Microcirculation Disorders in Patients with Severe COVID-19

Impaired microcirculation due to endothelial dysfunction in COVID-19 is considered to be the most important link in the pathogenesis of this disease. However, due to the complexity of its instrumental assessment in critically ill patients, the data available in the literature on specific manifestations of endothelial dysfunction are very contradictory.The objective: to determine the most characteristic capillaroscopic signs of microvascular disorders and to assess the state of microcirculation regulation in patients with severe COVID-19.Subjects and Methods. When admitted to the intensive care unit, 60 patients with COVID-19 and 12 patients with chronic cardiovascular pathology without COVID-19 (Comparison Group) were examined. All patients underwent microscopy of the microcirculatory bed of finger nail bed; the following parameters were assessed: diameters of the venous, arterial and transitional parts of capillaries, height of capillary loops, density of capillaries per 1 mm of the length of the perivascular zone, the average linear velocity of capillary blood flow (LVCBF), and thickness of the perivascular zone. The presence of avascular zones, the number of capillaries in the visualized field with circulating aggregates in the lumen, and the shape of capillaries were taken into account. In addition, an occlusion test using laser Doppler flowmetry was performed in 32 patients with COVID-19. The maximum post-occlusive increase in blood flow at the moment of cuff deflation was assessed, as well as changes in the mean value of post-occlusive blood flow relative to the baseline within 3 minutes after cuff deflation.Results. In 53 (88.3%) patients with COVID-19, abnormalities corresponding to chronic microcirculatory changes in the form of predominance of pathological capillary forms were detected. Microaggregates in the lumen of capillaries and decreased linear velocity of blood flow were revealed in 100% of cases. When comparing groups of patients with different outcomes, statistically significant differences were revealed between the LVCBF parameters (in the survivors - 354.35 ± 44.78 pm/sec, in the deceased - 278.4 ± 26.59 pm/sec), as well as between the values of the perivascular zones thickness (95.35 ± 15.96 microns versus 159.93 ± 19.90 microns). The results of the post-occlusion test revealed a significant difference between the groups in terms of the maximum post-occlusion gain (39.42 ± 3.85 BPU in the group with a favorable outcome, 27.69 ± 3.19 BPU in the group with an unfavorable outcome, 47.23 ± 1.78 BPU in the control group). In both groups, there was no increase in this parameter relative to the initial blood flow. At the same time, in the control group, the average index of post-occlusive blood flow was higher than the initial level.Conclusions. Acute microcirculation disorders with decreased linear velocity of capillary blood flow, circulation of aggregates, increased thickness of the perivascular zone were detected in all patients with severe COVID-19 but especially in those with unfavorable outcomes. Vascular tone regulation disorders were manifested by the absence of reactive hyperemia in response to acute ischemia, as well as a decrease in maximal flow-induced increase. These changes fit into the concept of endothelial dysfunction. Signs of chronic microcirculation disorders in most patients increase the risk of severe COVID-19.

Management of tracheostomies in the intensive care unit: a scoping review

ObjectivesWhile there is an extensive body of literature surrounding the decision to insert, and methods for inserting, a tracheostomy, the optimal management of tracheostomies within the intensive care unit (ICU) from after insertion until ICU discharge is not well understood. The objective was to identify and map the key concepts relating to, and identify research priorities for, postinsertion management of adult patients with tracheostomies in the ICU.DesignScoping review of the literature.Data sourcesPubMed, Embase and Cumulative Index to Nursing and Allied Health Literature were searched from inception to 3 October 2019. Additional sources were searched for published and unpublished literature.Eligibility criteriaWe included studies of any methodology that addressed the a priori key questions relating to tracheostomy management in the ICU. No restrictions were placed on language or year of publication.Data extraction and synthesisTitles and abstracts were screened by two reviewers. Studies that met inclusion criteria were reviewed in full by two reviewers, with discrepancies resolved by a third. Data were extracted for included studies, and results mapped along the prespecified research questions.Results6132 articles were screened, and 102 articles were included for detailed analysis. Protocolised weaning was found to be successful in liberating patients from the ventilator in several cohort studies. Observational studies showed that strategies that use T-pieces and high-flow oxygen delivery improve weaning success. Several lines of evidence, including one clinical trial, support early cuff deflation as a safe and effective strategy as it results in a reduced time to wean, shorter ICU stays and fewer complications. Early tracheostomy downsizing and/or switching to cuffless tubes was found to be of benefit in one study. A substantial body of evidence supports the use of speaking valves to facilitate communication. While this does not influence time to wean or incidence of complications, it is associated with a major benefit in patient satisfaction and experience. Use of care bundles and multidisciplinary team approaches have been associated with reduced complications and improved outcomes in several observational studies.ConclusionsThe limited body of evidence supports use of weaning protocols, early cuff deflation, use of speaking valves and multidisciplinary approaches. Clinical trials examining post-tracheostomy management strategies in ICUs are a priority.

Inflight leg cuff test does not identify the risk for orthostatic hypotension after long-duration spaceflight

Landing day symptoms from orthostatic hypotension after prolonged spaceflight can be debilitating, but severity of these symptoms can be unpredictable and highly individual. We tested the hypothesis that an impaired baroreflex response to an inflight leg cuff test could predict orthostatic intolerance on return to Earth. Eight male astronauts (44 ± 7 years of age (mean ± SD); mean mission length: 167 ± 12 days) participated in a standardized supine-to-sit-to-stand test (5 min–30s–3 min) pre- and postflight, and a 3 min thigh cuff occlusion test pre- and inflight with continuous monitoring of heart rate and arterial blood pressure. The arterial baroreflex was not changed inflight as shown by similar reductions in mean arterial pressure (MAP) response to leg cuff deflation (preflight −19 ± 2 mmHg vs. inflight −18 ± 5 mmHg). With the sit/stand test, the nadir of MAP was lower postflight (−17 ± 9 mmHg) than preflight (−11 ± 6 mmHg, p < 0.05). A greater increase in heart rate (25 ± 7; 16 ± 3 bpm) and decrease in stroke volume (−24 ± 11; −6 ± 4 mL) occurred with sit/stand postflight than leg cuffs inflight (p < 0.001). Inflight testing was influenced by elevated cardiac output resulting in a smaller drop in total peripheral resistance. Two of eight subjects exhibited orthostatic hypotension during the postflight stand test; their responses were not predicted by the inflight leg cuff deflation test. These results suggest that the baroreflex response examined by inflight leg cuff deflation was not a reliable indicator of postflight stand responses.

Blood flow in the brachial artery compressed by a cuff

Most non-invasive blood pressure measurements are based on the blood flow during the arm cuff deflation. In this paper, the measurement system for an investigation of a blood flow in the partially occluded brachial artery is presented. It allows us to record simultaneously the cuff pressure, Korotkoff sounds and the blood flow during the arm cuff deflation. The algorithms developed for digital processing of the recorded signals are described in detail. The results of analysis obtained for healthy subjects are presented and discussed.