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# (p. 375) Equipment Problems

Equipment Problems
Chapter:
Equipment Problems
DOI:
10.1093/med/9780199377275.003.0014
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date: 24 October 2020

Each operating room is equipped with a combination of devices that include an anesthesia machine or workstation, physiologic monitors, infusion pumps, an anesthesia information management system (AIMS) and clinical information systems. These may be grouped together in different combinations as an Anesthesia Machine or they may be used separately in the care of a patient undergoing a surgical, diagnostic, or therapeutic procedure. Because all of these devices are interconnected, failure in one may affect others that are connected to the same patient. This chapter discusses the management of malfunctioning patient care equipment.

## Breathing Circuit Malfunction: Low Pressure Condition after Induction of Anesthesia

### Definition

Failure to generate or sustain a positive pressure in the breathing circuit that is sufficient to ventilate the patient’s lungs.

### Presentation

• Breathing system fails pre-use checkout.

• During spontaneous ventilation, reservoir bag empties; FiO2 is less than intended; low FiO2 alarm sounds.

• During bag-assisted ventilation, bag empties easily when squeezed but the circuit is not pressurized and the lungs do not inflate.

• During positive pressure ventilation with a ventilator:

• Breathing system low pressure alarm is annunciated during case if properly set.

• Capnogram is abnormal or absent (apnea) leading to alarm.

• Ventilator standing bellows fails to fill or sinks to the bottom of its housing.

• Spirometry alarm for low tidal volume (TV) or minute volume (MV) is annunciated.

### Malfunction Details

The breathing system must be gas tight to ensure that the patient receives the correct gas mixture and that positive pressure is transmitted to the lungs during inspiration.

### Differential Diagnosis

• Leak in the anesthesia machine low-pressure system

• Breathing system disconnection or misconnection

• Breakage of, or leakage from, a breathing system component that may be obvious or concealed

• Leak around airway management device (tracheal tube, laryngeal mask airway [LMA])

• Gas leak from the bronchial tree (e.g., bronchopleural fistula)

### Immediate Management

• If the patient’s lungs cannot be ventilated, immediately disconnect the breathing circuit and attempt ventilation with a self-inflating manual ventilation device (SIMVD) connected to a source of oxygen.

• Inspect anesthesia workstation and breathing system for an obvious leak. Correct if possible. Call for help to repair the faulty component while continuing to care for the patient.

• If the leak is small, increase the fresh gas flow (FGF) to compensate while the cause is determined.

• Differentiate between a problem with the ventilator or breathing circuit up to the Y-piece and a problem with the elbow, tracheal tube, or LMA by switching the circuit to the reservoir bag, disconnecting the Y-piece from the swivel connector, blocking the Y-piece with a finger, closing the pop-off valve, and squeezing the bag to determine if the circuit can be pressurized.

• If the problem is with the equipment on the patient side, check swivel and elbow connectors and the tracheal tube pilot balloon or LMA seating. If necessary, prepare to change the airway device.

• If the problem is on the workstation side and increasing the fresh gas flow compensates for the gas leak, monitor the ventilation closely and be ready to replace the ventilator.

• If the leak is on the workstation side and cannot be compensated for by increasing FGF, disconnect the patient from the breathing system and ventilate the lungs with a SIMVD connected to an oxygen source if available (otherwise use room air). Call for help and replace the ventilator.

• Maintain anesthesia with intravenous agents.

### Diagnostic Studies

• A difference in inspired and expired tidal volumes indicates that there is a leak in the breathing system that may be proximal (e.g., a hole/defect in the circuit tubing) or distal to the Y-connector (e.g., tracheal tube cuff leak, poorly seated LMA). If the breathing system incorporates a flow sensor between the Y-piece and the patient’s airway (e.g., D-Lite flow sensor used in GE ADU workstation or optional in GE Aisys Carestation), a leak distal to the flow sensor can be distinguished from a leak in the circuit between the workstation and the flow sensor.

• Verify that the set ventilator TV agrees with inspired and expired TVs.

### Subsequent Management

• If the source of the leak cannot be determined, replace the anesthesia breathing system and/or ventilator as soon as feasible.

• Do not start another anesthetic until the equipment has been replaced or repaired.

• Refer to authorized service personnel.

### Risk Factors

• Failure to perform the manufacturer’s recommended pre-use checkout procedures.

