Acute Respiratory Failure

1. Acute Respiratory Failure

2. Respiratory System • Consists of two parts: • Gas exchange organ (lung): responsible for OXYGENATION • Pump (respiratory muscles and respiratory control mechanism): responsible for VENTILATION NB: Alteration in function of gas exchange unit (oxygenation) OR of the pump mechanism (ventilation) can result in respiratory failure

3. Normal Lung

4. Lung Anatomy

5. Normal Alveoli

6. Gas Exchange Unit Fig. 66-1

7. Normal ABGs • pH = 7.35-7.45 • CO2 = 35-45 • HCO3= 23-27

8. Respiratory and Metabolic Acidosis and Alkalosis • CO2 is an acid and is controlled by the Respiratory (Lung) system • HCO3 is an alkali and is controlled by the Metabolic (Renal) system • Respiratory response is immediate; Metabolic response can take up to 72 hours to respond (except in patients with COPD who are in a constant state of Compensation!)

9. ABG Interpretation Step 1: Check the pH: Is it acidotic or alkalotic or normal? pH below 7.35 is acidotic; pH above 7.45 is alkalotic If pH is normal, then the ABG is compensated; if pH not normal, then the ABG is uncompensated

10. ABG Interpretation (cont’d) Step 2. Check the CO2 and HCO3: • If the CO2 (acid) is above 45, the pt is acidotic; if the CO2 is below 35, the pt is alkalotic • If the HCO3 is above 27, the patient is alkalotic; if the HCO3 is below 23, the patient is acidotic

11. ABG Interpretation (cont’d) Step 3 If the CO2 is high (above 45), then the patient is in Respiratory Acidosis; if the CO2 is low (below 35), then the patients is in Respiratory Alkalosis. If the HCO3 is high (above 27), then the patient is in Metabolic Alkalosis; if the HCO3 is low (below 23), then the patient is in Metabolic Acidosis.

12. ABG Example #1 • pH = 7.36 • CO2 = 41 • HCO3 = 27 Diagnosis: ?

13. ABG Example #2 • pH = 7.49 • CO2 = 37 • HCO3 = 32 Diagnosis: ?

14. ABG Example #3 • pH = 7.29 • CO2 = 50 • HCO3 = 26 Diagnosis: ?

15. ABG Example #4 • pH = 7.40 • CO2 = 32 • HCO3 = 30 Diagnosis: ?

16. Acute Respiratory Failure • Results from inadequate gas exchange • Insufficient O2 transferred to the blood • Hypoxemia • Inadequate CO2 removal • Hypercapnia

17. Acute Respiratory Failure with Diffuse Bilateral Infiltrates

18. Acute Respiratory Failure • Not a disease but a condition • Result of one or more diseases involving the lungs or other body systems • NB: Acute Respiratory Failure: when oxygenation and/or ventilation is inadequate to meet the body’s needs

19. Acute Respiratory Failure • Classification: • Hypoxemic respiratory failure (Failure of oxygenation) • Hypercapnic respiratory failure (Failure of ventilation)

20. Classification of Respiratory Failure Fig. 66-2

21. Acute Respiratory Failure • Hypoxemic Respiratory Failure • PaO2 of 60 mm Hg or less (Normal = 80 - 100 mm Hg) • Inspired O2 concentration of 60% or greater

22. Acute Respiratory Failure • Hypercapnic Respiratory Failure • PaCO2 above normal (>45 mm Hg) • Acidemia (pH <7.35)

23. Hypoxemic Respiratory FailureEtiology and Pathophysiology • Causes: • Ventilation-perfusion (V/Q) mismatch • Shunt • Diffusion limitation • Alveolar hypoventilation

24. V-Q Mismatching I) V/Q mismatch • Normal ventilation of alveoli is comparable to amount of perfusion • Normal V/Q ratio is 0.8 (more perfusion than ventilation) • Mismatch d/t: • Inadequate ventilation • Poor perfusion

25. Range of V/Q Relationships Fig. 66-4

26. Hypoxemic Respiratory FailureEtiology and Pathophysiology Causes V/Q mismatch • COPD • Pneumonia • Asthma • Atelectasis • Pulmonary embolus

