Basic Machine Checkout Case File

Basic Machine Checkout Case File

Lydia Conlay, MD, PhD, MBA, Julia Pollock, MD, Mary Ann Vann, MD, Sheela Pai, MD, Eugene C. Toy, MD

Case 6

A 65-year-old man is undergoing a laparoscopic cholecystectomy. The case starts uneventfully, and the patient is paralyzed with a neuromuscular blocker, as is customarily used. After successful intubation, mechanical ventilation is attempted using the anesthesia machine’s ventilator, but the tidal volume is not delivered.

➤ How could this situation have been prevented?

➤ What is your next step in the management of this patient?

ANSWERS TO CASE 6:

Basic Machine Checkout

Summary: General anesthesia has been successfully initiated on a 65-year-old man, who is undergoing cholecystectomy. The patient is paralyzed and intubated, but the anesthesia machine is not functioning and ventilation is not being provided.

➤ How to have prevented this situation: This situation could have been prevented if the anesthesia machine had been checked properly prior to the beginning of the case.

➤ Next step in management: Any time a patient is not breathing, or in this situation, is unable to breathe for himself, the basic life support algorithm of “airway, breathing, circulation” should be followed. The airway or endotracheal tube is already in place. “Breathing” or ventilation can be provided with an Ambu bag, which is always available in an operating room should it be needed. Anesthesia is maintained with intravenous medications.

ANALYSIS

Objectives

1. Understand the basic components of an anesthesia machine, and how these components must be checked to ensure its safe operation.

2. Describe the 2008 recommendations for preanesthesia checkout procedures, and understand which must be performed prior to the first case of the day, and which must also be performed prior to “to-follow” cases using the same machine during the same day.

3. Become familiar with the necessary auxiliary and backup equipment required when an anesthetic is administered.

Considerations

This patient is intubated, paralyzed, and the anesthesia machine is not operational. The situation could have been avoided by a basic machine checkout. In February 2008, the American Society of Anesthesiologists (ASA), through its Committee on Equipment and Facilities, set forth “recommendations for preanesthesia checkout procedures (2008)” which outline the necessary checks to be performed on anesthesia delivery equipment before every anesthetic, and the backup equipment which may be needed in the event of machine malfunction. The patient should be ventilated with an Ambu bag until an operational machine can be brought to the operating room.

APPROACH TO

Basic Machine Checkout

The anesthesia machine is broken down into two main components: the circle system (or breathing circuit), and the machine proper. The circle system is made up of the anesthesia circuit tubing (hoses from machine to the patient and back, not shown in Figure 6–1), unidirectional valves, a flow spirometer, an adjustable pressure-limiting valve, a scavenging system outflow site, a freshgas inlet site, a CO2 absorber, an O2 sensor, a ventilator, and reservoir bag (Figure 6–1). Flow spirometers are generally located on the machine side of the expiratory valve. The O2 sensor is generally located on the inspiratory side to measure the concentration of oxygen inspired. In some situations, it may be located on the expiratory side, to measure the oxygen which has been exhaled.

The other component is the anesthesia machine proper, which receives gases, regulates the pressure and flow of those gases, allows addition of volatile anesthetics, and provides safety against an (accidental) hypoxic gas mixture. The anesthesia machine receives gas from internal pipes in the wall via wall connections which are gas specific. The oxygen, for example, is colored green and the gas plug-in will only attach to a (green) oxygen outlet. This is called the diameter index safety system (DISS). The gas mount on the anesthesia

Figure 6–1. Inspiratory (IV) and expiratory (EV) unidirectional valves, respectively. Adjustable pressure limiting valve (APL), and fresh-gas inlet (FGI). The ventilator is not shown but it would bypass the APL and reservoir bag.

machine is specific to each gas as well. For example, the pin on the oxygen tank will only fit the oxygen specific yoke on the anesthesia machine or in the institution’s basement (the source of piped gases). This is known as the pin index safety system. These systems combine to ensure that oxygen, instead of a hypoxic gas such as N2 is delivered through conduits labeled for oxygen.

