Effect of hypercapnia on arterial hypotension after induction of anaesthesia

We evaluated the effectiveness of intentional hypercapnia against hypotension after induction of anaesthesia with thiopental and isoflurane (TI) or propofol (P). For each group, 24 patients were anaesthetized with thiopental 4 mg kg−1 (TI) or propofol 2 mg kg−1 (P) for tracheal intubation and then lightly anaesthetized with isoflurane at 0.6% end-expiratory concentration (TI) or by 6 mg kg−1 h−1 infusion of propofol (P). In both anaesthesia groups, patients were randomly assigned to either normocapnia (end-tidal CO2 = 35 mmHg) or hypercapnia (end-tidal CO2 = 45 mmHg), which were achieved through adjusting the tidal volume. Systolic arterial pressure (SAP) 15 min after intubation was compared with the preanaesthetic baseline value. Under normocapnia, both TI and P induced a comparable, statistically significant suppression of SAP by approximately 20 mmHg from baseline. Hypercapnia prevented the decrease in SAP in TI but not in P. No patient in the TI-hypercapnia group experienced SAP below 100 mmHg, unlike those in the other groups. In conclusion, mild hypercapnia was effective in the prevention of hypotension in patients receiving thiopental followed by 0.6% end-expiratory isoflurane, but not in patients receiving 6 mg kg−1 h−1 propofol.