Association Between Preoperative Shock Index and Hypotension After Spinal Anaesthesia for Non- Elective Caesarean Section

Studies have shown that early hypovolemia is insufficient to produce changes in orthostatic heart rate (HR) or systolic blood pressure (SBP). Studies have shown that Shock Index (SI) as a useful indicator for acute hypovolemia. In healthy individuals, acute blood loss less than 450 mL rarely produces abnormal HR or SBP. As, several studies have shown that relationship of baseline heart rate and systolic blood pressure in predicting post spinal hypotension, this study aims to incorporate both the parameters and attempt to develop a single effective predictor for post spinal hypotension in the form of SI.

Methodology After approval from Institutional Review committee of B.P. Koirala Institute of Health Sciences, parturient undergoing non-elective caesarian of ASA PS grade II and urgency category 2 and 3, fulfilling the inclusion criteria will be informed about the study and written consent will be obtained either in labour room or in obstetric emergency ward. During this visit patient's data that includes age, indication of caesarean section, preoperative anxiety (APAIS), gestational age, and duration of fasting, height, weight, BMI and preoperative hemoglobin concentration will be recorded.

The study will be conducted in accordance with the ethical principles of the 1964 Declaration of Helsinki and STROBE (Strengthening the Reporting of Observational studies in Epidemiology) guidelines will be followed. Before patient is shifted to the operating room (OR), ranitidine 50 mg and metoclopramide 10 mg will be administered intravenously via 18 G cannula. The patient will be shifted to operating table and standard monitors 3 lead ECG, pulse oximetry and noninvasive blood pressure will be attached. Baseline vital signs heart rate and noninvasive SBP will be recorded in operation theatre in supine position with 15° left lateral tilt before administering spinal anaesthesia. NIBP will be measured by using cuff size with width of cuff bladder covering at least 40% of arm circumference and length at least 80% and will be measured from EDAN elite V8 monitors. 3 measurements of SBP will be recorded at 1 minute interval and its mean value will be taken as baseline SBP.

Also, shock index (HR/ SBP) will be calculated before administering spinal anaesthesia. At every 1 minute interval until delivery of baby, vitals parameters HR, SBP and MAP will be measured and shock index will be calculated in each time interval. Then, the patient will be placed in sitting position. Under all aseptic precautions, 2.2 ml of 0.5% hyperbaric bupivacaine with 10 µg fentanyl will be administered in sitting position in L4- L5 or L3- L4 interspace after confirmation of free flow of CSF with 25 G Quincke's needle and drug will be injected over 20 secs. Patient will be then immediately put into supine position with a right hip wedge. A 1 L co-loading of Ringer's lactate will be administered rapidly within 10 minutes via an 18 G intravenous line after administering spinal anaesthesia. Phenylepinephrine infusion will be started at 25 microgram/min immediately after the spinal injection. The sensory level of anaesthesia will be checked using loss of cold sensation with the use of alcohol soaked cotton swabs every minute until 20 mins. Surgery will be allowed once the bilateral sensory block height at T6 is achieved. Oxygen at 40% will be administered via nasal cannula at 2-4 L/min until delivery.

Hemodynamic parameters will be recorded at following time intervals: baseline, immediately after spinal anaesthesia, every minute for the first 15 minutes after spinal injection and every 2.5 mins until end of surgery. Hypotension will be treated with phenylephrine 50 µg bolus and rapid infusion of Ringer's lactate 200 ml. If bradycardia (HR< 55/min) is associated with hypotension, IV ephedrine 6 mg will be administered. If these measures fail and bradycardia is still persistent then an IV atropine 0.5 mg will be given. Intraoperative hypertension (defined as SBP greater than 120% of the baseline reading) will be managed by stopping norepinephrine infusion. The infusion will be resumed when blood pressure returns to the upper limit of the target range i.e. 20% above baseline.After delivery of the baby, 3 IU of oxytocin will be administered IV over ≥ 30 sec followed by an infusion of 10 IU/hr (oxytocin 40 IU in 500 ml of Hartmann's solution).

The total amount of intraoperative IV fluids administered and estimated blood loss will be measured. At the conclusion of the surgery, blood loss will be estimated by cumulative measurement of the following: the volume of blood in the suction canister (and subtracting the estimated amniotic fluid from the suction chamber); visual examination of the surgical sponges.

Intraoperative use of other uterotonic agent or blood transfusion will be recorded. The attending pediatrician will assess neonatal Apgar scores at 1 and 5 minutes after delivery.

Patients will be asked to report the occurrence of intraoperative nausea Incidence of intraoperative pruritus, shivering, and dizziness will also be recorded.

The primary outcome measures will be incidence of post spinal hypotension defined as SBP < 80% of baseline reading or SBP < 100 mmHg after administering of spinal anaesthesia until delivery of baby. The secondary outcome measures will be post-delivery hypotension is defined as SBP < 80% of baseline reading or SBP < 100 mmHg observed from starting oxytocin until end of surgery.

Data collection Baseline data (gestational age, preoperative hemoglobin, preoperative anxiety, uterine incision to delivery time, hemodynamic parameters) and outcome parameters will be collected in the paper case record form and entered in windows Microsoft excel spreadsheet and will use STATA version 15.0 for analysis.