Evaluation of Changes of Venous Return After Spinal and Epidural Analgesia and Anesthesia by Ultrasound Guided Vena Cava Diameter Measurement

After approval by the Institutional Review Board and patient consent, term pregnant patients (>37 week gestation) admitted to the obstetric service of Augusta University Medical Center, who require administration of neuraxial analgesia for labor or regional anesthesia for cesarean section, will be included in the study. The consent will be obtained by the attending, resident or medical student in which the investigators will explain to the patient the procedure, benefit, risk, cost and, confidentiality. The investigators plan to get the consent immediately after the patient arrived at the unit to avoid any interference with the delivery process. If the patient needs to go to an emergency cesarean section. This patient is not going to be included in the study. Demographic variables (age, BMI, Gravity, parity and gestation weeks) and hemodynamic variables (MAP and HR) will be recorded. All patients will be lying in supine position, breathing spontaneously. The ultrasound examination will be performed before commencement of the neuraxial procedure and will be repeated two minutes after administration of the neuraxial anesthetic. Ultrasound measurements will be made with a Sonosite Edge (Sonosite Inc. USA) machine and a C60X curved linear phased array transducer (Sonosite Inc.) set to abdominal mode. All measurements will be made by two attending anesthesiologists (ERP and AR) who have experience in transthoracic echocardiography, and a resident who receives the basic instruction to measure IVC diameter. The medical student will be present during the procedure and will ensure that the study echocardiographic views are taken.

The IVC will be visualized using a paramedian long-axis view via a subcostal approach according to guidelines of the American Society of Echocardiography. A two-dimensional image of the IVC will be obtained and pulsed wave Doppler will be used to differentiate from the aorta. Variations in IVC diameters will be assessed with M-mode applied 2 cm. distal to the right atrium. To ensure consistent measurements, each operator will take three images. The best quality images are chosen. Maximum and minimum IVC diameters during a single respiratory cycle will be measured.