Sir,
Traditional teaching prompts immediate switch-over to the manual-mode on encountering ventilator-malfunction, then systematically investigating the cause of leak. We describe a case of paradoxical inability to ventilate the patient in the manual-mode, with smooth ventilation in the volume control (VC), pressure control (PC), and volume control-autoflow (VC-AF) modes, prompting Valsalva manoeuvre (VM) institution in the PC-mode of our Drager-Perseus A-500 workstation, instead of the usual manual-mode.
VM is performed actively (awake patients), accidentally (straining/weight-lifting), or passively (intraoperative manual-mode).[1,2] VM is often requested by surgeons intraoperatively (thyroid/head-neck surgery, craniotomy) to unmask covert venous bleeders, and detect cerebrospinal fluid-leaks (spinal-surgery).[1,2] VM-administration utilises the “intermittent positive- pressure technique” [manual-mode; fresh gas flow (FGF) 2 L/min; partial-closure (40 cmH2O) of adjustable pressure-limiting (APL) valve; gentle manual squeezing of the reservoir-bag and compression maintained for 15–20 s].[2]
A 53-year-old male was posted for tongue-commando surgery. The surgeons requested VM towards surgery completion. On switching from VC-AF mode to manual-mode for VM-institution, the reservoir-bag remained collapsed despite increasing FGF to 8 L/min, fully closed APL-valve (70 cmH2O), and emergency oxygen-button activation. After affirming nasotracheal tube cuff-integrity (pilot-balloon compression), inflation with additional 2 mL air, pushing the existing oral-pack more snugly around the tube, tightening circuit connections, and replacing the right-angled connector, filter, reservoir-bag and the closed-circuit including Y-piece, in sequential steps, the leak persisted from an unidentifiable site. Since the peripheral oxygen saturation (SpO2) plummeted, emergency oxygenation was administered by an Ambu-bag. To resume volatile anaesthetics, the patient was shifted back on VC-AF mode once the SpO2 reached 100%. Fortunately, now the set tidal volume could be delivered (complete flow-volume loops). On switching to manual-mode for VM, there again occurred sudden inability to ventilate. Adequate ventilation in VC, PC and VC-AF modes negated breach in circuit-integrity (endotracheal tube to workstation-interface).[3] Finally, a different technique to deliver VM in PC-mode was devised (pressure-cap setting 35 cmH2O; positive end-expiratory pressure 30 cmH2O; lowest respiratory rate of 3 breaths/min [inherent safety feature of Perseus-workstation)] delivering raised airway pressure (35 cmH2O during inspiration; 30 cmH2O during expiration) until switching to manual mode in 20 s [Figure 1]. Jugular venous distension was observed. The bleeder unmasked consequent to VM was cauterised successfully.
Figure 1.
Administration of Valsalva manoeuvre in pressure control mode of Drager Perseus anaesthesia workstation
Subsequently, we pinpointed faulty seating of the sodalime canister (replaced intraoperatively, 5 h earlier, to rectify sodalime-exhaustion-induced rebreathing) for this anomaly. It was only partially installed in the canister-bracket, the canister-top being locked with the CLIC-adapter system, generating a large gas-leak by pressing open the spring-loaded rubber valve. The canister was removed and reset into position and viola; manual ventilation became possible.
In lesser machines, switching the sodalime-canister intraoperatively, disrupts controlled ventilation. High-end workstations (Perseus, Apollo, Zeus, Primus, Fabius) are endowed with the CLIC-adapter (Drägersorb CLIC-system; Dräger, Inc, Telford, Pennsylvania) fitted with a spring-loaded rubber valve allowing the machine to successfully pass a pre-use check minus a sodalime-canister (Drägersorb 800; Dräger, Inc) and permitting its intraoperative replacement without disruption of controlled ventilation and volatile anaesthetics. General Electric machines with EZ-Change Mode (Avance-CS2; GE Healthcare, Madison, WI) allow continued ventilation without leak while changing carbon dioxide (CO2)-absorbent.[4-6] Our machine had passed the pre-use check (including leak-test) with the canister in situ. An automatic leak-test could not be technically performed after intraoperative canister replacement. The end-tidal CO2 remained within normal limits with a FGF of 3 L/min without CO2-absorber in the circuit because during mechanical ventilation (inspiratory phase), the fresh gas decoupling valve (FGDV) closed, permitting positive pressure ventilation of the lungs, and in the expiratory phase, room-air entered the breathing circuit via the canister-leak reaching the lungs through the open FGDV.
The changes in ventilator graphs, agent concentration, and alarms were insidious and did not indicate an obvious entrapment.
The incident prompted us to order the optional radiofrequency identification sensor (exclusive to Perseus-workstation) which ensures the presence and proper installation of a sodalime-canister.
This report stresses thorough knowledge of the machine. However, only knowing the machine is not enough and one must also be a keen observer. While troubleshooting a large leak, one should be aware of a potential CLIC-adapter related sodalime-canister leak.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for 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 identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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