Background and Objectives The depressant activity on sympathetic tone of subarachnoid anesthetic block is well known. The aim of this study was to compare cardiovascular response to an incremental dose of subarachnoid anesthesia administered through a small-bore microcatheter with the response to single-dose spinal anesthesia.

Methods The 26 ASA I or II patients, 45-65 years old, who were undergoing elective gynecologic, urologic, or orthopaedic surgery, were randomized into two groups of 13 each: the first group (SSA) underwent single-shot spinal anesthesia with 1% hyperbaric bupivacaine (0.27 mg/kg), while the second group (CSA) received an incremental 5-mg bolus of the same solution via a subarachnoid 32-gauge microcatheter every 10 minutes. All patients were premedicated and prehydrated with Ringer's acetate 8-10 mL/kg, infused over a 30-minute period. Heart rate, systolic, mean, and diastolic arterial blood pressure, arterial blood gas analysis, and cardiac index (measured by the noninvasive indirect Fick method) were recorded prior to preoperative subarachnoid anesthesia and then 15, 30, and 45 minutes after the first local anesthetic administration.

Results The anthropometric parameters of the patients were homogeneous. No problems regarding anesthetic procedures occurred during the study, and none of the patients developed neurologic sequelae prior to discharge from the hospital. No relevant changes in blood gas parameters were found during the study in either the CSA or the SSA group. With regard to hemodynamic parameters, a significant reduction of systolic, diastolic, and mean arterial blood pressure was found in the SSA group following subarachnoid local anesthetic injection, while arterial pressures did not decrease in the CSA group. Cardiac index showed a nonsignificant increase with respect to baseline values in both groups, with no differences between groups during the study.

Conclusions In well-hydrated, healthy patients incremental local anesthetics offer adequate subarachnoid anesthesia with minimal hemodynamic effects.