ABSTRACT
BACKGROUND: The aim of our study was to use a quantitative measure of muscle strength to identify the muscle power at which the patient can safely ambulate unassisted after spinal anesthesia. METHODS: Twenty ASA physical status I and II patients undergoing elective perineal or lower abdominal surgery under spinal anesthesia were enrolled in the study. Spinal anesthesia was conducted using 10 mg heavy bupivacaine. The regression of motor block was assessed both qualitatively using the Bromage score and quantitatively by measuring the isometric contraction of the knee, hip, and ankle flexors every 15 minutes until the patient was able to ambulate unassisted. RESULTS: The rate of regression of the Bromage score was faster than regression of the isometric forces at all tested joints. As the median Bromage score reached 0 (no motor blockade), the mean±SD motor power recoveries at the knee, hip, and ankle were 28.2%±16%, 45.5%±24%, and 56.3%±28 %, respectively, and only 6 of 20 patients (30%, 95% confidence interval 10%-53%) were able to walk unassisted. After 75 minutes passed, 90% of the patients (95% confidence interval 56%-99%) were able to walk unassisted with mean motor power recovery of 63.6%±20%, 82.1%±27%, and 90.2%±24% at the knee, hip, and ankle, respectively. The area under the receiver operating characteristic curves was significantly higher with isometric contraction at different joints than the Bromage score (P<0.001). In addition, isometric contraction at different joints was effective in predicting the patients' ability to walk unassisted after subarachnoid block with prediction probabilities of 0.901, 0.948, and 0.958 for the knee, hip, and ankle, respectively, as compared with 0.752 for the Bromage score (P<0.001). CONCLUSION: Quantitative measurement of the degree of recovery of the motor power of the knee, hip, or ankle flexors is more accurate and superior to the qualitative Bromage score, as a predictor of the patient's ability to safely ambulate after spinal anesthesia. This may be recommended when assessing motor block when small-dose anesthetic solutions are used.