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RESPIRATORY FAILURE AND MECHANICAL VENTILATION

RESPIRATORY FAILURE AND MECHANICAL VENTILATION. ALOK SINHA Department of Medicine Manipal College of Medical Sciences Pokhara , Nepal.

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RESPIRATORY FAILURE AND MECHANICAL VENTILATION

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  1. RESPIRATORY FAILURE AND MECHANICAL VENTILATION ALOK SINHA Department of Medicine Manipal College of Medical Sciences Pokhara, Nepal

  2. Inability of the lungs to perform the function of gas exchange- the transfer of oxygen from inhaled air into the blood and the transfer of carbon dioxide from the blood into exhaled air Defined as a • PaO2 value of less than 60 mm Hg while breathing air • or a PaCO2 of more than 50 mm Hg

  3. Classification • Type 1 hypoxemic respiratory failure • Type 2 hypercapnic respiratory failure Acute Chronic

  4. Respiratory failure is caused by: 1. failure to oxygenate • characterized by decreased PaO2 2. failure to ventilate • characterized by increased PCO2

  5. Deoxygenated blood from pulmonary artery 1. Failure to oxygenate: • due to • decreased inspired O2 tension • increased CO2 tension • ventilation perfusion mismatch • Pneumonia • Oedema • P E • reduced O2 diffusion capacity • due to interstitial edema • fibrosis • thickened alveolar wall

  6. V/Q incresed = physiological dead space Pulmonary embolism Obliteration of blood vessels emphysema V/Q reduced = physiological shunt Collapse of alveoli – atelectasis Loss of surfactant Airway obst. - COPD Fluid filling Anatomical shunt increased – anastomosis between pulmonary & systemic vessels V – Q Mismatch

  7. Respiratory centers 2. Failure to ventilate Causes: • Airway • Chest wall • Respiratory muscles

  8. Hypoxemic (type I) PaO2 <60 mm Hg CO2 level may be normal or low associated with virtually all acute diseases of lung with V/Q mismatch Common causes C.O.P.D. Pneumonia Pulmonary edema Pulmonary fibrosis Asthma Hypercapnic (type II) PaCO2 of >50 mm Hg pH depends on the level of bicarbonate, dependent on the duration of hypercapnia caused by- Alveolar hypoventilation C.O.P.D. Neuromuscular disorders Guillain-Barré syndrome Diaphragm paralysis Amyotrophic lateral sclerosis Muscular dystrophy Myasthenia gravis severe obstruction with a FEV1 of less than 1 L or 35% of normal

  9. Pulmonary embolism Pulmonary arterial hypertension Pneumoconiosis Granulomatous lung diseases Cyanotic congenital heart disease Bronchiectasis Adult respiratory distress syndrome Fat embolism syndrome Chest wall deformities Kyphoscoliosis Ankylosing spondylitis Central respiratory drive depression Drugs - Narcotics, benzodiazepines, barbiturates Neurologic disorders - Encephalitis, brainstem disease, trauma Primary alveolar hypoventilation Obesity hypoventilation syndrome (Pickwickian Syn)

  10. Carol Yager (1960 – 1994) 730 KG BMI 252

  11. Acute respiratory failure develops over minutes to Hours No time for renal compen. pH is less than 7.3. clinical markers of chronic Hypoxemia- polycythemia corpulmonale Are absent Chronic respiratory failure develops over several days allowing time for renal compensation an increase in bicarbonat conc. pH -only slightly decreased. clinical markers of chronic hypoxemia polycythemia cor pulmonale Are present Acute and chronic respiratory failure

  12. Alveolar-to-arterial PaO2 difference (A-a Gradient) • Determines the efficiency of lungs at carrying out of respiration • Aa Gradient = (150 - 5/4(PCO2)) - PaO2 • Normal < 10mm • increase in alveolar-to-arterial PO2 above 15- 20 mm Hg indicates pulmonary disease as the cause of hypoxemia • Normal in Hypoventilation

  13. Signs Symptoms &

  14. Underlying disease process (pneumonia, pulmonary edema, asthma, COPD) • associated hypoxemia • hypercapnia

  15. Hypoxemia • Symptoms • shortness of breath • confusion & restlessness • Seizures • coma • Signs • Cyanosis • variety of arrhythmias from hypoxemia & acidosis • Polycythemia – in long-standing hypoxemia

  16. Asterix Hypercapnia • Vasodilation leading to • Morning headache • flushed skin & warm moist palms • full & bounding pulse • Extrasystoles & other arrythmias • muscle twitches • flapping tremors - asterixis • drowsiness

  17. ? Now answer this question- If you are forced to choose one of these, which one you will like to have Hypoxia Hypercapnia

  18. INVESTIGATIONS

  19. . • A.B.G. (arterial blood gases) • complete blood count • anemia • contribute to tissue hypoxia • polycythemia • indicate chronic hypoxemic respiratory failure • Associated organ involvement • R.F.T. • L.F.T.

