Reference Guide
Mechanical Ventilation
Ventilation modes, cardiac surgery settings, weaning, and troubleshooting
Mode Descriptions
- Volume-Controlled AC (VC-AC): Most common initial post-op mode. Delivers set tidal volume at set rate; patient may trigger additional breaths at same Vt
- Pressure-Controlled AC (PC-AC): Set inspiratory pressure; Vt varies with compliance. Useful when peak pressures are problematic
- SIMV with Pressure Support: Mixed mandatory/spontaneous breaths. Less commonly first-line
- Pressure Support (PSV/CPAP): Used for weaning and spontaneous breathing trials. Patient triggers all breaths
- APRV: Selected for refractory hypoxemia/ARDS; institution-dependent
Typical Fast-Track Settings
| Parameter | Typical Setting |
|---|---|
| Mode | Volume AC (or PC-AC) |
| Tidal Volume | 6–8 mL/kg predicted body weight (PBW) |
| Respiratory Rate | 12–16/min, titrated to PaCO₂ 35–45 mmHg |
| PEEP | 5 cmH₂O initially (titrate higher if hypoxemic) |
| FiO₂ | 60% on arrival, wean to SpO₂ 92–96% |
| I:E Ratio | 1:2 |
| Plateau Pressure Goal | ≤25–30 cmH₂O |
| Peak Inspiratory Pressure | ≤35 cmH₂O |
PBW Calculation
Predicted Body Weight:
Men = 50 + 2.3 × (inches over 60)
Women = 45.5 + 2.3 × (inches over 60)
Fast-track extubation within 6 hours is standard for uncomplicated cardiac surgery, associated with reduced ICU length of stay and VAP.
Hemodynamic Effects of PPV
- ↓ RV Preload — decreased venous return gradient (dominant cause of CO reduction in healthy patients)
- ↑ RV Afterload — increased PVR proportional to mean airway pressure, hyperinflation, hypoxia, hypercapnia, acidosis
- ↓ LV Afterload — decreased LV transmural pressure — beneficial in decompensated LV failure
- ↓ LV Preload — secondary to reduced RV output and septal shift (ventricular interdependence)
Clinical Implications
- In LV failure/pulmonary edema, PPV/NIV unloads the LV and reduces work — often therapeutic
- In RV failure, hypovolemia, tamponade, PPV may precipitously drop CO; use lowest effective PEEP and Vt
- After extubation in high-risk patients, prophylactic NIV applied immediately is recommended
Readiness Screening Criteria
- Resolution/improvement of underlying indication
- Awake, arousable, following commands
- Hemodynamic stability without escalating vasopressors
- FiO₂ ≤0.40–0.50, PEEP ≤5–8 cmH₂O, PaO₂/FiO₂ ≥150–200
- pH ≥7.25, adequate ventilation
- Intact cough, manageable secretions
- Adequate hemoglobin, acceptable rhythm and core temperature
SBT Protocol (2024 AARC Guidance)
- Use pressure support 5–8 cmH₂O rather than T-piece
- Duration 30–120 minutes (longer in high-risk patients)
- Conduct before noon when possible
- Do not increase FiO₂ during the trial
- RSBI (f/Vt) no longer required; routine RSBI may prolong ventilation unnecessarily
- Failure signs: RR >35, SpO₂ <90%, HR change >20%, SBP <90 or >180, agitation, diaphoresis, accessory muscle use
Alarm Guide
| Alarm | Likely Causes | Bedside Actions |
|---|---|---|
| High Peak Pressure | Secretions, bronchospasm, mainstem intubation, biting, kink, pneumothorax | Suction, check tube position/cuff, auscultate, check plateau pressure, CXR |
| High Plateau (>30) | Decreased compliance: edema, ARDS, pneumothorax, abdominal distension | Treat cause; reduce Vt; consider neuromuscular blockade in ARDS |
| Low Pressure / Low MV | Disconnect, circuit leak, cuff leak, extubation | Trace circuit; reconnect; reinflate cuff; manual bag |
| Auto-PEEP / Stacking | Short expiratory time, bronchospasm, high RR | Increase E-time, decrease RR/Vt, treat bronchospasm; brief disconnect |
| Apnea Alarm | Oversedation, neurologic deterioration | Assess; switch mode; bag if needed |
| High RR / Asynchrony | Pain, agitation, air hunger, fever | Treat cause; analgesia/sedation; adjust trigger/flow/rise time |
Lung-Protective Ventilation (ARDSNet)
- Vt 6 mL/kg PBW (may decrease to 4 mL/kg to keep Pplat ≤30 cmH₂O)
- Plateau pressure ≤30 cmH₂O; driving pressure (Pplat − PEEP) ≤15 cmH₂O
- Permissive hypercapnia, accepting pH ≥7.20–7.25
- PEEP/FiO₂ titration per ARDSNet table for SpO₂ 88–95%
- Prone positioning for PaO₂/FiO₂ <150 (minimum 16 h)
- Neuromuscular blockade considered in severe ARDS
- Conservative fluid balance once shock resolved
RV-Protective Considerations
- Minimize driving pressure and avoid hyperinflation
- Avoid permissive hypercapnia in patients with pulmonary hypertension or RV failure
- Aggressive correction of hypoxemia and acidosis
- Echo screening for acute cor pulmonale (~20–25% of ARDS)
- Norepinephrine first-line; inhaled pulmonary vasodilators (iNO 10–40 ppm, epoprostenol) for RV strain
- Consider VV-ECMO for severe refractory hypoxemia
S.K.
The World-Class Cardiac Intensivist
This content is for educational reference only. Always follow institutional protocols and exercise clinical judgment.