The Anesthesia Gas Machine

Michael P. Dosch CRNA MS
University of Detroit Mercy Graduate Program in Nurse Anesthesiology
This site is http://www.udmercy.edu/crna/agm/.

ANESTHESIA GAS MACHINE> COMPONENTS & SYSTEMS> PUTTING IT ALL TOGETHER: MACHINE CHECKLIST, MEDICOLEGAL, CLEANING & STERILIZATION

Putting it all together: Machine checklist, Medicolegal, Cleaning & sterilization

Anesthesia gas machine check

"Apparatus of reliable appearance engenders a strong feeling of security which is often not supported by facts. A critical attitude often forestalls unpleasant surprises." Lucien Morris, in Aldrete Lowe & Virtue Low Flow & Closed System Anesthesia Grune & Stratton 1979.

"One of the things I notice about the practice of anesthesia is the extensive use of protocols and procedures. As I learn more about anesthesia I realize how important protocols and procedures are to increase patient safety. As a lawyer I also see that these procedures can protect the anesthetist. Should the anesthetist be required to defend himself or herself, it may be difficult to remember the exact details of an anesthetic given years before. Sometimes, it is helpful to be able to testify that certain matters are always done by following careful procedures, even if you cannot remember what happened in a particular case. Giving an anesthetic clearly requires thought and judgment, but the importance of having and following procedures can not be minimized. If you begin your day or each operation checking out your anesthesia machine according to FDA guidelines, then even if you cannot remember what you did on February 1, 1995, you will know you checked the anesthesia machine because that is what you always do." Gene Blumenreich AANA Journal 2000;68:107-10.

Negative pressure leak check

Why neg. pressure check? Diagram of area proximal to check valve which is not checked with high-pressure methods. Click on the thumbnail, or on the underlined text, to see the larger version (25 KB).

Neg pressure leak test deviceNegative pressure leak test device. Click on the thumbnail, or on the underlined text, to see the larger version (12 KB).

Unidirectional valves (check valves) are present in many machines between the vaporizers and the common gas outlet. Without them (or internal vaporizer design modifications), the cycling of positive pressure in the breathing circuit leads to increases in vaporizer output (the pumping effect). A high pressure check of the breathing circuit (Food and Drug Administration [FDA] Checklist 1993 step 11 below or online at FDA Checklist 1993) will not detect leaks upstream of these valves, since the high pressure in the breathing circuit will only be transmitted upstream to the check valve, and no further. These are vulnerable areas. Glass flowtubes and internal vaporizer seals and rubber O-rings are susceptible to failure. A universal leak check that will work on any anesthesia machine is the FDA Checklist Step 5, which relies on negative pressure. Unfortunately, this step is not well-understood or practiced often enough, in part due to its reliance on an accessory suction bulb, which is meant to be applied to the common gas outlet. The bulb is pumped until it flattens: it will remain flat if no internal leaks are present proximal to the common gas outlet. The test is repeated with each vaporizer turned on.

Electronic checklists

The newer machines (Datex-Ohmeda S/5 ADU, Dräger Julian, NM 6000, Fabius GS) are unique in having a system checkout routine that is electronic and automated. The operator follows instructions to activate flows of gases, occlude the breathing circuit during the leak check, switch from manual to mechanical ventilation, open and close the pop off valve, or manually check various functions (suction, or emergency oxygen cylinder supply). It covers all the steps of the FDA Checklist, but this is apparent only after some study. The system checkout is logged, but may be bypassed in an emergency. Though it takes 3 to 6 minutes, the operator can perform other tasks simultaneously (such as filling syringes), so it does not appreciably slow morning preparation, unless one had not been accustomed to performing a morning gas machine checklist.

The electronic checklist for the S/5 ADU requires that the D-Lite sensor (gas analysis and volume/flow sensor connection) is disconnected, and the breathing circuit occluded by attaching it to a post. After the electronic checklist is complete, the breathing circuit with D Lite sensor is reassembled. The operator must do a high pressure check of the reassembled breathing circuit before using it on a patient.

Minimum test under life-threatening conditions

While there is no universally accepted machine checklist less than the full FDA Checklist, situations do arise in anesthesia for trauma or emergency cesarean section where there is neither time nor opportunity to fully check the anesthesia gas machine. The following checklist is suggested for these situations. It requires little if any additional time, and can add greatly to safety, and hence, peace of mind.

