Intro to the Anesthesia Machine
Angela Mordecai, DNP, CRNA and Bailey Freeman, DNP, CRNA
What Is the Anesthesia Machine?
The anesthesia machine is a life-support device that safely delivers a precise mix of oxygen, anesthetic gases, and air to the patient. It also allows for continuous monitoring and adjustment of these gases during anesthesia. If the ventilator is the lungs, the anesthesia machine is the brain that controls them.
How Does It Work?
Gas flows through a series of components before reaching the patient. Each step is essential for safety and precision:
- Oxygen Source: Comes from a pipeline or backup cylinder. It powers alarms, flows through the machine, and supports patient ventilation.
- Flowmeters: Measure and control gas flow in liters per minute. Each gas has its own flowmeter.
- Vaporizers: Convert liquid anesthetic into a carefully controlled vapor. This vapor mixes with fresh gas before reaching the patient.
- Fresh Gas Outlet: The final destination before gases enter the breathing circuit.
- Oxygen Flush Valve: Delivers 100% oxygen at high flow (~35–75 L/min). Use cautiously — bypasses vaporizers and can cause barotrauma.
What Does It Monitor?
Modern machines include real-time monitors that help assess ventilation, oxygenation, and circuit function:
- Pressure Gauge: Displays airway pressure — critical during manual ventilation.
- Volume Monitors: Show tidal volume and minute ventilation — helpful for confirming appropriate delivery.
- Capnography (ETCO₂): Measures exhaled carbon dioxide, ensuring the patient is ventilating adequately.
- Oxygen Analyzer: Confirms the percentage of oxygen delivered to the patient.
How Do I Check It?
Before every case, confirm proper machine function using a structured pre-use checklist:
- Gas sources (pipeline and cylinder) are connected and pressurized.
- Vaporizers are filled, turned off, and mounted securely.
- Flowmeters operate smoothly and register accurate flows.
- Monitors (ETCO₂, O₂ analyzer, pressure gauge) display appropriate values with test ventilation.
What Should I Document?
- Oxygen flow rate and volatile anesthetic agent used.
- Any abnormal pressure readings or machine behavior during the case.
- Confirmation that the anesthesia machine check was completed prior to use.
Scope Guide
Strategies
- Start each day with a full anesthesia machine check — don’t skip it, even if the machine looks “ready.”
- Understand where each gas travels, from wall to patient. This helps with troubleshooting in high-stress moments.
- Teach learners to trace gas flow using diagrams, videos, or physical demonstrations with real equipment.
Clinical Optimization
- Use oxygen analyzers and capnography in every case to detect disconnections or hypoventilation early.
- Adjust vaporizers and flow rates slowly and mindfully, matching the patient’s needs and anesthetic plan.
Pearls
- The oxygen flush valve bypasses vaporizers — never activate it during inspiration to avoid lung injury.
- Flowmeters are gas-specific. Read at the center of the float ball for accurate measurement.
- Sudden changes in pressure or waveform may indicate a circuit leak, kink, or machine issue — troubleshoot immediately.
References
- StatPearls. Anesthesia Machine. National Center for Biotechnology Information. https://www.ncbi.nlm.nih.gov/books/NBK572060/
- OpenAnesthesia. Gas Flow and Vaporizers. https://www.openanesthesia.org/keywords/vaporizers/
