It's time to regulate - The importance of accurate surgical-grade tourniquet autoregulation in blood flow restriction exercise applications.

OBJECTIVE: Evaluate the efficacy of five common blood flow restriction (BFR) systems to accurately maintain and autoregulate BFR pressure in the tourniquet cuff near target pressure throughout exercise. DESIGN: Randomised crossover design. SETTING: Laboratory. PARTICIPANTS: 15 healthy individuals. OUTCOME MEASURES: 1) Percentage of total BFR time that surgical-grade tourniquet autoregulation, defined as automatic and rapid self-regulation of cuff pressure to within ±15 mmHg of initial target pressure within 1 s in the presence of transient pressure changes associated with exercise, was provided; 2) pressure change in the BFR cuff throughout exercise, by comparing the initial target pressure to the measured pressure at completion of BFR exercise. RESULTS: One BFR system could provide surgical-grade tourniquet autoregulation for the whole duration (100 ± 0%) of the BFR exercise in all subjects. In two of the five BFR systems evaluated, measured cuff pressure at the end of exercise was not different (p < 0.05) to the initial target pressure. CONCLUSIONS: Surgical-grade tourniquet autoregulation is important to consistently and reliably apply a targeted BFR pressure stimulus. This may allow BFR methodology and protocols to be accurately implemented and controlled so that the results can be more meaningfully compared, leading to the potential optimization of applications.

Interface pressure sensor for IVRA and other biomedical applications.

The fabrication and testing of a minimally intrusive (2 mm high, 10 mm diameter) biomedical interface pressure sensor are described. Such sensors are needed for the implementation of improved safety features in the next generation of automated intravenous regional anaesthesia (IVRA) systems. The sensor utilizes a structured elastomer as a deflection element sandwiched between the plates of a parallel plate capacitor device. Simple mechanical modifications allow sensitivity and zero offset adjustment. The sensor is housed in a package machined from an engineering polymer. The device is easily calibrated using either a bench-top or an on-body calibration procedure. The device is particularly sensitive to cuff artefacts arising from variations in cuff-wrap tightness and folding of the cuff. As such, it offers some promise for detecting potential hazard conditions which can occur during conventional IVRA procedures. For the purpose of unit conversion, 1 Pa = 1 N/m2, 1 MPA = 1 N/mm2 and 40 kPa approximately equal to 300 mmHg.

Pediatric tourniquets: analysis of cuff and limb interface, current practice, and guidelines for use.

There are few clear guidelines on the proper use of tourniquets in pediatric surgery, in particular on how to set the tourniquet pressure, how to select the most appropriate cuff, and whether to use some type of soft padding beneath the cuff for limb protection. The authors could find only one published study specifically addressing pediatric cuff pressures, and no studies showing what types of cuff and/or padding create the smoothest skin surface under the cuff. Of 46 pediatric orthopaedic surgeons surveyed, 44 use a tourniquet 4.6 times per week on average and 2 have discontinued their use as a result of complications. To set cuff pressure, 13 of 44 use a standard value, 14 of 44 base pressure on age, extremity, and size, and 17 of 44 base cuff pressure on blood pressure. Thirty-four of 44 use skin protection under the cuff, but damage to the skin is common, accounting for 21 of the 67 reported complications. Nerve (15/67) and muscle (8/67) complications, related to both pressure and tourniquet time, were also reported. Using a molding and digital measurement technique, the authors compared the maximum wrinkle heights and the sums of all wrinkle heights in the skin surface under four different cuff/padding configurations. In a total of 44 trials on the upper arms and thighs of two healthy child volunteers, one type of pediatric cuff with a matching limb-protection sleeve designed and recommended by the manufacturer (Delfi) produced significantly fewer, less severe pinches and wrinkles in the skin surface than a second type of tourniquet cuff (Zimmer) with or without two layers of commonly available cast padding, and a third type (Kidde) with padding. With the second type of cuff, using cast padding reduced skin wrinkling compared to applying the same cuff on unprotected skin. In view of the survey, clinical literature, and results of this study, a guideline for use of pediatric tourniquets is proposed.

Unanticipated variations between expected and delivered pneumatic compression therapy after elective hip surgery: a possible source of variation in reported patient outcomes.

The differences between the pneumatic compression thromboprophylaxis delivered after elective total hip arthroplasties and that was expected were quantified before (49 patients) and after a concerted nursing education program (30 patients) that was designed to ensure maximum compliance and to verify the correct application of the devices. The expected therapy was not delivered to any of the patients monitored. Therapy was delivered only an average of 77.8% of the time during the expected treatment periods. During 99.9% of the expected therapy times, values of key outcomes-related parameters of the therapy delivered to the patients varied by >10% from expected values. These variations were not reduced significantly by medical and nursing education. This variation may be a significant confounding factor in comparatively evaluating thromboembolic disease outcome reports.

A compliance-independent pressure transducer for biomedical device-tissue interfaces.

The measurement of the interface pressure between a biomedical device and part of the human body is useful to improve the performance and safety of such devices during design. Testing of a selection of existing interface pressure transducers has demonstrated that many are dependent on device and tissue compliance. Such a transducer is useful only in an application where it has been calibrated for specific device-tissue compliance combinations. To overcome this limitation, the authors developed an interface pressure transducer whose output signal is not affected by changes in interface compliance. This enables the transducer to quantitatively measure pressure in many applications without the need to calibrate it for varying compliance conditions. Surgical retraction and surgical tourniquets were selected as demonstration applications for the developed transducer, because they represent a wide spectrum of device and tissue characteristics and properties, and are in common use.

A North American survey of intravenous regional anesthesia.

