Modern Anesthesia Machines Research Articles

Activated Charcoal Effectively Removes Inhaled Anesthetics from Modern Anesthesia Machines

If a malignant hyperthermia-susceptible patient is to receive an anesthetic, an anesthesia machine that has been used previously to deliver volatile anesthetics should be flushed with a high fresh gas flow. Conflicting results from previous studies recommend flush times that vary from 10 to 104 minutes. In a previously proposed alternative decontamination technique, other investigators placed an activated charcoal filter in the inspired limb of the breathing circuit. We placed activated charcoal filters on both the inspired and expired limbs of several contaminated anesthesia machines and measured the time needed to flush the machine so that the delivered concentrations of isoflurane, sevoflurane, and desflurane would be <5 parts per million (ppm). We next simulated the case for which malignant hyperthermia is diagnosed 90 minutes after induction of anesthesia and measured how well activated charcoal filters limit further exposure. Activated charcoal filters decrease the concentration of volatile anesthetic delivered by a contaminated machine to an acceptable level in <2 minutes. The concentrations remained well below 5 ppm for at least 60 minutes. When malignant hyperthermia is diagnosed after induction of anesthesia, we found that with charcoal filters in place, the current anesthesia machine may be used for at least 67 minutes before the inspired concentration exceeds 5 ppm. Activated charcoal filters provide an alternative approach to the 10 to 104 minutes of flushing that are normally required to prepare a machine that has been used previously to deliver a volatile anesthetic.

Functional characteristics of anesthesia machines with circle breathing system

Presently, the majority of anesthesia machines or workstations are ventilators that incorporate a classic circle system/circuit with a CO 2 absorber that allows rebreathing of exhaled gases. The performance characteristics of these machines are related to the physical structure of the breathing circuit. Limitations related to the classical circle breathing circuit are progressively disappearing with the arrival on the market of modern anesthesia machines with modified circular circuits, which offer a series of advantages in relation to the classic circular circuit. The present review describes the basic functional characteristics common to any anesthesia machine and that determine their clinical performance. The knowledge of these characteristics is essential for the clinical use of anesthesia machines and for analyzing their evolution.

Oxygen monitoring during low flow anaesthesia

Brody’s formula for estimating oxygen consumption is rarely used in low flow anaesthesia and most anaesthetists assume that 250 ml/min is sufficient for every adult. However there is a simple method of monitoring fairly accurately the oxygen consumption in real time, using the current standard equipment and monitoring in anaesthesia. The FiO2 and End Tidal oxygen concentrations are measured almost routinely with the modern anaesthetic machines. At sea level, these figures are almost exactly the same as percentages. Therefore, if the difference between FiO2 and ETO2 is calculated as a proportion of the minute ventilation, this gives the oxygen consumption ((FiO2 ETO2) 9 MV). I have found that the actual amount of oxygen taken up varies considerably between patients of similar weights and at different times during anaesthesia. Sometimes up to 450 ml/min. This simple calculation adds to the safety of low flow anaesthesia.

