Refractory Hypoxemia

Hannah Kieffer

Background

  • Inadequate arterial oxygenation despite high levels of inspired O2 or the development of barotrauma in mechanically ventilated pts
    • Oxygen index (MAP × FiO2 × 100/PaO2) < 40
  • Consider work up/interventions below if needing FiO2 >80%

Differential

  • Always first consider worsening of primary underlying process
  • Consider recent injuries/interventions, e.g., smoke inhalation, opioid administration and check dose, recent blood transfusion, etc.
  • Altered alveolar permeability/V-Q mismatch
    • PE, pneumothorax, fluid overload (severe pleural effusion/pulmonary edema), ventilator-associated pneumonia (VAP), new ARDS, diffuse alveolar hemorrhage
  • Shunting
    • Large lung consolidation, bronchus obstruction, intracardiac shunt, intrapulmonary shunt (pulmonary AVMs)

Evaluation

  • Always get CXR STAT if pt has new or worsening O2 requirement
    • Consider CT chest if patient stable enough
  • CBC, ABG
  • POCUS
    • Lack of lung sliding; pneumothorax)
    • RV enlargement/septal bowing/McConnell’s sign; RV strain in PE
  • TTE if stable and concerned for intracardiac shunt/acute HF decompensation
  • Bronchoscopy if concerned for mucous plug

Management algorithm for refractory hypoxemia

Initial triaging maneuvers

  • 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
  • Troubleshoot ventilator – see “Introduction to Vent Management” for more information
  • Optimize fluid status; consider diuresis/dialysis if not making significant urine
  • Reposition patient – elevated HOB, position “good lung” down

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 -> increased 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
  • ARDS net FiO2/PEEP Tables: At VUMC we typically use the Lower PEEP table
    • Note - Updated 2024 guidelines conditionally recommend use of higher PEEP (reduced mortality and fewer ventilator days) without prolonged lung recruitment maneuvers (higher mortality)

Lower PEEP/higher FiO2

FiO2

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.3

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.4

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.4

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.5

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.5

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.6

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.7

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.7

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

PEEP

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

5

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

5

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

8

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

8

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

10

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

10

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

10

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

12

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

FiO2

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.7

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.8

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.9

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.9

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.9

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

1.0

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

PEEP

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

14

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

14

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

14

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

16

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

18

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

18-24

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Higher PEEP/lower FiO2

FiO2

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.3

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.3

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.3

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.3

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.3

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.4

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.4

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.5

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

PEEP

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

5

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

8

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

10

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

12

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

14

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

14

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

16

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

16

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

FiO2

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.5

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.5-0.8

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.8

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

0.9

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

1.0

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

1.0

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

PEEP

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

18

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

20

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

22

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

22

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

22

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

24

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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 they improve 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
  • 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; note 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
  • No data that demonstrates superiority of any one ventilator mode over another

Venovenous (V-V) ECMO

  • CONSULT EARLY if a pt may be a candidate; allows ECMO team to assist with evaluation
  • Hypoxemia related indications:
    • PaO2/FiO2 < 50 with FiO2 >80% for >3h OR
    • PaO2/FiO2 < 80 with FiO2 >80% for >6h
    • PaO2 <40 mmHg despite maximal ventilator support
    • Murray Score ≥ 3
  • Absolute Contraindications:
    • Poor short-term prognosis/non-survival comorbidity (e.g. metastatic cancer)
    • Irreversible, devastating neurologic pathology
    • Irreparable cardiac damage and unsuitable for transplant/VAD
    • Chronic respiratory insufficiency without the possibility for transplant
    • Limitation of care orders (DNR)
  • Can calculate RESP score; predicts in-hospital survival with ECMO
  • Data:
    • Included in updated 2024 ATS practice guidelines
    • 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. ECMO group had a significant increase in ventilator-free days
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