Sodium Bicarbonate and Renal Function after Cardiac Surgery

Optimization of kidney function in cardiac surgery patients with intra-abdominal hypertension: expert opinion

Cardiac surgery-associated acute kidney injury (CSA-AKI) affects up to 42% of cardiac surgery patients. CSA-AKI is multifactorial, with low abdominal perfusion pressure often overlooked. Abdominal perfusion pressure is calculated as mean arterial pressure minus intra-abdominal pressure (IAP). IAH decreases cardiac output and compresses the renal vasculature and renal parenchyma. Recent studies have highlighted the frequent occurrence of IAH in cardiac surgery patients and have linked the role of low perfusion pressure to the occurrence of AKI. This review and expert opinion illustrate current evidence on the pathophysiology, diagnosis, and therapy of IAH and ACS in the context of AKI.

Hemolysis during open heart surgery in patients with hereditary spherocytosis - systematic review of the literature and case study

BACKGROUND

Due to the distinctive nature of cardiac surgery, patients suffering from hereditary spherocytosis (HS) are potentially at a high risk of perioperative complications resulting from hemolysis. Despite being the most prevalent cause of hereditary chronic hemolysis, the standards of surgical management are based solely on expert opinion.

OBJECTIVE

We analyze the risk of hemolysis in HS patients after cardiac surgery based on a systematic review of the literature. We also describe a case of a patient with hereditary spherocytosis who underwent aortic valve repair.

METHODS

This systematic review was registered in the PROSPERO international prospective register of systematic reviews (CRD42023417666) and included records from Embase, MEDLINE, Web of Science, and Google Scholar databases. The case study investigates a 38-year-old patient who underwent surgery for an aortic valve defect in mid-2022.

RESULTS

Of the 787 search results, 21 studies describing 23 cases of HS undergoing cardiac surgery were included in the final analysis. Hemolysis was diagnosed in five patients (one coronary artery bypass graft surgery, two aortic valve bioprosthesis, one ventricular septal defect closure, and one mitral valve plasty). None of the patients died in the perioperative period. Also, no significant clinical hemolysis was observed in our patient during the perioperative period.

CONCLUSIONS

The literature data show that hemolysis is not common in patients with HS undergoing various cardiac surgery techniques. The typical management of a patient with mild/moderate HS does not appear to increase the risk of significant clinical hemolysis. Commonly accepted beliefs about factors inducing hemolysis during cardiac surgery may not be fully justified and require further investigation.

Cardiac Surgery-Associated Acute Kidney Injury

AKI is a common and serious complication of cardiac surgery that has a significant impact on patient morbidity and mortality. The Kidney Disease Improving Global Outcomes definition of AKI is widely used to classify and identify AKI associated with cardiac surgery (cardiac surgery-associated AKI [CSA-AKI]) on the basis of changes in serum creatinine and/or urine output. There are various preoperative, intraoperative, and postoperative risk factors for the development of CSA-AKI which should be recognized and addressed as early as possible to expedite its diagnosis, reduce its occurrence, and prevent or ameliorate its devastating complications. Crucial issues are the inaccuracy of serum creatinine as a surrogate parameter of kidney function in the perioperative setting of cardiothoracic surgery and the necessity to discover more representative markers of the pathophysiology of AKI. However, except for the tissue inhibitor of metalloproteinase-2 and insulin-like growth factor binding protein 7 ratio, other diagnostic biomarkers with an acceptable sensitivity and specificity are still lacking. This article provides a comprehensive review of various aspects of CSA-AKI, including pathogenesis, risk factors, diagnosis, biomarkers, classification, prevention, and treatment management.

Acute Kidney Injury after Cardiac Surgery: Prediction, Prevention, and Management

Acute kidney injury (AKI) is a common complication in cardiac surgery patients, with a reported incidence of 20 to 30%. The development of AKI is associated with worse short- and long-term mortality, and longer hospital length of stay. The pathogenesis of cardiac surgery-associated AKI is poorly understood but likely involves an interplay between preoperative comorbidities and perioperative stressors. AKI is commonly diagnosed by using increases in serum creatinine or decreased urine output and staged using a standardized definition such as the Kidney Disease Improving Global Outcomes classification. Novel biomarkers under investigation may provide earlier detection and better prediction of AKI, enabling mitigating therapies early in the perioperative period. Recent clinical trials of cardiac surgery patients have demonstrated the benefit of goal-directed oxygen delivery, avoidance of hyperthermic perfusion and specific fluid and medication strategies. This review article highlights both advances and limitations regarding the prevention, prediction, and treatment of cardiac surgery-associated AKI.

