Advanced Respiratory Support — NIV, Weaning and Tracheostomy

Overview & definition

Advanced respiratory support is the set of skills that frame the respiratory failure beyond the intubation and the mechanical ventilation — the non-invasive ventilation (the CPAP and the BiPAP that avert or follow the intubation), the liberation from the mechanical ventilation (the spontaneous breathing trial, the weaning protocol, the difficult-to-wean patient), and the tracheostomy (the long-term airway for the patient who cannot be extubated). Together they are the higher respiratory skills the CICM examinor expects.[1][1]

The over-riding principle is that the prompt, the safe, the successful liberation is the goal of the mechanical ventilation — for every additional day on the ventilator raises the risk of the ventilator-associated pneumonia, the weakness and the mortality — and the NIV and the tracheostomy are the tools that facilitate it or that provide the alternative.[1]

Non-invasive ventilation: CPAP and BiPAP

Non-invasive ventilation is the positive-pressure ventilation delivered via a mask (or a helmet), without an endotracheal tube. It has two modes: the CPAP (the continuous positive airway pressure — a single positive pressure throughout the respiratory cycle, which splints the alveoli, recruits the collapsed lung, reduces the preload and the afterload of the heart, and improves the oxygenation) and the BiPAP (the bilevel positive airway pressure — an inspiratory positive airway pressure, the IPAP, and an expiratory positive airway pressure, the EPAP, which augments the tidal volume and unloads the respiratory muscles, improving the ventilation and the CO2 clearance).[1][1]

The physiological mechanism of the NIV benefit is the unloading of the fatiguing respiratory muscles — the positive pressure reduces the work of breathing (the pressure support does the work the patient cannot), and the CPAP recruits the collapsed alveoli and improves the compliance. The result is the reduced respiratory rate, the improved gas exchange, and the averted (or the shortened) intubation.[1]

The indications and evidence for NIV

The NIV is the first-line therapy for three conditions, each with a strong evidence base.[1][1]

• The COPD exacerbation with the respiratory acidosis (the pH below 7.35). The NIV (the BiPAP) is the first-line — it reduces the intubation rate, the mortality and the length of the stay, and it is the standard of care. The target is the pH correction (to above 7.35) and the PaCO2 reduction, with the settings titrated (the IPAP of 10 to 15, the EPAP of 4 to 5, the FiO2 for the 88 to 92 per cent saturation).
• The cardiogenic pulmonary oedema. The NIV (the CPAP or the BiPAP) is the first-line — it reduces the preload and the afterload (the CPAP), it unloads the failing heart, and it reduces the intubation rate. The CPAP alone is often sufficient.
• The immunocompromised patient with the respiratory failure. The NIV is the first-line — it reduces the intubation rate and the mortality (by avoiding the invasive ventilation and its infections in the vulnerable host).
• The post-extubation and the weaning-facilitating NIV — the evidence is more nuanced (below). [1]

Pathophysiology: the work of breathing and the respiratory muscle fatigue

The respiratory muscles behave like any skeletal muscle — they fatigue under a sustained load, and the fatigue leads to the rapid, shallow breathing (the low tidal volume, the high rate), the rising CO2 and the eventual failure. The work of breathing has three components: the elastic (the compliance of the lung and the chest wall — raised by the ARDS, the oedema, the fibrosis), the resistive (the airway resistance — raised by the COPD, the asthma, the secretions), and the threshold (the intrinsic PEEP of the COPD — the positive end-expiratory pressure that must be overcome before the inspiratory flow begins).[1]

The NIV unloads the muscles by the pressure support (which does the work of the inspiration) and the CPAP/EPAP (which counteracts the intrinsic PEEP and the elastic load). The result is the reduced work, the recovered muscles, and the time to treat the cause.[1]

Weaning from mechanical ventilation: the principles

The weaning is the liberation from the mechanical ventilation, and the principle is that the earlier the safe liberation, the better — the prolonged ventilation increases the complications. The daily assessment of the readiness (the resolution of the cause, the adequate oxygenation, the haemodynamic stability, the ability to protect the airway) is the first step, and the spontaneous breathing trial (the SBT) is the test.[1][1]

The Esteban trial (NEJM 1995) compared four methods of weaning — the T-piece, the SIMV, the pressure-support and the daily SBT — and found that the pressure-support and the daily SBT (the once- or twice-daily trial of the spontaneous breathing) were the fastest, the SIMV the slowest. The modern practice is the daily SBT (the low pressure support of 5 to 7 cmH2O, for 30 to 120 minutes), and if the patient tolerates it (the stable respiratory rate, the adequate gas exchange, no distress), the extubation follows.[1]

