acute

1. Jiunn-Song Jiang Acute Respiratory failure ?????

2. Jiunn-Song Jiang Respiratory failureLearning objectives Define respiratory failure Classify respiratory failure into hypoxemia and hypercapnic types Recognize signs and symptoms of respiratory failure Know alveolar gas equation, apply it to the evaluation of respiratory failure Know the changes in blood gases that accompany respiratory failure Beware of the major treatment of respiratory failure

3. Jiunn-Song Jiang Respiratory failure Respiration is gas exchange between the organism and its environment. �Inability of the lungs to meet the metabolic demands of the body. This can be from failure of tissue oxygenation and/or failure of CO2 homeostasis. � Clinically: Respiratory failure is defined as PaO2 <60 mmHg while breathing air or a PaCO2>50mmHg.

4. Jiunn-Song Jiang Respiratory system Function of respiratory system is to supply the body with oxygen for aerobic metabolism and to remove its major metabolic waste product CO2 Does it by 3 distinct mechanism Ventilation: Delivery of ambient air to the alveoli Diffusion: Movement of oxygen and carbon dioxide across the alveolar air sac and capillary wall Circulation: Method by which oxygen is carried from site of gas exchange to the cells where active metabolism occurs

5. Jiunn-Song Jiang Respiratory system

6. Jiunn-Song Jiang Respiratory System

7. Jiunn-Song Jiang Causes of respiratory failure 1. ?FiO2 2. Hypoventilation (? PaCO2,) Hypercapnic respiratory failure 3. V/Q mismatch (eg.COPD) 4. Diffusion limitation 5. Intrapulmonary shunt - Pneumonia - Atelectasis - CHF (high pressure pulmonary edema) - ARDS (low pressure pulmonary edema)

8. Jiunn-Song Jiang Respiratory failure & its components

9. Jiunn-Song Jiang Hypoxemic respiratory failure (Type I) PaO2 < 60mmHg with normal or low PaCO2, pH normal or high Most common form of respiratory failure Lung disease is severe to interfere with pulmonary O2 exchange, but over all ventilation is maintained Physiologic causes: V/Q mismatch and shunt

10. Jiunn-Song Jiang Case Study No. 1 60 y/o male comes ER c/o SOB. Tachypneic, tachycardic, diaphoretic and Cyanotic. Dx acute resp. failure and ABG�s Show PaCO2 30mmHg, pH 7.5, PaO2 55mmHg. The blood gas document Resp. failure due to primary O2 problem.

11. Jiunn-Song Jiang V/Q mismatch Ideally each alveolar capillary exchange unit would have perfect matching of ventilation and perfusion to ensure optimum gas exchange across each unit This does not happen even in normal individual where V/Q ranges in different lung regions from 0.63 to 3.0, mean overall is 1.0 In disease state, balance of V/Q may be disturbed further by V/Q inequality Intrapulmonary shunt

12. Jiunn-Song Jiang V/Q mismatch

13. Jiunn-Song Jiang Shunt

14. Jiunn-Song Jiang Response of V/Q inequality or shunt to oxygen

15. Jiunn-Song Jiang Diffusion abnormalities The process by which O2 and CO2 move passively across the alveolar capillary membrane that dependent upon its physical properties (thickness, area and diffusibility) and solubility of the gas Problem mainly in chronic, less so in acute respiratory failure

16. Jiunn-Song Jiang Causes of hypoxemic respiratory failure Caused by a disorder of heart, lung and blood. Etiology easier to assess by CXR abnormality: Normal CXR - Cardiac shunt (right to left) - Asthma, COPD - Pulmonary embolism

17. Jiunn-Song Jiang Causes of hypoxemic respiratory failure (cont'd.) Focal infiltrates on CXR - Atelectasis - Pneumonia Diffuse infiltrates on CXR - Cardiogenic Pulmonary Edema - Non-cardiogenic pulmonary edema (ARDS) - Interstitial pneumonitis or fibrosis - Infections

18. Jiunn-Song Jiang Hypercapnic Respiratory Failure (Type II) PaCO2 >50 mmHg Hypoxemia is always present pH depends on level of HCO3- HCO3- depends on duration of hypercapnia Renal response occurs over days to weeks

19. Jiunn-Song Jiang Case Study No. 2

20. Jiunn-Song Jiang Hypoventilation The relationship of VA, VCO2 and PaCO2 is expressed using a modification of Fick principle of mass balance that quantitates VCO2 as the product of VA and FACO2 PaCO2 =KVCO2/VA

21. Jiunn-Song Jiang Causes of hypercapnic respiratory failure Respiratory centre (medulla) dysfunction Drug over dose, CVA, tumor, hypothyroidism, central hypoventilation Neuromuscular disease Guillain-Barre, Myasthenia Gravis, polio, spinal injuries Chest wall/Pleural diseases kyphoscoliosis, pneumothorax, massive pleural effusion Upper airways obstruction Tumor, foreign body, laryngeal edema Peripheral airway disorder Asthma, COPD

22. Jiunn-Song Jiang Classification of respiratory failure

23. Jiunn-Song Jiang Acute vs. Acute on chronic hypercapnic respiratory failure (Type II) Acute Arterial pH is low Causes: - sedative drug over dose - acute muscle weakness such as myasthenia. - severe lung disease alveolar ventilation can not be maintained (i.e asthma or pneumonia) Acute on chronic This occurs in patients with chronic CO2 retention who worsen and have rising CO2, and low pH Mechanism: respiratory muscle fatigue

