Ventilation-perfusion ratio in perflubron during partial liquid ventilation

BACKGROUND: Functional magnetic resonance imaging (fMRI) of fluorine-19 allows for the mapping of oxygen partial pressure within perfluorocarbons in the alveolar space (Pao(2)). Theoretically, fMRI-detected Pao(2) can be combined with the Fick principle approach, i.e., a mass balance of oxygen uptake by ventilation and delivery by perfusion, to quantify the ventilation-perfusion ratio (Va/Q) of a lung region: The mixed venous blood and the inspiratory oxygen fraction, which are equal for all lung regions, are measured. In addition, the local expiratory oxygen fraction and the end capillary oxygen content, both of which may differ between the lung regions, are calculated using the fMRI-detected Pao(2). We investigated this approach by numerical simulations and applied it to quantify local Va/Q in the perfluorocarbons during partial liquid ventilation. METHODS: Numerical simulations were performed to analyze the sensitivity of the Va/Q calculation and to compare this approach with another one proposed by Rizi et al. in 2004 (Magn Reson Med 2004;52:65-72). Experimentally, the method was used during partial liquid ventilation in 7 anesthetized pigs. The Pao(2) distribution in intraalveolar perflubron was measured by fluorine-19 MRI. Respiratory gas fractions together with arterial and mixed venous blood samples were taken to quantify oxygen partial pressure and content. Using the Fick principle, the local Va/Q was estimated. The impact of gravity (nondependent versus dependent) of perflubron dose (10 vs 20 mL/kg body weight) and of inspired oxygen fraction (Fio(2)) (0.4-1.0) on Va/Q was examined. RESULTS: In numerical simulations, the Fick principle proved to be appropriate over the Va/Q range from 0.02 to 2.5. Va/Q values were in acceptable agreement with the method published by Rizi et al. In the experimental setting, low mean Va/Q values were found in perflubron (confidence interval [CI] 0.08-0.29 with 20 mL/kg perflubron). At this dose, Va/Q in the nondependent lung was higher (CI 0.18-0.39) than in the dependent lung regions (CI 0.06-0.16; P = 0.006; Student t test). Differences depending on Fio(2) or perflubron dose were, however, small. CONCLUSION: The results show that derivation of Va/Q from local Po(2) measurements using fMRI in perflubron is feasible. The low detected Va/Q suggests that oxygen transport into the perflubron-filled alveolar space is significantly restrained.

Observation of ventilation-induced Spo(2) oscillations in pigs: first step to noninvasive detection of cyclic recruitment of atelectasis?

High arterial partial oxygen pressure (Pao(2)) oscillations within the respiratory cycle were described recently in experimental acute lung injury. This phenomenon has been related to cyclic recruitment of atelectasis and varying pulmonary shunt fractions. Noninvasive detection of Spo(2) (oxygen saturation measured by pulse oximetry) as an indicator of cyclic collapse of atelectasis, instead of recording Pao(2) oscillations, could be of clinical interest in critical care. Spo(2) oscillations were recorded continuously in three different cases of lung damage to demonstrate the technical feasibility of this approach. To deduce Pao(2) from Spo(2), a mathematical model of the hemoglobin dissociation curve including left and right shifts was derived from the literature and adapted to the dynamic changes of oxygenation. Calculated Pao(2) amplitudes (derived from Spo(2) measurements) were compared to simultaneously measured fast changes of Pao(2), using a current standard method (fluorescence quenching of ruthenium). Peripheral hemoglobin saturation was capable to capture changes of Spo(2) within each respiratory cycle. For the first time, Spo(2) oscillations due to cyclic recruitment of atelectasis within a respiratory cycle were determined by photoplethysmography, a technology that can be readily applied noninvasively in clinical routine. A mathematic model to calculate the respective Pao(2) changes was developed and its applicability tested.

