Abstract
Introduction
Metered dose inhaler (MDI) reservoirs are commonly used in the hospital to deliver MDI medications to intubated patients on mechanical ventilation. The purpose of this study was to evaluate 3 methods of MDI delivery through an adult mechanical ventilator circuit.
Materials & Methods
A Siemens Servo 900C in the volume-control mode was used to ventilate a lung model with standardized settings: VE 9.6 L, respiratory rate 12 breaths/min, t₁ 20% (1 s), and an accelerating flow waveform (a modified ramp flow waveform). An 8-mm-ID endotracheal tube (ETT) was attached to a rubber test lung (TL). The humidifier was bypassed for all trials. Aerosolized albuterol was delivered by MDI using 3 different methods. Method 1-MDI was attached directly to the ETT between the Y and 15-mm adapter using the Medicomp actuator/adapter. Method 2-MDI was attached to the Monaghan Aerovent reservoir and placed on the inspiratory limb just proximal to the patient Y. Method 3-MDI was attached to the Aerosol Cloud Enhancer (ACE), positioned as in Method 2. Aerosol drug was captured at the distal ETT tip and was measured spectrophotometrically. The amount of drug at the end of the ETT was expressed as a percent of the measured output of the MDI. Data were analyzed using repeated-measures analysis of variance and Scheffe's test.
Results
Method 1 delivered 1.69%, Method 2 delivered 21.4%, and Method 3 delivered 46.3% of the total dose to the end of the ETT. The 3 methods differed significantly (p<0.001). Pairwise post-hoc comparisons showed that each method differed significantly from the other two methods (p < 0.05).
Conclusions
In an intubated adult-lung model being mechanically ventilated, the use of a reservoir device on the inspiratory limb of the ventilator circuit increases the percent of dose reaching the end of ETT. The DHD ACE delivered a significantly greater percent of dose as compared to the other two methods examined.
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