Mechanical ventilation (main): Difference between revisions
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==Modes==
==Background==
===Assist Control (AC)===
*Intubation and ventilation typically required for [[respiratory failure]] or airway protection/severe [[altered mental status]]
#(helps instigated breaths, extra breaths all of set TV)
## preset rate and TV
## pt able to trigger additional breaths (full assisted tidal volume)
#spontaneous breathing (above rate) is not allowed
#beneficial for patients requiring a high minute-ventilation (reduces oxygen consumption and CO2 production of the respiratory muscles)
#may worsen obstructive airway disease by air trapping or breath stacking


===Synchronous Intermittent Mandatory Ventilation (SIMV)===
===Categories of [[respiratory failure|Respiratory Failure]]===
#senses not to give with breathing if present, extra breaths of pt's TV
*Type 1 - [[Hypoxemia]]
#preset breaths in coordination with the respiratory effort
*Type 2 - [[hypercapnia|Hypercarbia]]
#spontaneous breathing allowed between breaths
*Type 3 - Perioperative
#synchronization attempts to limit the barotrauma by not delivering a breath when already maximally inhaled (vs. IMV)
*Type 4 - [[Shock]]
# for each additional breath triggered by pt, vent delivers variable TV depending on pt effort and condition of lung
# because of need for pt effort, not recommended for tired or septic pt


===Pressure Support (PS)===
==Patient Positioning<ref>Greenwood J. Good Lung UP or DOWN? Maneuvers to Improve Oxygenation in Acute Respiratory Failure. Updated 7/15/2014. https://umem.org/educational_pearls/2464/.</ref>==
#controls via pressure, good if pressures getting too high
*HOB elevation > 30 degrees
#limits barotrauma and decreases the work of breathing in the spontaneously breathing patient
*Reverse trendelenberg at 30 degrees in obese hypoventilaters
#level of pressure set (not TV) to assist spontaneous efforts
*Lateral decubitus for severe unilateral lung disease
#most ventilators allow back-up respiratory rate (in case of apnea)
**'''G'''ood lung to '''G'''round generally
#mode of choice in patients whose respiratory failure is not severe and who have an adequate respiratory drive (improved patient comfort, reduced cardiovascular effects, reduced risk of barotrauma, and improved distribution of gas)
**Good lung UP in these exceptions:
***Massive [[hemoptysis]] - prevent blood into dependent, good lung
***Large [[abscess]] - pus fills up dependent lung
***Unilateral [[emphysema]] - prevent hyperinflation


^For the paralyzed patient, there is no difference in minute-ventilation or airway pressures between A/C and SIMV
==See Also==
 
{{Mechanical ventilation pages}}
===CPAP===
{{Related Difficult Airway Pages}}
# needs spont breathing pt
# not for fatiguing pt
# no back up rate
 
===Control Mode===
# only in OR
# machine initiates and delivers breath
# fixed rate and TV


==Settings==
== Calculators ==
See:
{{Aa_Gradient_Calculator}}
*[[Ventilation (Settings)]]
*[[Ventilation (Weaning)]]
*[[Ventilation (Management)]]


==See Also==
==External Links==
*[[Ventilation (Non-Invasive)]]
*Vent basics resource: https://emcrit.org/wp-content/uploads/2010/05/Managing-Initial-Vent-ED.pdf


==References==
<references/>


[[Category:Airway/Resus]]
[[Category:Critical Care]]
[[Category:Pulm]]
[[Category:Pulmonary]]

Latest revision as of 16:32, 21 March 2026

Background

Categories of Respiratory Failure

Patient Positioning[1]

  • HOB elevation > 30 degrees
  • Reverse trendelenberg at 30 degrees in obese hypoventilaters
  • Lateral decubitus for severe unilateral lung disease
    • Good lung to Ground generally
    • Good lung UP in these exceptions:
      • Massive hemoptysis - prevent blood into dependent, good lung
      • Large abscess - pus fills up dependent lung
      • Unilateral emphysema - prevent hyperinflation

See Also

Mechanical Ventilation Pages

Airway Pages

Calculators

A-a O₂ Gradient

Alveolar-arterial (A-a) O₂ Gradient
Parameter Value
Age (years)
FiO₂ (%)
PaCO₂ (mmHg)
PaO₂ (mmHg)
A-a Gradient mmHg
Expected A-a mmHg (age-adjusted normal)
Interpretation
  • Normal A-a gradient ≈ (Age/4) + 4 on room air
  • Elevated A-a gradient suggests: V/Q mismatch, shunt, or diffusion impairment
  • Normal A-a gradient + hypoxia suggests: hypoventilation or low FiO₂
References
  • Formula: A-a = [FiO₂ × (Patm – PH2O)] – (PaCO₂/0.8) – PaO₂
  • Kanber GJ, et al. The alveolar-arterial oxygen gradient in young and elderly men during air and oxygen breathing. Am Rev Respir Dis. 1968;97(3):376-381. PMID 5637791.

External Links

References

  1. ↑ Greenwood J. Good Lung UP or DOWN? Maneuvers to Improve Oxygenation in Acute Respiratory Failure. Updated 7/15/2014. https://umem.org/educational_pearls/2464/.
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