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Refractory Hypoxemia

Amelia Muhs

Background

  • Inadequate arterial oxygenation despite high levels of inspired O2 or the development of barotrauma in mechanically ventilated pts
  • Generally start to consider the interventions below if needing FiO2 >80%
  • Differential:
    • Worsening underlying primary process (e.g. progressive ARDS)
    • PE
    • Pneumothorax
    • Fluid overload
    • Ventilator-associated Pneumonia
    • New ARDS

Evaluation:

  • Always get CXR STAT if pt has new or worsening O2 requirement
  • ABG
  • Can use POCUS to check for lung sliding (pneumothorax) or RV enlargement/septal bowing/McConnell’s sign (RV strain in PE)

Initial management

  • Remember – if at any point the pt is rapidly decompensating, you can always disconnect them from the vent and bag them until they recover/while calling for help
  • Early consideration of ECMO consult in appropriate pts (discuss with MICU fellow)
  • Optimize fluid status -> consider diuresis/dialysis if not making urine
  • Consider higher PEEP strategy
    • Increased PEEP -> higher mean airway pressure, generally improves oxygenation especially with diffuse pulmonary pathologies
      • Exceptions may include certain focal/shunt pathologies (e.g. dense lobar PNA)
      • Worsening oxygenation may occur with overdistension of alveoli -> increase dead space ventilation; generally determined empirically at the bedside
    • Titrate up slowly; generally do not exceed PEEP 18
      • Limited by high plateau pressures/barotrauma, overdistension/dead space ventilation, decreased preload/venous return
    • ARDSnet FiO2/PEEP Tables: At VUMC we typically use the Lower PEEP table

Lower PEEP/higher FiO₂

FiO₂ 0.3 0.4 0.4 0.5 0.5 0.6
PEEP 5 5 8 8 10 10
FiO₂ 0.7 0.7 0.7 0.8 0.9 0.9
PEEP 10 12 14 14 14 16
FiO₂ 0.9 1.0
PEEP 18 18-24

Higher PEEP/lower FiO₂

FiO₂ 0.3 0.3 0.3 0.3 0.3
PEEP 5 8 10 12 14
FiO₂ 0.4 0.4 0.5 0.5 0.5-0.8 0.8 0.9
PEEP 14 16 16 18 20 22 22
FiO₂ 1.0 1.0
PEEP 22 24
  • Other recruitment maneuvers
    • Reposition pt – can try elevating HOB or positioning so “good lung” is down
    • If concern for mucus plug, consider need for bronch
    • If concern for significant atelectasis can try recruitment maneuvers with the vent including sustained inflation (setting expiratory pressure to ~30 for ~30 seconds) and PEEP titration (setting PEEP to 20-25 and decreasing by 2cm at a time) – call the fellow before attempting

Management Algorithm for refractory hypoxemia:

  • Inhaled vasodilators: Distribute preferentially to well-ventilated alveoli -> local vasodilation -> improved V/Q matching
    • VUMC formulary preference: inhaled epoprostenol (aka Flolan)
    • Alternatives: inhaled milrinone, inhaled nitric oxide
    • Data suggest improved PaO2/FiO2; large RCT without evidence for mortality benefit
  • Deep sedation (RASS -4 or -5)
    • Promotes ventilator synchrony
  • Neuromuscular blockade (paralysis) – call your fellow before doing this
    • Rationale: maximal vent synchrony (eliminates residual chest wall/diaphragm tone)
    • Pt MUST be RASS -5 (need analgesia + sedation)
    • Trial one time IV push of vecuronium 0.1 mg/kg
    • If improved vent synchrony/oxygenation, consider cisatracurium (Nimbex) drip
    • Data are mixed  ACURASYS 2010 (improved 90-day mortality but underpowered likely overestimating benefit); ROSE 2019 (no difference in 90-day mortality)
  • Prone positioning (Need attending approval)
    • Pts with moderate to severe ARDS (PaO2/FiO2 ratio < 150)
    • At VUMC, we use regular ICU beds and manually flip pts; cycle prone 16h/supine 8h
    • When proning or supining a pt, always have a provider who can intubate in the room in case unplanned extubation occurs
    • Considerations: need a team of people to reposition, high risk of ET tube malposition, difficult to access lines/perform procedures, high risk of pressure injuries
    • Data: PROSEVA 2013 -> proning improved 28-day mortality; study c/b imbalances between groups
  • Alternative ventilator modes (usually PC or APRV/BiLevel/BiVent)
    • APRV/BiVent should be avoided in people with bad obstructive lung dx, hemodynamic instability, refractory hypercarbia
  • Venovenous (V-V) ECMO
    • Indications for hypoxemia:
      • PaO2/FiO2 < 50 with FiO2 >80% for >3h OR
      • PaO2/FiO2 < 80 with FiO2 >80% for >6h AND
      • Mechanical ventilation ≤ 1 week
    • Absolute Contraindications:
      • Poor short-term prognosis (e.g. metastatic cancer)
      • Irreversible, devastating neurologic pathology
      • Chronic respiratory insufficiency without the possibility for transplant
    • Can calculate RESP score -> predicts in-hospital survival with ECMO
    • CONSULT EARLY if a pt may be a candidate; allows ECMO team to assist with evaluation
    • Data:
      • CESAR 2009: improved 6-month survival without severe disability
      • EOLIA 2018: no mortality benefit but 28% crossover from control to ECMO arm dilutes potential effects