Influence of Subarachnoid Anesthesia in the Prone Position on the Energy of Circulation

Abstract

The energy supply of the body has an energy price, which is paid, in particular, by the myocardium. This price depends on the circulatory conditions, which can also be affected by iatrogenic factors, such as subarachnoid anesthesia (SA) in the prone position. Decreasing of a vascular tone under the influence of SA requires the myocardium to increase energy consumption to maintain an adequate cardiac index (CI). With a resistive type of circulation, autoregulation of blood circulation may become untenable, that requires artificial maintenance of vascular tone with the α1-adrenomimetics, that also contribute to an increase in energy expenditure by the myocardium. All this makes the assessment of blood flow energy relevant.The aim of the study was to study the effect of SA in the prone position on the energy of circulation.65 patients underwent transpedicular stabilization of 1-2 segments under SA in the prone position have been examined. On the eve of the operation, the prognostic index of hemodynamic instability (PIHI) has been determined by the N. Lysohub’s method. At three stages (the position on the back after performing SA, 5 and 20 minutes after turning on the prone position), kinetic (systolic index, ejection fraction, heart rate and SI), dynamic (effective, or average, AP — APe, central venous pressure, the difference between them — systemic perfusion pressure and specific peripheral vascular resistance) and hemic (blood oxygen content) indicators have been determined. Based on these indicators and the energy potential of oxygen (the energy obtained by glucose oxidation by 1 mol of oxygen), the following energy parameters have been calculated: flow power index (FPI), tissue power consumption index (TPCI), oxygen reserve (OR) and circulatory reserve index (CRI). APe was maintained at least 60 mm Hg during anesthesia by infusion and, if necessary, by administration of the α1- adrenomimetic phenylephrine. Patients have been retrospectively divided into 2 groups: patients of the VF1 group (n = 25) needed phenylephrine administration, and patients of the VF2 group (n = 40) did not need it.The following results have been obtained. The minimum PIHI in the VF1 group was 0.1, which made it possible to expect a high probability of hemodynamic instability, while in the VF2 group it was no higher than 0.05. The integral kinetic parameter CI in the groups did not differ significantly, but the energy consumption and their efficiency between the groups significantly differed. FPI in the VF1 group was significantly lower than in the VF2 group, although TPCI did not differ significantly between the groups. TPCI compliance with tissue needs was determined by OR, which was significantly lower in the VF1 group. The final parameter CRI was significantly lower in the VF1 group, although CI did not differ significantly from the VF2 group level. This indicates energy insufficiency of circulation in patients with a resistive type of circulation against the background of SA in the prone position, so with this type, the presence of which is confirmed by a high PIHI, preference should be given to another type of anesthesia.