Pulsus alternans during general anesthesia with halothane - Effects of permissive hypercapnia

Background: 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 cycl e length. It may be a sign of severe decompensated congestive heart failure . The authors infrequently encountered some cases of pulsus alternans durin g halothane anesthesia with spontaneous respiration in otherwise normal sub jects in association with high levels of end-tidal carbon dioxide. This stu dy was conducted to determine if there is any relation between this phenome na and hypercapnia. Methods: One hundred twenty patients undergoing elective lower extremity su rgery 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 the n confirmed by palpation of the radial artery. Results: Ten patients (8.3%) developed pulsus alternans together with eleva ted levels of end-tidal carbon dioxide (57 +/- 4 mmHg vs. 41 +/- 4 mmHg in patients without pulsus alternans [mean +/- SD]). The pulsus alternans disa ppeared after switching to controlled ventilation and 15-20% reduction in e nd-tidal carbon dioxide. During the period of pulsus alternans, vital signs and electrocardiography remained within normal limits. Conclusions:: There may be some relation between occurrence of pulsus alter nans and hypercapnia during halothane anesthesia. Pulsus alternans occurs i n a small fraction of spontaneously breathing, halothane-anesthetized patie nts. Although hypercapnia is clearly a factor, the mechanism of this phenom enon is unknown.