Biphasic extrathoracic pressure CPR. A human pilot study.

HYPOTHESIS Alternating intrathoracic pressure by means of a chest cuirass can cause perfusion and ventilation equal to or better than standard cardiopulmonary resuscitation (CPR) for humans in cardiac arrest. DESIGN Nonrandomized, nonblinded, crossover pilot study. SETTING Large urban emergency department. SUBJECTS Five adult normothermic, nontraumatic, out-of-hospital cardiac arrest patients unresponsive to standard advanced cardiac life support. METHOD Right atrial and aortic catheters were inserted for pressure measurement and blood gas analysis while the patient was receiving standard CPR by a pneumatic compression device (Thumper). The Thumper was then replaced by a chest cuirass (Hayek Oscillator). Pressure and blood gas measurements were then repeated. RESULTS The coronary perfusion pressure increased from -1.2 +/- 8.6 mm Hg to 6.2 +/- 6.9 mm Hg for a mean change of 7.4 +/- 3.1 mm Hg (p = 0.006). The compression phase gradient increased 10.0 +/- 21.9 mm Hg (p = 0.364). The venous to arterial PCO2 gradient decreased 44.5 +/- 32.3 mm Hg (p = 0.070). The oxygen extraction ratio increased 1.6 +/- 9.4 percent (p = 0.761). The mean arterial PO2 and PCO2 changed from 252 to 240 mm Hg (p = 0.836) and from 53 to 66 (p = 0.172) mm Hg, respectively. CONCLUSION The Hayek Oscillator chest cuirass produced a significant improvement in the coronary perfusion pressure. There was a trend for improved systemic perfusion as indicated by an improved compression phase gradient and venous to arterial PCO2 gradient, although this was not supported by the lack of improvement in the oxygen extraction ratio. The cuirass also adequately oxygenates and ventilates unassisted by positive pressure ventilation.