Desaturation Eighteen Minutes Into One-Lung Ventilation

The combination of falling saturation with a rising peak pressure narrows the field: a pure shunt from dependent-lung collapse would raise pressure modestly, but a jump from 22 to 36 cmH2O points to something obstructing or stiffening the ventilated lung.

Ranked:

1. Bronchial tube migration or malposition after positioning - a left-sided tube can advance into the left lower lobe bronchus, obstructing the left upper lobe, or the bronchial cuff can herniate over the carina. Turning and surgical retraction are the classic triggers.
2. Secretions, blood, or a mucus plug in the dependent lung - common in smokers and after manipulation; causes both obstruction and shunt.
3. Bronchospasm or inadequate depth - would typically show a sloping or upsloping capnogram and increased resistance; the capnogram is described as normal, which argues somewhat against it.
4. Pulmonary edema or aspiration - frothy secretions, falling compliance.
5. Pneumothorax - especially if a chest drain is clamped or misplaced; would add hypotension and rising ETCO2 if severe.
6. Pulmonary embolism - would not explain the rising airway pressure and typically causes hypotension and tachycardia.

Hypoxemia during one-lung ventilation also arises from dependent-lung atelectasis and from shunt through the non-dependent, unventilated lung, but neither explains a 14 cmH2O pressure rise by itself.

Work from least invasive and fastest to most invasive, and never skip the step of looking at the tube.

• Increase FIO2 to 1.0 if not already; it buys time but does not fix shunt physiology.
• Hand-ventilate and feel compliance; check tube depth at the teeth against the depth recorded when the patient was supine, and auscultate both sides.
• Suction both lumens - mucus or clot is a common and immediately fixable cause.
• Fiberoptic bronchoscopy through the tracheal and bronchial lumens to verify the bronchial cuff position, exclude carinal herniation, and clear secretions. This is the single highest-yield step and should not be deferred.
• Optimize the dependent lung: recruitment maneuver followed by PEEP titration (5–10 cmH2O) if atelectasis is the cause; recheck pressure and saturation after each change.
• Apply CPAP 1–2 cmH2O (up to 5) to the non-dependent, operative lung if the surgeon permits, which reduces shunt through the unventilated lung; coordinate with the surgeon before doing it.
• Check hemodynamics and depth of anesthesia; treat bronchospasm with a beta agonist if the pressure remains high after mechanical causes are excluded.
• Recruit and reassess after every intervention rather than stacking changes, so you know what worked.

Abandon one-lung ventilation when desaturation persists below roughly 90% despite a verified tube position, cleared airways, optimal PEEP, and CPAP to the operative lung, or if hypotension, arrhythmia, or ischemia develop. Continuing to chase a saturation in the high 80s while the patient becomes unstable converts a ventilation problem into a cardiac arrest.

The safe sequence:

• Tell the surgeon early - the moment you start bronchoscopy, not when the saturation is 82%. Surgeons can pause, pack, or clamp and allow two-lung ventilation briefly.
• Ask the surgeon to deflate the operative field and reinflate the non-dependent lung; resume two-lung ventilation with FIO2 1.0.
• Alternatively, ask the surgeon to clamp the pulmonary artery or apply a lung retractor so that intermittent two-lung ventilation is possible without losing exposure.
• Once saturation recovers above 95% and the patient is stable, decide with the surgeon whether to attempt one-lung ventilation again at a lower tidal volume, higher PEEP, or with continuous positive airway pressure to the operative side.
• Document the sequence and the rationale; the postoperative plan should include a lower threshold for intensive care and early chest imaging.