Cardiac Surgery Associated AKI Prevention Strategies and Medical Treatment for CSA-AKI

Acute kidney injury (AKI) is common after cardiac surgery. To date, there are no specific pharmacological therapies. In this review, we summarise the existing evidence for prevention and management of cardiac surgery-associated AKI and outline areas for future research. Preoperatively, angiotensin-converting enzyme inhibitors and angiotensin receptor blockers should be withheld and nephrotoxins should be avoided to reduce the risk. Intraoperative strategies include goal-directed therapy with individualised blood pressure management and administration of balanced fluids, the use of circuits with biocompatible coatings, application of minimally invasive extracorporeal circulation, and lung protective ventilation. Postoperative management should be in accordance with current KDIGO AKI recommendations.

Teprasiran, a Small Interfering RNA, for the Prevention of Acute Kidney Injury in High-Risk Patients Undergoing Cardiac Surgery: A Randomized Clinical Study

Supplemental Digital Content is available in the text.

Acute kidney injury (AKI) affects up to 30% of patients undergoing cardiac surgery, leading to increased in-hospital and long-term morbidity and mortality. Teprasiran is a novel small interfering RNA that temporarily inhibits p53-mediated cell death that underlies AKI.

Sodium Bicarbonate in Different Critically Ill Conditions: From Physiology to Clinical Practice

Intravenous sodium bicarbonate is commonly used in several critically ill conditions for the management of acute acidemia independently of the etiology, and for the prevention of acute kidney injury, although this is still controversial from a physiologic point of view.

ACUTE KIDNEY INJURY AFTER OPEN-HEART SURGERY PROCEDURES

Cardiac surgery-associated acute kidney injury (CS-AKI) is a major complication associated with increased morbidity and mortality. There are multiple diagnostic criteria for CS-AKI. Despite many new investigations available for improved AKI diagnostics, creatinine and urea remain the cornerstone of diagnostics in everyday clinical practice. There are three major pathophysiological mechanisms that contribute to kidney injury, i.e. renal hypoperfusion, inflammation with oxidative stress, and use of nephrotoxic agents. Some risk factors have been identified that can be modified during the course of treatment (use of nephrotoxic agents, duration of cardiopulmonary bypass, type of extracorporeal circulation, postoperative low cardiac output or hypotension). The aim of AKI prevention should always be to prevent aggravation of renal failure and, if possible, to avoid progression to renal replacement therapy, which in turn brings worse long-term outcomes.

Lower serum bicarbonate is associated with an increased risk of acute kidney injury

BACKGROUND

Lower serum bicarbonate levels are associated with an increased risk of kidney disease progression. Whether lower serum bicarbonate levels are associated with an increased risk of developing acute kidney injury (AKI) is unclear.

METHODS

We included 8393 patients from the Systolic Blood Pressure Intervention Trial (SPRINT) that had baseline serum bicarbonate levels and complete data available. AKI was a predetermined adjudicated adverse event that was determined by hospital admission and discharge records with AKI as a recorded diagnosis. Serum bicarbonate was examined in clinically significant cutoffs ≤ 24, 25-28 and > 28 mEq/L, with 25-28 mEq/L as the reference group. Cox proportional hazard models were used to examine the association between serum bicarbonate and development of AKI.

