Intern report PEARLS 2/25: mechanical ventilation, refractory hypoxemia respiratory failure, ECMO (and bonus on ILD and cocci)


Vent Basics – it’s about oxygenation (hypoxemia) and ventilation (hypercarbia)

  • Oxygenation – controlled by FiO2 and PEEP
  • Ventilation – controlled by respiratory rate and tidal volume


Modes of mechanical ventilation:

4 main modes we see in the ICU:

Mode Descriptions RR TV PS PEEP FiO2
Volume assist control Ventilator delivers a set # breaths/min, each w/ a set volume.  If pt triggers breath, ventilator delivers the set volume. Ö Ö   Ö Ö
Pressure control ventilation Ventilator delivers a set # breaths/min, each w/ a set inspiratory pressure (that’s greater than the PEEP). Ö   Ö Ö Ö
SIMV Ventilator delivers a set # breaths/min, each w/ a set volume. .  If pt triggers breath, ventilator does not deliver a set volume but provides a set pressure support. Ö Ö Ö Ö Ö
Pressure support Patient initiates all breaths and ventilator provides a set pressure support.     Ö Ö Ö


A few points we discussed:

  • This patient’s RR was quite high (in the 30s) which led to some discussion about a ddx:
    • 1) Inadequate sedation – the patient is uncomfortable and so they are tachypneic. These patients also often tend to be tachycardic, HTNsive
    • 2) Hypoxia – they are trying to compensate to increase their PaO2 (classically seen in PE)
    • 3) Resp compensation for metabolic acidosis (eg sepsis)
    • See recent blog post on respiratory alkalosis!
    • *remember for PS (which this patient was on), the pressure is set but the TV and RR are not.
    • *In ARDS, a patient is in VC mode and we aim for a lower TV (6cc/kg, as opposed to 8-10 cc/kg in normal lungs) with a higher RR.
  • The difference in peak and plateau pressures helps us determine resistance and can help narrow ddx:
    • Peak pressure is set in pts on Pressure Control or Pressure Support (and gives an idea to resistance in the airways + alveolar distention)
    • Plateau pressure is a measure of the dynamic resistance (resistance to alveolar distention)
    • A small delta (<10) suggests that there is an alveolar problem – eg PNA, ARDS, CHF, atelectasis (because there is high resistance in the alveoli, the plateau pressure is about as high as the peak pressure)
    • A big delta (>10) suggests that there is a problem in the airways – asthma, COPD, thick secretions, CF, kinked ETT (because there is low resistance in the alveoli so the plateau pressure is significantly lower than the peak pressure)


Management of Refractory Hypoxemia

  • Non-ventilator strategies:
    • Conservative use of fluids
    • Neuromuscular blockade
    • Prone positioning (contraindicated if unstable)
    • Inhaled NO
    • Consider ECMO
  • Ventilator strategies:
    • Increase PEEP (up to 20)
    • Increase inspiratory time
    • Increase inspiratory pressure
    • Recruitment maneuvers



  • Two types: VV (venovenous) and VA (venoarterial)
    • VV provides pulmonary bypass (heart needs to pump well for this to work!) (the oxygenated blood goes back into the IJ or RA and still needs to be pumped into the arterial system by the heart – can achieve PaO2 around 45-80 in a healthy heart)
    • VA provides cardiopulmonary bypass (the oxygenated blood goes into one of the big arteries – eg femoral artery often – can achieve PaO2 60-150)
  • Great diagram and table from a recent Cardiology AM report here:



BONUS: approach to ILD


BONUS: cocci serologies (old pearls:

  • Cocci COMPLEMENT FIXATION is QUANTITATIVE and correlates with disease activity!
    • Titer >1:16 = aggressive pulmonary disease OR disseminated disease


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