  20. Chest radiograph • frequently reveals the cause of respiratory failure • distinguishes between • cardiogenic • noncardiogenic pulmonary edema Echocardiography • when cardiac cause of acute respiratory failure is suspected • left ventricular dilatation • regional or global wall motion abnormalities • severe mitral regurgitation • provides an estimate of right ventricular function and pulmonary artery pressure in patients with chronic hypercapnic respiratory failure

  21. Other Tests • PFT • in the evaluation of chronic respiratory failure • ECG • to evaluate the possibility of a cardiovascular cause of respiratory failure • dysrhythmias resulting from severe hypoxemia and/or acidosis

  22. TREATMENT

  23. Hypoxemia • major immediate threat to organ function • oxygen supplementation and/or ventilatory assist devices • The goal is to assure adequate oxygen delivery to tissues, generally achieved with a • PaO2 of 60 mm Hg or more • SaO2 of greater than 92%

  24. Supplemental oxygen administered via • nasal prongs • face mask • in severe hypoxemia, intubation and mechanical ventilation often are required • Airway management • Adequate airway vital in a patient with acute respiratory distress • The most common indication for endotracheal intubation (ETT) is respiratory failure • What is the role of tracheostomy??

  25. Hypercapnia without hypoxemia • generally well tolerated • not a threat to organ function • hypercapnia should be tolerated until the arterial blood pH falls below 7.2 • hypercapnia and respiratory acidosis managed by • correcting the underlying cause • providing ventilatory assistance • Treatment of coexisting condition with approptiate drugs

  26. VENTILATION MECHANICAL

  27. Mechanical ventilation is a method to • mechanically assist or • replace spontaneous breathing

  28. Mechanical Ventilatior What is it? • Machine that generates a controlled flow of gas into a patient’s airways • Oxygen and air are received from cylinders or wall outlets blended according to the prescribed inspired oxygen tension (FiO2) • Delivered to the patient using one of many available modes of ventilation.The magnitude of rate and duration of flow are determined by the operator

  29. Ventilatory workload is increased by loss of lung compliance • inspiration/ventilation is usually supported to reduce O2 requirements and increase patient comfort

  30. Respiratory failure is caused by 1. Failure to ventilate • characterized by increased PCO2 2. Failure to oxygenate • characterized by decreased PaO2

  31. Failure to ventilate • Increase the patient’s alveolar ventilation • rate • depth of breathing by using mechanical ventilation

  32. Failure to oxygenate • Restoration and maintenance of lung volumes by using recruitment maneuvers • Recruitment maneuvers are used to reinflate collapsed alveoli: due to pressure generated by ventilator during inspiration alveoli are inflated • PEEP is used to prevent derecruitment

  33. What do we mean by PEEP ? Girl’s changing room

  34. PEEP • amount of pressure above atmospheric pressure present in the airway at the end of the expiratory cycle • PEEP improves gas exchange by • preventing alveolar collapse • recruiting more lung units • increasing functional residual capacity • redistributing fluid in the alveoli

  35. Dangers of PEEP • Overdistension of lungs – Barotrauma • Will increase intracranial tension • Reduce venous return to right side of heart leading to • reduced cardiac out put & hypotension • The ideal level of PEEP is that which prevents derecruitment of the majority of alveoli, while causing minimal overdistension

  36. Modes of ventilation: • Air flow continues until • a predetermined volume has been delivered – volume controlled • airway pressure generated – pressure controlled

  37. Flow reverses, when the machine cycles into the expiratory phase, the message to do this is • either at a preset time • preset tidal volume • preset percentage of peak flow

  38. Mechanical breaths may be • Controlled (Controlled mandatory ventilation -CMV) • ventilator is active • patient passive • assisted (Synchronised intermittent mandatory ventilation - SIMV) • patient initiates and may or may not participate in the breath

  39. Synchronized Intermittent Mandatory Ventilation(SIMV) • method of partial ventilatory support to facilitate liberation from mechanical ventilation • patient could breathe spontaneously while also receiving mandatory breaths • As the patient’s respiratory function improved, the number of assisted is decreased, until the patient breaths unassisted

  40. Iron Lung

  41. CONDITIONS REQUIRING MECHANICAL VENTILATION

  42. SCIENCE & ARTS Of mechanical ventilation

  43. Large tidal volumes overstretch alveoli and injure the lungs Small tidal volumes increase the contribution to dead space – wasted ventilation

  44. Large PEEP overstretch alveoli and injure the lungs Small PEEP does not correct V/Q mismatch & derecruitment

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