A new tracheal tube for difficult intubation

Effect of learning during an anaesthesiological multicentre trial

BACKGROUND

After the completion of a multicentre study, it was disputed whether becoming acquainted with a novel drug would affect dosing, and how many consecutive patients would be sufficient for this phenomenon.

METHODS

A post hoc analysis of the data on 408 patients from a multicentre study on propofol was performed to reveal a possible learning effect. For study purposes, the patients were given consecutive anaesthetic serial numbers per anaesthesiologist. Patients eligible for the study with serial numbers 3-8 (113) were included in the initial group, and numbers 12-17 (89) in the end group.

RESULTS

The patients in the end group opened their eyes (4.1 vs. 5.5 min, P < 0.05), gave their date of birth (4.5 vs. 6.3 min, P < 0.005) and walked sooner (27.1 vs. 49.8 min, P < 0.05) than the patients in the initial group. They received a higher dose of propofol at induction (2.37 vs. 2.26 mg kg-1, P < 0.05) and the last additional dose of propofol earlier (3.3 vs. 2.7 min, P < 0.05).

CONCLUSION

This study shows that the learning effect can influence the results in a multicentre study. Learning contamination may occur if a novel drug is dosed by clinical judgement, and if the allocation of patients into groups is markedly uneven during the different stages of the study.

Small tubes revisited

We measured the peak inflation and end expiratory pressure at the proximal and distal ends of two sizes of tracheal tube in men and women receiving positive pressure ventilation. There was a statistically significant increase in proximal inflation pressure when the smaller size of tube (6.5 mm for men, 6.0 mm for women) was used. There was no increase in distal inflation or end expiratory pressures. Clinically satisfactory positive pressure ventilation was obtained when 6.0 and 6.5 mm tracheal tubes were used. The advantages and disadvantages of using small sizes of tracheal tube are discussed.