• Failure to correctly assemble breathing system components. Note: Be especially careful when using a new model and especially when switching from one manufacturer’s equipment to that of another.

### Prevention

• Educate personnel in the correct operation of the workstation, including pre-use checkout.

• Use all available breathing system monitors and alarms. Early detection and intervention decrease the risk of an adverse outcome.

### Special Considerations

• Any connection can become disconnected or misconnected. Always re-check the breathing circuit and ventilator when re-entering an operating room after leaving for any reason.

Adams AP. Breathing circuit disconnections. Br J Anaesth. 1994; 73: 46–54.Find this resource:

ASA Sub-Committee on Equipment and Facilities. Recommendations for pre-anesthesia checkout procedures. 2008. Available at: www.asahq.org/For-Members/Clinical-Information/2008-ASA-Recommendations-for-PreAnesthesia-Checkout.aspx Accessed November 22, 2014.

Caplan RA, Vistica MF, Posner KL, Cheney FW. Adverse anesthetic outcomes arising from gas delivery equipment: a closed claims analysis. Anesthesiology. 1997; 87: 741.Find this resource:

Eisenkraft JB. Hazards of the anesthesia delivery system. In: Ehrenwerth J, Eisenkraft JB, Berry JM, eds. Anesthesia equipment: principles and applications. 2nd ed. Philadelphia: Elsevier-Saunders; 2013:591–520.Find this resource:

Mehta SP, Eisenkraft JB, Posner KL, Domino KB. Patient injuries from anesthesia gas delivery equipment: a closed claims update. Anesthesiology. 2013; 119: 788–785.Find this resource:

Raphael DT, Weller RS. A response algorithm for the low pressure alarm condition. Anesth Analg. 1988; 67: 876.Find this resource:

## Electric Power Failure

### Definition

• Loss of electrical power. May be caused by an electric utility company power outage, or failure within the facility (e.g., severing a cable during construction).

• Most facilities have backup generators that turn on automatically when a utility company supply failure occurs, but a period of several seconds to a minute may elapse before the backup generator supplies power after a failure. Some facilities in the hospital (e.g., the operating room) may have uninterruptible power supplies. These backup systems may fail during a fire or during natural disasters such as storms, earthquakes, or acts of terrorism.

### Presentation

• Room lighting fails.

• Electrical devices connected to line power turn off unless they have a battery backup or are connected to an uninterruptible power supply (UPS).

• Some or all anesthesia devices may shut down, depending on whether they have internal backup batteries.

• Local telephone and paging systems may shut down.

• Cardiopulmonary bypass machine, cell saver, electrocautery, robotic systems, and other life support or essential equipment will fail.

• If the failure is caused by a community power outage and emergency generators are activated, electrical power should be restored within a short period of time. During the transition, some electronic equipment (e.g., computers) may power down and take time to reset.

### Differential Diagnosis

• Failure of a supply outside the facility (e.g., excessive power demand during extremely hot or cold weather, weather-related power line failure, natural disasters, fire, earthquake, construction work).

• Unannounced construction work or a failure of individual circuits in the operating room (OR) (e.g., turned off accidentally, or by a tripped circuit breaker) causing shutdown of one or more electrical devices.

### Immediate Management

• Set up emergency portable lighting (flashlight, laryngoscope light, emergency flashlights mounted on wall in most ORs).

• Call for help. If the OR telephone system fails, use a cell phone.

• Ensure that the power loss is not due to patient or personnel electrocution.

• If an electrical panel is in the room, check for tripped circuit breakers.

• Ensure that all essential electrically powered equipment is connected to emergency power outlets in the OR; these are usually identifiable by a red wall plate.

• Check that oxygen pipeline gas supply and suction are functioning; otherwise, follow the protocol for oxygen pipeline failure.

• Check that the ventilator is functioning and that the patient’s lungs are being ventilated. If not, switch to manual ventilation by breathing system reservoir bag or self-inflating resuscitation bag.

• Discuss the situation with the surgeon/proceduralist. Abort the procedure if possible. If possible, awaken the patient.

• Re-establish patient monitoring. Obtain a battery powered transport monitor for electrocardiogram (ECG), noninvasive blood pressure (NIBP), capnography, pulse oximetry.

