T. G. Short

Critical incident reporting in the intensive care unit

Critical 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.

Closed loop control of anaesthesia: an assessment of the bispectral index as the target of control

We investigated the performance of a closed‐loop system for administration of general anaesthesia, using the bispectral index as a target for control. One hundred patients undergoing gynaecological or general surgery were studied. In 60 patients, anaesthesia was maintained by intravenous infusion of a propofol/alfentanil mixture. In 40, an isoflurane/nitrous oxide based technique was used. For each technique, patients were randomly allocated to receive either closed‐loop or manually controlled administration of the relevant agents (propofol/alfentanil or isoflurane), with an intra‐operative target bispectral index of 50 in all cases. Closed‐loop and manually controlled administration of anaesthesia resulted in similar intra‐operative conditions and initial recovery characteristics. During maintenance of anaesthesia, cardiovascular and electro‐encephalographic variables did not differ between closed‐loop and manual control groups and deviation of bispectral index from the target value was similar. Intra‐operative concentrations of propofol, alfentanil and isoflurane were within normal clinical ranges. Episodes of light anaesthesia were more common in the closed‐loop group for patients receiving propofol/alfentanil anaesthesia and in the manual group for patients receiving isoflurane/nitrous oxide anaesthesia. Convenience aside, the closed‐loop system showed no clinical advantage over conventional, manually adjusted techniques of anaesthetic administration.

Critical incident reporting in an anaesthetic department quality assurance programme

The critical incident technique was introduced as an additional form of quality assurance to an anaesthetic department of a major Hong Kong teaching hospital. In one year, 125 critical incidents were reported from over 16000 anaesthetics. The most common incidents reported concerned the airway, breathing systems, and drug administration, with inadequate checking of equipment a frequent associated factor. Human error was a factor in 80% of incidents. Critical incidents were reported for the time during which the patient was under the anaesthetists care. The majority occurred at induction or during anaesthesia, and were reported for all surgical subspecialties. Half of the incidents were detected by the anaesthetist and one third by monitoring equipment. Although there were improvements in anaesthetic care as a consequence of increased vigilance, critical incidents still occurred. Critical incident reporting highlighted problems not otherwise covered by case and peer reviews, and complemented our quality assurance programme.

Improvements in anaesthetic care resulting from a critical incident reporting programme

The rôle 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 standard practice 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.

Abdominal surgery alters the calibration of bioimpedance cardiac output measurement

The performance of impedance cardiography (TEBco), using the BoMed NCCOM3-R7S, and thermodilution (TDco) were compared in eight patients during major abdominal surgery. An opioid, volatile and relaxant anaesthetic technique was employed. This was supplemented with an epidural in five cases. Sets of three cardiac output readings, for both methods, were made at 10–20 min intervals throughout surgery. Data were compared using the Bland and Altman method, regression analysis and a nested model to measure variance components at different stages of surgery. Data from 157 sets of readings are presented. Agreement between the two devices was poor, with a ratio of TDco/TEBco of 115% and limits of agreement of 51–193%. The regression line was TDco=(0.98)×TEBco-0.95 with r=0.60. A more detailed analysis, using nested data, showed good repeatability with coefficients of variation of 5.4% for TDco and 4.8% for TEBco. During surgery shifts in the bias between the two devices occurred, which were related to changes in surgical conditions. Between shifts both devices showed good repeatability over time. Variance components were 0.27 within nested data and 0.082 between bias shifts, with a significantly greater overall component of 1.2 (ANOVA; P=0.0001). Shifts could be explained by deficiencies in the algorithm used to calculate TEBco. Current TEBco technology is too inaccurate for intra-operative use. However, under stable operating conditions TEBco and TDco showed good repeatability.

The Application of a Modified Proportional-Derivative Control Algorithm to Arterial Pressure Alarms in Anesthesiology

Objective. We have developed an arterial pressure alarm system based on a modified proportional-derivative (PD) controller algorithm, and prospectively tested its ability to predict significant hypotensive episodes, defined as systolic arterial pressure <80 mmHg, in comparison to conventional limit alarms. Methods. The alarm algorithm was tuned to detect hypotension using selected invasive arterial pressure traces taken from ten patients who had large intra-operative arterial pressure changes. The algorithms performance was then tested prospectively in comparison to conventional limit alarms and median filtered limit alarms, set at 85 mmHg and 90 mmHg, for its ability to predict hypotensive episodes in a further 100 patients who required invasive arterial pressure monitoring. Results. For the PD alarm algorithm, onset times for significant hypotensive episodes were between those of limit alarms set at 85 mmHg and 90 mmHg. Offset times were similar to the 85 mmHg limit alarms. The false positive rate was 34% compared with 45–64% for the other alarms (p < 0.01). Using our definitions, there was one false negative in the PD group, being a 15 second drop in observed arterial pressure, when a non invasive blood pressure cuff was inflated above the arterial line. Conclusions. An arterial pressure alarm system design based on a closed loop control algorithm offered improved performance over conventional limit alarms and in addition provided a graded output of severity of the hypotension.

An adaptation of the objective structured clinical examination to a final year medical student course in anaesthesia and intensive care.

The Department of Anaesthesia and Intensive Care at the Chinese University of Hong Kong provides a 4 week course in our specialty for final year medical students. Our curriculum covers basic concepts in anaesthesia and intensive care, management of common medical emergencies and the safe performance of basic practical skills. For the last 4 years we have used an adaptation of the Objective Structured Clinical Examination to assess learning. Question stations included the use of manikins to assess practical skills, such as cardiopulmonary resuscitation and airway management, identification and description of the use of equipment and interpretation of clinical scenarios and investigations. We believe that our adaptation of the Objective Structural Clinical Examination is better than traditional methods of examination and it has allowed us to identify deficiencies in our teaching methods. The Objective Structured Clinical Examination has been well received by our students and is perceived by them to be a fair reflection of their level of knowledge and skill attainment during the course.

Intravenous anaesthesia for children

Intravenous anaesthesia encompasses intravenous induction and intravenous maintenance of anaesthesia. Children dislike needles, and therefore there is a tendency to first consider inhalational methods for induction of anaesthesia. However intravenous anaesthesia is indicated when a rapid sequence induction is needed and many paediatric anaesthetists find intravenous induction rapid and safe when an intravenous catheter is in place or can be inserted without undue trauma. Also some children do not tolerate smelly gaseous induction! Until recently, irrespective of induction technique, anaesthesia was maintained by inhalational agents. Since the recent introduction of intravenous agents with suitable pharmacokinetic profiles there is increased interest in using intravenous agents to maintain anaesthesia. This trend is enhanced by the development of computer controlled infusion pumps which can deliver the drug according to a pharmacokinetic model. This article reviews the impact of developmental physiology on intravenous drug distribution, metabolism and elimination in children and presents current practice and some recent advances in intravenous anaesthesia for paediatric practice.