Prediction of tracheostomy tube size for paediatric long-term ventilation: an audit of children with spinal cord injury

Background. There are no published data to predict tracheostomy tube size as growth proceeds in children requiring long-term ventilation. Methods. A retrospective audit was undertaken of children having long-term ventilation, managed from the Southport spinal injuries unit. The dates of step-up in size of tracheostomy tube were noted together with the tube inside and outside diameters (ID and OD) and the lateral tracheal diameter. The data were aggregated for each increment in tube size to calculate the Pearson correlation coefficients for age and weight of the children. Linear regression was then used to generate predictive equations based on age and weight. Results. Out of 12 children, data from seven boys and two girls, with a mean age of 5.9 (range 1.5-13.75) yr, were obtained. Average length of follow-up was 7 yr, with an average of 3.5 tube changes per patient equating to a larger tube every 2 yr. The inside and outside tracheal tube diameters, as well as the lateral tracheal diameter, correlated significantly with age and weight (P < 0.01). The appropriate tracheostomy tube internal diameter is conveniently expressed by the formula: ID (mm)=(age yr)/3+3.5 Conclusions. The step-up in size of the tracheostomy tube as growth proceeds should be undertaken as a planned procedure at least every 2 yr to avoid nocturnal desaturation. Age appears to be a convenient and reliable predictor.