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MECHANICAL VENTILATION

MECHANICAL VENTILATION. KENNEY WEINMEISTER M.D. INDICATIONS FOR MV. Hypoxemia Acute respiratory acidosis Reverse ventilatory muscle fatigue Permit sedation and/or neuromuscular blockade Decrease systemic or myocardial oxygen consumption. INDICATIONS CONTINUED.

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MECHANICAL VENTILATION

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  1. MECHANICAL VENTILATION KENNEY WEINMEISTER M.D.

  2. INDICATIONS FOR MV • Hypoxemia • Acute respiratory acidosis • Reverse ventilatory muscle fatigue • Permit sedation and/or neuromuscular blockade • Decrease systemic or myocardial oxygen consumption

  3. INDICATIONS CONTINUED • Reduce intracranial pressure through controlled hyperventilation • Stabilize the chest wall • Protect airway • Neurologic impairment • airway obstruction

  4. TYPES OF CONVENTIONAL MV • Timed cycled • Home ventilators • Pressure cycled • Pressure controlled • Volume cycled • Flow cycled • Pressure support

  5. VOLUME VENTILATION • Controlled mechanical ventilation CMV • Assist-control AC • Synchronized intermittent mandatory ventilation SIMV • Which mode?

  6. VENTILATOR SETTINGS • Tidal volume • 10 to 15 mL/kg • Respiratory rate • 10 to 20 breaths/minute • normal minute ventilation 4 to 6 L/min • Fraction of inspired oxygen • Flow rate and I:E ratio

  7. PRESSURE SUPPORT VENTILATION • Flow cycled • preset pressure sustained until inspiratory flow tapers to 25% of maximal value • Comfortable • Used mainly as a weaning mode • Wean pressure until equivalent to air way resistance • peak - plateau pressure

  8. PRESSURE CONTROLED VENTILATION • Pressure cycled • Volume varies with lung mechanics • Minute ventilation is not assured • Improves oxygenation • recruitment of alveoli • Lessens volutrauma?

  9. SETTINGS FOR PRESSURE CONTROL VENTILATION • Inspiratory pressure • I:E ratio • 1:2, 1:1, 2:1, 3:1 • Rate • FIO2 • Peep

  10. PRESSURE REGULATED VOLUME CONTROLLED • Ventilate with pressure control • Preset volume • Inspiratory pressure is adjusted breath to breath • Minute ventilation is maintained

  11. INDICATIONS FOR PEEP • ARDS • Stabilize chest wall • Physiologic peep • Decrease Auto-peep?

  12. CONTRAINDICATIONS FOR PEEP • Increased intracranial pressure • Unilateral pneumonia • Bronchoplueral fistulae

  13. PEEP • Increases FRC • Recruits alveoli • Improves oxygenation • Best Peep • based on lower inflection of pressure volume curve

  14. TROUBLE SHOOTING VOLUME VENTILATION • High pressure alarm • Breath sounds • CXR • Low tidal volume • disconnected • Desaturation

  15. TROUBLE SHOOTING PRESSURE VENTILATION • Low tidal volumes or minute ventilation • Desaturation • Breath sounds • Patient agitation • CXR

  16. Sedation in Mechanically Ventilated Patients • Benzodiazepines • Opioids • Neuroleptics • Propofol • Ketamine • Dexmedetomidine

  17. Benzodiazepines • Lorazepam • Half-life 12 to 15 hours • Major metabolite inactive • Midazolam • Half-life 1-4 hours, increased in cirrhosis, CHF, obesity, elderly • Active metabolite

  18. Opioid • Morphine • Fentanyl • Hydromorphone

  19. Neuroleptics • Haloperidol • Mild agitation .5mg to 2mg • Moderate agitation 2 to 5 mg • Severe 10 to 20 mg • Side Effects • Acute dystonic reactions • Polymorphic VT • Neuroleptic malignant syndrome

  20. Propofol • Side Effect • Hypotension • Bradycardia • Anticonvulsant • Expensive • Use short term

  21. Ketamine • Dissociative anesthetic state • Direct cardiovascular stimulant • Brochodilator • Side Effects • Dysphoric reactions • increased ICP

  22. Dexmedetomidine • Centrally acting alpha 2 agonist • Approved for 24 hours or less • Side Effects • Hypotension • Bradycardia • Atrial fibrillation

  23. Maintenance of Sedation • Titrate dose to ordered scale • Motor Activity Assessment Scale MAAS • Sedation-Agitation Scale SAS • Ramsay • Rebolus prior to all increases in the maintenance infusion • Daily interruption of sedation

  24. NEUROMUSCULAR BLOCKING AGENTS • Difficult to asses adequacy of sedation • Polyneuropathy of the critically ill • Use if unable to ventilate patient after patient adequately sedated • Have no sedative or analgesic properties

  25. Neuromuscular Blocking Agents • Depolarizing • Bind to cholinergic receptors on the motor endplate • Nondepolarizing • Competitively inhibit Ach receptor on the motor endplate

  26. Depolarizing NMBASuccinylcholine • Rapid onset less than 1 minute • Duration of action is 7-8 minutes • Pseudocholinesterase deficiency • 1 in 3200 • Side Effects • Hyperthermia, Hyperkalemia, arrhythmias • Increased ICP

  27. Nondepolarizing Agents • Pancuronium • Drug of choice for normal hepatic and renal function • Atracurium or Cisatracurium • Use in patients with hepatic and/or renal insufficiency • Vecuronium • Drug of choice for cardiovascular instability

  28. No bubble is so iridescent or floats longer than that blown by the successful teacher.Sir William Osler

  29. MV IN OBTRUCTIVE AIRWAY DISEASE • Decrease barotrauma • related to mean airway pressure • Increase I:E • decrease TV and/or increase flow • Minimize auto-peep • auto-peep shown to cause most barotrauma • Permissive hypercapnea

  30. ARDS • Set peep to pressure shown at lower inflection point of pressure volume curve • Tidal volumes set below upper inflection point of pressure volume curve • Use pressure control ventilation early • Minimize volutrauma

  31. Ventilation With Lower Tidal Volumes • Tidal volume: 6 ml/kg • Male 50 + 0.91(centimeters of height-152.4) • Female 45.5+0.91(centimeters of ht - 152.4) • Decrease or Increase TV by 1ml/kg to maintain plateau pressure 25 to 30. • Minimum TV 4ml/kg • PaO2 55 - 88 mm Hg. Sats 88 to 95% • pH 7.3 to 7.45

  32. CASE EXAMPLE • 34 y/o female admitted with status asthmaticus and respiratory failure • You are called to see patient for inability to ventilate • Tidal volume 800 cc, FIO2 100%, AC 12 Peep 5 cm • PAP 70, returned TV 200 cc

  33. Case example continued • Examine patient • CXR • Sedate • Assess auto-peep • Increase I:E • Lower PAP and MAP • Reverse bronchospasm & elect. Hypovent.

  34. CONCLUSION • Three options for ventilation • volume, pressure, flow • Peep, know when to say no • Always assess to prevent barotrauma • ventilate below upper inflection point • assess static compliance daily • monitor for auto-peep

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