Ventilator Management 101 for New APPs: Moving Beyond the Basics of AC/VC

You learned the basics in school: Assist-Control, SIMV, pressure vs. volume. But walking up to a ventilator with a real patient attached feels different. This guide bridges the gap between textbook knowledge and bedside competence.

The Foundation: What the Ventilator Actually Does

At its core, mechanical ventilation does two things:

1. Oxygenation: Getting O2 into the blood (controlled by FiO2 and PEEP)
2. Ventilation: Removing CO2 from the blood (controlled by minute ventilation = RR × Tidal Volume)

Keep these separate in your mind. Hypoxemia and hypercarbia are different problems with different solutions.

The Modes You'll Actually Use

Volume-Controlled Ventilation (AC/VC)

You set: Tidal volume, respiratory rate, FiO2, PEEP The vent guarantees: That tidal volume with each breath Variable: Pressure (depends on compliance and resistance)

Use when: You need predictable ventilation (most patients)

Watch for: High peak pressures indicating worsening compliance or resistance

Pressure-Controlled Ventilation (AC/PC)

You set: Inspiratory pressure, respiratory rate, FiO2, PEEP The vent guarantees: That pressure level Variable: Tidal volume (depends on compliance)

Use when: High peak pressures on VC, ARDS, need to limit airway pressure

Watch for: Decreasing tidal volumes indicating worsening compliance

Pressure Support (PS)

You set: Pressure support level, FiO2, PEEP The patient controls: Rate, tidal volume, inspiratory time The vent provides: Pressure boost when patient initiates breath

Use when: Weaning, evaluating extubation readiness, spontaneous breathing trials

Watch for: Apnea, hypoventilation, patient fatigue

SIMV (Synchronized Intermittent Mandatory Ventilation)

Combines mandatory breaths with pressure support breaths. Historically used for weaning but largely fallen out of favor—associated with longer wean times in studies.

Initial Vent Settings: A Practical Approach

For a newly intubated patient without specific lung pathology:

Critical point: Tidal volume is based on IDEAL body weight, not actual weight. For a 5'10" male, IBW ≈ 73 kg, so 6 mL/kg = 438 mL. Obese patients don't need larger tidal volumes.

The ABG Adjustment Framework

Patient is Hypoxemic (PaO2 <60, SpO2 <90)

Step 1: Increase FiO2 (but try to keep <60%) Step 2: Increase PEEP (improves recruitment, V/Q matching) Step 3: Consider prone positioning if ARDS

Patient is Hypercarbic (PaCO2 elevated, pH <7.35)

Step 1: Increase respiratory rate (most common adjustment) Step 2: Increase tidal volume (cautiously, stay lung-protective) Step 3: Decrease dead space (shorten tubing, consider smaller filter)

Patient is Hypocarbic (PaCO2 low, pH >7.45)

Step 1: Decrease respiratory rate Step 2: If over-breathing vent, consider sedation or mode change

The High Pressure Alarm: A Systematic Approach

When the vent alarms for high pressure, think systematically:

Patient-Related

• Biting tube (try bite block)
• Coughing, dyssynchrony (assess sedation)
• Bronchospasm (listen to lungs, consider bronchodilators)
• Secretions (suction)
• Pneumothorax (check chest rise, breath sounds)

Circuit-Related

• Water in tubing (drain condensation)
• Kinked tubing (trace from vent to patient)
• Tube migration (check ETT position)

Disease-Related

• Worsening ARDS
• Auto-PEEP (check for breath stacking)
• Abdominal compartment syndrome (check bladder pressure)

ARDS and Lung-Protective Ventilation

For patients with ARDS, the evidence is clear: lung-protective ventilation saves lives.

The ARDSNet Protocol (Simplified)

• Tidal volume: 6 mL/kg IBW (may need to go to 4 mL/kg)
• Plateau pressure: <30 cmH2O
• PEEP: Use PEEP/FiO2 table as guide
• Permissive hypercapnia: Accept CO2 elevation to protect lungs
• pH goal: >7.20 (can buffer if needed)

Checking Plateau Pressure

1. Apply inspiratory hold for 0.5-1 seconds
2. Read plateau pressure at end of hold
3. If >30, consider reducing tidal volume or treating cause

Auto-PEEP: The Hidden Problem

Auto-PEEP (intrinsic PEEP) occurs when the patient doesn't fully exhale before the next breath—common in asthma, COPD, and with high respiratory rates.

Signs of Auto-PEEP

• Flow doesn't return to zero before next breath
• Breath stacking visible on waveforms
• Hypotension (decreased venous return)
• Difficulty triggering the ventilator

Treatment

• Decrease respiratory rate
• Decrease I:E ratio (more time for exhalation)
• Treat bronchospasm
• Consider external PEEP to match intrinsic PEEP (counterintuitive but effective)

Ventilator Asynchrony

Patient-ventilator dyssynchrony increases work of breathing and discomfort.

Common Types

• Trigger asynchrony: Patient trying to breathe but vent not responding
• Flow asynchrony: Flow delivery doesn't match patient demand
• Cycle asynchrony: Breath ends too early or too late

Solutions

• Adjust trigger sensitivity
• Increase flow rate (VC) or rise time (PC)
• Consider pressure support for spontaneously breathing patients
• Ensure adequate sedation if other measures fail

When to Call for Help

Don't hesitate to involve respiratory therapy and intensivists when:

• You can't maintain SpO2 >88% despite FiO2 100% and PEEP optimization
• Plateau pressure >30 cmH2O despite low tidal volume
• Severe respiratory acidosis (pH <7.20) despite maximal settings
• Patient appears to be fighting the ventilator despite sedation
• You're considering paralysis or prone positioning

Bottom Line for New APPs

1. Separate oxygenation from ventilation in your thinking
2. Calculate ideal body weight before setting tidal volume
3. Check plateau pressure regularly in sick patients
4. Use 6 mL/kg IBW as your default—it's lung-protective
5. Think systematically when alarms go off
6. Ask for help when things aren't improving

Ventilator management becomes intuitive with experience, but building on a solid foundation of understanding makes you a safer clinician from day one.