1. Respiratory Failure By: Dr.Samet.M Yazd University

2. Respiratory Failure Respiratory failure is a condition in which the respiratory system fails in one or both of its gas-exchanging functions: oxygenation carbon dioxide elimination

3. CLASSIFICATION Acute & Chronic   Hypercapnic: PaCO2 >45 mmHg   Hypoxemic: PaO2 <55 mmHg when FIO2 ≥0.60

4. Distinctions between acute and chronic respiratory failure Arterial blood gas values Presence of markers of chronic hypoxemia ( polycythemia or cor pulmonale) Abrupt changes in mental status

5. PATHOPHYSIOLOGY Controller dysfunction Pump dysfunction Airway system dysfunction Alveolar compartment dysfunction Pulmonary vascular dysfunction

6. Controller dysfunction “central apnea” Structural: meningoencephalitis, localized tumors or vascular abnormalities of the medulla,strokes affecting medullary control centers Pharmacologic: narcotic, sedative Metabolic: severe myxedema,hepati failure,advanced uremia,hypothermia Elevation of Pco2 in the CNS: chronic metabolic alkalosis (diuretic use) Obesity-hypoventilation syndrome COPD

7. Controller dysfunction “central apnea” Determine rate & depth of breathing Determine pattern of breathing Determine amount of effort for breathing 1.Awareness patient without sedative use can`t increase RR>12/min or make use of accessory muscles 2.Hypoxemia,Hypercapnia 3.PAo2-Pao2 was normal 4.Type II respiratory failure

8. Pump Dysfunction Decreased respiratory muscle strength: Muscle fatigue Recovery from acute respiratory failure, high respiratory rates, increased inspiratory time Disuse atrophy Prolonged mechanical ventilation, following phrenic nerve injury Electrolyte abnormalities Decreased motor neuron function: Decreased phrenic nerve output Polyneuropathy, Guillain-Barr´e syndrome, phrenic nerve transection or injury, Poliomyelitis Decreased neuromuscular transmission Myasthenia gravis, use of paralyzing agents Pharmacologic: paralyzing agents, corticosteroids, cholinergic crisis, aminoglycosides Structural abnormalities: Kyphoscoliosis,Obesity,Ascites,Distention,Flail chest,Thoracoplasty

9. Pump Dysfunction Paradoxical movement of diaphragm Respiratory distress Vital capacity<10ml/kg Inspiratory force<-20cmH2O RSBI>105 Transdiaphragmatic pressure EMG & NCV  Hypercapnia  Type II respiratory failure

10. Airways System Dysfunction Upper airways: acute epiglottitis, aspirated foreign body, tracheal tumor narrowing of the trachea or glottis by fibrotic tissue Lower airways: COPD, asthma, advanced cystic fibrosis

11. Airways System Dysfunction A greater transthoracic pressure gradient requirement The resistive work of breathing is increased Vo2 Tidal volume falls and dead space ventilation increases Respiratory muscle fatigue shallow breathing pattern Air trapping hyperinflation diaphragm flattening   Stirdor,Bronchospasm(wheez,rhonchi)   Raw>10 cmH2O/L/S  Type II respiratory failure

12. Alveolar Compartment Dysfunction Cardiogenic and noncardiogenic pulmonary edema Diffuse pneumonia Extensive pulmonary hemorrhage Aspiration of stomach contents Neardrowning Lung contusion  Hypoxemia,Hypercapnia  Type I respiratory failure

13. Alveolar Compartment Dysfunction Hypoxemia: Diffuse alveolar filling large right-to-left shunt Interstitial edema impair diffusion across the alveolar-capillary membrane Hypercapnia:   Increased ventilatory demand: Hypoxemia Vd / Vt, Elastic work of breathing (reduced lung compliance) Resistive work of breathing (airway narrowing and airway reactivity) Neural drive to breathe (mediated by pulmonary parenchymal vagal fibers)   Decreased ventilatory supply: Alveolar flooding Reduced lung elasticity Respiratory muscle fatigue Reduced blood supply to the diaphragm secondary to shock

14. Alveolar Compartment Dysfunction Consolidation bronchial sound,egophonia,dullness Static compliance<30 ml/cmH2O Type I respiratory failure

15. Pulmonary Vascular Dysfunction Symptoms & Signs of right HF: JVP,S3,RV heave,TR,S2 JVP,S3,RV heave,TR,S2 EKG RBBB,RV strain pattern EKG RBBB,RV strain pattern CX-Ray Pulmonary artery enlargement CX-Ray Pulmonary artery enlargement Type II respiratory failure

16. Respiratory Failure Type I: Acute Hypoxemic Respiratory Failure alveolar flooding and subsequent intrapulmonary shunt physiology alveolar flooding and subsequent intrapulmonary shunt physiology pulmonary edema, pneumonia, or alveolar hemorrhage pulmonary edema, pneumonia, or alveolar hemorrhage Type II: Alveolar hypoventilation impaired CNS drive to breathe, impaired strength with failure of neuromuscular function in the respiratory system, increased load on the respiratory system impaired CNS drive to breathe, impaired strength with failure of neuromuscular function in the respiratory system, increased load on the respiratory system Type III: Lung atelectasis perioperative respiratory failure perioperative respiratory failure Type IV: Hypoperfusion of respiratory muscles shock shock

17. Hypoxemic Respiratory Failure Alveolar hypoventilation Ventilation-perfusion Mismatch Shunt Diffusion limitation   PAO2 = FIO2 x (PB – PH2O) – PaCO2/R  PAO2 = 150 – 1.25 x PaCO2   PAo2 − Pao2 = [PIo2 − PaCo2/R] − Pao2

18. Hypoxemic Respiratory Failure Although changes in minute and alveolar ventilation can change Paco2 considerably, this is not so for Pao2. At a Pao2>55-60 mmHg,the effect of increasing ventilation on CaO2 is minimal,since the oxyhemoglobin dissociation curve is flat in this range. In the absence of underlying pulmonary disease, the hypoxemia accompanying alveolar hypoventilation is characterized by a normal alveolar-arterial oxygen gradient.

19. Hypercapnic Respiratory Failure Paco2 is determined: Rate of CO2 production (˙Vco2 ) rate of CO2 production # rate of CO2 elimination (CvCO2-CaCO2).CO.10 # 90-130 L/min/M2 Level of alveolar ventilation VA = K. ˙Vco2/Paco2 VE = K. (˙Vo2. RQ) / (Paco2 / [1 − Vd / Vt] ) ˙Vo2 = rate of O2 consumption RQ = respiratory quotient