SummaryCritical incident reporting was introduced into the intensive care unit (ICU) as part of the development of a quality assurance programme within our department. Over a 3-year period 281 critical incidents were reported. Factors relating to causation, detection and prevention of critical incidents were sought. Detection of a critical incident in over 50% of cases resulted from direct observation of the patient while monitoring systems accounted for a further 27%. No physiological changes were observed in 54% of critical incidents. The most common incidents reported concerned airway management and invasive lines, tubes and drains. Human error was a factor in 55% of incidents while violations of standard practice contributed to 28%. Critical incident reporting was effective in revealing latent errors in our 'system' and clarifying the role of human error in the generation of incidents. It has proven to be a useful technique to highlight problems previously undetected in our quality assurance programme. Improvements in quality of care following implementation of preventative strategies await further assessment.

SummaryA 41-year-old woman presented with the clinical features of methaemoglobinaemia after drinking Chinese herbal medicine. A life threatening methaemoglobin level of 68% was measured. Both clinical and laboratory diagnostic difficulties were encountered. The pitfalls of pulse oximeter, blood gas analysis and co-oximeter interpretation during diagnosis and after methylene blue administration are discussed. Methaemoglobinaemia is an unusual and potentially fatal condition in which haemoglobin is oxidised to methaemoglobin and loses its ability to bind and transport oxygen. We present a case of accidental ingestion of sodium nitrite to illustrate the pitfalls of management. Case historyA 41-year-old woman with a history of hypertension presented to the Accident and Emergency Department with dizziness and a bluish skin colour. These symptoms occurred 5 min after taking some Chinese herbal medicine. Her treatment for hypertension included metoprolol (daily dose of 100 mg) and sustained release nifedipine (daily dose of 20 mg). The Chinese herbal medicine included 6 g Natrii Sulfa, which was prescribed by a herbalist for weight loss. On admission, she was disorientated as to time and place. Physical examination showed brownish blue cyanotic discoloration of the skin and tachycardia. The rest of the physical examination was unremarkable. Her blood pressure was 126 ⁄ 49 mmHg with a heart rate of 110 beats.min . The pulse oximeter showed an S p O 2 of 77-80% on 100% oxygen. An arterial blood sample was drawn which was chocolate brown and did not change in colour after agitation in air. The arterial blood gas analysis showed pH 7.398, P a CO 2 4.49 kPa, P a O 2 42 kPa and BE ) 4 mmol.l )1 . Chest X-ray was normal. With no identifiable cardiopulmonary pathology and normal alveolar-arterial oxygen gradient, methaemogloblinaemia was suspected. The patient was transferred to the intensive care unit (ICU). After ICU admission, the patient's conscious level improved. Arterial blood was sent for analysis by cooximetry and variable wavelength spectrophotometer; blood samples were also taken for full blood count, renal function and toxicology screening. These showed the methaemoglobin concentration was 68% and the haemoglobin concentration 12.5 g.dl )1 . The spectrophotometer found a small absorption peak at 628 nm, which disappeared after addition of potassium cynanide. The diagnosis of methaemoglobinaemia was confirmed. Methylene blue (100 mg) was given intravenously. The serial oxygen saturation changes in the pulse oximeter, arterial blood gases as well as the methaemoglobin concentrations are shown in Figs 1 and 2. The skin and arterial blood colour became pink 30 min after methylene blue injection. The S p O 2 increased from 88% to 98% and the P a O 2 25 kPa. The methaemoglobin concentration dropped to 10.8% after 30 min of methylene blue treatment. On the second day of admission, the patient remained well. The methaemoglobin concentration dropped to 0.6% and haemoglobin concentration to 11.4 g.dl )1

The r d e of an anaesthetic incident reporting programme in improving anaesthetic safety was studied. The programme had been running for 4 to 5 years in three large hospitals in Hong Kong and more than 1000 incidents have been reported. The number of reports being made and frequency of the various categories of incident reported, did not alter during the study period. Sixty nine percent of incidents were considered to be preventable. Human error contributed to 76% of incidents and violations of standardpractice to 30% of incidents. The programme was effective in its ability to detect latent errors in the anaesthesia system and when these were corrected, incidents did not recur. The frequency with which various contributing factors were cited did not decrease with time. With the exception of problems dealt with by specific protocol development, the study found no evidence that an increasing awareness of the problem of human error was effective in reducing this kind of problem.

We have compared the pharmacokinetics of a bolus induction dose of propofol 2 mg kg-1 in 10 Chinese women undergoing elective Caesarean section with those in six non-pregnant Chinese women having laparoscopic sterilization. Blood propofol concentrations were measured using high pressure liquid chromatography with fluorimetric detection. Pharmacokinetic data were analysed by a model independent method based on statistical moment theory. Data from the laparoscopy group also underwent compartmental analysis, which produced similar kinetic results. Non-compartmental analysis estimated that the women undergoing Caesarean section had a similar elimination half-life (mean 81.27 (SD 18.87) min) and apparent volume of distribution at steady state (2.66 (0.63) litre kg-1) as non-obstetric patients (99.45 (29.40) min and 3.36 (1.87) litre kg-1). Clearance was more rapid in the Caesarean section group (39.32 (8.07) ml min-1 kg-1 vs 29.40 (8.72) ml min-1 kg-1) (P less than 0.05). The increased total body clearance may result from blood loss and delivery of the fetus and placenta at operation, although an increase in extrahepatic clearance is also possible.