Test-retest reliability of transfer function analysis metrics for assessing dynamic cerebral autoregulation to spontaneous blood pressure oscillations

Transfer function analysis (TFA) is a widely used method for assessing dynamic cerebral autoregulation in humans. In the present study, we assessed the test-retest reliability of established TFA metrics derived from spontaneous blood pressure oscillations and based on 5 min recordings. The TFA-based gain, phase and coherence in the low-frequency range (0.07-0.20 Hz) from 19 healthy volunteers, 37 patients with subarachnoid haemorrhage and 19 patients with sepsis were included. Reliability assessments included the smallest real difference (SRD) and the coefficient of variance for comparing consecutive 5 min recordings, temporally separated 5 min recordings and consecutive recordings with a minimal length of 10 min. In healthy volunteers, temporally separating the 5 min recordings led to a 0.38 (0.01-0.79) cm s-1 mmHg-1 higher SRD for gain (P = 0.032), and extending the duration of recordings did not affect the reliability. In subarachnoid haemorrhage, temporal separation led to a 0.85 (-0.13 to 1.93) cm s-1 mmHg-1 higher SRD (P = 0.047) and a 20 (-2 to 41)% higher coefficient of variance (P = 0.038) for gain, but neither metric was affected by extending the recording duration. In sepsis, temporal separation increased the SRD for phase by 94 (23-160)° (P = 0.006) but was unaffected by extending the recording. A recording duration of 8 min was required to achieve stable gain and normalized gain measures in healthy individuals, and even longer recordings were required in patients. In conclusion, a recording duration of 5 min appears insufficient for obtaining stable and reliable TFA metrics when based on spontaneous blood pressure oscillations, particularly in critically ill patients with subarachnoid haemorrhage and sepsis.

Alveolar cytokines and interferon autoantibodies in COVID-19 ARDS

Background

Type I interferon (IFN-I) and IFN autoantibodies play a crucial role in controlling SARS-CoV-2 infection. The levels of these mediators have only rarely been studied in the alveolar compartment in patients with COVID-19 acute respiratory distress syndrome (CARDS) but have not been compared across different ARDS etiologies, and the potential effect of dexamethasone (DXM) on these mediators is not known.

Methods

We assessed the integrity of the alveolo-capillary membrane, interleukins, type I, II, and III IFNs, and IFN autoantibodies by studying the epithelial lining fluid (ELF) volumes, alveolar concentration of protein, and ELF-corrected concentrations of cytokines in two patient subgroups and controls.

Results

A total of 16 patients with CARDS (four without and 12 with DXM treatment), eight with non-CARDS, and 15 healthy controls were included. The highest ELF volumes and protein levels were observed in CARDS. Systemic and ELF-corrected alveolar concentrations of interleukin (IL)-6 appeared to be particularly low in patients with CARDS receiving DXM, whereas alveolar levels of IL-8 were high regardless of DXM treatment. Alveolar levels of IFNs were similar between CARDS and non-CARDS patients, and IFNα and IFNω autoantibody levels were higher in patients with CARDS and non-CARDS than in healthy controls.

Conclusions

Patients with CARDS exhibited greater alveolo-capillary barrier disruption with compartmentalization of IL-8, regardless of DXM treatment, whereas systemic and alveolar levels of IL-6 were lower in the DXM-treated subgroup. IFN-I autoantibodies were higher in the BALF of CARDS patients, independent of DXM, whereas IFN autoantibodies in plasma were similar to those in controls.

PaCO2 trajectories in mechanically ventilated patients with COVID-19: A population-based cohort study

OBJECTIVE

To identify PaCO2 trajectories and assess their associations with mortality in critically ill patients with coronavirus disease 2019 (COVID-19) during the first and second waves of the pandemic in Denmark.

DESIGN

A population-based cohort study with retrospective data collection.

PATIENTS

All COVID-19 patients were treated in eight intensive care units (ICUs) in the Capital Region of Copenhagen, Denmark, between March 1, 2020 and March 31, 2021.

MEASUREMENTS

Data from the electronic health records were extracted, and latent class analyses were computed based on up to the first 3 weeks of mechanical ventilation to depict trajectories of PaCO2 levels. Multivariable Cox regression analyses were used to calculate adjusted hazard ratios (aHRs) for Simplified Acute Physiology Score 3, sex and age with 95% confidence intervals (CIs) for death according to PaCO2 trajectories.

MAIN RESULTS

In latent class trajectory models, including 25,318 PaCO2 measurements from 244 patients, three PaCO2 latent class trajectories were identified: a low isocapnic (Class I; n = 130), a high isocapnic (Class II; n = 80), as well as a progressively hypercapnic (Class III; n = 34) trajectory. Mortality was higher in Class II [aHR: 2.16 {1.26-3.68}] and Class III [aHR: 2.97 {1.63-5.40}]) compared to Class I (reference).

CONCLUSION

Latent class analysis of arterial blood gases in mechanically ventilated COVID-19 patients identified distinct PaCO2 trajectories, which were independently associated with mortality.

Thromboembolic and bleeding events in ICU patients with COVID-19: A nationwide, observational study

BACKGROUND

Intensive care unit (ICU) patients with Coronavirus disease 2019 (COVID-19) have an increased risk of thromboembolic complications. We describe the occurrence of thromboembolic and bleeding events in all ICU patients with COVID-19 in Denmark during the first and second waves of the pandemic.

METHODS

This was a sub-study of the Danish Intensive Care Covid database, in which all patients with SARS-CoV-2 admitted to Danish ICUs from 10th March 2020 to 30th June 2021 were included. We registered coagulation variables at admission, and all thromboembolic and bleeding events, and the use of heparins during ICU stay. Variables associated with thrombosis and bleeding and any association with 90-day mortality were estimated using Cox regression analyses.

