At what Train of Four (TOF) value can a patient with a history of respiratory disease be safely extubated?

Train of Four Ratio for Safe Extubation

You should extubate only when the quantitative Train-of-Four (TOF) ratio exceeds 0.90 (≥90%), and ideally aim for ≥0.95 to minimize postoperative pulmonary complications. 1, 2

The Critical Threshold: TOF ≥ 0.90

The evidence is unequivocal that objective neuromuscular monitoring with documentation of TOF ratio ≥0.90 is the only reliable method to ensure satisfactory recovery of neuromuscular function before extubation. 1 This threshold represents the minimum acceptable standard, not an aspirational goal.

Key physiological requirements at extubation include:

• Quantitative TOF ratio >0.90 measured at the adductor pollicis (hand muscles, not facial muscles) 1, 2
• Patient awake and responding to verbal commands 3, 2
• Regular spontaneous breathing pattern with adequate tidal volume (5-8 ml/kg) 3
• Hemodynamically stable without significant vasopressor support 3
• Respiratory rate 10-25 breaths per minute 3

Why TOF ≥ 0.95 May Be Superior

Recent high-quality evidence suggests that the traditional 0.90 threshold may be insufficient. A 2020 exploratory analysis of the POPULAR study (n=3,150 patients with quantitative monitoring) demonstrated that extubating at TOF >0.95 rather than >0.90 reduced postoperative pulmonary complications by an adjusted absolute risk reduction of 3.5%. 4 When comparing TOF >0.95 to the standard >0.9 threshold directly, the risk reduction was 4.9%. 4

This finding is particularly relevant for patients with respiratory disease, where even marginal residual neuromuscular blockade could precipitate respiratory complications.

Clinical Manifestations of Inadequate Recovery

Understanding what happens at suboptimal TOF ratios helps explain why higher thresholds matter:

At TOF ratio 0.70-0.90, patients experience: 5

• Diplopia and difficulty tracking moving objects (universal finding) 5
• Inability to strongly oppose incisor teeth until TOF >0.85 5
• Grip strength only 59% of baseline at TOF 0.70 5
• Significant subjective weakness—no volunteers felt "street ready" at TOF 0.70 5

Clinical outcomes with inadequate monitoring:

• Without quantitative monitoring, 48.8% of patients are extubated without adequate recovery (TOF <0.9) 6
• Using TOF ≥0.9 versus clinical assessment alone reduces upper airway obstruction from 45% to 14% in PACU 7
• Mild hypoxia (SpO2 90-93%) occurs in 12% with clinical assessment versus 1% with TOF monitoring 7

Monitoring Technique Matters

You must use quantitative (objective) monitoring—visual or tactile assessment is unreliable. 1, 2

• Acceleromyography or electromyography at the adductor pollicis (hand) is the gold standard 1, 2
• Facial muscle monitoring is inadequate and should not be used 1
• Continue monitoring after reversal agent administration to confirm achievement of TOF ≥0.9 before extubation 8

Special Considerations for Respiratory Disease Patients

For patients with pre-existing respiratory disease, the margin for error is narrower:

• Aim for TOF ≥0.95 rather than accepting 0.90 to provide additional safety buffer 4
• Ensure complete reversal of neuromuscular blockade before extubation 1
• Consider prophylactic non-invasive ventilation immediately after extubation for high-risk COPD patients 3
• Maintain head of bed elevation 30-45 degrees to limit aspiration risk 1, 3

Reversal Strategy Based on TOF Count

If you're still waiting for adequate recovery, your approach depends on the depth of blockade:

When TOF count = 1 (profound blockade): 8

• Do NOT administer neostigmine—it is ineffective and contraindicated at this depth 8
• If using rocuronium, proceed to Post-Tetanic Count (PTC) evaluation 8
• If PTC = 1-2, administer sugammadex 4 mg/kg for deep blockade reversal 8
• If PTC = 0, continue waiting and maintain anesthesia 8

When TOF ratio is measurable but <0.9:

• Administer appropriate reversal agent (sugammadex provides more reliable antagonism than neostigmine) 2
• Continue quantitative monitoring until TOF ≥0.9 (or ideally ≥0.95) is achieved 8, 2

Common Pitfalls to Avoid

• Never rely on clinical assessment alone—41.5% of patients are intubated without adequate neuromuscular blockade, and 48.8% are extubated without adequate recovery when quantitative monitoring isn't used 6
• Never use visual or tactile TOF assessment—quantitative measurement with accelerometer is mandatory for accuracy 3
• Never assume facial muscle TOF reflects laryngeal or diaphragmatic function—hand muscle monitoring is required 1
• Never extubate based on sustained head-lift alone—this can be achieved at TOF as low as 0.60, well below safe thresholds 5

Bottom Line Algorithm

1. Measure quantitative TOF ratio at adductor pollicis
2. If TOF <0.9: Do not extubate—administer reversal and continue monitoring
3. If TOF 0.9-0.94: Acceptable minimum, but consider waiting for ≥0.95 in respiratory disease patients
4. If TOF ≥0.95: Proceed with extubation if other criteria met (awake, hemodynamically stable, adequate spontaneous ventilation)
5. Continue monitoring in PACU with supplemental oxygen and readiness for reintubation 3