Scavenging system - See the unseen to avert disaster.

Sir,

The role of Anaesthesia gas scavenging system (AGSS) in reducing the exposure of operating room personnel to waste anaesthetic gases is well established. Literature highlights cases of AGSS hazards like misconnection, compression of the conduit tubing leading to increased airway pressures.[123] We report a case of ventilatory failure in the anaesthesia machine due to bypassing of the receiving system of AGSS.

A 46-year-old woman was posted for arthroscopic shoulder surgery. As per the hospital protocol, we proceeded to check the anaesthesia machine [Drager Fabius plus (Lübeck, Germany)] with piston type of ventilator. The anaesthesia machine could not pass the leak test repeatedly and the display reported ventilator failure.

The reservoir bag had collapsed and did not fill even when the oxygen (O 2) flush valve was activated. Pipeline pressure for the gases were adequate. Leak in the breathing circuit, carbondioxide (CO 2) absorber and reservoir bag were ruled out. On taking a closer look, we found that the scavenging hose of the open system AGSS was connected from the scavenging port of the anaesthesia machine to the wall socket of the disposal system directly, bypassing the receiving system as shown in Figure 1. The correct method of connection is shown in Figure 2. On further probing, it was discovered that following the previous case while cleaning the operation theatre, the receiving system jar was accidentally broken by the housekeeping staff and in a state of panic, the above connections were made. This was causing a negative pressure in the breathing system and ventilator.

Figure 1

Scavenging hose of the AGSS connected from the scavenging port of the anaesthesia machine (A) to the wall socket of the disposal system (C) directly [A→C]

Figure 2

Correct method of connection. Scavenging hose of the AGSS connected from the scavenging port of the anaesthesia machine (A) to the receiving system (B), from the receiving system (B) to the wall socket of the disposal system (C) [A→B→C]

Anaesthesia gas scavenging system consists of collecting assembly, transfer hoses, receiving system and disposal system for waste gases. The scavenging system is classified into active or passive system based on the type of disposal system. The waste gases collected from the anaesthesia machine are transferred through the hose to the receiving system.

The receiving system temporarily stores the waste gases from where they are continuously exhausted in a continuous volumetric fashion via the hose into the disposal system. The receiving system can be either open or closed. Now-a-days most of them are of the open type and have air breaks that entrain room air when there is insufficient expired gas and also as an escape route for gases if the system fails. Thus, receiving system is an important part of AGSS that prevents any increase in expiratory pressure or any negative pressure in the breathing system and ventilator.[4]

In our case, the receiving system was bypassed leading to sub-atmospheric pressure application at the scavenging port resulting in malfunction of the ventilator and anaesthesia machine. A potential harm to patient was prevented with a timely machine check prior to administration of anaesthesia and finding out the root cause.

The most neglected part of anaesthesia machine checklist is the scavenging system. Anaesthesiologists must be aware of the operational characteristics and functional anatomy of their anaesthesia workstations including the scavenging system. The integrity of the scavenging system should also be checked along with anaesthesia machine before each case to prevent mishaps.

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Conflicts of interest

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