Dead space and CO2 elimination related to pattern of inspiratory gas delivery in ARDS patients

Introduction: The inspiratory flow pattern influences CO2 elimination by affecting the time the tidal volume remains resident in alveoli. This time is expressed in terms of mean distribution time (MDT), which is the time available for distribution and diffusion of inspired tidal gas within resident alveolar gas. In healthy and sick pigs, abrupt cessation of inspiratory flow (that is, high end-inspiratory flow (EIF)), enhances CO2 elimination. The objective was to test the hypothesis that effects of inspiratory gas delivery pattern on CO2 exchange can be comprehensively described from the effects of MDT and EIF in patients with acute respiratory distress syndrome (ARDS). Methods: In a medical intensive care unit of a university hospital, ARDS patients were studied during sequences of breaths with varying inspiratory flow patterns. Patients were ventilated with a computer-controlled ventilator allowing single breaths to be modified with respect to durations of inspiratory flow and postinspiratory pause (T-P), as well as the shape of the inspiratory flow wave. From the single-breath test for CO2, the volume of CO2 eliminated by each tidal breath was derived. Results: A long MDT, caused primarily by a long TP, led to importantly enhanced CO2 elimination. So did a high EIF. Effects of MDT and EIF were comprehensively described with a simple equation. Typically, an efficient and a less-efficient pattern of inspiration could result in +/- 10% variation of CO2 elimination, and in individuals, up to 35%. Conclusions: In ARDS, CO2 elimination is importantly enhanced by an inspiratory flow pattern with long MDT and high EIF. An optimal inspiratory pattern allows a reduction of tidal volume and may be part of lung-protective ventilation

DMTs and Covid-19 severity in MS: a pooled analysis from Italy and France

We evaluated the effect of DMTs on Covid-19 severity in patients with MS, with a pooled-analysis of two large cohorts from Italy and France. The association of baseline characteristics and DMTs with Covid-19 severity was assessed by multivariate ordinal-logistic models and pooled by a fixed-effect meta-analysis. 1066 patients with MS from Italy and 721 from France were included. In the multivariate model, anti-CD20 therapies were significantly associated (OR = 2.05, 95%CI = 1.39–3.02, p < 0.001) with Covid-19 severity, whereas interferon indicated a decreased risk (OR = 0.42, 95%CI = 0.18–0.99, p = 0.047). This pooled-analysis confirms an increased risk of severe Covid-19 in patients on anti-CD20 therapies and supports the protective role of interferon

Pattern of inspiratory gas delivery affects CO(2) elimination in health and after acute lung injury.

Objective To avoid ventilator induced lung injury, tidal volume should be low in acute lung injury (ALI). Reducing dead space may be useful, for example by using a pattern of inspiration that prolongs the time available for gas distribution and diffusion within the respiratory zone, the mean distribution time (MDT). A study was conducted to investigate how MDT affects CO2 elimination in pigs at health and after ALI. Design and setting Randomised crossover study in the animal laboratory of Lund University Biomedical Center. Subjects and intervention Healthy pigs and pigs with ALI, caused by surfactant perturbation and lung-damaging ventilation were ventilated with a computer-controlled ventilator. With this device each breath could be tailored with respect to insufflation time and pause time (T I and T P) as well as flow shape (square, increasing or decreasing flow). Measurements and results The single-breath test for CO2 allowed analysis of the volume of expired CO2 and the volume of CO2 re-inspired from Y-piece and tubes. With a long MDT caused by long T I or T P, the expired volume of CO2 increased markedly in accordance with the MDT concept in both healthy and ALI pigs. High initial inspiratory flow caused by a short T I or decreasing flow increased the re-inspired volume of CO2. Arterial CO2 increased during a longer period of short MDT and decreased again when MDT was prolonged. Conclusions CO2 elimination can be enhanced by a pattern of ventilation that prolongs MDT. Positive effects of prolonged MDT caused by short T I and decreasing flow were attenuated by high initial inspiratory flow. Electronic supplementary material The online version of this article (doi:10.1007/s00134-007-0840-7) contains supplementary material, which is available to authorized users

