Background: The combined effect of age, weight, height, and vertebral column length (VCL) on the distribution of isobaric 0.5% bupivacaine within the subarachnoid space is unclear. The aim of the present study was to evaluate the combined influence of these patient variables on the upper sensory level and on its predictability.
Methods: In 100 patients who were above the age of 49 years, the age, weight, height, VCL, body surface (BS), and body mass index (BMI) were noted. Spinal puncture and subarachnoid drug administration were standardized. Cephalad spread of spinal anaesthesia (SA) was assessed by loss of temperature sensation and pinprick discrimination 15, 30, 60, 90, and 120 min following subarachnoid injection of 18 mg of plain 0.5% bupivacaine. Linear regression analysis was performed for each of the patient variables and the cephalad segmental spread of anaesthesia. Multiple regression analysis was used to test for combined correlation between patient variables and the sensory level of SA.
Results: No linear correlation was found between the patient variables and the sensory level of anaesthesia. In contrast, multiple regression analysis revealed that age (P<0.01), weight (P<0.05), and height (P<0.01) significantly contributed to the spread of anaesthesia. A squared multiple comparison coefficient between 0.10 and 0.21, however, is an indication that the predictive value of the combined variables remained rather low.
Conclusion: Multiple regression analysis revealed that age, weight, and height significantly correlated with the sensory level after subarachnoid injection of plain bupivacaine. The low predictive value suggests that patient factors other than age, weight, or height add to cephalad spread of SA.