Masimo Perfusion Index Versus Doppler for Tourniquet Effectiveness Monitoring.

BACKGROUND: In addition to a plethysmograph, Masimo pulse oximeters display a Perfusion Index (PI) value. This study investigated the possible usefulness of PI for monitoring limb tourniquet arterial occlusion. METHODS: Tactical Ratcheting Medical Tourniquets were applied to the thighs of 15 subjects. Tightening ended at one ratchet-tooth advance beyond Doppler- indicated occlusion. The times and pressures of Doppler and PI signal absences and returns were recorded. RESULTS: Intermittent PI signal error occurred in 149 of 450 runs (PI, 33% versus Doppler, 0%; p < .0001). PI signal loss lagged Doppler-indicated occlusion by 19 ± 15 seconds (mean ± standard deviation, p < .0001). PI Signal Return lagged tourniquet release by 13 ± 7 seconds (Doppler Signal Return took 1 ± 1 seconds following tourniquet release; p < .0001). PI failed to detect early Doppler audible pulse return in 30 of 39 occurrences. CONCLUSION: The PI available on Masimo pulse oximeters is not appropriate for monitoring limb tourniquet effectiveness.

Effects of Distance Between Paired Tourniquets.

BACKGROUND: In practice, the distance between paired tourniquets varies with unknown effects. METHODS: Ratcheting Medical Tourniquets were applied to both thighs of 15 subjects distally (fixed location) and proximally (0, 2, 4, 8, 12cm gap widths, randomized block). Applications were pair, single distal, single appropriate proximal. Tightening ended one-ratchet tooth advance past Doppler-indicated occlusion. Pairs had alternating tightening starting distal. RESULTS: Occlusion pressures were higher for: each single than respective individual pair tourniquet, each pair distal than respective pair proximal, and each single distal than respective single proximal (all p < .0001). Despite thigh circumference increasing proximally, occlusion pressures were lower with proximal tourniquet involvement (pair or single, p < .0001). Occlusion losses before 120 seconds occurred most frequently with pairs (0cm 4, 2cm 4, 4cm 6, 8cm 7, 12cm 5 for 26 of 150), in increasing frequency with increasingly proximal singles (0cm 0, 2cm 1, 4cm 1, 8cm 2, 12cm 6 for 10 of 150, p < .0001 for trend), and least with single distal (2 of 150, p < .0001). Paired tourniquets required fewer ratchet advances per tourniquet (pair distal 5 ± 1, pair proximal 4 ± 1, single distal 6 ± 1, single proximal 6 ± 1). Final ratchet tooth advancement pressure increases (mmHg) were greatest for singles (distal 61 ± 10, proximal 0cm 53 ± 7, 2cm 51 ± 9, 4cm 50 ± 7, 8cm 45 ± 7, 12cm 36 ± 7) and least in pairs (distal 41 ± 8, proximal 32 ± 7) with progressively less pair interaction as distance increased (pressure change for the pair tourniquet not directly advanced: 0cm 13 ± 4, 2cm 10 ± 4, 4cm 6 ± 3, 8cm 1 ± 2, 12cm -1 ± 2). CONCLUSIONS: Occlusion pressures are lower for paired than single tourniquets despite variable intertourniquet distances. Very proximal placement has a pressure advantage; however, pairs and very proximal locations may be less likely to maintain occlusion. Increasingly proximal placements also increase tissue at risk; therefore, distal placements and minimal intertourniquet distances should still be recommended.

Effectiveness of Pulse Oximetry Versus Doppler for Tourniquet Monitoring.

BACKGROUND: Pulse oximeters are common and include arterial pulse detection as part of their methodology. The authors investigated the possible usefulness of pulse oximeters for monitoring extremity tourniquet arterial occlusion. METHODS: Tactical Ratcheting Medical Tourniquets were tightened to the least Doppler-determined occluding pressure at mid-thigh or mid-arm locations on one limb at a time on all four limbs of 15 volunteers. A randomized block design was used to determine the placement locations of three pulse oximeter sensors on the relevant digits. The times and pressures of pulsatile signal absences and returns were recorded for 200 seconds, with the tourniquet being tightened only when the Doppler ultrasound and all three pulse oximeters had pulsatile signals present (pulsatile waveform traces for the pulse oximeters). RESULTS: From the first Doppler signal absence to tourniquet release, toe-located pulse oximeters missed Doppler signal presence 41% to 50% of the times (discrete 1-second intervals) and missed 39% to 49% of the pressure points (discrete 1mmHg intervals); fingerlocated pulse oximeters had miss rates of 11% to 15% of the times and 13% to 19% of the pressure points. On toes, the pulse oximeter ranges of sensitivity and specificity for Doppler pulse detection were 71% to 90% and 44% to 51%, and on fingers, the respective ranges were 65% to 77% and 78% to 83%. CONCLUSION: Use of a pulse oximeter to monitor limb tourniquet effectiveness will result in some instances of an undetected weak arterial pulse being present. If a pulse oximeter waveform is obtained from a location distal to a tourniquet, the tourniquet should be tightened. If a pulsatile waveform is not detected, vigilance should be maintained.

