Pulmonary Critical Care ------------- The Approach to Acute Respiratory Failure

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Pulmonary Critical Care-------------The
Approach to Acute Respiratory Failure

• By John J. Beneck MSPA, PA-C

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Objectives

• Understand lung function as it applies to
  pathological processes including
• Air movement
• Diffusion
• Circulation
• Gas transport
• Understand Acute Respiratory Failure with regard
  to
• Clinical manifestations
• Etiology
• Presentation
• Diagnosis
• Treatment

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Objectives (Cont)

• Understand the role of PPV in the care of
  respiratory failure
• Introduce various mechanical ventilation
  modalities and weaning strategies
• Understand ARDS with regard to
• Definition
• Presentation
• Diagnosis / Differential Diagnosis
• Etiology
• Complications
• Treatment
• Prognosis

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Abbreviations

• ARDS-Acute respiratory distress syndrome
• BNP-B type naturetic peptide
• CBC-Complete blood count
• CK-MB-MB fraction of creatinine kinase
• CMP-Complete metabolic panel
• CMV-Continuous mechanical ventilation
• DVT-Deep vein thrombosis
• ED-Emergency department
• F/U-Follow up
• FiO2-Fraction of inspired oxygen
• GI-Gastrointestinal
• Hb-Hemoglobin
• Mg-Magnesium
• MI-Myocardial infarction
• mmHg-Millimeters of mercury

• NIF-Negative inspiratory force
• NPPV-Noninvasive positive pressure ventilation
• PAO2-Partial pressure of oxygen in the alveoli
• PaO2/CO2-Partial pressure of oxygen and CO2 in
  the arteries
• Patm-Atmospheric pressure
• PH2O-Partial pressure of water vapor
• PCWP-Pulmonary capillary wedge pressure
• PE-Pulmonary embolus
• PNA-Pneumonia
• PPV-Positive pressure ventilation
• R-diffusion coefficient of CO2
• SOB-Short of breath
• VTE-Venous thromboembolism

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Case 1

• 18 year old male in ED with history of anxiety
  and acute onset of dyspnea and SOB. P 94, R 28,
  BP 132/78, T 37.0, SaO2 99 on room air.

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Case 2

• You are called for a 58 year old female admitted
  2 days prior with sepsis. Now with severe SOB. P
  110, R36, BP 105/66, T37.6, SaO2 90 on 4
  liter nasal cannula.

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Case 3

• You are called for a 78 year old male admitted 10
  hours prior for exacerbation of COPD. He is
  obtunded and barely rousable. P 88, R 6, BP
  146/88, T 36.8, SaO2 95 on 4 liter nasal
  cannula.
• ABG 7.13 / 103 / 86 / 33 / 93

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Lung Function

• Oxygenation
• Ventilation
• Dependent on circulation

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Air Movement - Breathing

• Negative intra-thoracic force
• The role of the pleura
• Compliance
• Airway resistance
• Radial traction dec resistance pulls on tubes
  to make a larger lumen

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Factors Affecting Intra-thoracic Force

• Trauma
• Neuromuscular disease
• Pleural effusion
• Pneumothorax
• Sedation

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Factors Affecting Compliance

• Chest wall compliance
• Trauma
• Hyper-expansion gets bigger b/c lungs push it
  out. Ribs lever against diaphragm. Dec chest
  wall compliance
• Pleural changes
• Lung compliance
• Interstitial edema
• Fibrosis
• Air trapping

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Factors Affecting Resistance

• COPD
• Asthma
• Pulmonary edema
• Airway edema

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Après Air Movement(What Comes Next)

• Diffusion in the lungs
• Circulation
• Diffusion in the tissues

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Circulatory Gas Transport

• Pulmonary circulation
• Gas transportability
• Systemic circulation

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Gas Diffusion

• Layers
• Surfactant
• Alveolar membrane
• Interstitial fluid
• Capillary membrane
• Plasma
• Healthy barrier is 0.5 microns
• Different gases behave differently

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Factors Affecting Diffusion

• Type of gas
• Membrane thickness
• Pressure gradient
• Blood flow

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Normal Oxygenation

• Its all about DIFFUSION
• Confounders
• Other gases N2, H2O, CO2, trace gases
• Speed of the blood
• Erythrocyte exposure time 0.75 - 0.25 seconds
• Diffusion membrane
• Hemoglobin status

(Rest)
(Exercise)
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Oxygen Cascade

• Inspired oxygen 160 mmHg
• Alveolar oxygen 100 mmHg
• Oxygen in blood 90 mmHg
• Dissolved in plasma
• Oxygen at tissue (mitochondrial) level
• 4 - 20 mmHg

