Potential biomarkers of tissue hypoxia during acute hemodilutional anemia in cardiac surgery: A prospective study to assess tissue hypoxia as a mechanism of organ injury

Bilateral nephrectomy impairs cardiovascular function and cerebral perfusion in a rat model of acute hemodilutional anemia

Anemia and renal failure are independent risk factors for perioperative stroke, prompting us to assess the combined impact of acute hemodilutional anemia and bilateral nephrectomy (2Nx) on microvascular brain Po2 (PBro2) in a rat model. Changes in PBro2 (phosphorescence quenching) and cardiac output (CO, echocardiography) were measured in different groups of anesthetized Sprague-Dawley rats (1.5% isoflurane, n = 5-8/group) randomized to Sham 2Nx or 2Nx and subsequently exposed to acute hemodilutional anemia (50% estimated blood volume exchange with 6% hydroxyethyl starch) or time-based controls (no hemodilution). Outcomes were assessed by ANOVA with significance assigned at P < 0.05. At baseline, 2Nx rats demonstrated reduced CO (49.9 ± 9.4 vs. 66.3 ± 19.3 mL/min; P = 0.014) and PBro2 (21.1 ± 2.9 vs. 32.4 ± 3.1 mmHg; P < 0.001) relative to Sham 2Nx rats. Following hemodilution, 2Nx rats demonstrated a further decrease in PBro2 (15.0 ± 6.3 mmHg, P = 0.022). Hemodiluted 2Nx rats did not demonstrate a comparable increase in CO after hemodilution compared with Sham 2Nx (74.8 ± 22.4 vs. 108.9 ± 18.8 mL/min, P = 0.003) that likely contributed to the observed reduction in PBro2. This impaired CO response was associated with reduced fractional shortening (33 ± 9 vs. 51 ± 5%) and increased left ventricular end-systolic volume (156 ± 51 vs. 72 ± 15 µL, P < 0.001) suggestive of systolic dysfunction. By contrast, hemodiluted Sham 2Nx animals demonstrated a robust increase in CO and preserved PBro2. These data support the hypothesis that the kidney plays a central role in maintaining cerebral perfusion and initiating the adaptive increase in CO required to optimize PBro2 during acute anemia.NEW & NOTEWORTHY This study has demonstrated that bilateral nephrectomy acutely impaired cardiac output (CO) and microvascular brain Po2 (PBro2), at baseline. Following acute hemodilution, nephrectomy prevented the adaptive increase in CO associated with acute hemodilution leading to a further reduction in PBro2, accentuating the degree of cerebral tissue hypoxia. These data support a role for the kidney in maintaining PBro2 and initiating the increase in CO that optimized brain perfusion during acute anemia.

Alternative blood transfusion triggers: a narrative review

BACKGROUND

Anemia, characterized by low hemoglobin levels, is a global public health concern. Anemia is an independent factor worsening outcomes in various patient groups. Blood transfusion has been the traditional treatment for anemia; its triggers, primarily based on hemoglobin levels; however, hemoglobin level is not always an ideal trigger for blood transfusion. Additionally, blood transfusion worsens clinical outcomes in certain patient groups. This narrative review explores alternative triggers for red blood cell transfusion and their physiological basis.

MAIN TEXT

The review delves into the physiology of oxygen transport and highlights the limitations of using hemoglobin levels alone as transfusion trigger. The main aim of blood transfusion is to optimize oxygen delivery, necessitating an individualized approach based on clinical signs of anemia and the balance between oxygen delivery and consumption, reflected by the oxygen extraction rate. The narrative review covers different alternative triggers. It presents insights into their diagnostic value and clinical applications, emphasizing the need for personalized transfusion strategies.

CONCLUSION

Anemia and blood transfusion are significant factors affecting patient outcomes. While restrictive transfusion strategies are widely recommended, they may not account for the nuances of specific patient populations. The search for alternative transfusion triggers is essential to tailor transfusion therapy effectively, especially in patients with comorbidities or unique clinical profiles. Investigating alternative triggers not only enhances patient care by identifying more precise indicators but also minimizes transfusion-related risks, optimizes blood product utilization, and ensures availability when needed. Personalized transfusion strategies based on alternative triggers hold the potential to improve outcomes in various clinical scenarios, addressing anemia's complex challenges in healthcare. Further research and evidence are needed to refine these alternative triggers and guide their implementation in clinical practice.