RESULTS

We included 1369 patients in this sub-study; 158 (12%, 95% confidence interval 10-13) had a thromboembolic event in ICU and 309 (23%, 20-25) had a bleeding event, among whom 81 patients (6%, 4.8-7.3) had major bleeding. We found that mechanical ventilation and increased D-dimer were associated with thrombosis and mechanical ventilation, low platelet count and presence of haematological malignancy were associated with bleeding. Most patients (76%) received increased doses of thromboprophylaxis during their ICU stay. Thromboembolic events were not associated with mortality in adjusted analysis (hazard ratio 1.35 [0.91-2.01, p = .14], whereas bleeding events were 1.55 [1.18-2.05, p = .002]).

CONCLUSIONS

Both thromboembolic and bleeding events frequently occurred in ICU patients with COVID-19. Based on these data, it is not apparent that increased doses of thromboprophylaxis were beneficial.

Diagnostic and prognostic performance of Mxa and transfer function analysis-based dynamic cerebral autoregulation metrics

Dynamic cerebral autoregulation is often assessed by continuously recorded arterial blood pressure (ABP) and transcranial Doppler-derived mean cerebral blood flow velocity followed by analysis in the time and frequency domain, respectively. Sequential correlation (in the time domain, yielding e.g., the measure mean flow index, Mxa) and transfer function analysis (TFA) (in the frequency domain, yielding, e.g., normalised and non-normalised gain as well as phase in the low frequency domain) are commonly used approaches. This study investigated the diagnostic and prognostic performance of these metrics. We included recordings from 48 healthy volunteers, 19 patients with sepsis, 36 with traumatic brain injury (TBI), and 14 patients admitted to a neurorehabilitation unit. The diagnostic (between healthy volunteers and patients) and prognostic performance (to predict death or poor functional outcome) of Mxa and the TFA measures were assessed by area under the receiver-operating characteristic (AUROC) curves. AUROC curves generally indicated that the measures were 'no better than chance' (AUROC ∼0.5) both for distinguishing between healthy volunteers and patient groups, and for predicting outcomes in our cohort. No metric emerged as superior for distinguishing between healthy volunteers and different patient groups, for assessing the effect of interventions, or for predicting mortality or functional outcome.

[Local immunopathology in COVID-19 associated lung injury]

Mechanisms of COVID-19-induced lung injury involve complex immunopathological events which are currently being elucidated. Studying immune mechanisms at the primary site of injury, i.e. the lower airways, are particularly informative. This review provides a brief introduction to the methods used to perform sampling from the lungs of critically ill patients with COVID-19, key immunopathological findings and a discussion on how immunosuppressants may exert their effects locally.

A Distinct Dexamethasone-Dependent Gene Expression Profile in the Lungs of COVID-19 Patients

The effects of dexamethasone (DXM) treatment on pulmonary immunity in COVID-19-associated acute respiratory distress syndrome (CARDS) remain insufficiently understood. We performed transcriptomic RNA-seq analysis of bronchoalveolar lavage fluid from 20 mechanically ventilated patients: 12 with CARDS (with or without DXM) and 8 non-COVID-19 critically ill controls. CARDS with DXM was characterized by upregulation of genes related to B-cell and complement pathway activation, antigen presentation, phagocytosis, and FC-γ receptor signaling. Most interferon-stimulated genes were upregulated in CARDS, particularly in CARDS without DXM. In conclusion, DXM treatment was not associated with regulation of proinflammatory pathways in CARDS but with regulation of other local immune responses. Clinical Trials Registration. NCT04354584.

Host Genetics and Antiviral Immune Responses in Adult Patients With Multisystem Inflammatory Syndrome

COVID-19 associated multisystem inflammatory syndrome (MIS) is a rare condition mostly affecting children but also adults (MIS-A). Although severe systemic inflammation and multiorgan dysfunction are hallmarks of the syndrome, the underlying pathogenesis is unclear. We aimed to provide novel immunological and genetic descriptions of MIS-A patients. Cytokine responses (IL-6, IL-1β, TNFα, CXCL10, type I, II and III interferons) following SARS-CoV-2 infection of peripheral blood mononuclear cells in vitro were analyzed as well as antibodies against IFNα and IFNω (by ELISA) in patients and healthy controls. We also performed whole exome sequencing (WES) of patient DNA. A total of five patients (ages 19, 23, 33, 38, 50 years) were included. The patients shared characteristic features, although organ involvement and the time course of disease varied slightly. SARS-CoV-2 in vitro infection of patient PBMCs revealed impaired type I and III interferon responses and reduced CXCL10 expression, whereas production of proinflammatory cytokines were less affected, compared to healthy controls. Presence of interferon autoantibodies was not detected. Whole exome sequencing analysis of patient DNA revealed 12 rare potentially disease-causing variants in genes related to autophagy, classical Kawasaki disease, restriction factors and immune responses. In conclusion, we observed an impaired production of type I and III interferons in response to SARS-CoV-2 infection and detected several rare potentially disease-causing gene variants potentially contributing to MIS-A.

[Hyperlactataemia]

It is a common but flawed presumption that blood lactate reflects the lactic acid production in the body's tissues. Lactate is formed directly from pyruvate and functions to dampen reductions in intracellular pH through lactate-H+ cotransport to the extracellular space. Though this may give rise to elevated blood lactate, increased lactate production is not the cause of metabolic acidosis in such instances. "Lactic acidosis" is thus an inappropriate term as it indicates causality and in this review, we suggest that in the future, the term "hyperlactataemia-associated metabolic acidosis" should be used instead.

Therapeutic benefits of proning to improve pulmonary gas exchange in severe respiratory failure: focus on fundamentals of physiology

New Findings

What is the topic of this review?

The use of proning for improving pulmonary gas exchange in critically ill patients.

What advances does it highlight?

