Therapeutic considerations

Restoring the balance between energy supply and demand

If fatigue results from the imbalance between energy supply and demand, the objectives of therapy must be to restore this balance. Energy supplies can be increased by treating hypoxemia and improving cardiac output, and the demands for energy can be decreased by treating bronchospasm or pulmonary edema. If the usual methods of restoring the balance between energy supply and demand fail, and clinical manifestations of inspiratory muscle fatigue persist, serious consideration must be given to resting the muscles by the use of artificial ventilation. Just how much rest is required is not known. Obviously, total rest is not required in normal subjects. If it were, recovery from experimental fatigue would not be possible. However, a body respirator that allows the diaphragm to rest may be useful for some patients. If these patients are in a chronic state of fatigue during quiet breathing, complete rest may restore their respiratory muscle function.

Recently, there has been a resurgence of interest in the delivery of positive-pressure ventilation with face or nasal masks to patients with COPD during acute respiratory failure. Compared with conventional treatment in patients who have an acute exacerbation of COPD, non-invasive ventilation may reduce the need for endotracheal intubation and decrease mortality (Biochard.. etal 1990). Furthermore, once these patients with severe airflow obstruction are intubated, ventilator dependence may be a serious problem. The latter could be due, at least in part, to respiratory muscle atrophy, as suggested by recent experimental evidence ( Le... Bourdelles et al 1994).

Chapter References

Aubier, M., et a/. (1982). Respiratory muscle contribution to lactic acidosis in low cardiac output. American Review of Respiratory Disease, 121, 648-52.

Brochard, L., Isabey, D., Piquet, J., Artigas, A., and Lemaire, F. (1990). Reversal of acute exacerbations of chronic obstructive lung disease by inspiratory assistance with a face mask. New England Journal of Medicine, 323, 1523-30.

Le Bourdelles, G., Viires, N., Boczkowski, J., Seta, N., Pavlovic, D., and Aubier, M. (1994). Effects of mechanical ventilation on diaphragmatic contractile properties in rats. American Journal of Respiratory Critical Care Medicine, 149, 1539-44.

Murciano, D., et al. (1988). Tracheal occlusion pressure: a simple index to monitor respiratory muscle fatigue during acute respiratory failure in COPD patients. Annals of Internal Medicine, 108, 800-5.

Viires, N., et al. (1983). Regional blood flow distribution in dog during induced hypotension and low cardiac output, spontaneous breathing, VS arterial ventilation. Journal of Clinical Investigation, 72,

935-47.

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