Inspiratory impedance threshold valve during CPR.

The use of an inspiratory impedance threshold valve (ITV) during cardiopulmonary resuscitation (CPR) should reduce intrathoracic pressure during natural chest recoil or active chest decompression. This might in turn improve venous return and thereby organ blood flow. The haemodynamic effects during both standard CPR and active compression-decompression (ACD)-CPR with and without the ITV, therefore, were studied in a well-established porcine model with cross-over design. Sixteen pigs were randomised to one of four methods initially, changing the method every fifth minute during mechanical chest compression at 100 min(-1). Myocardial blood flow was doubled when the valve was added to standard CPR, median (q25-q75) 14 (3-47) versus 27 (9-51) ml min(-1) 100 g(-1) (P=0.001). ACD-CPR caused a similar increase, while adding the ITV to ACD-CPR only tended to increase myocardial blood flow (P=0.077). Varying the technique had no effect on cerebral, kidney or carotid blood flow, coronary perfusion pressure, expired CO(2) concentrations or blood gases. The valve is a promising new tool in CPR, but more independent studies of the device are needed.