What hinders pulmonary gas exchange and changes distribution of ventilation in immobilized white rhinoceroses (Ceratotherium simum) in lateral recumbency?

Electrical impedance tomography measurements of regional ventilation and perfusion applied to etorphine-immobilized white rhinoceroses in lateral recumbency revealed a pronounced disproportional shift of the measured ventilation and perfusion toward the nondependent lung. The dependent lung was minimally ventilated and perfused, but still aerated. Perfusion was found primarily around the hilum of the nondependent lung. These shifts can explain the gas exchange impairments found in this study. Breath holding can redistribute ventilation.

Regional ventilation characteristics during non-invasive respiratory support in preterm infants

ABSTRACTObjectiveTo determine the regional ventilation characteristics during non-invasive ventilation in stable preterm infants. The secondary aims were to explore the relationship between indicators of ventilation homogeneity and other clinical measures of respiratory status.DesignProspective observational study.SettingTwo tertiary neonatal intensive care units.PatientsForty stable preterm infants born <30 weeks gestation receiving either continuous positive applied pressure (n=32) or nasal high-flow cannualae (n=8) at least 24 hours after extubation at time of study.InterventionsContinuous electrical impedance tomography imaging of regional ventilation during 60-minutes of quiet breathing on clinician-determined non-invasive settings.Main outcome measuresGravity-dependent and right-left centre of ventilation (CoV), percentage of whole lung tidal volume by lung region, and percentage of lung unventilated were determined for 120 artefact-free breaths/infant (4770 breaths included). Oxygen saturation, heart and respiratory rates were also measured.ResultsVentilation was greater in the right lung (mean (SD) 69.1 (14.9)%) total tidal volume and the gravity-nondependent lung; ideal-actual CoV 1.4 (4.5)%. The central third of the lung received the most tidal volume, followed by the non-dependent and dependent regions (p<0.0001 repeated measure ANOVA). Ventilation inhomogeneity was associated with worse SpO2/FiO2, (p=0.031, r2 0.12; linear regression). In those infants that later developed bronchopulmonary dysplasia (n=25) SpO2/FiO2 was worse and non-dependent ventilation inhomogeneity greater than in those that did not (both p<0.05; t test Welch correction).ConclusionsThere is high breath-by-breath variability in regional ventilation patterns during NIV in preterm infants. Ventilation favoured the gravity-nondependent lung, with ventilation inhomogeneity associated with worse oxygenation.

Lung inhomogeneities, inflation and [18F]2-fluoro-2-deoxy-D-glucose uptake rate in acute respiratory distress syndrome

The aim of the study was to determine the size and location of homogeneous inflamed/noninflamed and inhomogeneous inflamed/noninflamed lung compartments and their association with acute respiratory distress syndrome (ARDS) severity.In total, 20 ARDS patients underwent 5 and 45 cmH2O computed tomography (CT) scans to measure lung recruitability. [18F]2-fluoro-2-deoxy-d-glucose ([18F]FDG) uptake and lung inhomogeneities were quantified with a positron emission tomography-CT scan at 10 cmH2O. We defined four compartments with normal/abnormal [18F]FDG uptake and lung homogeneity.The homogeneous compartment with normal [18F]FDG uptake was primarily composed of well-inflated tissue (80±16%), double-sized in nondependent lung (32±27% versus 16±17%, p<0.0001) and decreased in size from mild, moderate to severe ARDS (33±14%, 26±20% and 5±9% of the total lung volume, respectively, p=0.05). The homogeneous compartment with high [18F]FDG uptake was similarly distributed between the dependent and nondependent lung. The inhomogeneous compartment with normal [18F]FDG uptake represented 4% of the lung volume. The inhomogeneous compartment with high [18F]FDG uptake was preferentially located in the dependent lung (21±10% versus 12±10%, p<0.0001), mostly at the open/closed interfaces and related to recruitability (r2=0.53, p<0.001).The homogeneous lung compartment with normal inflation and [18F]FDG uptake decreases with ARDS severity, while the inhomogeneous poorly/not inflated compartment increases. Most of the lung inhomogeneities are inflamed. A minor fraction of healthy tissue remains in severe ARDS.

“High Frequency/Small Tidal Volume Differential Lung Ventilation”: A Technique of Ventilating the Nondependent Lung of One Lung Ventilation for Robotically Assisted Thoracic Surgery

With the introduction of new techniques and advances in the thoracic surgery fields, challenges to the anesthesia techniques had became increasingly exponential. One of the great improvements that took place in the thoracic surgical field was the use of the robotically assisted thoracic surgical procedure and minimally invasive endoscopic thoracic surgery. One lung ventilation technique represents the core anesthetic management for the success of those surgical procedures. Even with the use of effective one lung ventilation, the patient hemodynamics and respiratory parameters could be deranged and could not be tolerating the procedure that could compromise the end result of surgery. We are presenting our experience in managing one patient who suffered persistent hypoxia and hemodynamic instability with one lung ventilation for robotically assisted thymectomy procedure and how it was managed till the completion of the surgery successfully.

The effect of supine exercise on the distribution of regional pulmonary blood flow measured using proton MRI

The Zone model of pulmonary perfusion predicts that exercise reduces perfusion heterogeneity because increased vascular pressure redistributes flow to gravitationally nondependent lung, and causes dilation and recruitment of blood vessels. However, during exercise in animals, perfusion heterogeneity as measured by the relative dispersion (RD, SD/mean) is not significantly decreased. We evaluated the effect of exercise on pulmonary perfusion in six healthy supine humans using magnetic resonance imaging (MRI). Data were acquired at rest, while exercising (∼27% of maximal oxygen consumption) using a MRI-compatible ergometer, and in recovery. Images were acquired in most of the right lung in the sagittal plane at functional residual capacity, using a 1.5-T MR scanner equipped with a torso coil. Perfusion was measured using arterial spin labeling (ASL-FAIRER) and regional proton density using a fast multiecho gradient-echo sequence. Perfusion images were corrected for coil-based signal heterogeneity, large conduit vessels removed and quantified (in ml·min−1·ml−1) (perfusion), and also normalized for density and quantified (in ml·min−1·g−1) (density-normalized perfusion, DNP) accounting for tissue redistribution. DNP increased during exercise (11.1 ± 3.5 rest, 18.8 ± 2.3 exercise, 13.2 ± 2.2 recovery, ml·min−1·g−1, P < 0.0001), and the increase was largest in nondependent lung (110 ± 61% increase in nondependent, 63 ± 35% in mid, 70 ± 33% in dependent, P < 0.005). The RD of perfusion decreased with exercise (0.93 ± 0.21 rest, 0.73 ± 0.13 exercise, 0.94 ± 0.18 recovery, P < 0.005). The RD of DNP showed a similar trend (0.82 ± 0.14 rest, 0.75 ± 0.09 exercise, 0.81 ± 0.10 recovery, P = 0.13). In conclusion, in contrast to animal studies, in supine humans, mild exercise decreased perfusion heterogeneity, consistent with Zone model predictions.