Preoperative moderate to severe anemia is associated with increased postoperative major adverse cardiac and cerebral events and pulmonary complications: a propensity score-matched analysis in hip fracture surgery patients over 80 years old

BACKGROUND

Anemia is a common health problem in the elderly. Preoperative anemia is a risk factor for postoperative outcomes in the elderly for hip fracture. The objective of the study was to explore the relationship between preoperative moderate to severe anemia and postoperative morbidity and mortality in hip fracture patients over 80 years old.

METHODS

We performed a retrospective cohort study exploring preoperative moderate to severe anemia and postoperative morbidity and mortality. Patients over 80 years old undergoing hip fracture surgery were included in the study. Data were collected for major adverse cardiac and cerebral events (MACCE), postoperative pulmonary complications (PPCs), in-hospital mortality, delirium, gastrointestinal complication, deep venous thrombus (DVT), acute renal failure, ICU admission, and perioperative transfusion > 2 units rate.

RESULTS

A total of 912 eligible patients were included for unmatched cohort analysis, and 512 patients were included for matched cohort analysis after propensity score matching. Baseline characteristics between the normal to mild anemia and moderate to severe anemia groups were significantly different. More patients in the moderate to severe cohort had a higher ASA classification grade III and female ratio. Patients in the moderate and severe anemia cohorts had more MACCE (unadjusted: odds ratio [OR] 1.968, 96% CI 1.090-3.555, P 0.023; adjusted: OR 1.929, 95% CI 1.014-3.668, P 0.045) and PPCs (unadjusted: OR 2.616, 95% CI 1.442-4.748, P 0.001; adjusted: OR 2.352, 95% CI 1.225-4.516, P 0.010) than patients with normal or mild anemia. However, the transfusion > 2 units rate was not significantly different between the two cohorts (unadjusted: OR 0.967, 95% CI 0.737-1.270, P 0.811; adjusted: OR 0.941, 95% CI 0.693-1.278, P 0.697). The in-hospital mortality, delirium rate, gastrointestinal complication, ICU admission, and DVT were similar. However, the in-hospital mortality was much higher (3.6%, 21/591 vs 1.6%, 5/321) in the moderate to severe anemia cohort. Furthermore, after propensity score-matched analysis, MACCE and PPCs were also significantly increased in the moderate to severe anemia cohort (OR 2.196 & 3.171, 95% CI 1.0794.470 & 1.563-6.436, P 0.027 & 0.001), which were in accordance with the unadjusted and adjusted results in the unmatched cohorts.

CONCLUSIONS

Moderate to severe preoperative anemia (< 11 g/dl) is associated with increased postoperative major adverse cardiac and cerebral events and pulmonary complications. Additionally, in-hospital mortality was not significant but was higher in the preoperative moderate to severe anemia cohort. Preoperative assessment and correction of hemoglobin level to above 11 g/dl might reduce MACCE, PPCs, and in-hospital mortality in hip fracture patients over 80 years old.

Transfusion thresholds in acute coronary syndromes

PURPOSE OF REVIEW

Anemia is prevalent in patients with acute coronary syndromes. In this setting, there is uncertainty and controversy surrounding the optimal transfusion strategy for managing anemia. The goal of this review is to summarize the current clinical evidence, guidelines, and future directions for managing transfusion in acute coronary syndromes.

RECENT FINDINGS

There is limited evidence from randomized trials evaluating restrictive versus liberal transfusion in patients hospitalized with and/or for acute coronary syndromes. The results from these studies suggest clinical equipoise between transfusion strategies for short term outcomes, and a trend toward favoring a liberal strategy for long term major adverse cardiac events. There is inconsistency across clinical practice guidelines with respect to the optimal strategy for managing anemia and transfusion in acute coronary syndromes due to insufficient evidence.

SUMMARY

More evidence is urgently needed to conclusively establish the optimal strategy for transfusion management in the setting of acute coronary syndromes. These data will directly inform harmonization of clinical practice guidelines. Future investigations should explore alternative strategies to hemoglobin for quantifying the degree of anemic stress for personalizing transfusion therapy, the effects on functional outcomes, and managing anemia following hospital discharge.