• The ECG can be monitored using the monitoring mode of a defibrillator

• Use a precordial or esophageal stethoscope to monitor ventilation

• Obtain a manual BP cuff and sphygmomanometer to monitor blood pressure. Palpate the pulse.

• Consider using a colorimetric CO2 detector or a battery powered semi-quantitative CO2 mainstream analyzer (e.g., Nellcor Easy Cap by Covidien, Masimo EMMATM Emergency Capnometer) to monitor CO2.

• Electronic workstations have a backup battery that will supply power for 30–45 minutes. Conserve battery power by switching off the ventilator and manually ventilate using the reservoir bag. Adjust the screen brightness control to the lowest possible setting.

• On workstations that normally have electronic display of gas flows, revert to 100% O2 from backup rotameter (Dräger Apollo®, Dräger Fabius® GS, GE S5/ADU®). If using a GE Aisys® workstation, switch to the “Alternate Oxygen” flowmeter.

• Reassign personnel to provide manual power (e.g., hand-ventilating the patient’s lungs cranking the cardiopulmonary bypass machine).

• Postpone elective surgical procedures until the electrical supply has been restored.

### Diagnostic Studies

Refer to authorized engineering and service personnel.

### Risk Factors

• Failure to regularly check emergency backup power supply systems and to maintain or repair as required. (Anesthesia personnel should always be represented on hospital equipment and facilities committees.)

• Unannounced construction or maintenance in the vicinity of the institution.

• Unannounced construction or maintenance in the vicinity of the ORs.

### Prevention

• Regularly test the emergency power supply to ensure that it starts without delay and that automatic transfer occurs as soon as the power is stabilized. Service and repair as needed.

• Provide adequate warning to all staff of any planned interruption of electrical power supply (e.g., maintenance or construction).

• Educate OR personnel about the power supply to the OR, how to react to a power supply failure, and about electrical safety.

• During checkout of the anesthesia devices, note the charge status of the backup battery.

• Regularly check all anesthesia devices to ensure that the batteries are charged and can maintain their charge. Replace backup batteries as necessary.

• Regularly check that battery-powered lighting/emergency flashlights are functional, can be easily found in a dark room, and charging in each anesthetizing location.

• Consider obtaining uninterruptible power supply (UPS) units for electrically powered devices (e.g., OR computers and anesthesia information management systems) that do not have a backup battery.

### Special Considerations

• Most facilities have backup generators that activate automatically during a power outage, and some areas within the hospital (e.g., the operating room) may be supplied with an uninterruptible power supply. However, these backup systems may fail during a fire or during natural disasters such as storms, earthquakes, terrorism act, and so on.

Carpenter T, Robinson ST. Response to a partial power failure in the operating room. Anesth Analg. 2010; 110: 1644–1646.Find this resource:

Eichhorn JH, Hessell EA. Electrical power failure in the operating room: a neglected topic in anesthesia safety. Anesth Analg. 2010; 110: 1519–1521.Find this resource:

Welch RH, Feldman JM. Anesthesia during total electrical failure, or what would you do if the lights went out? J Clin Anesthesiol. 1989; 1: 358–362.Find this resource:

Yasny J, Soffer R. A case of power failure in the operating room. Anesth Prog. 2005; 52: 65–69.Find this resource:

## Equipment Malfunction before Induction of Anesthesia

### Definition

Failure of one or more devices (e.g., ventilator, patient monitors, AIMS, Clinical Information Systems, TEE) that is deemed essential for the case fails to power up, does not successfully complete self-test or does not work as expected.

### Immediate Management

• If a critical piece of equipment (e.g., anesthesia workstation, physiologic monitor) has failed, do not induce anesthesia.

• Verify that the device is connected to a source of electricity and other required sources (e.g., gas, vacuum). Check for continuity of hoses and power cords.

• Check switches and knobs. Equipment malfunctions are frequently caused by incorrect control settings.

• If a computer (e.g., AIMS, clinical information system) is inoperative, attempt to reset using the front panel switch or by cycling the power.

• Contact biomedical engineering or an anesthesia technician to repair or replace faulty equipment. If equipment cannot be replaced or repaired, move the patient to another operating room.

• Depending on institutional policy it may be possible to proceed with surgery if some equipment is not functioning (e.g., a nonfunctional AIMS may be replaced by a paper-based anesthesia chart).

### Subsequent Management

• The affected operating room should be taken out of service until the equipment has been repaired or replaced.