The spontaneous breathing trial and the weaning protocol

The SBT is the low-pressure-support trial (the 5 cmH2O, for 30 to 120 minutes) that assesses the patient's ability to breathe without the ventilator. The tolerance is judged by the respiratory rate (under 35), the heart rate and the blood pressure (the stability), the gas exchange (the saturation above 90 per cent), and the absence of the distress (the diaphoresis, the accessory-muscle use, the agitation). The failure (the rising rate, the distress, the desaturation) returns the patient to the ventilator, and the cause is sought and treated.[1]

The weaning protocol — the nurse- or the respiratory-therapist-led protocol that performs the daily SBT and the readiness assessment — is superior to the physician-directed weaning (it shortens the duration). The rapid shallow breathing index (the RSBI, the f/VT ratio) — the respiratory rate divided by the tidal volume in litres — is a validated predictor of the weaning success (the RSPI below 105 predicts the success), though the clinical SBT is the definitive test.[1]

The post-extubation NIV question

The role of the NIV after the extubation is nuanced, and the evidence is mixed. The prophylactic NIV (for the high-risk patient — the COPD, the older, the cardiac) started immediately after the extubation reduces the reintubation and the mortality. The therapeutic NIV (for the patient who has developed the respiratory failure after the extubation) is more controversial — the Esteban trial (NEJM 2004) found it did not reduce the reintubation, and a concern of the delayed reintubation (with a higher mortality) was raised.[2]

The synthesis is: the prophylactic post-extubation NIV for the high-risk patient is beneficial; the therapeutic NIV for the established post-extubation failure must be used with caution (and the prompt reintubation if the NIV fails), because the delay to the reintubation is the harm.[2][1]

The difficult-to-wean patient and the NIV-assisted weaning

Some patients (the COPD, the neuromuscular weakness, the older with the cardiac comorbidity) fail the repeated SBTs and require the prolonged ventilation — the difficult-to-wean patient. The NIV-facilitated extubation (the extubation to the NIV, regardless of the SBT pass/fail) is a strategy for these patients, and the Burns systematic review (Thorax 2022) found it reduced the duration of the invasive ventilation, the mortality and the ventilator-associated pneumonia in the selected (mostly COPD) population.[3]

The principle is that the NIV-assisted weaning unloads the fatiguing muscles while avoiding the complications of the prolonged intubation — but it requires the patient to protect the airway and to tolerate the mask, and the failure is the prompt reintubation.[3][1]

Tracheostomy: timing, technique and decannulation

The tracheostomy is the long-term airway for the patient who cannot be extubated (the prolonged ventilation, the inability to protect the airway, the secretion clearance). The timing is the debated question — the early (within 2 to 4 days) versus the late (after 10 to 14 days) — and the TRACMAN trial (NEJM 2013) found that the early tracheostomy did not reduce the mortality or the ventilator-associated pneumonia, though it reduced the sedation and the ICU stay in some. The practice is individualised: the tracheostomy is considered for the patient expected to need the ventilation beyond 7 to 10 days, and the percutaneous dilatational technique (at the bedside, by the intensivist) is the standard.[1][1]

The decannulation (the removal of the tracheostomy) follows the successful weaning from the tracheostomy (the progressive downsizing, the tolerance of the capping, the effective cough and the secretion clearance), and the swallowing assessment. The principle is the graded, the assessed liberation from the tracheostomy, as from the endotracheal tube.[1]

Management: the structured liberation approach

The liberation from the mechanical ventilation is a structured, daily, protocolised process.[1][1]

1. Daily assessment of the readiness — the cause resolved, the oxygenation adequate (the FiO2 at or below 0.4, the PEEP at or below 8), the haemodynamics stable (no or low vasopressors), the ability to protect the airway.
2. The SBT — the 5 cmH2O pressure support for 30 to 120 minutes; the tolerance (the stable rate, the adequate gas, no distress) is the indication for the extubation.
3. The extubation — the assessment of the airway (the cuff leak, the laryngeal oedema risk), the cough and the secretions, the neurological status; the prophylactic NIV for the high-risk.
4. The NIV-assisted weaning for the difficult-to-wean — the extubation to the NIV, with the prompt reintubation for the failure.[3]
5. The tracheostomy for the prolonged ventilation (7 to 10 days) — the percutaneous, the bedside, the individualised timing.
6. The prevention of the failure — the treatment of the cause, the sedation minimisation, the early mobilisation, the nutritional support.

