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Continuous Positive Airway Pressure (CPAP)

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1 Continuous Positive Airway Pressure (CPAP)
Gold Cross Ambulance Continuous Positive Airway Pressure (CPAP) Airway Endorsement for EMT-Basic Sheridan Memorial Hospital Ruth Wyckoff, M.D. 21 January 2012 CPAP: Continuous Positive Airway Pressure The term ‘continuous positive airway pressure’ was coined in 1971 by Gregory et al to describe an elevated airway pressure therapy for spontaneously breathing, intubated neonates. Current application has expanded to include adults and more recently patients without an artificial airway. ‘The application of positive airway pressure throughout the whole respiratory cycle to spontaneously breathing patients’ (Keilty et al. 1992).

2 Outline Definition Goals Physiological effects Delivery systems
Applications Contraindications Complications CPAP Physiological Effects: History of CPAP. Effects on Lung Inflation (FRC) Ventilation and Perfusion Lung Compliance - Work of Breathing (WOB) CPAP Delivery Systems Flow Generator and CPAP Valve Low Flow Systems Isobaric Valves WhisperFlow Generator Competition Vital Signs VF100 and Drager CF800 Clinical Applications Emergency Room ICU General Ward Contraindications to CPAP Medical Contraindications Complications arising from CPAP

3 Definition Pressurized method of noninvasive ventilation with or without mechanical assistance.

4 Goals Reduce pre-hospital intubations
Increase functional residual capacity (FRC) Provide a stable airway pressure Decrease work of breathing (WOB)

5 Lung and Aveoli

6 Functional Residual Capacity (FRC)
Definition: Volume of gas remaining in lungs after expiration CPAP prevents alveolar 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. 6


8 Partial Pressure The pressure of a gas mixture is equal to the sum of the partial pressures of its constituents. This allows oxygen into the blood during inspiration and CO2 out during expiration. Example : Air at sea level has a pressure of 1000cm H20. Air is 21% oxygen and 79% nitrogen and other gasses. partial pressure of oxygen is 1000 X 21% = 210cm H20 We breathe in (inspire) in order to transfer oxygen into our bloodstream and we breathe out (expire) to carry away carbon dioxide. This process works because of ‘Partial Pressure’ ‘The pressure of a gas mixture is equal to the sum of the partial pressures of its constituents.’ Example : Air at sea level has a pressure of 760mm Hg. Air is 21% oxygen and 79% nitrogen. Therefore the partial pressure of oxygen is 760 X 21%= 159mm Hg. Question. What is the partial pressure of Nitrogen at sea level? 8

9 So why does oxygen pass into the blood?
Pressure Gradient So why does oxygen pass 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. Deoxygenated blood has a lower partial pressure of oxygen than alveolar air so oxygen transfers from the air into the blood. 9

10 CPAP and Patient Airway Pressure
‘The application of positive airway pressure throughout the whole respiratory cycle to spontaneously breathing patients. PATIENT AIRWAY PRESSURES This slide illustrates simulated breath traces at atmospheric pressure (0cm H2O), and at 5cm H2O CPAP. Note that for inhalation of air to occur when breathing without assistance (0cm H2O), the generation of a pressure gradient is required: the pressure within the lungs is negative compared to that in the atmosphere, and consequently air is drawn into the lungs. Conversely, during exhalation, the passive elastic recoil of the ribcage elevates the intrathoracic pressure to above the atmospheric level and is therefore positive, consequently forcing air out of the lungs. The larger the drop in pressure on inhalation (i.e. the more negative it gets) the greater the patient work of breathing. When breathing with the aid of CPAP, the pressure within the lungs always remains positive. 10

11 7.5cm H20 CPAP Atmospheric pressure can be expressed as 1000cm H2O
7.5cm H2O CPAP increases the 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 as CPAP alters the pressure gradient 1 cm H2O is equal to 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. 11

12 ARDS 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) 12

13 X-ray ARDS 13

14 Reducing fluid in the lungs
CPAP decreases intra-alveolar fluid volume Facilitates movement of water Move from less to more compliant Improves oxygenation, compliance

15 Redistribution of extravascular pulmonary fluid
Redistribution of extravascular lung water with positive end-expiratory pressure. From alveolar epithelium and pulmonary capillary endothelium to peribronchial and hilar regions

16 Pneumonia 16

17 Congestive Heart Failure (CHF)
Definition: Interstitial fluid interferes with gas exchange = pulmonary edema Increased myocardial workload Higher O2 demands Over age of /1000 patient Average length of stay (LOS) = 6.7 days Those intubated extend LOS Intubated pts have 4x mortality

