CPAP Continuous Positive Airway Pressure

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CPAP(Continuous Positive Airway Pressure)

• and its use in
• Cardiogenic Pulmonary Edema

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Case Study

• Call to residence _at_ 2146
• 76 y/o male, SOB
• On arrival
• Pt. seated upright in living room
• Conscious, obvious resp. distress, agitated
• Pale, diaphoretic, clammy, audibly congested
• Assessment/Questions/Initial Tx ?

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Case Study (contd)

• Incident Hx at rest, abrupt onset, now worse
• PMHx MI, CHF/Pulm. Edema, HPT, AAA repair, Renal
  Tumor, Rx
• Presentation sitting upright, tachypneic, 1-2
  word dyspnea, ?A/E bil. with coarse crackles
  throughout, now RSCP

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Case Study (contd)

• Vitals P 60, Irr, R 36-40, B/P 200/94, SpO2 76
  RA, Skin-Pale/Dia. /Cool
• Monitor Sinus with PVCs, 12-lead neg.
• Any other questions/info reqd?
• Tx?

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Case Study (contd)

• O2 - Device, FiO2?
• Position? Why?
• Rx Drug(s) of choice/availability/benefit
• Directive
• Goals of Tx?

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Case Study (contd)

• Current options to improve oxygenation/ventilation
  ?
• NRB mask - benefits/limitations
• BVM - benefits/limitations
• ETT - benefits/limitations
• Other options?

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Definitions

• CHF - inability of heart to maintain forward
  circulation of blood.
• Most severe manifestation pulmonary edema
• Pulmonary Edema - extravasation of fluid from
  pulmonary vasculature to interstitium/alveoli of
  lungs

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Pathophysiological Mechanisms

• Imbalance of Starling forces
• Damage to Alveolar/Capillary barrier
• Lymphatic obstruction/dysfunction
• Idiopathic

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Cardiogenic Pulmonary Edema

• Normal fluid shift/removal
• Opposing forces of plasma oncotic pressure and
  pulmonary capillary hydrostatic pressure
• Lymphatics remove excess
• Abnormal
• Volume in pulmonary veins/left atrial venous
  return exceeds left ventricular output
• ?pulmonary venous pressure
• ?capillary hydrostatic pressure

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Pulmonary Edema (contd)

• Pulmonary capillary pressure exceeds plasma
  colloidal osmotic pressure
• (Norm. PCWP 8-12 mmHg, Normal Colloidal Osmotic
  Pressure 25-28 mmHg)
• Fluid shifts to interstitium
• Lymphatic removal does not increase in proportion
  to fluid accumulation

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Pulmonary Edema (contd)

• Stages
• ?Lt. atrial pressure opens/distends small
  pulmonary vessels
• Fluid/colloids shift to interstitium
• Continual filtration overwhelms lymphatics
• Fluid accumulates/surround alveoli/bronchioles
  (compromises small airways first)
• Increases space between capillaries/alveoli
• Disrupts alveolar membrane-floods alveoli

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Pulmonary Edema (contd)

• Effects
• Decreases vital capacity
• Causes abnormalities in gas exchange
• Decreases respiratory volume
• Leads to hypoxemia

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Pulmonary Edema (contd)

• Vicious cycle ensues
• ?CO stimulates sympathetic activity
• Renin-Angiotensin-Aldosterone system
• Catecholamine production
• ? PVR
• ? MVO2
• exacerbates myocardial ischemia
• ? LV filling/emptying/function
• Further ? pulmonary capillary hydrostatic
  pressure
• More fluid shift

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Pulmonary Edema (contd)

• Cardiac causes
• CAD
• Loss of LV muscle/function
• Valvular heart disease
• Decreased diastolic ventricular compliance
• Congenital heart disease
• Myocarditis
• Infectious endocarditis
• ? B/P

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Pulmonary Edema (contd)

• Precipitated by
• Ischemia
• Dysrhythmia
• Cardiac/extra cardiac infection
• P.E.
• Physical/environmental stress
• Non-compliance/changes to Rx
• Dietary changes
• Iatrogenic volume overload
• Pregnancy
• Hyperthyroidism

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Differentials

• ARDS
• Anaphylaxis
• Acute anemia
• Bronchitis
• COPD
• Myopathies
• Pneumonia
• Pneumo
• Shock (septic)
• P.E.

