Patient examinations using electrical impedance tomography--sources of interference in the intensive care unit.

Electrical impedance tomography (EIT) is expected to become a valuable tool for monitoring mechanically ventilated patients due to its ability to continuously assess regional lung ventilation and aeration. Several sources of interference with EIT examinations exist in intensive care units (ICU). Our objectives are to demonstrate how some medical nursing and monitoring devices interfere with EIT measurements and modify the EIT scans and waveforms, which approaches can be applied to minimize these effects and how possible misinterpretation can be avoided. We present four cases of EIT examinations of adult ICU patients. Two of the patients were subjected to pulsation therapy using a pulsating air suspension mattress while being ventilated by high-frequency oscillatory or conventional pressure-controlled ventilation, respectively. The EIT signal modulation synchronous with the occurrence of the pulsating wave was 2.3 times larger than the periodic modulation synchronous with heart rate and high-frequency oscillations. During conventional ventilation, the pulsating mattress induced an EIT signal fluctuation with a magnitude corresponding to about 20% of the patient's tidal volume. In the third patient, interference with EIT examination was caused by continuous cardiac output monitoring. The last patient's examination was disturbed by impedance pneumography when excitation currents of similar frequency to EIT were used. In all subjects, the generation of functional EIT scans was compromised and interpretation of regional ventilation impossible. Discontinuation of pulsation therapy and of continuous cardiac output and impedance respiration monitoring immediately improved the EIT signal and scan quality. Offline processing of the disturbed data using frequency filtering enabled partial retrieval of relevant information. We conclude that thoracic EIT examinations in the ICU require cautious interpretation because of possible mechanical and electromagnetic interference.

A new technique for bedside placement of enteral feeding tubes: a prospective cohort study.

INTRODUCTION: To accomplish early enteral feeding in the critically ill patient a new transnasal endoscopic approach to the placement of postpyloric feeding tubes by intensive care physicians was evaluated. METHODS: This was a prospective cohort study in 27 critically ill patients subjected to transnasal endoscopy and intubation of the pylorus. Attending intensive care physicians were trained in the handling of the new endoscope for transnasal gastroenteroscopy for two days. A jejunal feeding tube was advanced via the instrument channel and the correct position assessed by contrast radiography. The primary outcome measure was successful postpyloric placement of the tube. Secondary outcome measures were time needed for the placement, complications such as bleeding and formation of loops, and the score of the placement difficulty graded from 1 (easy) to 4 (difficult). Data are given as mean values and standard deviation. RESULTS: Out of 34 attempted jejunal tube placements, 28 tubes (82%) were placed correctly in the jejunum. The duration of the procedure was 28 ± 12 minutes. The difficulty of the tube placement was judged as follows: grade 1: 17 patients, grade 2: 8 patients, grade 3: 7 patients, grade 4: 2 patients. In three cases, the tube position was incorrect, and in another three cases, the procedure had to be aborted. In one patient bleeding occurred that required no further treatment. CONCLUSIONS: Fast and reliable transnasal insertion of postpyloric feeding tubes can be accomplished by trained intensive care physicians at the bedside using the presented procedure. This new technique may facilitate early initiation of enteral feeding in intensive care patients.

Body and head position effects on regional lung ventilation in infants: An electrical impedance tomography study.

OBJECTIVE: To determine the effects of body and head positions on the spatial distribution of ventilation in nonintubated spontaneously breathing and mechanically ventilated infants using electrical impedance tomography (EIT). DESIGN AND SETTING: Prospective study in a neonatal intensive care unit. PATIENTS: Ten spontaneously breathing (gestational age 38 weeks, postnatal age 13 days) and ten mechanically ventilated infants (gestational age 35 weeks, postnatal age 58 days). INTERVENTIONS: Supine and prone postures with different head positions (midline and rotated to the left and right side). MEASUREMENTS AND RESULTS: The distribution of ventilation in the chest cross-section was repeatedly determined from EIT data in each body/head position studied. During spontaneous breathing the tidal volumes in the left lung region were reduced in the supine posture with the head turned to the left as well as in the prone posture with the head rotated to either side when compared with the supine posture with the head in the midline position. During mechanical ventilation the tidal volumes in the left lung region were unaffected by the body and head position except for the prone posture combined with the leftward head rotation which reduced them. In both types of ventilation the tidal volumes in the right lung region were unaffected by the change in body/head position. CONCLUSION: The results indicate that the spatial distribution of ventilation is influenced by the body and head position in spontaneously breathing infants. Prone posture with the leftward head rotation has the most prominent effect which is detectable even during mechanical ventilation.

Acoustic phenomena and valve dysfunction in cardiac prostheses: data acquisition and collection via the Internet.

BACKGROUND AND AIM OF THE STUDY: The study aim was to investigate whether: (i) by detection of changing acoustic sound phenomena, minimal changes in prosthetic valve function may be detected earlier than with echocardiography, invasive diagnosis or clinically; (ii) patients can record and pass on signals with a high level of reproducibility from any location via the Internet; and (iii) clinical data evaluation permits conclusions to be drawn on changes in the functional state of a prosthetic replacement valve. METHODS: Simulation studies were carried out using a mock circulation device. Aortic valve replacement (AVR) using extracorporeal circulation was performed in pigs, valve function was artificially disturbed, and valve sounds were recorded. Patients were equipped with briefcase-like devices to record their valve sounds after AVR and to transfer them via the Internet. RESULTS: Simulation studies produced a typical sound spectrum for each tested valve that remained constant under variable conditions. Experiments in animals proved that minimal changes in prosthetic valve function led to a significant change in the sound phenomena. The degree of sensitivity was significantly greater than that in echocardiographic control experiments. All patients in the clinical study regularly recorded and passed on their signals. Surveys revealed high acceptance and easy handling of the compiled devices. Valve dysfunctions were not detected. CONCLUSION: On-line registration of acoustic sound phenomena and ECG seems suited to detect minimal changes in prosthetic function. In particular, the registration of flow, acoustics and ECG envisaged at the next level opens up diverse potential applications for Internet-based, remote monitoring of patients following cardiac surgery or cardiologic treatment.