UNLABELLED: One thousand questionnaires concerning the techniques and complications of intravenous regional anesthesia (IVRA) were sent to 900 American and 100 Canadian anesthesiologists. Of the 321 respondents, 86% perform IVRA regularly. A wide variation in device-related and clinical aspects was found, ranging from acceptable to falling outside published guidelines. Anesthesiologists perform a median of four upper-limb IVR procedures per month, most often using 50 mL of lidocaine 0.5% at tourniquet pressures of 250 mm Hg or 100 mm Hg greater than the systolic blood pressure. Forearm, thigh, and calf IVRA are occasionally used. Complications, reported infrequently in the literature, were reported by respondents, including mistaken deflation of the cuff; dysphoria, dizziness, or facial tingling; seizures; cardiac arrests; and deaths. Although there was no correlation between complications and deviation from traditional practice, we recommend that IVRA be performed following recognized protocols by anesthesiologists who are familiar with the technique and trained to treat its potential complications. We recommend a protocol for IVRA. IMPLICATIONS: Intravenous regional anesthesia is a widely used anesthetic technique. A survey of 321 American and Canadian anesthesiologists indicates a wide variation in technique. Despite no correlation between complications and technique, the authors recommend that recognized protocols be used for this technique.

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.

Perineural pressures under the pneumatic tourniquet in the upper extremity.

The literature indicates that tourniquet-induced neurological injuries are relatively common and frequently occur at a subclinical level. In order to evaluate the pressure transmitted to the major peripheral nerves of the arm by an externally applied pneumatic tourniquet, a fully implantable biomedical pressure transducer was placed adjacent the radial, median and ulnar nerves in six cadaver upper extremities of average dimensions. This sensor allowed accurate, reproducible measurements of perineural pressures without requiring significant disruption of the normal anatomical structures of the test limb for its installation. At levels of tourniquet cuff inflation which are commonly used in clinical practice, there was little or no decrease in the pressure detected in the perineural regions over that applied to the surface of the limb. In addition, there was a steep gradient of perineural pressure between locations beneath the edge of the cuff and those under its midpoint. This was most marked at the highest levels of tourniquet inflation. At presently accepted levels of inflation, pneumatic tourniquet cuffs transmit high pressures to the peripheral nerves without any significant attenuation by the intervening soft tissues. The distribution of these forces is one which may subject the underlying nerves to deleterious shear forces, especially at higher levels of inflation.

New finger cuffs for use with digital tourniquets.

The advent of tourniquets employing digital technology has led to significant improvements in the safety and accuracy of surgical procedures performed with an occlusive cuff applied proximally on a limb. This article describes the evaluation of new cuffs used on fingers that may permit significantly lower pressures to be more safely and consistently employed. Our experimental studies would suggest that finger occlusion pressure is a function of cuff design, cuff width, finger circumference, and systolic blood pressure.

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 microprocessor-based 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.

Modification of IVAC 530 infusion pump for patient controlled analgesia.

This article describes an inexpensive device for delivering patient-controlled analgesia. Details of the necessary modifications of a standard IVAC 530 infusion pump are included. The total cost of the modified pump was $2200.

Complications of and improvements to breathing circuit monitors for anesthesia ventilators.

Despite significant improvements in the safety of anesthetic equipment in recent years, disconnection in the patient breathing circuit remains one of the most common types of preventable anesthetic mishaps. Many currently available breathing-circuit monitors cannot reliably detect several hazardous conditions in the breathing circuit. An improved breathing circuit monitor has been developed that reliably detects realistic simulations of many hazardous conditions. The software algorithm in this monitor stores the normal pressure waveform in the patient circuit, evaluates the ongoing waveform in terms of sets of absolute and relative criteria, and warns the operator when such criteria are not satisfied. A comprehensive technical and clinical evaluation is underway.

Clinical engineering and hospital accreditation in Canada.

In response to the growing concern over the management of medical technology in hospitals, and in view of recent changes pertaining to medical technology that have been made by the Joint Commission on Accreditation of Hospitals in the United States, the Canadian Council on Hospital Accreditation recently asked the Canadian Medical & Biological Engineering Society (CMBES) to prepare a brief on the proper role of clinical engineering in Canadian hospitals. The brief prepared by the CMBES outlines seven basic principles associated with clinical engineering, hospital accreditation, and the proper management of medical technology in hospitals. It appears that these principles may form the initial basis for changes to the Canadian Hospital Accreditation Guide and Questionnaires. A comparative assessment of the Canadian and American approaches by clinical engineers may help to advance the cause of better health care in both countries.

Complications of and improvements in pneumatic tourniquets used in surgery.

In North America, it is estimated that at least 10,000 pneumatic tourniquets are used in more than 1 million surgical procedures annually. The increasingly widespread use of pneumatic tourniquets in surgery of the extremities has been accompanied by continuing reports of injuries. Interest in tourniquet-induced complications has recently increased because of concern about potential legal liability. Results are presented from the investigation of 15 cases of complications suspected of being associated with the use of pneumatic tourniquets over an 18-month period. Factors leading to tourniquet-induced complications are identified, difficulties preventing an accurate estimate of the true incidence of such complications are reviewed, and the key elements of a program of inspections aimed at periodically assessing the safety and performance of pneumatic tourniquets are outlined. To reduce the hazards associated with the use of pneumatic tourniquets, a new microprocessor-based tourniquet is being developed. Initial results on a series of 30 patients indicate that the new microprocessor-based tourniquet-in addition to being significantly safer, more accurate, and more reliable-will considerably reduce operating costs by reducing the labor-intensiveness currently associated with tourniquet usage.