All the pregnant women who are planned for cesarean section will be enrolled in the study and assessed for eligibility. Patients who does not meet the inclusion criteria or those who refuse to participate will be excluded from study . Other enrolled parturient who meet the eligible criteria will be randomized and allocated to two study groups by computer generated numbers that will be concealed in sequentially numbered, opaque sealed envelopes. A day prior to surgery, eligible patients will be explained in detail about the purpose of study, need, benefits and risks of procedure. They will be instructed on the method used for sensory and motor assessments. In addition they will be explained about numerical rating scale of pain, how to use it and rate it during intraoperative period. Written informed consent will be obtained during pre anaesthetic checkup. Patients will be counselled about fasting protocol and asked to remain nil per oral of 2 hours for clear liquid, 6 hours for light foods and 8 hours for fatty food. Before surgery, premedication will be done with Tablet Pantoprazole 40 mg and Tablet Metoclopramide 10 mg at 10 pm the day before surgery and 6 am in morning of surgery. In pre-delivery room, a peripheral intravenous (IV) line will be established with 18-G IV cannula. Preloading will be done with 10 ml/kg of Lactated Ringer's solution. Baseline blood pressure, mean arterial pressure, heart rate, respiratory rate, SpO2, fetal heart rate will be recorded in pre-delivery room. In the operation theater: Standard monitor including electrocardiography, noninvasive blood pressure monitoring and pulse oximetry will be attached. Patient will be positioned in sitting position. Painting of the patient's back with 10% povidine iodine and draping with sterile drapes will be done. Identification of intervertebral space will be done and the skin will be infiltrated with lidocaine 2% under all aseptic precautions.25-gauge Quincke's spinal needle will be introduced at L3-L4 intervertebral space using a midline approach in sitting position. After ensuring free flow of cerebrospinal fluid, study drug will be given over 10 - 15 sec. Study drugs would be prepared as: In group B, Inj. 0.5% hyperbaric bupivacaine 11mg (2.2ml) will be prepared. In group BF, Inj. 0.5% hyperbaric bupivacaine 10 mg (2ml) with addition of 10mcg (0.2ml) fentanyl with total volume of 2.2 ml will be prepared. Immediately after administration of spinal anesthesia, patient will be positioned supine with wedge under right hip and the time will be recorded as "time-zero".

Fetal heart rates will be noted. Patients will receive oxygen 3L/min via nasal cannula if SpO2 decreases to \<95%.NIBP and HR will be assessed every 3 minute following SAB for 15 minutes or until delivery of baby and thereafter every 5 minutes till the end of surgery. SpO2 and ECG were monitored continuously throughout the study period. Sensory level will be assessed bilaterally along the mid clavicular line using spirit soaked cotton until block reached upto T6 dermatome. Motor block will be assessed based on Modified Bromage Scale. Surgery will be allowed as soon as upper sensory level reaches T6 and Bromage scale of M3.Thereafter, the level will be checked every 2 min until maximal sensory block level is confirmed. Intra operative pain will be assessed whenever the patient complains of pain or discomfort during surgery. If somatic pain occur (at time of incision to skin or subcutaneous tissue), spinal anesthesia will be converted to general anesthesia and excluded from study. For visceral pain, patient will be asked to express the pain in Numerical Rating Scale (0-10).

Assessment of visceral pain will be mainly done during ;- Delivery of baby with fundal pressure application, exteriorization of uterus, handling of other intraperitoneal organs like bowels, adnexa so as to clear off the secretions and blood, suturing of visceral peritoneum, placement of uterus back to abdominal cavity after repair. Each time NRS is 4 or more it will be considered as inadequate analgesia and inj. Fentanyl 25 mcg will be given IV bolus. Investigator will wait for 3 min for its adequate effect. If still pain persists, then the dose of fentanyl will be increased to 1 mcg/kg. After 2 doses of fentanyl, if pain still persists then Inj. Ketamine 0.5mcg/kg IV will be given. If still pain is unbearable, general anesthesia will be administered. The need to convert to general anesthesia will be noted. Following delivery of the baby, Inj. oxytocin 3 IU will be administered bolus. Continuous infusion of oxytocin drip will be given as per need after communicating with obstetrician. APGAR score of the neonate will be evaluated at 1 minute and 5 minutes.

Hypotension will be promptly treated with intravenous fluid bolus (200 ml) and Inj.

Mephentermine 6mg IV boluses, which will be repeated if necessary. If bolus dose of Mephentermine exceeds 30mg then Inj. Phenylephrine 50 mcg IV will be given. Inj. Atropine 0.6mg will be given if bradycardia occurs. If respiratory depression occur, it will be recorded and managed as -if RR ≤10 breaths /minutes then physical stimulus will be given (tapping a patient's shoulder with calling her name ). If RR is still not increased or RR ≤ 8 breaths /minutes then Inj. Nalaoxone 0.4 mg IV will be given and will be repeated after 2-3 min if necessary. Dose of Naloxone will not be exceeded 10mg/ day. Postoperatively, follow up will be done every 15 minutes if any intraoperative adverse events is noted, otherwise every 1 hourly to assess for any hemodynamic changes and adverse events related to study drug upto 6 hours. Then, monitoring of vitals, urine output and pain management will be done upto 18 hours.