Effects of mechanical ventilation on the electrocardiogram in adults

The effects of mechanical ventilation on the surface electrocardiogram (ECG) have not been systematically investigated and the anticipated changes such as rightward P and QRS axes shifts, reduced QRS voltage, and slow R-wave progression are not supported by definitive data. We sought to determine the effects of mechanical ventilation on the surface ECG in hemodynamically stable adults without active cardiopulmonary disease. Seventeen patients in good overall health who were undergoing elective outpatient surgery had serial ECGs done preoperatively, intraoperatively, and postoperatively. No clinically significant changes in QRS or P-wave axis were detected. R-wave progression was not altered and there were no significant differences in the QRS amplitudes pre-, intra-, or postoperatively in either the precordial or limb leads. The present study shows that hemodynamically stable patients without active cardiopulmonary disease undergoing elective surgery demonstrate relatively minor ECG changes from baseline despite the addition of positive pressure ventilation. Clinicians should not assume that substantial changes in P wave or QRS axis or amplitude in patients undergoing mechanical ventilation are due to the effects of positive pressure ventilation alone.