Abstract
Interruption of the breathing gas to a ventilated anaesthetized patient due to accidental disconnection or anaesthesia system malfunction may have serious consequences if not detected quickly. A series of tests which covers the range of foreseeable mechanical problems was developed and used to test the performance of three breathing gas interruption monitors, two commercially available and one developed at Vancouver General Hospital. The tests were designed to evaluate the performance of monitors as installed on anaesthesia systems under a variety of failure conditions, including endotracheal tube disconnection with and without occlusion of the opening, kinks in the inspiratory and fresh gas hoses, disconnection of the fresh gas hose, leaks in the breathing circuit, excessive high or low pressure in the scavenging circuit, continuing high breathing circuit pressure, and kinks in the circuit pressure sensing hose. Ability to detect both significant changes in ventilation variables and faults existing at initiation of ventilation were also tested over a representative range of ventilator and patient variables using circle, coaxial and paediatric circuits.
Only complete endotracheal tube disconnections with no obstruction of the opening were reliably detected by all three monitors. A commercial monitor with a single fixed-threshold alarm level also detected fresh gas interruptions in circle and adult coaxial circuits, but failed to alarm in response to any other fault condition. A monitor with selectable pressure thresholds and high, low, and continuing pressure limits detected just under half of the fault conditions. A microprocessorbased monitor developed at Vancouver General Hospital detected and correctly identified roughly 80 per cent of the faults.
The series of tests forms the basis for a Canadian Standards Association Preliminary Standard (Z168.10) and will allow hospitals to test the performance of breathing gas interruption monitors in use in their institutions. Comments on the test series are solicited.
Résumé
Chez un patient ventilé ľinterruption de ľapport des gaz par déconnection accidentelle ou un malfonctionnement du circuit anesthésique peut avoir des conséquences sérieuses si elle n’est pas détectée rapidement. Une série de lests qui couvre les problèmes mécaniques possibles a été développée et utilisée afin ďétudier la performance de trois moniteurs de détection de débit de gaz dont deux sont commercialement disponibles et un développé à ľHôpital Général de Vancouver. Les lests ont été planifiés afin ďévaluer la performance de ces moniteurs installés sur les machines ďanesthésie dans différentes conditions de bris de circuits incluant la déconnection du tube endotracheal avec ou sans occlusion de ľouverture, une coudure des tubulures de gaz frais et inspiré, une déconnection de la tubulure de gas frais, une fuite dans le circuit, une pression excessivement haute ou basse dans le circuit de scavenging, une pression élevée dans le circuit inspiratoire, et une coudure dans le tuyau détectant les variations de pression du circuit. La possibilité de détecter des changements significatifs dans les paramètres de ventilation et des erreurs à ľinitiation de la ventilation était aussi étudiée utilisant des circuits pédiatriques, coaxiaux et systèmes circulaires.
Seulement une déconnection du tube endotrachéal sans obstruction de ľouverture était détectée avec fiabilité par tous les moniteurs. Un moniteur commercial avec un seuil fixe du niveau ďalarme à détecté ľinterruption du débit de gaz frais dans le circuii circulaire et coaxial adulte, mais n’a pu déclencher ľalarme en réponse à ďautres bris du circuit. Un moniteur avec des seuils de pression variable a détecté un peu moins que la moitié des conditions du bris de circuit. Un moniteur basé sur un système de microprocesseur développé à ľHôpital Général de Vancouver a détecté et correctement identifié approximativement 80 pour cent des bris du circuit.
Cette série de tests constitue la base pour ľAssociation Canadienne des Normes (Z168.10) et permet aux hôpitaux de tester la performance des moniteurs utilisés dans leurs institutions. Des commentaires sur la série de tests sont sollicités.
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McEwen, J.A., Small, C.F. & Jenkins, L.C. Detection of interruptions in the breathing gas of ventilated anaesthetized patients. Can J Anaesth 35, 549–561 (1988). https://doi.org/10.1007/BF03020339
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DOI: https://doi.org/10.1007/BF03020339