27. Hypoxemic Respiratory FailureEtiology and Pathophysiology II) Shunt • An extreme V/Q mismatch • Blood passes through parts of respiratory system that receives no ventilation • d/t obstruction OR fluid accumulation • Not Correctable with 100% O2

28. Diffusion Limitations III) Diffusion Limitations • Distance between alveoli and pulmonary capillary is one- two cells thick • With diffusion abnormalities: there is an increased distance between alveoli (may be d/t fluid) • Correctable with 100% O2

29. Hypoxemic Respiratory FailureEtiology and Pathophysiology Causes Diffusion limitations • Severe emphysema • Recurrent pulmonary emboli • Pulmonary fibrosis • Hypoxemia present during exercise

30. Diffusion Limitation Fig. 66-5

31. Alveolar Hypoventilation IV) Alveolar Hypoventilation Is a generalized decrease in ventilation of lungs and resultant buildup of CO2

32. Hypoxemic Respiratory FailureEtiology and Pathophysiology Causes Alveolar hypoventilation • Restrictive lung disease • CNS disease • Chest wall dysfunction • Neuromuscular disease

33. Hypoxemic Respiratory FailureEtiology and Pathophysiology • Interrelationship of mechanisms • Hypoxemic respiratory failure is frequently caused by a combination of two or more of these four mechanisms • Effects of hypoxemia • Build up of lactic acid → metabolic acidosis → cell death • CNS depression • Heart tries to compensate → ↑ HR and CO • If no compensation: ↓ O2, ↑ acid, heart fails, shock, multi-system organ failure

34. Hypercapnic Respiratory FailureEtiology and Pathophysiology • Imbalance between ventilatory supply and demand • Occurs when CO2 is increased

35. Causes Hypercapnic Respiratory Failure I) Alveolar Hypoventilation and VQ Mismatch: • Ventilation not adequate to eliminate CO2 • Leads to respiratory acidosis • Eg. Narcotic OD; Guillian-Barre, ALS, COPD, asthma

36. Causes Hypercapnic Respiratory Failure II) VQ Mismatch: - Leads to increased work of breathing - Insufficient energy to overcome resistance; ventilation falls; ↑PCO2; respiratory acidosis

37. Hypercapnic Respiratory FailureCategories of Causative Conditions • I) Airways and alveoli • Asthma • Emphysema • Chronic bronchitis • Cystic fibrosis

38. Hypercapnic Respiratory FailureCategories of Causative Conditions • II) Central nervous system • Drug overdose • Brainstem infarction • Spinal cord injuries

39. Hypercapnic Respiratory FailureCategories of Causative Conditions • III) Chest wall • Flail chest • Fractures • Mechanical restriction • Muscle spasm

40. Hypercapnic Respiratory FailureCategories of Causative Conditions • IV) Neuromuscular conditions • Muscular dystrophy • Multiple sclerosis

41. Respiratory FailureTissue Oxygen Needs • Major threat is the inability of the lungs to meet the oxygen demands of the tissues

42. Respiratory FailureClinical Manifestations • Sudden or gradual onset • A sudden  in PaO2 or rapid  in PaCO2 is a serious condition

43. Respiratory FailureClinical Manifestations • When compensatory mechanisms fail, respiratory failure occurs • Signs may be specific or nonspecific

44. Respiratory FailureClinical Manifestations • Severe morning headache • Cyanosis • Late sign • Tachycardia and mild hypertension • Early signs

45. Respiratory FailureClinical Manifestations • Consequences of hypoxemia and hypoxia • Metabolic acidosis and cell death •  Cardiac output • Impaired renal function

46. Respiratory FailureClinical Manifestations • Specific clinical manifestations • Rapid, shallow breathing pattern • Sitting upright • Dyspnea

47. Respiratory FailureClinical Manifestations • Specific clinical manifestations • Pursed-lip breathing • Retractions • Change in Inspiratory:Expiratory ratio

48. Respiratory FailureDiagnostic Studies • Physical assessment • ABG analysis • Chest x-ray • CBC • ECG

49. Respiratory FailureDiagnostic Studies • Serum electrolytes • Urinalysis • V/Q lung scan • Pulmonary artery catheter (severe cases)

50. Acute Respiratory FailureNursing and Collaborative Management • Nursing Assessment • Past health history • Medications • Surgery • Tachycardia