Mechanical Ventilation

Master ventilator modes, initial settings, troubleshooting, weaning, and complications.

advanced120 min estimated4 lessons

Volume vs. Pressure Control: Choosing a Mode

The two fundamental ventilation strategies are volume control (VC) and pressure control (PC). In volume control, a set tidal volume is delivered regardless of the pressure required — the pressure varies with lung compliance and resistance. In pressure control, a set inspiratory pressure is applied and tidal volume varies with lung mechanics.

Volume control guarantees minute ventilation — critical when oxygenation or CO2 removal cannot be compromised. Pressure control limits peak airway pressure — important in ARDS or at risk of barotrauma. PRVC (Pressure-Regulated Volume Control) combines both: it targets a set volume while using the lowest pressure possible, adjusting breath to breath.

Volume control: guaranteed Vt, variable Paw — use when minute ventilation is critical
Pressure control: guaranteed Paw, variable Vt — use to limit barotrauma
PRVC: dual-control — targets Vt using lowest Paw possible
In VC, watch for high peak pressures indicating resistance/obstruction
In PC, watch for low Vt indicating worsening compliance

Clinical tip

When transitioning from PC to VC in an improving ARDS patient, set the target Vt to what was being delivered in PC mode to avoid sudden overdistension.

Initial Ventilator Settings

Starting a patient on mechanical ventilation requires setting mode, tidal volume, rate, FiO2, PEEP, and flow/I:E ratio.

For most adults: AC/VC mode, Vt 6–8 mL/kg IBW, RR 12–16, FiO2 1.0 initially then titrate to SpO2 92–96%, PEEP 5 cmH2O, flow 40–60 L/min (I:E ~1:2).

In ARDS: use lung-protective ventilation — Vt 4–6 mL/kg IBW, Plateau pressure <30 cmH2O, driving pressure <15 cmH2O, higher PEEP per ARDSNet table, permissive hypercapnia acceptable.

For COPD: avoid auto-PEEP by prolonging expiration (low RR 10–12, extended expiratory time, I:E 1:3 to 1:4).

Standard Vt: 6–8 mL/kg IBW (always use ideal body weight, not actual)
ARDS Vt: 4–6 mL/kg IBW — lung-protective ventilation
Plateau pressure target <30 cmH2O; driving pressure <15 cmH2O
Initial FiO2 1.0 then titrate; target SpO2 92–96% in most patients
COPD: low RR, prolonged expiration (I:E 1:3 or 1:4) to prevent auto-PEEP

Clinical tip

IBW for males: 50 + 2.3 × (height in inches - 60). For females: 45.5 + 2.3 × (height in inches - 60). Never use actual body weight for Vt calculation.

Weaning and Extubation Criteria

Weaning is the process of gradually reducing ventilatory support. The daily spontaneous breathing trial (SBT) is the cornerstone of weaning assessment.

Pre-SBT readiness criteria (ABCDEF bundle): Alert and cooperative, adequate Breathing (FiO2 ≤0.4, PEEP ≤5–8), hemodynamically stable, cause of respiratory failure improving.

SBT: Place patient on PS 5–8 cmH2O + PEEP 5 x 30–120 min. Pass criteria: RR <35, SpO2 >90%, HR and BP stable, no distress, RSBI (f/Vt) <105.

Extubation criteria: patent airway, adequate cough and secretion clearance, intact mental status, hemodynamically stable. Post-extubation stridor: racemic epinephrine and dexamethasone.

SBT: PS 5–8 + PEEP 5 for 30–120 min; RSBI <105 predicts extubation success
RSBI = RR ÷ Vt (in liters); <105 is threshold for extubation
Daily SBTs reduce ventilator days — don't delay when patient is ready
Post-extubation stridor: racemic epinephrine + dexamethasone
Failed extubation requires reintubation — high-flow NC or NIV may bridge

Clinical tip

RSBI is calculated with the patient breathing spontaneously — turn off all pressure support briefly, measure RR and Vt over 1 minute, divide.

Ventilator Complications and Troubleshooting

Ventilator-associated complications include: barotrauma (pneumothorax, pneumomediastinum), volutrauma (alveolar overdistension), VAP, oxygen toxicity, and auto-PEEP.

Auto-PEEP (intrinsic PEEP) occurs when expiration is incomplete — air trapping. Suspect in obstructive disease (COPD, asthma). Diagnose: occlude expiratory port at end-expiration, read pressure gauge. Treat: increase expiratory time, reduce RR, bronchodilators.

High peak pressure with normal plateau = increased resistance (secretions, bronchospasm, kinked tube). High peak AND plateau = decreased compliance (pneumothorax, ARDS, pulmonary edema, mainstem intubation).

For sudden deterioration on vent: DOPE — Displacement, Obstruction, Pneumothorax, Equipment failure.

DOPE mnemonic: Displacement, Obstruction, Pneumothorax, Equipment failure
Auto-PEEP: end-expiratory occlusion method; treat by prolonging expiration
High Ppeak + normal Pplat = resistance problem (secretions, bronchospasm)
High Ppeak + high Pplat = compliance problem (pneumothorax, pulmonary edema)
VAP prevention: HOB 30–45°, oral care, daily SAT/SBT, minimize sedation

Clinical tip

When a vented patient suddenly deteriorates, manually ventilate with a bag first — this immediately separates patient from equipment as a cause.

