Unusual cause for raised airway pressures related to anaesthesia workstation

Sir,

We would like to report an incident of raised airway pressures in a patient due to the lack of timely maintenance of the Datex-Ohmeda Aisys care station (GE Finland)^®. A 28 year old, American Society of Anaesthesiologists 1, patient with a history of a road traffic accident 5 h ago was rushed to the operating room with a Glasgow coma scale of 8/15. He had an uneventful rapid sequence induction and intubation with an 8.5 mm internal diameter cuffed endotracheal tube (ETT). After connecting the closed circuit of the Aisys^® to the (ETT) we noticed that the bag was tight and only 2-3 ml/kg of tidal volume could be delivered with high airway pressures (35 cm H₂O). Auscultation revealed equal bilateral air entry with no added sounds. The end-tidal CO₂ trace appeared as depicted below [Figure 1] without proper angles. Multiple differential diagnoses for raised airway pressure such as mucous plug, bronchospasm, endo-bronchial intubation, pneumothorax etc., were ruled out/treated with bronchodilators, ETT suctioning.[1] The plane of anaesthesia was also deepened, but all the above interventions showed no improvement in airway pressures.

Figure 1.

etCO2 prior to and after draining the condenser tap

It was during this time that we noticed that the fraction of inspired CO₂ on the agent monitor was 4 mm of Hg, prompting us to replace the CO₂ absorbent. When the CO₂ canister was removed from the circuit, the airway pressures normalised and it was possible to deliver adequate tidal volumes. However, when the canister with fresh absorbent was incorporated into the circuit, high airway pressures were observed again. At this time one of the anaesthetists opened the condenser drain on the Aisys^® [Figure 2] and let out 400 mL of foul smelling water. Once the water was drained the airway pressures and end-tidal CO₂ trace normalised [Figure 1] and adequate tidal volumes were delivered.

Figure 2.

Datex aisys condenser tap

The manufacturer recommends draining of the condenser water daily.[2] We are inclined to believe that routine maintenance was not performed adequately resulting in accumulation of water within the condenser. However, how this accumulation of water causes raised airway pressures cannot be explained. On enquiry with the company technical team, the rise in airway pressures was attributed to an increase in circuit resistance caused by accumulation of condensed water, again not mentioned in the service manual. We recommend that the condenser water be drained on a daily basis and that if high airway pressures are observed after intubation it should be considered as one of the causes. Apart from patient factors, machine and circuit factors must be ruled out in presence of high airway pressures.