Esmolol Indirectly Stimulates Vagal Nerve Activity in Endotoxemic Pigs

International audienceBACKGROUND: There is an increasing interest in beta-blockade as a therapeutic approach to sepsis following consistent experimental findings of attenuation of inflammation and improved survival with beta1 selective antagonist. However, the mechanism of these beneficial effects remains very uncertain. Thus, this study is aimed at investigating the effects of a beta-1 selective blockade on sympathetic/parasympathetic activity in endotoxin-challenged pigs using heart rate variability. The hypothesis is that an adrenergic blockade could promote parasympathetic activity. Indeed, the increase of parasympathetic activity is a mechanism recently described as beneficial in septic states. METHODS: Fifty-one endotoxin-challenged pigs were studied. After 30~min of endotoxin infusion and 30~min of evolution without intervention, the pigs were randomly assigned the placebo or esmolol treatment and were observed for 200~min. Overall heart rate variability was assessed continuously, in the temporal domain by standard deviation of RR intervals (SDNN, ms),and in the frequency domain by spectral powers of low frequency (LF, ms2\,\texttimes\,103/Hz) and high frequency (HF, ms2\,\texttimes\,103/Hz) bands. RESULTS: Variations of power in these frequency bands were interpreted as putative markers of sympathetic (LF) and parasympathetic (HF) activity. In LPS treated animals, Esmolol did not increase SDNN, but instead decreased LF and increased HF power. CONCLUSION: These spectral modifications associated to a beta-blocker treatment after an endotoxemic challenge are interpreted as a significant decrease of sympathetic activity and an indirect increase of vagal autonomic tone

Effect of inspired oxygen fraction on alveolar derecruitment in acute respiratory distress syndrome

Objective: High fractions of inspired oxygen (FIO2) used in acute lung injury (ALI) may promote resorption atelectasis. The impact of derecruitment related to high FIO2 in ALI is debated. We evaluated derecruitment with 100% vs. 60% FIO2 at two levels of positive end-expiratory pressure (PEEP). Patients: Fourteen consecutive patients with ALI were studied. Interventions: Recruited volume at two PEEP levels was computed from two pressure-volume curves, recorded from PEEP and from zero end-expiratory pressure, using the sinusoidal flow modulation method. PEEP-induced recruitment was measured during prolonged expiration as the difference between the two curves at a given pressure. PaO2/FIO2 was also measured. PEEP was 5 +/- 1 or 14 +/- 3 cmH(2)O and FIO2 was 60% or 100%, yielding four combinations. We looked for differences between the beginning and end of a 30-min period with each combination. Measurement and results: With low PEEP and 100% FIO2, recruited volume decreased significantly from 68 +/- 53 to 39 +/- 43 ml and PaO2/FIO2 from 196 +/- 104 to 153 +/- 83 mmHg. With the three other combinations (low PEEP and 60% FIO2 or high PEEP and 60% or 100% FIO2) none of the parameters decreased significantly. Conclusion: In mechanically ventilated patients with ALI the breathing of pure oxygen leads to derecruitment, which is prevented by high PEEP

Correction to: Esmolol indirectly stimulates vagal nerve activity in endotoxemic pigs

Following publication of the original article [1], the author reported these required corrections to Fig. 5 and Fig. 6

Correlation between clinical severity and different non-invasive measurements of carbon monoxide concentration: A population study

<div><p>Objectives</p><p>Carbon monoxide (CO) poisoning is a major concern in industrialized countries. Each year, thousands of victims, resulting in approximately 100 fatalities, are encountered in France. The diagnosis of CO poisoning is challenging; while carboxyhemoglobin (COHb) may be useful, it is a weak indicator of the severity of CO poisoning. This weak indicator may be a result of the delay between poisoning occurrence and the blood assay. Two apparatuses, CO oximeters and exhaled CO analyzers, now permit COHb to be determined outside hospitals. Our hypothesis is that these instruments allow the early measurement of COHb concentrations, which are more correlated with the severity of poisoning, expressed using the poisoning severity score (PSS).</p><p>Design</p><p>In an observational and retrospective cohort study, the distribution of COHb measurements obtained by CO oximetry or by exhaled CO analyzers was compared between groups of severity expressed using the PSS.</p><p>Setting</p><p>Data were collected in the Paris area from January 2006 to December 2010 by the French Surveillance System of CO poisoning.</p><p>Participants</p><p>All patients with CO poisoning reported to the French Surveillance System of CO poisoning.</p><p>Results</p><p>There was a significant difference in the COHb values obtained by CO oximetry between groups stratified according to PSS (p<0.0001). A significant difference in the values of exhaled CO was also observed between PSS groups (p = 0.006), although the relationship was not linear.</p><p>Conclusions</p><p>The COHb concentrations measured using CO oximetry, but not those measured using exhaled CO analyzers, were well correlated with the severity of CO poisoning.</p></div