Hyperventilation During CPR May Contribute to Poor Survival Rates

Excessive ventilation during cardiopulmonary resuscitation (CPR) is likely to increase intrathoracic pressure and decrease coronary perfusion pressure, according to a new study. Hyperventilation, which may occur during out-of-hospital CPR, probably contributes to the poor survival rates from cardiac arrest, the authors maintain.

Although the American Heart Association recommends 12-to-15 breaths per minute during CPR, a previous study found that cardiac arrests treated in-hospital were being treated with high ventilation rates, lead author Dr. Tom P. Aufderheide told Reuters Health.

To further investigate, his group observed EMS personnel as they performed CPR on 13 patients in cardiac arrest, none of whom survived. The findings appear in the rapid access issue of Circulation, to be published on April 27.

While treating the first seven cases, the paramedics administered ventilation at maximum rates averaging 37 breaths per minute (range, 19 to 49), so that positive airway pressures were maintained for 44.5% of the resuscitation time.

The other six cases were treated after the EMS personnel were retrained, and ventilation rates declined to an average maximum of 22 breaths per minute. Because ventilation duration was significantly longer, the percentage of time with positive pressure was 50%.

To determine the consequences of hyperventilation, Dr. Aufderheide, at the Medical College of Wisconsin in Milwaukee, and his colleagues evaluated three groups of seven pigs in cardiac arrest that were ventilated at 12, 20 or 30 breaths per minute, respectively.

Increased ventilation rate was associated with higher mean intrathoracic pressure (p < 0.0001), lower coronary perfusion pressure (p = 0.03) and higher arterial pH (p = 0.0006). In three more groups of pigs, six of seven ventilated at 12 breaths per minute (100% oxygen) survived, versus one of seven ventilated at 30 breaths per minute with 100% oxygen, and one of seven treated with 5% CO2/95% oxygen. The authors note that during the decompression phase of standard CPR, the small vacuum created within the chest draws venous blood back into the heart. In hyperventilated patients, persistently positive intrathoracic pressure decreases cardiac preload and cardiac output, and impedes right ventricular function. “We believe this is not an isolated phenomenon,” Dr. Aufderheide said, “and that excessive ventilation is commonly applied by all professional rescuers–doctors, nurses, paramedics and respiratory therapists.” He attributes the problem to the current emphasis during CPR training programs on airway management and the need to provide oxygen in patients who are not breathing. His group is currently evaluating a device invented by Dr. Keith G. Lurie at the University of Minnesota in Minneapolis. Dr. Aufderheide describes the device as “a ventilation timing light that flashes 12 times per minute for 1 second each time to assist breaths at the correct rate.” Quality assurance monitoring since submission of this paper has documented that the device establishes the correct rate and duration of ventilation. The “ResqPod Circulatory Enhancer,” under development by Advanced Circulatory Systems Inc. in Eden Prairie, Minnesota, is not yet commercially available and is approved for investigational use only. Circulation 2004;109.