Methemoglobin as a marker of acute anemic stress in cardiac surgery

Biological evidence supports plasma methemoglobin as a biomarker for anemia-induced tissue hypoxia. In this translational planned substudy of the multinational randomized controlled transfusion thresholds in cardiac surgery (TRICS-III) trial, which included adults undergoing cardiac surgery requiring cardiopulmonary bypass with a moderate-to-high risk of death, we investigated the relationship between perioperative hemoglobin concentration (Hb) and methemoglobin; and evaluated its association with postoperative outcomes. The primary endpoint was a composite of death, myocardial infarction, stroke, and severe acute kidney injury at 28 days. We observe weak non-linear associations between decreasing Hb and increasing methemoglobin, which were strongest in magnitude at the post-surgical time point. Increased levels of post-surgical methemoglobin were associated with a trend toward an elevated risk for stroke and exploratory neurological outcomes. Our generalizable study demonstrates post-surgical methemoglobin may be a marker of anemia-induced organ injury/dysfunction, and may have utility for guiding personalized approaches to anemia management. Clinicaltrials.gov registration NCT02042898.

Preoperative Hemoglobin <10 g/DL Predicts an Increase in Major Adverse Cardiac Events in Patients With Hip Fracture Over 80 Years: A Retrospective Cohort Study

Background

Preoperative anemia has been associated with perioperative morbidity and mortality in patients undergoing cardiac and non-cardiac surgery. Preoperative anemia is common in elderly hip fracture patients. The primary objective of the study was to explore the relationship between preoperative hemoglobin levels and postoperative major adverse cardiovascular events (MACEs) in hip fracture patients over 80 years.

Methods

The retrospective study enrolled hip fracture patients over 80 years from January 2015 to December 2021 in our center. The data were collected from the hospital's electronic database after approval by the ethics committee. The primary objective of the study was to investigate MACEs, and the secondary objectives included in-hospital mortality, delirium, acute renal failure, ICU admission rate, and transfusion (>2 U).

Results

912 patients were entered for final analysis. Based on the restricted cubic spline, the risk of preoperative hemoglobin (<10 g/DL) was associated with an increased risk of postoperative complications. With univariable logistic analysis, a hemoglobin level <10 g/DL was associated with increased MACEs [OR 1.769, 95% CI (1.074, 2.914), P = .025], in-hospital mortality [OR 2.709, 95% CI (1.215, 6.039), P = .015] and transfusion >2 U risk [OR 2.049, 95% CI (1.56, 2.69), P < .001]. Even after adjustment for confounding factors, MACEs [OR 1.790, 95% CI (1.073, 2.985), P = .026], in-hospital mortality [OR 2.81, 95% CI (1.214, 6.514), P = .016] and transfusion >2 U rate [OR 2.002, 95% CI (1.516, 2.65), P < .001] were still higher in the lower hemoglobin level cohort. Moreover, a log-rank test showed increased in-hospital mortality in the cohort with a preoperative hemoglobin level of <10 g/DL. However, there was no difference in delirium, acute renal failure, and ICU admission rates.

Conclusions

In conclusion, for hip fracture patients over 80 years, preoperative hemoglobin levels <10 g/DL might be associated with increased postoperative MACEs, in-hospital mortality, and transfusion >2 U.

A Rat Model of Clinically Relevant Extracorporeal Circulation Develops Early Organ Dysfunctions

In clinical practice, extracorporeal circulation (ECC) is associated with coagulopathy and inflammation, eventually leading to organ injuries without preventive systemic pharmacological treatment. Relevant models are needed to reproduce the pathophysiology observed in humans and preclinical tests. Rodent models are less expensive than large models but require adaptations and validated comparisons to clinics. This study aimed to develop a rat ECC model and to establish its clinical relevance. One hour of veno-arterial ECC or a sham procedure were achieved on mechanically ventilated rats after cannulations with a mean arterial pressure objective > 60 mmHg. Five hours post-surgery, the rats' behavior, plasmatic/blood biomarkers, and hemodynamics were measured. Blood biomarkers and transcriptomic changes were compared in 41 patients undergoing on-pump cardiac surgery. Five hours post-ECC, the rats presented hypotension, hyperlactatemia, and behavioral alterations. The same patterns of marker measurements (Lactate dehydrogenase, Creatinine kinase, ASAT, ALAT, and Troponin T) were observed in both rats and human patients. Transcriptome analyses showed similarity in both humans and rats in the biological processes involved in the ECC response. This new ECC rat model seems to resemble both ECC clinical procedures and the associated pathophysiology, but with early organ injury corresponding to a severe phenotype. Although the mechanisms at stake in the post-ECC pathophysiology of rats or humans need to be described, this new rat model appears to be a relevant and costless preclinical model of human ECC.