  1. High pressure test of the breathing circuit
    • Ensures there are no leaks distal to common gas outlet
  2. Check suction
  3. Observe and/or palpate breathing bag during preoxygenation
      Ensures
    • Adequate flow of oxygen
    • Good mask fit (very important)
    • The patient is breathing
    • The Bag/Vent switch is on "Bag" not "Vent"

With all new machines, the electronic checklist can be bypassed in emergencies. Whether this 30 second process is acceptable must be determined by each clinical practice. It has been suggested that the NM 6000 be left on if trauma or obstetric cases must be done on a moment's notice (Anesthesiology 2001;95:567-8). .The NM 6000 checklist can only be bypassed nine times. The S/5 ADU checklist can be bypassed an indefinite number of times, but it will display a visible, nagging message until the electronic checkout is performed. Since oxygen flow is mechanical in the ADU, the plan in one practice for obstetric emergencies is to leave the gas machine off. When a patient needs emergent general anesthesia, the oxygen flow is established for preoxygenation while the ADU is turned on and the checklist is bypassed. These actions can be accomplished in less than a minute- less time than is needed for preoxygenation to be complete.

FDA anesthesia gas machine checklist (1993)

This checklist is a modified version of the original: Step 10 (Check initial status of breathing system) is followed by Steps 12 (Check ventilator and unidirectional valves), 11 (Perform [high pressure] leak check of breathing system), and then 8 (Adjust and check scavenging system). The primary reason for the modification is to avoid leaving the Bag/Vent switch in "Vent" position after the checklist is complete, which fault is encouraged by the original checklist order. This modification was agreed upon after local peer review; it is suggested that this should occur anywhere such a modification is contemplated.

Modified Anesthesia Gas Machine Checklist

Introduction The anesthesia gas machine must be equipped with an ascending bellows ventilator and certain monitors (capnograph, pulse oximeter, oxygen analyzer, spirometer, breathing system pressure monitor with high and low pressure alarms). If not so equipped, the checklist must be modified.

  1. Verify backup ventilation equipment is available & functioning.
    • Contaminated oxygen supply, loss of oxygen supply pressure, and obstruction of the breathing system, though rare, cause the machine to be totally inoperable. So check for that Ambu!
  2. Check oxygen cylinder supply
    • One cylinder must be at least half full (1000 psi), according to the FDA Checklist (older versions called for 600 psi as the lower limit). This will allow gas machine function for 10-60 minutes, or longer.
    • It is not necessary to:
      1. Check any other cylinders beside oxygen
      2. "Bleed" the pressure off the cylinder pressure gauge after checking
    • Leave cylinder closed after checking.
    • While you're behind the machine, check suction, Ambu bag and extra circuit present. Also: gas analysis scavenged, scavenger caps all present, location of circuit breakers, any loose pipeline, electrical, or etc. connections, head strap, tank wrench, and color/date of CO2 absorbent.
  3. Check central pipeline supplies.
    • Check for proper connection at wall
    • Check the pipeline pressure gauge- should read approximately 50 psi.
    • It is not necessary to unhook pipeline connections at wall.
  4. Check initial status of low pressure system.
    • Remove oxygen analyzer sensor.
    • Check liquid level and fill vaporizers if necessary.
    • Check vaporizer interlock.
  5. Perform leak check of low pressure system.
    • Leaks as low as 100 mL/min may lead to critical decrease in the concentration of volatile anesthetic (creating a risk for intraoperative awareness), or permit hypoxic mixtures under certain circumstances.
    • Negative pressure leak test (10 sec.) is recommended.
    • Repeat for each vaporizer.
  6. Turn master switch on.
  7. Test flowmeters.
    • Check for damage, full range, hypoxic guard.
  8. Calibrate oxygen monitor (FDA Step 9)
    • It’s not the alphas and betas which kill them, it’s the little green O’s. - John Garde
    • Final line of defense against hypoxic mixtures.
    • Trust it until you can prove it wrong.
    • Mandatory for all general anesthetics, or when using the breathing circuit (for example during a propofol or other sedation)
    • Calibrate/daily check: expose to room air and allow to equilibrate (2 min). Then expose to oxygen source and ensure it reads near 100%
  9. Check initial status of breathing system (FDA Step 10)
    • Assemble circuit with all accessories.
  10. Test ventilation systems and unidirectional valves (FDA Step 12)
    • Test ventilator and observe action of unidirectional valves.
  11. Perform leak check of breathing system (FDA Step 11)
    • The "usual" high pressure check.
    • Let the gas out of the circuit through the popoff [APL] valve, not the elbow.
  12. Adjust and check scavenging system. (FDA Step 8)
    • If active (suction) is applied to a closed scavenger interface, check the positive and negative pressure relief valves of the interface.
    • If open interface, ensure that adequate suction is applied (the indicator float between the scribed lines).
  13. Check, calibrate, set alarm limits of all monitors
  14. Check final status of machine.
    • Vaporizers off
    • Bag/Vent switch to "bag" mode
    • APL open
    • Zero flows on flowmeters
    • Suction adequate
    • Breathing system ready

Note: May omit or abbreviate #1-9 between cases.