Pressures Under 3.8cm, 5.1cm, and Side-by-Side 3.8cm-Wide Tourniquets.

BACKGROUND: Applications of wider tourniquet are expected to occlude arterial flow at lower pressures. We examined pressures under 3.8cm-wide, 5.1cm-wide, and side-by-side-3.8cm-wide nonelastic strap-based tourniquets. METHODS: Ratcheting Medical Tourniquets (RMT) were applied mid-thigh and mid-arm for 120 seconds with Doppler-indicated occlusion. The RMTs were a Single Tactical RMT (3.8cm-wide), a Wide RMT (5.1cm-wide), and Paired Tactical RMTs (7.6cm-total width). Tightening completion was measured at one-tooth advance past arterial occlusion, and paired applications involved alternating tourniquet tightening. RESULTS: All 96 applications on the 16 recipients reached occlusion. Paired tourniquets had the lowest occlusion pressures (ρ < .05). All pressures are given as median mmHg, minimum-maximum mmHg. Thigh application occlusion pressures were Single 256, 219-299; Wide 259, 203-287; Distal of Pair 222, 183-256; and Proximal of Pair 184, 160-236. Arm application occlusion pressures were Single 230, 189-294; Wide 212, 161-258; Distal of Pair 204, 193-254, and Proximal of Pair 168, 148-227. Pressure increases with the final tooth advance were greater for the 2 teeth/cm Wide than for the 2.5 teeth/cm Tacticals (ρ < .05). Thigh final tooth advance pressure increases were Single 40, 33-49; Wide 51, 37-65; Distal of Pair 13, 1-35; and Proximal of Pair 15, 0-30. Arm final tooth advance pressure increases were Single 49, 41-71; Wide 63, 48-77; Distal of Pair 3, 0-14; and Proximal of Pair 23, 2-35. Pressure decreases occurred under all tourniquets over 120 seconds. Thigh pressure decreases were Single 41, 32-75; Wide 43, 28-62; Distal of Pair 25, 16-37; and Proximal of Pair 22, 15-37. Arm pressure decreases were Single 28, 21-43; Wide 26, 16-36; Distal of Pair 16, 12-35; and Proximal of Pair 12, 5-24. Occlusion losses before 120 seconds occurred predominantly on the thigh and with paired applications (ρ < .05). Occlusion losses occurred in six Paired thigh applications, two Single thigh applications, and one Paired arm application. CONCLUSIONS: Side-by-side tourniquets achieve occlusion at lower pressures than single tourniquets. Additionally, pressure decreases under tourniquets over time; so all tourniquet applications require reassessments for continued effectiveness.

Tourniquet pressures: strap width and tensioning system widths.

BACKGROUND: Pressure distribution over tourniquet width is a determinant of pressure needed for arterial occlusion. Different width tensioning systems could result in arterial occlusion pressure differences among nonelastic strap designs of equal width. METHODS: Ratcheting Medical Tourniquets (RMTs; m2 inc., http://www.ratcheting buckles.com) with a 1.9 cm-wide (Tactical RMT) or 2.3 cm-wide (Mass Casualty RMT) ladder were directly compared (16 recipients, 16 thighs and 16 upper arms for each tourniquetx2). Then, RMTs were retrospectively compared with the windlass Combat Application Tourniquet (C-A-T ["CAT"], http://combattourniquet.com) with a 2.5 cm-wide internal tensioning strap. Pressure was measured with an air-filled No. 1 neonatal blood pressure cuff under each 3.8 cm-wide tourniquet. RESULTS: RMT circumferential pressure distribution was not uniform. Tactical RMT pressures were not higher, and there were no differences between the RMTs in the effectiveness, ease of use ("97% easy"), or discomfort. However, a difference did occur regarding tooth skipping of the pawl during ratchet advancement: it occurred in 1 of 64 Tactical RMT applications versus 27 of 64 Mass Casualty RMT applications. CAT and RMT occlusion pressures were frequently over 300 mmHg. RMT arm occlusion pressures (175-397 mmHg), however, were lower than RMT thigh occlusion pressures (197-562 mmHg). RMT effectiveness was better with 99% reached occlusion and 1% lost occlusion over 1 minute versus the CAT with 95% reached occlusion and 28% lost occlusion over 1 minute. RMT muscle tension changes (up to 232 mmHg) and pressure losses over 1 minute (24±11 mmHg arm under strap to 40±12 mmHg thigh under ladder) suggest more occlusion losses may have occurred if tourniquet duration was extended. CONCLUSIONS: The narrower tensioning system Tactical RMT has better performance characteristics than the Mass Casualty RMT. The 3.8 cm-wide RMTs have some pressure and effectiveness similarities and differences compared with the CAT. Clinically significant pressure changes occur under nonelastic strap tourniquets with muscle tension changes and over time periods as short as 1 minute. An examination of pressure and occlusion changes beyond 1 minute would be of interest.