Acute Respiratory Failure: Recognition and Early Intervention

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Acute Respiratory FailureRecognition and Early
Intervention

• Carrie Samiec, D.O.
• Pulmonary Critical Care
• Franklin Square Hospital Center

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Definition Respiratory Failure

• Failure of the respiratory system in one or both
  of its gas exchange functions
• Oxygenation
• Carbon dioxide elimination
• Can be acute or chronic
• Documented by PaCO2 gt 50 mm of Hg or PaO2 lt 60 mm
  of Hg.

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Respiratory Failure Classification

• Hypoxemic
• PaO2 lt60 mmHg, normal or low PaCO2
• Hypercapnic
• PaCO2 gt50 mmHg, can also see hypoxemia
• Acute drop in blood pH (lt7.3)
• Acute
• Chronic
• Renal compensation, metabolic alkalosis,
  polycythemia, pulmonary hypertension, cor
  pulmonale

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Respiratory Failure Causes

• Upper airway dysfunction
• Lower airway obstruction
• Alveolar and pleural disease
• CNS causes

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Respiratory Failure Causes

• Upper airways obstruction
• gt Laryngomalacia
• gt Subglottic stenosis
• gt Laryngotracheobronchitis
• gt Tracheitis Epiglottitis
• gt Retropharyngeal / Peritonsillar abscess
• gt Acute hypertrophic tonsillitis
• gt Diphtheria
• gt foreign body, trauma, vocal cord palsy

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• Lower airway obstruction
• gt Bronchiolitis, Asthma, Foreign body
• Alveolar and pleural disease
• gt pneumonia, pulmonary edema, effusion
• empyma, pneumothorax, ARDS
• CNS causes
• gt Infections, injury, trauma, seizures
• gt tetanus, SMA, Polio
• gt AIDP, Phrenic nerve injury
• gt Myasthenia gravis, botulism,
• gt Muscle dystrophies, Polymyositis
• gt Congenital myopathies, muscle fatigue

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Respiratory Distresssigns of impending
respiratory failure

• Tachypnea, diaphoresis
• Exaggerated use of accessory muscles
• Intercostal, supraclavicular and subcostal
  retractions
• Paradoxical/abdominal breathing
• In neuromuscular disease, the signs of
  respiratory distress may not be obvious
• In CNS disease, an abnormally low respiratory
  rate, and shallow breathing are clues to
  impending respiratory failure

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Arterial Blood Gases

• Arterial Blood Gas analysis single most
  important lab test for evaluation of respiratory
  failure.

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Evaluation of Respiratory failure

• The following parameters are important in
  evaluation of respiratory failure
• PaO2
• PaCO2
• Alveolar-Arterial PO2 Gradient
• Hyperoxia Test
• Blood pH

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PaO2 / PaCO2

• Normal value depends on
• a. Position of patient during
  sampling
• b. Age of patient
• PaO2 (Upright) 104.2 -- 0.27 x age (Yrs)
• PaO2 (Supine) 103.5 0.47 x age (Yrs)
• PaCO2 normal value 35-45 mm of Hg
• unaffected by age/ positioning

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A - a Gradient

• PAO2 FiO2 x (PB - PH20) - PACO2 / R
• A-a gradient PAO2 - PaO2
• PB 760 mmHg (sea level)
• PH20 47 mmHg (100 humidity)
• (760 - 74) 713
• R 0.8
• A-a gradient
• FiO2 x 713 - (PaCO2 / 0.8) - PaO2

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Sample ABG

• 7.34 / 58 / 92 / 21 / 94 on 100 Fi02
• A - a gradient
• 1.0 x 713 - (58 / 0.8) - 92
• 713 - 72.5 - 92
• 640.5 - 92 548.5
• A - a gradient 548.5
• Severe defect in gas exchange/ hypoxemia

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Alveolar-Arterial O2 gradient

• Normal P(A-a)O2 gradient 5-10 mm of Hg
• A sensitive indicator of disturbance of gas
  exchange.
• Useful in differentiating extrapulmonary and
  pulmonary causes of resp. failure.
• For any age, an A-a gradient gt 20 mm of Hg is
  always abnormal.