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Pulmonary Math

• Alveolar gas equation (short)
• PAO2 (P atm - P H2O) x FiO2 - PaCO2 / R
• (760-47) x FiO2() PaCO2 / 0.8
• 713 x 0.21 40 / 0.8
• 150-50
• Approx 100 mmHg

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A(Alveolar)-a(Arterial) GradientA-a Gradient

• PAO2 PaO2
• (P atm P H2O) x FiO2 - PaCO2 / R - PaO2
  (obtained from ABG)
• (760-47) x FiO2() PaCO2 / 0.8 PaO2
• 713 x 0.21 40 / 0.8 PaO2
• 150 50 PaO2
• 100 PaO2
• Normal gradient Age/44
• In a healthy young adult, this is about 10 mmHg
  but can change dramatically with diseases
  affecting diffusion membrane

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Oxygen in the Blood

• Total O2
• Total O2 (Hb(g/dl) x 1.34 x SaO2) (PaO2 x
  0.003)
• (14 x 1.34 x 0.98) .
  (90 x 0.003)
• 18.4 ml/100ml blood .
  0.27 ml/100ml blood

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Point for Possible Confusion

• PaO2 and SaO2 are completely different, though
  interdependent measurements

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Oxyhemoglobin Dissociation Curve

• What moves it to the right?
• Lower pH
• Higher PaCO2
• Higher temp
• Higher level of 2,3 BPG
• Usually induced by chronic hypoxemia

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CO2 Transport

• CO2 transport
• 23 bound to Hb Carbaminohemoglobin
• 70 as HCO3 Bicarbonate
• 7 dissolved in plasma
• Volatile as H2CO3
• H20 CO2 H2CO3 H HCO3-
• Amount present is unmeasureable due to volatility
  but proportional to PaCO2

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Normal VentilationAir Movement Diffusion

• Inspiration
• Negative intrathoracic pressure via diaphragm and
  intercostal muscles
• Simple diffusion of O2 and CO2
• Expiration
• Positive intrathoracic pressure via relaxation of
  diaphragm and intercostals
• Lung recoil

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Working Together

• V/Q Ventilation / Perfusion
• Matching/mismatching
• Shunting
• PNA, pulmonary edema, atelectasis
• Dead space ventilation
• Pulmonary embolism
• Compensatory mechanisms
• Pulmonary arteriole constriction

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Acute Respiratory FailureWhere To Start

• Where does the problem lie?
• Air movement
• Apnea/Hypopnea
• Airway resistance
• Asthma
• Edema
• Lung or chest wall compliance
• Restriction/Trauma
• Interstitial fibrosis
• Air trapping

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Acute Respiratory FailureWhere Else

• Diffusion abnormalities
• Interstitial edema/fibrosis
• Gradient abnormalities
• Relation to diffusion membrane
• (A-a gradient)
• Ambient hypoxemia
• V/Q mismatch
• Shunting
• Dead space ventilation

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Acute Respiratory FailureWhere Else

• Blood flow
• Fast flow
• Rest vs. exercise
• Slow flow
• HF
• Pulmonary vascular resistance

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Acute Respiratory FailureWhere Else

• Gas transport
• Hemoglobin level
• Anemia
• Oxyhemoglobin dissociation

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Acute Respiratory FailureManifestations

• Hypoxemia
• Hypercapnia (ventilatory failure)
• ABG representation
• Rapid onset, severe V/Q mismatch

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Acute Respiratory Failure Etiology
Complication of another condition

• Pneumonia
• COPD
• Sepsis
• MI
• PE
• Pulmonary edema

• Pneumothorax
• Lung Path.
• Drugs
• Shock
• Trauma
• ARDS

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Acute Respiratory Failure Typical Presentation

• Respiratory distress
• ? Respiratory rate
• Use of accessory muscles of respiration
• Scalene m.
• Sternocleidomastoid m.
• Pectoralis Major m.
• Abdominals

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Acute Respiratory Failure Presentation (Cont)

• Coma
• Cyanosis
• Diaphoresis sweating
• Delirium
• Lethargy (esp. with COPD)
• CO2 narcosis / hypoxic drive

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Acute Respiratory Failure Mimics

• Anxiety
• Pain
• Agitation
• Panic attack
• Kussmauls breathing
• Cheyne-Stokes breathing between
  hypo/hyperventilation

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Acute Respiratory Failure Rapid Diagnostics

• ABG the way to know
• CXR
• PA/Lat vs. portable
• EKG
• CBC, CMP, Mg, CK-MB, Troponin I

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Acute Respiratory Failure Interventions

• Hypoxemia
• O2 delivery systems
• Nasal cannula/Oxymizer
• Simple mask - not used
• Partial rebreather mask - not used
• Venturi mask
• Non-rebreather mask
• To maintain PaO2 ? 60 or SaO2 ? 90

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Acute Respiratory Failure Interventions

