Patients will be recruited from the elective operating list of the neurosurgery department. The Principal Investigator will study the procedure and screen for inclusion and exclusion criteria. Written informed consent will be obtained if the participant is eligible for inclusion. Consenting patients will be included in the study protocol.  

A preoperative baseline heart rate (H.R.), blood pressure (B.P.) and baseline serum cortisol (S.C. Baseline) value will be obtained as part of the pre-anaesthetic evaluation, during the first meeting of the anaesthesiologist with the patient. Baseline demographics, hormonal profile, size and type of lesion based on preoperative MRI will be noted. The same preanesthetic preparation as per institutional protocol will be given to all the patients.  

On the day of the surgery, a serum cortisol sample will be obtained at 7:30 AM (SC 1). The same perioperative steroid therapy as per the institutional protocol will be given to all patients on the day of surgery. The steroid dose and timing of administration will be noted. Then the patient will be shifted to the operating room.Anaesthesia protocol will be standardized for all the patients included in the study.Under Lignocaine (2%), skin infiltration I.V. access will be obtained. The hemodynamic parameters: H.R. and B.P. will be noted. Patients will be preoxygenated for 3 minutes with FiO2 of 1.0 at a flow rate of 10L/min. Then the patient will be induced with fentanyl 2mcg/kg and propofol 2-3 mg/kg, targeted to attain a BIS value of 45-55, and vecuronium 0.1 mg/kg will be given after confirming mask ventilation and proceed with intubation. The patient will be mechanically ventilated in volume control ventilation (VCV) mode with a tidal volume of 6-8 ml/kg and minute ventilation (Mv) adjusted to maintain an ETCO2 of 35mm of Hg. Post intubation, Invasive Blood Pressure (IBP) with Pulse Pressure Variability (PPV) monitoring also will be established, and fluid deficit denoted by PPV >12 will be corrected. Serum cortisol (SC2) and an Arterial Blood Gas (ABG) analysis sample with serum lactate value will be sent. Anaesthesia will be maintained using a combination of Oxygen/Air (FiO2 0.5) and sevoflurane to maintain a MAC above 0.7, with a BIS target of 45-55, along with an infusion of atracurium of 0.06mg/kg/hour and fentanyl 1microgram/kg/hour. H.R., B.P. and PPV will be monitored continuously and noted every 10 minutes during the intraoperative period. A serum cortisol sample will be sent intraoperatively after the sphenoid drilling (SC3) to check for the hormonal profile after the period of maximum surgical stimulation. 

Unexplained hypotension will be defined as hypotensive episodes (a 20% fall in mean arterial pressure (MAP) from the baseline) lasting for >3 minutes and refractory to fluid administration and due to reasons other than sepsis, anaphylaxis, neurogenic, myocardial ischemia, venous air embolism, arrhythmias, hypovolemia or haemorrhage (Hypotension-X), which will be recorded with the time of occurrence and a serum cortisol sample (SC-X) will be sent during one such episodes, if any. Similarly, Hypertensive episodes (a 20% elevation in mean arterial pressure from baseline) will be marked as hypertension (HTN) and will be recorded with accompanying interventions, if any (e.g., adrenaline infiltration and iatrogenic changes in blood pressure for checking hemostasis). HTN, without any vasopressor stimulus or neural reflex, will be considered a pain stimulus and treated with 1 mcg/Kg bolus of Fentanyl. The maximum fall in MAP will also be noted. The maximum fall in MAP is defined as the baseline MAP before the induction minus the minimum MAP during the intraoperative period.  

The total volume of crystalloids and colloids used will be noted separately. The total cumulative dose of vasopressors (Mephentermine, Phenylephrine and Noradrenaline) will also be recorded separately at the end of the surgery. 

ABG with serum lactate will be sent at the end of the surgery. Incidence of postoperative complications like diabetes insipidus or hyponatremia in the immediate postoperative period also will be recorded.