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 Table of Contents  
ORIGINAL ARTICLE
Year : 2016  |  Volume : 3  |  Issue : 2  |  Page : 48-52

Oxygen delivery and carbon dioxide production as determinants of acute kidney injury during open heart surgery


Department of Anaethesia and Surgical Intensive Care, Faculty of Medicine, Alexandria University, Alexandria, Egypt

Date of Submission03-Oct-2015
Date of Acceptance23-Nov-2015
Date of Web Publication6-Sep-2016

Correspondence Address:
Tarek M Elromy
Abdelfattah Eltaweel street, Alandalus 4 building 3rd floor, fleming, Alexandria
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2356-9115.189787

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  Abstract 


Background Acute kidney injury (AKI) after cardiac surgery remains an important and frequent complication in patients undergoing cardiac surgery with CPB and is associated with a poor short-term and long-term prognosis. The incidence of cardiac surgery-associated (CSA)-AKI according to Acute Kidney Injury Network and RIFLE criteria varies between 3 and 50%. CSA-AKI requiring temporary renal replacement therapy occurs in 5–20% of these patients and is associated with a high mortality rate.
Objective The aim of the study was to evaluate the effect of lowest O2 delivery (DO2) and highest CO2 production (VCO2) during cardiopulmonary bypass as risk factors for postoperative AKI and correlate this effect with the postoperative value of plasma neutrophil gelatinase-associated lipocalin (NGAL) as an early biomarker for detection of AKI.
Patients and methods Seventy patients of both sexes, their ages varying between 18 and 60 years, scheduled for elective cardiac surgery by means of cardiopulmonary bypass were included in this study. DO2 and VCO2 on CPB as well as blood urea, serum creatinine, O2 content of arterial blood, and NGAL level were measured.
Results DO2 has an important role as a risk factor for AKI wherein values below 260 ml/min/m2 are associated with increased incidence of AKI. At the same time VCO2 appeared to have no role as a risk factor for AKI.
Conclusion Optimizing DO2 to tissues during CPB by increasing either hematocrit or pump flow is most important in preventing AKI. However, VCO2 level has no role. NGAL is an early and sensitive biomarker that can diagnose and predict the severity of AKI before serum creatinine is elevated.

Keywords: acute kidney injury, CO2 production, neutrophil gelatinase-associated lipocalin, O2 delivery


How to cite this article:
Elromy TM, Hashem AE, Hamouda SA, Abdel Razek A. Oxygen delivery and carbon dioxide production as determinants of acute kidney injury during open heart surgery. Res Opin Anesth Intensive Care 2016;3:48-52

How to cite this URL:
Elromy TM, Hashem AE, Hamouda SA, Abdel Razek A. Oxygen delivery and carbon dioxide production as determinants of acute kidney injury during open heart surgery. Res Opin Anesth Intensive Care [serial online] 2016 [cited 2020 Jun 4];3:48-52. Available from: http://www.roaic.eg.net/text.asp?2016/3/2/48/189787




  Introduction Top


Cardiac surgery-associated acute kidney injury (CSA-AKI) remains a major and frequent complication in patients undergoing cardiac surgery with CPB and is associated with a poor short-term and long-term prognosis. The incidence of CSA-AKI according to Acute Kidney Injury Network (AKIN) and RIFLE criteria varies between 3 and 50%. CSA-AKI requiring temporary renal replacement therapy (RRT) occurs in 5–20% of these patients and is associated with a high mortality rate [1].

CSA-AKI is caused by a variety of factors, including exogenous and endogenous toxins, metabolic abnormalities, ischemia and reperfusion injury, neurohormonal activation, inflammation, and oxidative stress. Postoperative kidney function deterioration has been shown to be an important predictor of morbidity and mortality [2]. In addition, the mortality rate from CSA-AKI when RRT is required is considerably higher than that for patients not requiring RRT [3].