RESULTS

The mean (SD) age, estimated glomerular filtration rate (eGFR), and serum bicarbonate level at baseline were 68 (9) years, 77 (23) ml/min/1.73m² and 26.3 (2.6) mEq/L, respectively. Participants with serum bicarbonate levels ≤ 24 mEq/L were more likely to be male and to have lower baseline eGFR. After a median follow-up time of 3.3 years, 293 participants developed AKI. More patients in the lower bicarbonate group developed AKI (6.1% vs 2.8% in the 25-28 mEq/L and 2.1% in the > 28 mEq/L). A bicarbonate level ≤ 24 mEq/L was associated with a significantly increased risk of AKI compared to those with a bicarbonate level of 25-28 mEq/L after full adjustment (HR 1.42, 95% CI 1.1-1.8).

CONCLUSION

Lower serum bicarbonate levels are an independent risk factor for the development of AKI.

Prevention of Cardiac Surgery-Associated Acute Kidney Injury: A Review of Current Strategies

Acute kidney injury is a common and often severe postoperative complication after cardiac surgery, and is associated with poor short-term and long-term outcomes. Numerous randomized controlled trials have been conducted to investigate various strategies for prevention of cardiac surgery-associated acute kidney injury. Unfortunately, most trials that have been conducted to date have been negative. However, encouraging results have been demonstrated with preoperative administration of corticosteroids, leukocyte filtration, and administration of inhaled nitric oxide intraoperatively, and implementation of a Kidney Disease: Improving Global Outcomes bundle of care approach postoperatively. These findings require validation in large, multicenter trials.

Acute kidney injury after cardiac surgery: prevalence, impact and management challenges

Acute kidney injury (AKI) is a major medical problem that is of particular concern after cardiac surgery. Perioperative AKI is independently associated with an increase in short-term morbidity, costs of treatment, and long-term mortality. In this review, we explore the definition of cardiac surgery-associated acute kidney injury (CSA-AKI) and identify diverse mechanisms and risk factors contributing to the renal insult. Current theories of the pathophysiology of CSA-AKI and description of its clinical course will be addressed in this review. Data on the most promising renal protective strategies in cardiac surgery, from well-designed studies, will be scrutinized. Furthermore, diagnostic tools such as novel biomarkers of AKI and their potential utility will be discussed.

Update on perioperative acute kidney injury

PURPOSE OF REVIEW

In this review, we discuss the latest updates on perioperative acute kidney injury (AKI) and the specific considerations that are relevant to different surgeries and patient populations.

RECENT FINDINGS

AKI diagnosis is constantly evolving. New biomarkers detect AKI early and shed a light on the possible cause of AKI. Hypotension, even for a short duration, is associated with perioperative AKI. The debate on the deleterious effects of chloride-rich solutions is still far from conclusion. Remote ischemic preconditioning is showing promising results in the possible prevention of perioperative AKI. No definite data show a beneficiary effect of statins, fenoldepam, or sodium bicarbonate in preventing AKI.

SUMMARY

Perioperative AKI is prevalent and associated with significant morbidity and mortality. Considering the lack of effective preventive or therapeutic interventions, this review focuses on perioperative AKI: measures for early diagnosis, defining risks and possible mechanisms, and summarizing current knowledge for intraoperative fluid and hemodynamic management to reduce risk of AKI.

Prevention of acute kidney injury and protection of renal function in the intensive care unit: update 2017 : Expert opinion of the Working Group on Prevention, AKI section, European Society of Intensive Care Medicine

BACKGROUND

Acute kidney injury (AKI) in the intensive care unit is associated with significant mortality and morbidity.

OBJECTIVES

To determine and update previous recommendations for the prevention of AKI, specifically the role of fluids, diuretics, inotropes, vasopressors/vasodilators, hormonal and nutritional interventions, sedatives, statins, remote ischaemic preconditioning and care bundles.

METHOD

A systematic search of the literature was performed for studies published between 1966 and March 2017 using these potential protective strategies in adult patients at risk of AKI. The following clinical conditions were considered: major surgery, critical illness, sepsis, shock, exposure to potentially nephrotoxic drugs and radiocontrast. Clinical endpoints included incidence or grade of AKI, the need for renal replacement therapy and mortality. Studies were graded according to the international GRADE system.

