Chrissy...
CPAP exerts a positive pressure in the chest (as the name implies but worth restating) and provides a beneficial hemodynamic effect by reducing preload and afterload.
The positive pressure exerted in the chest impinges on the vena cava causing blood return to the heart to be reduced. With reduced blood return comes reduced blood volume that the heart has to worry about pumping out. In other words reduced myocardial oxygen demand and relief for the already strained heart.
In CHF management, the immediate goal is to reduce pressure in the pulmonary vasculature to reduce the pressure gradient so that fluid can start to retreat back across the A-C membrane which decreases diffusion distance and improves gas exchange. This is why the priority is aggressive nitro dosing and CPAP and NOT lasix.
There is also a possibility of a negative hemodynamic effect. If your patient is already running a low B/P, the PEEP from CPAP may cause hypotension. In your CHF patient chances are the hormonal and sympathetic response is going to cause your patient's B/P to be elevated but not always so not a great concern but you definitely need to be aware of the hemodynamic effects involved with CPAP.
The mechanism in which CPAP works in Asthma and COPD is less understood and is debated. But it has been shown to reduce the work of breathing and is often effective when patients are refractory to traditional treatments.
Also, if you have it available... use a nasal cannula type EtCO2 filter line under the CPAP mask. It will not effect your mask seal.
Normally, your PEEP pressure is 5-10cmH20. Start at 5 and titrate up to 10. I usually do 5-7-10. As long as your at 10 or below your risks of adverse events are minimal. If your patient is not improving at 10cmH20 and deteriorating your patient is now a candidate for intubation more than likely.
CPAP prevents alveolar collapse by maintaining a constant pressure within them. A partially open airway is much easier to inflate than a closed one. Think of a balloon. When is it easier to inflate?? It's when you already have some air in it. Same concept. Also, with pulmonary edema the alveoli are prone to collapse. Surfactant washout can occur especially with near-drownings. Without surfactant our airways collapse (atelectasis). So CPAP helps mitigate this. This is where the decreased work of breathing comes into play. CPAP also recruits collapsed alveoli and makes them take part in gas exchange.
CPAP also causes increased surface area for gas exchange to occur. CPAP also usually makes bronchodilators more effective when administered inline with the CPAP.
If your not getting good PEEP make sure you have a good mask seal. If not, you will not achieve proper PEEP to be effective.
And very IMPORTANT. ACCLIMATE your patient to the CPAP. Don't just slap it on. Hold it on and coach the patient before securing. If need be, give a low dose benzo to reduce their anxiety. This step is VERY important.
Always remember that your patient has to be able to maintain their own airway. If the patient is or is becoming somnolent or head bobbing... its time to think intubation and bagging these patients.
Use your assessment and tools to gauge patient improvement. You should see SpO2 increase, EtCO2 decrease (could be decreasing cardiac output too in CHF), decreased work of breathing, reduced resp rate, and the patient will tell you if they are feeling better.
Don't be afraid to use CPAP. If unsure, use it. As a new medic I was intimidated by CPAP and quickly learned not to be scared of it. It is pretty harmless if a few basic principles are understood mainly related to the hemodynamic effects.
It sucks your service didn't feel the need to give proper education and training on the new skill of CPAP. Make Google your best friend and if you have any specific questions ask em here. CPAP is a life saver literally and prevents need for intubation. Once some of these patients go on the vent, they don't come off. It really turns em around.
I am exhausted and this all came out on auto-pilot so hopefully it makes sense to ya
