The autonomic nervous system (ANS) is cardinal for maintaining systemic homeostasis and is pivotal for the baseline regulation and modulation of vital cardiovascular, hemodynamic, respiratory, gastrointestinal, and body temperature regulating functions. Pathological perturbations of the ANS leading to cardiac dysautonomia (CAD) affect one in 1000 population. Autonomic dysfunction can occur from a variety of pathological conditions such as ischemic heart disease, systemic hypertension, diabetes mellitus, neurological illnesses, neurotrauma, and cervical spine diseases. When patients with dysautonomia present for surgical procedures, they may manifest severe hemodynamic responses that may be less responsive to pharmacological interventions. Pre-existing autonomic dysfunction accentuates perioperative hemodynamic fluctuations during stressful events like direct laryngoscopy, endotracheal intubation, and extubation, and can result in major adverse cardiac events (MACE). The complications arising from CAD can prolong the duration of hospital stay and contribute to morbidity and mortality. Preoperative diagnosis of CAD helps in anticipation of and preparation for potentially severe adverse events in the perioperative period. Most neurosurgical patients are not candidates for detailed ANS examination in the supine and standing positions due to their underlying neurological condition. Real-time assessment of heart rate variability (HRV) using the ANSiscope equipment provides information on the sympathovagal balance during the immediate preoperative period and aids in the simple rapid bedside assessment of CAD. This study aims to examine the incidence of CAD through HRV assessment in neurosurgical patients, identify the potential risk factors for CAD in this population, and evaluate the impact of CAD on perioperative outcomes.

Demographic and baseline clinical data including comorbid conditions and medication history will be collected. Baseline hemodynamic parameters - heart rate (HR) and systolic, diastolic, and mean blood pressure (SBP, DBP, MAP), rate pressure product (RPP) calculated as the product of HR and SBP and ANSindex (which informs the degree of dysautonomia and is derived noninvasively from a recording of 572 R wave to R wave intervals on an electrocardiogram) will be recorded in the immediate preoperative period.

Assessment of risk factors for preoperative CAD The investigators will explore potential risk factors for CAD in neurosurgical patients. The investigators postulate some known factors such as anxiety which will be diagnosed using the Visual analog scale for anxiety (VAS-A), age, gender, neurosurgical pathology, site-specific surgery (high cervical pathology, structural brain lesions, brainstem lesion, etc.), pre-existing diabetes mellitus and hypertension, and medications used for their treatment, higher American Society of Anesthesiology (ASA) grade, etc. to be associated with CAD in neurosurgical patients.

The investigators will explore the association between CAD and perioperative outcomes. Major Adverse Cardiac Events during Intra and postoperative period, in-hospital mortality, and duration of postoperative ICU and hospital stay.

Anesthesia will be administered as per the existing practice. Hemodynamic parameters HR, SBP, DBP, MAP at following time points - before and 1 and 2 min after induction of general anesthesia, before and at 1, 3, and 5 mins after tracheal intubation, and before and at 1, 3, and 5 mins after skull pin application, where applicable. Adverse hemodynamic events - persistent hypotension, arrhythmias, myocardial ischemia, cardiac failure, cardiac arrest) during the early (after anesthetic induction and before surgical incision), late (surgical incision to surgical closure) intraoperative period, recovery period (end of anesthesia to discharge from the operating room), post-anesthesia care unit (PACU) period (from arrival to discharge from PACU) and early postoperative period (up to 72 hours after surgery), neurological status (Glasgow Coma Scale) at hospital discharge, and duration of ICU and hospital stay will be recorded. The core temperature will be monitored during the intraoperative period to detect hypothermia (<35o C) or hyperthermia (>37.5 o C).

Sample size and statistical analysis Previous studies in the non-neurosurgical populations have determined the prevalence of CAD to vary from 25 to 73%. Considering an average prevalence of 50% in the neurosurgical population and a possible 5% margin of error, a sample size of 383 would be necessary for achieving a 95% confidence level. Hence the investigators plan to recruit 400 patients over a period of 1 year to account for potential dropouts from the study.

Data will be analyzed using Statistical Package for the Social Sciences (SPSS) or R software. Continuous variables will be compared by t-test, qualitative data by chi2 test, or Fisher exact test. Logistic regression will be used to identify the risk factors for cardiac autonomic dysfunction. A p < 0.05 will be considered statistically significant.

Inclusion Criteria:

• aged between 18 and 80 years
• belonging to ASA grade 1-4
• scheduled for craniotomies or spinal surgeries under anesthesia

Exclusion Criteria:

• scheduled for redo procedures
• patients with preoperative arrhythmias and cardiac failure
• patients on preoperative inotropic support
• pregnant neurosurgical patients

Consenting patients scheduled for neurosurgical procedures at the National Institute of Mental Health and Neurosciences, Bengaluru will be recruited if they fulfill the study inclusion criteria during the period of study duration

Individual participant data will be available with the Principal Investigator and shared with other researchers on request.