Good short-term agreement between measured and calculated tracheal pressure

Background. Tracheal pressure (P-tr) is required to measure the resistance of the tracheal tube and the breathing circuit. P-tr can either be measured with a catheter or, alternatively, calculated from the pressure-flow data available from the ventilator. Methods. Calculated P-tr was compared with measured P-tr during controlled ventilation and assisted spontaneous breathing in 18 healthy and surfactant-depleted piglets. Their lungs were ventilated using different flow patterns, tidal volumes (V-T) and levels of positive end-expiratory pressure. Results. In terms of the root mean square error (RMS), indicating the average deviation of calculated from measured P-tr, the difference between calculated and measured P-tr was 0.6 cm H2O (95% CI 0.58-0.65) for volume-controlled ventilation; 0.73 cm H2O (0.72-0.75) for pressure support ventilation; and 0.78 cm H2O (0.75-0.80) for bi-level positive airway pressure ventilation. Conclusion. The good agreement between calculated and measured P-tr during varying conditions, suggests that calculating P-tr could help setting the ventilator and choosing the appropriate level of support.