When it comes to the position of the surgical table during elective cesarean delivery, recent research has concluded that leaving the table flat does not impair neonatal acid–base status compared with the 15-degree tilt position.
The investigators also found that a 15-degree left lateral tilt had a negligible effect on maternal hemodynamic parameters (Figures 1 and 2), leading them to question whether current recommendations on maternal positioning during cesarean delivery under spinal anesthesia are still necessary.
According to Allison J. Lee, MD, assistant professor of anesthesiology at Columbia University Medical Center, in New York City, left lateral uterine displacement during cesarean delivery by tilting of the surgical table is a long-standing recommendation in obstetric anesthesia practice.
“But in reality, we know that most women who undergo cesarean delivery are not being tilted at 15 degrees,” Dr. Lee said. “So we wanted to figure out if this makes sense. We sought to answer the question of whether the tilted position is better than the supine position.”
Long-Standing Recommendation Still Needed?
If MRI is any indication, then the tilt position may well be outdated: A recent study has shown that at term, the inferior vena cava is almost completely compressed in both the supine position and with a 15-degree left lateral tilt (Anesthesiology 2015;122:286-293).
To help answer these questions, Dr. Lee and her co-investigators enrolled 100 healthy women with a single-fetus pregnancy into the trial; all were undergoing elective cesarean delivery with a standardized spinal anesthetic comprising 12 mg of bupivacaine, 15 mcg of fentanyl and 150 mcg of morphine.
The women were randomly assigned to either the supine horizontal position (n=50) or a 15-degree left lateral tilt of the surgical table (n=50) after spinal injection. Also initiated at the time of spinal dose was a coload of a 10-mL/kg lactated Ringer’s and phenylephrine infusion, titrated to achieve 100% baseline systolic blood pressure. The trial’s primary outcome was umbilical artery base excess.
As Dr. Lee reported at the 2016 annual meeting of the American Society of Anesthesiologists (abstract A2076), no differences were found between groups with respect to umbilical artery or vein base excess or pH between groups. The mean umbilical artery base excess in the supine group was –0.5±1.6 mmol/L, compared with –0.65±1.5 mmol/L in the tilt group (P=0.64). One neonate in each group required bag-mask ventilation, and one in the tilt group had an Apgar score of 5 at one minute; the five-minute Apgar score was 9 in all cases.
“Given these findings, we feel that if the mother’s blood pressure is controlled and kept at baseline levels, there’s probably no value in tilting women,” Dr. Lee said. “Furthermore, we found that in six cases where the patient was tilted, the surgeons actually couldn’t operate, and we had to put them supine.”
Mark C. Norris, MD, clinical professor of anesthesiology at Boston University, noted that previous research in awake patients has shown wide variability in how women respond to table positioning. “Some can lie supine without any problem, but then there’s a subset that clearly gets symptomatic,” he said. “And then there’s an even smaller subset that has demonstrable aortic compression.
“So what do you do when you get that patient who gets profoundly hypotensive, even after you give them vasopressors? Do you tilt them?”
“We actually had one patient who became significantly symptomatic in the supine position,” Dr. Lee replied. “So I think the key thing is to be able to identify those outliers who will benefit from being tilted.”
In another presentation whose lead author was Dr. Lee (abstract A2077), the investigators reported the effect of maternal positioning during cesarean delivery on maternal cardiac output and vasopressor requirements. Cardiac output, blood pressure and heart rate were recorded after five minutes in each of the supine and tilted positions, and then continuously throughout the procedure.
They found that the mean cardiac output at baseline was 8.08 L per minute in the supine group, and 8.41 L per minute in those who were tilted (P=0.002). At 15 minutes after spinal anesthesia, it was again significantly lower in supine patients (7.2 vs. 8.8 L/min; P=0.03). “We started to see differences by about eight minutes after the spinal,” Dr. Lee explained. “So it looks like there is something happening, but it’s not that remarkable.” The supine patients also required a greater total phenylephrine dose at 15 minutes (788.6±321 mcg) than their counterparts in the tilt position (611.4±228 mcg; P=0.0024).
Despite these differences, surgeons’ preferences became clear as the study progressed. “In general, the surgeons were much happier with the supine position,” said co-investigator Richard M. Smiley, MD, PhD, chief of obstetric anesthesia at NewYork-Presbyterian Hospital/Columbia University Medical Center, in New York City. “They would be jumping up and down wh en they opened the envelope and saw that the patient would be in the supine position.”
The way Dr. Smiley sees it, it’s time to critically reevaluate the benefits of the 15-degree tilt position. “The books all say 15 degrees, but it’s a number pulled out of thin air. More importantly, it’s a number that few anesthesiologists actually adhere to. We think we’re tilting patients 15 degrees, but it’s actually only 4 degrees or 6 degrees. And I’m pretty sure that based on imaging studies, that’s doing nothing.
“So the point is, we’re not doing it anyway; the patients don’t love to be tilted; and the surgeons hate it. So, why bother?”