Narkomed 6400 Anesthesia Machine Failure

To the Editor: We report a near-catastrophic failure in a Draeger Narkomed 6400 Anesthesia Machine and the operating room filling with smoke due to a failure of a capacitor in the power supply board electrical components. The Narkomed 6400 Anesthesia Machine (Draeger Medical, Inc., Telford, PA) had been in use on the day of the event. In the morning, machine power was switched on and all checkout procedures performed. Three cases were performed, anesthesia personnel were changed, and the machine ventilator test was performed. Five minutes after this last test with the Narkomed 6400 in standby mode, white smoke was observed to billow out of the bottom air vent of the Draeger Narkomed 6400 Anesthesia Machine. The room's air became very pungent, smelling of an electrical component burning. The operating room was evacuated and the fire department contacted. A respiratory technician/anesthesia tech quickly unhooked the Narkomed 6400 machine from the oxygen and nitrous oxide gas supply and disabled the power cord. The smoke from the machine decreased and then stopped. By the time the fire department arrived, the operating room's ventilation system had cleared the air and the machine was moved out of the surgical area. There were no tripped circuit breakers and no other electrical problems were observed in any other operating rooms. Subsequent analysis first noted that the power supply was a discontinued model and that the supplier of this power supply was no longer in business; therefore, the power supply was nonrepairable. The machine had undergone regular preventive maintenance through a contract with Draeger Medical Inc. Examination of the printed circuit board revealed a suspicious-looking capacitor, Capacitor C44, a can-type capacitor covered by a plastic sleeve. The plastic sleeve over the capacitor was ruptured revealing the top of the capacitor bulging upwards, which gave evidence that the capacitor venting mechanism had been actuated. This venting caused the white smoke to emanate from the anesthesia machine. This event was due to an internal failure of the capacitor. The Food and Drug Administration was not notified because Draeger stated this was caused by an internal failure of the capacitor and was an isolated event. Historically, operating room fires or explosions caused by anesthesia equipment were attributable to flammable anesthetic agents.1 Recently, contamination of pressurized gas systems with dust or oil2,3 or electrical fires from the sophisticated electronics in anesthesia monitors and machines have been reported.4,5 Although the incidence of equipment-related critical events is relatively low, morbidity associated with such events can be high.6 This event is an example of the risks that more complex and modern anesthesia machines bring to the operating rooms. Although no actual fire occurred, the operating room rapidly filled with acrid smoke. We were fortunate that this occurred between cases and patient safety was never compromised. In retrospect, the actions of operating room personnel were appropriate: notification of authorities, evacuation of all personnel from the affected area, complete gas supply disconnection, shut down and isolation of the anesthesia machine from flammable material. Had this occurred during a surgical procedure, immediate isolation of the entire surgical team from the pungent smoke and hazardous machine would have been necessary. Thomas E. Schulte, MD John H. Tinker, MD Department of Anesthesiology University of Nebraska Medical Center Omaha, Nebraska [email protected]

Minimum inspired oxygen concentration alarm

EDITOR: The use of anaesthetic machine and patient monitor alarms, in addition to clinical observation, can enhance patient safety, but it is very important that these limits are accurately set. The importance of these settings is highlighted by a critical incident which occurred recently in one of our theatres. Case report: An 8-yr-old, American Society of Anesthesiologists (ASA) I patient was scheduled for an elective ear, nose and throat procedure. Induction was uneventful and general anaesthesia was maintained with spontaneous ventilation via a laryngeal mask. The patient's head was draped and surgery commenced. An unobserved disconnection occurred at the junction of the circle-system breathing circuit tubing and the filter to which the gas analyser sampling line was attached (Fig. 1). The reduced movement of the reservoir bag was not initially noticed and the capnography trace continued as per normal. The inspired oxygen concentration decreased but the alarm did not sound as its setting had not been changed from the factory default of 18% for oxygen. Had it been set to above 21% it would have been activated. Fortunately the disconnection was discovered and the circuit reconnected before the patient sustained any harm.Figure 1.: Site of disconnection between circle breathing system and filter.The case prompted an audit at two hospitals in our region which demonstrated that the minimum inspired oxygen concentration alarm was changed from the factory reset by less than 10% of anaesthetists. Personal communication with a colleague from a neighbouring region revealed that two identical incidents had recently occurred in their hospital, and the same audit is at present being conducted in their hospital. Fortunately no patient suffered any harm as a result of the disconnections but the potential for patient awareness, movement, adverse airway events and hypoxia is evident. The use of an oxygen analyser is mandatory in accordance with the checklist for anaesthetic apparatus as set out by the Association of Anaesthetists of Great Britain and Ireland and is recommended in many other countries [1]. The Association guidelines however give no advice regarding the values to which the analyser's alarm limits should be set [2]. Oxygen concentrations are usually measured at either the fresh gas outlet or via the end-expired gas sampling line attached to, or near to, the filter. In addition to guarding against the delivery of hypoxic mixtures, the analyser (sampling end-tidal gases) can also help to detect problems with breathing circuit and ventilator integrity, and with alveolar hypoventilation [3,4]. A study by Knaack-Steinegger showed that disconnections were evident within 30 s using expired oxygen concentration alarms [5]. Disconnections are evident within a few breaths when using end-tidal gas monitoring with oxygen concentration alarms set to above 21%. Capnography alarms and the waveform are used by anaesthetists as a monitor for early detection of problems with patients' ventilation, including disconnections in the breathing system. In spontaneously breathing patients, where there is a disconnection proximal to the capnography sampling point, the capnography trace may well continue as per normal and hence this alarm would not detect the disconnection. An anaesthetic agent analyser is also useful to detect disconnections in a breathing system and guard against patient awareness, but factory default settings of 0% would need to be reset to minimum alveolar concentration (MAC) awake or above. The audit performed in our hospital also investigated the alarm settings of the agent analyser and found that in no theatres were the limits changed to above 0%. The oxygen alarms are often not set above 21% as doing so results in the alarm sounding when there is no (enriched) oxygen flowing through the circuit. This can be overcome by leaving the sampling line in continuity with the circuit and allowing a small quantity of oxygen to flow (most modern anaesthetic machines have a minimum oxygen flow preset). An alternate solution is to cap the circuit off at the end of the case. This also helps to prevent wastage of anaesthetic gases and stops the anaesthetic agent analyser alarm sounding (if set above 0%). Ventilator pressure alarms can detect leaks during mechanical ventilation, but they are not foolproof [6]. The minimum inspired oxygen alarm is a useful monitor but should be set above 21%, especially for spontaneously breathing patients and when the circuit is covered. Setting the anaesthetic agent alarm to above 0% further adds to patient safety. M. T. Dale D. Jadhav *Department of Anaesthesia, Critical Care and Pain Management, Leicester Royal Infirmary, Leicester, England

