How does NIV help with CHF?

There have been a few physicians who have explained to me that noninvasive ventilation helps patients with congestive heart failure (CHF), or pulmonary edema, because it forces fluid out of the lungs.  But this is a myth.

The true value of NIV for CHF is best described by Jeffrey Sankoff, MD, from Emergency Physicians: 

Contrary to popular belief, NIMV does NOT push edema fluid out of the lungs. Patients with acute CHF have an imbalance in the CO (cardiac output) of the right and left sides of the heart. With the inciting event (detailed above) the left ventricle becomes compromised but the right ventricle usually does not. So the right ventricle continues to pump forward a normal volume of blood but the left ventricle becomes unable to keep pace. Fluid backs up into the lungs resulting in capillary leak and pulmonary edema. With NIMV, the resultant positive intra-thoracic pressure decreases venous return (blood flowing back to the heart). This reduces right-sided CO to a level that the left heart can equal or even exceed. Fluid ceases to back up and will even begin to be reabsorbed as left ventricular CO improves. Pulmonary edema ceases to worsen and may even diminish, often rapidly.

I think it's essential to understand this, because I have also had physicians place patients on NIV with the hope that it would help with their breathing, but also that it might improve their blood pressure.  The truth is, however, the low blood pressure is a contraindication for NIV, and now you know why.