The Effect Of Tilt On Flow And Pressures In A Miniaturized Extracorporeal Life Support System

Hilary B Loge, MD1, Ryan Schutter, MD2, Brian J Gavitt, MD, MPH1, Jeremy Cannon, MD3, J Kevin Grayson, DVM, PhD1, B. Zane Atkins, MD, FACS1. 1Travis AFB, 2McConnell AFB, 3Ft Sam Houston

Objectives: Wounded warriors with severe lung injuries are currently being transported out of theater on extracorporeal life support (ECLS) via fixed-wing aircraft. There has been no systematic evaluation of the effects of in-flight patient position changes on circuit flows and pressures or on patient hemodynamics during transport. The first step in evaluation is to determine the effects of head up and head down tilt, simulating the angles of takeoff and landing, on the ECLS circuit and patient.

Methods: Swine were placed on the CardioHelpTM ECLS system, which is a miniaturized pump and circuit ideal for transport. Animals were placed in both a 15 degrees head up and 15 degrees head down position for periods of 30 minutes with a neutral period in between. Hemodynamics as well as circuit flow and pressures were recorded and compared to baseline.

Results: Cardiac output was significantly increased in both the head up (7.1 ± 0.2 L/min, p = 0.002) and head down positions (6.5 ± 0.3 L/min, p = 0.01) compared to neutral (5.5 ± 0.2 L/min).  Stroke volume was significantly increased in the head up position (71.6 ± 2.4 mL, p = 0.014) but not in the head down position (65.5 ± 4.0 mL, p = 0.07) compared to neutral (57.3 ± 4.0 mL). Venous drainage pressure in the ECLS circuit was significantly decreased in the head up position (-28.0 ± 1.5 mm Hg) compared to both neutral (-36.5 ± 2.2 mm Hg, p = 0.005) and head down (-33.3 ± 1.6 mm Hg, p = 0.027) positions.

Conclusion: Animals maintained their cardiac output while tilted. In fact, cardiac output increased in both the head up and head down positions. This suggests that patient positioning in an aircraft while on ECLS does not alter hemodynamics or circuit parameters during takeoff and landing. These findings also suggest that patient positioning for physical therapy and rehabilitation is safe while on ECLS support.

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