Mechanical Ventilation
immediate assessment
Confirm tube placement first, then establish a baseline: examination and imaging, sedation, initial ventilator settings, and an early blood gas.
- confirm the tube bilateral breath sounds, chest rise, capnography waveform, depth at the teeth (usually 21-23 cm at the incisors), portable chest x-ray: tip 3-5 cm above the carina.
- sedation and analgesia analgosedation infusion, e.g. fentanyl 25-100 mcg/hr + propofol 5-50 mcg/kg/min; analgesia first, sedation second
- default target Richmond Agitation-Sedation Scale (RASS) -2 to 0, light sedation (1); depth is not one fixed number for everyone
- lighter (RASS 0) when screening for extubation readiness or during a spontaneous awakening trial
- deeper only for specific indications: severe ARDS with significant patient-ventilator dyssynchrony, intracranial hypertension
- first ventilator settings mode volume control / assist-control; tidal volume 6-8 mL/kg PBW to start, 6 mL/kg PBW for ARDS or anyone at risk (2); rate 16-20/min; PEEP 5 cmH2O; FiO2 100% at intubation, then wean
- tidal volume by predicted body weight (PBW), not actual weight; calculation below
- first blood gas arterial blood gas at 30-60 min after any major setting change.
early red flags after intubation
- hypotension in the first minutes, this is common and expected, see ventilator troubleshooting.
- desaturation that does not correct with FiO2 100%, treat as an emergency.
- rising peak pressure or a sudden difficulty bagging, work through ventilator troubleshooting now.
define & classify
Every vent order specifies two things: the mode, and the trigger/cycling logic that decides when the machine delivers a breath.
| mode | what it means |
|---|---|
| Volume Control / Assist-Control (VC/AC) | you set a fixed tidal volume, machine delivers it every breath, pressure varies. Default starting mode for most ward/HDU intubations, including ARDS. |
| Pressure Control (PC) | you set a fixed inspiratory pressure, tidal volume varies with compliance. Used when peak pressures are a concern or in some obstructive physiology. |
| Pressure Support (PSV) | patient triggers and controls rate and depth, machine only supports each breath. Spontaneous mode, used once the patient is ready to breathe more on their own, not for the newly intubated. |
| SIMV | mix of mandatory and spontaneous breaths. Rarely the best first choice, mainly seen as an institutional default. |
Every intubated, hypoxemic, or at-risk patient gets lung-protective ventilation from the first breath, not once acute respiratory distress syndrome (ARDS) is confirmed (2). Diagnostic criteria: ARDS.
initial management
predicted body weight (PBW), not actual weight
- men PBW (kg) → 50 + 0.91 × (height cm – 152.4)
- women PBW (kg) → 45.5 + 0.91 × (height cm – 152.4)
calculator Ideal/Predicted Body Weight · MDCalc ↗︎
additional starting parameters
- I:E ratio 1:2, inspiratory flow 60 L/min, adjust if flow-time waveform shows incomplete exhalation.
- obstructive disease (severe asthma/COPD): rate lower, 10-14/min, higher inspiratory flow (around 70-100 L/min) to lengthen expiration and limit auto-PEEP; permissive hypercapnia usually needed (below).
oxygenation target
- SpO2 88-95% or PaO2 55-80 mmHg for ARDS / lung-protective ventilation: deliberately lower than normal; do not chase 100%.
- move PEEP and FiO2 together using a PEEP/FiO2 ladder, a simplified version of the ARDSNet low-PEEP (2) and ALVEOLI high-PEEP (3) tables:
| FiO2 | low-PEEP strategy | high-PEEP strategy |
|---|---|---|
| 0.3 | 5 | 5-12 |
| 0.4 | 5-8 | 14-16 |
| 0.5 | 8-10 | 16-18 |
| 0.6-0.7 | 10-14 | 18-20 |
| 0.8-0.9 | 14 | 20-22 |
| 1.0 | 18-24 | 22-24 |
the high-PEEP arm is for moderate to severe ARDS. See ARDS for when to step up to it.
post-intubation checklist
- chest x-ray to confirm tube position and screen for a new pneumothorax.