Gases for the anesthesia machine are either piped in from the wall are at a pressure of 50 psig, or received via an E-cylinder mounted on the machine containing a pressure regulator which reduces gas pressure to 45 to 50 psig. Gases pass through pressure sensors (further reducing the pressure), a vaporizer, and a flow meter before entering the circle system via the fresh-gas inflow. Since pressures of 45 to 55 psig would be damaging to the larynx and pulmonary parenchyma, additional pressure regulators ensure that only lowpressure gas enters the circle (breathing) system. Gases from the wall and from the E-cylinder mounted on the machine are connected in parallel to the anesthesia machine. But since the pressure is higher on the side coming from the wall, the E-cylinder remains as a backup in case the wall oxygen delivery system fails.

The American Society of Anesthesiologists has authored specific recommendations for preanesthesia checkout procedures of this complicated but vital device. The guidelines include 15 items that should always be performed before the first case of the day (see Table 6–1). Once the full checkout has been performed, it is only necessary to perform 8 of the steps for subsequent cases (items #2, 4, 7, 11-15). The items are listed in the order with which they should be performed, and not necessarily organized according to the specific components of the anesthesia machine and its ancillary or backup equipment.

ITEM #1. Verify that the auxiliary oxygen cylinder and self-inflating devices are available and functioning. The backup equipment for every anesthetic includes hand-ventilation equipment (Ambu bag) and an oxygen source (E-cylinder of oxygen). It is important to check the Ambu bag function to be sure that the valves work properly, the bag re-inflates, and that there are no holes in the bag. The equipment must work properly to generate positive pressure ventilation.

The oxygen E-cylinder should be nearly full and have a functioning regulator. An E-cylinder filled with oxygen contains 600 L of gas at a pressure of 2000 psig. If the pressure in the cylinder is less than 2000 psig, the amount of oxygen remaining in the cylinder can be estimated using Boyle law: (P1V1 = P2V2).

ITEM #2. Verify that patient suction is adequate to clear the airway. Suction is an auxiliary piece of equipment required for safe administration of an anesthetic. This equipment can be lifesaving in the event of aspiration, and/or difficult airway management which may require the removal of secretions or blood to allow visualization of the vocal cords. It must be checked before administration of each anesthetic.

ITEM #3. Turn on the anesthesia delivery system and confirm that AC power is available. It is important to note that the machine is not running on its battery power, which is intended for emergency situations. Indeed, most anesthesiologists have been in the situation where the power goes off in the operating room during a procedure.

Table 6–1 THE AMERICAN SOCIETY OF ANESTHESIOLOGISTS’PREANESTHESIA CHECKOUT PROCEDURES
ITEM	PROCEDURE	PERSONNEL
#1	Verify auxiliary oxygen cylinder and self-inflating devices are available and functioning	Provider and technician
#2	Verify patient suction is adequate to clear the airway	Provider and technician
#3	Turn on anesthesia delivery system and confirm that AC power is available	Provider and technician
#4	Verify availability of required monitors, including alarms	Provider and technician
#5	Verify that pressure is adequate on the spare oxygen cylinder mounted on the anesthesia machine	Provider and technician
#6	Verify that the piped gas pressures are ≥ 50 psig	Provider and technician
#7	Verify that vaporizers are adequately filled and, if applicable, that the filler ports are tightly closed	Provider and technician
#8	Verify that there are no leaks in the gas supply lines between the flow meters and the common gas outlet (internal leak test)	Provider and technician
#9	Test scavenging system function	Provider and technician
#10	Calibrate, or verify calibration of, the oxygen monitor and check the low oxygen alarm	Provider and technician
#11	Verify carbon dioxide absorbent is not exhausted (Sodasorb)	Provider and technician
#12	Breathing system pressure and leak testing (circle system leak test)	Provider and technician
#13	Verify that gas flows properly through the breathing circuit during both inspiration and exhalation	Provider and technician
#14	Document completion of checkout procedures	Provider and technician
#15	Confirm ventilator settings and evaluate readiness to deliver anesthesia care—anesthesia pause	Provider

ITEM #4. Verify the availability of the required monitors and alarms. Monitors are critical to patient care and must be checked before an anesthetic is administered. Basic monitoring includes sphygmomanometer (measurement of blood pressure), 2-lead ECG, pulse oximetry, temperature, and capnography (which measures end-tidal CO2). All equipment necessary for this monitoring must be present and functional. It is also important to be certain that alarms are set appropriately prior to the beginning of a case.

