Anesthesia Machine Components

Gas Supply System - Pressure Points

• Cylinder Pressures (High):
  • O₂: 2000-2200 psi (~137 bar)
  • N₂O: 745 psi (~51 bar); constant if liquid
  • Air: 1800-2000 psi (~137 bar)
• Pipeline Pressure (Intermediate):
  • Standard: 50-55 psi (3.4-3.8 bar)
• Pressure Regulators (1st Stage):
  • Reduce cylinder P to ~45 psi.
  • Ensures constant, ↓P.
• Pressure Relief Valves:
  • Prevents overpressure.
  • Cylinder: Burst disc, fusible plug.
  • Pipeline: Set > normal pipeline P.

⭐ N₂O cylinder P (745 psi) is constant with liquid N₂O; weigh to check volume.

Flow Control & Meters - Gas Highway

• Controls & measures gas flow to vaporizers.
• Flow Control Valves (Needle Valves):
  • Fine-tunes O₂, N₂O, Air flow.
• Flowmeters (Rotameters/Thorpe Tubes):
  • Tapered tubes; float shows flow. Read: bobbin top, ball center.
  • Accuracy: ±5% to ±10%.
  • 📌 O₂ flowmeter downstream (last).
  • Min. O₂ flow often 200-300 ml/min.
• Hypoxic Guard (Link-25): Min. 25% O₂ with N₂O.

⭐ O₂ flowmeter is last in sequence to prevent hypoxic mixture if an upstream (e.g., N₂O) flowmeter leaks.

Vaporizers - Dream Weavers

• Function: Adds precise volatile anesthetic vapor to Fresh Gas Flow (FGF).
• Location: Between flowmeters & Common Gas Outlet (CGO).
• Types:
  • Variable Bypass (Plenum): FGF splits (vaporizing chamber/bypass). Temperature compensated (e.g., bimetallic strip). For Isoflurane, Sevoflurane.
  • Measured Flow (Heated): Tec6 for Desflurane (heated to 39°C, pressurized ~2 atm).
• Safety Features: Agent-specific keyed fillers, interlock system (prevents >1 vaporizer ON), secure mounting.
• Hazards: Tipping (liquid agent in bypass → ↑output), overfilling, wrong agent, leaks.

⭐ > Desflurane's low boiling point (22.8°C) necessitates a specially heated and pressurized vaporizer (e.g., Tec6) for consistent, predictable delivery, unlike other common volatile agents.

Breathing Circuits - Patient's Lifeline

Delivers anesthetic gases, removes CO2.

• Types & Key Features:
  • Open: No rebreathing/reservoir (e.g., Schimmelbusch).
  • Semi-Open (Mapleson): No CO2 absorber; FGF critical.
    • Mapleson A (Magill): Best for Spontaneous Ventilation (SV). $FGF = MV$.
    • Mapleson D: Best for Controlled Ventilation (CV). $FGF = \textbf{1-2} \times MV$.
    • 📌 Mnemonic: "Dead A Live D" (D for CV, A for SV).
  • Closed/Semi-Closed (Circle System): Uses CO2 absorber (soda lime); low FGF.
    • Components: Unidirectional valves, absorber, APL valve.

⭐ Soda lime, the CO2 absorbent in circle systems, changes color (e.g., to violet) when exhausted.

Safety Mechanisms - Vigilant Protectors

• Oxygen Supply
  • Oxygen failure alarm (audible/visual). Low O₂ pressure alert.
  • Fail-safe valve: ↓/cuts N₂O if O₂ pressure < 25-30 psi.
  • Hypoxic guard (e.g., Link-25): minimum ~25% O₂ delivery with N₂O.
  • O₂ flush: high flow O₂ (35-75 L/min) to common gas outlet.
• Vaporizers
  • Interlock system: one volatile agent active at a time.
  • Keyed-fillers: agent-specific, prevent misfilling.
• Breathing Circuit
  • Pressure alarms: high (occlusion), low (disconnect).
  • APL valve: limits pressure in manual/spontaneous ventilation.
• Gas Connections
  • PISS (cylinders), DISS (pipelines): non-interchangeable.
  • Color coding for gas identification.

⭐ Capnography: mandatory for confirming ETT placement & monitoring ventilation.

High‑Yield Points - ⚡ Biggest Takeaways

• Hanger Yoke & PISS: Ensures correct cylinder attachment and gas-tight seal (Bodok seal).
• Pressure Regulators: Reduce high cylinder pressure to a constant, lower machine operating pressure (≈45 psig).
• Flowmeters (Rotameters): Measure gas flow; hypoxic guard links N₂O and O₂ flows. Read at top of bobbin.
• Vaporizers: Deliver calibrated volatile anesthetic concentration. Agent-specific with interlock safety.
• Oxygen Flush Valve: Provides high-flow O₂ (35-75 L/min) directly to common gas outlet, bypassing vaporizers.