RESULTS

We formulated 12 recommendations, 13 suggestions and seven best practice statements. The few strong recommendations with high-level evidence are mostly against the intervention in question (starches, low-dose dopamine, statins in cardiac surgery). Strong recommendations with lower-level evidence include controlled fluid resuscitation with crystalloids, avoiding fluid overload, titration of norepinephrine to a target MAP of 65-70 mmHg (unless chronic hypertension) and not using diuretics or levosimendan for kidney protection solely.

CONCLUSION

The results of recent randomised controlled trials have allowed the formulation of new recommendations and/or increase the strength of previous recommendations. On the other hand, in many domains the available evidence remains insufficient, resulting from the limited quality of the clinical trials and the poor reporting of kidney outcomes.

Postoperative acute kidney injury

Acute kidney injury (AKI) after cardiac surgery is a common and serious complication. Several definitions of AKI have been proposed recently, and include both increases in serum creatinine levels and decreases in urine output as diagnostic criteria. The pathophysiology of postoperative AKI is complex and involves both ischemic injury and systemic inflammation. Identifying risk factors, such as old age, underlying diabetes, heart failure, and obesity, may aid in the application of preventative methods for postoperative AKI. Additionally, recognizing different risks after different types of surgical procedures would be valuable. Novel biomarkers that could detect AKI more precisely at an earlier time point are being investigated. Several new biomarkers have been assessed in large multi-center studies and are believed to accommodate conventional clinical findings in diagnosing postoperative AKI. In high-risk patients, preventative measures, such as the maintenance of adequate hemodynamics and sufficient fluid resuscitation, could lower the incidence of postoperative AKI. Avoiding nephrotoxic agents and optimizing preoperative hemoglobin levels to avoid excessive transfusions would also be beneficial. In situations in which medical management fails to maintain sufficient urine output and acid-base and electrolyte homeostasis, early initiation of renal replacement therapy should be considered.

[Renal protection in intensive care : Myths and facts]

BACKGROUND

Acute kidney injury (AKI) is a common and severe complication in patients on the intensive care unit with a significant impact on patient mortality, morbidity and costs of care; therefore, renal protective therapy is most important in these severely ill patients.

AIM OF THE REVIEW

Many renal protective strategies have been postulated during the last decades, which are sometimes still in place as a kind of "myth" but which are not always proven by evidence-based "facts". The aim of this review is therefore to question and compare some of these "myths" with the available "facts".

RECENT FINDINGS

Most important for renal protection is the early identification of patients at risk for AKI or with acute kidney damage before renal function deteriorates further. A stage-based management of AKI comprises more general measures, such as discontinuation of nephrotoxic agents and adjustment of diuretic doses but most importantly early hemodynamic stabilization with crystalloid volume replacement solutions and vasopressors, such as noradrenaline. The aim is to ensure optimal renal perfusion and perfusion pressure. Patients with known arterial hypertension potentially need higher perfusion pressures. Large amounts of hyperchloremic solutions should be avoided. Volume overload and renal vasodilatory substances can also lead to further deterioration of kidney function. There is still no specific pharmacological therapy for renal protection.

Effect of perioperative sodium bicarbonate administration on renal function following cardiac surgery for infective endocarditis: a randomized, placebo-controlled trial

Background

Patients with infective endocarditis (IE) have an elevated risk of renal dysfunction because of extensive systemic inflammation and use of nephrotoxic antibiotics. In this randomized, placebo-controlled trial, we investigated whether perioperative sodium bicarbonate administration could attenuate postoperative renal dysfunction in patients with IE undergoing cardiac surgery.

Methods

Seventy patients randomly received sodium chloride (n = 35) or sodium bicarbonate (n = 35). Sodium bicarbonate was administered as a 0.5 mmol/kg loading dose for 1 h commencing with anesthetic induction, followed by a 0.15 mmol/kg/h infusion for 23 h. The primary outcome was peak serum creatinine (SCr) level during the first 48 h postoperatively. The incidence of acute kidney injury, SCr level, estimated glomerular filtration rate, and major morbidity endpoints were assessed postoperatively.