Preoperative checkout procedures for modern anesthesia machines in an emergency situation

Preoperative checkout procedures for modern anesthesia machines in an emergency situation

All in the name of progress

I read the letter (Langford. Anaesthesia 2002; 57: 313) concerning the incidents of unexpected anaesthetic machine failure and the importance of having an `Ambu' (self-inflating) bag as a back up. Similar critical incidents [1, 2] have been reported in our hospital and we have now made it a policy of keeping an ‘Ambu’ bag beside all the anaesthetic machines. Also, this prompted me to do a postal survey in the form of a questionnaire asking whether or not they have got an ‘Ambu’ bag and, if not, would they like to have an ‘Ambu’ bag as a back up in case of anaesthetic machine failure? The questionnaires were addressed to clinical directors and the operating department assistants of 50 NHS hospitals. Of 100 questionnaires, 64 were returned. The results of this survey indicated that 78% favoured the availability of an ‘Ambu’ bag beside the machine but in practice only 24% said it was available. How do we bridge this gap between availability and expectation? Whilst having accepted that the modern anaesthetic machines are sophisticated and have built-in safety features to warn the users about impending failure [3], as a part of risk management is it worth keeping an ‘Ambu’ bag with every anaesthetic machine?

The Evolution of the Anesthesia Machine

On October 16, 1846, medical science, and the world, learned that the pain caused by surgical operations had been conquered. Mankind now possessed a potion so pow­ erful, that a soul entranced by its fumes paid no mind to the horror that was sur­ gery in that age. That first demonstration taught another, more subtle lesson to those who would pursue this newly created medi­ cal art: to harness the properties of this potent liquor, to deliberately poison a person's breath and to alter the conscious­ ness of that living being would require a clever instrument of some precision. From that day forward, anesthetists have em­ ployed a variety of devices to deliver the gases and vapors of anesthesia to their pa­ tients. The modern anesthesia machine is a collection of components whose inven­ tion and refinement parallel the history of anesthesia practice and whose lineage can be traced back to that October morning in Boston one hundred and fifty years ago. The demonstration was set to begin this morning, bu t William Thomas Green Morton was in danger of being late. He was working feverishly on an instrument with which to administer the secret compound, so that he could claim as his own the break­ through that had eluded medicine for cen­ turies. He remembered vividly the failed attempt by his one-time partnel� Horace Wells, to make public a similar discovery, and vowed not to suffer the same humilia­ tion. As the time grew near, he continued to assemble what was to become the first working anesthesia inhaler in history. The appointed hour had come and passed, and now IS minutes late, Dr. Morton arrived in the operating theater j ust in time to stop the surgeon from cutting skin. It was the last-minute work on the inhaler that made him late, but it was that same inhaler that helped him announce to the world that a new era of medical practice had begun. Morton's ether inhaler was a two-necked glass globe that was stuffed with a few small sponges soaked with ether. It was a simple draw-over vaporizer, with a short non­ rebreathing mouthpiece, and an inlet for fresh atmospheric gas flow. This basic de­ sign was widely copied and modified, as the accounts of his amazing discovery spread across the globe. William Morton not only introduced the concept of surgical anesthesia, but also created the prede­ cessor of all anesthesia machines to fol­ low. The journey from this modest begin­ ning to the state-of-the-art computerized anesthesia workstations of today was com­ pleted in three stages, the first of which was the era of inhalers.

