In a few words 11: Bronchodilators and left heart failure
Acute left ventricular failure (LVF) involves increased capillary hydrostatic pressure encouraging a net fluid shift from circulation to interstitium. Colloidal oncotic pressure and lymphatic drainage cannot draw this fluid away sufficiently. Interstitial oedema results. Frequently airway narrowing leads to wheezing from oedema or acute bronchospasm. Bronchospasm is normally treated with bronchodilators since these smallest airways contain no cartilage and can collapse.
Bronchodilators typically increase heart rate and hence the work of the heart. In turn this can worsen ischaemia and the LVF. Worse, increased heart rate means blood is passing the alveoli faster. With alveoli ventilation decreased, gas exchange is further reduced. A ventilation perfusion mismatch results with blood passing through the lungs without being sufficiently oxygenated. In this case ventilation should be improved before pulmonary circulation is increased.
In LVF, fluid can enter the alveoli and wash out surfactant. Alveoli then collapse at end expiration and take more effort to reopen. CPAP helps hold them open reducing work of breathing. Administering bronchodilators to treat wheezing in LVF allows air in the alveoli to flow and escape more freely. This may actually aid alveoli collapse, decrease pressure in the alveoli and fluid shifting into the alveoli. Administering bronchodilators before ventilation is improved may be unhelpful in LVF. CPAP is a better option for ventilation in severe LVF even where there is wheezing.
Jeff Kenneally – www.Prehemt.com