Importance of assessing biomarkers and physiological parameters of anemia-induced tissue hypoxia in the perioperative period

Anemia is associated with increased risk of Acute Kidney Injury (AKI), stroke and mortality in perioperative patients. We sought to understand the mechanism(s) by assessing the integrative physiological responses to anemia (kidney, brain), the degrees of anemia-induced tissue hypoxia, and associated biomarkers and physiological parameters. Experimental measurements demonstrate a linear relationship between blood Oxygen Content (C_aO₂) and renal microvascular PO₂ (y = 0.30x + 6.9, r² = 0.75), demonstrating that renal hypoxia is proportional to the degree of anemia. This defines the kidney as a potential oxygen sensor during anemia. Further evidence of renal oxygen sensing is demonstrated by proportional increase in serum Erythropoietin (EPO) during anemia (y = 93.806*10^-0.02, r² = 0.82). This data implicates systemic EPO levels as a biomarker of anemia-induced renal tissue hypoxia. By contrast, cerebral Oxygen Delivery (DO₂) is defended by a profound proportional increase in Cerebral Blood Flow (CBF), minimizing tissue hypoxia in the brain, until more severe levels of anemia occur. We hypothesize that the kidney experiences profound early anemia-induced tissue hypoxia which contributes to adaptive mechanisms to preserve cerebral perfusion. At severe levels of anemia, renal hypoxia intensifies, and cerebral hypoxia occurs, possibly contributing to the mechanism(s) of AKI and stroke when adaptive mechanisms to preserve organ perfusion are overwhelmed. Clinical methods to detect renal tissue hypoxia (an early warning signal) and cerebral hypoxia (a later consequence of severe anemia) may inform clinical practice and support the assessment of clinical biomarkers (i.e., EPO) and physiological parameters (i.e., urinary PO₂) of anemia-induced tissue hypoxia. This information may direct targeted treatment strategies to prevent adverse outcomes associated with anemia.

Alterations in Fetal Doppler Parameters Before and Twenty-Four Hours After Radiofrequency Ablation for Twin Reversed Arterial Perfusion Sequence

Objective

To evaluate alterations in the fetal Doppler parameters of pump fetuses before and 24 h after radiofrequency ablation surgery for twin reversed arterial perfusion sequence (TRAPs).

Methods

This is a retrospective study of 28 pump fetuses in TRAPs and 28 normal control twins between 2016 and 2021. The fetal Doppler parameters, including the umbilical artery pulsatility index (UA-PI), middle cerebral artery peak systolic velocity (MCA-PSV), middle cerebral artery pulsatility index (MCA-PI), and cerebroplacental ratio (CPR), of the controls, and pump fetuses before and 24 h after surgery were compared.

Results

An increasing trend and a further increase in the MCA-PSV, MCA-PI, MCA-PSV Z score, and MCA-PI Z score after surgery were observed in pump fetuses with gestational age (GA) ≥20 weeks; however, such changes were not observed in those with a GA of <20 weeks. The UA-PI and CPR before and after surgery were not different between control and pump fetuses, whether the GA was ≥20 or <20 weeks.

Conclusion

In the middle second trimester, the pump fetus might suffer from high cardiac output rather than hypoxemia before surgery and congestive heart failure, or hemodilutional anemia after surgery. This may provide some theoretical evidence in favor of early intervention, rather than waiting for a more advanced GA, to avoid unnecessary hemodynamic alterations.

