The suitability of EIT to estimate EELV in a clinical trial compared to oxygen wash-in/wash-out technique.

INTRODUCTION: Open endotracheal suctioning procedure (OSP) and recruitment manoeuvre (RM) are known to induce severe alterations of end-expiratory lung volume (EELV). We hypothesised that EIT lung volumes lack clinical validity. We studied the suitability of EIT to estimate EELV compared to oxygen wash-in/wash-out technique. METHODS: Fifty-four postoperative cardiac surgery patients were enrolled and received standardized ventilation and OSP. Patients were randomized into two groups receiving either RM after suctioning (group RM) or no RM (group NRM). Measurements were conducted at the following time points: Baseline (T1), after suctioning (T2), after RM or NRM (T3), and 15 and 30 min after T3 (T4 and T5). We measured EELV using the oxygen wash-in/wash-out technique (EELVO2) and computed EELV from EIT (EELVEIT) by the following formula: EELVEITTx,y…=EELVO2+ΔEELI×VT/ΔZ. EELVEIT values were compared with EELVO2 using Bland-Altman analysis and Pearson correlation. RESULTS: Limits of agreement ranged from -0.83 to 1.31 l. Pearson correlation revealed significant results. There was no significant impact of RM or NRM on EELVO2-EELVEIT relationship (p=0.21; p=0.23). DISCUSSION: During typical routine respiratory manoeuvres like endotracheal suctioning or alveolar recruitment, EELV cannot be estimated by EIT with reasonable accuracy.

Ultrasound perfusion imaging: determination of thresholds for the identification of critically disturbed perfusion in acute ischemic stroke--a pilot study.

Ultrasound harmonic imaging of perfusion after ultrasound contrast agent (UCA) bolus injection (BHI) can detect cerebral perfusion deficits. In a pilot study, we evaluated the ability of time-intensity curve (TIC) measurements to differentiate between normal and hypoperfused brain areas in acute ischemic stroke. Ten patients with symptoms of acute middle cerebral artery infarction were investigated (SONOS 5500, Harmonic Imaging 1.6/3.8 MHz, diencephalic plane, 10 cm investigation depth, SonoVue 2.4 mL bolus). Peak signal increase (PSI), time-to-peak intensity (TPI) and area under the curve (AUC) were calculated for 60 regions-of-interest (ROIs) in each patient. Reference methods: Perfusion- and diffusion-weighted MRI (PWI/DWI) within 4 h before/after BHI (PWI threshold: 4 s). Receiver operating characteristics (ROC) analysis defined cut-off values for each TIC variable to distinguish between normal and affected brain areas as defined by PWI/DWI. In five patients, PWI showed a perfusion delay >4 s; seven patients had a DWI lesion. In three patients, both PWI and DWI findings showed pathology; one patient had a normal MRI of the insonation plane. Cut-off values for PWI delay: PSI: 5.53% (sensitivity .98, specificity .89); TPI: 4.04 s (sensitivity .74, specificity .69) and AUC: .63 (sensitivity .94, specificity .58). Referred to the mean value in unaffected brain areas the relative thresholds were 17.6%, 109.5% and 16.1%, respectively. Regarding DWI, only for PSI, a significant cut-off value was defined: 10.86%, sensitivity .84, specificity .60 (34.6% of mean). In conclusion, these thresholds distinguish between normal and affected brain areas in acute ischemic stroke.