key: cord-0712291-1g6x5grl
authors: Fullick, James; Oliver, Michael
title: “Water, water, everywhere”: a challenge to ventilators in the COVID-19 pandemic
date: 2020-05-01
journal: Br J Anaesth
DOI: 10.1016/j.bja.2020.04.077
sha: 17a9fc865435829e6046d5d61a67ba43528aa2fd
doc_id: 712291
cord_uid: 1g6x5grl

nan

C O R R E S P O N D E N C E "Water, water, everywhere": a challenge to ventilators in the COVID-19 pandemic James Fullick 1, * and Michael Oliver 2 1 Newport, UK and 2 Cardiff, UK *Corresponding author. E-mail: james.fullick@nhs.net Keywords: COVID-19; pandemic; resource management; ventilator; water trap EditordWith the spread of coronavirus disease 2019 (COVID-19), intensive care facilities have been rapidly overwhelmed across the UK and elsewhere. 1 In general, the UK has fewer doctors and fewer ICU beds per capita than most of Europe. 2 Many hospitals have spread into the recovery unit of theatres and are using anaesthetic machines to ventilate patients. We write from a South Wales district general hospital that has moved patients into our recovery facility as an outreach ICU to discuss some of the challenges and potential solutions of the use of anaesthetic machines in long-term ventilation.

The anaesthetic machines used in the expanded ICU within Newport hospital are the Mindray WATO Ex-65 (Mindray). These use standing gas-driven bellows to provide driving pressure and are connected to a heated circle system, and passive humidification and heating are provided by distal and proximal heat and moisture exchange (HME) filters. One of the main issues we have encountered in ventilating these patients for durations outside the routine scope of anaesthetic machines is water condensation within the 22 mm tubing. This condensation has been sufficient to cause almost complete obstruction and create an oscillating obstructive flow trace.

Humidification of inspired air is required in the intubated patient to preserve mucociliary function, clearance of secretions, and gas exchange of the respiratory system. Disruption of these can cause damage and difficulty in ventilation, even in normal lungs. Over 24 h,~250 ml of water is lost from the respiratory tract, 3 and a portion of this will collect in the breathing system, which requires multiple disconnections to drain water from the breathing circuit. Several methods are proposed to counteract this: increasing fresh gas flow to at least minute ventilation, decreasing breathing circuit length, and introduction of water traps into the breathing circuit.

By increasing fresh gas flow, the relative humidity in the circle system is reduced by increasing circuit gas turnover with dry gas. This was partially effective, but this strategy should be discussed with the works and estates team to ensure that the maximal oxygen flow rates are possible. Increased numbers of ventilated patients and the introduction of CPAP noninvasive ventilation as a viable first-line therapy can exhaust oxygen supplies if all patients require higher flows to match minute ventilation.

Decreasing the length of the breathing circuit partially helps with this issue but can exhaust the proximal HME more rapidly. It is also difficult to achieve once a patient has been admitted, intubated, and connected to the anaesthetic machine.

Water traps act as a reservoir for condensed water within the circuit. There are several models available but, as with many supply chains, they are difficult to purchase in a pandemic scenario. They sit between the patient and the anaesthetic machine on the expiratory limb and act to collect condensation via gravity. A further limitation of many of these water traps is that they do not allow the system to be emptied without disconnection. Several options were explored including the design of water traps that could be 3D printed and attached to the circuit, including a Luer lock system to extract water using a syringe. This would reduce circuit disconnections and create a large reservoir before ventilation became affected, with the caveat of using an untested medical device. The design of this trap went through several stages, from a sealed reservoir with a large volume (Fig 1a) to a smaller reservoir that could be emptied using a Luer lock syringe (Fig 1b) .

A final water trap design was created using an HME filter with the filter material removed and connected in the middle of the expiratory limb of the circuit. A needle-free connector was added to the inline sampling port to allow removal of condensation using a syringe without disconnection (Fig 1c) . This design is simple, quick to create using available resources, user friendly, and uses the minimal number of connections. A more complex design using a short in-line suction catheter (Fig 1d) was also proposed, however it requires more complex connections that increase the risk of disconnects, turbulent flow, or leaks. An empty HME filter provides around a 55 ml volume reservoir, with the addition of a 15e22 mm connector increasing this to 75 ml. The more complex connection with in-line suction can contain 80 ml.

We submit this as a creative solution to a practical problem encountered in the use of anaesthetic machines as long-term ventilators for COVID-19 patients. Awareness, consideration, and discussion of this and other issues arising should be encouraged to improve the care and safety of these at-risk patients.

The authors declare that they have no conflicts of interest.

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Initial design using large reservoir of >300 ml. (b) Refined design with Luer lock port for aspirating condensation. (c) Simplified design with available materials using an empty heat and moisture exchange (HME) filter and needle-free connector. (d) Modified HME filter with yconnector and in-line suction