Hyperventilation during CPR may be deadly

Susan Jeffrey

April 05, 2004

Dallas, TX - A new study has identified a tendency by emergency medical services (EMS) personnel to hyperventilate patients during cardiopulmonary resuscitation (CPR) of out-of-hospital cardiac arrest. A follow-up animal study showed ventilation rates similar to those used in the field resulted in increased intrathoracic pressures, decreased coronary perfusion pressures, and reduced survival.

The report appears online as a rapid access publication April 5, 2004 and will be published in the April 27, 2004 issue of Circulation[1].

"Oxygenating the patient has always been a fundamental mainstay of resuscitative efforts, and until now, there has been no known detrimental effect" of hyperventilation, lead author Dr Tom P Aufderheide (Medical College of Wisconsin, Milwaukee) told heartwire . The overall survival rate from cardiac arrest in the US is only about 5%, he said. "Excessive ventilation may be contributing to that poor outcome."

Coauthor of the study was Dr Keith G Lurie (University of Minnesota, Minneapolis).

The threat of positive pressure

The new observation was an incidental finding during the process of a completely different study, Aufederheide said. Researchers were accompanying rescuers on calls, measuring the number and duration of ventilations given. After seven patients, they noticed that the mean ventilation rate was about 37 breaths per minute, much higher than the 12 to 15 breaths per minute recommended by current American Heart Association guidelines for patients with a secured airway during CPR.

Training was then offered to the EMS personnel stressing the need for a lower ventilation rate, the authors note. In the subsequent six patients, ventilations fell to about 22 breaths per minute. However, ventilations were also a slightly longer duration after training, about 1.18 seconds per breath compared with 0.85 seconds before training, meaning that the percentage of time that a positive pressure was recorded in the lungs was still about 47%. No patient in this small sample survived.

During the decompression phase in CPR, the researchers explain, a vacuum is created within the chest, drawing venous blood back to the heart. Frequent ventilations mean that less blood returns to the right heart between compressions, potentially reducing the effectiveness of CPR.

To look at the consequences of excessive ventilation on outcomes, they went on to study a cardiac-arrest model in pigs, attempting to replicate the effects of the same rates of hyperventilation seen in the patients. Pigs ventilated at higher rates had lower survival as well as significantly increased mean intrathoracic and decreased coronary perfusion pressures.

Survival in an animal model of CPR by ventilation rate (breaths per minute)

End point

12 bpm (100% O2)

30 bpm (100% O2)

30 bpm (95% O2+5% CO2)

p

Survival (n)

6/7 1/7 1/7 0.006

 

"Additional education of CPR providers is urgently needed to reduce these newly identified and deadly consequences of hyperventilation during CPR," the researchers conclude. "Individuals who perform CPR as a part of their professional practice should monitor ventilation rates during cardiac arrest and limit them to 12 breaths per minute," Aufderheide said.

"This is the first paper of its kind documenting the potentially detrimental effects of hyperventilation and will really be valuable in targeting further research," Dr Mary Fran Hazinski ( Vanderbilt University Medical Center, Nashville, TN, American Heart Association Emergency Cardiac Care Program) told heartwire .

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