Delivery of sevoflurane using a neonatal ventilator
Burstal and Threlfo have adapted and bench tested a neonatal ventilator to deliver sevoflurane for neonatal anaesthesia. They did this to deliver low minute volumes with precision in neonates with uncuffed endotracheal tubes. Most neonatal intensive care (NICU) ventilators achieve this by measuring and controlling expiratory tidal volume in contrast to most anaesthetic machines that measure and control inspiratory volume.
The investigators’ design incorporates an Acutronic Fabian HFO ventilator connected to a Diamedica draw-over vaporiser (due to the need for low resistance) and a bespoke scavenging system. A cleverly designed open interface scavenger cap was fashioned to fit over the Fabian expiratory valve which used wall suction and room air entrainment. Gas sampling was via a 22g cannula inserted into the patient circuit connected to a Datex Ohmeda E-CAIO gas analyser.
Their tests showed that with flows of 4 and 8L/min the settings and delivery of sevoflurane were linear, the scavenging apparatus was effective and did not affect volumes or pressures. They found that these results were consistent across the most settings of the Fabian ventilator. However, delivery of sevoflurane was elevated and unreliable in high frequency oscillation mode. The modifications cost approximately $5000.00 and was compliant with ANZCA requirements and required minimal training to use.
The investigators used relatively high flows (4 and 8L/min) as is required with neonatal ventilators in NICU due to the use of uncuffed endotracheal tubes. It would be interesting to compare the accuracy, efficiency and safety of this system to a standard anaesthetic machine in a neonate with a MicrocuffTM endotracheal tube where leak was eliminated and much lower flows could be used.
Take Home Message
Burstal and Threflo have presented a clever and relatively simple adaption of a NICU ventilator to anaesthetic machine that provides a neat solution to the difficulties of administering volatile anaesthetic while delivering accurate tidal volumes to neonates during anaesthesia. I question the usefulness of such a device in very small babies in whom an opioid heavy anaesthesia is preferred over sevoflurane with its significant hypotensive and possibly toxic effects.
Reviewed by: Dr Meredith Betts