Proning places the lung in its ‘natural’ posture, and thus optimises the ventilation‐perfusion distribution, which enables lung protective ventilation and the alleviation of potentially life‐threatening hypoxaemia in COVID‐19 and other types of critical illness with respiratory failure.

Abstract

The survival benefit of proning patients with acute respiratory distress syndrome (ARDS) is well established and has recently been found to improve pulmonary gas exchange in patients with COVID‐19‐associated ARDS (CARDS). This review outlines the physiological implications of transitioning from supine to prone on alveolar ventilation‐perfusion (V˙A--Q˙) relationships during spontaneous breathing and during general anaesthesia in the healthy state, as well as during invasive mechanical ventilation in patients with ARDS and CARDS. Spontaneously breathing, awake healthy individuals maintain a small vertical (ventral‐to‐dorsal) V˙A/Q˙ ratio gradient in the supine position, which is largely neutralised in the prone position, mainly through redistribution of perfusion. In anaesthetised and mechanically ventilated healthy individuals, a vertical V˙A/Q˙ ratio gradient is present in both postures, but with better V˙A--Q˙ matching in the prone position. In ARDS and CARDS, the vertical V˙A/Q˙ ratio gradient in the supine position becomes larger, with intrapulmonary shunting in gravitationally dependent lung regions due to compression atelectasis of the dorsal lung. This is counteracted by proning, mainly through a more homogeneous distribution of ventilation combined with a largely unaffected high perfusion dorsally, and a consequent substantial improvement in arterial oxygenation. The data regarding proning as a therapy in patients with CARDS is still limited and whether the associated improvement in arterial oxygenation translates to a survival benefit remains unknown. Proning is nonetheless an attractive and lung protective manoeuvre with the potential benefit of improving life‐threatening hypoxaemia in patients with ARDS and CARDS.

Reliability of the mean flow index (Mx) for assessing cerebral autoregulation in healthy volunteers

BACKGROUND

Mean flow index (Mxa) for evaluating dynamic cerebral autoregulation is derived using varying approaches for calculation, which may explain that the reliability ranges from poor to excellent. The comparability, repeatability, stability, and internal consistency of approaches have not previously been assessed.

METHODS

We included 60 recordings from resting healthy volunteers and calculated Mxa using four different approaches: three without overlapping calculations, using intervals for averaging wave-form data (blocks) of 3, 6, and 10 s, and correlation periods (epochs) of 60, 240, and 300 s (3-60-F, 6-240-F, and 10-300-F); and one using 10-second blocks, 300 s epochs, and overlaps of 60 s (10-300-60). The comparability between the approaches was assessed using Student's t test, intraclass correlation coefficients (ICC), and Bland-Altman plot.

RESULTS

Overall, 3-60-F resulted in a higher Mxa than the other indices (p < 0.001, for all). The reliability when comparing all the approaches ranged from moderate to good (ICC: 0.68; 95%CI: 0.59-0.84), which was primarily due to similarities between 10-300-F and 10-300-60 (ICC: 0.94; 95%CI: 0.86-0.98). The reliability when comparing the first and last half was poor for 10-300-F and ranged from poor to moderate for the other approaches. Additional random artifacts resulted in poor reliability for 10-300-F, while the other approaches were more stable.

CONCLUSIONS

Mxa in general has a low sensitivity to artifacts, but otherwise seems highly dependent on the approach, with a repeatability that is moderate at best. The varying accuracy and precision renders Mxa unreliable for classifying impaired cerebral autoregulation when using healthy adults for comparison.

The role of lactate in sepsis and COVID-19: Perspective from contracting skeletal muscle metabolism

NEW FINDINGS

What is the topic of this review? Lactate is considered an important substrate for mitochondria in the muscles, heart and brain during exercise and is the main gluconeogenetic precursor in the liver and kidneys. In this light, we review the (patho)physiology of lactate metabolism in sepsis and coronavirus disease 2019 (COVID-19). What advances does it highlight? Elevated blood lactate is strongly associated with mortality in septic patients. Lactate seems unrelated to tissue hypoxia but is likely to reflect mitochondrial dysfunction and high adrenergic stimulation. Patients with severe COVID-19 exhibit near-normal blood lactate, indicating preserved mitochondrial function, despite a systemic hyperinflammatory state similar to sepsis.

ABSTRACT

In critically ill patients, elevated plasma lactate is often interpreted as a sign of organ hypoperfusion and/or tissue hypoxia. This view on lactate is likely to have been influenced by the pioneering exercise physiologists around 1920. August Krogh identified an oxygen deficit at the onset of exercise that was later related to an oxygen 'debt' and lactate accumulation by A. V. Hill. Lactate is considered to be the main gluconeogenetic precursor in the liver and kidneys during submaximal exercise, but hepatic elimination is attenuated by splanchnic vasoconstriction during high-intensity exercise, causing an exponential increase in blood lactate. With the development of stable isotope tracers, lactate has become established as an important energy source for muscle, brain and heart tissue, where it is used for mitochondrial respiration. Plasma lactate > 4 mM is strongly associated with mortality in septic shock, with no direct link between lactate release and tissue hypoxia. Herein, we provide evidence for mitochondrial dysfunction and adrenergic stimulation as explanations for the sepsis-induced hyperlactataemia. Despite profound hypoxaemia and intense work of breathing, patients with severe coronavirus disease 2019 (COVID-19) rarely exhibit hyperlactataemia (> 2.5 mM), while presenting a systemic hyperinflammatory state much like sepsis. However, lactate dehydrogenase, which controls the formation of lactate, is markedly elevated in plasma and strongly associated with mortality in severe COVID-19. We briefly review the potential mechanisms of the lactate dehydrogenase elevation in COVID-19 and its relationship to lactate metabolism based on mechanisms established in contracting skeletal muscle and the acute respiratory distress syndrome.