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Causes of Hypoxemia

• Low PiO2 at high altitude
• Hypoventilation Normal A-a gradient
• V/Q mismatch increased A-a gradient
• R/L shunt increased A-a gradient

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Hypoventilation-Diagnosis

• PaO2
• PaCO2 is always increased
• A-a gradient is normal ( 10 mm of Hg)
• Hyperoxia Test dramatic rise in PO2

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V/Q mismatch- Diagnosis

• PaO2
• A-a gradient is elevated
• PaCO2 may or may not be elevated
• Hyperoxia test Dramatic rise in PaO2

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V/Q Mismatch

• Most common cause of hypoxemia
• Causes include
• Decreased ventilation COPD, ILD
• Hypo/hyperperfusion PE
• Minute ventilation increases due to chemoreceptor
  stimulation
• Corrects with hyperoxia/100 oxygen

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R-L shunt diagnosis

• PaO2 is
• PaCO2 is usually normal unless shunt is severe
  (gt60)
• A-a gradient is
• Hyperoxia Test Poor / No response

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Shunt Physiology

• Shunt occurs when deoxygenated blood bypasses
  ventilated alveoli and mixes with oxygenated
  blood
• Results in decreased arterial O2 content
• Intracardiac shunts
• ASD, VSD, PFO
• Intrapulmonary shunts
• PNA, Pulm edema, AVMs

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Hypercapnia Causes

• Acute Hypoventilation
• CNS depression drugs, stroke, seizure
• Neuromuscular disease ALS, MS, Guillain-Barre,
  MG, C-spine injury
• Severe low V/Q mismatch
• COPD, Asthma, ARDS
• Chronic hypoventilation
• OSA, obesity

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Status of ABG

• It is not possible to predict PaO2 and PaCO2
  accurately using clinical criteria.
• Thus, the diagnosis of Respiratory failure
  depends on results of ABG studies.

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Respiratory failureInterventions

• Supportive therapy
• Upon arrival to the bedside
• Establish factors contributing to resp failure
• Use ABG to identify type of resp failure
• Choose therapies based on physiology and severity
• Specific therapy

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Assessment Supportive Therapy

• Secure the airway (ABCs)
• Pulse oximetry, vital signs
• Oxygen by mask, nasal cannula, bag-valve mask
• Proper positioning
• Nebulization if indicated
• Blood sampling Routine, electrolytes, ABG
• Secure IV access
• CXR upright AP lateral views

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Hypoxemic / Non - Hypercapnic respiratory failure

• The major problem is PaO2.
• If due to low V/Q mismatch oxygen therapy.
• If due to pulmonary intra-parenchymal shunts
  (ARDS), assisted ventilation with PEEP may be
  needed.
• If due to intracardiac R-L shunt O2 therapy is
  of limited benefit. Surgical/advanced
  intervention is often needed.

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Hypercapnic Respiratory failure

• Key decision is whether mechanical ventilation is
  required or not.
• In Acute respiratory acidosis Mechanical
  ventilation must be strongly considered.
• Chronic Resp acidosis patient should be followed
  closely, mech ventilation is rarely required.
• In acute-on-chronic respiratory failure, the
  trend of acidosis over time is a crucial factor.

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Mechanical Ventilation Indications

1. PaO2lt 55 mm Hg or PaCO2 gt 60 mm Hg despite 100
   oxygen therapy.
2. Deteriorating respiratory status despite oxygen
   and nebulization therapy
3. Anxious, sweaty, or lethargic patient with
   deteriorating mental status.
4. Respiratory fatigue for relief of metabolic
   stress due to work of breathing or underlying
   condition (sepsis, MI, CHF, etc.)

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Mechanical Ventilation Strategies

• Non-Invasive Ventilation
• CPAP / BIPAP
• Invasive Ventilation
• AC, VC, PC, Bilevel ventilation

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Non-Invasive Ventilation

• BIPAP should be considered in patients with
  mild-moderate respiratory failure
• Must have intact airway, airway-protective
  reflexes, appropriate mentation
• NOT for excessive secretions, obtunded patient,
  vomiting, severe agitation
• Bridge therapy to stave off intubation and
  reverse resp. failure acutely while other
  therapies are administered

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Non-Invasive Ventilation

• Proven beneficial in clinical trials for
• Acute exacerbations of COPD, Asthma, CHF
• Not clear for PNA, ALI
• Unloads respiratory muscles and work-of-breathing
• Recruits alveoli with adjustable PEEP
• May increase cardiac output in CHF

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Clinical Follow-up

• Patients with respiratory insufficiency require
  very close follow-up
• Usually need close interval assessments
• ICU or Intermediate/Step down units
• Continuous pulse-ox monitoring, cardiac and
  hemodynamic monitoring
• Most need pulmonary and/or critical care input
  and management

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• Thank you!