Microcirculatory Effects of Selective Receptor Blockade During Hemorrhagic Shock Treatment With Vasopressin: Experimental Study in the Hamster Dorsal Chamber

Effects of Vasopressin Receptor Agonists during the Resuscitation of Hemorrhagic Shock: A Systematic Review and Meta-Analysis of Experimental and Clinical Studies

BACKGROUND

The clinical impact of vasopressin in hemorrhagic shock remains largely unknown.

OBJECTIVE

This systematic review and meta-analysis was designed to investigate the effects of vasopressin receptor agonists during the resuscitation of hemorrhagic shock.

METHODS

A systematic search of PubMed (MEDLINE), Scopus, and PubMed Central was conducted for relevant articles. Experimental (animal) and clinical studies were included. The primary objective was to investigate the correlation of vasopressin receptor agonist use with mortality and various hemodynamic parameters.

RESULTS

Data extraction was possible in thirteen animal studies and two clinical studies. Differences in risk of mortality between patients who received a vasopressin receptor agonist were not statistically significant when compared to those who were not treated with such agents [RR (95% CI): 1.17 (0.67, 2.08); p = 0.562; I² = 50%]. The available data were insufficient to conduct a meta-analysis assessing the effect of vasopressin receptor agonists on hemodynamics. Drawing safe conclusions from animal studies was challenging, due to significant heterogeneity in terms of species and dosage of vasopressin receptor agonists among studies.

CONCLUSIONS

Differences in risk of mortality between patients who received a vasopressin receptor agonist were not statistically significant when compared to those who were not treated with such agents after hemorrhagic shock. More data are needed to deduce certain conclusions.

Therapeutic interventions to restore microcirculatory perfusion following experimental hemorrhagic shock and fluid resuscitation: A systematic review

Objective

Microcirculatory perfusion disturbances following hemorrhagic shock and fluid resuscitation contribute to multiple organ dysfunction and mortality. Standard fluid resuscitation is insufficient to restore microcirculatory perfusion; however, additional therapies are lacking. We conducted a systematic search to provide an overview of potential non‐fluid‐based therapeutic interventions to restore microcirculatory perfusion following hemorrhagic shock.

Methods

A structured search of PubMed, EMBASE, and Cochrane Library was performed in March 2020. Animal studies needed to report at least one parameter of microcirculatory flow (perfusion, red blood cell velocity, functional capillary density).

Results

The search identified 1269 records of which 48 fulfilled all eligibility criteria. In total, 62 drugs were tested of which 29 were able to restore microcirculatory perfusion. Particularly, complement inhibitors (75% of drugs tested successfully restored blood flow), endothelial barrier modulators (100% successful), antioxidants (66% successful), drugs targeting cell metabolism (83% successful), and sex hormones (75% successful) restored microcirculatory perfusion. Other drugs consisted of attenuation of inflammation (100% not successful), vasoactive agents (68% not successful), and steroid hormones (75% not successful).

Conclusion

Improving mitochondrial function, inhibition of complement inhibition, and reducing microvascular leakage via restoration of endothelial barrier function seem beneficial to restore microcirculatory perfusion following hemorrhagic shock and fluid resuscitation.

Dissociation between macro- and microvascular parameters in the early phase of hemorrhagic shock

Hemorrhagic shock (HS) therapy is based on macrohemodynamic improvement, but it is not clear if this therapy correlates directly with increases in tissue perfusion. Aiming to clarify this point, we compared norepinephrine (NE, a vasoconstrictor), sodium nitroprusside (NP, a vasodilator) and levosimendan (LEV, an inodilator) treatments on macro and microvascular parameters using the hamster dorsal skinfold chamber preparation. One hour after HS, animals received Ringer's lactate (RL) solution within 10 min, then animals received RL, NP, NE and LEV during 90 min via jugular vein. Macrovascular variables: mean arterial pressure (MAP), heart rate (HR), maximal ventricle pressure (MVP), change in ventricular pressure over time (dP/dt) and microvascular variables: arteriolar and venular diameters, functional capillary density (FCD) and red blood cell velocity (RBCV) were evaluated at baseline, 60 min after HS, 60 and 90 min after treatments. Lactate blood concentrations were evaluated at baseline, 60 min after HS and 90 min after treatments. Hematocrit (Hct), cardiac output (CO), stroke volume (SV) and number of rolling and adhered leukocytes were assessed at 90 min after treatments. Data were considered significant when p < 0.05. NE increased significantly all macrohemodynamic variables compared to baseline (except MAP), and it was the only treatment that increased Hct, CO and SV significantly. NE decreased significantly all microvascular variables in comparison to baseline. NP increased HR, FCD and RBCV and reduced MVP and dP/dt significantly. LEV decreased MVP and dP/dt, arteriolar diameter and FCD and augmented RBCV significantly in comparison to baseline. Blood concentration of lactate increased significantly 60 min after HS. Leukocyte rolling and adhesion were not different between groups. We concluded that, early, during hemorrhagic shock, norepinephrine associated to fluid therapy improved macrohemodynamic parameters but failed to improved microvascular flow. Conversely, sodium nitroprusside association had the opposite effect. Despite its inodilator properties, levosimendan did not improve macro or microhemodynamic parameters when combined to fluid therapy.

Hemorrhagic Shock and the Microvasculature

The microvasculature plays a central role in the pathophysiology of hemorrhagic shock and is also involved in arguably all therapeutic attempts to reverse or minimize the adverse consequences of shock. Microvascular studies specific to hemorrhagic shock were reviewed and broadly grouped depending on whether data were obtained on animal or human subjects. Dedicated sections were assigned to microcirculatory changes in specific organs, and major categories of pathophysiological alterations and mechanisms such as oxygen distribution, ischemia, inflammation, glycocalyx changes, vasomotion, endothelial dysfunction, and coagulopathy as well as biomarkers and some therapeutic strategies. Innovative experimental methods were also reviewed for quantitative microcirculatory assessment as it pertains to changes during hemorrhagic shock. The text and figures include representative quantitative microvascular data obtained in various organs and tissues such as skin, muscle, lung, liver, brain, heart, kidney, pancreas, intestines, and mesentery from various species including mice, rats, hamsters, sheep, swine, bats, and humans. Based on reviewed findings, a new integrative conceptual model is presented that includes about 100 systemic and local factors linked to microvessels in hemorrhagic shock. The combination of systemic measures with the understanding of these processes at the microvascular level is fundamental to further develop targeted and personalized interventions that will reduce tissue injury, organ dysfunction, and ultimately mortality due to hemorrhagic shock. Published 2018. Compr Physiol 8:61-101, 2018.

Trauma-Related Critical Care

BACKGROUND

Post-trauma resuscitation has evolved based on civilian and wartime experiences over the last decade. Similarly, data from large multicenter randomized trials have changed the management of critically ill trauma patients in the intensive care unit.

METHODS

This is a review of the literature focusing on areas relevant to the management of trauma patients in the intensive care unit.

RESULTS

The following topics are included: (1) ventilator management, (2) trauma sepsis, (3) use of vasopressors in hemorrhage, (4) glucose control, (5) nutrition, and (6) hemodynamic monitoring.

CONCLUSION

This review demonstrated the most recent data of trauma-related critical care. Further studies will be needed to settle growing controversies in the management of critically injured patients.