Predicting Spinal Hypotension in Cesarean Section

Spinal anesthesia is the preferred anesthetic technique for cesarean section due to its rapid onset, reliability, and minimal neonatal drug exposure. However, spinal anesthesia-induced hypotension (SAIH) remains the most common and clinically significant complication, with an incidence ranging between 10% and 80% of parturients. The resulting maternal hypotension can lead to symptoms such as nausea, vomiting, and dizziness. At the same time, severe or sustained decreases in blood pressure may compromise uteroplacental perfusion, causing fetal acidosis and distress. Therefore, early prediction and prevention of hypotension are paramount to ensure maternal and neonatal safety.

Several hemodynamic and anthropometric factors have been investigated as potential predictors of SAIH, including baseline blood pressure, heart rate, and indices reflecting intravascular volume or autonomic tone. Among these, the modified shock index (MSI), calculated as the ratio of heart rate to mean arterial pressure, has been proposed as a noninvasive marker of hemodynamic stability and cardiovascular reserve. Likewise, body mass index (BMI), waist circumference (WC), and the body roundness index (BRI) have been associated with alterations in central blood volume, vascular compliance, and sympathetic responsiveness, which may influence susceptibility to post-spinal hypotension.

Pregnancy induces profound physiological changes, including decreased systemic vascular resistance and increased circulating blood volume, which alter cardiovascular responses to sympathetic blockade. These adaptations may interact with individual body composition and baseline hemodynamic parameters, modifying the risk of hypotension. Despite these associations, the predictive utility of anthropometric indices, such as BRI and WC, alongside conventional measures like BMI and MSI, has not been clearly established in obstetric anesthesia.

Symphyseal fundal height (SFH) and AC measurements indirectly indicate compression of the inferior vena cava (IVC). AC and VCL have previously been found to be highly predictive of block level in operations of non-pregnant patients performed under SA with isobaric bupivacaine.

Therefore, this prospective observational study was designed to evaluate the predictive value of waist circumference, body roundness index, body mass index, and modified shock index in identifying parturients at risk for spinal anesthesia-induced hypotension during cesarean delivery. By determining reliable preoperative indicators, this study aims to contribute to individualized risk assessment and the development of preventive strategies in obstetric anesthesia practice.

The study followed a parallel study strategy. Erciyes University's ethical committee approved the study on 2025/82. Patients provided informed consent before the procedure. Patients with pre-existing or pregnancy-induced hypertension, cardiovascular or cerebrovascular disease, contraindications to spinal anesthesia, weighing < 50 kg or > 110 kg, and heights higher than 170 cm or shorter than 150 cm were eliminated. Informed written consent was acquired from all patients participating in the trial.

There was no premeditation among the patients. The patient had standard monitoring, including non-invasive blood pressure, ECG, and pulse oximetry, with recorded baseline blood pressure and heart rate measurements. Two 20-gauge intravenous cannulas will be inserted, and an IV-balanced solution will be administered using these routes. The patient's age, height, weight, and ASA class were recorded. Height (cm), body weight (kg), waist circumference (WC; cm), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and heart rate (HR) were measured by assistants using a hemodynamic monitor and tape measure. Body mass index (BMI) was computed as weight (kg) divided by height squared (m²). The girth of the midpoint between the lowest point of the rib and the upper edge of the iliac crest was calculated as the waist circumference (WC). The Body Roundness Index (BRI) was calculated using the formula BRI=364.2-365.5×(√1-((WC/(2π))²/(0.5×Height)²). The modified shock index (MSI) was calculated as follows: MSI (heart rate/MAP). After skin infiltration with lidocaine 2%, a 25-gauge Whitacre spinal cannula, 25 G x 3 1/2" (0.5 x 90 mm), with an introducer spinal needle, was placed at the L3-4 vertebral interspace with the patient in a sitting position. After cerebrospinal fluid aspiration, the following anesthetic solutions were delivered over 5 seconds. Patients received a 0.5% hyperbaric bupivacaine volume, calculated based on their height and weight, at a dose of 0.5%. A dosage was derived using Harten's dose chart formulated for Caucasian parturients.

All patients received supplemental oxygen. Bradycardia (defined as a heart rate < 60 beats/min) was treated with 0.5 mg of intravenous atropine. Hypotension, defined as a reduction in baseline systolic blood pressure of >20%, a systolic blood pressure <100 mmHg, or a mean arterial pressure <65 mmHg, was treated with 10 mg of intravenous ephedrine. In the event of dizziness, nausea, or vomiting, the patient was administered 5 mg of ephedrine. To prevent postoperative nausea and vomiting, 4 mg of intravenous ondansetron was administered. Additionally, 1.5 g of intravenous cefuroxime was given prior to the incision for surgical site infection prophylaxis. A surgical incision was necessary when pinprick sensation was lost bilaterally in the T6 dermatome. If the sensory blockage was inadequate 5 minutes after spinal anesthesia insertion, the assessor placed the patient in a 10-degree head-down tilt. If patients experienced discomfort during the procedure, a 0.5 mg/kg propofol and 0.25 mg/kg ketamine bolus were administered via the venous route. If these efforts proved ineffective, the option of switching to general anesthesia was provided. Following birth, 100 IU carbetocin was administered as a uterotonic by gradual intravenous infusion. Paracetamol IV 1000 mg was administered after the procedure. Postoperative analgesia was constituted by TAP block with 20 ml of 0.25% bupivacaine bilaterally.

The upper sensory level of anesthesia was evaluated by systematically measuring the loss of pinprick sensation at the midclavicular line at 2-minute intervals; additionally, motor block was assessed using the Bromage scale.