Monitoring the weaning patient

Monitoring divides into the SBT tolerance, the respiratory muscle reserve, and the complications.[1][1]

• The SBT tolerance — the respiratory rate (under 35), the heart rate and the blood pressure (the stability), the saturation (above 90 per cent), the absence of the distress.
• The respiratory muscle reserve — the RSBI (the f/VT, under 105 predicts the success), the maximal inspiratory pressure (the negative inspiratory force), the trend of the tidal volume and the rate.
• The complications — the laryngeal oedema (the cuff-leak test), the secretion retention, the cardiac ischaemia (the weaning stress), and the delirium. [1]

Prognosis and extubation failure

The prognosis of the weaning is the prognosis of the underlying disease, but the time to the successful liberation is itself a prognostic marker — the prolonged ventilation (beyond 7 days) carries a higher mortality and morbidity (the ventilator-associated pneumonia, the ICU-acquired weakness). The extubation failure (the reintubation within 48 to 72 hours) occurs in about 10 to 20 per cent of the patients, and it is associated with a higher mortality — particularly when the reintubation is delayed (the NIV failing, the patient tiring). The principle is the prompt, the safe, the protocolised liberation, and the prompt reintubation for the failure.[2][1]

Advanced mechanical ventilation modes

Beyond the NIV and the weaning lies the choice of the mode of the mechanical ventilation itself — the volume versus the pressure, the dual control, the closed-loop and the proportional modes, and the alarms and the troubleshooting that frame the ventilator at the bedside. The over-riding principle is that no advanced mode has proven a mortality benefit over the standard lung-protective ventilation (the volume control, the 6 mL/kg predicted body weight, the plateau below 30 cmH2O, the driving pressure below 15) — the advanced modes are the tools for the difficult-to-ventilate and the dyssynchronous patient, not a replacement for the fundamentals.[4][7]

The classification of a mode rests on three phase variables — the trigger (what starts the breath), the limit (what governs the delivered breath), and the cycle (what ends the breath). The volume control is the time/flow/volume; the pressure control is the time/pressure/time; the pressure support is the patient/pressure/flow. To name the three phase variables is to understand the mode.[7]

Volume control (VC)

The volume control guarantees the tidal volume (the set volume is delivered regardless of the lung compliance) and the pressure is the variable (it rises with the low compliance). The flow is constant (the square-wave pattern), the inspiration is time-cycled, and the peak airway pressure reflects the resistance and the compliance combined. The risk is the high pressure in the low-compliance lung (the ARDS) — managed by the inspiratory hold (the plateau pressure, below 30 cmH2O) and the upper pressure alarm. The VC is the standard, the safe and the easy-to-monitor mode, and it is the foundation of the lung-protective ventilation.[4][7]

Pressure control (PC)

The pressure control guarantees the inspiratory pressure (the set pressure is held throughout the inspiration) and the tidal volume is the variable (it changes with the compliance). The flow is decelerating (the high initial flow that falls toward the zero), the inspiration is time-cycled, and the peak pressure EQUALS the plateau pressure (the constant inspiratory pressure — no resistive overshoot, no need for an inspiratory hold). The advantage is the better gas distribution in the heterogeneous lung (the ARDS, the pneumonia, the lobar consolidation) and the lower peak pressure; the risk is the variable tidal volume (the falling compliance drops the Vt, the rising compliance overdistends). The PC requires the close monitoring of the delivered tidal volume.[7]

Pressure support ventilation (PSV)

The pressure support is the spontaneous mode — the patient triggers each breath (the trigger is the flow or the pressure drop at the airway), the ventilator delivers the set pressure support to augment the inspiration, and the breath cycles off when the inspiratory flow falls to the threshold (the cycling-off criterion, typically the 25 per cent of the peak flow). The PSV is the weaning mode (the SBT is the PSV at the 5 to 7 cmH2O) and the spontaneous-breathing mode of the ventilator. The advantage is the patient-controlled breathing (the rate, the Vt and the inspiratory time are patient-set); the risks are the inadequate support in the fatiguing patient (the fatigue → the failure) and the leak-related asynchrony (the NIV).[1]

Synchronised intermittent mandatory ventilation (SIMV)

The SIMV combines the mandatory breaths (the ventilator-delivered, the volume or the pressure, at the set rate) with the spontaneous breaths (the patient-triggered, supported by the pressure support). The mandatory breaths are synchronised to the patient effort (the ventilator waits for the trigger window before delivering the mandatory breath). The SIMV was historically popular but the evidence (the Brochard 1994, the Esteban 1995) showed it is the slowest and the least successful weaning method — the intermittent mandatory breaths impose the variable load on the diaphragm. The SIMV is now reserved for the initial support and the specific situations (the partial ventilatory support with the backup rate), not for the weaning.[1][8]

