ABSTRACT
Introduction and Objectives COVID-19 can cause serious respiratory complications. One form of treatment utilises aerosolised therapeutics concurrently with mechanical ventilation (MV). Clinicians have adopted low tidal volume ventilation (LTV) strategies (4-6 mL/kg body weight)1 in these patients. Nebuliser performance is typically characterised in accordance with international ventilatory standard ISO274272 (ISO ventilation). The objective of this study was to compare the aerosol dose delivered to a simulated adult model with either LTV ventilation or ISO ventilation settings. Methods A 2.5 ml dose of 1 mg/ml of salbutamol (GlaxoSmithKline Ltd., Ireland) was aerosolised with a vibrating mesh nebuliser (VMN) (Aerogen Ltd., Ireland) positioned on the dry side of the humidifier within a dual limb circuit (Fisher & Paykel, New Zealand) during simulated MV (Servo-I, Maquet, Sweden). Two adult breath patterns were generated: 1) ISO ventilation, Tidal Volume VT: 500 mL, Breathing Rate BR = 15 BPM, Inhalation Exhalation ratio I:E: 1:1, and 2) LTV, VT: 400 mL, BR = 20 BPM, I:E: 1:2. A capture filter (Respirgard, Baxter, Ireland) was placed between the ETT (8.0 mm, Flexicare Medical Inc., UK) and the test lung. The mass of drug was determined using UV spectrophotometry (276 nm). Results are expressed as the percentage of the nominal dose placed in the nebuliser's medication cup. All testing was performed in triplicate. Results The results of this study, presented in figure 1, highlight the difference in the aerosol dose delivered to the simulated patient at the two different ventilatory settings. Conclusions Study results confirm that a simulated adult patient undergoing MV utilising LTV ventilation strategy would receive approximately half of the aerosol dose delivered in comparison with the ISO ventilation parameters typically used in reporting nebuliser performance. These findings should provide clinicians with an approximation of the administered dose that is delivered. This may be useful when optimising aerosol dosing strategies during LTV ventilation in COVID-19 patients.