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CRITICAL CARE AND TRAUMA

Intrathoracic Pressure Regulation Improves 24-Hour Survival in a Porcine Model of Hypovolemic Shock

Demetris Yannopoulos, MD^*, Scott McKnite, BSc, Anja Metzger, PhD, and Keith G. Lurie, MD^||¶

From the *Department of Cardiology, University of Minnesota; Minnesota Medical Research Foundation, Hennepin County Medical Center, Minneapolis, Minnesota; Advanced Circulatory Systems, Inc., Eden Prairie, Minnesota; Cardiac Arrhythmia Center at the University of Minnesota; ||Department of Emergency Medicine, Hennepin County Medical Center; and ¶Minneapolis Medical Research Foundation, Minneapolis, Minnesota.

Address correspondence and reprint requests to Keith G. Lurie, MD, Minneapolis Medical Research Foundation, 914 South 8th St., 3rd Floor, Minneapolis, MN 55404. Address e-mail to klurie{at}advancedcirculatory.com.

BACKGROUND: The intrathoracic pressure regulator (ITPR) plus positive pressure ventilation (PPV) has been shown to improve coronary and cerebral perfusion pressures during hypovolemia by improving mean arterial blood pressure and by decreasing right atrial and intracranial pressures. We hypothesized that application of intermittent negative intrathoracic pressure in a pig model of severe hypovolemic hypotension would increase 24-h neurological intact survival rates.

METHODS: Eighteen isoflurane-anesthetized pigs were bled 55% of their estimated blood volume and were then prospectively randomized to either ITPR treatment with –8 mm Hg endotracheal pressure plus PPV or only PPV alone for 90 min. All survivors were reinfused with their own blood. Arterial blood gases, end-tidal CO₂, and aortic pressures were monitored for the 90 min and neurological evaluation was performed at 12 and 24 h after reinfusion.

RESULTS: ITPR plus PPV treatment for 90 min prevented the progression of metabolic acidosis and significantly improved mean arterial blood pressure (mean over 90 min, 55 ± 3 vs 35 ± 2.4 mm Hg, P < 0.001) when compared with controls. Twenty-four hour survival significantly improved with use of the ITPR when compared with untreated controls: 9/9 (100%) vs 1/9 (11%), P < 0.01.

CONCLUSIONS: Use of the ITPR plus PPV for 90 min significantly increased arterial blood pressure and 24 h neurologically intact survival rates compared with controls treated with PPV alone.

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