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RESPIRATORY · FOUNDATIONS
The modes of neonatal respiratory support, the settings that matter, and how to adjust them to the baby and the blood gas.
THE ESCALATION LADDER
Neonatal respiratory support is a ladder. The modern approach is to support without intubating wherever possible - CPAP first - and to escalate only as needed. Most escalation here is in the context of prematurity.
A small flow of oxygen for isolated, mild hypoxaemia with little work of breathing.
Heated, humidified gas at 2-8 L/min. Comfortable, washes out nasopharyngeal dead space and gives some distending pressure. Useful for milder disease and for weaning off CPAP.
The workhorse for preterm RDS. A constant distending pressure (~5-8 cmH₂O) maintains FRC, splints the airway and cuts work of breathing - often avoiding intubation altogether.
CPAP plus intermittent inflations through nasal prongs - a step up that still avoids an endotracheal tube.
Intubation and mechanical breaths when non-invasive support fails, the baby is apnoeic/exhausted, or for surfactant and stabilisation.
Tiny breaths at high frequency around a constant mean airway pressure - for severe disease, air leak or when conventional ventilation is failing.
NON-INVASIVE SUPPORT
A single continuous pressure throughout the breath. By holding alveoli open at end-expiration it recruits and maintains FRC, improves oxygenation, splints the upper airway and reduces the work of breathing.
First-line for preterm RDS - early CPAP reduces the need for ventilation and surfactant. Typical pressure 5-8 cmH₂O; you mainly adjust pressure and FiO₂.
Heated humidified flow that flushes dead space and delivers a small, variable distending pressure - generally better tolerated than CPAP.
Good for milder disease and for weaning, but the pressure delivered is less predictable than CPAP, so it is usually a step down from CPAP rather than a substitute in severe RDS. In some centres, respiratory-stable infants can feed orally on high-flow.
CONVENTIONAL VENTILATION
Almost every ventilator decision comes back to two near-independent goals: getting oxygen in, and getting CO₂ out. Keeping them separate is the key to adjusting settings calmly.
Mean airway pressure is set mostly by PEEP (and by PIP and inspiratory time). To improve oxygenation: ↑ FiO₂ or ↑ PEEP / mean airway pressure to recruit more lung.
Tidal volume comes from the amplitude (PIP − PEEP). To lower CO₂: ↑ PIP (bigger breaths) or ↑ rate. To raise CO₂: do the reverse.
THE SETTINGS
| Setting | What it is | Mainly affects |
|---|---|---|
| PEEP | Pressure held at end-expiration | Oxygenation (maintains FRC, recruits alveoli) |
| PIP | Peak inspiratory pressure | Tidal volume → CO₂ removal (and oxygenation via MAP) |
| Rate | Mechanical breaths per minute | CO₂ removal (minute ventilation = rate × tidal volume) |
| FiO₂ | Fraction of inspired oxygen | Oxygenation |
| Ti | Inspiratory time | Mean airway pressure / oxygenation; set with lung time constants in mind |
MODES
A "mode" describes how the ventilator decides when and how to deliver a breath - how much the machine does versus how much the baby does. The settings above (PIP, PEEP, rate...) stay the same; the mode is the orchestration.
