Jet Nebulization During Mechanical Ventilation: Mass Balance Analysis

The interaction between nebulizer technology and mechanical ventilation can be confusing. Mesh technology has recently been quantified using the mass balance, a technique that measures all aerosol delivered and lost in ventilator circuits. Data for jet nebulizers are limited, and ventilator technology has changed over time. The present study was designed to better define aerosol behavior during jet nebulization by testing device position, gas source, humidification, inspiratory time (T_I), and circuit compliance.

Using radiolabeled particles, mass balance and output rate were measured for the AeroTech nebulizer placed close to the ventilator (IP), Y-piece (YP), and proximal to ETT (DY) in aerosol HME or humidified settings. The nebulizer was driven continuously (8 L/m, 50 PSIG) or by breath actuation (BA) during volume control ventilation at two inspiratory times (T_I 0.7 and 0.55 s). Five ventilators and two circuits with different tubing compliance were tested. Radiolabeled saline (3 mL, Tc^99m) was nebulized. A well counter measured filters inhaled and expiratory mass (IM, EM), and nebulizer residual (NR). Tubing deposition was measured with a gamma camera. A shielded ratemeter measured output rate and treatment time.

Mass balance ranged from 96 to 104% (no. = 66). IM obtained with IP, HME circuit, continuous nebulization (29.8 ± 5%), IP, and BA (26.8 ± 4%); with humidification, continuous (15 ± 1%), BA (27.1 ± 4). Lowest IM at YP position, HME (8.8 ± .6%). Circuit losses ≤20%. EM was lowest for IP (19.2 ± 2%) and highest for YP and DY (46 ± 3%). NR was higher with BA (43.1 ± 6 vs 37.1 ± 3, P = .002). Higher tubing compliance lowered IM (21.8 ± .7% vs 28.3 ± 3% [no. = 9], P = .01). Treatment time for IP, continuous, HME circuit (10 min), and BA circuit (50 min). Changing T_I (0.55 s) reduced IM and further increased treatment time.

Optimal conditions for jet nebulization were IP position, HME circuit, continuous nebulization, and stiff tubing. Humidification should be supplied with an aerosol HME. If active humidification, IP breath-actuated was most efficient but with marked increase in treatment time.