Changes in kidney perfusion and renal cortex metabolism in septic shock: an experimental study

Endothelial Glycocalyx

The endothelial glycocalyx (EG) is the most luminal layer of the blood vessel, growing on and within the vascular wall. Shedding of the EG plays a central role in many critical illnesses. Degradation of the EG is associated with increased morbidity and mortality. Certain illnesses and iatrogenic interventions can cause degradation of the EG. It is not known whether restitution of the EG promotes the survival of the patient. First trials that focus on the reorganization and/or restitution of the EG seem promising. Nevertheless, the step "from bench to bedside" is still a big one.

Molecular nephrology: types of acute tubular injury

The acute loss of kidney function has been diagnosed for many decades using the serum concentration of creatinine - a muscle metabolite that is an insensitive and non-specific marker of kidney function, but is now used for the very definition of acute kidney injury (AKI). Fortunately, myriad new tools have now been developed to better understand the relationship between acute tubular injury and elevation in serum creatinine (SCr). These tools include unbiased gene and protein expression analyses in kidney, urine and blood, the localization of specific gene transcripts in pathological biopsy samples by rapid in-situ RNA technology and single-cell RNA-sequencing analyses. However, this molecular approach to AKI has produced a series of unexpected problems, because the expression of specific kidney-derived molecules that are indicative of injury often do not correlate with SCr levels. This discrepancy between kidney injury markers and SCr level can be reconciled by the recognition that many separate subtypes of AKI exist, each with distinct patterning of molecular markers of tubular injury and SCr data. In this Review, we describe the weaknesses of isolated SCr-based diagnoses, the clinical and molecular subtyping of acute tubular injury, and the role of non-invasive biomarkers in clinical phenotyping. We propose a conceptual model that synthesizes molecular and physiological data along a time course spanning from acute cellular injury to organ failure.

Peripheral Muscle Near-Infrared Spectroscopy Variables are Altered Early in Septic Shock

BACKGROUND

Noninvasive evaluation of muscle perfusion using near-infrared spectroscopy (NIRS) coupled with a vascular occlusion test (VOT) may provide an early and simple marker of altered perfusion and microcirculatory function in sepsis.

OBJECTIVE

The aim of the study was to compare the time-course of NIRS-derived variables with systemic measures of perfusion in an experimental model of peritonitis.

METHODS

Peritonitis was induced in eight anesthetized, mechanically ventilated, adult sheep (24-34 kg), by injecting autologous feces into the peritoneal cavity. Animals were followed until death or for a maximum of 30 h. Muscle tissue oxygen saturation (StO2) was determined using NIRS on the right posterior leg and arterial VOTs were performed by intermittent intra-aortic balloon inflation. Microdialysis was used to measure muscle lactate and pyruvate levels.

RESULTS

Muscle StO2 was significantly lower than baseline values from 8 h after sepsis induction, but with considerable intersubject variability. The NIRS VOT ascending (Asc) slope decreased to values <120%/min in most animals from 12 h after sepsis induction. Muscle lactate/pyruvate ratios were higher than baseline from 16 h after sepsis induction. Mixed venous oxygen saturation (SvO2) decreased to <70% and blood lactate levels increased to >2 mmol/L in most of the animals only 24 and 28 h after sepsis induction, respectively. Muscle NIRS StO2 correlated strongly with femoral venous oxygen saturation (r = 0.820) and moderately with SvO2 (r = 0.436).

CONCLUSIONS

The muscle NIRS Asc slope after a VOT is altered earlier than global markers of tissue hypoperfusion during sepsis. This simple noninvasive test can detect early changes in peripheral perfusion in sepsis.

Renal autoregulation in experimental septic shock and its response to vasopressin and norepinephrine administration

Evidence suggests that septic shock patients with chronic arterial hypertension may benefit from resuscitation targeted to achieve higher blood pressure values than other patients, possibly as a result of altered renal autoregulation. The effects of different vasopressor agents on renal autoregulation may be important in this context. We investigated the effects of arginine vasopressin (AVP) and norepinephrine (NE) on renal autoregulation in ovine septic shock. Sepsis was induced by fecal peritonitis. When shock developed (decrease in mean arterial pressure to <65 mmHg and no fluid-responsiveness), animals were randomized to receive NE or AVP in a crossover design. Before the switch to the second vasopressor, the first vasopressor was discontinued for 30 minutes to ensure complete washout of the first vasopressor. Renal autoregulation was evaluated by recording the change in renal blood flow (RBF) in response to manual, stepwise reductions in renal inflow pressure. In this model, the lower limit of renal autoregulation was not significantly altered 6 hours after sepsis induction (59±9 vs. 64±7 mmHg at baseline, p=0.096). After development of shock, the autoregulatory threshold was lower with AVP than with NE (59±5 vs. 65±7 mmHg, p=0.010). However, RBF was higher with NE both at the start of autoregulatory measurements (206±58 vs. 170±52 mL/min; p=0.050) and at the autoregulatory threshold (191±53 vs. 150±47 mL/min; p=0.008). As vasopressors may have different effects on renal autoregulation, blood pressure management in patients with septic shock should be individualized and take into account drug-specific effects.

The effects of acute renal denervation on kidney perfusion and metabolism in experimental septic shock

BACKGROUND

Perfusion deficits likely play an important role in the development of renal dysfunction in sepsis. Renal denervation may improve kidney perfusion and metabolism.

METHODS

We randomized 14 female sheep to undergo bilateral surgical renal denervation (n = 7) or sham procedure (n = 7) prior to induction of sepsis. Renal blood flow (RBF) was measured with a pre-calibrated flowprobe. Laser Doppler probes were implanted to measure cortical and medullary perfusion. Cortical glucose, lactate and pyruvate levels were measured using the microdialysis technique. Creatinine clearance was determined. Sepsis was induced by peritonitis and fluid resuscitation was provided to avoid hypovolemia.

RESULTS

RBF and cortical perfusion were higher in the denervated group during the first 6 h after induction of sepsis (P < 0.001 and P < 0.05, respectively), while medullary perfusion decreased similarly in both groups. After hypotension developed, RBF decreased to similar levels in both groups. Cortical pyruvate and lactate levels were lower in the denervated animals (P < 0.001 and P < 0.001, respectively). There were no differences between groups in creatinine clearance, urine output or time to oliguria.

CONCLUSION

Denervation thus caused an early increase in RBF that was distributed towards the kidney cortex. Although associated with an attenuation of early cortical metabolic alterations, denervation failed to prevent the deterioration in renal function.