| Mode | What it is | In practice |
|---|---|---|
| Pressure-limited, time-cycled | The classic neonatal mode, also called conventional ventilation or IPPV (SIPPV when every breath is triggered). You set PIP, PEEP, rate and Ti; each breath is delivered up to the set pressure for the set time. Tidal volume rises and falls with lung compliance. | Simple and widely used - but watch that tidal volumes don't creep up as the lung improves. |
| SIMV | Synchronised intermittent mandatory ventilation. A set number of mandatory breaths are timed to the baby's own efforts; breaths taken in between are unsupported (or get a little pressure support). | The usual weaning mode - turn the mandatory rate down as the baby does more of the work. |
| A/C (PTV) | Assist-control / patient-triggered ventilation. Every breath the baby triggers gets a full ventilator breath, with a backup rate for apnoea. | More support than SIMV - the baby effectively sets the rate. |
| PSV | Pressure support. The baby controls the timing and rate; the ventilator adds a set pressure to each spontaneous breath and cycles off as inspiratory flow falls. | Often combined with SIMV; comfortable, good for weaning. |
| Volume guarantee (VG / VTV) | Layered on a pressure mode: you set a target tidal volume (~4-6 mL/kg) and the ventilator adjusts PIP breath-to-breath to deliver it. | Limits over-distension; reduces death and CLD vs fixed-pressure ventilation. |
The same modes as an exam-style grid - who triggers the breath, what ends it, and which breaths get supported:
| Mode | Triggered by | Cycled by | Breaths supported | In a phrase |
|---|---|---|---|---|
| IMV | Nothing - machine timer | Time (fixed Ti) | A set rate, ignoring the baby | Ventilator-driven and asynchronous |
| SIMV | Infant (mandatory breaths only) | Time (fixed Ti) | A set number of breaths, not every one | Supports a set number of breaths |
| A/C (PTV) | Infant - every breath (+ backup rate) | Time | Every triggered breath | Supports every breath |
| PSV | Infant (patient-driven) | Flow (cycles off as flow falls) | Every spontaneous breath | Patient-driven |
| Volume guarantee | As the host mode | Pressure adjusts to hit target volume | Targets a set tidal volume | Targets volume by varying pressure |
| NAVA | Diaphragm signal (Edi catheter) | Neural - the baby's own drive | Support proportional to effort | Support scaled to the baby's neural drive |
AT THE BEDSIDE
A blood gas points to which setting to move. Always interpret alongside the baby, the chest and the trend - and aim for gentle, lung-protective targets rather than perfect numbers.
| The problem | First moves |
|---|---|
| High CO₂ (respiratory acidosis) | ↑ rate and/or ↑ PIP / tidal-volume target |
| Low CO₂ | ↓ rate and/or ↓ PIP |
| Low O₂ (hypoxaemia) | ↑ FiO₂ and/or ↑ PEEP / mean airway pressure |
| High O₂ (hyperoxia) | ↓ FiO₂ first, then wean PEEP |
SPECIFIC THERAPIES
Surfactant replaces what the immature lung lacks. It can be given prophylactically or as rescue once RDS is established.
INSURE (INtubate-SURfactant-Extubate) returns the baby quickly to CPAP. LISA / MIST delivers surfactant through a thin catheter while the baby stays on CPAP and keeps breathing - associated with less CLD.
HIGH-FREQUENCY VENTILATION
High-frequency oscillatory ventilation abandons the idea of "breaths" altogether. Some centres use HFOV as a primary lung-protective strategy, not only as rescue. The lung is held open at a constant distending pressure while gas is oscillated back and forth very fast - often 8-15 Hz (480-900 a minute) - moving tidal volumes so small they can be less than the anatomical dead space. Expiration is active (actively pulled out), and gas exchange happens through mechanisms beyond simple bulk flow.
| Control | What it does | Mainly affects |
|---|---|---|
| Mean airway pressure (MAP) | The constant distending pressure that holds the lung open and recruits alveoli | Oxygenation (with FiO₂) |
| Amplitude (ΔP / "power") | The size of the oscillation - the visible chest "wiggle" | Tidal volume → CO₂ removal |
| Frequency (Hz) | How fast it oscillates. Counter-intuitively, a lower frequency delivers a larger tidal volume | CO₂ removal (↓ Hz → more CO₂ cleared) |
| FiO₂ | Fraction of inspired oxygen | Oxygenation |
Severe RDS failing conventional ventilation, air leak (gas exchange at lower peak pressures), PPHN, CDH and severe MAS. The tiny tidal volumes make it lung-protective.
Optimal lung volume is everything. Too much MAP over-distends the lung and impedes venous return; too little lets it collapse. Follow the chest wiggle, the CXR (aim for ~8-9 posterior ribs of expansion) and the gases.
DO NO HARM
The ventilator that saves the lung can also injure it. Ventilator-induced lung injury is a major driver of chronic lung disease, so the goal is the least support that achieves safe targets.
Volutrauma (over-distension from big tidal volumes), atelectotrauma (repeated collapse and re-opening from too little PEEP), and oxygen toxicity all drive inflammation and CLD.
Use adequate PEEP to avoid collapse, small tidal volumes (volume targeting), permissive hypercapnia, and the lowest FiO₂ that meets the SpO₂ target. Prefer non-invasive support and wean actively.
Where ventilation meets the conditions and the underlying physiology: