Contents
Indications for Mechanical Ventilation
- Failure to oxygenate (refractory hypoxemia despite high FiOâ‚‚)
- Failure to ventilate (rising PaCOâ‚‚ with respiratory acidosis)
- Inability to protect the airway (depressed LOC, GCS ≤8)
- Excessive work of breathing / impending respiratory fatigue
Core Ventilator Settings
- Tidal Volume (Vt): 6–8 mL/kg ideal body weight (6 mL/kg in ARDS)
- Respiratory Rate (RR): set rate of breaths/min; affects COâ‚‚ clearance
- FiO₂: 21–100%; titrate to lowest level keeping SpO₂ ≥92%
- PEEP: positive end-expiratory pressure, usually 5 cm Hâ‚‚O baseline
- I:E ratio: normal 1:2; prolonged expiration in obstructive disease
Ventilator Modes
- Assist-Control (AC): every breath (patient- or time-triggered) gets full support — most rest for the patient
- SIMV: set mandatory breaths are synchronized; spontaneous breaths get less support
- Pressure Support (PSV): spontaneous breaths only, augmented by set pressure — a weaning mode
- CPAP: continuous pressure, no set breaths — patient does all the work
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Start Free Practice →Volume vs Pressure Control
- Volume control: guarantees Vt; pressure varies — watch for high peak pressures
- Pressure control: guarantees pressure; Vt varies with lung compliance
- In stiff lungs (ARDS), pressure control or low-Vt volume control limits barotrauma
- Plateau pressure goal <30 cm Hâ‚‚O to protect the lungs
PEEP and Auto-PEEP
- PEEP keeps alveoli open at end-expiration, improving oxygenation and recruiting lung
- High PEEP can ↓venous return → hypotension and can cause barotrauma
- Auto-PEEP (breath stacking): incomplete exhalation traps air — common in COPD/asthma
- Fix auto-PEEP by allowing more expiratory time (↓RR, ↓Vt, ↑expiratory flow)
Ventilator Alarms
- High-pressure alarm: obstruction, biting, kinked tube, secretions, coughing, bronchospasm, pneumothorax
- Low-pressure / low-volume alarm: disconnection, cuff leak, circuit leak, extubation
- Always assess the patient first; if in doubt, disconnect and bag with 100% Oâ‚‚
- A sudden high-pressure alarm + absent breath sounds + hypotension = suspect tension pneumothorax
Adjusting the Vent from the ABG
- To fix oxygenation (low PaOâ‚‚/SpOâ‚‚): increase FiOâ‚‚ and/or PEEP
- To fix ventilation (high PaCOâ‚‚): increase RR and/or tidal volume (minute ventilation)
- Minute ventilation = RR × Vt; it controls CO₂ removal
- Make one change at a time and recheck an ABG in ~20–30 minutes
Weaning and Spontaneous Breathing Trials
- Daily readiness: adequate oxygenation (PaOâ‚‚/FiOâ‚‚ ratio), hemodynamic stability, awake, minimal pressors
- SBT: trial on CPAP/low PSV or T-piece for 30–120 minutes
- RSBI (RR ÷ Vt in liters) <105 predicts successful weaning
- Pair daily sedation interruption (SAT) with the breathing trial (SBT)
VAP Prevention Bundle
- Head of bed elevated 30–45° unless contraindicated
- Daily sedation vacation and assessment of readiness to extubate
- Oral care with chlorhexidine; subglottic suctioning
- Peptic ulcer and DVT prophylaxis as part of the bundle
Complications & Nursing Priorities
- Barotrauma/volutrauma: high pressures/volumes → pneumothorax
- Hemodynamic compromise: positive pressure ↓preload → hypotension
- Confirm tube placement (EtCOâ‚‚, bilateral breath sounds, CXR); secure the tube
- Monitor cuff pressure (20–30 cm H₂O), sedation, and skin/oral integrity
Can you answer these 3 CCRN questions?
Here are 3 questions in the style of our premium bank. The full rationale explains exactly why the right answer is right — and why the distractors trap most test-takers.
Premium Practice Question
A ventilated COPD patient becomes hypotensive with rising peak pressures and a prolonged expiratory waveform that never returns to baseline. What is the most likely problem?
- Tension pneumothorax
- Auto-PEEP (breath stacking)
- Pulmonary embolism
- Endotracheal cuff leak
Rationale: An expiratory flow that does not return to zero before the next breath indicates air trapping (auto-PEEP), which raises intrathoracic pressure and drops venous return causing hypotension....
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Premium Practice Question
An ABG on AC/volume control shows pH 7.30, PaCOâ‚‚ 55, PaOâ‚‚ 95. Which change best corrects the abnormality?
- Increase FiOâ‚‚
- Increase respiratory rate
- Increase PEEP
- Decrease tidal volume
Rationale: The problem is ventilation (high PaCOâ‚‚ with respiratory acidosis); increasing the rate raises minute ventilation and clears COâ‚‚. Oxygenation is already adequate....
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Premium Practice Question
A patient on the ventilator triggers a high-pressure alarm, then desaturates with absent left-sided breath sounds and tracheal deviation. The priority action is to:
- Increase the FiOâ‚‚ to 100%
- Prepare for needle decompression
- Suction the endotracheal tube
- Obtain a stat chest x-ray
Rationale: The picture is a tension pneumothorax, a life threat requiring immediate needle decompression before imaging....
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Related CCRN Guides
Frequently Asked Questions
What is the difference between AC and SIMV?
In Assist-Control (AC), every breath the patient triggers receives full ventilator support, giving the most respiratory rest. In SIMV, only the set mandatory breaths are fully supported and synchronized; breaths the patient takes between them are spontaneous and less supported, which is why SIMV is sometimes used during weaning.
How do I fix a high PaCOâ‚‚ on the ventilator?
High PaCO₂ means inadequate ventilation. Increase minute ventilation by raising the respiratory rate and/or tidal volume. Recheck an ABG about 20–30 minutes after the change.
What causes a high-pressure ventilator alarm?
High-pressure alarms reflect increased resistance or decreased compliance: secretions, biting or a kinked tube, bronchospasm, coughing, mucus plugging, or pneumothorax. Always assess the patient; if you cannot resolve it, disconnect and manually ventilate with 100% oxygen.
What is auto-PEEP?
Auto-PEEP (intrinsic PEEP or breath stacking) occurs when a breath is delivered before the previous one is fully exhaled, trapping air. It is common in COPD and asthma and is treated by allowing more expiratory time — lowering the rate or tidal volume and increasing expiratory flow.
What does an RSBI predict?
The Rapid Shallow Breathing Index (respiratory rate divided by tidal volume in liters) below 105 predicts a successful spontaneous breathing trial and readiness to wean from the ventilator.
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