Post-spinal hypotension is a common side-effect of subarachnoid block. Vasopressors are generally used to correct this. Phenylephrine is the vasopressor of choice for management of post-spinal hypotension in cesarean section. Since the risk of developing post-spinal hypotension is six times less in severely preeclamptic parturients compared to healthy parturients, the dose of phenylephrine required to treat hypotension in preeclamptics should also be different from that of healthy parturients. However, data on the efficacy of phenylephrine required to treat post-spinal hypotension in preeclamptic paturients is lacking. Therefore this study is designed to evaluate and compare the efficacy of phenylephrine required to treat post-spinal hypotension in preeclamptic and normotensive parturients.

Aim:

To evaluate and compare the efficacy of phenylephrine required to treat post-spinal hypotension in preeclamptic and normotensive parturients scheduled for cesarean section under subarachnoid block.

Objectives:

To evaluate and compare preeclamptic and normotensive parturientsscheduled for cesarean section under subarachnoid block with respect to:

1. Total dose of phenylephrine required to treat hypotension from the time of administration of SAB till baby delivery
2. Dose of phenylephrine required to treat the first episode of hypotension
3. Incidence of first bolus dose of phenylephrine being effective in treating hypotension
4. Total number of hypotensive episodes
5. Neonatal APGAR scores at 1^st and 5^th minute after birth and umbilical arterial cord blood pH
6. Maternal complications like bradycardia, rebound hypertension, nausea/vomiting etc.

Methodology

After obtaining due clearance from institutional ethics committee, a written, informed consent will be obtained from each participant prior to recruiting them for the study. Previously healthy parturients with age group between 18 and 40 years, with singleton term pregnancy will be included. Patients with history of diabetes, cardiovascular and cerebrovascular diseases, placenta previa, abruptio placenta, fetal abnormalities, cord prolapse or nuchal cord, fetal malformations and those having any contraindication to SAB will be excluded from the study.

Patients with diagnosed preeclampsia (SBP ≥140 mm Hg or DBP ≥90 mm Hg after 20 week gestation with proteinuria) will be included in group P and those with normal blood pressure will be included in group N. Blinding of the parturients to group allocation would not be possible because group allocation would be done on the basis of presence or absence of preecplampsia. The blood pressure which will be displayed on the monitor throughout the intraoperative period will preclude blinding to the presence of preeclampsia.

All patients would receive aspiration prophylaxis. Routine monitors will be attached. Left uterine displacement will be given. Baseline HR, SBP, DBP, mean BP and SpO2 will be measured.Intravenous access will be secured and co-loading will be initiated. Under all aspetic and antiseptic precautions, SAB will be given in sitting position. Hyperbaric bupivacaine (0.5%) 10 mg (height <150 cm) or 12.5 mg (height >150 cm) will be injected slowly. Pulse rate and SBP, DBP and mean BP will be recorded at Ts and subsequently every minute till the delivery of the baby. Further measurements of hemodynamic parameters will be done every 5 min till the completion of the surgery. Level of block will be noted.Hypotension (MAP ≤70% of baseline value or SBP <100 mm Hg whichever is higher; termed as the hypotensive value) will be treated with intravenous bolus of 50 µg phenylephrine. Further boluses of 50 µg phenylephrine will be administered every minute till the BP is above the hypotensive value. This will be considered as first hypotensive episode. If, after correction of first hypotensive episode, hypotension develops again, it will be considered as another hypotensive episode and will be treated similarly. Maternal side effects like bradycardia (HR <50/min), reactive hypertension (MAP >20% of baseline), nausea, vomiting etc. from the period of spinal injection to the delivery of the baby will be noted and treated accordingly. Umbilical artery blood samples will be obtained and sent for blood gas analysis. Neonatal APGAR score will be recorded at 1^st and 5^th min of birth.

The main observations related to efficacy of phenylephrine would be the total dose phenylephrine required to treat hypotension, the dose of phenylephrine required to treat the first hypotensive episode and the incidence of first bolus dose of phenylephrine being effective to manage the first hypotensive episode.

Maternal adverse events would be measured in terms of incidence of bradycardia and rebound hypertension. Neonatal outcome measures would include APGAR scores and umbilical arterial pH.

As ancillary observations, the percentage of patients who develop post-spinal hypotension out of the total number of parturients recruited in that particular group will also be calculated.

Sample Size and Statistical Analysis:

Since there is lack of data on the effective dose of phenylephrine required to treat hypotension in preeclamptic parturients, this would be conducted as a pilot study. A minimum of 60 parturients will be enrolled, till there is a total of 30 parturients (normotensive and hypertensive each) who develop hypotension requiring vasopressor administration for the management of post-spinal hypotension according to the criteria described in the study in each of the group.

Comparison of qualitative data will be done using Chi-square test and Fischer’s exact test and comparison of quantitative will be done using Student’s t-test. A p-value <0.05 will be taken as statistically significant.