The Use of Passive Leg Raise Test to Predict Hypotension in Patients Undergoing Urological Procedures under Spinal Anesthesia

Abstract

• Patient refusal of spinal anesthesia • Coagulation disorders • Local infection at the site of spinal injection • Patients with a known history of hypersensitivity to local anesthetics of the amide type • BMI >30 Kg ⁄ m² • Anatomical deformities of the spine eg., kyphoscoliosis All patients had an overnight fast of 8 hours and received routine intravenous prehydration consisting of lactated Ringer's solution 500 ml 30 min before the PLR test and spinal anesthesia. Routine monitors was attached to the patients including ECG, pulse oximetry and non invasive blood pressure measurement Portable noninvasive hemodynamic monitor (electrical cardiometry) was placed for continuous monitoring of heart rate (Figure 1), cardiac output and stroke volume by placement of four electrodes, two dual-electrode skin sensors on the upper thorax or back, and two on the flanks or lateral sub coastal regions. Before administration of spinal anesthesia, hemodynamic parameters were measured using electrical cardiometry for the PLR test with the patient lying flat. Patients were still for 5 min to obtain stable hemodynamic measurements , following which a custom 45 degree wedge was placed under the legs to elevate them while continuously recording cardiac output by electrical cardiometry. After 5 min, the wedge was removed and the legs were returned to the normal resting position. The he-modynamic response to PLR was quantified as the percent change in cardiac output from the baseline condition to the maximum cardiac output achieved during the second or third minute following the leg raise. Patients were divided into two groups based on their hemodynamic response to the PLR test. They were considered fluid responsive (PLR positive) when cardiac output increased by more than 12%. Patients not meeting this criterion were considered fluid nonresponsive (PLR negative). After completion of the PLR test, routine preparations for operation under spinal anesthesia were made, standard monitoring with electrocardiography, automated Non-Invasive Arterial Pressure (NIAP) measurement, and pulse oximetry was performed Electrical Cardiometry was positioned so that the anesthesiologist was blinded to its measurements (including the PLR test).Clinical decision-making was based solely on routine blood pressure, ECG and pulse ox-imetry. Spinal anesthesia was induced in the sitting position at the level of L 4-5 interspaces with a midline approach using a 22G Quincke needle under aseptic conditions. After confirmation of free flow and clear cerebrospinal fluid, Heavy Bupivacaine(0.5%) 3ml with 25 µg fentanyl was injected intrathecally over 15-20 seconds and maintenance fluid (1.5 ml/kg/hr) using crystalloid (Hartmann's solution) was infused continuously in all patients. Patients were then turned to the supine position for 3-5 minutes and the height of the block was assessed. Meanwhile, heart rate, sys-temic arterial blood pressure, and oxygen saturation were monitored. When a T6 Sensory level was achieved, then patients were placed in the lithotomy position and surgery started. Systemic arterial pressure was recorded at 3 minutes intervals at the onset of the block, 5 minutes intervals for the following 30 minutes , then 15 minutes intervals until the resolution of the block. Oxygen was administered to all patients via a nasal cannula and ephedrine was administered as a 5 mg bolus if hypotension occurred, Post spinal hypotension was defined as mean arterial blood pressure decreased by >20% of the patient's lowest baseline value (taken after the PRL test and before spinal anesthesia). The number of patients with post-spinal hypotension and the number of boluses of ephedrine given were compared between groups with preoperative positive and negative baseline PLR tests. Primary outcome To test effectiveness of PLR test as predictor for spinal hypotension in patients undergoing elective urological procedures. Secondary outcome parameters Evaluate effect of ephedrine in controlling hypotension in these patients. Statistical analysis Data were coded and entered using the statistical package SPSS version 22. Data was summarized using mean and standard deviation for quantitative variables and frequencies (number of cases) and relative frequencies (percentages) for categorical variables. Comparisons between groups were done using unpaired t test for comparing categorical data, Chi square (χ2) test was performed. Exact test was used instead when the expected frequency is less than 5 Correlations between quantitative variables were done using Spearman correlation coefficient P values less than 0.05 were considered as statistically significant .