Mechanical Ventilation Basics Mini Course - Chapter 1 - Terminology And Concepts

Mini-Course: Basics of Mechanical Ventilation
Chapter 1: Terminology and Concepts
Full course only accessible on Patreon:   / whiteboardmedicine  

🫁Study Guide: Mechanical Ventilation Terminology

1. Basic Concepts
**Ventilator**A machine that delivers gas (usually air or oxygen) into the lungs under positive pressure to assist or replace spontaneous breathing.
Positive Pressure Ventilation**Delivery of gas to the lungs by pushing air in under pressure; exhalation occurs passively when pressure is released.
Tidal Volume (VT or TV)The volume of gas delivered (or exhaled) with each breath, typically 6–8 mL/kg of ideal body weight in adults.
Respiratory Rate (RR)Number of breaths delivered by the ventilator per minute.
Fraction of Inspired Oxygen (FiO₂)The percentage of oxygen in the gas mixture delivered to the patient (e.g., 0.21–1.0).
Positive End-Expiratory Pressure (PEEP)The pressure maintained in the airways at end expiration to prevent alveolar collapse; typical settings are 5–10 cm H₂O.
Peak Inspiratory Pressure (PIP)The highest pressure reached during inspiration; reflects airway resistance and lung/chest wall compliance.
Plateau Pressure (Pplat)Pressure measured during an inspiratory pause (no flow); estimates alveolar pressure and lung compliance.
Compliance**Change in volume per change in pressure (ΔV/ΔP);
Static compliance**: measured at zero flow (VT / [Pplat – PEEP])
Dynamic compliance**: measured during airflow (VT / [PIP – PEEP])

Key Ventilator Settings & Parameters
• Inspiratory-to-Expiratory Ratio (I:E Ratio)
Ratio of time spent in inspiration versus expiration (e.g., 1:2, 1:1.5).
• Flow Rate
The speed at which gas is delivered during inspiration (L/min).
• Inspiratory Pause / Hold
A pause at end-inspiration (no flow) used to measure Pplat.
• Trigger Sensitivity
Threshold (pressure or flow) that determines how easily the patient can initiate a ventilator breath.
• Rise Time (Pressurization Time)
Time taken for the ventilator to reach set inspiratory pressure in pressure-targeted modes.

4. Monitoring & Alarms
• Waveforms
o Pressure–time curve: shows airway pressure over time
o Flow–time curve: shows inspiratory and expiratory flow
o Volume–time curve: shows delivered volume
• Alarm Types
o High pressure: often due to secretions, bronchospasm, or decreased compliance
o Low pressure: disconnection or leak
o High/low tidal volume: patient effort change or circuit issue
o Apnea: no breaths detected in a set interval

5. Advanced Terminology
• Driving Pressure (ΔPdriving)
Difference between Pplat and PEEP; an indicator of lung stress (keep less than 15 cm H₂O).
• Auto-PEEP (Intrinsic PEEP)
Unintended retention of pressure at end expiration due to incomplete exhalation (air trapping).
• Permissive Hypercapnia
Strategy allowing elevated PaCO₂ to reduce ventilator-induced lung injury by using lower VT.
• Recruitment Maneuver
Transient increase in airway pressure (e.g., sustained inflation at 30–40 cm H₂O for 30–40 s) to open collapsed alveoli.
• Pressure–Volume (P–V) Loop
Graphical representation of pressures versus volumes; useful to assess compliance and detect overdistension or collapse.
• Electrical Impedance Tomography (EIT)
Noninvasive imaging technique to monitor regional lung ventilation.
• Ventilator-Associated Lung Injury (VALI)
Injury from mechanical ventilation due to barotrauma, volutrauma, atelectrauma, or biotrauma.
• Esophageal Pressure Measurement
Used as a surrogate for pleural pressure to calculate transpulmonary pressure and guide PEEP.

6. Troubleshooting & Clinical Pearls
• High PIP but Normal Pplat
Increased airway resistance (e.g., bronchospasm, secretions, kinked tube).
• High Pplat
Low compliance (e.g., ARDS, pulmonary edema, pneumothorax).
• Auto-PEEP Detection
Look for elevated baseline on expiratory flow–time curve and rising intrinsic PEEP; manage with increase expiratory time or reduce RR/VT.
• Patient–Ventilator Asynchrony
Mismatch between patient effort and ventilator support; adjust trigger sensitivity, flow rate, or mode.
• Weaning
Gradually reduce support (e.g., decrease PS or mandatory breaths) and assess readiness trials (e.g., T-piece, CPAP trial).

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