Results

The peak SCr during the first 48 h postoperatively (bicarbonate vs. control: 1.01 (0.74, 1.37) mg/dl vs. 0.88 (0.76, 1.27) mg/dl, P = 0.474) and the incidence of acute kidney injury (bicarbonate vs. control: 29% vs. 23%, P = 0.584) were similar in both groups. The postoperative increase in SCr above baseline was greater in the bicarbonate group than in the control group on postoperative day 2 (0.21 (0.07, 0.33) mg/dl vs. 0.06 (0.00, 0.23) mg/dl, P = 0.028) and postoperative day 5 (0.23 (0.08, 0.36) mg/dl vs. 0.06 (0.00, 0.23) mg/dl, P = 0.017).

Conclusions

Perioperative sodium bicarbonate administration had no favorable impact on postoperative renal function and outcomes in patients with IE undergoing cardiac surgery. Instead, it was associated with possibly harmful renal effects, illustrated by a greater increase in SCr postoperatively, compared to control.

Trial registration

ClinicalTrials.gov, NCT01920126. Registered on 31 July 2013.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1591-z) contains supplementary material, which is available to authorized users.

Haptoglobin and Free Haemoglobin during Cardiac Surgery—is there a Link to Acute Kidney Injury?

Acute kidney injury (AKI) is frequently observed after cardiac surgery (CS) with cardiopulmonary bypass (CPB). Multiple mechanisms underlie this phenomenon, including CPB-dependent haemolysis. Haemoglobin is released during haemolysis, and free haemoglobin (frHb) causes tubular cell injury after exceeding the binding capacity of haptoglobin (Hp). The objective of this study was to investigate the influence of perioperative changes in frHb and Hp levels on the incidence of CS-associated (CSA) AKI. After receiving local ethics committee approval and obtaining informed consent from our patients, we analysed the data pertaining to 154 patients undergoing CPB surgery. We recorded frHb and Hp concentrations pre-, intra- and postoperatively and defined AKI using the Kidney Disease Improving Global Outcomes (KDIGO) classification. We observed that frHb levels increased significantly during surgery and then decreased at ten hours thereafter and that Hp levels decreased during surgery and remained at low levels until the first postoperative day. We noted a moderate negative correlation between frHb and Hp levels. AKI was identified in 45.5% of patients; however, there was no significant difference in frHb or Hp levels between patients with and without AKI. We did not observe a relationship between frHb or Hp levels and CSA AKI and thus could not confirm the hypothesis that patients with higher baseline Hp concentrations experience a lower incidence of AKI than patients with lower baseline Hp concentrations.

Sodium bicarbonate does not prevent postoperative acute kidney injury after off-pump coronary revascularization: a double-blinded randomized controlled trial

BACKGROUND

Acute kidney injury (AKI) is a common morbidity after off-pump coronary revascularization. We investigated whether perioperative administration of sodium bicarbonate, which might reduce renal injury by alleviating oxidative stress in renal tubules, prevents postoperative AKI in off-pump coronary revascularization patients having renal risk factors.

METHODS

Patients (n=162) having at least one of the following AKI risk factors were enrolled: (i) age >70 yr; (ii) diabetes mellitus; (iii) chronic renal disease; (iv) congestive heart failure or left ventricular ejection fraction <35%; and (v) reoperation or emergency. Patients were evenly randomized to receive either sodium bicarbonate (0.5 mmol kg^-1 for 1 h upon induction of anaesthesia followed by 0.15 mmol kg^-1 h^-1 for 23 h) or 0.9% saline. Acute kidney injury within 48 h after surgery was assessed using the Acute Kidney Injury Network criteria.

RESULTS

The incidences of AKI were 21 and 26% in the bicarbonate and control groups, respectively (P=0.458). Serially measured serum creatinine concentrations and perioperative fluid balance were also comparable between the groups. The length of postoperative hospitalization and incidence of morbidity end points were similar between the groups, whereas significantly more patients in the bicarbonate group required prolonged mechanical ventilation (>24 h) relative to the control group (20 vs 6, P=0.003).

CONCLUSIONS

Perioperative sodium bicarbonate administration did not decrease the incidence of AKI after off-pump coronary revascularization in high-risk patients and might even be associated with a need for prolonged ventilatory care.

CLINICAL TRIAL REGISTRATION

NCT01840241.

