Refractory Hypoxemia

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
  • ET tube obstruction/malposition
  • Fluid overload
  • Ventilator-associated Pneumonia
  • New ARDS

Evaluation:

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

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)
  • After talking with the fellow/attending, you can start process by placing “Inpatient consult to ECMO adult” in Epic
• 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: We usually use the Lower PEEP table

• 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:

1.  Inhaled vasodilators

• 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

2.  Deep sedation (RASS -4 or -5)

• Promotes ventilator synchrony

3.  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, cannot achieve with dexmedetomidine alone, which does not have amnestic properties)
• 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)

4.  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 16 hrs/supine 8 hrs
• When proning or supining a pt, always have a provider who can intubate in the room in case unplanned extubation occurs (anesthesia or pulm attending)
• 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 complicated by imbalances between groups

5.  Alternative ventilator modes (usually Pressure Control or APRV/BiLevel/BiVent)

• Always ask for help from a fellow or attending before switching to a mode that you do not know how to trouble shoot!
• APRV/BiVent should be avoided in people with bad obstructive lung disease, hemodynamic instability, refractory hypercarbia

6.  Venovenous (V-V) ECMO

• Indications for hypoxemia:
  • PaO2/FiO2 < 50 with FiO2 >80% for >3 hrs OR
  • PaO2/FiO2 < 80 with FiO2 >80% for >6 hrs 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
• Goal must be clear upfront  bridge to recovery, transplant, or transplant decision
• Can calculate RESP score  predicts in-hospital survival with ECMO
• CONSULT EARLY if a pt may be a candidate; does not commit pt to procedure but 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