Improving Embryologists’ Sleep Quality: Implementation of a Weight-Based Monitoring System for Gamete and Embryo Cryostorage

Abstract

Background: Storage of gametes and embryos in our laboratories represents the highest concentration of risk for an ART clinic. A single storage tank may contain material of several hundred patients and vacuum failure is a scenario that haunts embryologists’ nightmares. Temperature sensors are currently the most prevalent mechanism for ‘alarming’ storage tanks, however, such approaches are akin to closing the gate after the horses have bolted. Aim: To assess the implementation of a fully redundant, weight-based monitoring system for ensuring the security of liquid nitrogen storage tanks in a high-capacity ART unit. Method: Forty flat-bed scales were fitted with alarm conversion units allowing a standard ‘open/closed’ alarm output to be relayed in the event a reading fell below the user defined weight limit. Output was routed through a security monitoring system via phone line and mobile-SIM, with no overlap of the existing, internet-based temperature probe system. Relationship between liquid nitrogen level (HC35 vessel), tank weight and temperature reading (probe positioned at top of canister), was established by sequential measurements. Results: Addition of the flat bed scales proved minimally disruptive to the space allocation per tank, requiring no additional ‘width’ but a slight increase in ‘depth’ behind tanks to accommodate the screen support. As expected, a clear, linear relationship was evident between liquid nitrogen level and tank weight, with every 1cm drop in liquid nitrogen equating to approximately 0.5kg weight loss. Concerningly, the temperature probe remained below -190∘ with just 0.5cm of liquid nitrogen remaining, only rising above the alarm trigger threshold once nitrogen had fully evaporated, resulting in a precipitous rise to above devitrification temperature in a matter of hours. Conclusion: Introducing a weight-based tank monitoring system is both feasible and effective. This system provides vastly superior performance in the timely identification of impending tank failure, allowing ample opportunity to ensure safe relocation of material.