Acute kidney injury following cardiac surgery: current understanding and future directions

Acute kidney injury (AKI) complicates recovery from cardiac surgery in up to 30 % of patients, injures and impairs the function of the brain, lungs, and gut, and places patients at a 5-fold increased risk of death during hospitalization. Renal ischemia, reperfusion, inflammation, hemolysis, oxidative stress, cholesterol emboli, and toxins contribute to the development and progression of AKI. Preventive strategies are limited, but current evidence supports maintenance of renal perfusion and intravascular volume while avoiding venous congestion, administration of balanced salt as opposed to high-chloride intravenous fluids, and the avoidance or limitation of cardiopulmonary bypass exposure. AKI that requires renal replacement therapy occurs in 2–5 % of patients following cardiac surgery and is associated with 50 % mortality. For those who recover from renal replacement therapy or even mild AKI, progression to chronic kidney disease in the ensuing months and years is more likely than for those who do not develop AKI. Cardiac surgery continues to be a popular clinical model to evaluate novel therapeutics, off-label use of existing medications, and nonpharmacologic treatments for AKI, since cardiac surgery is fairly common, typically elective, provides a relatively standardized insult, and patients remain hospitalized and monitored following surgery. More efficient and time-sensitive methods to diagnose AKI are imperative to reduce this negative outcome. The discovery and validation of renal damage biomarkers should in time supplant creatinine-based criteria for the clinical diagnosis of AKI.

Prediction and Prevention of Acute Kidney Injury after Cardiac Surgery

The incidence of acute kidney injury after cardiac surgery (CS-AKI) ranges from 33% to 94% and is associated with a high incidence of morbidity and mortality. The etiology is suggested to be multifactorial and related to almost all aspects of perioperative management. Numerous studies have reported the risk factors and risk scores and novel biomarkers of AKI have been investigated to facilitate the subclinical diagnosis of AKI. Based on the known independent risk factors, many preventive interventions to reduce the risk of CS-AKI have been tested. However, any single preventive intervention did not show a definite and persistent benefit to reduce the incidence of CS-AKI. Goal-directed therapy has been considered to be a preventive strategy with a substantial level of efficacy. Many pharmacologic agents were tested for any benefit to treat or prevent CS-AKI but the results were conflicting and evidences are still lacking. The present review will summarize the current updated evidences about the risk factors and preventive strategies for CS-AKI.

Sodium Bicarbonate Prevents Contrast-Induced Nephropathy in Addition to Theophylline: A Randomized Controlled Trial

In this study, we investigated whether hydration with sodium bicarbonate is superior to hydration with saline in addition to theophylline (both groups) in the prophylaxis of contrast-induced nephropathy (CIN). It was a prospective, randomized, double-blinded study in a university hospital on 2 general intensive care units (63% of investigations) and normal wards.After approval of the local ethics committee and informed consent 152 patients with screening serum creatinine ≥1.1 mg/dL and/or at least 1 additional risk factor for CIN undergoing intravascular contrast media (CM) exposure were randomized to receive a total of 9 mL/kg bicarbonate 154 mmol/L (group B; n = 74) or saline 0.9% (group S; n = 78) hydration within 7 h in addition to intravenous application of 200 mg theophylline. Serum creatinine was determined immediately before, 24 and 48 h after CM exposure. As primary endpoint we investigated the incidence of CIN (increase of serum creatinine ≥0.5 mg/dL and/or ≥25% within 48 h of CM).Both groups were comparable regarding baseline characteristics. Incidence of CIN was significantly less frequent with bicarbonate compared to sodium hydration (1/74 [1.4%] vs 7/78 [9.0%]; P = 0.035). Time course of serum creatinine was more favorable in group B with decreases in serum creatinine after 24 h (-0.084 mg/dL [95% confidence interval: -0.035 to -0.133 mg/dL]; P = 0.008) and 48 h (-0.093 mg/dL (-0.025 to -0.161 mg/dL); P = 0.007) compared to baseline which were not observed in group S.In patients at increased risk of CIN receiving prophylactic theophylline, hydration with sodium bicarbonate reduces contrast-induced renal impairment compared to hydration with saline.

