PHYSIOLOGIC MONITORING FROM THE TRACHEA

Monitoring body-core temperature from the trachea: comparison between pulmonary artery, tympanic, esophageal, and rectal temperatures

INTRODUCTION

We designed an endotracheal tube (ETT) for acquiring body-core temperature from the trachea. This ETT had two temperature sensors, one attached to the inside surface of the cuff, the other mounted on the ETT shaft underneath the cuff. The ETT was evaluated in vitro and in dogs to determine: 1) optimal position of temperature sensors and 2) the responsiveness, accuracy, and resistance to ventilatory artifacts.

METHODS

In vitro. An artificial trachea assessed the response-time and accuracy of ETT temperature sensors to abrupt temperature changes and ventilatory flow-rates. In vivo. Body temperature in 5 dogs was lowered to approximately 26 degrees C then elevated toward 39 degrees C using a heat exchanger during carotid-jugular bypass. ETT temperature measurements were compared simultaneously with those from the artificial trachea (in vitro) or from the pulmonary artery, tympanic cavity, esophagus, and rectum of dogs using dry and humidified gas.

RESULTS

Cuff temperature sensor responded quickly and accurately to temperature changes and was less prone than the tube sensor to ventilatory and humidity artifacts. During carotid-jugular bypass, in vivo tube and cuff mean temperatures averaged 1.4 degrees C and 0.36 degree C lower, respectively, than pulmonary artery temperatures. There were no statistical differences (P > 0.05) between cuff temperatures and those measured from the pulmonary artery, tympanic cavity, esophagus, and rectum. Heating and humidifying the inspiratory gas of dogs with a water-bath humidifer or heat moisture exchanger (HME) had minimal effects on the cuff temperature sensor. An in-line HME increased in vivo tube temperature from baseline values by 1.13 +/- 0.80 degree C, while cuff temperature increased by 0.21 +/- 0.24 degree C.

CONCLUSION

The cuff of the ETT is a reliable site for measuring body-core temperature in intubated patients.

Monitoring normal and aberrant electrocardiographic activity from an endotracheal tube: comparison of the surface, esophageal, and tracheal electrocardiograms

INTRODUCTION

We designed an endotracheal (ET) tube with orthogonally spaced ECG cuff electrodes. This ET tube was evaluated in dogs and sheep to determine (1) whether ECGs recorded from our tube were sufficient to make accurate clinical decisions concerning heart rate and rhythm; and (2) whether metallic cuff electrodes in direct contact with the trachea could induce mucosal burn injury during episodes of defibrillation.

METHODS

Using experimental animals, we obtained ECGs from their tracheae and compared our findings with ECGs obtained from surface and esophageal electrodes. The electrical activity of the heart was modified by increasing the depth of anesthesia, occluding the left coronary artery, and administering beta-adrenergic drugs. Before the dogs were euthanized, they were subjected to episodes of transthoracic and intrathoracic defibrillation at energy levels of 200 to 400 J. A postmortem pathological examination of the trachea was performed to determine the incidence of mucosal burn injury.

RESULTS

Tracheal electrocardiography provided valid information on heart-rate monitoring and certain morphology profiles. The R-R, PR, QRS, and QT intervals measured from the trachea had a correlation of 1.0, 0.96, 0.83, and 0.98, respectively, when compared with the same intervals obtained from surface electrodes. Two tracheae subjected to intrathoracic defibrillation at > 300 J revealed evidence of minor burn injury. Some localized epithelium loss was displayed in all tracheae; we attributed this to tracheal intubation.

CONCLUSION

Tracheal electrocardiography may be useful in trauma patients who require intubation where injury precludes placement of chest ECG electrodes.