Start with the pressure–time waveform, then practice on the Servo-u alone or with a jet ventilator running alongside. Clinical statements are cited; anything tagged model describes what this simulation does, not a clinical claim.
Change any ventilator or patient setting. The last breath before your change is saved, and once the baby settles you'll see the two breaths overlaid with the change in each number.
Each one loads a patient and starting settings. Some change on their own after a few seconds. Read what to watch, make a change, then open the teaching point.
Pressure is held constant for the set Ti and flow decelerates; if pressure starts to fall during inspiration, flow increases to hold it[2].
Pressure is set as PC above PEEP[2]. If airway pressure reaches the upper pressure limit, the ventilator cycles to expiration[2].
The first breath is a volume-controlled test breath whose plateau pressure sets the next breath's pressure[2]. After that, pressure changes between breaths in steps of at most 3 cmH₂O[2].
The ceiling is 5 cmH₂O below the upper pressure limit, where "Regulation pressure limited" appears[2]. Not recommended with circuit leakage[2].
Every breath is patient-triggered and pressure is adjusted toward the set VT[2]. The first breath uses 10 cmH₂O, the next three can each rise up to 20 cmH₂O, then steps are at most 3 cmH₂O[2]. Apnea switches it to volume-controlled backup[2].
Set mandatory pressure-control breaths with pressure support in between; if the patient hasn't triggered within 90% of the SIMV period, a mandatory breath is delivered[2]. SIMV (VC) + PS is not available in the neonatal category[1].
The patient triggers every breath; expiration starts when flow falls to the End inspiration percentage (infant default 30%) or after 1.5 s in infants[2]. CPAP is PS set to zero; apnea switches to pressure-control backup[2].
The jet is pressure-limited and time-cycled and runs alongside a conventional ventilator[15]. The conventional ventilator supplies PEEP and, when used, a few background breaths[15].
The quick reference guide gives conventional PEEP of 7–12 cmH₂O for neonates, a sigh rate generally 0–5 bpm, and a conventional I-time of 0.4 s[14]. One pathway prefers CPAP, especially with air leak, and uses background breaths only as sighs[15].
The Servo-u's neonatal RR range starts at 4 b/min[1], so the lab offers CPAP or PC sighs at 4–10.
HFJV ΔP (PIP − PEEP) is the primary determinant of PaCO₂; I-time and rate are secondary[14].
Resting lung volume supported by PEEP and the mean airway pressure are crucial for PaO₂[14]. Raising the jet rate also raises MAP by shortening expiratory time[16].
Servo is the driving pressure the jet adjusts automatically to hold PIP[14]. Servo changes are early signs of a change in the patient[14].
One guideline suspects trapping when jet-measured PEEP exceeds set PEEP by more than 1.5–2 cmH₂O[16]. Trapping is best addressed by decreasing or stopping the background rate, then lowering jet rate in 60-bpm steps[15][14].
The jet pushes gas in; between pulses the lung empties by recoil, so the time between pulses matters. Lowering the rate lengthens exhalation time[14].
The 2022 European RDS guidelines suggest starting volume targeting around 5 ml/kg with a safe maximum PIP of about 25–30 cmH₂O; required VT usually varies around 5–7 ml/kg[5].
One regional guideline uses usually 5 ml/kg (range 4.5–7) and notes research values of 3.5–8 ml/kg[7].
The lab colors VTe green at 4–7 ml/kg and alarms below 3.5 or above 8. Follow your unit's protocol.
A 2017 Cochrane review of 20 trials found volume-targeted ventilation reduced death or BPD at 36 weeks, pneumothorax, hypocarbia and grade 3–4 IVH versus pressure-limited ventilation[6]. It lets pressure wean in real time as compliance improves[5].
One nursing guideline gives an ideal minute volume of 0.2–0.3 l/kg/min[12]. PEEP that keeps the lung open is judged by the point where FiO₂ is lowest; overdistension raises the risk of air leaks and PIE[5].
One neonatal NAVA guideline sets Edi trigger at 0.5 µV, starts NAVA level around 1–2 cmH₂O/µV, and titrates in 0.2 steps to keep Edi peak about 5–15 µV on invasive NAVA[8].
In ventilated neonates, overdistended volume–pressure loops show smaller volume gains with each further pressure rise, a flattening at the top[9].
The time to inflate to 63% of the final volume or deflate by 63%[10]. Because it's exponential, 3τ reaches 1 − e⁻³ ≈ 95% and 5τ about 99%.
In a neonatal lung-model study, shorter expiratory time raised the risk of inadvertent PEEP, which was highest with compliant lungs[11]. On the jet, expiratory time between pulses is only about 0.12 s at 420 bpm with a 0.020 s I-time (60 ÷ 420 − 0.020).
One neonatal nursing guideline uses DOPE for acute deterioration on mechanical ventilation, including disconnecting and hand-ventilating when equipment is suspected[12].
Surfactant can rapidly affect oxygenation and lung compliance, and support can be modified in response[13].
| What you see in the lab | Model cause | Scenario |
|---|---|---|
| VT drops in PC; pressure climbs in PRVC | Compliance fell or resistance rose | Pneumothorax; Secretions |
| VTi ≫ VTe; volume ends above zero | ETT leak | Large ETT leak |
| Total PEEP above set | Te shorter than 3τ | Air trapping |
| Flat top on the P–V loop; amber lungs | Overdistension | Overdistension |
| Servo falls on the jet | Compliance down or resistance up | Jet: pneumothorax, secretions |
| Servo rises on the jet | Compliance up or leak | Jet: compliance improving, extubation |
Manufacturer documents describe device behavior; guidelines and studies support clinical statements. Where Getinge's public Servo-u documents did not describe a behavior, the Servo-i modes guide from the same manufacturer is cited. Check your unit's user's manuals for your software versions.