Fluorocarbons facilitate lung recruitment

OBJECTIVE

"Open the lung and keep it open" is increasingly accepted as a fundamental principle for mechanical ventilation. However, it is sometimes very difficult, or impossible, to recruit the diseased lung. We questioned whether one could facilitate recruitment by using a low dose of fluorocarbon in a model previously shown to be non-recruitable by conventional sustained inflation maneuvers.

DESIGN AND SETTING

Experimental prospective study in a university laboratory.

ANIMALS AND INTERVENTIONS

Nine saline-lavaged rabbits subjected to prolonged large tidal volume mechanical ventilation to establish significant lung injury were randomly allocated to two groups: control [High Frequency Oscillation (HFO) alone: n=4] or 1 ml/kg fluorocarbon (FC) treated (HFO/FC: n=5) for 2+1 h (experiment 1). An additional four similarly prepared animals were treated by single-lung instillation of 0.5 ml/kg dose of fluorocarbon and underwent serial computerized tomography scans at a series of predetermined step-wise pressure increase in both lungs (experiment 2).

MEASUREMENTS AND RESULTS

In experiment 1 there was a very significant improvement in oxygenation in HFO/FC group (PaO(2) increased from 108 mmHg to 424+/-81 mmHg; P<0.05) while there was no significant change in the control group. In experiment 2 lung volumes were determined using three-dimensional reconstruction. The lung having fluorocarbon showed a 2.4-fold increase in lung volume at inflation pressure of 15 cmH(2)O compared to the lung without fluorocarbon.

CONCLUSIONS

We propose that the low equilibrium surface tension and positive spreading coefficient of fluorocarbon facilitates lung recruitment by ungluing adherent surfaces in this model of lung injury.

Cough capacity in patients with muscular dystrophy

Cough capacity was evaluated in 22 patients with muscular dystrophy (MD) using subjective cough assessment, cough flow-volume curves, maximum expiratory pressures (MEP), forced vital capacity (FVC), and peak expiratory flow rates (PEFR). In ten of the 22 patients transients of peak flow were generated during cough flow-volume maneuvers, indicating dynamic compression of the airways, which is considered important in the physiology of an efficient cough. Patients who could not generate peak flow transients had significantly reduced PEFR, FVC, and MEP values. Measurement of MEP was the most sensitive predictor of flow transient production during coughing; all of the patients who exhibited transients had MEP values of above 60 cmH2O, whereas the highest value of MEP recorded in patients without transients was 45 cmH2O. Three of the 12 patients who were unable to generate flow transients were considered to have an adequate cough by subjective assessment. We concluded that the measurement of MEP is extremely useful for assessment of cough strength in patients with MD.