• Examine the operating room carefully for factors that may have caused the initial problem (e.g., a tripped circuit breaker that interrupts power to an anesthesia workstation)

### Risk Factors

• Improperly maintained equipment. Moving equipment from one location to another may cause cables or hoses to become partially disconnected. This may not be obvious unless they are examined carefully.

• Inadequate training on complex equipment, including anesthesia workstations.

### Prevention

• Test all equipment before the patient enters the room.

## Computer Network Failure

### Definition

• Failure of the OR computer network. May be restricted to one OR, the entire OR complex, or the entire facility.

### Presentation

• The hospital information system is not responding.

• The AIMS may or may not be charting measurements for ventilator and physiologic monitors, depending upon how it is connected to the other anesthesia devices.

• The AIMS cannot connect to the hospital information system to retrieve patient data or lab results, or cannot address network printers.

• The duration of the outage depends upon its cause, the structure of the network, and the level of redundancy.

### Immediate Management

• Determine whether the AIMS is acquiring data from the workstation and physiologic monitors. If not, revert to paper record keeping.

• Check for loose or unplugged data cables. Consider rebooting computers that do not have a life support function.

• Report the network failure. Many hospital IT departments do not have equipment that automatically signals a network failure.

### Subsequent Management

• If the data network outage affects a hospital-wide electronic health record system, consider postponing surgery until alternate methods of retrieving patient information are available.

### Risk Factors

• Routine data center maintenance.

• Faulty network equipment.

• Unannounced construction or maintenance in the vicinity of the institution.

• Unannounced construction or maintenance in the vicinity of the ORs.

### Special Considerations

• Periodically review “downtime” procedures.

• A plan should be in place to retrieve laboratory results and other critical information if the network should malfunction.

• Paper anesthesia records should be available for emergency use in all anesthetizing locations.

Fujii S, Moriwaki K, Sanuki M, et al. Loss of anesthesia records during network failure of anesthesia management information system: a case of malfunction of backup system. Masui. 2014; 63: 575–577.Find this resource:

## (p. 385) Oxygen Pipeline Failure

### Definition

Oxygen pipeline supply pressure to the workstation is either absent or below the minimum oxygen pressure required for normal function of the anesthesia workstation.

### Presentation

• Workstation fails pre-use checkout.

• Low oxygen supply pressure alarm is annunciated in workstation.

• If there is a problem with the central supply, a low oxygen pressure alarm may sound in the OR control center.

• O2 flow at main and auxiliary flow meters decreases or stops; the oxygen flush valve fails.

• Other gases supplied to machine (N2O, Heliox, possibly air) stop flowing.

• Oxygen-powered pneumatic ventilator stops working; apnea alarms sound (i.e., low pressure, low tidal volume, absent capnogram).

### Malfunction Details

• Pipeline supply of oxygen at 50 psig or 3–5 Bar(g) enters the workstation intermediate pressure system and supplies the following:

• 55 psig diameter indexed safety system (DISS) oxygen outlet (to drive jet ventilator, venturi suction device)

• Pneumatically powered ventilator

• Auxiliary flowmeter (e.g., for nasal cannula)

• O2 flush

• Main oxygen flow meter

• Alternate oxygen flow meter (GE Aisys® workstation)

• Low oxygen pressure alarm

• Fail-safe mechanism

• Failure of the central oxygen supply or the pipeline to the OR, pipeline system closed off or obstructed (e.g., by debris)

• Obstruction of the hose connecting the oxygen wall outlet to the workstation.

### Differential Diagnosis

• Leak in anesthesia machine oxygen system

• Obstruction or kinking of hose between wall oxygen outlet and workstation

• Debris in the pipeline system or a malfunctioning wall oxygen outlet

• Shutoff valve outside the OR is in the OFF position.

• Unannounced maintenance of pipeline system

• Failure of connection between bulk oxygen storage vessel and pipeline system.

### Immediate Management

• Confirm loss of pipeline oxygen pressure by checking the pipeline supply pressure gauge on workstation. Check O2 flush operation.

• Open the reserve O2 cylinder on the gas machine or ventilator.

• Minimize oxygen use.

• Use the lowest O2 flow possible (closed-circuit technique if possible).

• Switch off the pneumatic ventilator; use spontaneous or manual ventilation. (Most anesthesia ventilators use oxygen as the driving gas.)

