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Physiology of mechanical ventilation upload

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A simple presentation about the physiology of mechanical ventilation...

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Physiology of mechanical ventilation upload

  1. 1. PHYSIOLOGY OFMECHANICAL VENTILATION Dr Deepa C MD
  2. 2. The Origin of Mechanical Ventilation“But that life may…be restored to the animal, an openingmust be attempted in the trunk of the trachea, in which atube of reed or cane should be put; you will then blow intothis, so that the lung may rise again and the animal take inair. …and as I do this, and take care that the lung is inflatedin intervals, the motion of the heart andarteries does not stop…” Andreas Wesele Vesalius, 1543
  3. 3. RESPIRATORY SYSTEM• Ventilating pump - Respiratory control centres in the brain - Connecting tracts and nerves - Chest wall and respiratory muscles• Gas-exchange system - Lungs
  4. 4. Intrapleural-10 cm H₂O Intrapleural -2.5 cm H₂O
  5. 5. POSITIVE PRESSURE VENTILATIONInflate the lungs by exerting positive pressureon the airway  forcing the alveoli to expandduring inspiration
  6. 6. SPONTANEOUS Patm Palv ∆P Flow BREATHING Inspiration 0 -1 +1 Into lungsEnd-inspiration 0 0 0 No flow Expiration 0 +1 -1 Out of lungsEnd-expiration 0 0 0 No flowPOSITIVE PR. Pinsp Palv ∆P FlowVENTILATION Inspiration 20 0 +20 Into lungsEnd-inspiration 20 20 0 No flow Expiration 0 20 -20 Out of lungsEnd-expiration 0 0 0 No flow
  7. 7. TRANSMURAL PRESSURE “Pressure across the wall”Difference in pressure between the inside (Pi) and theoutside (Po) of any structure EQUILIBRIUM VOLUME of a structureThe volume it contains when the transmural pressure(Pi - Po) is zero
  8. 8. LUNG COMPLIANCE (DISTENSIBILITY)- change in volume per unit change in pressure - ∆V/∆P Static compliance = Tidal volume Pplat – PEEP (measured when there is no air flow) Dynamic compliance = Tidal volume Ppeak – PEEP (measured when air flow is present)
  9. 9. ELASTANCEThe retractive (recoil) force generated by therecoil of an elastic structureInversely related to complianceA less compliant lung has higher elastance
  10. 10. RESISTANCE Resistance = ∆P/Flow Inversely proportional to R⁴WORK OF BREATHING - work performed bythe respiratory muscles in stretching theelastic tissues of the chest wall and lungs(elastic work – 65%), moving inelastictissues(7%) and moving air through therespiratory passages(28%)
  11. 11. Pplat & Ppeak• PLATEAU PRESSURE - is the pressure needed to maintain lung inflation in the absence of air flow• Measured by occluding the ventilator 3-5 sec at the end of inspiration• PEAK INSPIRATORY PRESSURE - Pressure used to deliver the tidal volume by overcoming non- elastic (airways) and elastic (lung parenchyma) resistance
  12. 12. PENDELLUFT EFFECT
  13. 13. A. Increased Airway B. Decreased Compliance Resistance of Lungs & Chest Wall PIP PIP Pplat Pplat
  14. 14. Tidal Volume = Inspiratory Flow x Inspiratory Time (ml) (ml/sec) (sec) ∆ Pressure = Inspiratory Flow x Resistance ∆ Pressure = Ppeak – Pplat
  15. 15. DEAD SPACE & SHUNT DEAD SPACE – wasted ventilation(no gas exchange due to absent perfusion) eg.; pulmonary embolism SHUNT – wasted perfusion eg.; atelectatic segment, one-lung ventilation
  16. 16. POSITIVE END EXPIRATORY PRESSURE (PEEP)Increases the end expiratory or baseline airwaypressure to a value greater than atmospheric pr. onventilator manometerINDICATIONS• Intrapulmonary shunt and refractory hypoxemia• Decreased FRC and lung compliance• Useful in maintaining pulmonary function in non- cardiogenic pulmonary edema, especially ARDS
  17. 17. PHYSIOLOGY OF PEEPOpens up collapsed alveoli and prevents alveolarcollapse during exhalation PEEP Decreases alveolar distending pressure Increases FRC by alveolar recruitment Improves ventilation Increases V/Q, improves oxygenation, decreases work of breathing
  18. 18. • Prevents early airway closure and alveolar collapse at the end of expiration• Increases(and normalizes) the functional residual capacity (FRC) of the lungs• Facilitates better oxygenation Note: PEEP is intended to improveoxygenation, not to provide ventilation, whichis the movement of air into the lungs followedby exhalation
  19. 19. Increases surface area for gas exchange by opening the collapsed alveoliTranslocation of fluid to peribroncheal region in pulm edema
  20. 20. DISEASES WHERE PEEP IS USED • ARDS/ALI • Cardiogenic pulmonary edema • Unilateral lung ventilation & postop hypoxemia • COPDCOMPLICATIONS ASSOCIATED WITH PEEP • Barotrauma • Diminish cardiac output • Regional hypoperfusion • Augmentation of I.C.P. • Paradoxical hypoxemia • Hypercapnoea and respiratory acidosis
  21. 21. SPONTANEOUS BREATHING
  22. 22. POSITIVE PRESSURE BREATHS
  23. 23. Indications for mechanical ventilation • Ventilatory failure • Oxygenation failure • Excessive ventilatory workload • Impending respiratory failure
  24. 24. VENTILATORY FAILURE Drug overdose Spinal cord injury Head injury & stroke Neuromuscular dysfunction Sleep disorders Acute airflow obstruction Chest trauma Postoperative – thoracic & upper abdominal Electrolyte imbalance General anaesthesia
  25. 25. OXYGENATION FAILURE &INCREASED VENTILATORY WORKLOAD  Acute lung injury/ARDS  Acute severe airflow obstruction  Dead space ventilation  Shunts  Congenital heart diseases  Shock  High metabolic rate & Obesity  General anaesthesia & Postop
  26. 26. GOALS OF MECHANICAL VENTILATION Maintain patient comfort Allow a normal, spontaneous breathing pattern whenever possible Maintain a PaCO₂ between 35 - 45 mmHg Maintain a PaO₂ sufficient to meet cellular O₂ demands but avoid oxygen toxicity Avoid acid-base and electrolyte imbalances Avoid respiratory muscle fatigue and atrophy
  27. 27. EFFECTS OF POSITIVE PRESSURE VENTILATION Decrease in venous return Decrease in cardiac output Decrease in pulmonary capillary blood flow Increase in pulmonary vascular resistance Increase in central venous pressure Increased intracerebral venous pressure Decreased CSF absorption Increased intraabdominal pressure
  28. 28. Contd… Increased vasopressin secretion Decreased GFR & urine output Increased fluid retention Paradoxical fall in PaO₂ Barotrauma/volutrauma Ventilator-associated pneumonia Oxygen toxicity Prolonged intubation – airway problems Pressure sores Ventilator dependence
  29. 29. AUTO-PEEP or INTRINSIC PEEP Airflow obstruction Low I:E ratios Increased respiratory rate Low flowsLeads to dynamic hyperinflation
  30. 30. AUTO-PEEP or INTRINSIC PEEP
  31. 31. DYNAMIC HYPERINFLATION Expiratory flow obstruction Increased rate Decreased expiratory time
  32. 32. MONITORING Physical examination for all body systems focusing on the resp system Assess the patient for decreased cardiac output Administer a sedative as ordered to relax the patient Evaluate the settings of mechanical ventilator Ensure patient safety ( side rails )..
  33. 33. Thank you

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