Abstract 2621: Transthoracic Impedance Changes may be used to recognize Esophageal Intubation during Cardiac Arrest
Objectives: Undetected mal-positioned or dislodged ventilation tubes during cardiac arrest have fatal consequences. No single method can reliably detect tube position and possibilities for continuous monitoring are restricted during such low-flow states. Transthoracic impedance can be measured via the standard defibrillation pads and changes in transthoracic impedance are related to changes in lung volume and chest configuration. In a prospective trial we tested the ability of such changes to distinguish between esophageal and tracheal ventilations in non-circulated patients.
Methods: After end of futile resuscitation in victims of out-of-hospital cardiac arrest transthoracic impedance was measured with a prototype defibrillator based on Philips Heartstart 4000 by use of a sinusoidal excitation current of 3 mA and 32 kHz across a lead II position of the pads. Ventilation variables were collected with a spirometer-capnography unit (CO2SMO® Plus!, Novametrix) during tracheal ventilations and after repositioning of the tube; during esophageal ventilations for paired comparisons.
Results: We registered 123 esophageal and 178 tracheal ventilations in nine patients. In each patient, transthoracic impedance changes associated with ventilations were always larger during tracheal than esophageal ventilations (mean difference 1.3 Ohm (95% CI 1.0, 1.5), P<0.001), and all such changes above 1.2 Ohm were associated with tracheal ventilations, while all changes below 0.4 Ohm were associated with esophageal ventilations. Individual thresholds obtained by subtracting 0.5 from the individual’s mean transthoracic change associated with tracheal ventilations, predicted esophageal tube position with sensitivity 0.99 and specificity 0.97.
Conclusion: Transthoracic impedance changes may be used to detect mal-positioned and dislodged tubes also during situations without spontaneous circulation. Our predictive values must be retested in another population.