18 Pulmonary Edema

19 Radiographic evidence

20 COPD and Asthma Both with increased WOB Hypercapnia
Higher mortality with intubation Difficulity to wean once intubated

21 Acute Respiratory Distress Syndrome (ARDS)
Characteristics Hypoxemia Reduced compliance Large intrapulmonary shunt CPAP in early stages may Correct hypoxemia Improve compliance Reduce intrapulmonary shunt (Schmidt 1975) CPAP AND ADULT RESPIRATORY DISTRESS SYNDROME. ARDS Characteristics: Hypoxemia Reduced Compliance Large Intrapulmonary Shunt CPAP in early stages may: Correct Hypoxemia Improve Compliance Reduce Intrapulmonary Shunt (Shmidt 1975) 21

22 Essential Components Of A CPAP System
1. Flow generator 2. CPAP valve ESSENTIAL COMPONENTS OF A CPAP SYSTEM. 1. Flow Generator. 2. CPAP Valve. The flow generator should ideally be able to provide flows to exceed all possible PIFRs AND be able to do so at the required oxygen percentage. The resistor, either set at specific threshold levels or adjustable to required level, will provide a resistance to the flow through the circuit, allowing the pressure to elevate within the whole respiratory tract up to the prescribed level. The circuit pressure will be maintained at this threshold level only if the valve remains open. This is only achieved by ensuring flow constantly passes through the valve. Ideally the valve should be flow-independent and thus prevent large swings in the circuit pressure from the intended level. CPAP delivery is affected by the quality of these 2 components. The goal is to deliver CPAP without circuit pressure changes.

23 Whisperflow Flow Generators
The Whisperflow Variable Flow Generator.

24 Caradyne Isobaric CPAP Valve
The caradyne CPAP valve is a disposable valve with 22mm inlet and outlet connections. There are 7 different pressure ratings available: 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, and 20.0 cmH20.

25 Patient Connections - Face Mask
1. Sealing Face Mask 2. Nasal Mask 3. E.T. Tube 4. Tracheostomy Tube 5. Sealing Mouthpiece When choosing the mode of patient connection always ensure it is the most appropriate, and that if applicable the correct size is also chosen. For example, due to the necessity of a good seal when using a mask the correct sizing of the mask is particularly important. Many patients complain of the discomfort experienced with some inflatable full face masks. This can be for a number of reasons: It is painful on the bridge of the nose; air leaks to eyes; the straps block vision; etc. Poor patient compliance will inevitably result, which could have been avoided by careful consideration first of the patient and their condition. Many various sizes of “Rib Cushion” face mask are available from caradyne designed to suit individual patient needs and hence improve patient comfort.

26 The High Flow System In Operation
Air Supply In In order to maintain circuit pressure it is important to keep the CPAP valve open. Therefore there will always be some flow through the valve even during patient inspiration. This can be verified by examining the valve disc during inspiration or by placing a hand over the valve exhaust port to ensure that there is flow during both breath phases. Peak Flow rates will reduce after a short time on CPAP. The flow through the circuit should be adjusted after the patient stabilizes so that: 1. Oxygen wastage is minimised. 2. Noise generated is kept to a minimum. Total Flow 60 L/min

27 Application of CPAP

28 Application Continued


30 Clinical Applications of CPAP
Condition Area for Treatment ARDS Emergency CHF/Pulmonary edema Emergency Acute Respiratory Failure Emergency COPD/Asthma Emergency Anesthesia Pre Operative Atelectasis ICU/General Ward Alternative to Mechanical Ventilation ICU/General Ward Weaning from Mechanical Ventilation ICU/General Ward Sleep Apnea Home CPAP has been successfully shown to treat the medical conditions described above.

31 Contraindications Relative Absolute Claustrophobia Cardiac/resp arrest
Nasal Congestion Mouth breathing Absolute Cardiac/resp arrest Hypotension Need for emergent airway Pneumothorax Facial or neurological injuries, deformities Upper airway obstruction High risk of aspiration Unconscious CONTRA-INDICATIONS OF MASK CPAP. Hypercapnic patients may have a reversed respiratory drive, and rely on low levels of oxygen to trigger a breath rather than the much more sensitive trigger of CO2 active in normal subjects. A patient whose respiratory drive is now sensitive only to low levels of oxygen must not therefore be administered oxygen as this will knock out the respiratory drive and as a result lead to a reduction of the respiratory rate, with the consequent elevation of PaCO2. CPAP should not be used with patients with an undrained pheumothorax. An emphysematous bulla within the lungs presents a risk when any type of positive airway pressure is applied to the lungs. A bulla is a large area of the lungs that has broken down to form a hole. Bullae are very brittle and present a risk of bursting. Hypovolemia is a low blood volume. Administering CPAP may reduce both blood pressures and cardiac output. Although no true contra-indications have been identified in the literature, CPAP should not be administered to patients with unstable facial fractures, excessive facial lacerations, laryngeal trauma, or a recent tracheal or esophageal anastomosis. Patients at risk of vomiting (those with gastrointestinal bleeding or ileus) may also need to be excluded.

