Loss Of Fresh Gas Flow Due To Malposition Of Vaporizer: An Oft Repeated Anaesthetic Misadventure

摘要

We report a case of complete loss of fresh gas supply at anesthesia machine outlet due to malposition of vaporizer on to the manifold where it was lifted off and tilted up on one side. We also re-emphasize on the importance of strictly adhering to the recommendations for pre-use checks in the Anesthesia machine checklist, and by the manufacturers; and also for an effective collaboration amongst the operating room personnel. INTRODUCTION Equipment malfunction contributes to morbidity and mortality in anaesthesia. About one fourth of equipment problems are related to human error.1,2 An integral component of anesthesia machine is vaporizer, which if not used as per specifications leads to a variety of anesthetic complications. We highlight a case where improper use of the vaporizer led to failure to ventilate intraoperatively. CASE REPORT A 40 year old male patient, ASA Grade I, was posted for acromian decompression. The surgery was planned under general anaesthesia. The Blease Sirius Spacelabs anesthesia workstation (Blease Medical Equipment Limited, Washington, USA) passed the daily electronic system check and the circle breathing circuit was also manually checked using thumb occlusion test before the case. The BleaseDatum L Series halothane and sevoflurane vaporizers already mounted on the machine were each checked by performing leak pressure test .Standard monitors were attached and baseline parameters recorded. After premedication and preoxygenation, the patient was induced with 5mg/kg of thiopentone and 0.1mg/kg vecuronium; mask ventilation with 2.0% sevoflurane and N2O and O2 was performed. The patient was intubated, bilateral air entry checked; and switched over to volume controlled ventilation. The vital parameters remained stable. After intubation, it was decided to shift the patient on isoflurane. The technician replaced the already mounted upstream halothane vaporizer with the isoflurane vaporizer. The dial concentration was set at 2.0% aiming to maintain MAC 1.0. Soon after, there was a low minute volume alarm and the bellows were collapsing. Immediately cuff leak, disconnections, loosening of CO2 canister, and sticking of unidirectional valves were checked. But there was none. The patient was taken on bag and the flows increased but the patient could not be ventilated even with the adjustable pressure limiting valve fully closed; which was free of obstruction. The patient could only be ventilated by activating the oxygen flush; even this was shortlived as enough pressure could not be generated and the bag quickly emptied once the O2 flush was released. So the patient was taken on auxiliary common gas outlet but of no avail; the bag remained empty and could be filled only with the oxygen flush. There was no gas flow at the outlet despite the bobbins floating in the flowmeter.Meanwhile a good check was kept on the patient's vital parameters that remained stable, probably because of those desperate intermittent oxygen flushes and was taken on manual resuscitator. As the cause of failure to ventilate could not be located, the remaining case was conducted on a changed anesthesia machine maintaining anesthesia with isoflurane, intermittent intravenous boluses of fentanyl and vecuronium. The patient was successfully reversed; conscious and oriented. The previous anesthesia machine was inspected and nothing was found functionally wrong except that the isoflurane vaporizer was slightly (<10degree) tilted to one side, lifted up on the right and the locking lever was not in place, the concentration control dial could be turned on clockwise and when the test lung was attached, it barely inflated.