VANCOUVER, B.C. – Trendelenburg position does not materially increase ventilator pressures during laparoscopic gynecologic surgery, according to investigators from McMaster University in Hamilton, Ont.
The use of the Trendelenburg position can sometimes cause tension in the operating room. Surgeons need to roll the small bowel out of the pelvis to get access to their gynecologic targets, but anesthesiologists worry that they’ll have to turn up ventilator pressures – and risk barotrauma – if women are placed in a head-down position. It’s unclear from previous studies if pressures really need to be increased when using a moderate Trendelenburg position, Dr. Stephen Bates, a professor of obstetrics and gynecology at McMaster University, said at a meeting sponsored by the AAGL.
Dr. Stephen Bates
To find out, Dr. Bates and his colleagues monitored peak inspiratory pressures (PIP), pneumoperitoneum pressures, degrees of Trendelenburg, and other factors as 100 women underwent laparoscopic hysterectomies performed by a total of seven surgeons. The women were aged 46 years, on average, and had a mean body mass index of 29 kg/m2.
The surgeons opted for an average of 10 degrees Trendelenburg, which resulted in a 1.9 cm H20 (7%) increase in PIP from horizontal positioning, up from a mean of 26.7 to 28.6 cm H20.
“By all anesthesia standards, this is a trivial change and clinically insignificant,” Dr. Bates said in an interview. “The traditional dogma is that if you put patients in Trendelenburg, you’ll increase the difficulty of ventilating them. That was not the case.”
But body mass index, and to a greater degree pneumoperitoneum pressures, did predict increased ventilator pressures among the women.
“The higher pneumoperitoneum pressures are, the harder it is to ventilate,” Dr. Bates said. “There’s [almost] a linear relationship between PnP [pneumoperitoneum pressures] and ventilator pressures.”
When pneumoperitoneum pressures were reduced from 15 to 10 mm Hg, PIP fell by approximately 10%, but the surgeons – all blinded to the reduction in PnP – did not notice any deterioration in their surgical views, he said.
Taken together, the findings suggest a new way to negotiate Trendelenburg positioning in the operating room. “Anesthesiologists and gynecologic surgeons should consider minimizing the pneumoperitoneum pressure rather than reducing the degree of Trendelenburg,” Dr. Bates said.
The researchers also tested an inflatable pillow that lifted women’s buttocks a few inches above the table. The hope was that it would reduce the degree of Trendelenburg needed for their operations, and subsequently reduce PIP. Surgeons were able to decrease Trendelenburg by about 4 degrees with the pillow, but consistent with the study’s overall findings, it made no real difference in PIP. There was a clinically insignificant drop of 0.3 cm H20, from a mean of 28.6 to 28.3 cm H20, Dr. Bates said.
Dr. Bates reported having no financial disclosures.