32 Common Complications With CPAP
Irritation to skin and eyes Nasal congestion Dry nose, epistaxis Sore throat Barotrauma Gastric distention Reduced cardiac output Hypoventilation COMMON COMPLICATIONS ASSOCIATED WITH CPAP. 1. Pressure Sores - Since the advent of soft, self-sealing masks, these complications are usually limited to nasal-bridge pain and erythema at the site of application. However these symptoms can be reduced by the prior application of materials such as “Granuflex”. Another less serious complication of the mask is patient discomfort or intolerance. 2. Gastric Distension - The most significant potential complication cited by early critics were aerophagia and aspiration of gastric contents. However, the levels of CPAP used (<10 cm H2O) are usually not associated with gastric distension. If this complication occurs, it is easily remedied by naso-gastric intubation, with regular aspiration. Gastric aspiration related to CPAP via face mask has never been reported in the literature. 3. Pulmonary Barotrauma - With mask CPAP, as with any positive-pressure therapy, the potential for distension and pulmonary barotrauma is always present. However, in investigations cited by Branson (1985) only one of 196 patients developed evidence of barotrauma (pneumomediastinum), representing a complication rate of 0.5%. The low incidence of barotrauma in these patients may be attributed to the use of spontaneous breathing as the method of ventilatory support. To further minimise this risk the status of the patient’s lung disease should be considered when prescribing CPAP. 4. Reduced Cardiac Output - Positive-pressure therapy has been associated with a decrease in cardiac output by Gong (1983). However, heamodynamic embarrassment in patients treated with the levels of CPAP described in that report was most often due to hypovolemia. In Branson’s report cardiovascular depression did not occur in patients with adequate volume status. 5. Hypoventilation - A potentially lethal complication of mask CPAP is hypoventilation, which may occur with excessive levels of CPAP. Overdistension of normal lung units can increase the ratio of dead space to tidal volume and result in CO2 retention. Hypoventilation may also occur in patients who become lethargic and weak. All patients receiving CPAP therapy should be closely monitored, and if CO2 retention is identified, intubation and mechanical ventilation should be instituted. 6. Fluid Retention - The application of CPAP causes a reduction in urine output secondary to reduced renal perfusion, redistribution of renal blood flow and increased antidiuretic hormone secretion. It is often necessary to modify fluid therapy or employ diuretics when applying positive airway pressure if fluid retention and odema are to be avoided. Alternatively, the depression of cardiovascular and renal function which may occur with CPAP may be treated successfully with inotropic agents.

33 CPAP Training Flow Sheet
No Exclusion Criteria Present -Respiratory/Cardiac Arrest Pt.unable to follow commands Unable tp maintain patent airway independently Major Trauma Suspicion of a Pneumothorax Vomiting or Active GI Bleed Obvious signs/Symptoms of Pulmonary infection 2 or more of the following Respiratory Distress Inclusion Criteria Retractions of accessory muscles Brochospasm or Rales on Exam Respiratory Rate > 25/min. O2 Sat. < 92% on high flow O2 Administer CPAP using Max FIO2 Stable or Improving Reassess Patient Deteriorating Continue CPAP Continue COPD/Asthma/Pulmonary Edema Protocol Contact Medical Control with a Report -Contact Medical Control with report Discontinue CPAP unless advised by Medical Control Continue Asthma/COPD/Pulmonary Edema Protocols ,

34 Supporting Literature
JAMA December 28, 2005 “Noninvasive Ventilation in Acute Cardiogenic Edema”, Massip et. al. Meta-analysis with good to excellent data 45% reduction in mortality 60% reduction in need to intubate Kosowsky JM, et al. EMS transports for difficulty breathing: is there potential role for CPAP in prehospital setting?. Acad Emerg Med Oct; 7(10) 1165. Strict criteria but demonstrated small number of pts benefit

35 Cont’d Literature Reviews in Cardiovascular Medicine, vol. 3 supl , “Role of Noninvasive Ventilation in the Management of Acutely Decompensated Heart Failure” “Though BLPAP has theoretical advantages over CPAP, there are questions regarding its safety in a setting of CHF. The Key to success in using NIV to treat severe CHF is proper patient selection, close patient monitoring, proper application of the technology, and objective therapeutic goals. When used appropriately, NIV can be a useful adjunct in the treatment of a subset of patients with acute CHF at risk for endotracheal intubation.”

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