Preoperative Low Serum Bicarbonate Levels Predict Acute Kidney Injury After Cardiac Surgery

Acute kidney injury (AKI) after cardiac surgery is a common and serious complication. Although lower than normal serum bicarbonate levels are known to be associated with consecutive renal function deterioration in patients with chronic kidney injury, it is not well-known whether preoperative low serum bicarbonate levels are associated with the development of AKI in patients who undergo cardiac surgery. Therefore, the clinical implication of preoperative serum bicarbonate levels on AKI occurrence after cardiac surgery was investigated. Patients who underwent coronary artery bypass or valve surgery at Yonsei University Health System from January 2013 to December 2014 were enrolled. The patients were divided into 3 groups based on preoperative serum bicarbonate levels, which represented group 1 (below normal levels) <23 mEq/L; group 2 (normal levels) 23 to 24 mEq/L; and group 3 (elevated levels) >24 mEq/L. The primary outcome was the predicated incidence of AKI 48 hours after cardiac surgery. AKI was defined according to Acute Kidney Injury Network criteria. Among 875 patients, 228 (26.1%) developed AKI within 48 hours after cardiac surgery. The incidence of AKI was higher in group 1 (40.9%) than in group 2 (26.5%) and group 3 (19.5%) (P < 0.001). In addition, the duration of postoperative stay in a hospital intensive care unit (ICU) was longer for AKI patients and for those in the low-preoperative-serum-bicarbonate-level groups. A multivariate logistic regression analysis showed that low preoperative serum bicarbonate levels were significantly associated with AKI even after adjustment for age, sex, hypertension, diabetes mellitus, operation type, preoperative hemoglobin, and estimated glomerular filtration rate. In conclusion, low serum bicarbonate levels were associated with higher incidence of AKI and prolonged ICU stay. Further studies are needed to clarify whether strict correction of bicarbonate levels close to normal limits may have a protective role in preventing further AKI development.

Does sodium bicarbonate infusion really have no effect on the incidence of acute kidney injury after cardiac surgery? A prospective observational trial

Introduction

Postoperative acute kidney injury (AKI) is a frequently observed phenomenon after cardiac surgery with cardio-pulmonary bypass (CPB); this severe complication is associated with adverse patient outcomes. There are multiple mechanisms involved in AKI during cardiac surgery, including CPB-dependent hemolysis. An IV infusion of sodium bicarbonate, which leads to urine alkalization, may play a role in preventing AKI. Recently, several trials have investigated the effect of sodium bicarbonate and reported controversial results. The purpose of this investigation was to investigate the following question. Under what circumstances can sodium bicarbonate prevent postoperative AKI?

Methods

We analyzed data from 342 patients undergoing CPB surgery at the University Hospital Goettingen, Germany. A total of 174 patients received a preemptive dose of sodium bicarbonate. Directly after the induction of anesthesia, the continuous infusion of 0.15 mmol/kg body weight/h was started and continued until 2 pm on the first postoperative day. Patients who were not treated with sodium bicarbonate formed the control group (n = 168). To verify the AKI risk configuration of each group, we surveyed risk factors and determined the commonly used clinical predictive score according to Thakar and colleagues. We recorded the concentration of free hemoglobin (fhb) to estimate the amount of CPB-dependent hemolysis. The definition of AKI was acquired by applying the AKI-network (AKIN) classification over the course of five postoperative days.

Results

Patients who received the sodium bicarbonate infusion showed a significantly lower incidence (35.6 vs. 50%) of AKI than that of patients who did not receive the infusion (p = 0.01). AKIN levels 2 and 3 were also more frequent when sodium bicarbonate was not administered. Particularly, in the low-risk cohort (<3 Thakar points), the incidence of AKI was significantly reduced (26 vs. 46%) when patients received sodium bicarbonate (p = 0.01), whereas in the high-risk patients, no significant reduction was observed.

Conclusion

In this study, we observed that low-risk patients particularly benefited from the preventive treatment with sodium bicarbonate. The incidence of AKI was significantly reduced in low-risk patients while there was no statistically significant difference in the high-risk patient cohort.

Trial registration

DRKS00007616, Registered 12 December 2014.