 The annular space. The clearance between the head of the float and the flow tube is known as the annular space.

 upper portion › orificial › Density is dominant  lower portion: › tubular › Viscosity is dominant

 The oxygen flow control knob is physically distinguishable: › distinctively fluted › projects beyond the other knobs › larger in diameter  All knobs: › color-coded › chemical formula or name marked on each › protected with a shield or barrier

 FLOW TUBES: › tapered glass tubes › double flow tubes  better visual discrimination at low flow rates 200ml to 1 L/min and 1 to 10 to 12 L/min  connected in series  total gas flow is that shown on the higher flow meter INDICATOR FLOATS AND FLOAT STOPS:  floats: plumb-bob, rotating skirted, ball  float stops: visible  SCALE: › marked directly on the flow tube or to the right of the tube › Rib guides are used in some flow tubes  SAFETY FEATURES: › individually hand-calibrated › The tube, float, and scale make an inseparable unit ( The entire set must be replaced if any component is damaged)

 An oxygen leak from the flow tube can produce a hypoxic mixture regardless of the arrangement of the flow tubes

 Sticking of the indicator float  damaged float can cause inaccurate readings  Backpressure from the breathing circuit  not aligned properly in the vertical  ambiguous scales

 The output represented in L/minute:  graphically  numerically  or both  Even when electrical power is totally interrupted, oxygen should continue to flow (flow control valves are non electronic)  Small conventional pneumatic “fresh gas” or “total flow” indicator

 prevent the creation and delivery of a hypoxic mixture  minimum oxygen concentration at the common gas outlet is between 23% and 25%  Limitations:  Wrong Supply Gas  Defective Pneumatics or Mechanics  Leaks Downstream  Inert Gas Administration  Dilution of Inspired Oxygen by Volatile Anesthetics

 Ohmeda Link-25 Proportion-Limiting Control system

 North American Dräger Oxygen Ratio Monitor Controller

 Allows direct communication between the oxygen high-pressure circuit and the low-pressure circuit  Actuation of the valve delivers 100% oxygen at 35 to 75 L/min to the breathing circuit  Provide a high-pressure oxygen source suitable for jet ventilation in ??  Hazards: › Barotrauma (if the anesthesia machine does not incorporate fresh gas decoupling or an appropriately adjusted inspiratory pressure limiter) › Patient awareness

 “old” copper kettle–like technology  “new” computerized control technology Physics:  Vapor Pressure (boiling point: desflurane 22.8°C, isoflurane 48.5°C, halothane 50.2°C, enflurane 56.5°C, and sevoflurane 58.5°C)  Latent Heat of Vaporization (number of calories required to change 1 g of liquid into vapor without a change in temperature)  Specific Heat ( the number of calories required to increase the temperature of 1 g of a substance by 1°C)  Thermal Conductivity (the speed at which heat flows through a substance)

 Flow Rate Output is less than the dial setting at very low and very high flow rates (<250 mL/min and 15 L/min)  Backpressure (pumping effect, is more pronounced at low flow rates, low dial settings, and low levels of liquid anesthetic)  Temperature (Automatic temperature-compensating mechanisms)  Carrier Gas Composition (sudden transient decrease in vaporizer output)

Simplified schematic of the Ohmeda Tec–type vaporizer

Simplified schematic of the North American Dräger Vapor 19.n and 20.n vaporizers