# Reduction of Pre/Afterload in CHF using C/BiPAP



## 8jimi8 (Mar 21, 2010)

*Use of CPAP and BiPAP in Acute Respiratory Failure* - Scott Rappard

"There is still controversy on how and why CPAP works in CHF. There is no dispute that it reduces the work of breathing by improving atelectasis and V/Q ratios. Some studies have suggested it also improves preload and afterload and that there is actually an improvement in cardiac index. Of even more interest, studies out of Toronto by Bradley suggest that up to 50% of patients with CHF have sleep apnea. In these patients, the use of CPAP not only improves sleep, but leads to an improvement in ejection fraction that lasts into the daytime hours when they are awake. It is postulated that CPAP reduces preload and also afterload. It is possible that obstructive sleep apneas can put a severe strain on the heart by markedly increasing afterload and leading to hypertension."

Thanks to Nancy Morrison, consulting Respirologist at the QE II Health Sciences Center, Halifax, N.S., for reviewing the draft copy of this article.
References:
1. Kramer N. et al, Randomized, prospective trial of noninvasive positive pressure ventilation in acute respiratory failure, Am.J.Respir.Crit.Care Med, Vol 151, 1995, 1799-1806
2. Poponick Janet et al, Use of a Ventilatory Support System (BIPAP) for Acute Respiratory Failure in the Emergency Department, Chest, Vol 116, 1999, 166-171
3. Brochard L et al, Noninvasive Ventilation for Acute Exacerbations of COPD, NEJM, 1995, 333:817-822.
4. Antonelli et al, A Comparison of Noninvasive Positive-Pressure Ventilation and Conventional Mechanical Ventilation in Patients with Acute Respiratory Failure, NEJM 1998; 339, 429-35
5. Bersten AD et al, Treatment of severe cardiogenic pulmonary edema with
continuous positive airway pressure delivered by face mask. NEJM, 1991; 325:1825-30
6. Lin M et al, Reappraisal of CPAP therapy in acute pulmonary edema: short-term results and long-term follow up. Chest 1995; 107; 1379-86.
7. Mehta S.. et al Randomized, prospective trial of bilevel versus continuous positive airway pressure in acute pulmonary edema Crit Care Med 1997; 25: 620-628.
8. Hillberg et al, Noninvasive Ventilation, NEJM 1997; 337: 1746-1752
9. Atlantic Thoracic Conference in October in Halifax NS 1999
www.theberries.ca/archives/cpap.html


Can anyone chime in with some details about how these reductions in preload and afterload occur?


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## boingo (Mar 21, 2010)

Increase intrathorasic pressure = decrease venous return.


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## 8jimi8 (Mar 21, 2010)

but how does this reduce afterload?


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