Transthoracic Echocardiographic Monitoring of Cardiac Output Effects of Colloid Preload and Crystalloid Coload During Cesarean Delivery Under Spinal Anesthesia

This prospective randomized controlled, double-blind study will be conducted at the obstetrics and gynecology operation room, at Qassim University Medical City.

Written informed consent will be obtained from eligible subjects on the day of the surgery. The study subjects will be randomized using the R software, version 3.5.2 (R Core Team, 2018; R Foundation for Statistical Computing, Vienna, Austria). Subjects will randomly be assigned to 2 equal groups (combined and crystalloid coload) using the permuted block randomization method with randomly selected block sizes of 4 and 6. The group allocation codes will be hidden in sequentially numbered, opaque, sealed envelopes that will be opened only after assessing the eligibility and obtaining the consent from the subjects. The study subjects and the outcome assessors will be blinded to the study group.

Spinal anesthesia will be conducted will be assessed respectively by an anesthesiologist not involved in the study.

All transthoracic cardiography images will be obtained by the second investigator who have the experience of accomplishing > 500 cases before starting the study using the technique and guidelines reported in American Society of Echocardiography . During obtaining the images intraoperatively, the investigator will be separated from the surgical field by a sterile drape, and the ultrasound probe will be covered with a sterile cover.

The study subjects will enter the operating room, lying supine on the operating table with slight left lateral position by tilting the operating table to the left. Standard monitors will be attached to all patients (noninvasive blood pressure, pulse oximeter, and electrocardiography). Basal systolic blood pressure and heart rate will be recorded after a period of rest, the average of 3 readings, 2 minutes apart will be recorded. Basal transthoracic cardiography images will be obtained.

Two 18-gauge intravenous cannula will be inserted in two large veins of the right forearm, one for IV fluids, and the other for phenylephrine infusion. In the combination group, patients will receive 250 mL of human albumin 5% (Human Albumin 50 gm/L, BAXTER, Austria) immediately before induction of spinal anesthesia (SA), over 10 minutes using an infusion pump (Fresenius Kabi Agilia Volumat MC Infusion Pump, Germany), and 750 mL of Ringer's lactate solution, to be started during the intrathecal injection of the local anesthetic, and infused over 15 minutes. In the crystalloid coload group, patients will receive 1000 mL of Ringer's lactate solution, to be started during the intrathecal injection of the local anesthetic, and infused over 15 minutes. In both groups, phenylephrine infusion will be given prophylactically, and will be started during the intrathecal injection of the local anesthetic at a dose ranging from 25-50 mcg/minute to maintain the SBP within 20 % of the basal readings. After administering the study solutions, Ringer's lactate will be attached to the IV cannula and will be administered at a rate of 1 mL/min; no other fluids will be administered until clamping of the umbilical cord (end of the study period).

In the sitting position, spinal anesthesia will be conducted by intrathecal injection of hyperbaric bupivacaine 12.5 mg 0.5% and fentanyl 15 microgram, using 27-gauge pencil point spinal needle at L3-L4 intervertebral space.

Surgery will be started after reaching at least an upper sensory level of T4; below this level, spinal anesthesia will be considered failed and patients will be excluded from the study.

SV and CO will be measured at 5 time points (basal readings, 1 minute after SA, 5 minutes after SA, immediately after delivery of the baby and clamping the cord, and 1 hour after the end of the study). SBP and HR will be recorded ever minute till the delivery of the baby, then every 3 minutes till the end of the surgery.

Inclusion criteria

• American Society of Anesthesiologists physical status II parturients with full term singleton pregnancies scheduled for elective cesarean delivery under spinal anesthesia.

Exclusion criteria

• Height <150 cm, weight <55 kg, and body mass index ≥40 kg/m2.
• Women presenting in labor or having any contraindication to spinal anesthesia (patient refusal, increased intracranial pressure, coagulation disorders, or local skin infection).
• Chronic or pregnancy-induced hypertension; baseline systolic blood pressure >140 mm Hg.
• Hemoglobin <10 g/dL.
• Diabetes mellitus.
• Cardiovascular, cerebrovascular, or renal disease.
• Polyhydramnios or fetal abnormalities.