Seasickness or Postoperative Nausea and Vomiting? A Retrospective Review of Patients Receiving Anesthesia at Sea Onboard the USNS Comfort.

INTRODUCTION: The USNS Comfort is a 1,000-bed hospital ship that provides full perioperative and surgical capabilities in a maritime environment. Patients may undergo surgery while the ship is pierside, anchored, or underway at sea. Postoperative nausea and vomiting (PONV) is a common anesthetic complication, but ship motion and sea state introduce an additional vestibular stimulus that is not captured by traditional PONV risk models. This study evaluated whether operating environment was associated with PONV after elective surgery aboard the USNS Comfort during a humanitarian mission.

MATERIALS AND METHODS: This IRB-approved retrospective cohort study reviewed all patients who underwent elective surgery aboard the USNS Comfort between June 11 and August 9, 2025. Patient demographics, operative environment, procedure type, anesthetic technique, total room time, tobacco use, volatile anesthetic use, and intraoperative PONV prophylaxis were collected from perioperative records. Patients with documented PONV or postoperative rescue antiemetic use were compared with those without PONV. Continuous variables were analyzed with Mann-Whitney U or Kruskal-Wallis testing, and categorical variables were analyzed with Chi-square or Fisher's exact testing. Post hoc chi-square testing with Bonferroni correction and a sensitivity analysis limited to general anesthesia cases were performed. Limited logistic regression was performed on the operative environment, anesthetic method, and total room time to generate odds ratios and 95% confidence intervals for these variables.

RESULTS: Among 241 surgical patients, 22 developed PONV, for an overall incidence of 9.13%. PONV differed significantly by operating environment, increasing from 5.45% pierside to 15.38% while anchored and 20.83% while at sea (P value .011). When PONV rates were compared directly at each operating environment, PONV was also associated with general anesthesia (P value .022), volatile anesthetic use (P value .010), female sex (P value .050), longer room time (P value .001), and greater use of prophylactic antiemetics (P value .008), likely reflecting provider recognition of higher-risk patients. Baseline characteristics across operating environments were generally similar, though room times were longer while anchored and at sea (P value .021.) In the general anesthesia subgroup (118 patients), the association with operating environment persisted, with PONV rates of 26.09% anchored and 40.00% at sea when compared to 8.24% pierside (P value .003). Limited multivariable regression for all patients also demonstrated an association between a site of anchored (OR 3.34, 95% CI: 1.15-9.70) or at sea (OR 4.93, 95% CI: 1.34-18.14) compared to pierside.

CONCLUSIONS: PONV after shipboard surgery varied significantly by operating environment, with the highest rates occurring when surgery was performed at sea. These findings suggest that ship motion and sea state may meaningfully influence postoperative outcomes beyond traditional anesthetic and patient-specific risk factors. This study provides real-world evidence that maritime conditions should be considered in perioperative planning. Future studies should evaluate broader postoperative outcomes, refine prophylaxis strategies that address both PONV and motion sickness physiology, and inform surgical decision-making for humanitarian, operational, and combat care at sea.