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Assessing the Need for Mechanical Ventilation

Assessing the Need for Mechanical Ventilation. Principle of Mechanical Ventilation. Disease path physiology. Respiratory failure mechanisms. Target the illness Avoid Complications. Mechanical Ventilation: Device. Introduction. Breathing. Ventilation. Respiration.

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Assessing the Need for Mechanical Ventilation

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  1. Assessing the Need for Mechanical Ventilation

  2. Principle of Mechanical Ventilation • Disease path physiology. • Respiratory failure mechanisms. • Target the illness • Avoid Complications.

  3. Mechanical Ventilation: Device

  4. Introduction Breathing Ventilation Respiration

  5. Breath to Ventilate to Respirate to Oxygenate • Always eat when you are hungry, • Always drink when you are dry, • Always wash when you are dirty, • Don't stop breathing, or you'll die!

  6. MV limit Breathing Moving air in and out the upper Airway Ventilation Moving air in and out the lungs External Respiration Gas exchange : Alveolar/Capillary level Internal Respiration Oxygen use by the body cells

  7. Non Respiratory functionOf the Respiratory system

  8. Principle of Mechanical Ventilation Neuromuscular Disorders

  9. Definitions • Acute respiratory failure occurs when: • pulmonary system is no longer able to meet the metabolic demands of the body • Hypoxaemic respiratory failure: • PaO2 < 60 mmhg when breathing room air • Hypercapnic respiratory failure: • PaCO2 >50 mmhg

  10. Assessment for the needfor Mechanical ventilation Circulation or labs Hypoxia, hypercapnia

  11. Decrease GCS Neuromuscular CVA COPD Asthma Mechanical Ventilator challenge Airway secretions Stridor Bleeding Pneumonia Atelectasis Pulmonary emboli Edema

  12. Gas Excange Mechanical Ventilation- 1

  13. Mechanical Ventilator challenge

  14. Oxygen in • Depends on • PAO2 • Diffusing capacity/ Diffusioncoeffecient • Surface are of membrane available for gas trnasfusion • Membrane thickness • Perfusion • Ventilation-perfusion matching • MV • Increase PAo2 • Improve Atelectasis • Improve ventilation V gas = A* D* (P1-P2)/ T

  15. MV increase Oxygenation PAO2= PiO2 – PACo2 ( FiO2+ 1-FiO2 ) For FiO2 less than 0.6 PAO2 = FiO2 (PB- PH2O) – Paco2 * 1.2 R PAO2 = FiO2 ( 760- 47) – PaCOco2 * 1.2 Ideal Alveolar Air Equation

  16. Pio2= 160 Pico2= 0.3 Peo2= 120 Peco2= 27 PAo2= 104 PAco2= 40 PAo2= 104 PAo2= 40 Pao2= 104 Pvco2= 40 Pvo2= 40 Pvco2= 45 Pao2= 104 Pvco2= 40 P02= 40 Pco2= 45 Po2= 40 Pco2= 45 Tissue Cells

  17. Most common causes of Hypoxia FIO2 Ventilation without perfusion (deadspace ventilation) Hypoventilation Diffusion abnormality Normal Perfusion without ventilation ( shunting)

  18. Normal V/ Q matching

  19. V/Q mismatch: shunting, Dead Space Perfusion

  20. Qs/ QT= CcO2- CaO2 / Cco2 – CvO2 Shunting QT Qc Qs PAO2=104 mmHgPACO2= 45 mmHg CcO2 CvO2

  21. MV and Shunting • Intra-cardiac • Any cause of right to left shunt • egFallot’s, Eisenmenger • Intra-pulmonary • Pneumonia • Pulmonary oedema • Atelectasis • Collapse • Pulmonary haemorrhage or contusion

  22. Mechanical Ventilation and Shunt Qs/ QT= CcO2- CaO2 / Cco2 – CvO2 CaO2= HG * 1.34 * SaO2 + PaO2 * 0.003 CcO2= HG * 1.34 * FiO2 + PAO2 * 0.003

  23. FIO2 Ventilation without perfusion (dead space ventilation) Hypoventilation Diffusion abnormality Normal Perfusion without ventilation (shunting)

