Spontaneous Breathing Trial Simulator — спроба спонтанного дихання для відлучення від апарату ШВЛ
Prolonged, unnecessary mechanical ventilation carries serious risks: ventilator-associated pneumonia, diaphragm atrophy from disuse, delirium, ICU-acquired weakness, and longer hospital stays. Daily, structured screening against objective readiness criteria — rather than waiting for a physician's subjective impression — is the single intervention most consistently shown to shorten time on the ventilator.
Daily screening protocols (following ABCDEF-bundle and ATS/ACCP guidance) check four domains before a spontaneous breathing trial is even attempted:
1. Oxygenation adequacy: • PaO2/FiO2 ratio > 150–200 on FiO2 ≤ 0.4–0.5 • PEEP ≤ 5–8 cmH2O • SpO2 ≥ 88–92% on these settings
2. Hemodynamic stability: • No or minimal vasopressor/inotrope support • No active myocardial ischemia • Heart rate and blood pressure within an acceptable range without escalating therapy
3. Adequate mentation: • Richmond Agitation-Sedation Scale (RASS) roughly -1 to 0 — arousable, not agitated • Sedation minimized or interrupted (daily sedation vacation) • Able to follow simple commands
4. Ventilatory mechanics and reserve: • Afebrile, no significant metabolic derangement • Adequate cough and airway-clearance capacity anticipated • No plans for surgery or procedures in the immediate window
Only when all four domains pass does the team proceed to an actual spontaneous breathing trial — screening itself does not predict extubation success, it simply identifies who is safe to test.
Landmark trials (Ely et al., NEJM 1996; Kress et al., NEJM 2000) showed that daily screening protocols paired with a "wake up and breathe" approach reduce both ventilator days and ICU length of stay — without increasing reintubation rates.
Once screening criteria are met, the ventilator is switched from full support (assist-control, high pressure support) to a minimal-support mode: low-level pressure support ventilation (typically 5–8 cmH2O, sometimes with zero PEEP or CPAP) or a T-piece circuit that delivers humidified oxygen with no mechanical assistance at all. A trial timer starts, and the patient must now generate essentially all of their own work of breathing.
Two techniques dominate clinical practice, and multiple randomized trials show broadly similar extubation outcomes between them:
T-piece trial: • The patient is disconnected from the ventilator circuit entirely • A T-shaped adapter delivers humidified, oxygen-enriched gas past the endotracheal tube • No pressure support at all — the closest approximation to "breathing on their own" • Slightly higher work of breathing due to endotracheal tube resistance not being compensated
Low-level pressure support (5–8 cmH2O): • Ventilator remains connected; each patient breath is augmented by a small pressure boost • The pressure roughly offsets the added resistance of the endotracheal tube and circuit • Considered by many as a better simulation of the *post-extubation* work of breathing than a T-piece
Trial duration: • Most protocols use 30 minutes; some extend to 120 minutes for patients with a longer ventilation history or reduced reserve • Trials beyond 30 minutes do not meaningfully improve predictive accuracy in most patients — the diaphragm shows the signs of failure (or does not) quite early
Throughout the trial, the bedside team continuously tracks respiratory rate, tidal volume, oxygen saturation, heart rate, blood pressure, and visible signs of increased work of breathing (accessory muscle use, paradoxical abdominal motion, diaphoresis, anxiety). The single most validated bedside index calculated from these measurements is the Rapid Shallow Breathing Index.
Yang and Tobin (New England Journal of Medicine, 1991) introduced the RSBI — also called the "f/VT ratio" — as a simple bedside measurement combining rate and depth of breathing into a single predictive number:
RSBI = respiratory rate (breaths/min) ÷ tidal volume (liters)
A rapid, shallow breathing pattern (high rate, low volume) produces a high RSBI and signals impending respiratory muscle fatigue — the diaphragm and accessory muscles cannot sustain adequate ventilation and are compensating with an inefficient pattern. A slow, deep breathing pattern (low rate, adequate volume) produces a low RSBI and signals reserve.
RSBI < 105 breaths/min/L is the classic threshold associated with weaning success; RSBI ≥ 105 is associated with a substantially higher risk of weaning failure. Because the underlying inputs (rate and volume) are already displayed on every ventilator, RSBI can be computed in seconds without any special equipment.
