Spinal anesthesia-induced hypotension is one of the most frequent and clinically significant complications of obstetric anesthesia, occurring in up to 50-80% of parturients undergoing elective cesarean section. Preoperative anxiety has been shown to potentiate hemodynamic instability through autonomic nervous system activation, thereby increasing susceptibility to spinal hypotension.

This prospective, randomized, controlled trial aims to evaluate the effect of a standardized 5-minute mindfulness-based breathing exercise administered immediately prior to spinal anesthesia on the hemodynamic response in pregnant women scheduled for elective cesarean section. Eligible participants will be randomized in a 1:1 ratio into two parallel groups: the Mindfulness-Based Breathing Exercise Group and the Control Group receiving standard preoperative care.

The breathing intervention consists of slow diaphragmatic breathing at a rate of approximately 6 breaths per minute (4-second inhalation through the nose, 6-second exhalation through the mouth), guided by a standardized script delivered by a trained anesthesiologist or nurse. Participants in the intervention group will be instructed to silently repeat the phrase "My body is relaxing as I exhale" with each exhalation, incorporating a mindfulness component.

The primary outcome is the maximum decrease in systolic arterial pressure (SAP) within the first 10 minutes following spinal anesthesia induction. Secondary outcomes include preoperative state anxiety scores (STAI-5), early spinal hypotension incidence, heart rate changes, and vasopressor requirements.

The study will be conducted at Atatürk University Faculty of Medicine, Department of Anesthesiology and Reanimation, Erzurum, Turkey, in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines.

Background and Rationale Spinal anesthesia-induced hypotension is the most common hemodynamic complication in obstetric anesthesia, with reported incidence rates ranging from 50% to 80% in parturients undergoing elective cesarean section. The underlying pathophysiology involves sympathetic blockade-mediated arteriolar and venous vasodilation, resulting in decreased systemic vascular resistance and reduced venous return, further compounded by aortocaval compression exerted by the gravid uterus.

Current prophylactic strategies including left uterine displacement, fluid co-loading, and vasopressor infusion remain the standard of care. However, these pharmacological approaches may be associated with tachycardia, hypertension, and inter-individual response variability, underscoring the need for complementary non-pharmacological interventions.

Preoperative anxiety exerts measurable effects on autonomic nervous system balance, potentially amplifying sympathetic tone and increasing hemodynamic instability following neuraxial blockade. Slow, controlled breathing exercises have been shown to enhance baroreflex sensitivity and augment parasympathetic vagal activity, suggesting that a brief mindfulness-based breathing intervention may attenuate sympathetic hyperactivity through an "autonomic preconditioning" mechanism.

Randomization and Allocation Concealment Participants will be randomized in a 1:1 ratio using a computer-generated random number sequence. Allocation concealment will be ensured through sequentially numbered, opaque, sealed envelopes (SNOSE), opened only after the patient has been transferred to the operating room and immediately before spinal anesthesia induction.

Intervention Protocol Participants in the intervention arm will receive a 5-minute guided mindfulness-based breathing exercise prior to spinal anesthesia, consisting of slow diaphragmatic breathing at approximately 6 breaths per minute (4-second nasal inhalation, 6-second oral exhalation). During each exhalation, participants silently repeat: "My body is relaxing as I exhale."

Anesthesia Management All participants will receive spinal anesthesia in the sitting position with intrathecal administration of 11.2 mg hyperbaric bupivacaine + 15 mcg fentanyl + 150 mcg morphine. Hypotension will be defined as a decrease in systolic arterial pressure (SAP) exceeding 20% from baseline and treated with norepinephrine or ephedrine. Bradycardia will be defined as heart rate ≤50 bpm and treated with intravenous atropine (1 mg).

Statistical Analysis All analyses will be performed using IBM SPSS Statistics (Statistical Package for the Social Sciences) version 20. Normality will be assessed using Shapiro-Wilk and Kolmogorov-Smirnov tests. Between-group comparisons will be performed using independent samples t-test or Mann-Whitney U test as appropriate. Categorical variables will be compared using chi-square test. Statistical significance will be set at p<0.05.

Sample Size Sample size was calculated using G*Power 3.1.9.7 software. A clinically meaningful difference of 4.5 mmHg in maximum SAP decrease (effect size = 0.48) was determined to require 70 participants per group at 80% power and 95% confidence level. Accounting for potential dropout, 150 participants (75 per group) will be enrolled.

Inclusion Criteria:

Pregnant women aged 18-45 years Singleton pregnancy Gestational age 37 weeks or greater American Society of Anesthesiologists (ASA) physical status classification II Scheduled for elective cesarean section under spinal anesthesia Body mass index (BMI) 35 kg/m2 or less Ability to comprehend verbal instructions and perform the breathing exercise Provision of written informed consent

Exclusion Criteria:

Emergency cesarean section Hypertensive disorders of pregnancy (gestational hypertension, preeclampsia, eclampsia, HELLP syndrome) Placenta previa, placental abruption, or active antepartum hemorrhage Multiple pregnancy Contraindications to spinal anesthesia Failed spinal anesthesia requiring conversion to general anesthesia Chronic hypertension or chronic hypotension Known cardiac disease (arrhythmia, valvular disease, cardiomyopathy) Diabetes mellitus with autonomic neuropathy Thyroid dysfunction Chronic pulmonary disease potentially affecting respiratory pattern Body mass index greater than 35 kg/m2 Regular use of beta-blockers, calcium channel blockers, alpha-agonists, or alpha-antagonists Regular use of anxiolytics, antidepressants, sedatives, or chronic opioids Diagnosed anxiety disorder, panic disorder, major depressive disorder, or other psychiatric illness Regular use of psychiatric medications Cognitive impairment or communication difficulties Attention or compliance problems precluding adequate performance of the breathing exercise Prior regular practice of meditation, yoga, or mindfulness-based training

"Individual participant data will not be shared, as this is an academic thesis study conducted at a single center. Patient confidentiality will be maintained in accordance with applicable data protection regulations. Anonymized aggregate results will be reported in the final publication."

Due to the nature of the intervention, blinding of participants and care providers is not feasible in this trial. However, outcome assessor blinding will be implemented to minimize measurement bias. Hemodynamic data (systolic arterial pressure, heart rate, and peripheral oxygen saturation) will be recorded prospectively by a designated investigator who is blinded to group allocation and has no involvement in the administration of the breathing exercise or the randomization process. This single-blind design ensures that primary and secondary hemodynamic outcome measurements are obtained independently of treatment assignment, thereby reducing the risk of assessment bias.