During operative hysteroscopy, fluid used to distend the uterus can sometimes be absorbed into the bloodstream through opened myometrial veins, a complication known as operative hysteroscopy intravascular absorption (OHIA) syndrome. This systemic absorption can cause fluid overload, pulmonary oedema and cerebral oedema. A new single-centre case series, published in BMC Women’s Health, reports that in six patients who developed the syndrome during bipolar hysteroscopic surgery with 0.9% saline distension, all showed an unexpected rise in measured carboxyhaemoglobin (COHb) that coincided with the point of worst clinical deterioration.
The researchers behind the study hypothesised that this apparent COHb elevation may arise from two mechanisms acting together. Electrosurgical tissue vaporization can generate gas, including carbon monoxide, which may enter the circulation and be genuinely absorbed. In addition, electrosurgically generated intravascular gas or particulate matter may interfere spectrophotometrically with the blood-gas analyser, making the measured COHb appear higher than the true value. The study’s authors suggest that both mechanisms may contribute to the observed elevations.
The retrospective study identified patients who developed new intraoperative hypoxaemia together with confirmed or suspected OHIA syndrome during bipolar hysteroscopic surgery with 0.9% saline distension between July 2025 and August 2026. Six such patients were identified, and the researchers extracted demographic, fluid-balance and serial arterial blood-gas data from their records.
All six women had a median age of 51 years, a median body mass index of 24.7 kg/m2, and an ASA physical status of II. Each developed hypoxaemia, with a median nadir oxygen saturation measured by pulse oximetry of 91%. They also showed an abrupt fall in end-tidal carbon dioxide and a mixed metabolic–respiratory acidosis, with a median nadir pH of 7.139.
Fluid absorption left a clear signature in the blood chemistry. Three of the six patients developed saline-induced hyperchloraemic metabolic acidosis, and one further patient showed borderline elevation in chloride, with a median peak chloride concentration of 117 mmol/L across the group. The median irrigation-fluid deficit was 2,000 mL, and every patient had a deficit of at least 1,000 mL, indicating substantial absorption of the distension medium.
The most striking finding was the behaviour of the measured carboxyhaemoglobin. All six patients showed an apparent peak COHb elevation, with a median peak of 15.2% and a range from 5.3% to 29.1%. These peaks occurred at the same time as the nadir pH, the point of most severe acidosis, and the measured values declined as the patients recovered. Three of the patients also developed pleural effusion.
All six patients recovered with diuretics, corticosteroids and supportive care, and none died. The authors emphasise that the syndrome is a recognised but serious complication of hysteroscopic surgery, in which the distension medium enters the circulation and can precipitate fluid overload affecting the lungs and brain.
The study’s conclusion is that OHIA syndrome during bipolar surgery with saline distension is consistently associated with an unexpected elevation of carboxyhaemoglobin that coincides with clinical deterioration. The authors suggest that this apparent elevation likely reflects both genuine absorption of carbon monoxide generated by electrosurgical tissue vaporization and spectrophotometric interference from intravascular gas or particulate matter.
Based on these observations, the authors propose that monitoring for an unexpected carboxyhaemoglobin rise may serve as a real-time adjunctive clue to detect sudden intraoperative cardiovascular decline and prompt earlier intervention for the syndrome. They stress that this is a hypothesis-generating finding from a small retrospective series, and that prospective studies are warranted to validate carboxyhaemoglobin as a diagnostic marker and to distinguish between true carbon monoxide exposure and analytical interference.
As a single-centre case series of six patients, the study cannot establish how frequently this pattern occurs in the wider population of patients undergoing hysteroscopic surgery, nor can it confirm the underlying mechanism. The authors note that the measured COHb values are described as apparent elevations precisely because the contribution of analytical interference has not yet been separated from genuine carbon monoxide absorption. Until such prospective validation is carried out, the finding stands as a clinical observation that may alert surgical and anaesthesia teams to watch for this unusual laboratory signature during bipolar hysteroscopic procedures with saline distension.
Subject of Research: A case series of six patients describing operative hysteroscopy intravascular absorption syndrome with apparent carboxyhaemoglobin elevation during bipolar hysteroscopic surgery.
Article Title: Operative hysteroscopy intravascular absorption syndrome presenting with apparent carboxyhaemoglobin elevation: a single-centre case series of six patients
Article References: Xu, Z., Wang, H., Cai, D., Yang, B., Song, Y., & Wu, D. (2026). Operative hysteroscopy intravascular absorption syndrome presenting with apparent carboxyhaemoglobin elevation: a single-centre case series of six patients. BMC Women's Health. https://doi.org/10.1186/s12905-026-05039-0
Image Credits: AI Generated
DOI: 10.1186/s12905-026-05039-0
Keywords: operative hysteroscopy, intravascular absorption syndrome, carboxyhaemoglobin, bipolar hysteroscopic surgery, saline distension, hypoxaemia, metabolic acidosis, fluid overload, electrosurgery, spectrophotometric interference, case series, BMC Women's Health
News Source: Ophelia Keating. (October 28, 2026). Research report: Operative hysteroscopy intravascular absorption syndrome presenting with apparent carboxyhaemoglobin elevation: a single-centre case series of six patients. Scienmag.
