The Combination of General Anaesthesia and Epidural Block I: The Effects of Sequence of Induction on Haemodynamic Variables and Blood Gas Measurements in Healthy Patients

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Abstract
The haemodynamic effects of epidural block, administered before or after general anaesthesia, were investigated in twelve healthy women scheduled for elective gynaecological surgery. The effects of 10° head down tilt and administration of atropine 0.6 mg intravenously were also determined. Haemodynamic measurements included systolic (SAP), diastolic (DAP) and mean (MAP) arterial pressure, heart rate (HR), cardiac output (CO) and systemic vascular resistance (SVR). In those receiving general anaesthesia first (Group A) (thiopentone/suxamethonium/N2O/O2) significant changes occurred only at the time when epidural block and general anaesthesia were both present: SAP, DAP and MAP (-22%, p < 0.001) were reduced compared to awake control values, however changes in HR, CO and SVR were not significant. In those receiving epidural block first (Group B) (1.5% lignocaine, mean dose 270 mg), MAP was reduced by 20% (p < 0.01) from awake control values after epidural block and there was a further reduction to 35% below control (p < 0.001) when general anaesthesia was induced. These changes were accompanied by a significant reduction in SVR. Comparison of all variables between Group A and Group B showed no clinically significant differences, indicating that the order of performance of epidural block (before or after general anaesthesia) did not affect haemodynamic variables. Head down tilt resulted in no haemodynamic changes in the presence of general anaesthesia or epidural block alone and only minimal changes when the two were combined. In contrast, intravenous atropine (0.6 mg) resulted in a return of arterial pressures to essentially baseline values in both Group A and Group B (HR increased 84%, p < 0.001; MAP increased 37%, p < 0.001; CO increased 70%, p < 0.001).