Embedded method of LOP measurement enables accurate, effective and simple prescription of personalized tourniquet cuff pressures in a clinical setting
Tourniquets are used to control arterial and venous blood flow in many situations, including to create a bloodless surgical field and perform blood flow restriction therapy. Advances in automatic, pneumatic tourniquet technology has improved the safety, accuracy and reliability of surgical tourniquet systems with the implementation of lower, controlled and personalized pressures with reduced applied pressure gradients .
Personalization of tourniquet pressure requires accurate measurement of patient’s limb occlusion pressure (LOP). This can be measured automatically through two different methods; ‘distal LOP’ method and ‘embedded LOP’ method. The ‘distal LOP’ method measures LOP using a distal sensor applied to the patient’s finger or toe of the operating limb, using photoplethysmography to detect volumetric changes in peripheral blood circulation. The ‘embedded LOP’ method measures LOP using a dual-purpose tourniquet cuff acting as both patient sensor and pneumatic effector. The embedded LOP method was recently developed and offers several advantages over the distal LOP method. Firstly, the embedded LOP method circumvents the need for a separate, complex and costly distal sensor, which can affect the sterile field in a surgical setting. Secondly, placing and removing the distal sensor takes time which can affect the perioperative workflow, and the success of LOP measurement using a distal sensor is dependent on variables affecting the measurement of low peripheral blood flow . Therefore, the embedded LOP method offers several advantages over the distal LOP method for use in clinical settings.
Both the embedded and distal LOP methods have been found to have clinically acceptable accuracy compared to the manual doppler ultrasound method [1, 3]. However, the level of agreement between the embedded and distal methods of LOP measurement (i.e. how similar LOP measurement is between the two methods) had not been compared. A recent study by Hughes et al., published in the BMC Biomedical Engineering Journal, investigated whether the embedded and distal methods of LOP measurement have clinically acceptable agreement .
Methodology & Results
Hughes et al. compared the differences in pairs of LOP measurement in the upper and lower limbs of 81 healthy individuals. The two methods are said to have a clinically acceptable level of agreement if the difference (mean ± standard error) in LOP measurement, standard deviation of the differences and the uncertainty (95% confidence interval) of this measurement were within ±15 mmHg. This pressure window is selected because of the following: In tourniquet application during surgery, it is common for cuff pressure to deviate from the pressure setpoint due to limb manipulation. Surgical tourniquet systems utilize a ±15 mmHg pressure alarm window, whereby if the cuff pressure deviates from the pressure setpoint by >15 mmHg, an audiovisual alarm is triggered.
LOP measurement using the embedded LOP method was -0.81 ± 0.75 mmHg (bias ± standard error) lower than the distal LOP method. The standard deviation of the mean difference was 10.35 mmHg, and the 95% confidence interval of the mean difference was -2.29 to 0.66 mmHg.
Conclusions & implications
The difference in LOP measurement between the embedded and distal methods is well within the existing standard of a ±15 mmHg pressure alarm window. These results show that the embedded and distal methods of LOP measurement demonstrate clinically acceptable agreement. The findings support the use of the embedded LOP method of automatic LOP measurement using dual-purpose tourniquet cuffs to enable accurate, effective and simple prescription of personalized tourniquet cuff pressures in a clinical setting.
 Masri BA, Day B, Younger AS, Jeyasurya J. Technique for Measuring Limb Occlusion Pressure that Facilitates Personalized Tourniquet Systems: A Randomized Trial. Journal of Medical and Biological Engineering. 2016 Oct 1;36(5):644-50.