Refractory Hypoxemia

Lauren Taylor

Background

  • Definition: Inadequate arterial oxygenation despite high levels of inspired O2 or the development of barotrauma in mechanically ventilated patients.
  • See ‘Hypoxia and Hypoxemia’ for review of basic principles.
  • Consider work up/interventions below if requiring FiO2 >80%.

Background

  • Definition: Inadequate arterial oxygenation despite high levels of inspired O2 or the development of barotrauma in mechanically ventilated patients.
  • See ‘Hypoxia and Hypoxemia’ for review of basic principles.
  • Consider work up/interventions below if requiring FiO2 >80%.

Management

ARDSnet FiO₂/PEEP Tables

FiO2Low PEEP
(cmH₂O)		High PEEP
(cmH₂O)
0.355-14
0.45-814-16
0.58-1016-20
0.61020
0.710-1420
0.81420-22
0.914-1822
1.018-2422-24

Initial triaging maneuvers

  • Troubleshoot ventilator – See “Introduction to Vent Management” for more information
  • Pulmonary hygiene – consider suction, HTS 3% nebs, cough assist, oscillating PEP devices (flutter valve), and chest physiotherapy
  • Optimize fluid status; consider diuresis/dialysis if not making significant urine
  • Reposition patient – elevated HOB, position “good lung” down (unless massive hemoptysis is suspected, then “bad lung” down)
  • If patient is rapidly decompensating, you can always provide Bag-Valve-Mask ventilation until help arrives

Consider higher PEEP strategy

  • Generally, improves oxygenation through increasing mean airway pressure which leads to alveolar recruitment and prevention of alveolar collapse.
    • 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 and overdistension increasing risk of barotrauma.
    • Can also lead to decreased venous return/preload.
  • ARDS net FiO2/PEEP Tables:
    • Updated 2024 guidelines conditionally recommend use of higher PEEP (reduced mortality and fewer ventilator days) without prolonged lung recruitment maneuvers (higher mortality) although In the VUMC MICU we tend to use lower PEEP strategies.

Inhaled vasodilators

  • Inhaled epoprostenol (Flolan) leads to preferential vasodilation of well-ventilated lung regions which redirects blood flow away from poorly ventilated (shunted) regions, thereby improving V/Q matching.
  • Alternatives: Inhaled nitric oxide, Inhaled milrinone.
  • Data: Despite improvement in PaO2/FiO2, inhaled vasodilators have not been shown to reduce mortality or increase ventilator-free days in ARDS.

Ventilator Synchrony

  • Deep sedation (RASS -4 or -5).

Neuromuscular blockade (need fellow or attending approval)

  • Eliminates residual chest wall/diaphragm tone.
  • Patient 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)

  • Patients with moderate to severe ARDS (PaO2/FiO2 ratio < 150).
  • Cycle: prone 16h/supine 8h.
  • When repositioning, always have a provider who can intubate in case of accidental extubation.
  • 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 demonstrated 28 day mortality benefit to early and prolonged proning (16 hours per day) in patients with moderate to severe ARDS.

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 mmHg with FiO2 >80% for >3h OR
    • PaO2/FiO2 < 80 mmHg 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).
  • Calculate RESP score; predicts in-hospital survival with ECMO.
  • Data: 
    • Pooled analysis of CESAR 2009 and EOLIA 2018 demonstrated that 90-day mortality was lower with ECMO.
    • Included in 2024 ATS practice guidelines as a conditional recommendation (following optimization of less invasive therapies) due to several limitations of available data and practical concerns.
Last updated on