Cataract Surgery Patients Experience Less Pain and Anxiety With Nitrous Oxide

Nitrous oxide (N₂O) anesthesia — known for its prompt action and quick recovery — has already been employed in fields such as dentistry and obstetrics, but is little studied in its potential application to cataract removal. A single-center, retrospective investigation published in Clinical Ophthalmology explores whether N₂O can lessen anxiety and pain, without causing uneven vital signs in a cohort of patients undergoing phacoemulsification, compared with a similar group not undergoing added N₂O. All received local anesthetic.

The case group included 50 eyes of 39 participants, and a control set, or “air group” comprised of 30 eyes of 24 individuals. Two experienced surgeons performed the procedures at a hospital in Japan between October 12, 2021 and December 23, 2021. After gathering vital signs immediately prior to surgery, patients in the case group inhaled 30% low-concentration N₂O through a nasal cannula until the conclusion of the operation, which lasted approximately 8 minutes. Recorded classical piano music was played for all surgeries, every participant was conscious, and no other preoperative sedative medications were administered.

There was no disorientation or any significant adverse events from N₂O, and vital signs remained stable in both groups. Investigators measured subjective factors with a visual analogue scale (VAS) scored 0 to 100. Although intraoperative anxiety was comparable in both cohorts, anxiety level in the case set significantly decreased compared with the air-only group (P =.002). Pain was also significantly reduced for nitrous oxide participants in comparison with control patients (P =.014). Nausea showed little intergroup difference (P =.41).

“Although further studies are warranted to elucidate the safety of N₂O anesthesia in ophthalmic surgery, our results suggest that N₂O anesthesia could be effective in other ophthalmic surgeries such as vitreous, glaucoma, and ptosis surgeries,” the investigators wrote. “These surgeries generally take longer and sometimes cause more patient anxiety and pain than cataract surgery.”

Regarding objective signs, blood pressure (BP) changes during the procedure were similar between groups — systolic BP (P =.093) and diastolic BP (P =.23), but heart rate was significantly lowered in the N₂O set by -4.8±4.8 bpm, compared to the air cohort, -0.6±5.8 bpm (P =.001). Change in oxygen saturation significantly improved in case patients, by 1.6±1.4%, as opposed to -0.03±0.7% for air-only individuals (P <.001). Ultrasound and surgery times were comparable between groups.

In multivariate analysis, data also revealed that for participants receiving N₂O, two factors correlated with anxiety reduction; younger age (P =.045) and higher preoperative VAS anxiety score (P =.0001). No correlations with any variable appeared for anxiety change in control patients. Therefore, the investigation suggests N₂O may be especially effective for younger individuals, or those with greater anxiety about the procedure.

Limitations of this analysis included a somewhat small sample at a single center, and sampling bias that is intrinsic to retrospective designs. 

If N₂O is used safely to diminish anxiety and pain, this anesthetic may contribute to stabilization of vital signs during cataract removal, the investigation concludes.