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Treatment

• ABCs
• Improve oxygenation/ventilation
• O2 to keep SpO2 gt 90
• Assist ventilations or provide non-invasive
  positive pressure ventilation
• 3 Goals
• ? Preload
• ? Afterload
• Inotropic support

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Treatment (contd)

• Preload reduction
• ?s pulmonary capillary hydrostatic pressure
• ?s rate of fluid shift
• Afterload reduction
• ?s CO
• ?s Renal perfusion
• Inotropic support
• For those that wont tolerate preload/afterload
  reduction 2º to hypotension

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Nitroglycerin

• Vasodilator
• Used with normotensive/hypertensive patients
• Most effective, predictable and rapid-acting Rx
  available for preload reduction
• Often occurs within 5 min.
• Usually with some afterload reduction as well

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Nitroglycerine (contd)

• ?s MVO2 by ?ng workload
• ?s coronary blood flow
• ?s forward blood flow
• ?s pulmonary hydrostatic pressure/pulmonary
  congestion
• SL spray
• Onset 1-3 min.
• Half-life 5 min.

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Furosemide (Peterborough Region Only)

• Long-standing mainstay of therapy
• Thought to have two physiological effects
• Immediate venodilation
• Diuretic affect
• May in fact be more harmful than beneficial
• Move away from use in many prehospital services

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Morphine (Peterborough Region Only)

• Third drug in classic treatment
• Again, thought to have two major benefits
• Preload/Afterload reduction through vasodilation
• Anxiolytic/Analgesic effects
• No sound evidence supports morphine-mediated
  preload reduction
• Recent studies show morphine use an independent
  predictor of mortality
• Use has declined both in-hospital and prehospital

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Non-invasive Ventilation

• Delivery of ventilatory support without need of
  invasive artificial airway
• Will often eliminate the need for
  intubation/tracheostomy
• Benefits
• Easier to wean off ventilator
• Preserves normal cough/swallowing/speech
  mechanisms

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NPPV (contd)

• Two methods
• BiPAP (Bilevel Positive Airway Pressure)
• CPAP (Continuous Positive Airway Pressure)

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CPAP

• Delivered by nasal or face mask
• Pt. breathes through mask against a continuous
  positive a/w pressure
• Can be delivered by either volume or pressure
  controlled ventilator
• Delivers set pressure with each breath,
  maintained throughout the respiratory cycle

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CPAP (contd)

• Mechanism
• Increases gas exchange 2º to increased alveolar
  ventilation
• Prevents alveolar collapse during exhalation by
  maintaining a positive intra-alveolar pressure
• ?s intrathoracic pressure, reducing
  preload/afterload and improving cardiac output

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CPAP (contd)

• Benefits
• Reduces need for intubation
• Pt. saves energy otherwise spent trying to reopen
  collapsed alveoli
• ? WOB improves alveolar ventilation while
  simultaneously resting respiratory muscles
• ?s metabolic rate/substrate need to fuel
  respiratory effort

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CPAP (contd)

• Advantages
• Avoidance of intubation-related trauma
• Decreased incidence of nosocomial pneumonia
• Enhances pt. comfort
• Shorter duration of ventilator use/facilitates
  weaning
• Decreased hospital stay
• Decreased costs

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CPAP (contd)

• Usage
• Currently utilized primarily in-hospital setting
  and by critical care EMS systems
• Also used in-home
• Wide-scale EMS use previously limited by
  cost/complexity of technology
• Newer technology and sig. reduced costs lend to
  increased use pre-hospital
• Numerous systems incorporating CPAP as standard
  for pulmonary edema therapy