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08/05/2017

Hémorragie: De la glace sur le visage ?

Face Cooling Increases Blood Pressure during Simulated Blood Loss

B. Johnson et Al. Proceedings of Experimental Biology 2017 Chicago 

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Une constatation qui ne devrait pas surprendre ceux qui s'intéressent à la médecine de plongée et au réflexe d'immersion (1, 2, 3, 4), dont le facteur principal de déclenchement est l'exposition de la face à de l'eau froide.

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Introduction

Blood loss causes central hypovolemia and in severe instances, it can decrease blood pressure and lead to cardiovascular decompensation. Simple and quick interventions that can be used to prevent cardiovascular decompensation in pre-hospital settings could be a valuable tool for first responsders. Cooling the forehead and cheeks using an ice/water slurry mixture has been shown to increase blood pressure for over 15 minutes. Therefore, face cooling could be used to mitigate decreases in blood pressure during blood loss.

Purpose

We tested the hypothesis that face cooling during simulated blood loss will increase blood pressure. Methods Ten healthy participants (22 ± 2 years, 3 women) completed two randomized trials on separate days. Both trials began with 30 mmHg of lower body negative pressure (LBNP) to simulate blood loss for 6 minutes. Then, either a 2.5 L plastic bag of an ice/water slurry mixture (0 ± 0°C) (LBNP+FC) or a 2.5 L plastic bag of thermoneutral water (34 ± 1°C) (LBNP+SHAM) was placed on the forehead and eyes and 30 mmHg of LBNP was maintained for an additional 15 minutes.

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We continuously measured blood pressure (Penaz method), heart rate (ECG), stroke volume (Modelflow), cardiac output, total peripheral resistance, and forehead temperature throughout the protocol.

Results

Forehead temperature did not change from LBNP (34.2 ± 0.6°C) to LBNP+SHAM (33.9 ± 1.4°C, P > 0.999) and decreased from LBNP (34.4 ± 0.5°C) to LBNP+FC (11.0 ± 1.6°C, P < 0.001). Mean arterial pressure did not change from LBNP (82 ± 10 mmHg) to LBNP+SHAM (80 ± 8 mmHg, P = 0.978), but markedly increased during LBNP+FC. The peak increase from LBNP (77 ± 9 mmHg) was observed after 3 minutes of LBNP+FC (98 ± 15 mmHg, P < 0.001). Heart rate during LBNP (76 ± 14 bpm, P = 0.978) was not different from LBNP+SHAM (75 ± 13 bpm). Heart rate was lower throughout LBNP+FC beginning at 2 minutes of FC (60 ± 16 bpm) versus LBNP (80 ± 19 bpm, P < 0.001). Stroke volume did not change from LBNP (72 ± 15 mL) to LBNP+SHAM (67 ± 18 mL, P = 0.857). However, stroke volume increased from LBNP (78 ± 16 mL) to LBNP+FC, and peaked after 5 minutes of FC (97 ± 32 mL, P < 0.001). Cardiac output did not change from LBNP (5.4 ± 1.0 L/min) to LBNP+SHAM (4.9 ± 1.0 L/min, P > 0.415). Cardiac output slightly decreased from LBNP (6.2 ± 1.5 L/min) to 2 minutes of LBNP+FC (5.3 ± 1.6 L/min, P = 0.038). Total peripheral resistance did not change from LBNP (15.6 ± 3.7 mmHg/L/min) to LBNP+SHAM (17.3 ± 3.2 mmHg/L/min, P = 0.613). Total peripheral resistance throughout LBNP+FC was greater than LBNP. The peak increase in total peripheral resistance was observed after 2 minutes of LBNP+FC (20.0 ± 6.2 mmHg/L/min) versus LBNP (13.2 ± 3.9 mmHg/L/min, P < 0.001).  

Conclusions

Face cooling during simulated moderate blood loss increases blood pressure through an increase in total peripheral resistance. Although more research is warranted, face cooling during blood loss is a potential simple and quick intervention that could delay cardiovascular decompensation.  Support or Funding InformationUniversity at Buffalo IMPACT Award

| Tags : choc, hémorragie

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