ITEM #5. Verify that the pressure is adequate on the spare oxygen cylinder mounted on the anesthesia machine.

ITEM #6. Verify that piped gas pressures are ≥ 50 psi. Next it is necessary to confirm the wall pressure is 50 psig and that the oxygen cylinder mounted to the anesthesia machine is full (2000 psig, 600 L). This confirms a sound connection to the wall, and the presence of a supply of oxygen in case of an emergency. Occasionally, the connections to the wall may imperfect, and the ancillary oxygen supply depleted—without knowledge of the anesthetist. These checks prevent this potentially hazardous situation.

ITEM #7. Verify that vaporizers are adequately filled. This prevents the vaporizer from being empty at a time when it would be hazardous to stop and refill it, such as during the induction of a patient with a difficult airway.

ITEM #8. Verify that there are no leaks in the gas supply lines between the flow meters and the common gas outlet. This is also known as the internal leak test. One way it is performed is by a negative pressure leak test. This involves placing a collapsed bulb on the fresh-gas outlet and seeing if it reinflates with each vaporizer open. For many modern machines, the circle system leak test (described in the following paragraph) with each vaporizer open also identifies any internal leaks within the anesthesia machine via pressure backflow through the fresh-gas inflow. Each vaporizer should be filled if necessary, and the filler cap replaced tightly.

ITEM #9. Check the scavenging system’s function. As gas is vented from the circle or breathing system, it enters a scavenging system to avoid operating room contamination. Scavenging systems are open (gas is removed constantly), or closed (waste gases are re-circulated). Open systems are most common since they do not have pressure valves. Scavenging systems are also either active or passive. An active system includes a vacuum in the system. Checking this system entails ensuring there are no kinks in the hoses, that the open system is not clogged (or the pressure valves are properly functioning), and that the vacuum is set properly. Most anesthesia machines have an indicator on or near the rear of the machine which indicates that the scavenger is working appropriately.

ITEM #10. Calibrate, or verify the calibration of the oxygen monitor and check the low oxygen alarm. The alarms signaling low oxygen are checked by disconnecting or turning off the oxygen sources (wall and tank), and an alarm will sound. The oxygen monitor’s calibration is checked by observing that it accurately reflects 100% when pure oxygen is flushed through the circle, and then by removing the sensor to allow it to equilibrate to room air, and then observing a reading of 21% oxygen. The sensor must then be replaced into the breathing circuit, and the absence of a leak confirmed. Failing to do so is one of the more common mistakes in the machine checkout procedure.

ITEM #11. Verify carbon dioxide absorbent is not exhausted. The CO2 absorber is checked to ensure that it is not more than 50% exhausted. When the absorber changes color, it needs to be replaced. The replacement of an absorber, without an appropriate seal, is also a common source of leaks.

ITEM #12. Breathing system pressure and leak testing. Part of the anesthesia equipment checkout includes checking the circle system. The circle system is checked to be sure there are no leaks by occluding the y-piece, building up 30 cm H2O pressure and with no flow, and verifying the pressure does not decline. The last part of the circle system to check is the O2 sensor which calibrated 100% oxygen and often room air.

