II. Lateral Tilt at Cesarean Section

Abstract

A ortocaval compression (ACC) in parturients occurs when the uterus compresses the abdominal aorta and inferior vena cava (IVC). This compression can lead to maternal hypotension and uteroplacental hypoperfusion. However, potentially significant ACC is difficult to detect before a regional block because many patients have no signs or symptoms. Thus, predicting the patient in whom profound hypotension may occur after sympathectomy during regional anesthesia is difficult as well. A noninvasive technique for identifying patients with significant ACC would be helpful as invasive techniques, such as radiologic angiography, are not practical for routine clinical use. This prospective observational study was designed to measure changes in cardiac output (CO) and other maternal hemodynamic values at different degrees of lateral tilt. The authors hypothesized that this would allow them to identify the presence of IVC compression in term parturients.The authors recruited nonlaboring parturients at term who were to undergo elective cesarean section. Standard monitoring was applied, including noninvasive arterial pressure monitoring at 1-minute intervals on the left arm, ECG, pulse oximetry, and continuous cardiotocography. A second noninvasive arterial pressure monitor was placed on the patient's left calf for measuring lower limb arterial pressure (AP). Intermittent measurements of CO, stroke volume, and systemic vascular resistance were obtained using suprasternal Doppler ultrasound. Patient hemodynamic measurements were made before spinal anesthesia with the operating table placed at 4 levels of left lateral tilt sequentially applied: 0 degrees (lying completely supine), 7.5 degrees, 15 degrees, and 90 degrees (complete left lateral with the hips and knees slightly flexed). Patients were kept in each tilted position for at least 5 minutes to allow for stabilization of the parameters before hemodynamic measurements were taken. A Z20 mm Hg difference in CO was thought to be evidence of significant IVC compression and a Z20 mm Hg difference in AP between the upper and lower limb was thought to reflect aortic compression.Of 170 patients who provided consent, 157 patients had complete data sufficient for analysis. No patients had episodes of hypotension or fetal heart rate abnormalities during the study period. CO was on an average 5% higher when patients were positioned at 15-and 90-degree tilt compared with 0-and 7.5-degree tilt. CO values at the 0, 7.5, 15, and 90-degree positions were 5.9, 5.9, 6.2, and 6.3 L/min, respectively (P = 0.001 for comparisons between 15-and 90-degree tilt compared to 0-and 7.5-degree tilt). Stroke volume values were 74, 74, 76, and 78 mL, respectively (no difference detected) and systemic vascular resistances were 1006, 1024, 934, and 979, respectively (P = 0.003, for comparisons between 15-and 90-degree tilt compared with 0-and 7.5-degree tilt). Heart rates were 81, 80, 80, and 82 bpm, respectively (no difference). In 11 patients who had a Z20% difference in CO between tilted positions, the me...