Performance of Lactate and CO2-Derived Parameters in Predicting Major Postoperative Complications After Cardiac Surgery With Cardiopulmonary Bypass: Protocol of a Diagnostic Accuracy Study

Background: CO₂-derived parameters are increasingly used to identify either low-flow status or anaerobic metabolism in shock resuscitation. However, the performance of CO₂-derived parameters in cardiac surgical patients is poorly understood. This study aims to compare the performance of lactate and CO₂-derived parameters in predicting major postoperative complications after cardiac surgery with cardiopulmonary bypass. Methods: This is a prospective, single-center, diagnostic accuracy study. All patients who receive elective cardiac surgery involving cardiopulmonary bypass will be screened for study eligibility. Blood samples will be taken for the calculation of CO₂-derived parameters, including the venous-arterial difference in CO₂ partial pressure (PCO₂ gap), venous-arterial difference in CO₂ content to arterial-venous O₂ content ratio (Cv-aCO₂/Ca-vO₂), and venous-arterial difference in CO₂ partial pressure to arterial-venous O₂ content ratio (Pv-aCO₂/Ca-vO₂) at ICU admission, and 3, 6, and 12 h later. Baseline, perioperative data will be collected daily for 7 days; patients will be followed up for 28 days to collect outcome data. The primary endpoint is the occurrence of major postoperative complications. Receiver-operating characteristics (ROC) curve analysis will be carried out to assess the predictive performance of lactate and CO₂-derived parameters. The performance of the ROC curves will be compared. Discussion: The performance of lactate and CO₂-derived parameters in predicting major postoperative complications will be investigated in the non-sepsis population, which has not been extensively investigated. Our study will compare the two surrogates of respiratory quotient directly, which is an important strength. Trial Registration: ChiCTR, ChiCTR2000029365. Registered January 26th, 2020, http://www.chictr.org.cn/showproj.aspx?proj=48744.

Intraoperative renal hypoxia and risk of cardiac surgery-associated acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is common after cardiac surgery requiring cardiopulmonary bypass. Renal hypoxia may precede clinically detectable AKI. We compared the efficacy of two indices of renal hypoxia, (i) intraoperative urinary oxygen tension (UPO₂ ) and (ii) the change in plasma erythropoietin (pEPO) during surgery, in predicting AKI. We also investigated whether the performance of these prognostic markers varies with preoperative patient characteristics.

METHODS

In 82 patients undergoing on-pump cardiac surgery, blood samples were taken upon induction of anesthesia and upon entry into the intensive care unit. UPO₂ was continuously measured throughout surgery.

RESULTS

Thirty-two (39%) patients developed postoperative AKI. pEPO increased during surgery, but this increase did not predict AKI, regardless of risk of postoperative mortality assessed by EuroSCORE-II. For patients categorized at higher risk by EuroSCORE-II >1.98 (median score for the cohort), UPO₂  ≤10 mmHg at any time during surgery predicted a 4.04-fold excess risk of AKI (p = .04). However, UPO₂ did not significantly predict AKI in lower-risk patients. UPO₂ significantly predicted AKI in patients who were older, had previous myocardial infarction, diabetes, lower preoperative serum creatinine, or shorter bypass times. pEPO and UPO₂ were only weakly correlated.

CONCLUSIONS

Intraoperative change in pEPO does not predict AKI. However, UPO₂ shows promise, particularly in patients with higher risk of operative mortality. The disparity between these two markers of renal hypoxia may indicate that UPO₂ reflects medullary oxygenation whereas pEPO reflects cortical oxygenation.

Dynamic responses of renal oxygenation at the onset of cardiopulmonary bypass in sheep and man

INTRODUCTION

The renal medulla is susceptible to hypoxia during cardiopulmonary bypass (CPB), which may contribute to the development of acute kidney injury. But the speed of onset of renal medullary hypoxia remains unknown.

METHODS

We continuously measured renal medullary oxygen tension (MPO₂) in 24 sheep, and urinary PO₂ (UPO₂) as an index of MPO₂ in 92 patients, before and after induction of CPB.

RESULTS

In laterally recumbent sheep with a right thoracotomy (n = 20), even before CPB commenced MPO₂ fell from (mean ± SEM) 52 ± 4 to 41 ±5 mmHg simultaneously with reduced arterial pressure (from 108 ± 5 to 88 ± 5 mmHg). In dorsally recumbent sheep with a medial sternotomy (n = 4), MPO₂ was even more severely reduced (to 12 ± 12 mmHg) before CPB. In laterally recumbent sheep in which a crystalloid prime was used (n = 7), after commencing CPB, MPO₂ fell abruptly to 24 ±6 mmHg within 20-30 minutes. MPO₂ during CPB was not improved by adding donor blood to the prime (n = 13). In patients undergoing cardiac surgery, UPO₂ fell by 4 ± 1 mmHg and mean arterial pressure fell by 7 ± 1 mmHg during the 30 minutes before CPB. UPO₂ then fell by a further 12 ± 2 mmHg during the first 30 minutes of CPB but remained relatively stable for the remaining 24 minutes of observation.