RSBI is powerful but not sufficient alone — it is one input among several tracked in parallel:
• SpO2: sustained desaturation below ~88–90% signals inadequate gas exchange reserve • Heart rate: a sustained rise of >20% from baseline, or new arrhythmia, suggests cardiopulmonary strain • Blood pressure: hypertension or hypotension developing during the trial suggests autonomic/cardiac stress • Work-of-breathing signs: accessory muscle recruitment, nasal flaring, paradoxical (see-saw) abdominal breathing, diaphoresis, and visible anxiety or agitation are qualitative but clinically weighty • Mental status: new agitation or somnolence during the trial is an early failure signal
Experienced clinicians weigh the trend over the trial, not just a single snapshot — a patient whose RSBI is climbing minute by minute is behaving very differently from one whose values are stable, even if both are momentarily below 105.
RSBI has excellent sensitivity but only moderate specificity — meaning a low RSBI reliably identifies patients ready to wean, but a borderline or elevated RSBI alone should not automatically fail a trial without considering the full clinical picture.
At the end of the trial window (or the moment any failure criterion is met), the team makes a binary determination: pass or fail. This decision drives everything that follows — either proceeding toward extubation or returning the patient to fuller ventilator support to rest and be reassessed later.
A trial is stopped and scored as a FAIL if any of the following develop at any point during the trial:
• Respiratory rate > 35 breaths/min (or a marked, sustained increase from baseline) • RSBI rising toward or beyond 105 breaths/min/L • SpO2 falling below ~88–90% despite supplemental oxygen • Heart rate rising more than ~20% from baseline, new significant arrhythmia, or signs of ischemia • Systolic blood pressure rising above ~180 mmHg or falling below ~90 mmHg • Increasing agitation, diaphoresis, or visible accessory muscle use / paradoxical breathing • Patient-reported severe dyspnea or distress
A trial is scored as a PASS if the patient sustains acceptable rate, volume, oxygenation, and hemodynamics — without distress — for the entire planned duration (commonly 30 minutes, up to 120 minutes for higher-risk patients).
A failed SBT is a normal, expected part of weaning for a meaningful fraction of patients and should not be viewed as a complication. When a trial fails, the ventilator is returned to a comfortable, fully supportive setting to rest the respiratory muscles, the underlying cause of failure is investigated (fluid overload, unresolved infection, inadequate nutrition, electrolyte derangement, residual sedation), and the readiness screen is repeated — typically the following day.
Repeated early trials (rather than waiting many days) remain the best strategy: most patients who eventually wean successfully do so within a few daily attempts once the underlying illness is on a recovery trajectory.
A passed spontaneous breathing trial is necessary but not sufficient for extubation. The airway itself must also be assessed: can the patient protect it from aspiration, clear secretions with an effective cough, and maintain consciousness sufficient to respond to problems? Only when both breathing capacity and airway protection are adequate does the team proceed — and vigilant monitoring continues well after the tube comes out.
Passing the SBT confirms the respiratory pump can sustain ventilation, but extubation also requires confidence the upper airway can protect itself once the tube is gone:
• Cough strength: an effective, forceful cough (sometimes semi-quantified by peak cough flow) is needed to clear secretions without the tube • Secretion burden: copious secretions requiring suctioning more often than roughly every 2 hours raise aspiration and re-obstruction risk • Mental status: sufficient alertness to respond to airway compromise and follow commands • Cuff-leak test (selected high-risk patients — prolonged intubation, traumatic intubation, large tube): an absent or low cuff leak suggests laryngeal edema and risk of post-extubation stridor/airway obstruction
When both the SBT and the airway-protection assessment are favorable, the endotracheal tube is removed.
Roughly 10–20% of patients who are extubated after a passed SBT still develop respiratory distress within 48–72 hours and require reintubation. Because reintubation itself is associated with worse outcomes (not simply a marker of a sicker patient, but an event that adds its own risk), the hours immediately after extubation call for the same intensity of monitoring as the trial itself:
• Continuous SpO2 and cardiac monitoring • Frequent respiratory rate, work-of-breathing, and mental-status checks • Non-invasive ventilation or high-flow nasal oxygen is often applied prophylactically in higher-risk patients to reduce reintubation risk • Early recognition of stridor, increasing secretions, fatigue, or desaturation allows rapid intervention before a full crisis develops
Successful weaning is therefore best understood as a process, not a single moment — daily screening, a supported trial, an evidence-based pass/fail decision, and continued vigilance after extubation together determine whether liberation from the ventilator truly succeeds.
Because reintubation carries independent risk, clinicians deliberately favor a cautious, criteria-based approach over rushing extubation — the goal is the first attempt succeeding, not simply the earliest possible attempt.