Intraoperative IOP Patterns Dependent Upon Surgical Position

Patterns of intraoperative change in intraocular pressure (IOP) are significantly different based on the postural position the patient is placed in, according to research published in BMC Ophthalmology. 

Researchers conducted this cross-sectional observational study to assess the outcomes of surgical positioning on intraoperative IOP. The study looked at 325 participants (mean age, 54.8±14.1 years, 40.6% men, 59.4% women) undergoing a nonocular surgery between January and December 2019. All patients received general anesthesia in the supine position and were then placed in lithotomy position (76 patients), lateral position (96 patients), prone position (102 patients), or supine position (51 patients) based on what was appropriate for their surgery. They were all returned to supine position at the end of surgery. IOP was measured using a handheld tonometer on 9 separate occasions:at baseline, after admission of general anesthesia, 10 minutes following admission, 10 minutes following positioning, 1 hour into surgery, 2 hours into surgery, 4 hours into surgery, 10 minutes prior to the end of surgery, and before discharge. 

Analysis was completed to assess mean IOP, IOP change throughout surgery, and comparison of IOP between positions. 

Mean IOPs in the left and right eyes respectively were 18.5±2.6 mm Hg and 18.2±2.7 mm Hg in the lithotomy position, 19.3±4.2 mm Hg and 18.9±3.4 mm Hg in the lateral position, 19.9±3.6 mm Hg and 20.0±3.4 mm Hg in the prone position, and 19.1±3.3 mm Hg and 18.9±3.6 mm Hg in the supine positions. Patient IOP rose above 24 mm Hg in 34.2% of participants in the lithotomy position, 89.4% of participants in the lateral position, 48.5% of participants in the prone position, and 13.7% of participants in the supine position.

In both the right and left eyes, the IOP showed statistically significant differences at each timepoint in the lithotomy, lateral, and supine positions (P <.05) and the final IOP measurement prior to exit from the operating room was significantly higher than IOP measured after general anesthesia was given in the prone position (P <.01). The researchers report that their study shows IOP is likely to increase as head-down angle increases (F value=4.85, P <.05). Participants at a lower than 20° angle had mean IOP of 15.7±2.3 mm Hg. Those with a head angle of 20° to 30° had a mean IOP of 16.9±1.6 mm Hg. Patients with a head down angle of more than 30° had a mean IOP of 17.5±2.5 mm Hg. Multivariate analysis revealed that postural position and baseline IOP were correlated with the differences found in IOP before and after surgery (P <.01). 

“Nurses in the operation room should pay attention to the placement of the lateral recumbent lumbar bridge position,” the study authors advise. “Direction compression should be avoided. And it’s encouraged to reduce the head-low angle or keep the upper body supine under the premise of ensuring the operation of the physician.”

Each position resulted in differing IOP changes throughout surgery, the researchers report. The study authors urge surgical teams to carefully monitor IOP intra- and postoperatively when patients undergo surgery in the lateral recumbent position, head-low foot-high lithotomy position, or prone position to prevent and manage adverse ocular effects. 

A limitation of this study is the inability to measure IOP in the prone position due to instrumental limitations of the handheld tonometer. Additionally, researchers did not collect follow-up data on ocular adverse effects.