Compartmental immunophenotyping in COVID-19 ARDS: A case series

Background

Severe immunopathology may drive the deleterious manifestations that are observed in the advanced stages of coronavirus disease 2019 (COVID-19) but are poorly understood.

Objective

Our aim was to phenotype leukocyte subpopulations and the cytokine milieu in the lungs and blood of critically ill patients with COVID-19 acute respiratory distress syndrome (ARDS).

Methods

We consecutively included patients less than 72 hours after intubation following informed consent from their next of kin. Bronchoalveolar lavage fluid was evaluated by microscopy; bronchoalveolar lavage fluid and blood were assessed by 10-color flow cytometry and a multiplex cytokine panel.

Results

Four mechanically ventilated patients (aged 40-75 years) with moderate-to-severe COVID-19 ARDS were included. Immature neutrophils dominated in both blood and lungs, whereas CD4 and CD8 T-cell lymphopenia was observed in the 2 compartments. However, regulatory T cells and T_H17 cells were found in higher fractions in the lung. Lung CD4 and CD8 T cells and macrophages expressed an even higher upregulation of activation markers than in blood. A wide range of cytokines were expressed at high levels both in the blood and in the lungs, most notably, IL-1RA, IL-6, IL-8, IP-10, and monocyte chemoattactant protein-1, consistent with hyperinflammation.

Conclusion

COVID-19 ARDS exhibits a distinct immunologic profile in the lungs, with a depleted and exhausted CD4 and CD8 T-cell population that resides within a heavily hyperinflammatory milieu.

Soluble ectodomain CD163 and extracellular vesicle-associated CD163 are two differently regulated forms of 'soluble CD163' in plasma

CD163 is the macrophage receptor for uptake of hemoglobin-haptoglobin complexes. The human receptor can be shed from the macrophage surface owing to a cleavage site for the inflammation-inducible TACE/ADAM17 enzyme. Accordingly, plasma ‘soluble CD163’ (sCD163) has become a biomarker for macrophage activity and inflammation. The present study disclosed that 10% of sCD163 in healthy persons is actually extracellular vesicle (EV)-associated CD163 not being cleaved and shed. Endotoxin injection of human volunteers caused a selective increase in the ectodomain CD163, while septic patients exhibited high levels of both soluble ectodomain CD163 and extracellular vesicle (EV) CD163, the latter representing up 60% of total plasma CD163. A poor prognosis of septic patients measured as the sequential organ failure assessment (SOFA) score correlated with the increase in membrane-associated CD163. Our results show that soluble ectodomain CD163 and EV CD163 in plasma are part of separate macrophage response in the context of systemic inflammation. While that soluble ectodomain CD163 is released during the acute systemic inflammatory response, this is not the case for EV CD163 that instead may be released during a later phase of the inflammatory response. A separate measurement of the two forms of CD163 constituting ‘soluble CD163’ in plasma may therefore add to the diagnostic and prognostic value.

Alveolar recruitment of ficolin-3 in response to acute pulmonary inflammation in humans

BACKGROUND

Ficolins serve as soluble recognition molecules in the lectin pathway of complement. They are known to participate in the systemic host-response to infection but their role in local pulmonary defence is still incompletely understood. The purpose of this study was to clarify whether acute lung and systemic inflammation induce recruitment of lectins in humans.

METHODS

Fifteen healthy volunteers received LPS intravenously (IV) or in a lung subsegment on two different occasions. Volunteers were evaluated by consecutive blood samples and by bronchoalveolar lavage 2, 4, 6, 8, or 24h after LPS (n=3 in all groups), and gene expression patterns and protein levels of mannose-binding lectin (MBL) and ficolins were determined.

RESULTS

Endobronchial LPS was associated with an increase in alveolar ficolin-3 and MBL levels (p<0.04 and p<0.001, respectively). IV LPS elicited a pronounced acute phase response with an increase in CRP (p<0.001) and plasma ficolin-1 protein levels (p<0.001), whereas no changes were observed in ficolin-1 gene expression patterns (p=0.11) or plasma protein levels of MBL, ficolin-2, or ficolin-3.

CONCLUSIONS

LPS induces a tissue-specific recruitment of ficolin-3 and ficolin-1 in the lung and systemic compartment, respectively, suggesting an important role of distinct lectin complement pathway initiators in the local pulmonary and systemic host defence.

The Dynamic cerebral autoregulatory adaptive response to noradrenaline is attenuated during systemic inflammation in humans

Vasopressor support is used widely for maintaining vital organ perfusion pressure in septic shock, with implications for dynamic cerebral autoregulation (dCA). This study investigated whether a noradrenaline-induced steady state increase in mean arterial blood pressure (MAP) would enhance dCA following lipopolysaccharide (LPS) infusion, a human-experimental model of the systemic inflammatory response during early sepsis. The dCA in eight healthy males was examined prior to and during an intended noradrenaline-induced MAP increase of approximately 30 mmHg. This was performed at baseline and repeated after a 4-h intravenous LPS infusion. The assessments of dCA were based on transfer function analysis of spontaneous oscillations between MAP and middle cerebral artery blood flow velocity measured by transcranial Doppler ultrasound in the low frequency range (0.07-0.20 Hz). Prior to LPS, noradrenaline administration was associated with a decrease in gain (1.18 (1.12-1.35) vs 0.93 (0.87-0.97) cm/mmHg per s; P < 0.05) with no effect on phase (0.71 (0.93-0.66) vs 0.94 (0.81-1.10) radians; P = 0.58). After LPS, noradrenaline administration changed neither gain (0.91 (0.85-1.01) vs 0.87 (0.81-0.97) cm/mmHg per s; P = 0.46) nor phase (1.10 (1.04-1.30) vs 1.37 (1.23-1.51) radians; P = 0.64). The improvement of dCA to a steady state increase in MAP is attenuated during an LPS-induced systemic inflammatory response. This may suggest that vasopressor treatment with noradrenaline offers no additional neuroprotective effect by enhancing dCA in patients with early sepsis.

