The Effects Of Controlled Hypotension On Glutathione S-Transferase And Gastric Mucosal PH

IntroductionControlled hypotension was often used to reduce intraoperative blood loss and the transfusion of allogeneic blood. At the same time it will provide good surgical conditions. But when MAP is too low , the blood flow to tissues will decrease. This may result in a dangerous disturbance of oxygenation. So the safety of controlled hypotension is very important. Most of previous studies were mainly focused on vital organs. However, the cerebral and coronary vascular system is characterized by well - functioning autoregulatory mechanisms. Splanchnic blood pressure - flow autoregulation is much less effective than the autoregulation of the brain, heart, or the kidneys. Therefore, controlled hypotension may result in a decreased blood flow to liver and other splanchnic organs before the hypoxia of vital organs. Several studies have indicated that the measurement of the cy-tosolic liver enzyme glutathione S - transferase (GST) may provide a very sensitive indicator of hepatocellular integrity. And i - pH, PgCO₂, PCO₂gap will provide a sensitive indicator of gastric intramucosal acidosis.ObjectiveTo investigate the effects of nicardipine or sodium nitroprusside — induced hypotension on splanchnic perfusion.Materials And MethodsPatients: Fourty - five patients, ASA physical status I - â…¡ , scheduledfor decompression laminectomy, were divided randomly into group C, group N and group S. Methods: All patients were premedicated with i. m. atropine (0. 5mg) 30 minutes before induction of anesthesia, which was induced by midazo-lam (0.04mg/kg) , vecuronium (0.1 mg/kg) , fentany (4jjtg/kg) , propofol (2 mg/kg). A constant fresh gas flow of 2 L/min was used during maintenance of anesthesia. Ventilation was performed in both groups with 50% nitrous oxide in oxygen. The ventilation pattern was adjusted to maintain PaCO2 between 35 and 45mmHg. Anesthesia was maintaind by continuous i. v. infusion of propofol and remifentanil with intermittent vecuronium, and adjusted by inhalation of isoflu-rane ( < 1% ) according to heart rate and blood pressure. Crystalloids and gelatin were given to maintain central venous pressure (CVP) at 8 - 12cmH2O. Routine intraoperative monitoring included continuous invasive measurement of mean arterial blood pressure (MAP) and central venous pressure ( CVP). Controlled hypotension was initiated 30 minutes after the beginning of the operation. Group N received a controlled hypotension by infusion of nicardipine and Group S received a controlled hypotension by infusion of sodium nitroprusside. In group N and group S, mean arterial pressure (MAP) was maintained at 60 ±5mmHg. In group C, mean arterial pressure (MAP) was maintained at MAP(T0) ± lOmmHg. The arterial blood samples were taken for measurements of pHa, BE, Hb, GST before hypotension(T0), at 30 min(Tj) , 60 min(T2) during hypotension. Data of i - pH, PgCO2, PCO2gap were recorded at the same time points as above. GST activities were measured using biochemical method. I — pH, Pg-CO2 , PCO2gap was measured by gastric tonometry. Data are shown as the means ± standard deviation. Statistical analysis was performed using the paired t - test and unpaired t - test. P <0. 05 was considered clinically significant.Results1. At T2 GST was increased significantly compared with that at To in group N and group S(P<0.01);GST in group N and group S was significantly greater than that in group C at T2(P <0.05).2. In group N and group S, PgCO2and PCO2gap was increased and i - pH was decreased significantly at Tl and T2than that at To( P < 0. 01). At T1 and T2, PgCO2and PCO2gap was greater and i - pH was lower in group N and group S than that in group C( P <0. 05 ) .Conclusion1. Nicardipine or Sodium nitroprusside - induced hypotension may result in a disturbance of gastric intramucosal perfusion within 30 minutes and a increase of GST within 60 minutes;2. The difference of vasodilating agents seems unimportant;3. I - pH, PgCO2, PCO2 gap and GST should be monitored during controlled hypotension as sensitive indicators of the hypoxia of local tissues.