Mechanical Ventilation
Last updated: 26-Nov-2011 2:23 PM 
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Indications for Mechanical Ventilation

Mechanical ventilation is indicated for acute or chronic respiratory failure (insufficient oxygenation and/or aveolar ventilation).  Should be considered early in course of illness and not delayed until emergent need.

  • Acute Pulmonary Parenchymal Disease
    • Pneumonitis - infectious, aspiration, inhalation injury
    • ARDS/ALI
  • Cardiogenic Pulmonary Edema
    • Acute MI
    • Cardiomyopathy
    • Intravascular overload
  • Severe Sepsis/Septic Shock
  • Airway Disease
    • COPD
    • Asthma
  • Neurologic Condition
    • Drug Overdose
    • Guillain-Barre
    • Myasthenia gravis
    • Chest wall disease
  • Chest Trauma
  • General anesthesia

The decision to intubate should be based on clinical judgement of entire clinical situation.  Some clinical findings supporting intubation:

Loss of ventilatory reserve
Respiratory rate >35 breaths/min
Tidal volume <5 mL/kg
Vital capacity <10 mL/kg
Negative inspiratory force Weaker than -25 cmH20
Minute ventilation <10 L/min
Rise in PCO2 >10 mmHg
Refractory hypoxemia
Alveolar-arterial gradient (FiO2 = 1.0) >450
PaO2/PAO2 <0.15
PaO2 with supplemental O2

<55 mmHg

General Principles

  • Minute ventilation of 8-10mL/kg based on ideal body weight for height
  • Respiratory rate of 12-16 
  • Keep in mind patient's chronic conditions and existing compensatory processes

General Principles for ARDS/ALI

  • Low Tidal Volumes
    • 6mL/kg based on ideal body weight
    • Reduce ventilator-associated lung injury on top of exisitng acute insult
    • Compensate for adequate minute ventilation with increased respiratory rate
  • High PEEP
    • Recruits collapsed alveoli
      • Improved oxygenation
      • Reduction of alveolar overdistension with more alveoli sharing each tidal breath
      • Reduction of cyclic atelectasis injury
    • Increase PEEP until plateau airway pressure of 28-30 cm H20 is reached

General Principles for COPD/Asthma

  • Decreased Respiratory Rate
    • 4 breaths per minute less than patient's normal RR.  Usually 8-10 respirations per minute
    • Allows for adequate expiration, decreasing auto-PEEP/hyperinflation
  • Lower Tidal Volumes
    • 7-8mL/kg based on ideal body weight
    • Reduces hyperinflation
    • Decreases alveolar overdistension in already stiff lungs
  • PEEP
    • Reduces work of breathing without aggravating hyperflation
    • Aim for 80% or less of auto-PEEP

References

  • Courey A, Hyzy R. Overview of mechanical ventilation. UpToDate, Feb 2, 2010. www.uptodate.com
  • Siegel M, Hyzy R. Mechanical ventilation in acute respiratory distress syndrome. UpToDate, Oct 10, 2011. www.uptodate.com
  • Jubran A, Tobin M. Mechanical ventilation in acute respiratory failure complicating COPD. UpToDate, Aug 30, 2011. www.uptodate.com
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