The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

DIRECTION AND EXTENT OF AIRFLOW ALTERS MUCUS MOVEMENT.



Maryam Zamanian M.D., Eric Walter M.D., Alexander Adams FAARC, RRT, John Marini M.D. Healthpartners/Regions Hospital, St. Paul, Minnesota

Background:
Secretion retention can be a significant problem for intubated patients receiving mechanical ventilatory support. With airway access guaranteed, secretion clearance can usually be managed but the problem can become critical during weaning attempts. To our knowledge, the influence of ventilator settings on secretion retention has not been previously investigated. We developed a model for testing the movement of thick airway secretions under various ventilatory/impedance conditions.

Methods:
An airway circuit between a test lung (Michigan Instruments) and ventilator (Servo I, Maquet) was constructed to evaluate factors associated with mucus movement under a wide range of ventilator settings (flow, f, VT, PEEP) and impedance conditions (compliance, resistance). A synthetic mucoid analog was prepared using Polyethylene oxide 25322-68-3 (Dow Chemical, Midland, MI) and injected into a narrowed segment of the circuitry at end inspiration. The distance and direction of "mucus" movement was tracked from 30 sec to 5 minutes post injection.

Results:
Mucus movement (T-distance for towards lungs, E-distance for expelled from lungs) was measured under 99 conditions. For the same tidal volume, greater inspiratory flowrates (10,20,40 L/min) drove mucus towards the lungs from the point of injection (2, 5, 11 mm, respectively). The effect of decreased compliance (left table) was to expel mucus away from the lungs as expiratory flow increased. When generated by increasing frequency, autoPEEP (aPEEP) tended to defend the lungs from advancing mucus (right table).

Compliance Expiratory Flow E-Distance
.15 -15 0
.12 -17 0
.09 -19 0
.06 -22 0
.03 -30 3.3
.01 -60 6.3


f aPEEP T-Distance
10 8 3.1
14 9 1.9
19 10 1.9
25 11 1.5
29 12 1.2

Conclusions: In this model, we demonstrated interaction between ventilator/impedance settings and mucus movement. Mucus tended to be expelled by low compliance and autoPEEP while elevating inspiratory flow settings drove mucus toward the lungs. Generally, the direction and magnitude of airflow affected mucus movement.

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