Case 1: On 2lst July, 1990 (a Saturday afternoon), a patient at Caritas Hospital, Hong Kong, underwent emergency Caesarean section. The operation took place in an operating room which is separate from the main suite, and is used for emergency only. It does not have bulk gas supply pipelines.
The unpremedicated patient was pre-oxygenated via a Magill breathing circuit, given thiopentone and suxamethonium in appropriate doses, and intubated. A 50% mixture of nitrous oxide and oxygen with 0.5% halothane was given via a Manley MP3 ventilator with a fresh gas flow of 6L/minute. Monitoring was by means of an oximeter, a non-invasive blood pressure recorder, and an EKG. No oxygen analyzer or capnograph was in use
When the suxamethonium had worn off, alcuronium was given, and the baby was delivered in good condition shortly after. Up to this time, the anaesthesia had been uneventful, but a bradycardia then developed, followed by severe hypotension. At one stage, cardiac arrest appeared, but a detached EKG electrode was replaced, with return of the trace to the screen.
Halothane was discontinued and the pulse rose, although the patient remained hypotensive. A few ventricular premature beats were noted. The operation was rapidly completed and the patient reversed. She breathed satisfactorily, but did not wake up, and she was therefore sent to Intensive Care where her saturation was noted to be 92-93% despite an FI02 of 0.4. A blood gas estimation revealed a pH of 7.106 and PaCO2 Of 51 mmHg.
One hour later, she recovered consciousness, and appeared well. The baby made satisfactory progress.
Pattern of N20 Problems
Case 2: On the following day (a Sunday), another woman was also given general anaesthesia in the same operating room for Caesarean section, utilizing an identical technique to Case 1. In this patient, tachycardia, and hypertension (I 60/120) developed within minutes of induction, together with a few ventricular ectopics. FiO2 was increased to 1.0, and the baby delivered with an Apgar of 6, rising to 9 at five minutes. Nitrous oxide was reintroduced, and tachycardia and hypertension reappeared.
At the conclusion of the operation 20 minutes later, the patient was grossly agitated and confused. She was given diazepam 5 mgm IV and temporarily settled, but 30 minutes later was again uncontrollable. Since she had been given 15 mg of alcuronium less than 20 minutes before reversal , a consultant who was called at this time thought she may have been inadequately reversed, but a further dose of neostigmine had no affect on her disturbed behavior, so she was given midazolam 5 mg, went to sleep and recovered consciousness six hours later. No blood gases were taken from her. Her baby was also in a satisfactory condition.
On Monday 23rd July, a senior anaesthetist removed all drugs from ” operating room, and carried out a mechanical check of the anaesthesia machine, and on Tuesday 24th, a routine service of the machine was performed under the Hospital’s maintenance contract. Neither of these checks included gas analysis.
Incident Again Points to Gas
Case 3: On Wednesday 25th July, during an identical general anaesthesia for Caesarean section, the patient developed multiple ventricular premature beats within three minutes of induction. The blood pressure fluctuated between hypertension and hypotension as nitrous oxide was alternately discontinued and reintroduced. On reversal, this patient was unresponsive, although breathing adequately. She took three hours to recover consciousness.
A more detailed check of the anaesthetic machine was now done, using a Cardiocap apparatus, originally to determine whether the halothane vaporizer was faulty but no leaks were detected with the vaporizer in the off position.
Tainted Tank Targeted
However, when the nitrous oxide flow-meter was turned on, the C02 reading rapidly went “off-scale:’ Reduction of the How of “nitrous oxide” and increase in flow of oxygen suggested that the contents of the nitrous oxide cylinder were predominantly C02, and subsequent analysis proved it to be 95% C02, 5% air.
On inspection, although its valve was pin-indexed for nitrous oxide, most of the blue paint was missing from the cylinder, swept around the shoulder, and no label was present to indicate its contents.
In view of the fact that the same company had supplied this cylinder as had been involved in an earlier hypoxic death in Hong Kong when a liquid gas container (LGC) had been mistitled with nitrogen instead of oxygen, there was considerable publicity and alarm generated by this case.
The company’s response has been to undertake a radical upgrading of its quality control measures, including the adoption of a new, tamper-proof seal complete with bar-code, and unless this seal is intact, hospitals have now been instructed not to accept delivery of cylinders. In the case of LGC’S, a certificate of purity which accompanies the vessel is valid for only 48 hours, and if expired, the LGC must be returned to the company for checking.
The most Rely explanation for the latest incident seems to be that an illicit gas-filling and merchandising business was being operated by a person or persons on the company staff, and one of the products of this black market found its way into the normal stockpile. Though an exhaustive inquiry into the previous bulk liquid oxygen accident failed to establish how the misfilling with nitrogen occurred, one plausible theory is that on that occasion the oxygen LGC was misfilled by an industrial user who had an urgent need for nitrogen, an empty oxygen LCG, and a friendly business associate who was prepared to decant some nitrogen into the LGC for him. Wry little of the contents were used before the ‘oxygen’ LGC was returned to the company in exchange for a new delivery. Back at the company yard, the “oxygen” LGC was noted to be nearly full (although mistakenly with nitrogen), and as was the practice at that time, was “topped up” and reissued, this time to a hospital.
It has since been pointed out by anaesthesiologists and others that medical and industrial gas supplies should be segregated, at least as far as gas containers, stockpiles, and distribution are concerned. A changeover of all medical compressed go containers (CGC’s) to pin-indexing is now being undertaken in Hong Kong, which will effectively segregate medical and industrial CGC’S. Since LGC’s cannot be effectively “sealed ” their problem has been handled differently, with each container being tested prior to leaving the company premises, and accompanied by the above mentioned certificate.
The clinical features of these cases will be reported more fully in the appropriate literature, but it is interesting to note that only one patient (case 2) presented the unconventional picture of hypercarbia (tachycardia and hypertension), and no doubt the diverse abnormalities manifested by these patients delayed appreciation of the true cause of the problem.
The de-bate on monitoring was also reactivated by these events. A committee of anesthesiologists, convened to advise the government of Hong Kong, pointed out that although capnography would have enabled this problem to be diagnosed earlier, the function of monitoring is not to substitute for quality control on the part of the manufacturer. The medical and hospital community have a right to expect purity of medicaments, including medical gases, from their suppliers. Fortunately, as far as Hong Kong is concerned, the steps which have now been taken by the company are reassuringly strict, and the possibility that episode such as those of 1989 and 1990 will be repeated, appears negligible
Professor Ross Holland, at the time of this writing, was Professor and Head, Department of Anesthesiology, Queen Mary Hospital, University of Hong Kong.