Download mechanical ventilation

MECHANICAL VENTILATION
KENNEY WEINMEISTER M.D.
INDICATIONS FOR MV
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Hypoxemia
Acute respiratory acidosis
Reverse ventilatory muscle fatigue
Permit sedation and/or neuromuscular
blockade
• Decrease systemic or myocardial oxygen
consumption
INDICATIONS CONTINUED
• Reduce intracranial pressure through
controlled hyperventilation
• Stabilize the chest wall
• Protect airway
– Neurologic impairment
– airway obstruction
TYPES OF
CONVENTIONAL MV
• Timed cycled
– Home ventilators
• Pressure cycled
– Pressure controlled
• Volume cycled
• Flow cycled
– Pressure support
VOLUME VENTILATION
• Controlled mechanical ventilation CMV
• Assist-control AC
• Synchronized intermittent mandatory
ventilation SIMV
• Which mode?
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
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
PRESSURE CONTROLED
VENTILATION
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Pressure cycled
Volume varies with lung mechanics
Minute ventilation is not assured
Improves oxygenation
– recruitment of alveoli
• Lessens volutrauma?
SETTINGS FOR PRESSURE
CONTROL VENTILATION
• Inspiratory pressure
• I:E ratio
– 1:2, 1:1, 2:1, 3:1
• Rate
• FIO2
• Peep
PRESSURE REGULATED
VOLUME CONTROLLED
• Ventilate with pressure control
• Preset volume
• Inspiratory pressure is adjusted breath to
breath
• Minute ventilation is maintained
INDICATIONS FOR PEEP
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ARDS
Stabilize chest wall
Physiologic peep
Decrease Auto-peep?
CONTRAINDICATIONS FOR
PEEP
• Increased intracranial pressure
• Unilateral pneumonia
• Bronchoplueral fistulae
PEEP
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Increases FRC
Recruits alveoli
Improves oxygenation
Best Peep
– based on lower inflection of pressure volume
curve
TROUBLE SHOOTING
VOLUME VENTILATION
• High pressure alarm
– Breath sounds
– CXR
• Low tidal volume
– disconnected
• Desaturation
TROUBLE SHOOTING
PRESSURE VENTILATION
• Low tidal volumes or minute ventilation
• Desaturation
– Breath sounds
– Patient agitation
– CXR
Sedation in Mechanically
Ventilated Patients
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Benzodiazepines
Opioids
Neuroleptics
Propofol
Ketamine
Dexmedetomidine
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
Opioid
• Morphine
• Fentanyl
• Hydromorphone
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
Propofol
• Side Effect
– Hypotension
– Bradycardia
• Anticonvulsant
• Expensive
• Use short term
Ketamine
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Dissociative anesthetic state
Direct cardiovascular stimulant
Brochodilator
Side Effects
– Dysphoric reactions
– increased ICP
Dexmedetomidine
• Centrally acting alpha 2 agonist
• Approved for 24 hours or less
• Side Effects
– Hypotension
– Bradycardia
– Atrial fibrillation
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
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
Neuromuscular Blocking Agents
• Depolarizing
– Bind to cholinergic receptors on the motor
endplate
• Nondepolarizing
– Competitively inhibit Ach receptor on the
motor endplate
Depolarizing NMBA
Succinylcholine
• 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
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
No bubble is so iridescent or
floats longer than that blown by
the successful teacher.
Sir William Osler
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
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
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
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
Case example continued
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Examine patient
CXR
Sedate
Assess auto-peep
Increase I:E
Lower PAP and MAP
Reverse bronchospasm & elect. Hypovent.
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