Hemodynamic Responses and Oxygen Availability in Unanesthetized Dogs during Apnea / 대한마취과학회지

BACKGROUND: This study examined hemodynamic variables, oxygen delivery, extraction, and consumption in response to acute progressive hypoxia and hypercarbia in the setting of apnea. METHODS: Apnea was induced in 9 healthy mongrel dogs by disconnecting animals from mechanical ventilation of 30 minutes with pure oxygen. Hemodynamic variables, oxygen transport, extraction, and consumption were rapidly and repeatedly measured using pulmonary arterial and arterial catheters until cardiac output was undetectable. RESULTS: The baseline PaO2, PaCO2, pH, base excess were 318 +/- 137 mm Hg, 36 +/- 3.5 mm Hg, 7.30 +/- 0.06, 6.81 +/- 2.65 mmol/l respectively. Hypercarbia and hypoxemia (76 +/- 33 mm Hg) was first noted at 1 and 4 minute respectively. Base excess was not changed. Indices of preload (PCWP and CVP) were increased early in the time course (p<0.05). In contrast, indices of afterload (SVR) increased later, just before cardiac decompensation began (p<0.05). No significant reduction of cardiac output, oxygen delivery, extraction, and consumption was detected just until abrupt cardiac decompensation started, 5 minute. CONCLUSIONS: These data suggest that the early increase in preload was primarily due to hypercarbia whereas the late increase in afterload was due to hypoxemia, but the main cause of acute cardiac decompensation was a critical decrease in arterial oxygen tension with some contribution of increased preload and afterload.

The Appropriate Inflow Rates of Oxygen and Nitrous Oxide in Adult General Anesthesia / 대한마취과학회지

BACKGROUND: During adult general anesthesia, we used 3~5 L/min of fresh gas flow(FGF) but low FGF are employed, the amount of anesthetic consumption and air contamination can be reduced. The aim of this study was to determine the minimal appropriate inflow rate of oxygen and nitrous oxide during semiclosed circle technique. METHODS: We selected 40 patients, ASA group 1 or 2, scheduled for elective, nonabdominal surgery under general anesthesia with semiclosed circle system. Anesthesia was maintained with 50% oxygen, nitrous oxide and enflurane, controlled ventilation was used; rate of 10/min, tidal volume of 10 ml/kg. After induction and vital signs stabilized, FGF was changed to 4 L, 3 L, 2 L and 1L/min at interval of 30 minutes. We observed mean airway pressure and arterial blood gas tensions. RESULTS: The changes of mean airway pressure did not correlated with fresh gas inflow rate. In arterial blood gas analysis, PaO2 showed a decreasing tendency significantly according to decreasing fresh gas inflow rate(p<0.01) but there were no clinical hypoxemia in all patients. There were no significant changes in pH, PaCO2 and base excess. CONCLUSIONS: We consider that FGF of 1~2 L/min is appropriate during adult general anesthesia because of economic and ecological advantages. Also, we consider low flow technique with below 1L/min can be used safely and effectively under proper gas monitoring such as oxygen analyzer, capnometer.