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Correspondence Vaporizer overfilling To the Editor: In December, 1989, a three-year-old boy undergoing a hernia operation at a Windsor hospital is believed to have received a halothane overdose, and was left neurologically impaired. When a consultant inspected the eight Penlon AM I000 anaesthesia machines in the hospital a week or so after the incident, every vaporizer (Penlon PPV incorporating a keyed fdler) was found to be overfdled. Our investigation revealed that the same individual fdled all of the vaporizers before use, and that he used improper fdling procedures. Simulations which we conducted with these filling errors produced about ten times the intended vapour concentrations. Several factors - newly installed anaesthesia systems, inadequate training, and failure of the sight glass to indicate an overfdled vaporizer - probably make this case of multiple overfdling unique. However, the conditions leading to overt'riling are not unique, and we review them here to encourage caution.
Conditions necessaryfor overfilling To overfdl a vaporizer attached to the anaesthetic machine with the gas flow off: 1 The Concentration Dial must be turned ON; and 2 The seal between the bottle neck and fdling adaptor must be broken (e.g., by intentionally loosening the bottle cap or having an incompatibility between the keyed fdler and the bottle neck). Since the vaporizing chamber and bottle neck are both open to atmosphere under these conditions, liquid will flow from the bottle until the fluid level in the vaporizer reaches the height of the bottle neck, unless the bottle empties or the vaporizer incorporates an overfdl in the failer block.
Overfilling volumes and vaporizer performance When correctly fdled, there is a large space above the liquid in the vaporizing chamber to enable saturation of the carrier gas flowing through the wick asembly. During overfdling, liquid displaces gas from this space. If the space becomes completely fdled, then liquid can be displaced into the manifold or bypass gas flow and deliver an overdose. Alternatively, the level may be sufficiently high that any pumping effect from a ventilator may cause a bolus of liquid to be ejected. To reach these critical
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overfdling levels, we found it was necessary to introduce 130 ml more than the normal fdling volume. Thus, if a vaporizer is partially fdled, a single 250 ml bottle of halothane or enflurane contains enough liquid to overfdl the vaporizer critically. If the vaporizer is overfdled, but below the critical level, the vapour output may be reduced rather than increased. For example, when the PPV Vaporizer was overfdled by more than 3/8 of a bottle (halothane), the vapour output was observed to decrease with increased overfdling, falling to zero just before critical overfilling was reached. Unless the vaporizer performance was immediately evaluated with an agent analyzer, any such incident would likely go unreported.
Sight glass The liquid level in the sight glass is usually a reliable indicator of overfdling. However, the design of the PPV Vaporizer involved with this case (now modified) allowed an air bubble to become trapped at the top of the sight glass when overfdled. Coupled with some ambiguity over the FULL marking, this allowed the impression to be formed that it was just full when it was overt'died.
Overfill drain In the past, overfdl drains on the dual-port fdler block of vaporizers provided some protection against overfdling, although they were susceptible to clogging. However, most manufacturers eliminated this drain (to minimize pollution from agent leaking during Idling) when singleport fdler designs were introduced. Since the Windsor incident, Penlon has redesigned the PPV to include an overfill drain. The CSA Standard Z168.3-M84 acknowledges the importance of protection against vaporizer overfdling. However, clause 15.12.1.2 only tests for protection against overfdling under a single fault condition (vaporizer ON). Consequently, vaporizers without an overfdl drain can be certified to this standard, although proposals to require an overfill drain are under discussion. An overfdl drain on a vaporizer fitted with the keyed filling system will not provide absolute security against overfdling under all conditions of malfunction or misuse; however, it will provide protection against some commonly known f~ling errors or malfunctions. As long as the keyed filler system is used, we believe that the overfill drain, or its equivalent, should be included.
78 Alex Sinclair PhD Jos Van Bergen Health and Welfare Canada REFERENCE 1 Medical Devices Alert No. 101. Leakage and breakage of anaesthetic bottles of forane and possible damage to metal filling adaptors. Health Protection Branch, Ottawa, January 24, 1992.
Anaesthetists and the right to die TO the Editor: With its recent judgement in the case of Nancy B., the judiciary system in Quebec has upheld the right of the mentally competent patient to request cessation of life support treatment. ~ This judgement reflects the ethical position to which a majority of physicians and society in general have evolved. To every right corresponds a duty. If, after mental competence has been demonstrated and all other options considered at length, a patient decides to exercise his/her right to request cessation of life support treatment, then it becomes the duty of the patient's physician to assist the patient in withdrawing technological support while ensuring that the patient does not suffer. For the ventilator-dependent patient, such as Nancy B., terminating treatment humanely necessitates the administration of doses of sedative drugs which by themselves might cause death even in a normal individual. As the fine line between preventing suffering and actively terminating life becomes inevitably obscured, physicians become uncomfortable with carrying out this duty. Because of this and because of their fear of not giving enough, physicians may be tempted to request the services of anaesthetists to assist them in carrying out their duty. In the case of Nancy B., an anaesthetist was present at her bedside along with her doctor when sedation was administered and the ventilation disconnected. 2 As society in general, and the medical community in particular, is likely to evolve gradually toward the recognition of an increasing number of indications for "humane" cessation of treatment (i.e., cessation of treatment with sedation) and as the boundary between cessation of treatment with sedation and active euthanasia becomes more obscured, anaesthetists may be increasingly requested to render such services. A recent article in the
CANADIAN JOURNALOF ANAESTHESIA New England Journal of Medicine 3 went as far as suggesting that anaesthetists are ideally suited to perform active euthanasia and should probably be the only physicians licensed to do so, if and when this practice becomes acceptable. As anaesthetists, we should reflect on the implications of this situation for our specialty. Do we want our role to evolve according to these demands that are likely to be addressed to us? We believe that such acts as administering heavy sedation for withdrawal of life support treatment are the duty of the attending physician, as he or she is primarily responsible for the outcome of the ethical decision process. To invite an anaesthetist to attend or to actually administer the medication is not only unnecessary, it is also undesirable. It is unnecessary because the administration of generous doses of long-lasting sedative drugs, ideally suited for this situation, is in the realm of competence of many, if not all, physicians. It is undesirable because it will encourage the formation of a group of physicians who may become desensitized to such interventions while allowing those who are involved in the ethical decision process to distance themselves from the consequences of their decision. This may eventually allow for laxity in the ethical decision process. We fear the personal cost to anaesthetists of helping to carry out decisions in which they are not, and should not, in most circumstances, be involved. Furthermore, we do not want to become associated in the minds of our patients with the act of terminating life, as this might well interfere with their ability to trust that we will do our utmost to support their own life. Gis61e Hemmings MD Fred C. Salevsky MD Paul A. Sloan MD Mark Angle MD Fiona E. Ralley MD Daniel Chartrand MD Sally Weeks MD Anne Moore MD Marlene Gauthier MD Richard Catchlove MD Raymond Hasel MD Jean-Frangois Courval MD Department of Anaesthesia Royal Victoria Hospital Montreal, Quebec REFERENCES 1 Cour Sup~rieure, Province de Quebec, District de Qu6bec. Nancy B. demanderessevs Hftel Dieu de Qu6bec, d6fende-
