New diagnostic approaches to monitor irrigating fluid absorption

Abstract

Rinsing the endoscopic operating field with an irrigating solution entails the risk of absorption of the fluid. The physiological consequences of such absorption are explored and two new methods for monitoring the amount of absorption are proposed.

Methods: (Paper 1). 25 anesthetized pigs were randomized to control or continuous infusion of 100 ml/kg over 90 min of either glycine 1.5%, mannitol 3% or mannitol 5%. Several invasive measurements and calculations were performed to describe the pathophysiological processes. (Paper 2). Exhaled air nitrous oxide (N2O) concentrations were measured in 12 volunteers receiving intravenous infusions, containing dissolved nitrous oxide and simulating fluid absorption. (Paper 3). Comparison of N2O and ethanol for detecting absorption in 86 patients, at 2 centres, undergoing transurethral resection of the prostate (TURP) in spinal anesthesia. (Paper 4). A 3-part evaluation of glucose as a tracer in fluid absorption detection. Part 1 was a clinical study in 250 patients undergoing TURP with and without a glucose-containing irrigant. Part 2 investigated the glucose kinetics in 10 volunteers receiving 20 ml/kg of acetated Ringer's solution with 1% glucose over 30 min. In part 3, data was used for computer simulations of various absorption patterns.

Results: (Paper 1). Infusions rendered a hypokinetic hypotensive state. Intracellular volume expansion, intracranial pressure elevation and myocardial damage were greater for glycine 1.5%. (Paper 2). N2O is a useful tracer for noninvasive fluid absorption monitoring. It identifies the pattern and the volume of absorption with a 95% predicition interval of ± 200 ml. (Paper 3). The N2O method is feasible in a clinical setting. Agreement with the ethanol method was volume dependent and about twice that of N2O versus known volume. (Paper 4). Sodium and glucose showed a strong inverse linear relation for all patients including diabetics. The glucose levels almost doubled after the experimental infusions, which volume diluted the plasma by 17.7%. Simulations showed that the infused volume correlated with the rise in glucose where an increase by more than 1.4 mmol/L could detect absorption with 95% confidence.

Conclusion: The pathophysiological process and treatment rationale of massive nonelectrolytic irrigating fluid absorption was outlined. The N2O method allows noninvasive online monitoring of irrigating fluid absorption with better resolution and similar or better prediction of absorbed volume compared to the ethanol method. Glucose can be used as a tracer for retrospective evaluation of irrigating fluid absorption.