Dual control modes: PRVC, VC+ and AutoFlow

The dual control modes combine the volume guarantee with the pressure limitation — the volume-targeted, the pressure-limited ventilation. The operator sets the target tidal volume and the upper pressure limit; the ventilator delivers the pressure-control-type breath (the decelerating flow) and measures the resulting volume, then adjusts the inspiratory pressure breath-by-breath to deliver the target volume at the lowest possible pressure. The PRVC (the pressure-regulated volume control, Maquet/Getinge), the VC+ (the Hamilton) and the AutoFlow (the Dräger) are the proprietary names for the same concept. The advantage is the guaranteed volume with the pressure-minimised gas distribution — the modern ventilator default. The risk is the silent rise of the pressure to chase the falling compliance — the ventilator will raise the pressure toward the set limit breath-by-breath, and a high or default limit can allow the injurious pressures. Manage by the tight upper pressure limit (a few cmH2O above the working pressure) and the daily watching of the plateau and the driving pressure.[7]

APRV and BiLevel — the two-level pressure modes

The airway pressure release ventilation (the APRV) and the BiLevel (the DuoPAP, the Bilevel) are the two-level pressure modes. The APRV applies a continuous high pressure (the Phigh, the 25 to 35 cmH2O) held for a long time (the Thigh, the 4 to 6 seconds), with the brief releases to the low pressure (the Plow, the 0 to 5 cmH2O, for the short Tlow, the 0.4 to 0.8 seconds). The spontaneous breathing occurs throughout the cycle (the key feature — the diaphragm keeps working, the sedation is lighter, the venous return is preserved, the muscle atrophy is reduced). The high mean airway pressure recruits the alveoli (the oxygenation); the release generates the ventilation (the CO2 clearance). The Tlow is the single most important setting — titrate so the expiratory flow returns to the 50 to 75 per cent of the peak (the partial release). Too long → the derecruitment; too short → the air-trapping and the auto-PEEP.[7]

The BiLevel is the controlled variant with the set mandatory breaths (the pressure-controlled breaths at the high level, with the time-cycled transitions). The BiLevel is for the patient needing the recruitment and the synchrony benefits of the two-level mode but with the guaranteed minimum minute ventilation (the tiring patient, the marginal drive). The APRV is avoided in the obstructive disease (the COPD, the asthma) for the dynamic hyperinflation risk from the inverse ratio. No proven mortality benefit; the salvage or the adjunct for the recruitable, stiff lung of the ARDS.[7]

Closed-loop ventilation: ASV

The adaptive support ventilation (the ASV, Hamilton) is the closed-loop mode — the operator sets the target minute ventilation (as the percentage of the predicted, typically the 100 per cent) and the ventilator measures the compliance and the resistance each breath, then computes the rate-and-tidal-volume combination that achieves the target at the minimum work of breathing (the Otis optimum, based on the expiratory time constant). The ventilator continuously adapts the pattern to the changing mechanics and the patient drive — more support when the drive is low, the spontaneous breathing when the drive returns. The ASV is the automated mode — useful for the variable drive and the weaning (it reduces the clinician interventions and shortens the weaning in some trials), but it does not prove the mortality benefit over the protocolised conventional weaning.[7]

Proportional modes: PAV+ and NAVA

The proportional assist ventilation (the PAV+) and the neurally adjusted ventilatory assist (the NAVA) are the proportional modes — the support tracks the instantaneous patient effort. The PAV+ measures the elastance and the resistance each breath, the clinician sets the gain (the percentage of the work the ventilator does — typically the 50 to 80 per cent), and the support is the flow-and-volume-proportional — a small effort yields the small support, a large effort the large support. The patient governs the rate, the Vt, the flow and the inspiratory time. The NAVA uses the electrical activity of the diaphragm (the EAdi, via the specialised nasogastric electrode catheter) to trigger and to drive the support — the neural signal, the proportional pressure (the cmH2O per microvolt of EAdi). The advantage is the superior synchrony (the neural trigger eliminates the ineffective triggering and the auto-triggering, the cycling matches the neural inspiratory time) and the patient-governed breathing. The NAVA is the best mode for the NIV with the large leaks (the pneumatic triggers fail in the leak; the EAdi does not). The risks — the PAV+ requires the reliable elastance/resistance measurement (the coughing, the leaks disturb it); the NAVA depends on the intact neuromuscular drive (the high cervical cord injury, the phrenic nerve injury, the severe neuromuscular disease, the deep sedation or the paralysis) and the correctly placed catheter. Always set the backup pneumatic mode for the NAVA.[7]

Closed-loop oxygenation

The closed-loop oxygenation (the AutoMix, the O2-Closed Loop, the FreeO2) is the emerging automation of the FiO2 — the ventilator (or the HFNC) titrates the FiO2 to the target SpO2, reducing the hyperoxia and the hypoxia. The benefit is the reduced nursing workload and the lower mean FiO2 (the lung-protective and the oxygen-toxicity avoidance). The closed-loop oxygenation is not yet the standard, but it is a growing area — the closed-loop systems (the ASV with the auto-oxygenation, the SmartCare) move toward the fully automated ventilation. [1]