Clinical Reference
Ventilator Modes & Waveforms
Pressure / flow / volume patterns for each mode, clinical use, and PB980 labels.
Reading Ventilator Waveforms
Pressure–Time (Paw)
Shows airway pressure over time. Ppeak reflects total resistive + elastic load. Pplat (end-inspiratory pause) reflects only elastic load. Pplat ≤ 30 cmH₂O targets alveolar protection in ARDS.
Flow–Time
Above zero = inspiratory flow; below zero = expiratory. Square wave = volume control. Decelerating = pressure control or PSV. Auto-PEEP appears when expiratory flow has NOT returned to zero before the next breath.
Volume–Time
Rises during inspiration, returns to zero (baseline) during expiration. Mismatch between set and exhaled VT = circuit/cuff leak. In PC mode, changing volume with stable pressure signals a compliance or resistance change.
Volume Control (VC / VC+)
When to use
Default mode for most ICU patients. ARDS lung-protection: 6 mL/kg IBW, Pplat ≤ 30 cmH₂O.
Volume Control (VC) / VC+
NBRC Pearl
Ppeak ≠ Pplat. The difference reflects airway resistance. Always monitor Pplat for alveolar overdistension.
Pressure Control (PC)
When to use
When precise airway pressure control is needed. High resistance states, neonatal/pediatric care.
Pressure Control (PC)
NBRC Pearl
VT varies with changes in compliance and resistance — monitor exhaled VT closely with any lung mechanics change.
Pressure Support (PSV)
When to use
Weaning trials, NIV (BiPAP), augmenting spontaneous breathing. Patient must have intact drive.
Pressure Support (PS) — within CPAP/PS mode
NBRC Pearl
PS too high → patient becomes passive (no drive). Too low → increased WOB. Target RR 12–25, VT 6–8 mL/kg.
PRVC / VC+ (Pressure-Regulated Volume Control)
When to use
Combines VC volume guarantee with PC decelerating flow. Used in ARDS and post-op patients.
VC+ / Volume Support (VS) — see note
NBRC Pearl
On PB980: VC+ = controlled mode, VS = spontaneous mode. Other vents call this PRVC, AutoFlow, APV, or Adaptive Pressure Control.
APRV / BiLevel (Airway Pressure Release Ventilation)
When to use
Refractory ARDS, improves oxygenation by maintaining high mean airway pressure. Allows spontaneous breathing.
BiLevel / APRV
NBRC Pearl
TLow set to 0.2–0.8 s to prevent de-recruitment. Titrate so expiratory flow returns to 50–75% of peak at end-TLow.
SIMV (Synchronized Intermittent Mandatory Ventilation)
When to use
Largely replaced by PSV/SBT protocols. Evidence does NOT support SIMV over PSV for weaning (Brochard 1994).
SIMV+PS (mandatory breaths + PS for spontaneous breaths)
NBRC Pearl
SIMV does not accelerate weaning vs. PSV trials and SBTs. Avoid for primary weaning strategy when possible.
CPAP (Continuous Positive Airway Pressure)
When to use
SBT before extubation, non-invasive OSA therapy, post-extubation support.
CPAP/PS (at 0 PS = pure CPAP)
NBRC Pearl
A 30-minute CPAP or T-piece SBT predicts successful extubation better than gradual SIMV weaning (Yang & Tobin 1991).
Puritan Bennett 980 — Mode Quick Reference
| PB980 Mode | Generic Name | Volume Guaranteed | Notes |
|---|---|---|---|
| VC | Volume Control | Yes (set VT) | Square flow, rising pressure waveform |
| PC | Pressure Control | No (varies) | Square pressure, decelerating flow |
| VC+ | Adaptive Pressure / PRVC | Yes (target VT) | Auto-adjusts driving pressure breath-to-breath |
| VS | Volume Support | Yes (target VT) | Spontaneous mode; PS auto-adjusts to maintain VT |
| CPAP/PS | CPAP + Pressure Support | No | Patient controls rate; PS augments each breath |
| APRV/BiLevel | APRV | No | PHigh / PLow / THigh / TLow settings |
| PAV+ | Proportional Assist Vent. | No | Amplifies patient effort in proportion; needs intact drive |
| SIMV + VC/PC/VC+ | SIMV | Mandatory only | Spontaneous breaths need separate PS setting |
Source: Medtronic/Covidien PB980 Operator Manual. Verify against your unit's installed software version.
Vapotherm HVNI — High-Flow Nasal Cannula
What it is
Vapotherm is not a mechanical ventilator — it delivers heated, humidified, precisely blended air/O₂ through small-bore nasal prongs at high velocities. The high flow washes out nasopharyngeal dead space and creates a small CPAP-like effect (+1–3 cmH₂O), reducing work of breathing without intubation.
Key Parameters
Clinical Use
Watch For Failure
SpO₂ not improving or RR >30 after 1–2 h at ≥40 L/min and FiO₂ ≥0.60 → escalate to NIV or intubation. ROX index (SpO₂/FiO₂ ÷ RR) <4.88 at 12 hours predicts HFNC failure.
Other HFNC systems: Fisher & Paykel Optiflow (Airvo 2), Teleflex HiFlO, Breas Nippy 4+, TNI SoftFlow. Same physiology; flow rates and humidification differ.
Auto-PEEP (Intrinsic PEEP / Air Trapping)
Auto-PEEP occurs when the next breath triggers before exhalation is complete — air accumulates progressively. Common in COPD, asthma, and high RR/VT settings.
Waveform Signs
Expiratory flow has NOT returned to zero baseline before the next breath triggers on the flow-time scalar.
Bedside Detection
Occlude the expiratory port at end-expiration (expiratory hold) — the ventilator displays the trapped pressure.
Management
↓ RR, ↓ VT, ↑ expiratory time (I:E ≥ 1:3), treat bronchospasm. Consider applied PEEP ≤ 80% of measured auto-PEEP.
For board exam preparation. Always consult manufacturer operator manuals and current AARC/ATS/ERS guidelines for patient care.