  24. Dead Space Perfusion PAO2=104mmHg PACO2=40 mmHg

  25. MV and Dead Space Perfusion • Pulmonary emboli • Low blood pressure • Blood loss • Cardiac pump failure • High intra alveolar pressure • Inappropriate massive vasodilatation

  26. Pulmonary Fibrosis Pulmonary edema Thick Alveolar secretions Diffusion abnormalities PAO2=104 PACO2=45 75% 92%

  27. Hypoventilation Brainstem Spinal cord Airway Nerve root Nerve Lung Pleura Neuromuscular junction Chest wall Respiratory muscle Sites at which disease may cause ventilatory disturbance

  28. Co2 wash-out Mechanical Ventilation Challenge-2

  29. Carbon Dioxide Elimination

  30. CO2 elimination= 200 ml/L CO2 elimination= 200 ml/L Hypoventilation PACO2= 80mmHg VA= 2 L/min PACO2= 80 mmHg VA= 4 L/min PACO2= 40 mmHg Plasma PaCO2= 40 Plasma PaCO2= 80 CO2 (1.2 mmol) + H2O ==== H2Co3 (1 molecule) === Hco3 + H CO2 (2.4 mmol) + H2O ==== H2Co3 (2 molecule) === Hco3 + H CO2 Production 200 ml/min Fever, Seizures, Hyper metabolic state Overfeeding Hyperthyroidism

  31. Work of Breathing MV challenge-3 Resistance and Elastance

  32. Force length

  33. Parenchyma Airways Resistance to Flow Resistance to Expansion Elastics Raw Pressure E Pressure R Volume Flow Pmus = Resistance x flow+Elastance x volume

  34. Asthma, COPD Secretions Croup, Epiglottitis WOB: Mechanical Ventilation Pleural Effusion, Pneumothorax Alveolar Edema Ascites Obesity

  35. summery • Restore breathing and protect airways • Optimize Minute Ventilation • Improve ventilation/perfusion relationship • Decrease work of breathing • Improve oxygenation

  36. summery • Does not correct every path physiology of respiratory failure. • Corrects only certain types of hypoxia • Does not replace the non respiratory function of the lungs. • Using Mechanical Ventilation without knowing the mechanism of a particular respiratory failure could be detrimental.

  37. Thank You Thank You

  38. Mechanical Ventilation: Indications • Ventilation abnormalities • Respiratory muscle dysfunction • Respiratory muscle fatigue • Chest wall abnormalities • Neuromuscular disease • Decreased ventilatory drive • Increased airway resistance and/or obstruction

  39. Mechanical Ventilator challenge

  40. Volume Flow

  41. Pmus = Elastance x volume + Resistance x flow

  42. Mechanical Ventilation: Indications • Oxygenation abnormalities • Refractory hypoxemia • Need for positive end-expiratory pressure (PEEP) • Excessive work of breathing Demands Alveolar ventilation

  43. Oxygen Carbon dioxide Water vapour Nitrogen

  44. Oxygen in • Depends on • PAO2 • FIO2 • PACO2 • Alveolar pressure • Ventilation • Diffusing capacity • Perfusion • Ventilation-perfusion matching

  45. Pmus +Pvent = elastance x volume + resistance x flow Unassisted spontaneous inspiration P mus= elastance x volume + resistance x flow Assisted ventilation of a paralyzed patient P vent = elastance x volume + resistance x flow

  46. Oxygenation The primary goal of oxygenation is to maximize O2 delivery to blood (PaO2) • Alveolar-arterial O2 gradient (PAO2 – PaO2) • Equilibrium between oxygen in blood and oxygen in alveoli • A-a gradient measures efficiency of oxygenation • PaO2 partially depends on ventilation but more on V/Q matching • Oxygenation in context of ICU • V/Q mismatching • Patient position (supine) • Airway pressure, pulmonary parenchymal disease, small-airway disease • Adjustments: FiO2 and PEEP V/Q Matching. Zone 1 demonstrates dead-space ventilation (ventilation without perfusion). Zone 2 demonstrates normal perfusion. Zone 3 demonstrates shunting (perfusion without ventilation).

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