mechanical ventilation kenney weinmeister m.d. indications for mv hypoxemia acute respiratory...
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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 I:E 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
• I:E ratio– 1:2, 1:1, 2:1, 3:1
• 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 I:E– 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 45.5+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
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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 I:E
• 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