MECHANICAL VENTILATION

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MECHANICAL VENTILATION

• KENNEY WEINMEISTER M.D.

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INDICATIONS FOR MV

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

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INDICATIONS CONTINUED

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

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TYPES OF CONVENTIONAL MV

• Timed cycled
• Home ventilators
• Pressure cycled
• Pressure controlled
• Volume cycled
• Flow cycled
• Pressure support

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VOLUME VENTILATION

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

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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 IE ratio

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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

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PRESSURE CONTROLED VENTILATION

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

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SETTINGS FOR PRESSURE CONTROL VENTILATION

• Inspiratory pressure
• IE ratio
• 12, 11, 21, 31
• Rate
• FIO2
• Peep

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PRESSURE REGULATED VOLUME CONTROLLED

• Ventilate with pressure control
• Preset volume
• Inspiratory pressure is adjusted breath to breath
• Minute ventilation is maintained

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INDICATIONS FOR PEEP

• ARDS
• Stabilize chest wall
• Physiologic peep
• Decrease Auto-peep?

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CONTRAINDICATIONS FOR PEEP

• Increased intracranial pressure
• Unilateral pneumonia
• Bronchoplueral fistulae

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PEEP

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

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TROUBLE SHOOTING VOLUME VENTILATION

• High pressure alarm
• Breath sounds
• CXR
• Low tidal volume
• disconnected
• Desaturation

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TROUBLE SHOOTING PRESSURE VENTILATION

• Low tidal volumes or minute ventilation
• Desaturation
• Breath sounds
• Patient agitation
• CXR

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Sedation in Mechanically Ventilated Patients

• Benzodiazepines
• Opioids
• Neuroleptics
• Propofol
• Ketamine
• Dexmedetomidine

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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

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Opioid

• Morphine
• Fentanyl
• Hydromorphone

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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

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Propofol

• Side Effect
• Hypotension
• Bradycardia
• Anticonvulsant
• Expensive
• Use short term

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Ketamine

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

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Dexmedetomidine

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

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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

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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

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Neuromuscular Blocking Agents

• Depolarizing
• Bind to cholinergic receptors on the motor
  endplate
• Nondepolarizing
• Competitively inhibit Ach receptor on the motor
  endplate

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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

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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

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No bubble is so iridescent or floats longer than
that blown by the successful teacher.Sir
William Osler
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MV IN OBTRUCTIVE AIRWAY DISEASE

• Decrease barotrauma
• related to mean airway pressure
• Increase IE
• decrease TV and/or increase flow
• Minimize auto-peep
• auto-peep shown to cause most barotrauma
• Permissive hypercapnea

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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

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Ventilation With Lower Tidal Volumes

• Tidal volume 6 ml/kg
• Male 50 0.91(centimeters of height-152.4)
• Female 45.50.91(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

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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

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Case example continued

• Examine patient
• CXR
• Sedate
• Assess auto-peep
• Increase IE
• Lower PAP and MAP
• Reverse bronchospasm elect. Hypovent.

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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