The effects of mechanical ventilation on hepato-splanchnic perfusion

PURPOSE OF REVIEW: Mechanical ventilation is a cornerstone of ICU treatment. Because of its interaction with blood flow and intra-abdominal pressure, mechanical ventilation has the potential to alter hepato-splanchnic perfusion, abdominal organ function and thereby outcome of the most critically ill patients. RECENT FINDINGS: Mechanical ventilation can alter hepato-splanchnic perfusion, but the effects are minimal (with moderate inspiratory pressures, tidal volumes, and positive end-expiratory pressure levels) or variable (with high ones). Routine nursing procedures may cause repeated episodes of inadequate hepato-splanchnic perfusion in critically ill patients, but an association between perfusion and multiple organ dysfunction cannot yet be determined. Clinical research continues to be challenging as a result of difficulties in measuring hepato-splanchnic blood flow at the bedside. SUMMARY: Mechanical ventilation and attempts to improve oxygenation such as intratracheal suctioning and recruitment maneuvers, may have harmful consequences in patients with already limited cardiovascular reserves or deteriorated intestinal perfusion. Due to difficulties in assessing hepato-splanchnic perfusion, such effects are often not detected.

A new approach in virtopsy: Postmortem ventilation in multislice computed tomography

Although postmortem imaging has gained prominence in the field of forensic medicine, evaluation of the postmortem lung remains problematic. Specifically, differentiation of normal postmortem changes and pathological pulmonary changes is challenging and at times impossible. In this study, five corpses were ventilated using a mechanical ventilator with a pressure of 40 mbar (40.8 cm H(2)O). The ventilation was performed via an endotracheal tube, a larynx mask or a continuous positive airway pressure mask. Postmortem computed tomographic images of the lungs before and with a ventilation of 40 mbar (40.8 cm H(2)O) were evaluated and the lung volumes were measured with segmentation software. Postmortem ventilation led to a clearly visible decrease of both the density in the dependant parts of the lungs and ground glass attenuation, whereas consolidated areas remained unchanged. Furthermore, a mean increase in the lung volume of 2.10 l was seen. Pathological changes such as septal thickening or pulmonary nodules in the lung parenchyma became more detectable with postmortem ventilation. Intracorporal postmortem mechanical ventilation of the lungs appears to be an effective method for enhancing detection of small pathologies of the lung parenchyma as well as for discriminating between consolidation, ground glass attenuation and position-dependent density.

Deep ocean ventilation, carbon isotopes, marine sedimentation and the deglacial CO2 rise

The link between the atmospheric CO2 level and the ventilation state of the deep ocean is an important building block of the key hypotheses put forth to explain glacial-interglacial CO2 fluctuations. In this study, we systematically examine the sensitivity of atmospheric CO2 and its carbon isotope composition to changes in deep ocean ventilation, the ocean carbon pumps, and sediment formation in a global three-dimensional ocean-sediment carbon cycle model. Our results provide support for the hypothesis that a break up of Southern Ocean stratification and invigorated deep ocean ventilation were the dominant drivers for the early deglacial CO2 rise of ~35 ppm between the Last Glacial Maximum and 14.6 ka BP. Another rise of 10 ppm until the end of the Holocene is attributed to carbonate compensation responding to the early deglacial change in ocean circulation. Our reasoning is based on a multi-proxy analysis which indicates that an acceleration of deep ocean ventilation during the early deglaciation is not only consistent with recorded atmospheric CO2 but also with the reconstructed opal sedimentation peak in the Southern Ocean at around 16 ka BP, the record of atmospheric δ13CCO2, and the reconstructed changes in the Pacific CaCO3 saturation horizon.

Dexmedetomidine vs midazolam or propofol for sedation during prolonged mechanical ventilation: two randomized controlled trials

Long-term sedation with midazolam or propofol in intensive care units (ICUs) has serious adverse effects. Dexmedetomidine, an α(2)-agonist available for ICU sedation, may reduce the duration of mechanical ventilation and enhance patient comfort.

Perception of non-invasive ventilation in adult Swiss intensive care units

The real utilisation scenario of non-invasive ventilation (NIV) in Swiss ICUs has never been reported. Using a survey methodology, we developed a questionnaire sent to the directors of the 79 adult ICUs to identify the perceived pattern of NIV utilisation. We obtained a response rate of 62%. The overall utilisation rate for NIV was 26% of all mechanical ventilations, but we found significant differences in the utilisation rates among different linguistic areas, ranging from 20% in the German part to 48% in the French part (p <0.01). NIV was mainly indicated for the acute exacerbations of COPD (AeCOPD), acute cardiogenic pulmonary edema (ACPE) and acute respiratory failure (ARF) in selected do-not-intubate patients. In ACPE, CPAP was much less used than bi-level ventilation and was still applied in AeCOPD. The first line interface was a facial mask (81%) and the preferred type of ventilator was an ICU machine with an NIV module (69%). The perceived use of NIV is generally high in Switzerland, but regional variations are remarkable. The indications of NIV use are in accordance with international guidelines. A high percentage of units consider selected do-not-intubate conditions as an important additional indication.

