Microcirculatory Function during Endotoxemia—A Functional Citrulline-Arginine-NO Pathway and NOS3 Complex Is Essential to Maintain the Microcirculation

Competition for the amino acid arginine by endothelial nitric-oxide synthase (NOS3) and (pro-)inflammatory NO-synthase (NOS2) during endotoxemia appears essential in the derangement of the microcirculatory flow. This study investigated the role of NOS2 and NOS3 combined with/without citrulline supplementation on the NO-production and microcirculation during endotoxemia. Wildtype (C57BL6/N background; control; n = 36), Nos2-deficient, (n = 40), Nos3-deficient (n = 39) and Nos2/Nos3-deficient mice (n = 42) received a continuous intravenous LPS infusion alone (200 μg total, 18 h) or combined with L-citrulline (37.5 mg, last 6 h). The intestinal microcirculatory flow was measured by side-stream dark field (SDF)-imaging. The jejunal intracellular NO production was quantified by in vivo NO-spin trapping combined with electron spin-resonance (ESR) spectrometry. Amino-acid concentrations were measured by high-performance liquid chromatography (HPLC). LPS infusion decreased plasma arginine concentration in control and Nos3−/−compared to Nos2−/−mice. Jejunal NO production and the microcirculation were significantly decreased in control and Nos2−/−mice after LPS infusion. No beneficial effects of L-citrulline supplementation on microcirculatory flow were found in Nos3−/−or Nos2−/−/Nos3−/−mice. This study confirms that L-citrulline supplementation enhances de novo arginine synthesis and NO production in mice during endotoxemia with a functional NOS3-enzyme (control and Nos2−/−mice), as this beneficial effect was absent in Nos3−/−or Nos2−/−/Nos3−/−mice.

Sublingual microcirculatory alterations during the immediate and early postoperative period: A systematic review and meta-analysis

BACKGROUND: The incidence of postoperative microcirculatory flow alterations and their effect on outcome have not been studied extensively. OBJECTIVE: This systematic review and meta-analysis was designed to investigate the presence of sublingual microcirculatory flow alterations during the immediate and early postoperative period and their correlation with complications and survival. METHODS: A systematic search of PubMed, Scopus, Embase, PubMed Central, and Google Scholar was conducted for relevant articles from January 2000 to March 2021. Eligibility criteria were randomized controlled and non-randomized trials. Case reports, case series, review papers, animal studies and non-English literature were excluded. The primary outcome was the assessment of sublingual microcirculatory alterations during the immediate and early postoperative period in adult patients undergoing surgery. Risk of bias was assessed with the Ottawa-Newcastle scale. Standard meta-analysis methods (random-effects models) were used to assess the difference in microcirculation variables. RESULTS: Thirteen studies were included. No statistically significant difference was found between preoperative and postoperative total vessel density (p = 0.084; Standardized Mean Difference (SMD): –0.029; 95%CI: –0.31 to 0.26; I2 = 22.55%). Perfused vessel density significantly decreased postoperatively (p = 0.035; SMD: 0.344; 95%CI: 0.02 to 0.66; I2 = 65.66%), while perfused boundary region significantly increased postoperatively (p = 0.031; SMD: –0.415; 95%CI: –0.79 to –0.03; I2 = 37.21%). Microvascular flow index significantly decreased postoperatively (p = 0.028; SMD: 0.587; 95%CI: 0.06 to 1.11; I2 = 86.09%), while no statistically significant difference was found between preoperative and postoperative proportion of perfused vessels (p = 0.089; SMD: 0.53; 95%CI: –0.08 to 1.14; I2 = 70.71%). The results of the non-cardiac surgery post-hoc analysis were comparable except that no statistically significant difference in perfused vessel density was found (p = 0.69; SMD: 0.07; 95%CI: –0.26 to 0.39; I2 = 0%). LIMITATIONS: The included studies investigate heterogeneous groups of surgical patients. There were no randomized controlled trials. CONCLUSIONS: Significant sublingual microcirculatory flow alterations are present during the immediate and early postoperative period. Further research is required to estimate the correlation of sublingual microcirculatory flow impairment with complications and survival.