• Ventilatory support
• BIPAP (NPPV) non invasive pos pressure when we
  think it will only be for a short time.
• Endotracheal intubation
• Mechanical ventilation (PPV)

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Reasons to Intubate

• Airway obstruction
• Airway protection
• Secretion management
• Unresponsive hypoxemia
• Ventilation management
• Acidosis
• Apnea
• Injury/toxicity
• Anesthesia

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Mechanical Ventilation Modes

• CMV controlled mechanical ventilation
• A/CMV assist/control mechanical ventilation
• IMV/SIMV synchronized intermittent mandatory
  ventilation
• PSV pressure support ventilation
• PCV pressure control ventilation
• PEEP positive end expiratory pressure

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Consequences of PPV

• Barotrauma
• Vent. assoc. lung injury
• Hemodynamic effects
• Hemodynamic monitoring changes
• Muscle atrophy

• Impaired mucociliary clearance
• O2 toxicity
• GI
• Splanchnic / Renal
• Cerebral
• Auto PEEP

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Consequences of PPV (Cont)

• Auto PEEP

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CMV - Weaning Modalities

• Treat underlying illness or cause of respiratory
  failure to maximum effect.
• Treat complications.
• Then...

• Wean O2 / PEEP
• ? Assist Breaths
• Use of PSV
• NIF
• At least -20 cmH2O
• F/U ABG

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Acute Lung Injury (ALI)

• Acute and persistent lung inflammation with
  increased vascular permeability
• 3 clinical features
• Bilateral infiltrates
• PaO2 / FiO2 ratio 201-300 (room air PaO2 ? 60)
• Lower value worse disease
• No evidence of ? left atrial pressure
• PCWP 18 mmHg or less

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Acute Respiratory Distress Syndrome (ARDS)

• Definition
• Severe end of the spectrum of acute lung
  injury

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Acute Respiratory Distress Syndrome

• ALI - worse
• PaO2 / FiO2 ratio 200 or less
• Room air PaO2 ? 40
• Diffuse alveolar damage
• Low lung compliance
• ? vascular permeability
• ?? diffusion gradient

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ARDS Presentation

• Initial
• Severe Hypoxemia
• Tachypnea / Dyspnea
• Diffuse rales
• Rapid decline and need for mechanical ventilation
• ABG
• Acute respiratory alkalosis so hypoxic that
  they are hyperventilationg
• Severe hypoxemia

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ARDS Dx

• Initially resembles CHF or Pulmonary Edema
• Importance of clinical course
• Swan Ganz catheter
• BNP or NT-Pro BNP

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ARDS Etiology
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ARDS Occurrence

• Approx. 190,600 cases / yr
• 15 ICU pts
• 20 mech vent pts

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ARDS DDx

• Diffuse alveolar hemorrhage
• Acute interstitial pneumonia
• Idiopathic acute eosinophilic pneumonia
• Carcinoma

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ARDS Complications

• Mostly related to CMV
• Barotrauma
• Nosocomial Pneumonia
• Multisystem failure
• DVT pt not mobile
• GI bleed
• Malnutrition
• Catheter related infections
• Drug effects

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ARDS Tx

• O2
• Prudent sedation / paralysis
• Analgesia
• Diuresis
• PPV

• Nutritional support
• Glucose control
• VTE prophylaxis
• GI prophylaxis
• Prudent transfusions
• Monitor for nosocomial pneumonia

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ARDS Prognosis

• 25-30 mortality
• Multisystem failure
• Variable outcomes in survivors
• Long term neurocognitive impairment
• Ventilatory impairment resolves

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Remember the Cases?

• 18 year old male in ED with history of anxiety
  and acute onset of dyspnea and SOB. P 94, R 28,
  BP 132/78, T 37.0, SaO2 99 on room air. Panic
  attack
• You are called for a 58 year old female admitted
  2 days prior with sepsis. Now with severe SOB. P
  110, R36, BP 105/66, T37.6, SaO2 90 on 4
  liter nasal cannula. Give more o2, investigate,
  ddx ARDS
• You are called for a 78 year old male admitted 10
  hours prior for exacerbation of COPD. He is
  obtunded and barely rousable. P 88, R 6, BP
  146/88, T 36.8, SaO2 95 on 4 liter nasal
  cannula. Partially comp resp acidosis. Went into
  acute resp failure on acute resp acidosis.
  Decreased resp drive.
• ABG 7.13 / 103 / 86 / 33 / 93
• R.O.M.E. ?

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  Pathophysiologic Consequences of Positive
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  UpToDate, Waltham, MA, 2006.
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  Respiratory Distress syndrome Definition
  Epidemiology Diagnosis and Etiology. In
  UpToDate, Rose, BD (Ed), UpToDate, Waltham, MA,
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