In Reply:—

Patient safety is of paramount consideration in the design of all Draeger Medical products (Telford, Pennsylvania). In his letter, Dr. Gross offers an opinion about the safety of the Narkomed 6000 that is not substantiated by data or factual evidence and is based on an incomplete understanding of the machine design. In his conclusion, Dr. Gross states that “If an electrical or electronic failure occurs, it is impossible to deliver positive-pressure ventilation manually . . . ” Dr. Gross also states in his conclusion that “a failure in the internal power supply circuitry could result in inability to provide positive-pressure ventilation.” Both of these statements are incorrect. In fact, even if both internal and external power sources fail, internal pneumatic controls ensure that manual ventilation is always possible, including fresh gas and anesthetic delivery, as long as the main switch is in the “on” position, and a supply of gas is available. Recognizing the possibility of power failure, this feature was a fundamental objective of the Narkomed 6000 design team from the outset of the design process. In his letter, Dr. Gross raised three specific issues that will be addressed individually.

In his first point, Dr. Gross talks about “an emergency situation, with the machine turned off.” None of the current Narkomed models are designed to be used in any situation with the machine turned off. When any current Narkomed anesthesia machine is turned on, fresh gas and anesthetic agent are immediately available as long as there is a gas supply. In the case of the Narkomed 6000, turning on the machine makes fresh gas available immediately and pressurizes the ventilator control valves needed to support manual ventilation. In the event of an emergency, it only makes sense to turn the machine on so that the flowmeters can be used to support any manner in which the machine will be used. It is not clear what type of emergency Dr. Gross envisions in which it would be desirable to use any Narkomed machine in the “off” position.

In his second point, Dr. Gross comments on the self-test process of the Narkomed 6000 ventilator and the time required to cancel this process. When the main switch on the Narkomed 6000 is turned to the “on” position, the ventilator executes a self-test process. This is another safety feature that ensures that the ventilator is functioning properly and informs the user about any leaks or internal sensor problems. Evidence that clinicians often fail to detect machine faults, despite a recommended anesthesia machine checklist, supports the value of the automated self-test as a means to enhance detection of ventilator problems. 1Dr. Gross is correct in observing that while the ventilator self-test process is active, it is not possible to provide manual ventilation. However, the automated self-test can be canceled at any time by pressing the standby key, in which case either manual or mechanical ventilation is possible within 30 s. If the ventilator self-test is canceled, the machine tracks the time since the last automated self-test was performed and reminds the user when another self-test should be performed. In hospitals where trauma patients or other emergencies demand immediate availability of the ventilator, the Narkomed 6000 can be left in the “on” position continuously. Standby modes for both the ventilator and the monitor are provided to suppress alarms and conserve power while keeping the machine immediately available for use.

The ventilator-bypass button to which Dr. Gross alludes (actually called the ventilator override switch) is another safety feature that is provided in the unlikely event that the ventilator controls do not respond. This button disables the electrical supply to the ventilator and, as in the case of all current Narkomed models, manual ventilation is immediately possible as long as gas pressure from either wall supply or a cylinder is available. The ventilator override switch is not intended to be used to bypass the start-up process.

In his third point, Dr. Gross describes the unlikely but not impossible scenario of the Narkomed 6000 being turned off and then on again while functioning on battery power. If the machine is turned off when using battery power, Dr. Gross is correct in his observation that a shutdown process begins, which ultimately turns off all power to the machine. This shutdown process takes approximately 4 min to complete and is designed to preserve battery power so the machine will start normally if it must be used before AC power is restored. The shutdown process cannot be interrupted after it begins so that if the Narkomed 6000 is turned on before the shutdown process is completed, although the ventilator will start its self-test process, monitoring functions will not be available, and all power will be turned off when the shutdown process concludes. Dr. Gross is not correct, however, in his statement that “manual positive-pressure ventilation may not be possible” in this situation. If battery power is available when the main switch is turned to “on,” the ventilator begins its usual start-up process, which can be allowed to proceed or can be canceled as described previously. If all electrical power to the machine shuts off at the conclusion of the shutdown process, manual ventilation is always immediately available as long as the main switch is in the “on” position and there is a supply of gas to the machine.

Although Dr. Gross does not define what he considers to be an emergency in his letter, I assume from his comments he is referring to a situation in which manual ventilation is required. The Narkomed 6000 is designed with many safety features that can be used in such an emergency. Like any current-model Narkomed anesthesia machine, the Narkomed 6000 is designed always to allow for manual ventilation independent of whether electrical power is available. Even if AC power fails and the batteries have been drained, as long as the main switch is in the “on” position and there is a supply of gas, pneumatic controls ensure that manual ventilation is possible. Furthermore, every Narkomed 6000 is equipped with an auxiliary oxygen flowmeter that supplies oxygen independent of whether the machine is turned on. Both prudent practice and the Food and Drug Administration Anesthesia Apparatus Checkout Recommendation dictate that an alternative means of ventilation, such as a self-inflating bag, be readily available in all anesthetizing locations. *Such a device can be connected to the auxiliary oxygen flowmeter on the Narkomed 6000 to deliver oxygen to a patient irrespective of the state of the anesthesia machine.

The Narkomed 6000 is an evolutionary computer-based anesthesia workstation that brings a number of advanced monitoring and ventilation capabilities to the operating room while still supporting manual ventilation, including gas and vapor delivery, in the event of a total electronic failure. Like any sophisticated medical device, using the Narkomed 6000 effectively requires proper training and education. The opinion expressed by Dr. Gross about the safety of the Divan ventilator and the Narkomed 6000 is based on an incomplete understanding of the machine design. Furthermore, with more than 8,000 Divan ventilators in use on Draeger Medical products worldwide and more than 500 Narkomed 6000 workstations in use in North America, his opinion is contrary to clinical experience. However, Draeger Medical appreciates the opportunity to explain the emphasis on safety that underlies the Narkomed 6000 design.

March MG, Crowley JJ: An evaluation of anesthesiologists’ present checkout methods and the validity of the FDA checklist. A nesthesiology 1991; 75: 724–9