Clinical cases

Sudden Rise in Peak Airway Pressure

A 55-year-old intubated for ARDS is on AC/VC: Vt 450 mL, RR 18, FiO2 0.5, PEEP 10. Ppeak suddenly rises from 32 to 52 cmH2O. Pplat is 28 cmH2O.

What is the most likely cause, and what is your first intervention?

High Ppeak with normal Pplat indicates increased airway resistance. Most likely cause: secretions, bronchospasm, or kinked ET tube. First intervention: suction.

Ppeak reflects both resistance AND compliance, while Pplat reflects only compliance. When Ppeak rises but Pplat stays normal, resistance is the problem. Suction first; if unchanged, auscultate for bronchospasm and administer bronchodilator. Check tube position and rule out kinked circuit.

Weaning Assessment

A 45-year-old is being evaluated for extubation after 5 days of ventilation for pneumonia. FiO2 0.35, PEEP 5, awake and following commands. During SBT on PS 5/PEEP 5, RR = 24, Vt = 380 mL.

Calculate the RSBI and determine if extubation is appropriate.

RSBI = 24 ÷ 0.38 = 63. RSBI <105 indicates readiness for extubation.

RSBI (Rapid Shallow Breathing Index) = RR ÷ Vt in liters. A value <105 predicts successful extubation. This patient also meets other criteria: low FiO2/PEEP, awake, cooperative. Proceed with extubation and monitor closely.

Know this for NBRC

IBW calculations — males 50 + 2.3/inch over 60; females 45.5 + 2.3/inch over 60
ARDS: 4–6 mL/kg IBW, Pplat <30, driving pressure <15
RSBI <105 = extubation candidate; calculated as RR ÷ Vt(L)
DOPE for acute vent deterioration
Auto-PEEP: end-expiratory hold; treat with longer expiration
High Ppeak + normal Pplat = resistance; high Ppeak + high Pplat = compliance
FiO2 >0.6 for >48h risks oxygen toxicity — always try to reduce

Key facts

ARDS Vt: 4–6 mL/kg IBW; Pplat <30 cmH2O; driving pressure <15 cmH2O
IBW male: 50 + 2.3 × (inches over 60); IBW female: 45.5 + 2.3 × (inches over 60)
RSBI <105 predicts successful extubation; >105 predicts failure
Auto-PEEP: occlude expiratory port at end-expiration to measure
DOPE: Displacement, Obstruction, Pneumothorax, Equipment
Normal I:E ratio: 1:2; COPD: 1:3 to 1:4; inverse ratio in ARDS: 1:1 to 2:1
FiO2 >0.60 for >24–48 hours risks oxygen toxicity (absorption atelectasis)
SBT: CPAP/PS 5–8 cmH2O for 30–120 min; reassess daily
Driving pressure = Pplat – PEEP; target <15 cmH2O in ARDS
PEEP reduces FiO2 requirements by recruiting alveoli

NBRC pearls

RSBI = f/Vt — use liters for Vt! (e.g., RR 20, Vt 0.45 L → RSBI = 44.4)
Plateau pressure measured during end-inspiratory hold with no flow
Driving pressure = Pplat – PEEP (not peak pressure minus PEEP)
ARDSNet protocol: start Vt 6 mL/kg IBW, can decrease to 4 if needed
NBRC often asks: what to do when Ppeak rises but Pplat stays same — suction/bronchodilator

Memory tricks

DOPE = Displacement, Obstruction, Pneumothorax, Equipment — for acute vent deterioration
For ARDS: 'Low and slow' — low Vt, low pressures, slow RR
RSBI <105 = patient 'one-oh-five to be free'

Common mistakes

Using actual body weight instead of IBW for Vt calculation
Not checking plateau pressure — peak pressure alone is insufficient
Delaying daily SBTs in patients ready to wean
Forgetting auto-PEEP in COPD/asthma patients with high RR or long I-time
Setting FiO2 1.0 and forgetting to titrate down
Not including PEEP when calculating driving pressure

Mechanical Ventilation

Volume vs. Pressure Control: Choosing a Mode

Initial Ventilator Settings

Weaning and Extubation Criteria

Ventilator Complications and Troubleshooting

Clinical cases

NBRC pearls

Memory tricks

Common mistakes

Related topics

Mechanical Ventilation

Volume vs. Pressure Control: Choosing a Mode

Initial Ventilator Settings

Weaning and Extubation Criteria

Ventilator Complications and Troubleshooting

Clinical cases

NBRC pearls

Memory tricks

Common mistakes

Related topics

Lessons

Volume vs. Pressure Control: Choosing a Mode

Initial Ventilator Settings

Weaning and Extubation Criteria

Ventilator Complications and Troubleshooting

Clinical cases

NBRC pearls

Memory tricks

Common mistakes

Related topics

Lessons

Volume vs. Pressure Control: Choosing a Mode

Initial Ventilator Settings

Weaning and Extubation Criteria

Ventilator Complications and Troubleshooting

Clinical cases

NBRC pearls

Memory tricks

Common mistakes

Related topics