Postmortem ventilation: A new method for improved detection of pulmonary pathologies in forensic imaging

Postmortem imaging has gained prominence in the field of forensic pathology. Even with experience in this procedure, difficulties arise in evaluating pathologies of the postmortem lung. The effect of postmortem ventilation with applied pressures of 10, 20, 30 and 40mbar was evaluated in 10 corpses using simultaneous postmortem computed tomography (pmCT) scans. Ventilation was performed via a continuous positive airway pressure mask (n=5), an endotracheal tube (n=4) and a laryngeal mask (n=1) using a portable home care ventilator. The lung volumes were measured and evaluated by a segmentation technique based on reconstructed CT data. The resulting changes to the lungs were analyzed. Postmortem ventilation at 40mbar induced a significant (p<0.05) unfolding of the lungs, with a mean volume increase of 1.32l. Small pathologies of the lung such as scarring and pulmonary nodules as well as emphysema were revealed, while inner livores were reduced. Even though lower ventilation pressures resulted in a significant (p<0.05) volume increase, pathologies were best evaluated when a pressure of 40mbar was applied, due to the greater reduction of the inner livores. With the ventilation-induced expansion of the lungs, a decrease in the heart diameter and gaseous distension of the stomach was recognized. In conclusion, postmortem ventilation is a feasible method for improving evaluation of the lungs and detection of small lung pathologies. This is because of the volume increase in the air-filled portions of the lung and reduced appearance of inner livores.

Measurement of ventilation and cardiac related impedance changes with electrical impedance tomography

Introduction Electrical impedance tomography (EIT) has been shown to be able to distinguish both ventilation and perfusion. With adequate filtering the regional distributions of both ventilation and perfusion and their relationships could be analysed. Several methods of separation have been suggested previously, including breath holding, electrocardiograph (ECG) gating and frequency filtering. Many of these methods require interventions inappropriate in a clinical setting. This study therefore aims to extend a previously reported frequency filtering technique to a spontaneously breathing cohort and assess the regional distributions of ventilation and perfusion and their relationship. Methods Ten healthy adults were measured during a breath hold and while spontaneously breathing in supine, prone, left and right lateral positions. EIT data were analysed with and without filtering at the respiratory and heart rate. Profiles of ventilation, perfusion and ventilation/perfusion related impedance change were generated and regions of ventilation and pulmonary perfusion were identified and compared. Results Analysis of the filtration technique demonstrated its ability to separate the ventilation and cardiac related impedance signals without negative impact. It was, therefore, deemed suitable for use in this spontaneously breathing cohort. Regional distributions of ventilation, perfusion and the combined ΔZV/ΔZQ were calculated along the gravity axis and anatomically in each position. Along the gravity axis, gravity dependence was seen only in the lateral positions in ventilation distribution, with the dependent lung being better ventilated regardless of position. This gravity dependence was not seen in perfusion. When looking anatomically, differences were only apparent in the lateral positions. The lateral position ventilation distributions showed a difference in the left lung, with the right lung maintaining a similar distribution in both lateral positions. This is likely caused by more pronounced anatomical changes in the left lung when changing positions. Conclusions The modified filtration technique was demonstrated to be effective in separating the ventilation and perfusion signals in spontaneously breathing subjects. Gravity dependence was seen only in ventilation distribution in the left lung in lateral positions, suggesting gravity based shifts in anatomical structures. Gravity dependence was not seen in any perfusion distributions.