Early detection of AKI is deemed important to develop therapeutic concepts to treat or at least ameliorate a renal insult. The currently used clinical markers of renal function, such as blood urea nitrogen, serum creatinine, estimated creatinine clearance, and urine output, may not reflect the actual change in GFR [4]. Within the last few years various biomarkers reflective of ischemic tubular injury have been developed to accomplish this task; among them is neutrophil gelatinase-associated lipocalin (NGAL), which is detected in the plasma and free filtrated through the glomerulus [5],[6].

The role of O2 delivery (DO2) and CO2 production (VCO2) on CPB as causative factors in the development of AKI during CPB was investigated in the present study. AKI was diagnosed according to the AKIN criteria.


  Aim Top


The aim of the study was to evaluate the effect of lowest DO2 and highest VCO2 during cardiopulmonary bypass as risk factors for postoperative AKI and correlate this effect with the postoperative value of plasma NGAL as an early biomarker for detection of AKI.


  Patients and methods Top


This study was carried out in Alexandria Main University Hospitals on 70 patients. Patients of both sexes, their ages varying between 18 and 60 years, scheduled for elective cardiac surgery by means of cardiopulmonary bypass were included.

Patients with preoperative abnormal renal functions as judged by laboratory investigations such as of urea and creatinine and by radiological investigations such as ultrasound were excluded from the study. In addition, patients with Cleveland score more than 4 were excluded.

Measurements include

The following measurements were taken: DO2 on bypass, VCO2 during CPB, blood urea, serum creatinine, creatinine clearance, AKIN classification for AKI, hemoglobin, serum lactate, O2 content of arterial and mixed venous blood and arteriovenous oxygen content difference, NGAL, duration of surgery, duration of anesthesia, total CPB time, aortic cross-clamping time, intraoperative complications, the need for inotropes, and postoperative complications.

Statistical analysis

Data were checked, entered, and analyzed using SPSS (version 19; SPSS Inc., Chicago, Illinois, USA), and expressed as mean±SD for quantitative variables and as number and percentage for categorical variables. The χ2 or Fisher’s exact test, analysis of variance (F test,), and least significant difference (when analysis of variance was significant) were used for comparison between groups. P values less than 0.05 were considered statistically significant.


  Results Top


In the present study there was a significant difference between the study groups concerning patient sex, CPB time, cross-clamp time, nadir DO2 during CPB, serum creatinine, serum urea, eGFR, and plasma NGAL.

A nonsignificant positive correlation was found between plasma NGAL at 6 h postoperatively and AKIN criteria at 24 h and a significant positive correlation at 48 and 72 h.

A nonsignificant correlation was found between nadir DO2 during CPB and AKIN criteria at 24 h and a significant inverse correlation at 48 and 72 h in the AKI group.

There was also a significant inverse correlation between nadir DO2 during CPB and NGAL at 6 h in the AKI group and a nonsignificant inverse correlation in the non-AKI group.

The receiver operating characteristic curves determined for AKI showed a diagnostic value of 0.558 for nadir hematocrit during CPB for prediction of AKI after cardiac surgery; the threshold was 23.5%, sensitivity was 25%, specificity was 76%, positive predictive value (PPV) was 29.41%, negative predictive value (NPV) was 71.70%, and accuracy was 61.43%.

The diagnostic value of nadir DO2 during CPB for prediction of AKI after cardiac surgery using CPB was 0.832. The threshold was 260%, sensitivity was 65%, specificity was 86%, PPV was 65%, NPV was 86%, and accuracy was 80%.

The diagnostic value of DO2/VCO2 ratio during CPB for prediction of AKI after cardiac surgery using CPB was 0.538. The threshold was 5.3%, sensitivity was 70%, specificity was 30%, PPV was 28.57%, NPV was 71.43%, and accuracy 41.43% [Figure 1],[Figure 2],[Figure 3],[Figure 4],[Figure 5] and [Table 1],[Table 2],[Table 3],[Table 4],[Table 5].
Figure 1 Correlation between neutrophil gelatinase-associated lipocalin (NGAL) at 6 h and Acute Kidney Injury Network (AKIN) on each day in the acute kidney injury group.

