Why the phantom p-wave during general anesthesia?

Although atrioventricular junctional rhythm (AVJR) is frequently encountered during general anesthesia, its genesis is poorly understood. The present study was undertaken to test the hypothesis that AVJR is promoted by hypocarbia. One hundred patients (69 females, 31 males), ASA Physical Status Class I, who were 20 to 30 years old, were studied. One-half of the patients were induced with thiopental and maintained with 0.5 to 2.1% isoflurane, 70% nitrous oxide (N2O) and oxygen. The other half of the patient population was induced with thiopental and fentanyl or alfentanil and maintained with the opioid, 70% N2O and oxygen. During maintenance, each patient was hyperventilated to an endtidal carbon dioxide level of 20 to 25 mm Hg and the electrocardiogram recorded to determine if the p-wave disappeared, which is the obvious manifestation of AVJR. During normocarbia, none of the 100 patients developed AVJR. During hypocarbia, the incidences of AVJR during isoflurane-N2O anesthesia and opioid-N2O anesthesia of 18% and 26%, respectively, were significant by chi-square analysis. Consequently, the data suggest that hypocarbia may promote AVJR during general anesthesia.