QTc Interval in Cesarean Section Patients

Study design and setting:

Researchers designed a prospective randomized study to compare the effects of spinal anesthesia and general anesthesia on the QT interval in patients undergoing elective cesarean section delivery. The study has been approved by the local Institutional Review Board (Ethics Committee of Health Science University Haseki Training and Research Hospital, Istanbul, Türkiye; approval date: 04 October 2023; approval number: 169-2023). The research was performed acoording to the Declaration of Helsinki, and written informed consent was obtained from all participants The study was carried out at a university affiliated hospital with 700-bed in Istanbul, Türkiye between October 4 2023 and December 4 2023.

Patient selection and group allocation The patients enrolled in the study were selected from 64 consecutive pregnant women who scheduled for an elective cesarean section delivery (Figure 1). Exclusion criteria were baseline QTc >440 ms, use of medications that affect the QTc interval, family history of long QT syndrome, electrocardiographic evidence of arrhythmia and/or conduction abnormalities, or the presence of a permanent pacemaker, contraindications to spinal anesthesia (high intracranial pressure, injection site infection, coagulation disorders, severe hypovolemia, aortic and/or mitral stenosis), history of spinal surgery, congenital spinal deformity or neuromuscular disease, anemia, electrolyte imbalance, significant cardiopulmonary/hepatic/renal disesase, obesity (Body Mass Index > 30 kg/m2), an American Society of Anesthesiologists (ASA) physical classification ≥III or refusal to participate.

In the preoperative ward an intravenous (iv) line was obtained and all the patients received 10 ml/kg isotonic saline) within 20 minutes. The patients were randomly allocated to either the spinal anesthesia group (Group S) or the general anesthesia group (Group G) using sealed envelope method by an independent investigator and then were transferred to the operating room.

Anesthesia procedure In the operating room the patients received isotonic saline at a rate of 8 mL/kg/h for intravenous hydration and prexoxgenation was obtained via face mask for 3 minutes (8 L/min).

In the group G anesthesia was induced with using 1 µg/kg fentanyl and 2-2.5 mg/kg propofol. Muscle relaxation was achieved with 0.6 mg/kg rocuronium and endotracheal intubation was performed with an experienced anesthesiologist at the first attempt. Following intubation, mechanical ventilation was provided in volume-controlled mode using an anesthesia machine (Dräger Primus, Dräger Medical Systems, Inc., Danvers, MA, USA), with a tidal volume set at 6-8 mL/kg based on ideal body weight and a positive end-expiratory pressure of 5 cmH₂O. The respiratory rate was adjusted to maintain end-tidal carbon dioxide (EtCO2) levels between 32 and 36 mmHg. Anesthesia was maintained with sevoflurane at 0.8-1.0 minimum alveolar concentration (MAC) in an oxygen-air mixture (Fraction of inspired oxygen [FiO₂]= 0.4) until the delivery of neonate. Subsequently 1.2 MAC of sevoflurane, additional doses of rocuronium (0.15 mg/kg) and fentanyl (1 µg/kg) were used for the maintenance of anesthesia. At the end of the procedure, residual neuromuscular blockade was antagonized with intravenous sugammadex at a dose of 4 mg/kg. Tracheal extubation was carried out once the patient was fully awake, breathing spontaneously with adequate tidal volumes.

In the group S, the patiets were placed into a sitting position and spinal anesthesia was achieved at either the L4 or L5 interspace using a 25-gauge Whitacre pencil-point spinal needle under strict sterile conditions after intradermal injection of 1 mL 2% lidocaine hydrochloride. Once free flow of cerebrospinal fluid was observed, 12.5 mg (2.5 mL) of hyperbaric bupivacaine (Marcaine Spinal 0.5% Heavy; AstraZeneca, Türkiye) was injected into the subarachnoid compartment for 30 seconds. Following the patients were immediately placed in a supine position and tilted 15 degrees to the left until the delivery of neonate. Oxygen was delivered to patients via a face mask at a rate of 5 L/min. Pinprick test was used to evaluate the level of sensory blockade and T6 dermatome level was considered as acceptable for surgery.

Monitoring Non-invasive blood pressure (NIBP), heart rate (HR), peripheral oxygen saturation (SpO₂), and continuous electrocardiographic (ECG) monitoring were performed throughout the procedure using a standard anesthesia monitor (BeneView T8 Patient Monitor, Shenzhen Mindray Bio-Medical Electronics Co., Ltd., Shenzhen, China). QT interval measurements were automatically obtained from lead II, and corrected QT (QTc) values were derived by applying Bazett's formula (QTc = QT/√RR [s]) via the ECG monitoring system.

Duration of QTc intervals were measured and recorded at predefined time points: prior to anesthesia induction in the general anesthesia group (QTc-pre) or before intrathecal injection in the spinal anesthesia group (QTc-pre); at 1, 5, 10 and 15 minutes following endotracheal intubation or intrathecal injection, and following surgical slosure (QTc-post). The difference between the longest and shortest QTc values (ΔQTc) obtained from QTc measurements taken at five-minute intervals was also recorded.

Data collection Demographic and clinical variables, including age, sex, height, weight, body mass index (BMI), comorbidities, and American Society of Anesthesiologists (ASA) physical status were documented. In Group S, the maximum sensory block level was assessed. Cardiopulmonary adverse events such as hypotension (mean arterial pressure ≤ 70 mmHg), hypertension (systolic ≥ 160 mmHg and/or diastolic ≥ 90 mmHg), bradycardia (heart rate ≤ 50 beats/min), tachycardia (heart rate ≥ 100 beats/min), hypoxemia (SpO₂ < 90%) and arrhythmia were also recorded.

Statistical analysis Statistical Package for Social Sciences software for Windows (SPSS, version 27.0; IBM, Chicago, IL, USA) was used to analyse of study data. Quantitative variables were expressed as mean ± standard deviation (SD), while categorical variables were represented as patient numbers and percentages. Normality of quantitative variables was assessed using the Kolmogorov-Smirnov/Shapiro-Wilk test. Normally distrubeted data were compared between the groups using independent Student's t-test, while the Mann-Whitney U test was applied for non-normally distributed variables. Categorical variables were compared using chi-squared or Fisher's exact tests. Duration of QTc within each group were evaluated using repeated measures analysis of variance with Bonferroni correction. Based on a previous study, the duration of QTc was 428 ± 26 ms after C/S performed with spinal anesthesia. Power analysis with α = 0.05 and β = 0.2 revealed that a minimum 25 patients per goup was required to detect at least a 20 ms difference in QTc duration in pregnant patients undergoing general anesthesia. A p-value <0.05 was considered statistically significant.