Electrical impedance tomography (EIT) is a non-invasive imaging technology that has been extensively studied for monitoring lung function of neonatal and adult subjects, especially in neonatal intensive care unit (NICU) and intensive care unit (ICU) environments. The sources of the total impedance in these applications include internal organs, near-boundary tissues, electrode-skin impedance, electrodes and conducting wires. This total impedance must be considered for system design and setting voltage gain since it will contribute to the measured voltage. To adapt a single instrument for use on infants and adults, we studied the difference between the impedance near the skin in both classes of patients. We used a simultaneous multi-source EIT (SMS-EIT) system to make impedance measurements. Characteristic resistance was calculated for two different current patterns: one that is more sensitive to boundary region impedance and another that is more sensitive to interior changes. We present ratios of these resistances to assess the relative contribution of near-skin effects to the overall impedance. Twenty adult ICU subjects (10 male, 10 female, age: 49.05  ±  16.32 years (mean  ±  standard deviation)) and 45 neonates (23 male, 22 female, gestational age: 37.67  ±  2.11 weeks, postnatal age, 2.56  ±  2.67 d) were studied at Columbia University Medical Center. Impedance measurements at 10 kHz were collected for approximately one hour from each subject. The characteristic resistance ratio for each subject was computed and analyzed. The result shows the impedance at or near the skin of newborns is significantly higher than in adult subjects.

AbstractObjective:To evaluate the relationship betweenStaphylococcus aureusnasal and tracheal colonization and infection in medical intensive care unit (MICU) patients. The primary outcome was the incidence ofS. aureusinfection in colonized versus non-colonized patients.Design:Prospective, observational cohort study. Patients admitted to the MICU during the study period were screened forS. aureusnasal and tracheal colonization by culture and a PCR assay twice weekly. Demographic, clinical, and microbiologic data were collected in the MICU and for 30 days after discharge. PFGE and antibiotic susceptibility testing were performed on allS. aureusnasal, tracheal, and clinical isolates.Results:Twenty-three percent of patients (47 of 208) were nasally colonized withS. aureus. Twenty-four percent of these patients developedS. aureusinfections versus 2% of noncolonized patients (P< .01). Nine of 11 patients with both nasal colonization and infection were infected by their colonizing strain. Two of 47 nasally colonized patients developed an infection with a different strain ofS. aureus. Fifty-three percent of intubated patients with nasal colonization (10 of 19) had tracheal colonization withS. aureusas opposed to 4.9% of intubated, non-colonized patients (3 of 61) (P< .01). Parenteral antibiotics were ineffective at clearing nasal colonization. PCR detectedS. aureuscolonization (nasal and tracheal) within 6.5 hours with a sensitivity of 83% and a specificity of 99%.Conclusions:The incidence ofS. aureusinfection was significantly elevated in nasally colonized MICU patients. Techniques to rapidly detect colonization in this population may make targeted topical prevention strategies feasible. (Infect Control Hosp Epidemiol 2005;26:622-628)