Checking the Anaesthesia Machine: Miller's Anesthesia (10th Edition)

Overview

The 15 ASA Items for Pre-Anaesthesia Checkout

Item 1: Verify Auxiliary Oxygen Cylinder and Self-Inflating Manual Ventilation Device Are Available and Functioning

• A self-inflating manual ventilation device (e.g., Ambu bag) in every anaesthetic location
• A separate oxygen cylinder independent of the wall supply and machine

Item 2: Verify Patient Suction Is Adequate to Clear the Airway

• Adequate negative pressure (typically ≥ −80 mmHg)
• Suction tubing and Yankauer catheter properly connected
• No obstruction in the system

Item 3: Turn On Anaesthesia Delivery System and Confirm That AC Power Is Available

Item 4: Verify Availability of Required Monitors and Check Alarms

• Pulse oximeter
• ECG
• Non-invasive blood pressure
• Capnograph (EtCO₂)
• Temperature monitor
• Gas analyser / agent monitor

• Confirm cables are plugged in and monitors are powered on
• Check and reset alarm thresholds — alarm settings may drift between cases due to provider manipulation
• Departmental default alarm settings can be programmed into the workstation and confirmed by technicians, but the provider bears final responsibility for alarm correctness for their specific patient

Item 5: Verify That Pressure Is Adequate on the Spare Oxygen Cylinder Mounted on the Anaesthesia Machine

• Open the E-cylinder valve(s) on the back of the machine
• Read the cylinder gauge pressure
• Replace if pressure is inadequate
• Air and N₂O cylinders need checking only if those gases are required

Item 6: Verify That Piped Gas Pressures Are ≥ 50 psig

• Confirm pipeline pressure gauges show ≥ 50 psig for oxygen (and other gases in use)
• Inspect supply hoses and connections
• Confirm oxygen content in the inspiratory limb is > 90%
• The oxygen supply failure alarm should be tested by disconnecting the wall oxygen supply and shutting off the tank — this is the only way to confirm the alarm functions correctly (though this manoeuvre is not mandated by the ASA Recommendations)

Item 7: Verify That Vaporizers Are Adequately Filled and Filler Ports Are Tightly Closed

• Check agent level in the sight glass before every case using an inhaled anaesthetic
• Refill if needed (using the keyed filler system)
• Confirm the filler port is tightly closed after filling — an open or improperly sealed port is a source of vapour leak and occupational exposure
• Not all automated self-tests include a low-agent alarm — manual verification prevents intraoperative light anaesthesia and awareness

Item 8: Verify That No Leaks Are Present in the Gas Supply Lines Between the Flowmeters and the Common Gas Outlet

• The check valve prevents breathing circuit pressure from being transmitted retrograde into the low-pressure section
• A negative-pressure leak test uses a bulb syringe:
  1. Turn all vaporisers to the "on" position and set flowmeters to zero
  2. Disconnect the common gas outlet from the breathing circuit
  3. Attach a suction bulb syringe to the common gas outlet
  4. Squeeze the bulb to create negative pressure
  5. A competent (leak-free) low-pressure section will hold the collapsed bulb in a deflated state; a leak will cause the bulb to re-inflate
  6. Repeat with each vaporiser open

• Close the APL valve, occlude the Y-piece
• Pressurise the circuit to ~30 cmH₂O using the O₂ flush
• Monitor for pressure decay
• A significant leak indicates a problem in either the breathing circuit or the low-pressure section

⚠️ Machines with an outlet check valve cannot use the positive-pressure method to detect low-pressure leaks. The check valve blocks retrograde flow.

Item 9: Test Scavenging System Function

• Confirm the scavenging interface device is properly connected to the APL valve and ventilator relief valve
• Confirm adequate negative pressure (for active systems) or open reservoir bag (for passive systems)
• Assess flow within the scavenging circuit
• The scavenging system must be functional to protect both the patient and operating room staff from chronic waste gas exposure

Item 10: Calibrate, or Verify Calibration of, the Oxygen Monitor and Check the Low-Oxygen Alarm

• The oxygen monitor sensor must be calibrated daily
• Calibration typically involves exposing the sensor to room air (21% O₂) for low-end calibration and 100% oxygen for high-end calibration
• The low-oxygen alarm must be confirmed functional
• The alarm threshold is typically set at 18–25% to warn of a hypoxic mixture
• Since this check verifies the integrity of the oxygen concentration monitoring, it is one of the most critical daily steps

