Transthoracic impedance changes as a tool to detect malpositioned tracheal tubes.
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.


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 ohms (95% CI 1.0, 1.5), P<0.001), and all such changes above 1.2 ohms were associated with tracheal ventilations, while changes below 0.4 ohms always were associated with oesophageal ventilations. By subtracting 0.5 ohms from the individual mean transthoracic change associated with tracheal ventilations, tube position was predicted with sensitivity 0.99 and specificity 0.97.


CONCLUSIONS
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.
Kramer-Johansen
Jo
J
Institute for Experimental Medical Research, Ullevål University Hospital, N-0407 Oslo, Norway. jo.kramer-johansen@medisin.uio.no
Eilevstjønn
Joar
J
Olasveengen
Theresa Mariero
TM
Tomlinson
Ann-Elin
AE
Dorph
Elizabeth
E
Steen
Petter Andreas
PA
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019540:Area Under Curve; D002307:Cardiography, Impedance; D016887:Cardiopulmonary Resuscitation; D047548:Defibrillators; D004947:Esophagus; D005240:Feasibility Studies; D005260:Female; D006323:Heart Arrest / Q000628:therapy*; D006801:Humans; D007442:Intubation, Intratracheal / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012372:ROC Curve; D012680:Sensitivity and Specificity