• Ensure that the auxiliary oxygen flow is off.

• Announce the failure. Call for help and for additional backup oxygen tanks.

• Alert the surgeon, personnel in other ORs, and the engineering department.

• If workstation has pipeline supply of air and the patient will tolerate a lower FiO2, consider decreasing FiO2 to conserve oxygen.

• If the ventilator is driven by O2 and use of compressed air is not possible, hand-ventilate with room air using a self-inflating resuscitation bag and maintain anesthesia using intravenous agents.

• Postpone elective surgical procedures until the pipeline oxygen supply has been restored and an adequate supply of backup oxygen cylinders is available.

### Diagnostic Studies

• Use the oxygen analyzer to ensure that the patient is receiving an adequate FiO2.

• Ensure that the patient is maintaining an adequate SpO2.

• Refer to authorized engineering and service personnel.

### Risk Factors

• Failure to perform manufacturer recommended pre-use checkout procedures

• Unannounced construction in the vicinity of the OR

• Unannounced pipeline maintenance

• Filling of bulk oxygen storage vessel by unqualified personnel.

### Prevention

• Teach all anesthesia providers how to prepare, operate, and troubleshoot the anesthesia workstation.

• Check for normal pipeline pressure before starting an anesthetic, and periodically throughout the day.

• Check all hose connections between wall and workstation for tightness, leaks, and condition.

### Special Considerations

• Ensure that backup tank of oxygen on the anesthesia gas machine is tightly secured in the hanger yoke before starting an anesthetic.

• Ensure that the tank is full, and then turn it off. If the tank is left open, oxygen may leak out between the tank and the hanger yoke, and if the pipeline pressure drops below 45 psig, oxygen will be drawn from the tank. In either case, the backup tank will slowly become depleted.

• Ensure that all anesthesia personnel have received instruction and practiced changing the oxygen tank on the anesthesia gas machine.

• Consider having a backup supply of E size O2 tanks that are filled to 3000 psig and will deliver 1000 liters of gaseous O2, and that have a regulator and DISS oxygen connection that can provide oxygen at 50 psig. If the pipeline supply fails, the oxygen hose can be disconnected from the wall outlet and connected to the 55 psig DISS connector on the tank. These tanks can be stored in a central location within the operating room and distributed as necessary during a pipeline failure.

Lorraway PG, Savoldelli GL, Joo HS, Chandra DB, Chow R, Naik VN. Management of simulated oxygen supply failure: is there a gap in the curriculum? Anesth Analg. 2006; 103: 865–867.Find this resource:

Schumacher SD, Brockwell RC, Andrews JJ. Bulk liquid oxygen supply failure. Anesthesiology. 2004; 100: 186–189.Find this resource:

Weller J, Merry A, Warman G, Robinson B. Anaesthetists management of oxygen pipeline failure: room for improvement. Anaesthesia. 2007; 62: 122–126.Find this resource:

## (p. 388) Ventilator Failure after Induction of Anesthesia

### Definition

• The ventilator does not deliver the desired volume of inspired gas to the patient’s lungs.

### Presentation

• Ventilator bellows movement is abnormal (irregular, sticking) or absent.

• Ventilator does produce normal sounds during inspiration.

• One or more ventilator alarms are activated (e.g., low/high tidal volume, minute ventilation; low, high, or continuing pressure).

• Physiologic monitors may indicate inadequate ventilation (low or high end-tidal carbon dioxide; low SpO2).

• Clinical signs of hypoventilation/apnea include failure of the chest to move normally during ventilation, absence of breath sounds on auscultation, and a patient who is attempting to breathe spontaneously.

### Pathophysiology

• Bellows ventilators are powered by a compressed gas (usually oxygen but some may use compressed air) while piston ventilators are driven by an electric motor. Both designs use electronic controls that control the mechanical parts (i.e., the piston, or valves to control the compressed gas). An electronics failure in either type of ventilator or failure of the gas supply to bellows ventilators will render the system inoperative.

• Ventilator operation may not be intuitively obvious. An anesthesia provider who is unfamiliar with the system may unintentionally select an incorrect mode, resulting in failure to ventilate.

• The ventilator must be connected correctly to a properly configured breathing system.

• Fresh gas flow may be absent or inadequate to overcome a small leak in the breathing system.