Does the Age of Packed Red Blood Cells, Donor Sex or Sex Mismatch Affect the Sublingual Microcirculation in Critically Ill Intensive Care Unit Patients? — A Secondary Interpretation of a Retrospective Analysis

BackgroundIn vitro studies have thoroughly documented the impact of storage lesions in packed red blood cells (pRBC) on erythrocyte oxygen carrying capacity due to older age of blood products. While studies have examined the effect of pRBC age on patient outcome, only few data exist on the microcirculation, their primary site of action.MethodsIn this secondary analysis, we examined the relationship between the age of pRBC and changes of microcirculatory flow (MCF) in 54 patients. Data from the Basel Bedside assessment Microcirculation Transfusion Limit study (Ba2MiTraL), investigating the effects of one pRBC on the sublingual MCF provided the basis of this study. ResultsMean change from pre-to post-transfusion proportion of perfused vessels (∆PPV) was +8.8% (IQR: -0.5 – 22.5), 5.5% (IQR: 0.1–10.1), and +4.7% (IQR: -2.1 – 6.5) after transfusion of fresh (≤ 14 days old), medium (15 to 34 days old), and old (≥ 35 days old) pRBC, respectively. Values for the microcirculatory flow index (MFI) were +0.22 (IQR: -0.1 – 0.6), +0.22 (IQR: 0.0 – 0.3), and +0.06 (IQR: -0.1 – 0.3) for the fresh, medium, and old pRBC age groups, respectively.Lower ∆PPV and transfusion of older blood were correlated with a higher Sequential Organ Failure Assessment (SOFA) score of patients upon admission to the intensive care unit (ICU) (p=0.01). However, regression models showed no overall significant correlation between pRBC age and ∆PPV (p=0.2). No correlation between donor’s sex or a mismatch between donor and recipient sex was found.ConclusionWe detected no significant correlation between age of pRBC and change in MCF between pre- and post-transfusion among all investigated patients. However, in patients with a higher SOFA score upon ICU admission, there might be a negative effect on the proportion of perfused microcirculatory vessels after transfusion of older blood.

Effects of remote ischemic conditioning on microcirculatory alterations in patients with sepsis: a single-arm clinical trial

Background Remote ischemic conditioning (RIC) is a promising technique that may protect organs and tissues from the effects of additional ischemic episodes. However, the therapeutic efficacy of RIC in humans with sepsis remains unknown. We hypothesized that RIC might improve sublingual microcirculation in patients with sepsis. Methods This prospective single-arm trial was performed in a mixed ICU at a tertiary teaching hospital. We included patients with sepsis or septic shock within 24 h of ICU admission. The RIC procedure comprised 3 cycles of brachial cuff inflation to 200 mmHg for 5 min followed by deflation to 0 mmHg for another 5 min. The procedure took 30 min. RIC was performed at the time of study inclusion and repeated after 12 and 24 h. Sublingual microcirculatory measurements were obtained before and after each RIC procedure using a Cytocam®-incident dark-field (IDF) device (Braedius Medical, Huizen, The Netherlands). The microcirculatory data were compared with a historical control. Data are reported as the medians along with the 25th and 75th percentiles. Results Twenty-six septic patients with a median age of 65 (57–81) years were enrolled in this study. The median Acute Physiology and Chronic Health Evaluation (APACHE) II and Sequential Organ Failure Assessment (SOFA) scores at admission were 20 (13–23) and 10 (9–12), respectively. All patients were receiving vasopressors. After the 1st RIC procedure, the microvascular flow index (MFI) and the proportion of perfused vessels (PPV) among small vessels were significantly higher than before the procedure, with pre- and post-treatment values of 2.17 (1.81–2.69) and 2.59 (2.21–2.83), respectively, for MFI (p = 0.003) and 87.9 (82.4–93.8) and 92.5 (87.9–96.1) %, respectively, for PPV (p = 0.026). This result was confirmed by comparison with a historical control group. We found no change in microcirculatory flow or density parameters during repeated RIC after 12 h and 24 h. Conclusion In patients with sepsis, the first remote ischemic conditioning procedure improved microcirculatory flow, whereas later procedures did not affect sublingual microcirculation. Trial registration NCT04644926, http://www.clinicaltrials.gov. Date of registration: 25 November 2020. Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT04644926.