Effects of short-term mechanical hyperventilation on cerebral blood flow and dynamic cerebral autoregulation in critically ill patients with sepsis

In sepsis, higher PaCO2 levels are associated with impaired dynamic cerebral autoregulation (dCA), which may expose the brain to hypo- and hyperperfusion during acute fluctuations in blood pressure. We hypothesised that short-term mechanical hyperventilation would dCA in critically ill patients with sepsis. Seven mechanically ventilated septic patients were included. We assessed dCA before and after 30 min of mechanical hyperventilation. Transfer function analysis of spontaneous oscillations in transcranial Doppler-based middle cerebral artery blood flow velocity (MCAv) and invasive mean arterial blood pressure was used to assess dCA. Mechanical enhance hyperventilation reduced the median PaCO2 from 5.3 (IQR, 5.0-6.5) to 4.7 (IQR, 4.2-5.1) kPa (p < 0.05). This was associated with a reduction in the median MCAv from 57 (IQR, 33-68) to 32 (IQR, 21-40) cm sec(-1) (p < 0.05). Apart from a small increase in gain in the low frequency range (2.32 [IQR 1.80-2.41] vs. 2.59 (2.40-4.64) cm mmHg(-1) sec(-1); p < 0.05), this was not associated with any enhancement in dCA. In conclusion, cerebral CO2 vasoreactivity was found to be preserved in septic patients; nevertheless, and in contrast to our working hypothesis, short-term mechanical hyperventilation did not enhance dCA.

Inflammation-Induced Changes in Circulating T-Cell Subsets and Cytokine Production During Human Endotoxemia

Observational clinical studies suggest the initial phase of sepsis may involve impaired cellular immunity. In the present study, we investigated temporal changes in T-cell subsets and T-cell cytokine production during human endotoxemia. Endotoxin (Escherichia coli lipopolysaccharide 4 ng/kg) was administered intravenously in 15 healthy volunteers. Peripheral blood and bronchoalveolar lavage fluid (BALF) were collected at baseline and after 2, 4, 6, 8, and 24 hours for flow cytometry. CD4⁺CD25⁺CD127lowFoxp3⁺ regulatory T cells (Tregs), CD4⁺CD161⁺ cells, and activated Human leukocyte antigen, HLA-DR⁺CD38⁺ T cells were determined. Ex vivo whole-blood cytokine production and Toll-like receptor (TLR)-4 expression on Tregs were measured. Absolute number of CD3⁺CD4⁺ (P = .026), CD3⁺CD8⁺ (P = .046), Tregs (P = .023), and CD4⁺CD161⁺ cells (P = .042) decreased after endotoxin administration. The frequency of anti-inflammatory Tregs increased (P = .033), whereas the frequency of proinflammatory CD4⁺CD161⁺ cells decreased (P = .034). Endotoxemia was associated with impaired whole-blood production of tumor necrosis factor-α, interleukin-10, IL-6, IL-17, IL-2, and interferon-γ in response to phytohaemagglutinin but did not affect TLR4 expression on Tregs. No changes in the absolute count or frequency of BALF T cells were observed. Systemic inflammation is associated with lymphopenia, a relative increase in the frequency of anti-inflammatory Tregs, and a functional impairment of T-cell cytokine production.

Dynamic cerebral autoregulation to induced blood pressure changes in human experimental and clinical sepsis

Previous studies have demonstrated that dynamic cerebral autoregulation to spontaneous fluctuations in blood pressure is enhanced following lipopolysaccharide (LPS) infusion, a human experimental model of early sepsis, whereas by contrast it is impaired in patients with severe sepsis or septic shock. In this study, we hypothesized that this pattern of response would be identical during induced changes in blood pressure. Dynamic cerebral autoregulation was assessed in nine healthy volunteers and six septic patients. The healthy volunteers underwent a 4-h intravenous infusion of LPS (total dose: 2 ng kg^-1 ). Mean arterial blood pressure (MAP, arterial transducer) and middle cerebral artery blood flow velocity (MCAv, transcranial Doppler ultrasound) were recorded continuously during thigh-cuff deflation-induced changes in MAP for the determination of a modified rate of regulation (RoR). This was performed before and after LPS infusion in healthy volunteers, and within 72 h following clinical diagnosis of sepsis in patients. In healthy volunteers, thigh-cuff deflation caused a MAP reduction of 16 (13-20) % at baseline and 18 (16-20) % after LPS, while the MAP reduction was 12 (11-13) % in patients (P<0·05 versus volunteers at baseline; P<0·01 versus volunteers after LPS). The corresponding RoR values increased from 0·46 (0·31-0·49) s^-1 at baseline to 0·58 (0·36-0·74) s^-1 after LPS (P<0·05) in healthy volunteers, whereas they were similar to values observed in patients [0·43 (0·36-0·52) s^-1 ; P = 0·91 versus baseline; P = 0·14 versus LPS]. While our findings support the concept that dynamic cerebral autoregulation is enhanced during the very early stages of sepsis, they remain inconclusive with regard to more advanced stages of disease, because thigh-cuff deflation failed to induce sufficient MAP reductions in patients.

T cell subsets in human airways prior to and following endobronchial administration of endotoxin

BACKGROUND AND OBJECTIVES

Bronchial instillation of lipopolysaccharide (LPS) provides a reversible model of lung inflammation that may resemble early stages of acute respiratory distress syndrome (ARDS). We investigated the distributions of T-cell subsets in the human airways and sought to determine whether pro- and anti-inflammatory T cells are involved in the local immune response to lung inflammation.

