Pulsus alternans during general anesthesia with halothane: effects of permissive hypercapnia

Pulsus alternans is a classic type of abnormal pulse. It can be defined as a regular alternation of pulse amplitude in which runs of weak and strong beats follow each other alternatively without any change in cycle length. It may be a sign of severe decompensated congestive heart failure. The authors infrequently encountered some cases of pulsus alternans during halothane anesthesia with spontaneous respiration in otherwise normal subjects in association with high levels of end-tidal carbon dioxide. This study was conducted to determine if there is any relation between this phenomena and hypercapnia.

One hundred twenty patients undergoing elective lower extremity surgery were selected. Halothane was used for maintenance of anesthesia, and the patients were allowed to breath spontaneously. The occurrence of pulsus alternans was determined by plethysmographic display of pulse wave and then confirmed by palpation of the radial artery.

Ten patients (8.3%) developed pulsus alternans together with elevated levels of end-tidal carbon dioxide (57 +/- 4 mmHg vs. 41 +/- 4 mmHg in patients without pulsus alternans [mean +/- SD]). The pulsus alternans disappeared after switching to controlled ventilation and 15-20% reduction in end-tidal carbon dioxide. During the period of pulsus alternans, vital signs and electrocardiography remained within normal limits.

There may be some relation between occurrence of pulsus alternans and hypercapnia during halothane anesthesia. Pulsus alternans occurs in a small fraction of spontaneously breathing, halothane-anesthetized patients. Although hypercapnia is clearly a factor, the mechanism of this phenomenon is unknown.