Item 11: Verify Carbon Dioxide Absorbent Is Not Exhausted

• Assess the CO₂ absorbent granules for colour change (e.g., ethyl violet indicator turns purple when exhausted)
• However, colour change is not as reliable as capnographic evidence of exhausted absorbent — a visually normal-appearing absorbent may still be nonfunctional
• Capnometry must be used with every anaesthetic using the circle system
• The provider should remain vigilant for inspired CO₂ > 0 on the capnogram during the case
• It is no longer recommended for providers to breathe into the circuit manually to test absorbent function

Item 12: Breathing System Pressure and Leak Testing

1. Positive pressure can be generated and sustained in the breathing circuit
2. The APL (adjustable pressure-limiting) valve properly relieves excess pressure

1. Set ventilator to "bag" / manual mode
2. Set all gas flows to zero
3. Close the APL valve completely
4. Occlude the patient Y-piece (finger or test cap)
5. Pressurise the circuit to approximately 30 cmH₂O using the O₂ flush button
6. The circuit passes if pressure holds for at least 10 seconds without decay
7. Any pressure drop → inspect all connections, tubing, absorber canister (a common leak site, especially after absorbent changes)

• After pressurising, open the APL valve fully and confirm pressure drops rapidly to zero
• To test pressure-limiting function: set APL to 30 cmH₂O, occlude Y-piece, set fresh gas flow to ~5 L/min — confirm pressure stabilises near the APL set point

Automated circuit leak tests are a feature of most modern workstations. They also calculate breathing system compliance to guide accurate tidal volume delivery. The automated test should be performed with the circuit that will actually be used. If circuit size or configuration changes between patients, a fresh compliance calibration may be required.

Item 13: Verify That Gas Flows Properly Through the Breathing Circuit During Inspiration and Expiration

1. Attach a test lung (or spare breathing bag) to the patient Y-piece
2. In manual mode, ventilate the test lung via the breathing bag
3. Then actively "exhale" (squeeze) the test lung back — mimicking a patient's exhalation
4. Repeat in a to-and-fro motion while watching:
   • The inspiratory unidirectional valve (should open on inspiration, close on exhalation)
   • The expiratory unidirectional valve (should open on exhalation, close on inspiration)
5. Proper valve function ensures CO₂ is directed through the absorber and not rebreathed

Item 14: Document Completion of Checkout Procedures

• Provides a contemporaneous record for medicolegal purposes
• Supports quality improvement and auditing
• Establishes accountability

Item 15: Confirm Ventilator Settings and Evaluate Readiness to Deliver Anesthesia Care

• Set ventilator parameters appropriate for the upcoming patient (tidal volume, rate, PEEP, I:E ratio)
• Confirm APL valve is open (for manual/spontaneous breathing mode at start)
• Confirm fresh gas flow is appropriate
• Verify the workstation is in manual/spontaneous mode (not ventilator mode) before induction

Automated Machine Checkout Procedures

1. No single automated checkout checks all required items — manual steps remain mandatory
2. Automated checks differ between manufacturers and models
3. Many providers do not fully understand what their machine's automated procedure actually tests
4. Providers frequently make false assumptions about what automated checks cover
5. Some automated compliance calculations are only performed in the full daily checkout, not before every case — meaning compliance calibration may not be repeated if you swap circuits mid-day

Miller's emphasises: "When developing a local PAC procedure, providers should gain familiarity with their machine's automated checkout procedure through the user manual. If an important item is not specifically part of the described self-check, it should not be assumed that it can be neglected."

The MS MAIDS Mnemonic (Anesthesia Time-Out)

Developing a Local PAC Checklist

• Ergonomically ordered — minimise redundant movements and wasted time
• As short as possible, yet detailed enough that critical items are not omitted
• Quality control tool — standardised across all providers
• Assign responsibilities clearly — distinguish what is provider-only vs. may be delegated to a technician
• Reflect the specific equipment in use — a generic checklist cannot account for machine-specific design differences (e.g., presence or absence of an outlet check valve)

Summary Table: Frequency and Responsibility