Deep ocean ventilation, carbon isotopes, marine sedimentation and the deglacial CO2 rise

The link between the atmospheric CO2 level and the ventilation state of the deep ocean is an important building block of the key hypotheses put forth to explain glacial-interglacial CO2 fluctuations. In this study, we systematically examine the sensitivity of atmospheric CO2 and its carbon isotope composition to changes in deep ocean ventilation, the ocean carbon pumps, and sediment formation in a global 3-D ocean-sediment carbon cycle model. Our results provide support for the hypothesis that a break up of Southern Ocean stratification and invigorated deep ocean ventilation were the dominant drivers for the early deglacial CO2 rise of ~35 ppm between the Last Glacial Maximum and 14.6 ka BP. Another rise of 10 ppm until the end of the Holocene is attributed to carbonate compensation responding to the early deglacial change in ocean circulation. Our reasoning is based on a multi-proxy analysis which indicates that an acceleration of deep ocean ventilation during early deglaciation is not only consistent with recorded atmospheric CO2 but also with the reconstructed opal sedimentation peak in the Southern Ocean at around 16 ka BP, the record of atmospheric δ13CCO2, and the reconstructed changes in the Pacific CaCO3 saturation horizon.

Alternating one lung ventilation using a double lumen endobronchial tube and providing CPAP to the non-ventilated lung in a dog

INTRODUCTION: This case report describes the anaesthetic management of exploratory thoracoscopy and alternating one lung ventilation (OLV) in a dog with a pulmonary bulla, and the application of continuous positive airway pressure (CPAP) to the non-ventilated lung for preventing and treating hypoxia. CASE HISTORY: A 6-year-old, male castrated Border collie was scheduled for exploratory thoracoscopy to investigate spontaneous pnemothorax that had not resolved with repeated suction. Specific requirements for the thoracoscopy were alternating OLV to allow the surgical access to the right middle lobe and its removal, and the examination of the left hemithorax to rule out the presence of other lesions. DIAGNOSIS AND MANAGEMENT: Selective lung ventilation was performed with a double lumen endobronchial tube (DLT), inserted under endoscopic guidance. After a short period of two lung ventilation during preparation of the surgical field, alternating OLV was performed, combining CPAP, provided to the non-ventilated lung via a Mapleson D breathing system, and positive end-expiratory pressure (PEEP) applied to the ventilated lung. Left OLV occurred first and resection of the right middle pulmonary lobe was successfully performed; right OLV followed to allow the examination of the left hemithorax. DISCUSSION AND CONCLUSIONS: The combination of CPAP and PEEP resulted in a satisfactory intra-operative management of hypoxemia. Alternating OLV can be performed successfully by using a DLT. CPAP, commonly employed in human medicine, should be considered an important tool in the anaesthetic management of OLV in small animals.

Evolution of gene expression changes in newborn rats after mechanical ventilation with reversible intubation

Mechanical ventilation (MV) is life-saving but potentially harmful for lungs of premature infants. So far, animal models dealt with the acute impact of MV on immature lungs, but less with its delayed effects. We used a newborn rodent model including non-surgical and therefore reversible intubation with moderate ventilation and hypothesized that there might be distinct gene expression patterns after a ventilation-free recovery period compared to acute effects directly after MV. Newborn rat pups were subjected to 8 hr of MV with 60% oxygen (O(2)), 24 hr after injection of lipopolysaccharide (LPS), intended to create a low inflammatory background as often recognized in preterm infants. Animals were separated in controls (CTRL), LPS injection (LPS), or full intervention with LPS and MV with 60% O(2) (LPS + MV + O(2)). Lungs were recovered either directly following (T:0 hr) or 48 hr after MV (T:48 hr). Histologically, signs of ventilator-induced lung injury (VILI) were observed in LPS + MV + O(2) lungs at T:0 hr, while changes appeared similar to those known from patients with chronic lung disease (CLD) with fewer albeit larger gas exchange units, at T:48 hr. At T:0 hr, LPS + MV + O(2) increased gene expression of pro-inflammatory MIP-2. In parallel anti-inflammatory IL-1Ra gene expression was increased in LPS and LPS + MV + O(2) groups. At T:48 hr, pro- and anti-inflammatory genes had returned to their basal expression. MMP-2 gene expression was decreased in LPS and LPS + MV + O(2) groups at T:0 hr, but no longer at T:48 hr. MMP-9 gene expression levels were unchanged directly after MV. However, at T:48 hr, gene and protein expression increased in LPS + MV + O(2) group. In conclusion, this study demonstrates the feasibility of delayed outcome measurements after a ventilation-free period in newborn rats and may help to further understand the time-course of molecular changes following MV. The differences obtained from the two time points could be interpreted as an initial transitory increase of inflammation and a delayed impact of the intervention on structure-related genes.