Scavenging tubing compression: A rare cause for anaesthesia ventilator malfunction.

Sir,

A 4-year-old boy weighing 12 kg was scheduled for laparoscopic orchidopexy for the right undescended testis. An anaesthesia machine with circle system (Datex-Ohmeda, Aestiva/5, GE Healthcare, Madison, WI, USA) and an anaesthesia ventilator (7100 Anesthesia Ventilator, GE Healthcare, Madison, WI, USA) were checked as per the standard departmental protocol. General anaesthesia was induced using fentanyl, thiopentone and atracurium. After confirming endotracheal intubation, mechanical ventilation was initiated in volume-controlled mode (tidal volume [TV] 110 ml, respiratory rate 18/min and I:E ratio 1:2). The patient was positioned for surgery and the anaesthesia workstation moved to the side for the surgeon to operate from the head end. When the ventilator circuit was reconnected, it was observed that the ventilator display showed 'sustained peak airway pressure (Paw)' and stopped delivering tidal volume. This alarm was activated despite the achieved pressure of 20 cm H2O and set pressure limit being 30 cm H2O [Figure 1a]. On switching over to manual mode of ventilation, the normal Paw was re-established. The rest of the intraoperative period remained uneventful. Once the procedure was over and the child shifted out of the theatre, the ventilator was tested again on similar settings using a test lung. This resulted in activation of the same alarm and the ventilator once again stopped delivering tidal volume. A change in flow sensor also did not rectify the problem. Further evaluation of the machine and breathing circuitry revealed that the scavenging system transfer tubing was completely obstructed by one of the wheels of the anaesthesia machine [Figure 1b]. After moving the wheel and relieving the obstruction, the ventilator started delivering the set tidal volume and the problem was resolved.

Figure 1

Ventilator monitor showing 'sustained Paw' alarm (a) and anaesthesia workstation wheel compressing scavenging tubing (b)

In our case, the scavenging system used was of passive, open interface type and a corrugated tube was usually connected to exhalation port for disposal of the gases to the atmosphere. When the anaesthesia machine was moved during the intraoperative period, one of the wheels ran over the scavenging tubing and led to complete obstruction. Obstruction or kinking of the scavenging system transfer tubing usually results in the development of auto-positive end-expiratory pressure[1] or increases the airway pressures.[2] However, in this particular scenario, it resulted in complete failure of ventilation. As per the user manual of 7100 Anaesthesia Ventilator, 'sustained Paw' alarm will be activated whenever the Paw is greater than set pressure limit for 15 s and the user action recommended is to check circuitry for kinks, blockages and disconnections or to consider calibrating the flow sensors.[3] Interestingly, in this scenario, display showed 'sustained Paw' and stopped delivering completely despite a Paw of 20 cm H2O which is far less than the set pressure limit, i.e., 30 cm H2O.

Movement of anaesthesia machine during intraoperative period is common while managing paediatric cases where children will be shifted to edges of the table for lithotomy position and for laparoscopic procedures. During such movements, anaesthesiologists are usually more vigilant to avoid kinking and disconnections of the breathing circuits, but less importance is given to avoiding the compressions and disconnections of the scavenging transfer tubing. This report highlights the importance of routine checking of the scavenging tubing for any obstruction/disconnection after movement of anaesthesia machine to avoid such untoward problems.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.