Effects of capillary refill time-vs. lactate-targeted fluid resuscitation on regional, microcirculatory and hypoxia-related perfusion parameters in septic shock: a randomized controlled trial

Background Persistent hyperlactatemia has been considered as a signal of tissue hypoperfusion in septic shock patients, but multiple non-hypoperfusion-related pathogenic mechanisms could be involved. Therefore, pursuing lactate normalization may lead to the risk of fluid overload. Peripheral perfusion, assessed by the capillary refill time (CRT), could be an effective alternative resuscitation target as recently demonstrated by the ANDROMEDA-SHOCK trial. We designed the present randomized controlled trial to address the impact of a CRT-targeted (CRT-T) vs. a lactate-targeted (LAC-T) fluid resuscitation strategy on fluid balances within 24 h of septic shock diagnosis. In addition, we compared the effects of both strategies on organ dysfunction, regional and microcirculatory flow, and tissue hypoxia surrogates. Results Forty-two fluid-responsive septic shock patients were randomized into CRT-T or LAC-T groups. Fluids were administered until target achievement during the 6 h intervention period, or until safety criteria were met. CRT-T was aimed at CRT normalization (≤ 3 s), whereas in LAC-T the goal was lactate normalization (≤ 2 mmol/L) or a 20% decrease every 2 h. Multimodal perfusion monitoring included sublingual microcirculatory assessment; plasma-disappearance rate of indocyanine green; muscle oxygen saturation; central venous-arterial pCO2 gradient/ arterial-venous O2 content difference ratio; and lactate/pyruvate ratio. There was no difference between CRT-T vs. LAC-T in 6 h-fluid boluses (875 [375–2625] vs. 1500 [1000–2000], p = 0.3), or balances (982[249–2833] vs. 15,800 [740–6587, p = 0.2]). CRT-T was associated with a higher achievement of the predefined perfusion target (62 vs. 24, p = 0.03). No significant differences in perfusion-related variables or hypoxia surrogates were observed. Conclusions CRT-targeted fluid resuscitation was not superior to a lactate-targeted one on fluid administration or balances. However, it was associated with comparable effects on regional and microcirculatory flow parameters and hypoxia surrogates, and a faster achievement of the predefined resuscitation target. Our data suggest that stopping fluids in patients with CRT ≤ 3 s appears as safe in terms of tissue perfusion. Clinical Trials: ClinicalTrials.gov Identifier: NCT03762005 (Retrospectively registered on December 3rd 2018)

Resuscitation with PEGylated carboxyhemoglobin preserves renal cortical oxygenation and improves skeletal muscle microcirculatory flow during endotoxemia

PEGylated carboxyhemoglobin (PEGHbCO), which has carbon monoxide-releasing properties and plasma expansion and oxygen-carrying properties, may improve both skeletal microcirculatory flow and renal cortical microcirculatory Po2 (CµPo2) and, subsequently, limit endotoxemia-induced acute kidney injury. Anesthetized, ventilated Wistar albino rats ( n = 44) underwent endotoxemic shock. CµPo2 was measured in exposed kidneys using a phosphorescence-quenching method. Rats were randomly assigned to the following five groups: 1) unresuscitated lipopolysaccharide (LPS), 2) LPS + Ringer’s acetate (RA), 3) LPS + RA + 0.5 µg·kg·−1min−1 norepinephrine (NE), 4) LPS + RA + 320 mg/kg PEGHbCO, and 5) LPS + RA + PEGHbCO + NE. The total volume was 30 mL/kg in each group. A time control animal group was used. Skeletal muscle microcirculation was assessed by handheld intravital microscopy. Kidney immunohistochemistry and myeloperoxidase-stained leukocytes in glomerular and peritubular areas were analyzed. Endotoxemia-induced histological damage was assessed. Plasma levels of IL-6, heme oxygenase-1, malondialdehyde, and syndecan-1 were assessed by ELISA. CµPo2 was higher in the LPS + RA + PEGHbCO-resuscitated group, at 35 ± 6mmHg compared with 21 ± 12 mmHg for the LPS+RA group [mean difference: −13.53, 95% confidence interval: (−26.35; −0.7156), P = 0.035]. The number of nonflowing, intermittent, or sluggish capillaries was smaller in groups infused with PEGHbCO compared with RA alone ( P < 0.05), while the number of normally perfused vessels was greater ( P < 0.05). The addition of NE did not further improve CµPo2 or microcirculatory parameters. Endotoxemia-induced kidney immunohistochemistry and histological alterations were not mitigated by PEGHbCO 1 h after resuscitation. Renal leukocyte infiltration and plasma levels of biomarkers were similar across groups. PEGHbCO enhanced CµPo2 while restoring skeletal muscle microcirculatory flow in previously nonflowing capillaries. PEGHbCO should be further evaluated as a resuscitation fluid in mid- to long-term models of sepsis-induced acute kidney injury.