CONCLUSIONS

Renal medullary hypoxia is an early event during CPB. It starts to develop even before CPB, presumably due to a pressure-dependent decrease in renal blood flow. Medullary hypoxia during CPB appears to be promoted by hypotension and is not ameliorated by increasing blood hemoglobin concentration.

Guidelines for enhanced recovery after cardiac surgery. Consensus document of Spanish Societies of Anesthesia (SEDAR), Cardiovascular Surgery (SECCE) and Perfusionists (AEP)

The ERAS guidelines are intended to identify, disseminate and promote the implementation of the best, scientific evidence-based actions to decrease variability in clinical practice. The implementation of these practices in the global clinical process will promote better outcomes and the shortening of hospital and critical care unit stays, thereby resulting in a reduction in costs and in greater efficiency. After completing a systematic review at each of the points of the perioperative process in cardiac surgery, recommendations have been developed based on the best scientific evidence currently available with the consensus of the scientific societies involved.

Mechanisms of perioperative brain damage in children with congenital heart disease

Congenital heart disease, particularly cyanotic congenital heart disease (CCHD), may lead to a neurodevelopmental delay through central nervous system injury, more unstable central nervous system development, and increased vulnerability of the nervous system. Neurodevelopmental disease is the most serious disorder of childhood, affecting the quality of life of children and their families. Therefore, the monitoring and optimization of nerve damage treatments are important. The factors contributing to neurodevelopmental disease are primarily related to preoperative, intraoperative, postoperative, genetic, and environmental causes, with intraoperative causes being the most influential. Nevertheless, few studies have examined these factors, particularly the influencing factors during early postoperative care. Children with congenital heart disease may experience brain damage during early heart intensive care due to unstable haemodynamics and total body oxygen transfer, particularly early postoperative inflammatory reactions in the brain, blood glucose levels, and other factors that potentially influence long-term neural development. This study analyses the forms of structural and functional brain damage in the early postoperative period, along with the recent evolution of research on its contributing factors.

Renal microvascular oxygen tension during hyperoxia and acute hemodilution assessed by phosphorescence quenching and excitation with blue and red light

PURPOSE

The kidney plays a central physiologic role as an oxygen sensor. Nevertheless, the direct mechanism by which this occurs is incompletely understood. We measured renal microvascular partial pressure of oxygen (P_kO₂) to determine the impact of clinically relevant conditions that acutely change P_kO₂ including hyperoxia and hemodilution.

METHODS

We utilized two-wavelength excitation (red and blue spectrum) of the intravascular phosphorescent oxygen sensitive probe Oxyphor PdG4 to measure renal tissue PO₂ in anesthetized rats (2% isoflurane, n = 6) under two conditions of altered arterial blood oxygen content (C_aO₂): 1) hyperoxia (fractional inspired oxygen 21%, 30%, and 50%) and 2) acute hemodilutional anemia (baseline, 25% and 50% acute hemodilution). The mean arterial blood pressure (MAP), rectal temperature, arterial blood gases (ABGs), and chemistry (radiometer) were measured under each condition. Blue and red light enabled measurement of P_kO₂ in the superficial renal cortex and deeper cortical and medullary tissue, respectively.

RESULTS

P_kO₂ was higher in the superficial renal cortex (~ 60 mmHg, blue light) relative to the deeper renal cortex and outer medulla (~ 45 mmHg, red light). Hyperoxia resulted in a proportional increase in P_kO₂ values while hemodilution decreased microvascular P_kO₂ in a linear manner in both superficial and deeper regions of the kidney. In both cases (blue and red light), P_kO₂ correlated with C_aO₂ but not with MAP.

CONCLUSION

The observed linear relationship between C_aO₂ and P_kO₂ shows the biological function of the kidney as a quantitative sensor of anemic hypoxia and hyperoxia. A better understanding of the impact of changes in P_kO₂ may inform clinical practices to improve renal oxygen delivery and prevent acute kidney injury.

