Acute Respiratory Failure: Recognition and Early Intervention

1. Acute Respiratory Failure:Recognition and Early Intervention Carrie Samiec, D.O. Pulmonary & Critical Care Franklin Square Hospital Center

2. 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 > 50 mm of Hg or PaO2 < 60 mm of Hg.

3. Respiratory Failure Classification • Hypoxemic • PaO2 <60 mmHg, normal or low PaCO2 • Hypercapnic • PaCO2 >50 mmHg, can also see hypoxemia • Acute drop in blood pH (<7.3) • Acute • Chronic • Renal compensation, metabolic alkalosis, polycythemia, pulmonary hypertension, cor pulmonale

4. Respiratory Failure: Causes • Upper airway dysfunction • Lower airway obstruction • Alveolar and pleural disease • CNS causes

5. Respiratory Failure: Causes • Upper airways obstruction: > Laryngomalacia > Subglottic stenosis > Laryngotracheobronchitis > Tracheitis & Epiglottitis > Retropharyngeal / Peritonsillar abscess > Acute hypertrophic tonsillitis > Diphtheria > foreign body, trauma, vocal cord palsy

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

7. Respiratory Distress:signs 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

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

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

10. 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

11. 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

12. 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

13. 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 > 20 mm of Hg is always abnormal.

14. 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

15. Hypoventilation-Diagnosis • PaO2 • PaCO2 is always increased • A-a gradient is normal (≤ 10 mm of Hg) • Hyperoxia Test : dramatic rise in PO2

16. V/Q mismatch- Diagnosis • PaO2 • A-a gradient is elevated • PaCO2 may or may not be elevated • Hyperoxia test : Dramatic rise in PaO2

17. 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

18. R-L shunt: diagnosis • PaO2 is • PaCO2 is usually normal unless shunt is severe (>60%) • A-a gradient is • Hyperoxia Test : Poor / No response

19. 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

20. 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

21. 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.

22. Respiratory failure:Interventions • 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

23. 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

24. 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.

25. 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.

26. Mechanical Ventilation: Indications • PaO2< 55 mm Hg or PaCO2 > 60 mm Hg despite 100% oxygen therapy. • Deteriorating respiratory status despite oxygen and nebulization therapy • Anxious, sweaty, or lethargic patient with deteriorating mental status. • Respiratory fatigue: for relief of metabolic stress due to work of breathing or underlying condition (sepsis, MI, CHF, etc.)

27. Mechanical Ventilation: Strategies • Non-Invasive Ventilation: • CPAP / BIPAP • Invasive Ventilation: • AC, VC, PC, Bilevel ventilation

28. 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

29. 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

30. 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

31. Thank you!