Passive Leg Raising Predicts Hypotension Induced By Propofol Induction

Background and ObjectiveIn clinical, body position alters the effect of gravity on body function to induce hemodynamic change. Special positions commonly adopted to meet clinical need. Passive leg raising (PLR) is a positional change from the semi-recumbent position or the supine position to the lower limbs elevated at 30°,45°,60°.PLR may potentially increase cardiac preload and then cardiac output by shifting venous blood from the legs and splanchnic compartment towards the thorax. Lifting legs in the event of circulatory collapse is a rescue maneuver that has been used for years by first-aid rescuers. As a simple way to increase cardiac preload, PLR has recently been reported to assess fluid responsiveness and indirectly judge volume status then guide volume therapy. These reports aroused our interest, every anaesthetist working in clinical knows that during the anesthesia induction, most of the patients will encounter decrease of BP and HR apparent, which may be partly related to the patient's pre-induction volume status. We can avoid the related side effects caused by volume treatment blindly if we can estimate the volume status and volume responsiveness before the anesthesia induction and judge whether the patient is responsive to the fluid therapy. We can also supply enough fluid or choose appropriate anesthesia methods to avoid hypotension, cardiac ischemia and other complications during anesthesia induction. Our study is aimed to explore whether preoperative passive leg raising induced hemodynamic change is correlated to hemodynamic change during propofol induction and to confirm their correlation degree, so that we can evaluate whether PLR induced hemodynamic change as a basis of the selection of anesthesia induction plan and fluid management.MethodsA total of 65 ASA I-II patients, aged 18-55 years, who were scheduled for elective surgery under general anesthesia with trachea intubation were enrolled. After the patient entering into the operating room, peripheral intravenous cannula and radial artery cannula were placed. BeneView T8 multi-function monitor was used to monitor Electrocardiogram (ECG), Pulse Oxygen Saturation (SpO2), Invasive Blood Pressure (IBP) and other hemodynamic parameters detected by Impedance Cardiogram (ICG) module. After 5 minutes of rest at the 45°semi-recumbent position (base position), blood pressure (BP), heart rate (HR), stroke volume (SV) and cardiac output (CO) were measured as basis values before PLR. Then the patient was transferred in the trunk supine with lower limbs lifted at 45°, that is PLR position, during the period of PLR position the BP, HR, SV, CO were recorded in 2 minutes at 30s interval. Before anesthesia induction, patients were then transferred in supine position, BP, HR, CO and SV values were measured as the pre-aesthesia base values after 5 minutes rest. Under breathing 100% oxygen (6L/min), patients were induced with the propofol target-controlled infusion (target concentration 4ug/ml). BP, HR, CO and SV values were measured at 30s interval from the start of propofol infusion to the loss of patient's eyelash reflection. Based on the mean arterial blood pressure (MAP ) decrease of >30% during propofol induction, a11 the patients were divided into hypotension group and non-hypotension group, the predicting power of propofol induced hypotension by PLR induced hemodynamic changes were analyzed. ResultsSV and CO increased by 16%±2% (P<0.05), 15%±3% (P<0.05) respectively from baseline to PLR, while HR had no significant change (P >0.05). SBP, DBP, MAP were decreased after PLR by 7%±2%, 7%±1%, 6%±1% (P <0.05). BP, HR, CO and SV were significantly decreased after propofol administration (P <0.05). PLR induced SV change (PLR-ΔSV) and PLR induced CO change (PLR-ΔCO) were correlated with the change of BP (include SBP, DBP and MAP) during propofol induction, and with greatest correlation (r) with the MAP change. The correlation coefficient of PLR-ΔSV and PLR-ΔCO with propofol induction induced MAP change were -0.84 and -0.83 respectively. PLR-ΔSV and PLR-ΔCO were significantly different between hypotension group and non-hypotension group (P<0.05). After propofol induction, PLR-ΔSV≧16% predicted hypotension with a sensitivity of 0.89 and a specificity of 0.95, PLR-ΔCO≧15% predicted propofol induced hypotension with a sensitivity of 0.88 and a specificity of 0.92.Conclusion1. PLR induced changes of SV and CO were well correlated with the decrease of MAP induced by propofol induction.2. PLR-ΔSV≧16% or PLR-ΔCO≧15% could predict propofol induced hypotension.