Importance of the gas machine checklist

As recently as May 2000 (Health Devices 2000;29:188-9) it was reported that failure to check a disposable breathing circuit led to a patient fatality. Studies have shown the need for providers to improve their skills at checking gas machines with known faults (or perhaps the need for improved equipment)- see AANA Journal 2000;68:497-505, and AANA Journal 1996;64:277-82. The Closed Claims study of gas delivery equipment (Anesthesiology 1997;87:741-8) concluded that misuse of equipment was three times more prevalent than equipment failure, and that educational and preventive strategies were needed.

Risk management, quality assurance, standards, and medicolegal

Risk Management encompasses pre and post-op visits, avoiding treating patients indifferently, maintaining vigilance and high standards of care, peer review, and continuing education. For anesthesia equipment, it means daily checks and appropriate maintenance. The Safe Medical Device Act 1990 mandates a report to the FDA when equipment contributes to severe injury or death. Preventive maintenance should be done at regular intervals as called for in the operating manuals by qualified, factory-trained and approved service technicians. Vaporizers should be inspected, tested and calibrated per manufacturer's guidelines.

Quality assurance deals with objective, systematic monitoring, and the evaluation of the quality and appropriateness of patient care. Waste anesthesia gas testing can help to protect personnel and identify machines with problems. Anesthesia personnel can be held liable for knowledge of material in the anesthesia gas machine operating manual, maintenance guide, and any warnings given by the manufacturer (which are monitored and approved by the FDA the same way drug package inserts are).

AANA Monitoring Standards 1992 have implications for equipment. Capnography and pulse oximetry are so ubiquitous, that they may be considered integral parts of the machine itself. Gas machines are required to have a breathing system disconnect monitor with alarm, an oxygen analyzer, and an oxygen supply failure alarm. These monitoring standards also mandate a safety check daily and between cases (as needed), preventive maintenance, and machines that conform to national and state standards. The FDA Checklist for anesthesia equipment also emphasizes ascending ventilator bellows, and certain monitors (capnograph, pulse oximeter, oxygen analyzer, spirometer, and a breathing system pressure monitor with high and low pressure alarms).

Cleaning and sterilization

It is controversial whether equipment can transmit infection, though some cases have certainly been documented. Most, if not all, would agree that sterilization is essential after use on a patient with known or suspected infection of the respiratory tract, especially with virulent organisms like pseudomonas aeruginosa. Likewise, we should protect compromised patients from contamination arising from our equipment. In any case, handwashing between patients, as well as universal precautions are mandatory in anesthetic practice.

Housekeeping during administration of anesthesia will limit the spread of contamination:

Cleaning equipment means removal of foreign matter without special attempts to kill microorganisms. Equipment should be pre-rinsed as soon as possible after use to prevent drying of organic material; then soaked, removal of soil, rinsing and drying.

Sterilization

Moist heat methods

Liquid sterilization

Useful for heat sensitive equipment, but recontamination possible during drying and re-wrapping. Of several agents (chlorhexidine Hibitane®, phenolic compounds, hexachlorophene, ethyl or isopropyl alcohols), glutaraldehyde is the only one effective against both tubercule bacillus and viruses.

The Steris system uses peracetic acid in a low-temperature, 30 minute cycle to sterilize objects such as laryngoscope blades and fiberoptic laryngoscopes.

Chemical gas sterilization

Ethylene oxide (ETO) is a synthetic gas widely used, especially for heat or moisture-sensitive items like rubber and plastic. Kills bacteria, spores, fungi, larger viruses. Can be various patient reactions if not aerated (in wrapper) sufficiently after ETO exposure. The gas is also explosive and toxic.

Other means

Gamma radiation kills all bacteria, spores and viruses. Used for sterilization of disposable equipment - not practical for everyday needs of hospitals.

Care of specific equipment

The Centers for Disease Control has a collection of useful information relating to bloodborne & universal precautions.

Questions?
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