• Alteration in thoracic compliance during the procedure may necessitate a change in ventilator parameters.

• Breathing system or airway obstruction

• Failure of the pneumatic and/or electrical power supply to the ventilator

• Failure of a ventilator component (may be mechanical, electronic, computer control system, or pneumatic)

• Failure of breathing system flow sensor. Properly functioning flow sensors are required for the normal operation of most modern ventilators.

• Failure of the decoupling valve in a ventilator that uses fresh gas decoupling.

### Differential Diagnosis

• Ventilator turned off or set to an incorrect mode.

• Failure of the ventilator pressure relief valve (stuck open and leaking or stuck closed, causing a high pressure condition in breathing system)

• Obstructed inspiratory side of the breathing circuit

### Immediate Management

• Immediately switch to manual ventilation with the reservoir bag, fill the circuit using the oxygen flush, and attempt to ventilate the patient. If this is successful, continue manual ventilation while troubleshooting.

• If the breathing circuit cannot be filled by operating the oxygen flush, ventilate the patient’s lungs using a SIMVD (e.g., Ambu) bag. If a source of compressed oxygen or air is available, a Bain circuit may be used. In the absence of back-up ventilation equipment, mouth-to-tracheal tube ventilation may be necessary.

• Call for assistance. Continue to monitor the patient and ask an anesthesia technician or another anesthesia provider to troubleshoot and correct the problem.

• Check the breathing circuit for disconnections, misconnections, and other sites of gas leakage (e.g., perforated tubing). Check that the pipeline gas supply is functioning; if not, switch to backup cylinder supplies.

• If the circuit fills from the oxygen flush or flowmeters, but the patient’s lungs cannot be ventilated, switch to a SIMVD, a Bain circuit, or other alternative ventilation system. Look for a possible obstruction on the inspiratory side of the circle system (e.g., a stuck inspiratory unidirectional valve, occluded inspiratory limb). (Note: Plastic packaging may completely or partially cover the end of a breathing hose.)

• If unable to ventilate the patient’s lungs with any backup system, consider an airway obstruction (e.g., kinked tracheal tube, herniated cuff, mucus plug or foreign matter in the tube or bronchial tree, endobronchial intubation, bronchospasm, tension pneumothorax).

• If potent volatile anesthetics cannot be administered, maintain anesthesia using a total intravenous anesthesia (TIVA) technique.

• Ensure that ventilation and oxygenation are maintained using the backup system if necessary, until the failure has been identified and the problem corrected.

• If the problem cannot be corrected by an anesthesia caregiver or anesthesia technician, the workstation should be withdrawn from clinical use until it is repaired by manufacturer-authorized service personnel.

### Diagnostic Studies

• Ensure that the patient is receiving adequate FiO2 using an oxygen analyzer.

• Ensure that the patient has an adequate SpO2.

• Refer to authorized engineering and service personnel.

### Risk Factors

• Failure to perform manufacturer’s recommended pre-use checkout procedures

• Failure to maintain or service the anesthesia gas machine according to manufacturer’s recommendations

• Unfamiliarity with the operation of the workstation/ventilator

### Prevention

• All anesthesia providers should receive training in the use of the anesthesia workstation.

• Some newer workstations use fresh gas decoupling to prevent changes in tidal volume when fresh gas flow rate, respiratory rate, or I:E ratio are altered. The user must understand the differences between this design and that of the traditional systems.

• Perform proper pre-use checkout of the workstation and ventilator

• Properly maintain and service all equipment according to manufacturer’s recommendations.

• Confirm correct assembly of the breathing circuit, function of unidirectional valves, and ability to ventilate a test lung (i.e., a reservoir bag) connected at the Y-piece of the circle system in both manual/bag and automatic/ventilator modes, and proper function of bag/ventilator selector switch.

• Before starting an anesthetic, ensure that an alternative means to ventilate the patient’s lungs (e.g., a self-inflating manual ventilation device) is immediately available and functioning.

### Special Considerations

• Standard E cylinders on the anesthesia machine are filled to approximately 2200 psig and deliver approximately 684 L of gaseous O2 at 1 atmosphere pressure.

• To estimate the time remaining to emptying of an E cylinder at a given flow rate, use the formula:

• $Display mathematics$

• e.g., If pressure = 1000 psig and flow rate is 10 L/min:

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