METHODS

Bronchoalveolar lavage (BAL) was performed in 15 healthy volunteers, after which Escherichia coli LPS (4 ng/kg) was administered. BAL was repeated at 2, 4, 6, 8 or 24 h after instillation of LPS.

RESULTS

BALF CD4+ and CD8+ T cells were characterized by expression of activation markers (HLA-DR+CD38+), the proportion of cells expressing naïve markers (CD45RA+CD27+CCR7+) was lower, and that of cells expressing effector memory markers (CD45RA-CD27+CCR7-) was higher, compared with peripheral blood. Bronchial LPS induced a local inflammatory response with recruitment of CD4+ (P=0.014), CD8+ T cells (P=0.034), an increase in the proportion of CD4+CD25+CD127lowFoxp3+ regulatory T cells (Tregs) (P=0.045) and a tendency towards an increase in CD4+CD161+ cells (P=0.071) were observed.

CONCLUSIONS

A unique distribution of T cells with little day-to-day variation was found in human airways. An increase in Tregs after endobronchial LPS suggests a role for Tregs during early stages of pulmonary inflammation.

Transcompartmental inflammatory responses in humans: IV versus endobronchial administration of endotoxin*

OBJECTIVES

Transcompartmental signaling during early inflammation may lead to propagation of disease to other organs. The time course and the mechanisms involved are still poorly understood. We aimed at comparing acute transcompartmental inflammatory responses in humans following lipopolysaccharide-induced pulmonary and systemic inflammation.

DESIGN

Randomized, double-blind, placebo-controlled, crossover study.

SETTING ICU SUBJECTS

Healthy male volunteers.

INTERVENTIONS

Fifteen volunteers (mean age, 23; SD, 2 yr) received Escherichia coli endotoxin (lipopolysaccharide, 4 ng/kg) IV or endobronchially on two different study days. Groups were evaluated by bronchoalveolar lavage at baseline (0 hr) and 2, 4, 6, 8, or 24 hours postchallenge. Cardiorespiratory variables were continuously recorded throughout the study day, and plasma and bronchoalveolar lavage fluid markers of inflammation were measured.

MEASUREMENTS AND MAIN RESULTS

IV endotoxin elicited a systemic inflammatory response with a time-dependent increase and peak in tumor necrosis factor-α, interleukin-6, and leukocyte counts (all p < 0.001). Furthermore, a delayed (6-8 hr) increase in bronchoalveolar lavage fluid interleukin-6 concentration (p < 0.001) and alveolar leukocyte count (p = 0.03) and a minor increase in bronchoalveolar lavage fluid tumor necrosis factor-α were observed (p = 0.06). Endobronchial endotoxin was followed by progressive alveolar neutrocytosis and increased bronchoalveolar lavage fluid tumor necrosis factor-α, interleukin-6, and albumin (all p < 0.001); a systemic inflammatory response was observed after 2-4 hours, with no change in plasma tumor necrosis factor-α.

CONCLUSIONS

Acute lung or systemic inflammation in humans is followed by a transcompartmental proinflammatory response, the degree and differential kinetics of which suggests that the propagation of inflammation may depend on the primary site of injury.

Progressive intracranial hypertension and cerebral hypoperfusion in a fatal case of cerebral aspergilloma

We report a case of cerebral aspergilloma in a 25-year-old immunoincompetent man admitted to a general intensive care unit. Monitoring of intracranial pressure was instigated and revealed hour-long epochs of severe intracranial hypertension, despite a normal opening pressure, with decreases in cerebral perfusion pressure. We documented that this was associated with cerebral hypoperfusion by transcranial Doppler ultrasound. The present case illustrates that severe intracranial hypertension may evolve despite a normal opening pressure; it furthermore shows that continuous monitoring of intracranial pressure may be used to predict changes in cerebral haemodynamics in critically ill patients with neuroinfection.

Poor agreement between transcranial Doppler and near-infrared spectroscopy-based estimates of cerebral blood flow changes in sepsis

BACKGROUND

Continuous monitoring of cerebral blood flow (CBF) may be valuable in critically ill patients with sepsis. In this study, we compared spatially resolved near-infrared spectroscopy (NIRS) to transcranial Doppler ultrasound (TCD)-derived estimates of noradrenaline-associated changes in CBF in such patients.

METHODS

Mean arterial blood pressure (MAP) was elevated by increasing the noradrenaline infusion rate in eight mechanically ventilated, critically ill patients diagnosed with severe sepsis or septic shock. The associated changes in CBF were assessed by simultaneous ipsilateral NIRS (ScO(2)) and TCD (middle cerebral artery blood flow velocity, MCAv) measurements.

RESULTS

A total of fifteen simultaneous NIRS- and TCD-derived assessments of noradrenaline-associated changes in CBF were obtained. MAP was increased from 74 (median; interquartile range (IQR), 71-90) to 100 (median; IQR, 93-115) mmHg (P<0·05), which was associated with an increase in MCAv of 14% (median; IQR, 2-22; P<0·05), whereas no changes were observed in ScO(2) ; 1% (median; IQR, [-4]-3; P = 0·96). A Bland-Altman plot was used to compare the two methods and showed a poor agreement between NIRS- and TCD-derived estimates with a relative bias of 14% and limits of agreement of -18% to 45% change in CBF.

CONCLUSION

Our findings stress that TCD and NIRS cannot be used interchangeably for monitoring changes in cerebral haemodynamics in critically ill patients with sepsis receiving vasopressor treatment with noradrenaline.

Lipopolysaccharide infusion enhances dynamic cerebral autoregulation without affecting cerebral oxygen vasoreactivity in healthy volunteers

INTRODUCTION

Sepsis may be associated with disturbances in cerebral oxygen transport and cerebral haemodynamic function, thus rendering the brain particularly susceptible to hypoxia. The purpose of this study was to assess the impact of isocapnic hypoxia and hyperoxia on dynamic cerebral autoregulation in a human-experimental model of the systemic inflammatory response during the early stages of sepsis.

