Effect of a 20% Reduction in Hyperbaric Bupivacaine Dose on High Spinal Block Incidence in Cesarean Delivery

Incidence of high spinal block (HSB)

The incidence of high spinal block (HSB), defined as the presence of both of the following criteria within 15 minutes of intrathecal drug administration: 1. Sensory block exceeding the T4 dermatome: * Assessed bilaterally using the pinprick test (with a 25-gauge blunt needle) and cold sensation (using an alcohol swab) * The upper sensory level was recorded as the most cephalad dermatome with complete loss of sensation to both pinprick and cold * A block was considered to have exceeded T4 if the loss of sensation was documented above the T4 dermatome (i.e., ≥ T3 or higher) on at least one side 2. Hemodynamic instability, defined as any of the following (thresholds informed by Klöhr et al., 2010, and Kinsella et al., 2018): * A decrease in systolic blood pressure (SBP) exceeding 30% below baseline (baseline SBP was defined as the mean of three preoperative measurements taken in the supine position with left uterine displacement)

Predictive Performance of the Risk-Prediction Score

The predictive performance of the risk-prediction score for the primary outcome (HSB) was assessed at both timepoints described in Step 1 (pre-randomization, dose-blind score; and post-randomization, dose-aware score). For each score version, the following were calculated against the observed incidence of HSB: * Area under the receiver operating characteristic curve (AUC) * Sensitivity, specificity, and Youden's index at the pre-specified risk-category cutoffs (≤ 14, 15-21, and \> 21 points) * Agreement between the pre- and post-randomization risk categories This secondary outcome was pre-specified to determine whether the dose-blind (pre-randomization) score retains adequate predictive accuracy relative to the dose-aware (post-randomization) score, in order to establish whether the tool can be applied prospectively - before the anesthetic dose is chosen - for preoperative prediction of the risk of high spinal block. The statistical methods used to evaluate this outcome are detailed in

Neonatal Outcomes

Neonatal outcomes were assessed using Apgar scores (Apgar, 1953) recorded at 1 minute and 5 minutes after delivery by the attending neonatologist or pediatrician, who was blinded to group allocation. The Apgar score was assessed based on five parameters: heart rate, respiratory effort, muscle tone, reflex irritability, and color, each scored from 0 to 2, giving a total score ranging from 0 to 10.

Maternal Satisfaction

Maternal satisfaction was assessed postoperatively using a validated five-point Likert scale questionnaire, administered by a blinded research assistant 4-6 hours after surgery (once the patient was fully recovered from the neuraxial block and able to provide informed responses). The Likert Scale: Participants were asked to respond to the following statement: "Overall, how satisfied were you with your anesthetic experience during the cesarean delivery?"

Hemodynamic Stability

Hemodynamic stability was evaluated intraoperatively by monitoring predefined cardiovascular endpoints and therapeutic interventions. Hypotension was defined as a decrease in systolic blood pressure (SBP) greater than 30% from baseline, an absolute SBP below 90 mmHg, or a mean arterial pressure (MAP) below 65 mmHg at any point during the procedure. Bradycardia was defined as a heart rate below 50 beats per minute. Pharmacological and fluid interventions were quantified as the total intraoperative requirements of vasopressors (cumulative doses of ephedrine in milligrams and/or phenylephrine in micrograms), anticholinergics (cumulative dose of atropine in milligrams), and intravenous fluids (total volume of crystalloid infused in milliliters). All physiological parameters were recorded at baseline (preoperative), immediately following spinal injection ($T\_0$), at 1, 3, 5, 7, 10, 12, and 15 minutes post-injection, and subsequently every 5 minutes until the completion of surgery.