Continuous Positive Airway Pressure CPAP

Objectives Define CPAP Understand pathophysiology EMS applications Protocol implementation

What is CPAP??? CPAP increases pressure in the lungs and holds open collapsed alveoli, pushes more oxygen across the alveolar membrane, and forces interstitial fluid back into the pulmonary vasculature. This improves oxygenation, ventilation and ease of breathing. The increased intrathoracic pressure decreases venous return to the heart and reduces the overwhelming preload (pressure in the ventricles at the end of diastole). This lowers the pressure that the heart must pump against (afterload), both of which improve left ventricular function.

So why does oxygen pass into the blood? Pressure Gradient Deoxygenated blood has a lower partial pressure of oxygen than alveolar air so oxygen transfers from the air into the blood. The blood supply arriving at the alveoli carries deoxygenated blood. This means that the oxygen has been used as the blood has been circulated round the body. Oxygen passes from the alveolar air into the blood because the partial pressure of oxygen in the alveolar air is higher than that in the blood arriving at the lungs It also applies the other way too! Blood arriving at the lungs has a higher partial pressure of carbon dioxide than the alveolar air, hence CO2 leaves the blood and is expired.

CPAP alters the pressure gradient! 7.5cm H20 CPAP 1cm H2O is equal to 0.735mm Hg. 7.5cm H2O CPAP increases the partial pressure of the alveolar air by approximately 1%. This increase in partial pressure ‘forces’ more oxygen into the blood. Even this comparatively small change is enough to make a clinical difference. 1 cm H2O is equal to 0.735 mm Hg. A 7.5cm H2O C.P.A.P. valve increases atmospheric pressure at sea level by 5.51mm Hg, and this in turn increases the partial pressure of the alveolar air by approximately 1%. This increase in partial pressure ‘forces’ more oxygen into the blood. Even this comparatively small change is enough to make a clinical difference.

Perfusion Refers to the process of circulating blood through the pulmonary capillary bed In order for perfusion to occur, the following must be intact: A properly functioning heart (pump) Proper vascular “size” Adequate blood volume / hemoglobin

The Requirements Of CPAP The real requirement is for Continuous CONSTANT Positive Airway Pressure A stable airway pressure as prescribed in order to reduce work of breathing (WOB) THE REQUIREMENTS OF CPAP The real requirement is for Continuous CONSTANT Positive Airway Pressure with minimal fluctuations in system pressure between inspiration and expiration. This CONSTANT pressure will help reduce the patient Work of Breathing, which is important since it reduces the resistance to airflow that is present in lung disease.(Gherini 1979) Some systems meet the basic criteria for CPAP, that is to say the system pressure remains positive (higher than atmospheric pressure). However, due to marked swings in the level of pressure throughout the breathing cycle, and particularly at peak inspiratory flows, the effectiveness of these systems should be closely examined, since they can actually increase the work of breathing. (WOB)

CPAP is oxygen therapy in its most efficient form. Simple Masks Venturi Masks Humidifiers CPAP CPAP IS OXYGEN THERAPY IN ITS MOST EFFICIENT FORM Medium concentration oxygen mask: Unable to deliver an accurate oxygen % since the patient inspiratory flow is not taken into account. Venturi mask: Deliver accurate concentrations at 24%, 28%, 35%, 40%, 60%; however, the higher the % the greater the necessity to humidify especially long term use. Humidified Oxygen: Able to deliver up to 60% O2, but only accurate up to a Peak Inspiratory Flow Rate (PIFR) of 22 Lpm above which the % is diluted according to the patient’s demand. CPAP: The only system capable of delivering up to 100% humidified oxygen at flow rates of up to 140 Lpm, thus satisfying all clinical requirements.

Important Aim Of CPAP Is To Increase Functional Residual Capacity (FRC) Volume of gas remaining in lungs at end-expiration CPAP distends alveoli preventing collapse on expiration Greater surface area improves gas exchange THE IMPORTANT AIM OF CPAP IS TO INCREASE FUNCTIONAL RESIDUAL CAPACITY (FRC) FRC is volume of air remaining in lungs at end-expiration. Lung diseases culminating in respiratory failure are commonly associated with a reduction in FRC. The beneficial effects of a distending pressure applied to the airways at end-expiration by PEEP or CPAP stem from the increase in FRC leading to improved gas exchange. CPAP distends alveoli preventing collapse. A greater alveolar surface area improves gas exchange. Greater saturations are possible without increasing SaO2. In a study in which CPAP was given to fit athletes, Gherini (1979) reported that, in all subjects, FRC increased proportionally with the level of CPAP administered. This was accompanied by a 45% reduction in the inspiratory work if breathing.