ITEM # 13. Verify that gas flows properly through the breathing circuit during both inspiration and exhalation. The proper functioning of inspiratory and expiratory valves ensures unidirectional gas flow. These valves can be checked visually by observing their movement. A more rigorous evaluation involves attaching an extra breathing bag to the inspiratory port (the other breathing bag is attached at the standard position on the bag mount), and then pressurizing the breathing circle to 30 cm H2O (Figure 6–2). If the adjustable pressure limiting valve is closed, the only way for gas to escape is retrograde through the expiratory valve. If no pressure decline is noted, then the adjustable pressure limiting valve is opened thus creating a pressure gradient retrograde across the inspiratory valve by the bag attached and inflated there. If that bag does not deflate, then the inspiratory valve is competent. To verify antegrade gas movement through the valves as well as ventilator function, a breathing bag is attached to the circuit at the elbow (similar to an “artificial lung”) and the ventilator is turned on. The bag should inflate and deflate appropriately. During this step the ventilator can be set to the appropriate tidal volume and rate for the upcoming patient.

ITEM # 14. Document completion of checkout procedures.

ITEM #15. Confirm ventilator settings and evaluate readiness to deliver anesthesia care.

Anesthesia Pause. Documentation and confirmation of proper preparation in the form of a pause constitute the last two steps in the ASA machine checkout recommendations.

Modern anesthesia machines are very diverse and constantly changing. The ASA recommends that every anesthesia department adopt a checkout procedure for each specific machine used in its institution. Some machines have computerized machine checks. Even if these machine checks are utilized, manual checks are still added to ensure all the components of the ASA guidelines are met.

Ensuring a proper functioning machine will avoid situations like the one described where a patient is rendered unconscious and the machine malfunction is discovered. When the anesthesia machine fails, emergency equipment such as an Ambu bag is available, and the anesthetic can be readily converted

Figure 6–2. An extra bag attached at inspiratory port, and the system pressurized.

to an intravenous technique. If the surgical procedure has not yet begun then initial incision should be delayed until equipment issues are resolved.

Comprehension Questions

6.1. Which of the following guarantees that the hoses for oxygen and nitrous oxide will not be     switched?

    A. Diameter index safety system

    B. Inspiratory unidirectional valve

    C. Scavenging system

    D. Flow spirometer

6.2. You are administering anesthesia in a location that does not have an oxygen supply line. The E-cylinder that you are using reads 500 psig. Your oxygen flows are 10 L/min. Approximately how long does it take for your E-cylinder to empty?

    A. 5 minutes

    B. 15 minutes

    C. 50 minutes

    D. 100 minutes

6.3. What is the purpose of the scavenging system?

    A. To retrieve anesthetic gases for reuse and cost savings.

    B. To retrieve exhaled gases for warming and humidification of inhaled gases.

    C. To retrieve anesthetic gases and reduce operating room contamination.

    D. To retrieve exhaled gases to use as carriers and reduce total freshgas flow.

ANSWERS

6.1. A. The diameter index safety system is used at the connection to wall gas supply lines. The pin index system is used at the yoke assembly on the anesthesia machine. Both of these systems are in place to ensure correct gas connections.

6.2. B. A full E-cylinder of oxygen contains 600 L of gas at a pressure of 2000 psig. Using Boyle law (P1V1 = P2V2) the volume of the partially depleted cylinder can be calculated, V2 = (P1V1)/P2 or V2 = (P1/P2) × V1. There is a quarter tank left, and therefore a quarter of 600 L, or 150 L. At 10 L/min, this volume of gas would last 15 minutes.

6.3. C. The purpose of the scavenging system is to reduce the amount of anesthetic gas in the operating room. The National Institute of Occupational Safety and Health has set standards for anesthetic gas

levels in the operating room. For example, there is to be no more than 2 ppm (parts per million) of a volatile anesthetic if used alone, and no more than 0.5 ppm of a volatile anesthetic when used in conjunction with nitrous oxide in the operating room. The maximum amount of nitrous oxide allowed in the operating room is 25 ppm (50 ppm in the dental office).

Clinical Pearls

➤ Routine check of anesthesia equipment is mandatory.

➤ Ambu bag and oxygen tent are essential equipment in case of machine failure

References

Design Guidelines for Effective Anesthesia Apparatus Checkout. www.asahq.org/clinical/ FINALCheckoutDesignguidelines02-08-2008.pdf.

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