Transthoracic impedance changes as a tool to detect malpositioned tracheal tubes

Abstract

Background: Undetected malpositioned or dislodged ventilation tubes during cardiac arrest have fatal consequences, and no single method can detect the tube position reliably during such low-flow states. We wanted to test the ability of impedance changes as measured across the chest via the standard defibrillation pads to distinguish between oesophageal and tracheal ventilations in non-circulated patients. Materials and methods: After the end of futile resuscitation transthoracic impedance was measured with a prototype defibrillator, and ventilation variables were collected with a spirometer-capnography unit during tracheal ventilations and after repositioning of the tube; during oesophageal ventilations for paired comparisons. Results: We registered 123 oesophageal and 178 tracheal ventilations in nine patients. Transthoracic impedance changes associated with ventilations were always larger during tracheal than oesophageal ventilations (mean difference 1.3 Ω (95% CI 1.0, 1.5), P < 0.001), and all such changes above 1.2 Ω were associated with tracheal ventilations, while changes below 0.4 Ω always were associated with oesophageal ventilations. By subtracting 0.5 Ω from the individual mean transthoracic change associated with tracheal ventilations, tube position was predicted with sensitivity 0.99 and specificity 0.97. Conclusion: Transthoracic impedance changes may be used to detect malpositioned and dislodged tubes also during situations without spontaneous circulation. Our predictive values must be retested in another population. © 2007 Elsevier Ireland Ltd. All rights reserved.