Physiological Effects Of CPAP Increases PSO2 Increases FRC Reduces work of breathing PHYSIOLOGICAL EFFECTS OF CPAP. Increases FRC Reduces Patient Work of Breathing Reduces V/Q Mismatch and Shunt The positive pressure increases the volume of air left in the lungs at the end of expiration. CPAP provides an increase in FRC (Gherini 1976). As a result of the increase in FRC additional areas of lung are recruited into the gas exchange process and allows an improvement in blood gas values. Since CPAP shifts the lung volume along the compliance curve it reduces the patient work of breathing. In addition, as more alveoli now participate in the gas exchange process the V/Q mismatch is corrected and the fraction of shunt is reduced.

Indications for Use Treatment of severe respiratory distress CHF/COPD/Asthma RR>25 bpm Retractions, accessory muscle use or fatigue SAO2 < 94% at any time Near drowning Pt must be able to maintain own airway and be able to follow commands.

Exclusion Criteria BP <90 mmHg Unconscious Inadequate respiratory rate Cardiac arrest Unable to obtain adequate seal Pnuemothorax Active emesis

CPAP And Pulmonary Edema Severe pulmonary edema is a frequent cause of respiratory failure CPAP increases functional residual capacity CPAP increases transpulmonary pressure CPAP improves lung compliance CPAP improves arterial blood oxygenation CPAP redistributes extravascular lung water (Rasanen 1985) CPAP AND PULMONARY odema. Severe pulmonary odema is a frequent cause of respiratory failure. CPAP increases FRC. CPAP increases transpulmonary pressure. CPAP improves lung compliance. 10 cm CPAP improves arterial blood oxygenation. CPAP redistributes extravascular lung water.

Redistribution Of Extravascular Lung Water With CPAP REDISTRIBUTION OF EXTRAVASCULAR LUNG WATER WITH PEEP. The application of PEEP to the edematous lung decreases intra-alveolar fluid volume, increases interstitial lung water, and facilitates the movement of water from the less compliant interstitial spaces where gas exchange occurs to the more compliant interstitial spaces. This redistribution of interstitial water improves oxygenation, lung compliance, and ventilation/perfusion matching when applied in either cardiogenic or non-cardiogenic pulmonary odema.

Benefits/Advantages of CPAP CPAP reduces work of breathing by keeping the “wet” alveoli open If the alveoli are open at the end of expiration, energy is not consumed on the next inhalation Work of breathing is reduced relieving respiratory muscle fatigue

Benefits/Advantages of CPAP A higher alveoli pressure will result in a stoppage of fluid movement into the alveoli Increase in airway pressure results in improved gas exchange

CPAP And Acute Respiratory Failure CPAP overcomes inspiratory work imposed by auto-peep CPAP prevents airway collapse during exhalation CPAP improves arterial blood gas values CPAP may avoid intubation and mechanical ventilation (Miro 1993) CPAP AND ACUTE RESPIRATORY FAILURE. CPAP overcomes inspiratory work imposed by auto-PEEP. CPAP prevents airway collapse during exhalation and has the effect of ‘splinting the airways’ CPAP improves arterial blood gas values. CPAP may avoid intubation and mechanical ventilation. (Miro 1993)

What about the Emphysema Patient?

Important Point Emphysema patients do not respond predictably to CPAP

As a general rule… The larger the “barrel chest” and the more pronounced the accessory muscles, the more caution we should use with CPAP

What is needed for CPAP application. Oxygen source capable of producing 50 psi. Flow regulator which delivers either a fixed oxygen concentration at 30% or an adjustable flow regulator. Venturi Micro channels 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. What are some signs and symptoms of respiratory distress??

