In a patient who develops acute respiratory distress syndrome after inhalation of hydrogen fluoride, what extracorporeal membrane oxygenation (ECMO) strategy should be employed?

ECMO Strategy in Hydrogen Fluoride-Induced ARDS

In hydrogen fluoride inhalation injury causing ARDS, venovenous (VV) ECMO should be initiated early (within 7 days) when severe hypoxemia persists despite optimized conventional therapies, but only after mandatory pre-ECMO rescue interventions including prone positioning and neuromuscular blockade have been attempted. 1

Critical Distinction: No Unique ECMO Strategy for Hydrogen Fluoride

There is no specific or different ECMO strategy for hydrogen fluoride-induced ARDS compared to ARDS from other causes. 2 The key principle is that hydrogen fluoride inhalation creates a potentially reversible respiratory injury, making it an appropriate indication for ECMO as a "bridge to recovery." 2 Survival rates of 55-86% have been reported in severe hypoxemic respiratory failure from reversible causes, which supports ECMO consideration in this toxicological context. 1

Mandatory Pre-ECMO Optimization Sequence

Before considering ECMO cannulation, you must exhaust these interventions in order:

• Lung-protective ventilation: Tidal volume 4-6 mL/kg ideal body weight, plateau pressure <30 cmH₂O (ideally <28 cmH₂O for ≥6 hours triggers ECMO consideration). 3, 4

• Early prone positioning: Initiate within ≤48 hours of ARDS onset, maintain for ≥12-16 hours daily when PaO₂/FiO₂ <150 mmHg. 1, 4 Prone positioning can restore right ventricular function and reduce ventilator-induced lung injury. 3

• Neuromuscular blockade: Cisatracurium infusion for ≤48 hours during the first 48 hours of severe ARDS, combined with deep sedation. 1, 4

• Optimal PEEP titration: PEEP ≥12 cmH₂O based on gas exchange and hemodynamics. 3

Critical pitfall: Delayed ECMO after prolonged mechanical ventilation (>7-9.6 days) is associated with markedly worse survival; do not wait too long once criteria are met. 1, 5

ECMO Initiation Criteria (Slow-Entry vs. Fast-Entry)

Fast-Entry Criteria (Immediate ECMO)

• PaO₂ <55-60 mmHg or SpO₂ <88% despite FiO₂ >0.70 and optimal PEEP for >2 hours. 1, 6
• PaO₂/FiO₂ <70 mmHg for ≥3 hours despite optimization. 3, 4

Slow-Entry Criteria (ECMO after 24-96 hours of conventional therapy)

• PaO₂/FiO₂ <80 mmHg for ≥3 hours or <100 mmHg for ≥6 hours. 3, 4
• pH <7.20-7.25 for ≥6 hours due to uncompensated hypercapnia (PaCO₂ >60 mmHg). 3, 4
• Plateau pressure >28 cmH₂O for ≥6 hours despite lung-protective strategies. 3, 1

Important nuance: The fast-entry group in one study showed 100% survival (11/11 patients) versus 60% in the slow-entry group, suggesting earlier intervention for life-threatening hypoxemia may improve outcomes. 6

VV-ECMO vs. VA-ECMO Selection Algorithm

Choose VV-ECMO (Preferred for Isolated Respiratory Failure)

• Adequate cardiac function on echocardiography. 3, 1
• No requirement for vasopressors >0.5 µg/kg/min norepinephrine. 3
• Mean arterial pressure ≥65 mmHg with minimal support. 3
• VV-ECMO provides better outcomes than VA-ECMO in pure respiratory failure. 1

Choose VA-ECMO (Combined Cardiopulmonary Failure)

• Severe cardiogenic shock with very low cardiac output and reduced LV ejection fraction on echocardiography. 3, 1
• Norepinephrine requirement >0.5 µg/kg/min. 3, 1
• Evidence of right ventricular overload: systolic pulmonary artery pressure >40 mmHg with acute cor pulmonale. 3, 1

Critical assessment: Echocardiography is mandatory to determine VV versus VA mode selection. 1

Institutional Requirements (Non-Negotiable)

• Minimum annual volume: 20-25 ECMO cases per year; centers with higher volumes have significantly better outcomes. 1, 4, 5
• 24/7 multidisciplinary ECMO team: Physicians, nurses, perfusionists, ECMO specialists. 1, 5
• Nurse-to-patient ratio: 1:1 to 1:2 for ECMO patients. 1, 5
• Mobile ECMO retrieval capability: Hospitals without ECMO must have formal pathways for 24/7 mobile team retrieval to prevent delayed transfer. 1, 5

If your center does not meet these criteria, immediate transfer to a high-volume ECMO center is mandatory. 1, 5

Monitoring During ECMO

• Continuous arterial blood pressure and ECMO flow monitoring. 3, 1
• Repeated echocardiography (especially for VA-ECMO to detect left ventricular overload). 3, 1
• Daily fluid balance, central venous oxygen saturation (SvO₂), and lactate levels. 3, 1
• Hourly activated clotting time (ACT) checks targeting 180-220 seconds. 1

Major Complications to Anticipate

• Bleeding: Occurs in 37% of VV-ECMO patients and 75.3% of VA-ECMO patients; intracranial hemorrhage in up to 6%. 1, 5
• Thrombotic events: 42% of VV-ECMO patients experience thrombotic complications. 1
• Acquired von Willebrand syndrome (AVWS): Develops in almost all ECMO patients within hours, contributing to bleeding risk. 1, 5
• Pneumothorax: Occurred in 15/21 patients in one series. 6

Absolute Contraindications

• Uncontrolled coagulopathy or contraindications to anticoagulation. 1, 2
• Severe intracranial hemorrhage. 5, 2
• Irreversible brain damage. 5, 2
• Advanced metastatic cancer or severe multi-organ dysfunction (SOFA score >15). 5, 2

Ventilator Management During ECMO

Once ECMO is established, transition to ultra-lung-protective "rest" settings:

• Significantly reduce peak and mean airway pressures, tidal volume, ventilatory rate, and FiO₂. 6, 7
• Maintain adequate PEEP to prevent atelectotrauma. 7
• Monitor transpulmonary pressure to avoid barotrauma. 7

Avoid high-frequency oscillatory ventilation (HFOV): It increases mortality (relative risk ≈1.41) and offers no advantage. 1