ABSTRACT
Objective To assess the influence of changes in alveolar ventilation on gastro-intestinal perfusion measured via a nasogastric tonometer.Methods Sixteen ASA Ⅰ - Ⅱ patients ( 7 male, 9 female) aged 15-67 yr, undergoing elective intracranial operation were included in this study. The patients were premedicated with oral ranitidine 150 mg and intramuscular phenobarbital 0.1 g and atropine 0.5 mg. Anesthesia was induced with midazolam 1-2 mg, fentanyl 2 ?g? kg-1 , propofol 1.5-2.0 mg ? kg-1 and vecuronium 0.1 mg ? kg-1 , and maintained with 0.5%-2.0% isoflurane inhalation and intermittent iv boluses of fentanyl and vecuronium. The patients were intubated and mechanically ventilated after induction of anesthesia. The ventilatory settings were : RR 10 bpm; FGF 1 L? min-1; I: E = 1:2; the initial VT was 7 ml? kg-1 (T1 ) which was gradually increased to 8 ml ?kg-1(T2), 9ml?kg-1(T3) and 10 ml?kg-1 (T4) and then returned to 7 ml ? kg-1 again. Each VT was maintained for 1 h. A nasogastric tonometer (Tonocap, Datex-Ohmeda, Finland) was inserted into stomach and automatically measured gastric intramucosal CO2 tension (PgCO2) every 10 min. Radial artery was cannulated for direct MAP monitoring and blood sampling. Blood gas analysis was performed every hour at various VT levels. Gastric-to-arterial pH gap and gastric-to-arterial PCO2 gap [P(g-a)CO2] were calculated.Results PgCO2 decreased during T2_4 (hyperventilation phase) (P