thiopental and Cardiac-Tamponade

The hemodynamic effects of changes in PaCO2 during intermittent positive pressure ventilation (IPPV) were studied in nine dogs with acute cardiac tamponade. During steady state light thiopental anesthesia, measurements were performed during hypocarbia (24.0 +/- 2.6), normocarbia (40.4 +/- 2.4), and hypercarbia (56.8 +/- 3.1 mm Hg; mean +/- SD). The study was carried out at a standardized level of cardiac tamponade that gave a 60% reduction in cardiac output (CO) at normocarbia. Changes in airway pressure were avoided by adding CO2 to the inspiratory gas to obtain the desired PaCO2. Hypercarbia increased pericardial pressure 2-4 mm Hg and significantly decreased CO. During hypocarbia CO increased as pericardial pressure decreased 3-6 mm Hg. These findings are the reverse of changes seen when tamponade is not present. The changes in pericardial pressure most likely influence myocardial tone and cardiac volume and, thus, CO. The results suggest that patients with cardiac tamponade requiring general anesthesia should not breathe spontaneously if there is any danger of respiratory depression and hypercarbia.

Topics: Acute Disease; Anesthesia, Intravenous; Animals; Carbon Dioxide; Cardiac Tamponade; Dogs; Hemodynamics; Hypercapnia; Intermittent Positive-Pressure Ventilation; Positive-Pressure Respiration; Thiopental

Topics: Anesthesia; Anesthesia, Endotracheal; Anesthesiology; Cardiac Surgical Procedures; Cardiac Tamponade; Halothane; Humans; Hypotension; Lidocaine; Mitral Valve; Nitrous Oxide; Oxygen; Pericardial Effusion; Succinylcholine; Thiopental; Thoracic Surgery