CPAP Use and Operation

We now have Continuous Positive Airway Pressure (CPAP) devices on each ambulance. Please take the time to familiarize yourself with the use of this very important piece of equipment.

What is CPAP?
CPAP stands for Continuous Positive Airway Pressure. The basic principle of CPAP is to apply a tight fitting mask to the patient controlled by a regulator designed to provide a high flow of variable or fixed oxygen concentration. The most important feature to CPAP is a flow restriction device at the exhalation port of the mask, which works the same way as Positive End Expiratory Pressure (PEEP). By placing the patient’s airways under a constant level of pressure throughout the respiratory cycle, fluid and other obstructions will hopefully be "pushed" back where they belong.

What is needed for CPAP?

• Oxygen source capable of producing 50 psi
• Flow regulator which delivers either a fixed oxygen concentration at 30%. The flow generator works by what is known as the venturi effect. When you attach it to the primary regulator of the oxygen cylinder and deliver 50 psi through it, the device "sucks" in room air which is used to dilute the 100% oxygen from the cylinder.
• Tight fitting mask to which the oxygen/air mixture output of the generator is attached and applied to the patient.
• Positive End-Expiratory Pressure (PEEP) valve connected to the exhalation port which maintains a constant pressure in the circuit. Each PEEP valve is rated at a certain level measured in centimeters of water (cmH2O) usually in increments of 2.5. The most commonly used levels are 5 or 7.5. 5.0cmH2O is what we will be utilizing per Dr. Davis.

What are the indications for the use of CPAP?
CPAP is indicated for the treatment of severe respiratory distress, refractory to initial treatments of high-flow O2 , without increase in O2 saturation, and/or decrease in breathing workload, seen in chronic obstructive pulmonary disease (COPD), congestive heart failure (CHF) and to a lesser degree in asthma.

How does CPAP work for these conditions?
In order to better understand how CPAP works, here is a brief review of the conditions that would warrant use of CPAP:

In COPD, the lung has lost its normal elastic recoil and the alveoli and terminal bronchioles have become stiff with scar tissue. During a COPD exacerbation these terminal bronchioles collapse during exhalation leading to air trapping in the alveoli. This is why the COPD patient breathes through pursed lips (increasing PEEP) and uses active muscle contraction to exhale (aka accessory muscle usage). By doing so, they are keeping the pressure in the terminal bronchioles elevated to prevent their collapse.

In CHF, the lymphatic system can remove an estimated 10-20 mL of fluid per hour in the normal, healthy lung. Under stress, the lymphatic system can remove additional fluid through increased flow. When this capability is exceeded, fluid initially accumulates in the interstitial spaces, resulting in interstitial edema. When the volume exceeds the capacity of the interstitium, the tight junctions of the alveolar epithelium are damaged, and the fluid floods into the alveolar air spaces.

In asthma there is bronchospasm and the work of breathing is increased as the patient strives to move air in and out of the lungs.

The common factor to all three of these conditions is the increased work of breathing and the inability to effectively remove carbon dioxide from the system. As COPD, CHF, and asthma worsens, the patient’s minute ventilation (size of each breath multiplied by the breaths per minute) goes down. Less air movement results in carbon dioxide levels rising which causes a narcotic like effect on the brain further diminishing ventilatory rate. The combined effects of fatigue and rising carbon dioxide in the system leads to further lowering of the ventilatory rate and the patient suffers a respiratory arrest.

How does CPAP work?????
CPAP splints the alveoli open, thereby preventing alveolar collapse and allowing unimpeded alveolar ventilation. CPAP also decreases preload and afterload, improves lung compliance, increases functional residual capacity, and decreases work of breathing.

So why CPAP and not Endotracheal Intubation?
First and foremost, we all know that patients who are in need of complete airway control, need to be intubated. However, we also know that most patients, for whom respiratory failure/arrest is imminent, may be intubated and not come off mechanical ventilation for several days to weeks. This is not very beneficial for the patient in the long run. Mortality rises the longer a patient has to depend on mechanical ventilation and the ability to wean these patients decreases dramatically. Patient’s, again, who need complete control of the airway would not benefit from CPAP.

One major benefit to CPAP is that it provides much needed ventilatory splinting and support while you are able to administer medications specific for the proper treatment of the patient. In other words, if you are treating an asthma or COPD patient, you can concurrently administer bronchodilators to assist the CPAP, as well as in CHF/Pulmonary edema patients, you can concurrently administer lasix, NTG and morphine, to help aid in decrease of preload and afterload. In essence, CPAP takes the patient who is close to needing intubation and rapidly reverses their condition. Studies have proven that CPAP dramatically reduces the need for intubation which is associated with significant complications and death in these patients.

Important information about CPAP
Additionally, because of increased intra-thoracic pressure and cardiovascular effects of CPAP, a patient's blood pressure could drop, making it necessary to monitor their blood pressure carefully and provide focused treatment to keep it above 90 mmHg. Some contraindications that you need to remember in using CPAP:

• Patient less than eight years of age
• Unable to maintain a patent airway
• Decreased level of consciousness (LOC)
• Pneumothorax
• Facial trauma/burns
• Systolic BP < 90 mmHg
• Recent surgery to face or mouth
• Epistaxis
• Patient unable to tolerate mask or pressure

Steps to administration of CPAP
This is a review of the use of CPAP. If you have any questions, please contact me.

Respiratory emergencies are one of our more frequent calls. You are called to a 76-year old male who is complaining of dyspnea. Upon arrival, you find the patient sitting on a chair leaning forward. He is diaphoretic, cyanotic and has a respiratory rate of 48. Upon auscultation you hear fine crackles throughout both lung fields and he is hypertensive.

Protocols support the use of high-flow oxygen therapy and appropriate medications. Having done this you observe no immediate change in his respiratory distress and his SpO2 is only 78%. Although many patients respond rapidly to standard treatment, a significant number of patients do not. You are often faced with making a decision regarding what is best for the patient: intubate or try a non-invasive therapy. What do you do?

A few things to remember...
If you reach the point that air is blowing out of the air intake on the device your oxygen flow is too high.

When swapping from portable to main oxygen tanks warn the patient that the flow will stop for a few seconds but they will still be able to breathe, then swap quickly!

Vitals need to be recorded every 5 minutes!!

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