bris du circuit. Un moniteur avec des seuils de pression variable a détecté un peu moins que la moitié des conditions du bris de circuit. Un moniteur basé sur un système de microprocesseur développé à ľHôpital Général de Vancouver a détecté et correctement identifié approximativement 80 pour cent des bris du circuit.Cette série de tests constitue la base pour ľAssociation Canadienne des Normes (Z168.10) et permet aux hôpitaux de tester la performance des moniteurs utilisés dans leurs institutions. Des commentaires sur la série de tests sont sollicités.

Development and initial clinical evaluation of pre-robotic and robotic surgical retraction systems

A prerobotic positioning system for retractors was developed to replace and improve upon the manual techniques and mechanical apparatus that are now commonly used during surgical procedures. The system is a lightweight, pneumatically powered, electronically controlled positioner having ball joints between the three members. The combination of ball joints and 90 degrees bent connecting shafts provides a versatile spherical geometry whereby redundant methods exist to achieve the same position of the end effector, thereby allowing the surgeon to avoid intermediate obstacles during setup and use. Besides being easy to control and position, the devices major advantage is a predictable and reliable locking strength of the ball joints (minimum 25 ft-lb at 100 psi).<<ETX>>

New Technique for Measuring Limb Occlusion Pressure Facilitates Personalized Tourniquet Systems A Randomized Trial

Category: Basic Sciences/Biologics Introduction/Purpose: Optimal tourniquet safety depends on accurately determining the minimum pressure necessary to achieve a bloodless surgical field, known as a patient’s limb occlusion pressure (LOP). However, LOP is not yet routinely measured in all patients due to limitations of current techniques. We have evaluated a novel technique for measuring the LOP through the tourniquet cuff that overcomes many limitations of current LOP measurement techniques. Methods: The new technique of measuring LOP involves the use of unique dual-purpose disposable tourniquet cuffs along with a tourniquet instrument containing LOP calculation sensors and software. A randomized crossover multicenter trial with 143 pre-surgical or post-surgical patients enrolled in the study. Pneumatic cuffs were applied to the non-operative upper and lower limbs and LOP was measured using the new technique and the Doppler ultrasound technique. For each patient a set of four LOP measurements was taken, using the new technique (experimental) and the Doppler technique (control) on one upper and one lower limb. Blinding was achieved during LOP measurement by using two experimenters and blinding the experimenter who measured the LOP using Doppler ultrasound from the LOP reading using the new automatic technique. Participants were blinded from all LOP measurement results by keeping the displays of measurement equipment out of their view. Results: The differences between the new technique and Doppler technique were neither statistically nor clinically significant and the new technique is as robust as the Doppler technique. The results of this study can be used to develop personalized tourniquet systems consisting of unique dual-purpose cuffs connected to instruments suitable for measuring tourniquet LOP with the new measurement technique. The simplicity, effectiveness, and accuracy of this technique should lead to broader clinical usage and acceptance of LOP measurement, thus leading to safer, personalized pressures in surgical tourniquet applications. Conclusion: The new technique is equally robust as the Doppler technique. Both techniques worked successfully in the 252 limbs from which usable data was collected. Of the 34 limbs for which there were data collection errors or exclusion, only two measurements were excluded because of an instrument error using the automatic technique compared to one measurement excluded because of a Doppler technique measurement error.

Automated Intravenous Regional Anesthesia For Upper And Lower Limbs

A system has been developed for the automated administration of anesthesia to limbs to reduce hazards associated with the current technology and practice of intravenous regional anesthesia (IVRA) and improve quality and consistency with variations in skill, knowledge, and experience of physicians and paramedical staff. Clinical trials of the system have indicated that an automated approach may facilitate the increased use of IVRA in limb surgery and the adaptation of IVRA to common surgical procedures presently employing general anesthesia.