RESUMO
OBJECTIVE: To validate a simple method avoiding discard volumes in pediatric patients with indwelling arterial and venous lines. DESIGN: Zero-discarding was achieved by passive extracorporeal arteriovenous backflow via standard single pressure transducer equipment. We tested backflow distances (10, 20 and 30 cm beyond the sampling port), corresponding to withdrawal volumes of 0.6 ml, 0.8 ml and 1.0 ml, respectively, in comparison to conventional sampling with discard of 0.6 ml. With the backflow technique, the "withdrawal volume" was flushed back to the patient after sampling. We enrolled 120 patients who were allocated to either of the following paired sampling procedures: 10 cm versus conventional, 20 cm versus conventional, 30 cm versus conventional and two paired conventional samples. The order of the sampling was randomly allocated. Bias and precision were determined using Bland-Altman diagrams and algorithms. RESULTS: No appreciable difference was found for blood gases, hemoglobin, potassium and calcium between the backflow technique and conventional sampling. Sodium results and blood glucose showed a bias towards higher values with the backflow technique (mean difference, sodium, 0.9 mmol/l; glucose, mean difference 0.5 mmol/l, standard deviation 0.44 mmol/l). CONCLUSIONS: The backflow technique provides reliable results for blood gases and electrolytes. However, in patients at risk of hypoglycemia, the backflow method should not be used to monitor blood glucose levels.