Preoperative heart rate variability as apredictor of post induction hypotension in elective surgeries under General Anaesthesia - A prospective observational study in a tertiary care Hospital, Bhubaneswar, India.

Hypotension can occur after intravenous induction of anesthesia and if severe or prolonged, may be associated with peri-operative ischaemia and morbidity . Some patients are less able to compensate, including those who are volume-depleted, have poor cardiovascular reserve or pre-existing autonomic dysfunction. Patients with diabetes the elderly and patients on chronic medications such as ACE inhibitors  are at greater risk of post-induction hypotension. Identifying at-risk patients is important in deciding on doses and method of induction, however few objective risk markers have been shown to predict hypotension. Low heart rate variability (HRV) may be a useful screening tool as it has been shown to reflect autonomic dysfunction and predict hypotension in some patient groups including those with diabetes and cardiovascular diseases . However, few studies have looked at pre-operative HRV as a risk marker for post-induction hypotension in a general or sub-speciality surgical patient population. Routine assessment of preoperative HRV by anesthesiologists during pre-anesthesia checks is still rarely performed. So in this study, we will try to find out how preoperative HRV measurement might influence post-induction hemodynamics. Patients will be recruited at pre-admission assessment and patient characteristics, medications and medical and surgical comorbidities will be recorded as a part of the routine pre-anesthetic assessment. HRV will be measured using the Powerlab-26T, Lab Chart 8, HRV version 2.0 by AD Instruments, in a quiet, mildly illuminated room, at room temperature, between 14:00 and 17:00 the day before the surgery. After a stabilization period of 10 min, recordings will be obtained in three consecutive positions (supine-1, standing, and supine-2), each lasting 5min. The first supine position (supine-1) will be an adaptive one, the active standingposition (standing) represents autonomic load, and anothersupine position (supine-2) is the final position for an overall evaluation of the spectral parameters of HRV.All patients will have bowel preparation before surgery and will be allowed clear fluids until 2 hours before surgery. All routine physiological monitoring (ECG, noninvasive arterial blood pressure, SPO2, end-tidal CO2, temperature) will beperformed. Immediately before induction, all participants will receive i.v. midazolam (0.08mg/kg), inj. Glycopyrrolate 0.2 mg and inj fentanyl (1-2µg/kg). General anesthesia will be then induced with propofol (1-3mg/kg). The induction dose will be decided based on the clinical judgment of the treating anesthesiologists who are unaware of the purpose of the study and blinded to HRV data. Rocuronium(1mg/kg) will be administered to facilitate tracheal intubation and balanced anesthesia will be maintained with sevoflurane in the oxygen-air mixture (1:1 l/min). Ventilation will be achieved through a ventilator to get an end-tidal CO2 of 30-35 mm of Hg and anend-tidal sevoflurane concentration of 1MAC.

The study period will be from induction of anaesthesia to surgical incision at least up to 10 minutes after induction. Patients will be divided into two groups; those who willexperience post-induction hypotension (hypotensive group) versus those who will remain hemodynamically stable (normotensive group). Post-induction hypotension will bedefined as a reduction in systolic BP and MAP >30% baseline occurring within 10 min of induction combined with one or more of the following criteria: a systolic BP≤80 mmHg, a MAP ≤60 mmHg or use of vasopressor within 10 min of induction. Hypotensive episodes (MAP <80 mmHg, lasting & gt;5 min) will be managed with eitherphenylephrine and/or ephedrine boluses. All episodes of hypotension and the number of interventions to treat these episodes during the period from the induction of general anaesthesia to the surgical incision will be recorded. An intervention to treat hypotension will be defined as a bolus of 40 mcg of phenylephrine or 5 mg ephedrine. All blood pressure values in the study will be recorded from the non-invasive blood pressure cuff cycling every 2.5 min to maintain consistency.