Anesthesiology APPLIED Exam › Thoracic and respiratory

Postoperative mechanical ventilation and weaning

Thoracic and respiratory·~5 min read· Physician-reviewed✓ Sourced · 3

Stem

A 71-year-old man, 92 kg and 178 cm, with COPD and an ejection fraction of 40%, arrives in the ICU intubated after a 9-hour open thoracoabdominal aneurysm repair with 4 L of crystalloid and 3 units of blood. The next morning he is awake and following commands on FiO2 0.4 and PEEP 8, PaO2 is 92 mmHg, and he is on low-dose norepinephrine that is being weaned.

Question

The surgeon asks whether he can be extubated this morning. How will you decide, and how will you liberate him from the ventilator?

Ideal answer

HeadlineOnly when the reason he stayed intubated has resolved, proven by a structured trial. He is at the edge on oxygenation and still on norepinephrine, so I wean that first.

Lung-protective while he waits: tidal volume 6–8 mL/kg predicted body weight, plateau below 30 cmH2O,¹ and sedation minimized every day.²
Readiness screen: cause improving, FiO2 0.4 or less on PEEP 8 or less, PaO2/FiO2 200 or more, hemodynamically stable on minimal or no vasopressor, awake, with a cough.³
Breathing trial, 30–120 minutes, pressure support 5–8 cmH2O, rather than a T-piece for the first trial.²^,3
Passes and protects his airway: extubate to noninvasive ventilation, because COPD, heart failure and a long operation make him high risk.²
Fails: find out why before trying again, and no repeat trial for 24 hours.³

Breaking down the answer

Protective settings — 6 mL/kg PBW to start, up to 8 if he double-triggers, plateau below 30; driving pressure (plateau minus PEEP) predicts outcome better than tidal volume or plateau alone, so I keep it low.¹
A screen, not "he's awake" — each criterion targets a common cause of failure: oxygenation, hemodynamics, mental status and cough. This is judgment: the examiner wants a checklist, not a feeling.
The trial predicts better than any single number — RSBI (rate divided by tidal volume in liters) below 105 predicts success, and maximal inspiratory pressure of −20 to −25 cmH2O or more negative suggests adequate strength, but each is one data point.³
Paired sedation and breathing trials — protocols that minimize sedation shorten ventilation; propofol or dexmedetomidine rather than benzodiazepines.²
Airway protection — strong cough, manageable secretions and an intact gag. A patient who passes the trial but cannot clear secretions fails extubation.
Cuff leak in the right patients — after prolonged intubation, airway surgery or a traumatic intubation; below about 110 mL predicts stridor.³ If he fails it: systemic steroids at least 4 hours before extubation,² for example methylprednisolone 20 mg every 4 hours starting 12 hours before.
Post-extubation support — high-flow nasal oxygen also reduces reintubation.²^,3 I do not use noninvasive ventilation to rescue established failure, because it delays reintubation.

Follow-up question

Thirty minutes into his breathing trial, his rate is 38, SpO2 88%, heart rate 125 and blood pressure 175/95, and he is sweating. What is happening and what do you do?

Follow-up answer

HeadlineHe has failed: rate above 35, SpO2 below 90% and rising pressure.³ I return him to full support and tell the team: no extubation today.

Then causes, cardiac first with an ejection fraction of 40%: weaning-induced pulmonary edema from the rise in venous return and afterload on spontaneous breathing, myocardial ischemia, and fluid overload after a big resuscitation. Also residual neuromuscular block, oversedation, bronchospasm, pneumonia, metabolic alkalosis, low phosphate and fatigue. I get an ECG, troponin, echo and chest radiograph, and diurese if the ventricle is filling high. His diaphragm rests and the trial repeats after 24 hours, because fatigued muscle does not recover in minutes.³

Pitfalls that cost points

Extubating because the patient is "awake" without assessing cough, secretions and gas exchange.
Running the trial repeatedly the same day after a failure.
Ventilating with 10 mL/kg tidal volumes because the patient "came from the OR".

Rapid-fire

Q: Why can weaning cause pulmonary edema? A: Spontaneous breathing lowers intrathoracic pressure, raising venous return and left ventricular afterload, which unmasks a stiff or ischemic ventricle.

Q: Why is driving pressure important? A: Plateau minus PEEP reflects strain relative to functional lung size, and it predicts outcome better than tidal volume or plateau pressure alone.¹

Q: What does maximal inspiratory pressure tell you? A: A value of −20 to −25 cmH2O or more negative suggests adequate muscle strength, but it is effort-dependent.³

Q: Why extubate an obese or COPD patient to noninvasive ventilation? A: Preventive noninvasive ventilation in high-risk patients lowers reintubation, by preventing atelectasis and upper airway collapse in the first hours.²

Q: Which first trial does the guideline prefer? A: Inspiratory pressure augmentation of 5–8 cmH2O rather than T-piece or CPAP.²

Numbers to know

Item	Value
Tidal volume	6 mL/kg PBW, up to 8; plateau <30 cmH2O¹
Readiness screen	FiO2 ≤0.4, PEEP ≤8, PaO2/FiO2 ≥200³
Breathing trial	30–120 min, pressure support 5–8 cmH2O or T-piece³
Trial success	RR <35, SpO2 >90%, HR <140, SBP 80–180 mmHg³
Driving pressure	<15 cmH2O
RSBI	<105 breaths/min/L³
Cuff leak	<110 mL predicts stridor; steroids ≥4 h before extubation³^,2

Sources

1.Mechanical Ventilation in Adult Patients with ARDS: ATS/ESICM/SCCM Clinical Practice Guideline · ATS/ESICM/SCCM, 2017 · thoracic.org
2.Liberation from Mechanical Ventilation in Critically Ill Adults: ATS/ACCP Clinical Practice Guideline (executive summary) · ATS/ACCP, 2017 · thoracic.org
3.Ventilator Weaning and Spontaneous Breathing Trials; an Educational Review · Emergency (Tehran), PMC, 2016 · pmc.ncbi.nlm.nih.govZein et al.; readiness criteria (Table 1), SBT methods and success criteria, RSBI, MIP, cuff leak.

Facts on this page were checked against these sources on Oct 14, 2026. Guidelines change; confirm doses against current institutional protocols.