METHODS

A total of ten healthy volunteers were exposed to acute isocapnic inspiratory hyperoxia (FIO₂ = 40%) and hypoxia (FIO₂ = 12%) before and after a 4-hour lipopolysaccharide (LPS) infusion (2 ng kg-1). Middle cerebral artery blood follow velocity was assessed using transcranial Doppler ultrasound, and dynamic autoregulation was evaluated by transfer function analysis.

RESULTS

Transfer function analysis revealed an increase in the phase difference between mean arterial blood pressure and middle cerebral artery blood flow velocity in the low frequency range (0.07-0.20 Hz) after LPS (P<0.01). In contrast, there were no effects of either isocapnic hyperoxia or hypoxia on dynamic autoregulation, and the cerebral oxygen vasoreactivity to both hyperoxia and hypoxia was unaffected by LPS.

CONCLUSIONS

The observed increase in phase suggests that dynamic cerebral autoregulation is enhanced after LPS infusion and resistant to any effects of acute hypoxia; this may protect the brain from ischaemia and/or blood-brain barrier damage during the early stages of sepsis.

Haemophilus influenzae type f meningitis in a previously healthy boy

Non-serotype b strains of Haemophilus influenzae are extremely rare causes of acute bacterial meningitis in immunocompetent individuals. We report a case of acute bacterial meningitis in a 14-year-old boy, who was previously healthy and had been immunised against H influenzae serotype b (Hib). The causative pathogen was identified as H influenzae serotype f (Hif), and was successfully treated with ceftriaxone. An immunological evaluation revealed transient low levels of immunoglobulins but no apparent immunodeficiency was found 2 years after the clinical insult.

Discrepant fibrinolytic response in plasma and whole blood during experimental endotoxemia in healthy volunteers

Background

Sepsis induces early activation of coagulation and fibrinolysis followed by late fibrinolytic shutdown and progressive endothelial damage. The aim of the present study was to investigate and compare the functional hemostatic response in whole blood and plasma during experimental human endotoxemia by the platelet function analyzer, Multiplate and by standard and modified thrombelastography (TEG).

Methods

Prospective physiologic study of nine healthy male volunteers undergoing endotoxemia by means of a 4-hour infusion of E. coli lipopolysaccharide (LPS, 0.5 ng/kg/hour), with blood sampled at baseline and at 4 h and 6 h. Physiological and standard biochemical data and coagulation tests, TEG (whole blood: TEG, heparinase-TEG, Functional Fibrinogen; plasma: TEG±tissue-type plasminogen activator (tPA)) and Multiplate (TRAPtest, ADPtest, ASPItest, COLtest) were recorded. Mixed models with Tukey post hoc tests and correlations were applied.

Results

Endotoxemia induced acute SIRS with increased HR, temperature, WBC, CRP and procalcitonin and decreased blood pressure. It also induced a hemostatic response with platelet consumption and reduced APTT while INR increased (all p<0.05). Platelet aggregation decreased (all tests, p<0.05), whereas TEG whole blood clot firmness increased (G, p = 0.05). Furthermore, during endotoxemia (4 h), whole blood fibrinolysis increased (clot lysis time (CLT), p<0.001) and Functional Fibrinogen clot strength decreased (p = 0.049). After endotoxemia (6 h), whole blood fibrinolysis was reduced (CLT, p<0.05). In contrast to findings in whole blood, the plasma fibrin clot became progressively more resistant towards tPA-induced fibrinolysis at both 4 h and 6 h (p<0.001).

Conclusions

Endotoxemia induced a hemostatic response with reduced primary but enhanced secondary hemostasis, enhanced early fibrinolysis and fibrinogen consumption followed by downregulation of fibrinolysis, with a discrepant fibrinolytic response in plasma and whole blood. The finding that blood cells are critically involved in the vasculo-fibrinolytic response to acute inflammation is important given that disturbances in the vascular system contribute significantly to morbidity and mortality in critically ill patients.

Disassociation of static and dynamic cerebral autoregulatory performance in healthy volunteers after lipopolysaccharide infusion and in patients with sepsis

Sepsis is frequently complicated by brain dysfunction, which may be associated with disturbances in cerebral autoregulation, rendering the brain susceptible to hypoperfusion and hyperperfusion. The purpose of the present study was to assess static and dynamic cerebral autoregulation 1) in a human experimental model of the systemic inflammatory response during early sepsis and 2) in patients with advanced sepsis. Cerebral autoregulation was tested using transcranial Doppler ultrasound in healthy volunteers (n = 9) before and after LPS infusion and in patients with sepsis (n = 16). Static autoregulation was tested by norepinephrine infusion and dynamic autoregulation by transfer function analysis (TFA) of spontaneous oscillations between mean arterial blood pressure and middle cerebral artery blood flow velocity in the low frequency range (0.07-0.20 Hz). Static autoregulatory performance after LPS infusion and in patients with sepsis was similar to values in healthy volunteers at baseline. In contrast, TFA showed decreased gain and an increased phase difference between blood pressure and middle cerebral artery blood flow velocity after LPS (both P < 0.01 vs. baseline); patients exhibited similar gain but lower phase difference values (P < 0.01 vs. baseline and LPS), indicating a slower dynamic autoregulatory response. Our findings imply that static and dynamic cerebral autoregulatory performance may disassociate in sepsis; thus static autoregulation was maintained both after LPS and in patients with sepsis, whereas dynamic autoregulation was enhanced after LPS and impaired with a prolonged response time in patients. Hence, acute surges in blood pressure may adversely affect cerebral perfusion in patients with sepsis.

