Operative hysteroscopy intravascular absorption syndrome presenting with apparent carboxyhaemoglobin elevation: a single-centre case series of six patients

Operative hysteroscopy intravascular absorption (OHIA) syndrome—systemic absorption of uterine distension medium through opened myometrial veins—causes fluid overload, pulmonary oedema and cerebral oedema. Concurrent electrosurgically generated gas may enter the circulation and apparently elevate carboxyhaemoglobin (COHb). We hypothesised that spectrophotometric interference from electrosurgically generated intravascular gas may act in concert with genuinely absorbed carbon monoxide (CO) to elevate the measured COHb. We retrospectively identified patients who developed new intraoperative hypoxaemia together with confirmed or suspected OHIA syndrome during bipolar hysteroscopic surgery with 0.9% saline distension (July 2025–August 2026); six such patients were identified, and demographic, fluid-balance and serial arterial blood-gas (ABG) data were extracted. All six women (median age 51 years; BMI 24.7 kg/m 2 ; ASA II) developed hypoxemia (median nadir SpO 2 91%), an abrupt fall in end-tidal CO 2 , and a mixed metabolic–respiratory acidosis (median nadir pH 7.139). Among them, three developed saline-induced hyperchloraemic metabolic acidosis, with borderline elevation in one further patient (median peak Cl- 117 mmol/L). Median irrigation-fluid deficit was 2,000 mL (≥ 1,000 mL in all). All showed apparent peak COHb elevation (15.2%, range 5.3–29.1%) coincident with the nadir pH, declining with recovery. Three developed pleural effusion. All recovered with diuretics, corticosteroids, and supportive care; none died. The study shows that operative hysteroscopy intravascular absorption syndrome during bipolar surgery with saline distension is consistently associated with an unexpected elevation of carboxyhaemoglobin that coincides with clinical deterioration. 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. 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. Prospective studies are warranted to validate carboxyhaemoglobin as a diagnostic marker and to distinguish between true carbon monoxide exposure and analytical interference.