Next Logical Step

I appreciate Hartmann and colleagues' letter outlining the next logical step of our bench study,¹ a clinical trial of the use of the vibrating mesh micropump technology for ribavirin delivery. Although the use of aerosolized ribavirin remains controversial, the patient selection by Hartmann et al appears to be on target with the latest supporting evidence of potential benefit. Therapies offered within respiratory care are without conclusive evidence. In these cases, it is a balance of risk versus benefit. For the most part, many of the therapies we provide are low risk, and therefore the smallest of beneficial therapies are studied in clinical trials.

Continuous aerosol delivery in the mechanically ventilated patient with traditional jet nebulizers or in the case of ribavirin delivery via the small-particle aerosol generator (SPAG) can place the patient at additional risk of complications for a host of reasons surrounding the addition of flow within the ventilator circuit. Respiratory therapists for years have compensated for this known complication by being physically present during intermittent aerosol drug delivery to provide a near continuous clinical assessment and if necessary intervention. This continuous assessment is not possible when these treatments are prolonged past the traditional 10–15 min timeframe.

Since the introduction of the vibrating mesh micropump technology, the capability to monitor pulmonary mechanics and ventilator operation during aerosol delivery is possible, because the vibrating mesh micropump does not add additional flow to the circuit. This improves the safety profile of this delivery method. The vibrating mesh micropump may provide a safer delivery with similar results to that of SPAG, but we cannot ignore the many unknowns of this drug therapy, nor should we let the use of this proposed delivery method blindly open the door for widespread application without further study. Let's review a couple of unknowns mentioned in the letter. First, the team switched ventilators according to a manufacturer recommendation. This introduces a variation in practice, circuit change, and exposes the patient with ARDS to a disconnect from the ventilator circuit. Was this really necessary, because the team was properly filtering the expiratory gases? Second, the team quickly identified crystallization after the 22 mL (2-h drug delivery), which lead them to change their practice and rinse after each therapy session. This again led to a disconnection in an immunocompromised patient with severe lung disease. Disconnects in mechanically ventilated patients have been associated with a hypoxia related to a decrease in functional residual capacity, and they potentially increase the chances of ventilator-associated pneumonia. The crystallization found also raises the question of loss of drug delivery and where else it may have been building up that was not seen. Could it be in the endotracheal tube? Not turning the humidifier off likely reduced the crystallization after humidifier use to that seen before humidifier use. Third, the team felt the need to double filter the expiratory limb with good intentions of protecting the integrity of the expiratory valve, transducers, and clinicians. However, the rationale of using 2 identical high-efficiency particulate air (HEPA) filters designed to filter to the same micron particle level does not appear to be logical. This likely only adds resistance to expiratory flow and potentially exposes the patient to an additional risk. Changing a single HEPA filter following the 2-h aerosol delivery would have alleviated concerns of an incompetent filter. Last, although this case had an outcome we all would hope for, it is not clear whether this was the result of the aerosolized ribavirin therapy or a combination of efforts.

We are a profession known to deliver low-volume, high-risk therapies well. Yet, we must consider the risk of every intervention and look beyond our 4 walls to determine whether there is a better method on the horizon. I applaud the Hartmann group's use of the Journal and for assessing the risk and benefits in this extreme situation. They appropriately interpreted our study and logically chose the more frequently used and perceived safer vibrating mesh micropump over the less frequently utilized and potentially higher risk SPAG device. Their critical analysis of the literature allowed them to choose the appropriate patient, drug, and device, leading to a safe delivery of the potentially beneficial aerosolized ribavirin and overall wonderful care.

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