Troubleshooting the defect in the sampling line of the side stream capnograph
Year: 2024
Type: article
Abstract: Dear Editor, A 75-year-old male patient was undergoing lumbar discectomy under general endotracheal anaesthesia with pressure support ventilation (Drager Perseus A500 anaesthesia workstation, Draeger Medical GmbH, Moislinger Allee 53-55, D-23542 Lubeck, Germany) under low-flow anaesthesia [1.1-L fresh gas flow with oxygen (O2): nitrous oxide (N2O) at 55:45 and minimum alveolar concentration (MAC) of 1.0 with sevoflurane]. At a peak airway pressure of 17 cmH2O, the tidal volumes achieved were 450–470 mL, with the end-tidal carbon dioxide (ETCO2) at 30–32 mmHg. While positioning the C-arm, the intravenous fluid stand (IV stand) located next to the anaesthesia machine was moved aside by operating room staff, who inadvertently pushed the IV stand into the path of the gas sampling line. The resultant stretch on the sampling line was immediately noticed, and the IV stand was moved out of the way of the sampling line and C-arm. Though there was no visible disconnection or damage to the sampling line, within a minute of this event, a double-hump pattern in the ETCO2 trace was observed. This was accompanied by a sudden drop in ETCO2 (24 from 32 mmHg), MAC (0.7 from 1.0), and the inhaled as well as the exhaled concentrations of sevoflurane, O2 and N2O [Figure 1a], although the patient’s vitals and the ventilatory parameters remained unchanged. As the gas sampling line was stretched before this, its connections were inspected immediately. At the water trap, the sampling line was found to be partially loosened [Figure 1b, Video 1], possibly by the pull and stretch caused during the movement of the IV stand. All measurements returned to the prior established range immediately upon tightening this connection [Figure 1c, Video 1]. Further course of surgery and anaesthesia were uneventful. {"href":"Single Video Player","role":"media-player-id","content-type":"play-in-place","position":"float","orientation":"portrait","label":"Video 1","caption":"","object-id":[{"pub-id-type":"doi","id":""},{"pub-id-type":"other","content-type":"media-stream-id","id":"1_jlkvjfzc"},{"pub-id-type":"other","content-type":"media-source","id":"Kaltura"}]} Figure 1: (a) The double-humped pattern of the capnograph waveform, with reduced minimum alveolar concentration and inspired and expired gas values. (b) The sampling line attachment site at the machine where a problem was detected (the sampling line being not fully threaded to the machine end). (c) The capnograph waveform and gas values return to normal immediately after resolving the problemFailure to recognise a faulty sampling line as the cause in such a scenario may lead to erroneous interpretation of low cardiac output (low ETCO2), patient awareness (low MAC), or discontinuation of inhalational anaesthesia (reversal in inhaled and exhaled gas values). Defective male-to-male Luer lock connector/damage to the sampling line contributed to the ‘double-hump’/‘tails-up’ pattern during mechanical ventilation.[1-5] Loosely fit sampling line caused the problem in this report. This ‘double-hump’/‘tails-up’ pattern in phase 3 of the waveform capnogram is characterised by early low CO2 (air entrainment through the defective/damaged sampling line) and subsequent high CO2 with the initiation of inspiration [build-up of positive pressure within the sampling line (with the inspiratory valve still occluded) preventing further air entrainment].[1-3] The hump/tail size varies with the positive end-expiratory pressure (PEEP) applied during mechanical ventilation, with the highest difference at PEEP 5 cmH2O. This difference progressively narrows with incremental increases in PEEP until it disappears at PEEP 10 cmH2O.[2] Despite a fault in the sampling line, a ‘double-hump’/‘tails-up’ pattern may not be observed during (a) controlled ventilation with zero end-expiratory pressure (ZEEP) due to continuous air entrainment during all phases of respiration,[2] (b) spontaneous ventilation as the pressure within the sampling line does not vary much during different phases of respiration although the pattern reappears when positive pressure breaths are given,[3] and (c) manual breaths in a patient with abolished spontaneous breathing efforts (± neuromuscular blockade) if the PEEP effect created by the partially occluded airway pressure relief valve (usually between 10 and 20 cmH2O) is sufficient enough to prevent air entrainment during both phases of respiration.[1] In conclusion, anaesthesiologists should be aware of the characteristic pattern changes of waveform capnogram and erroneous gas values caused by a faulty sampling line and should be able to quickly interpret the fault based on the type of ventilation and the applied positive end-expiratory pressure. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient consented to his images and other clinical information to be reported in the journal. The patient understands that his name and initials will not be published and due efforts will be made to conceal his identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
Source: Indian Journal of Anaesthesia
Author: Umesh Goneppanavar
Language: English
Subfield: Anesthesiology and Pain Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: diamond
OpenAlex ID: W4402540701