Low-flow anaesthesia.

Although many anaesthesia machines are equipped with circle rebreathing systems, inhalational anaesthesia remains frequently performed using relatively high fresh-gas flows. The major advantages of rebreathing techniques can be achieved only if the fresh-gas flow is reduced to 1 l.min-1 or less. Although there are potential risks associated with low-flow anaesthesia, modern anaesthesia machines meet all the technical requirements for the safe use of low-flow techniques if they are used in conjunction with equipment for monitoring inhaled and exhaled gas concentrations; these monitors are already increasingly available and, in the near future, are likely to become an obligatory safety standard in many countries. For both economic and ecological reasons, the use of new inhalational anaesthetics, with low tissue solubility and low anaesthetic potency, can be justified only if the efficiency of administration is optimised by using low-flow anaesthetic techniques.

A simplified concept for controlling oxygen mixtures in the anaesthetic machine--better, cheaper and more user-friendly?

Modern anaesthetic machines are equipped with several safety components to prevent delivery of hypoxic mixtures. However, such a technical development has increased the complexity of the equipment. We report a reconstructed anaesthetic machine in which a paramagnetic oxygen analyzer has provided the means to simplify the apparatus. The new machine is devoid of several components conventionally included to prevent hypoxic mixtures: oxygen failure protection device, reservoir O2 alarm, N2O/air selector, and proportioning system for oxygen/nitrous oxide delivery. These devices have been replaced by a simple safety system using a paramagnetic oxygen analyzer at the common gas outlet, which in a feed-back system cuts off the supply of nitrous oxide whenever the oxygen concentration falls below 25%. The simplified construction of the anaesthetic machine has important consequences for safety, cost and user-friendliness. Reducing the complexity of the construction also simplifies the pre-use checkout procedure, and an efficient 5-point check list is presented for the new machine.

Evolution of the anaesthetic machine

Anaesthetists have always taken a particular interest in the apparatus they use. Their original anaesthetic machines of the 1840s were not purpose-built devices but merely adaptations of other scientific or domestic apparatus. They were soon replaced by specific simple apparatus which could be widely used in all the known surgery of that era. This second generation of equipment could still be used today but has instead been replaced many times over the last 150 years by apparatus of increasing sophistication. Up until recently the evolution of the anaesthetic machine had mirrored the evolution of the speciality itself — this is because the majority of apparatus was built by the anaesthetist or at his request. Modern anaesthetic machines are rarely designed by the profession directly and no longer provide such insights into practice. There is now a much blander uniformity in this machinery which has become so sophisticated in an attempt to minimise faults and errors. Anaesthetic audit studies continue to highlight human error or ignorance as the major cause of morbidity and mortality and there is a danger that our machines are evolving in the wrong direction in the hands of industry rather than in our own.

Oxygen pipeline supply failure: A coping strategy

Oxygen is the most vital drug administered during anesthesia. The delivery of hypoxic or even anoxic gas mixtures during anesthesia has been reported. Because such occurrences often meet with disaster, modern anesthesia machines have a system of alarms to warn against the delivery of hypoxic or anoxic gas mixtures and also to warn of the failure of the oxygen pipeline supply. We describe the occurrence of a sudden failure of the oxygen pipeline supply, and discuss a strategy for coping with this emergency.

The Anatomy of Modern Anesthesia Machines

The Anatomy of Modern Anesthesia Machines

ARTIFICIAL RESPIRATION IN MICE DURING THORACIC SURGERY: A SIMPLE INEXPENSIVE TECHNIC.

During experiments designed to determine the effect of unilateral thymectomy on the unilateral development of thymic lymphoma in mice (1,2) an apparatus for artificial respiration with positive pressure oxygen in mice was developed. Use of the device permits wide surgical exposure of the thorax and approximates the conditions accomplished by modern anesthesia machines. Because the device decreases the hazard of pneumothorax during experimental surgery on mice and is inexpensive to construct, the apparatus is presented for possible interest to other investigators.The apparatus consists of 3 parts: 1) a flow valve, bubble meter, and high pressure limit assembly; 2) a valve to provide intermittent oxygen flow, and 3) an endotracheal catheter (Fig. 1.)1. Flow valve, bubble meter, and high pressure limit assembly. The regulation of small amounts of oxygen is accomplished by use of a screw clamp on the oxygen supply rubber tubing which leads directly from the reducing valve of a standard oxygen tank. The rate o...