Renal tissue Po2sensing during acute hemodilution is dependent on the diluent

Sensing changes in blood oxygen content ([Formula: see text]) is an important physiological role of the kidney; however, the mechanism(s) by which the kidneys sense and respond to changes in [Formula: see text] are incompletely understood. Accurate measurements of kidney tissue oxygen tension ([Formula: see text]) may increase our understanding of renal oxygen-sensing mechanisms and could inform decisions regarding the optimal fluid for intravascular volume resuscitation to maintain renal perfusion. In some clinical settings, starch solution may be nephrotoxic, possibly due to inadequacy of tissue oxygen delivery. We hypothesized that hemodilution with starch colloid solutions would reduce [Formula: see text] to a more severe degree than other diluents. Anesthetized Sprague-Dawley rats ( n = 77) were randomized to undergo hemodilution with either colloid (6% hydroxyethyl starch or 5% albumin), crystalloid (0.9% saline), or a sham procedure (control) ( n = 13–18 rats/group). Data were analyzed by ANOVA with significance assigned at P < 0.05. After hemodilution, mean arterial pressure (MAP) decreased marginally in all groups, while hemoglobin (Hb) and [Formula: see text] decreased in proportion to the degree of hemodilution. Cardiac output was maintained in all groups after hemodilution. [Formula: see text] decreased in proportion to the reduction in Hb in all treatment groups. At comparably reduced Hb, and maintained arterial oxygen values, hemodilution with starch resulted in larger decreases in [Formula: see text] relative to animals hemodiluted with albumin or saline ( P < 0.008). Renal medullary erythropoietin (EPO) mRNA levels increased more prominently, relative to other hypoxia-regulated molecules (GLUT-1, GAPDH, and VEGF). Our data demonstrate that the kidney acts as a biosensor of reduced [Formula: see text] following hemodilution and that [Formula: see text] may provide a quantitative signal for renal cellular responsiveness to acute anemia. Evidence of a more severe reduction in [Formula: see text] following hemodilution with starch colloid solution suggests that tissue hypoxia may contribute to starch induced renal toxicity.

Renal hemodynamics and oxygenation during experimental cardiopulmonary bypass in sheep under total intravenous anesthesia

Renal medullary hypoxia may contribute to the pathophysiology of acute kidney injury, including that associated with cardiac surgery requiring cardiopulmonary bypass (CPB). When performed under volatile (isoflurane) anesthesia in sheep, CPB causes renal medullary hypoxia. There is evidence that total intravenous anesthesia (TIVA) may preserve renal perfusion and renal oxygen delivery better than volatile anesthesia. Therefore, we assessed the effects of CPB on renal perfusion and oxygenation in sheep under propofol/fentanyl-based TIVA. Sheep (n = 5) were chronically instrumented for measurement of whole renal blood flow and cortical and medullary perfusion and oxygenation. Five days later, these variables were monitored under TIVA using propofol and fentanyl and then on CPB at a pump flow of 80 mL·kg^-1·min^-1 and target mean arterial pressure of 70 mmHg. Under anesthesia, before CPB, renal blood flow was preserved under TIVA (mean difference ± SD from conscious state: -16 ± 14%). However, during CPB renal blood flow was reduced (-55 ± 13%) and renal medullary tissue became hypoxic (-20 ± 13 mmHg versus conscious sheep). We conclude that renal perfusion and medullary oxygenation are well preserved during TIVA before CPB. However, CPB under TIVA leads to renal medullary hypoxia, of a similar magnitude to that we observed previously under volatile (isoflurane) anesthesia. Thus use of propofol/fentanyl-based TIVA may not be a useful strategy to avoid renal medullary hypoxia during CPB.

Factors that confound the prediction of renal medullary oxygenation and risk of acute kidney injury from measurement of bladder urine oxygen tension

AIM

Urinary oxygen tension (uPO₂ ) may provide an estimate of renal medullary PO₂ (mPO₂ ) and thus risk of acute kidney injury (AKI). We assessed the potential for variations in urine flow and arterial PO₂ (aPO₂ ) to confound these estimates.

