Humidity devices in vitreoretinal surgery

Purpose: To assess a humidity device used in vitreoretinal surgery. Methods: Infrared absorption spectroscopy analysis of absolute water content (absolute humidity) was determined for a typical vitreoretinal air infusion line with and without the humidifying device. A variety of experimental laboratory conditions were utilized and designed to mimic those found in the operating room. The effect on physical parameters, such as flow rates and resistance to flow, were also determined. Results: While large bore infusion (LBI) lines had a negligible effect on flow rate and resistance to flow (reduction in infusion pressure), the standard 20G infusion line (SI) reduced flow rate and infusion pressure by approximately 25%. When used together, the humidifying device and SI reduced flow rate and infusion pressure by one third. The humidifying device was found to add 6.5 mg/L water content to the air infusion line system. Typical operating room (OR) air contains 9.5 mg/L water content, and 43.876 mg/L water content is required to saturate air at body temperature. Conclusion: To eliminate dehydration as a cause of intraocular morbidity, one must first saturate the infused air. If the visual field defects and other complications are eliminated, this would be good evidence for saturating infused air. As infusion pressure (flow rate) influences dehydration rate, unless saturated air is used, infusion pressure cannot be considered an independent variable in the analysis of field defects.