- nasogastric or orogastric tube, especially if bag-mask ventilated before intubation.
- secure the tube, note depth at the teeth.
- set ventilator alarms, do not leave defaults unchecked.
- arterial line and repeat blood gas if the patient is unstable or on high settings.
reassess
- 30-60 min after intubation arterial blood gas. Adjust rate for pH/CO2, adjust PEEP/FiO2 for oxygenation.
- pH < 7.30 raise respiratory rate first (up to about 35/min, beyond which auto-PEEP defeats it), or raise tidal volume if plateau pressure allows.
- every ventilator or PEEP change recheck plateau pressure and driving pressure, not just oxygenation.
- daily sedation interruption or targeted light sedation, spontaneous breathing trial readiness screen once the underlying problem is improving.
advanced management
pressures, know these on every patient
- peak pressure reflects airway resistance plus compliance. Read on the ventilator at end-inspiration during flow.
- plateau pressure hold an inspiratory pause, read the pressure once flow stops. Reflects alveolar/compliance pressure alone. Keep < 30 cmH2O (4).
- driving pressure plateau minus PEEP; keep as low as tidal volume and PEEP limits allow. < 15 cmH2O is associated with better survival in observational data (5), not an RCT-proven target: do not sacrifice PEEP or oxygenation to chase it.
- a peak-plateau gap > 5 cmH2O points to an airway/resistance problem, not compliance. Full workup in ventilator troubleshooting.
permissive hypercapnia
- to keep tidal volume and plateau pressure protective, let PaCO2 rise: accept pH down to about 7.20-7.25 without correcting it.
- avoid in raised intracranial pressure, severe pulmonary hypertension, and significant uncompensated metabolic acidosis, discuss these with ICU.
- a bicarbonate infusion can buy time for pH but does not treat the underlying problem.
when the numbers do not add up
- persistent hypoxemia despite FiO2 and PEEP titration → reassess for ARDS and its escalation ladder, see ARDS.
- rising pressures, new dyssynchrony, or sudden decompensation → go to ventilator troubleshooting.
troubleshooting
This page covers starting and running a stable vent. For an acute problem on the vent, in-the-moment logic lives on the dedicated page.
- sudden desaturation, high pressure alarm, or a struggling patient → full DOPE-style workup in ventilator troubleshooting.
- hypotension right after intubation → same page, plus hypotension.
- persistent desaturation on the vent → oxygen desaturation and ARDS.
escalation / ICU
call ICU / anesthesia urgently for
- plateau pressure > 30 cmH2O despite reducing tidal volume to 4 mL/kg PBW.
- P/F ratio < 150 on FiO2 ≥ 0.6 and PEEP ≥ 10 = moderate to severe ARDS territory, ICU-level care; a general severity flag, not a formal criteria set (prone-positioning cutoffs use a lower PEEP, see ARDS).
- refractory hypoxemia or hypercapnia despite maximal ward/HDU-level titration.
- hemodynamic instability requiring escalating vasopressors alongside ventilation.
- any sudden, unexplained decompensation on the vent that does not resolve with the immediate DOPE checks.
pearls & pitfalls
- tidal volume by predicted body weight, never actual weight: a short, heavy patient does not get a bigger tidal volume.
- a normal peak pressure does not rule out a compliance problem, always check the plateau pressure separately.
sources
| source | type |
|---|---|
| 1. SCCM PADIS guideline | guideline |
| 2. ARDSNet / ARMA trial, NEJM 2000 | RCT |
| 3. ALVEOLI trial, NEJM 2004 | RCT |
| 4. ATS/ESICM/SCCM ARDS guideline, 2017 | guideline |
| 5. Amato et al., driving pressure, NEJM 2015 | cohort |
dosing above follows international guidance. Verify against the current Kuwait / MOH or hospital protocol where locally sensitive.
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Last updated · September 2026