METHODS

In 28 sheep urine flow, uPO₂ , aPO₂ and mPO₂ were measured during development of septic AKI. In 65 human patients undergoing cardiac surgery requiring cardiopulmonary bypass (CPB) uPO₂ and aPO₂ were measured continuously during CPB, and in a subset of 20 patients, urine flow was estimated every 5 minutes.

RESULTS

In conscious sheep breathing room air, uPO₂ was more closely correlated with mPO₂ than with aPO₂ or urine flow. The difference between mPO₂ and uPO₂ varied little with urine flow or aPO₂ . In patients, urine flow increased abruptly from 3.42 ± 0.29 mL min^-1 to 6.94 ± 0.26 mL min^-1 upon commencement of CPB, usually coincident with reduced uPO₂ . During hyperoxic CPB high values of uPO₂ were often observed at low urine flow. Low urinary PO₂ during CPB (<10 mm Hg at any time during CPB) was associated with greater (4.5-fold) risk of AKI. However, low urine flow during CPB was not significantly associated with risk of AKI.

CONCLUSIONS

uPO₂ provides a robust estimate of mPO₂ , but this relationship is confounded by the simultaneous presence of systemic hyperoxia and low urine flow. Urine flow increases and uPO₂ decreases during CPB. Thus, CPB is probably the best time to use uPO₂ to detect renal medullary hypoxia and risk of post-operative AKI.

Met-Hemoglobin Is a Biomarker for Poor Oxygen Delivery in Infants Following Surgical Palliation

BACKGROUND

Infants with cyanotic congenital heart disease demonstrate wide fluctuations in hemoglobin (Hb), oxygen saturation, and cardiac output following palliation. Methemoglobin (Met-Hb), the product of Hb oxidation, may represent a compensatory mechanism during hypoxia and may be utilized as a biomarker.

METHODS

Arterial and venous Met-Hb levels were obtained from infants requiring palliation. The primary outcome was to describe the relationship between Met-Hb and other indices of tissue oxygenation (venous saturation, estimated arteriovenous oxygen difference [Est AV-Diff], and lactate). Secondary outcomes were to determine the impact of elevated Met-Hb levels ≥1.0% and the effect of red blood cell (RBC) transfusion on Met-Hb levels.

RESULTS

Fifty infants and 465 Met-Hb values were studied. Venous Met-Hb levels were significantly higher than arterial levels (venous: 0.84% ± 0.36% vs arterial: 0.45% ± 0.18%; P < .001). Venous Met-Hb demonstrated a significant inverse relationship with venous oxygen saturation (R = -0.6; P < .001) and Hb (R = -0.3, P < .001) and a direct relationship with the Est AV-Diff (R = 0.3, P < .001). A total of 129 (29.6%) venous Met-Hb values were elevated (≥1.0%) and were associated with significantly lower Hb and venous saturation levels and higher Est AV-Diff and lactate levels. Methemoglobin levels decreased significantly following 65 RBC transfusions (0.94 ± 0.40 vs 0.77 ± 0.34; P < .001). Linear mixed models demonstrated that higher venous Met-Hb levels were associated with lower measures of tissue oxygenation and not related to any preoperative clinical differences.

CONCLUSION

Methemoglobin may be a clinically useful marker of tissue oxygenation in infants following surgical palliation.

Role of anesthesiologists in managing perioperative anemia

PURPOSE OF REVIEW

Anemia can contribute negatively to a patient's morbidity and mortality. Which treatment options do exist and what role do anesthesiologists play in management of perioperative anemia treatment? This review gives an overview about recent findings.

RECENT FINDINGS

Patient Blood Management and standards for the management and treatment of anemia have been established worldwide. Various logistic settings and approaches are possible. With a special focus on cardiovascular anesthesia, intravenous iron is a therapeutic option in the preoperative setting. Autologous blood salvage is a standard procedure during surgery. Restrictive transfusion triggers in adult cardiac surgery have been shown to be beneficial in the majority of studies. Elderly patients and defined comorbidities might require higher transfusion triggers. Both, intravenous and oral iron increase hemoglobin values when given prior to surgery. Oral iron is effective when given several weeks prior to elective surgery. Erythropoietin is a treatment decision individualized to each patient.

SUMMARY

Within the previous 18 months, important publications have demonstrated the established role of anesthesiologists in managing perioperative anemia. A substantial pillar for anemia treatment is the implementation of Patient Blood Management worldwide.