Teaching baroreflex physiology to medical students: a comparison of quiz-based and conventional teaching strategies in a laboratory exercise

Quiz-based and collaborative teaching strategies have previously been found to be efficient for the improving meaningful learning of physiology during lectures. These approaches have, however, not been investigated during laboratory exercises. In the present study, we compared the impact of solving quizzes individually and in groups with conventional teaching on the immediate learning during a laboratory exercise. We implemented two quizzes in a mandatory 4-h laboratory exercise on baroreflex physiology. A total of 155 second-year medical students were randomized to solve quizzes individually (intervention group I, n = 57), in groups of three to four students (intervention group II, n = 56), or not to perform any quizzes (control; intervention group III, n = 42). After the laboratory exercise, all students completed an individual test, which encompassed two recall questions, two intermediate questions, and two integrated questions. The integrated questions were of moderate and advanced difficulty, respectively. Finally, students completed an evaluation form. Intervention group I reached the highest total test scores and proved best at answering the integrated question of advanced difficulty. Moreover, there was an overall difference between groups for student evaluations of the quality of the teaching, which was highest for intervention group II. In conclusion, solving quizzes individually during a laboratory exercise may enhance learning, whereas solving quizzes in groups is associated with higher student satisfaction.

Two cases of infectious purpura fulminans and septic shock caused by Capnocytophaga canimorsus transmitted from dogs

We report 2 cases of Capnocytophaga canimorsus-induced septicaemia complicated by purpura fulminans in previously healthy individuals, both of whom had been exposed to dog saliva prior to disease. They both presented with purpuric skin lesions, as well as the tetrad of abdominal symptoms, haemolytic anaemia, metabolic acidosis, and renal failure, which may be common in C. canimorsus-associated purpura fulminans. The patients survived after treatment with broad-spectrum antibiotics and supportive intensive care. C. canimorsus should be considered as a possible cause of infectious purpura fulminans in the unresolved critically ill patient with a history of dog exposure.

Effects of different angiotensins during acute, double blockade of the renin system in conscious dogs

Evidence of biological activity of fragments of ANG II is accumulating. Fragments considered being inactive degradation products might mediate actions previously attributed to ANG II. The study aimed to determine whether angiotensin fragments exert biological activity when administered in amounts equimolar to physiological doses of ANG II. Cardiovascular, endocrine, and renal effects of ANG II, ANG III, ANG IV, and ANG-(1-7) (6 pmol.kg-1.min-1) were investigated in conscious dogs during acute inhibition of angiotensin I-converting enzyme (enalaprilate) and aldosterone (canrenoate). Furthermore, ANG III was investigated by step-up infusion (30 and 150 pmol.kg-1.min-1). Arterial plasma concentrations [ANG immunoreactivity (IR)] were determined by an ANG II antibody cross-reacting with ANG III and ANG IV. Metabolic clearance rates were higher for ANG III and ANG IV (391 +/- 19 and 274 +/- 13 ml.kg-1.min-1, respectively) than for ANG II (107 +/- 13 ml.kg-1.min-1). ANG II increased ANG IR by 60 +/- 7 pmol/ml, blood pressure by 30%, increased plasma aldosterone markedly (to 345 +/- 72 pg/ml), and plasma vasopressin transiently, while reducing glomerular filtration rate (40 +/- 2 to 33 +/- 2 ml/min), sodium excretion (50 +/- 7 to 16 +/- 4 micromol/min), and urine flow. Equimolar amounts of ANG III induced similar antinatriuresis (57 +/- 8 to 19 +/- 3 micromol/min) and aldosterone secretion (to 268 +/- 71 pg/ml) at much lower ANG IR increments ( approximately 1/7) without affecting blood pressure, vasopressin, or glomerular filtration rate. The effects of ANG III exhibited complex dose-response relations. ANG IV and ANG-(1-7) were ineffective. It is concluded that 1) plasma clearances of ANG III and ANG IV are higher than those of ANG II; 2) ANG III is more potent than ANG II in eliciting immediate sodium and potassium retention, as well as aldosterone secretion, particularly at low concentrations; and 3) the complexity of the ANG III dose-response relationships provides indirect evidence that several effector mechanisms are involved.

Effects of truncated angiotensins in humans after double blockade of the renin system

Angiotensins different from ANG II exhibit biological activities, possibly mediated via receptors other than ANG II receptors. We studied the effects of 3-h infusions of ANG III, ANG-(1-7), and ANG IV in doses equimolar to physiological amounts of ANG II (3 pmol. kg-1. min-1), in six men on low-sodium diet (30 mmol/day). The subjects were acutely pretreated with canrenoate and captopril to inhibit aldosterone actions and ANG II synthesis, respectively. ANG II infusion increased plasma angiotensin immunoreactivity to 53 +/- 6 pg/ml (+490%), plasma aldosterone to 342 +/- 38 pg/ml (+109%), and blood pressure by 27%. Glomerular filtration rate decreased by 16%. Concomitantly, clearance of endogenous lithium fell by 66%, and fractional proximal reabsorption of sodium increased from 77 to 92%; absolute proximal reabsorption rate of sodium remained constant. ANG II decreased sodium excretion by 70%, potassium excretion by 50%, and urine flow by 80%, whereas urine osmolality increased. ANG III also increased plasma aldosterone markedly (+45%), however, without measurable changes in angiotensin immunoreactivity, glomerular filtration rate, or renal excretion rates. During vehicle infusion, plasma renin activity decreased markedly ( approximately 700 to approximately 200 mIU/l); only ANG II enhanced this decrease. ANG-(1-7) and ANG IV did not change any of the measured variables persistently. It is concluded that 1) ANG III and ANG IV are cleared much faster from plasma than ANG II, 2) ANG II causes hypofiltration, urinary concentration, and sodium and potassium retention at constant plasma concentrations of vasopressin and atrial natriuretic peptide, and 3) a very small increase in the concentration of ANG III, undetectable by usual techniques, may increase aldosterone secretion substantially.