What is needed for CPAP application. Oxygen source capable of producing 50 psi. Flow regulator which delivers either a fixed oxygen concentration at 30% or an adjustable flow regulator. Venturi Micro channels 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. What are some signs and symptoms of respiratory distress??

CPAP Contraindications CPAP may be contraindicated for patients with any of these conditions: Unconscious Apnea Pneumothorax Decreased cardiac output and gastric distention Severe facial injury Hypotension secondary to hypovolemia Uncontrolled vomiting

Explain the Procedure to your Patient Explain to your patient that in order to get the best possible results from a CPAP device. Ask them to inhale through the nose and exhale through the mouth against the pressure produced by the CPAP machine. If they do not know what to expect, it is similar to the air felt when sticking your head out of the car window when moving.

The Whisperflow Here is a step by step review of the operation of the Whisperflow CPAP device.      Properly assess pt for baseline Pulse Oximetry     Attach high pressure hose to portable tank using short adapter hose. It may be best to load the patient first and start CPAP early in the transport: conserves portable tank for ER transfer.    Assemble mask and tubing, don't forget to place the filter on air intake of the CPAP device   

The Whisperflow Prepare mask, strap rearrangement might be necessary Explain the procedure to the patient. Turn the unit on (all the way) & turn the FLOW on (all the way) Prepare mask,  strap rearrangement might be necessary Have the patient place the mask on his/her face tightly. Some "coaching" will help the patient transition from holding the mask near their face to creating a seal.  It's OK for the patient to hold the mask without using the straps if they're more comfortable that way. When he is comfortable with the feeling of the mask  you may secure it to his head tightly so that no leaks are noticed.

Final Application Steps After loading the patient to the unit  you'll need to transfer to the onboard oxygen. Do it quickly - turn on the main first! Next you'll need to fine-tune the unit by decreasing the FLOW until a slight outward flow is felt while the patient inhales. You can easily add nebulized albuterol to the patient's treatment by cutting the tubing at a joint  and inserting a 'T' and nebulizer with 6 liters oxygen attached. By using the patient's pulse-ox level as a guide you may adjust the amount of oxygen up to achieve desired oxygen saturation, usually 90 -93%.

If the mask is not tolerated after coaching…remove it!!!

A few things to remember... When the flow valve is open all the way, with the oxygen valve closed,  you are giving the patient 28% oxygen and a portable tank will last quite some time! By increasing the oxygen flow, you'll use more liters per minute - as much as 140! Be careful, you'll run out! 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!

At 28-30% FiO2 , a full tank should last approximately: Oxygen Tanks At 28-30% FiO2 , a full tank should last approximately: D cylinder=28 minutes E cylinder=40-50 minutes M cylinder=about 4 hours FiO2 is fraction of inspired oxygen. (at 100% FiO2 a D cylinder tank will last approximately 3-4 minutes. Use what you need, but be prepared with additional cylinders)

Case Study for CPAP 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. http://www.eresp.com/CPAPosSim.swf

Works Cited and Thank You Thank you to EMS Personnel at Dallas Ambulance, ST Paul Fire, Salem Fire, Rural Metro, Washington Co EMS, MTCI, Albany Fire, Marion County, and Mercy Flights for sharing information regarding CPAP. The following websites were also use as resources. http://www.dhfs.state.wi.us/ems/EMSsection/Protocols/CPAP/CPAP_Protocol.pdf http://www.ems1.com/columnists/dan-white/articles/390898-A-Look-at-CPAP-for-EMS http://caradyne.respironics.com/whisperflow.htm http://phillydan.spaces.live.com/Blog/cns!B2AD15EED4F62B2B!236.entry http://elearning.respironics.com/main_ProdTrainCourse_pr.asp http://www.jcems.net/cgi-bin/news.cgi  http://www.eresp.com/CPAPosSim.swf http://www.miamitwp.org/fireems/training/skill_sheet_ems.htm  http://www.emsresponder.com/features/article.jsp?id=1738&siteSection=16 http://www.maconnc.org/ems/CPAP.html http://www.merginet.com/index.cfm?pg=airway&fn=CPAPuser http://emsstaff.buncombecounty.org/inhousetraining/cpap/cpap_overview2.htm http://www.doctorfowler.com/lecturepage.shtml

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