24. Jiunn-Song Jiang Diagnosis of respiratory failure History and physical examination Laboratory

25. Jiunn-Song Jiang Respiratory symptoms in respiratory failure Mental function: headache, visual disturbance, confusion, memory loss, hallucination, loss of consciousness. Dyspnea (resting vs. exertional) Cough, sputum volume and purulency, chest pain

26. Jiunn-Song Jiang Physical examination in respiratory failure

27. Jiunn-Song Jiang Laboratory testing in respiratory failure ABG: PO2, PCO2, PH Measurement of respiratory mechanism: Spirometry (FVC, FEV1..), respiratory muscle pressures Chest imaging: CXR, CT, V/Q scan Other test: Hg/Hct, BUN, Cr�

28. Jiunn-Song Jiang A-a O2 gradient

29. Jiunn-Song Jiang A-a O2 gradient

30. Jiunn-Song Jiang Management of Respiratory Failure Principles: Hypoxemia may cause death in RF Primary objective is to reverse and prevent hypoxemia Secondary objective is to control PaCO2 and respiratory acidosis Treatment of underlying disease Patient's CNS and CVS must be monitored and treated

31. Jiunn-Song Jiang Oxygen Therapy Tissue hypoxia occurs (normal Hb & C.O.) Venous PaO2 <20 mmHg a SaO2 <40% Arterial PaO2 < 38 mmHg a SaO2 <70% Supplemental O2 therapy is essential titration based on SaO2, PaO2 levels and PaCO2 O2 dose either flow rate (L/min) or FiO2(%) Goal is to prevent tissue hypoxia Increase arterial PaO2 > 60 mmag(SaO2 > 90%) pr venous SaO2 > 60%

32. Jiunn-Song Jiang Risks of Oxygen Therapy O2 toxicity: very high levels (>1000 mmHg) CNS toxicity and seizure lower levels (FiO2 > 60%) and longer exposure FiO2 35 to 40% can be safely tolerated indefinitely Capillary damage, leak and pulmonary fibrosis CO2 narcosis PaCO2 increase secondary to combination of a) abolition of hypoxic drive to breathe b) increase in dead space PaCO2 may increase severely to cause respiratory acidosis, somnolence and coma

33. Jiunn-Song Jiang Mechanical ventilation Noninvasive with a mask Invasive with an endotracheal tube MV can be volume or pressure cycled For hypercapnia: MV increases alveolar ventilation and lowers PaCO2, corrects pH rests fatigues respiratory muscles For hypoxemia: O2 therapy alone does not correct hypoxemia caused by shunt Most common cause of shunt is fluid filled or collapsed alveoli (Pulmonary edema)

34. Jiunn-Song Jiang Positive End Expiratory Pressure (PEEP) PEEP increases the end expiratory lung volume (FRC) PEEP recruits collapsed alveoli and prevents re-collapse FRC increases, therefore lung becomes more -compliant Reversal of atelectasis diminishes intrapulmonary shunt Excessive PEEP has adverse effects: decreased cardiac output barotrauma (pneumothax, pneumomediastinum) increased physiologic dead space increased work of breathing

35. Jiunn-Song Jiang Positive End Expiratory Pressure (PEEP) PEEP has no �prophylactic� role in preventing pts with no or minimal lung injury from progressing to ARDS PEEP doesn�t reduce EVLW but rather redistribute it from the alveoli to interstitium; Discontinuation of PEEP (even suctioning) is associated with alveolar flooding & deterioration in oxygenation

36. Jiunn-Song Jiang Positive End Expiratory Pressure (PEEP) ?PEEP should be added in increments of 3 ~5 cmH2O; During PEEP trial, alveolar recruitment & lung mechanics (lung compliance) tend to be complete after 5~8 breaths When further + ?PEEP do not alter lung compliance or actually cause it fall (lung hyper-expansion); this is often a point at which PEEP will have adverse effect on VR ; hypotension & tachycardia may be observed

37. Jiunn-Song Jiang Positive End Expiratory Pressure (PEEP) A fall of BP with + ?PEEP mandates lower PEEP until circulatory volume is increased (increasing circulating Hb is preferred ) or vasoactive drugs are added to maintain VR at higher PEEP During recovery phase of ARDS, ? ?PEEP 2~3 cmH2O , with several hours of observation between adjustment If volume administration must be increased in response to excessive reduction in Ppw, consideration should be first given to increasing circulating Hb On occasion, even small decrement of PEEP will be associated with sudden arterial desaturation, perhaps related to alveolar flooding or collapse related to surfactan deficiency or dysfunction If volume administration must be increased in response to excessive reduction in Ppw, consideration should be first given to increasing circulating Hb On occasion, even small decrement of PEEP will be associated with sudden arterial desaturation, perhaps related to alveolar flooding or collapse related to surfactan deficiency or dysfunction

38. Jiunn-Song Jiang Therapy of cardiogenic pulmonary edema

39. Jiunn-Song Jiang Indication for intubation & MV in cardiogenic pulmonary edema Hypotension, even of modest degree Clinical evidence of nonresolving ischemia LVF refractory to medical support Complex arrythmias When angiography or surgery are required for ischemic or valvular heart disease

40. Jiunn-Song Jiang Therapy of cardiogenic pulmonary edema

41. Jiunn-Song Jiang Therapy of cardiogenic pulmonary edema Inotropic support Dobutamine 5?10ug/kg/min Afterload Reduction Treatment of anxiety to lower systemic blood pressure(c.g, morphine sulfate) Specific antihypertensive therapy Nifidipine(10?20 mg PO or SL) Sodium nitroprusside for accelerated hypertension Intraaortic balloon pumping(IABP) for refractory ventricular failure