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Figure 2 Correlation between nadir O2 and neutrophil gelatinase-associated lipocalin (NGAL) 6 h in the acute kidney injury (AKI) and non-AKI groups.

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Figure 3 Correlation between nadir O2 and Acute Kidney Injury Network (AKIN) on each day in the acute kidney injury group.

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Figure 4 Receiver operating characteristic curve for nadir O2 in the diagnosis of acute kidney injury patients.

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Figure 5 Receiver operating characteristic curve for O2 delivery/CO2 production (DO2/VCO2) in the diagnosis of acute kidney injury patients.

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Table 1 Comparison between the two groups according to creatinine, urea, and eGFR

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Table 2 Comparison between the two groups according to demographic data

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Table 3 Comparison between the two groups according to different studied parameters

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Table 4 Neutrophil gelatinase-associated lipocalin level in the two groups

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Table 5 Nadir O2 delivery and peak CO2 production during CPB in the two groups

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  Discussion Top


Comparison between the two groups concerning DO2 and VCO2 showed that DO2 was significantly correlated with AKI and that VCO2 had no role as a risk factor for AKI. Also NGAL was an early and sensitive biomarker for early diagnosis and estimation of severity of kidney injury.

Plasma NGAL level measured before CPB was not statistically significantly different between the two groups, whereas it was statistically significantly higher in AKI patients 6 h postoperatively. Similarly, Paarmann et al. [7] used serum creatinine and eGFR for the diagnosis of AKI, and found that plasma NGAL increased immediately and 2 h postoperatively in the AKI group. Also, Delcroix et al. [8] in a prospective study carried out on 50 cardiac surgery patients to evaluate the efficiency of urine and plasma NGAL in the detection of AKI found that plasma NGAL level more than 149 µg/ml could be a sensitive biomarker for detection of AKI postoperatively. In contrast, Koyner et al. [9] reported that plasma NGAL was not a useful predictor of AKI when measured within the first 6 h following cardiac surgery, but urinary NGAL was superior to conventional biomarkers in the early diagnosis of CSA-AKI.

In the present study there was a significant positive correlation between NGAL measured at 6 h postoperatively and AKIN criteria measured on the second and third days postoperatively for the diagnosis of AKI. This is consistent with the study by Haase et al. [10], who found that NGAL level was a useful early predictor of AKI; they also found that urine, plasma, or serum NGAL had prognostic value for clinical outcomes such as association with RRT and mortality [10].

Peak VCO2 during CPB was not significantly different between the two groups; however, there was a significant difference between the two groups as regards nadir DO2, with higher incidence of AKI below 260 ml/min/m2. Similarly, Ranucci et al. [11] identified that DO2 levels less than 260 ml/min/m2 during CPB were associated with increased lactate formation. In the same study they found that values of DO2 less than 272 ml/min/m2 during CPB were associated with an increased rate for acute renal failure with a sensitivity of 68% and specificity of 68% [11].

When nadir arterial oxygen content and nadir venous oxygen content during CPB were compared with values measured before CPB, a statistically significant difference between the two groups was found.

In the present study the receiver operating characteristic curve for nadir hematocrit in the diagnosis of AKI patients showed the following results: the diagnostic performance of nadir hematocrit for prediction of AKI after cardiac surgery using CPB was 0.558, the threshold was 23.5%, sensitivity was 25%, specificity was 76%, PPV was 29.41%, NPV was 71.70%, and accuracy was 61.43%.

There was a significant inverse correlation between nadir DO2 during CPB and AKIN classification on the second and third days and a significant inverse correlation between nadir DO2 on CPB and NGAL measured at 6 h postoperatively. In contrast, a nonsignificant inverse correlation was seen between NGAL measured at 6 h postoperatively and nadir DO2 on CPB for the non-AKI group.

Ranucci et al. [11] found the same results and concluded that DO2 on CPB is the most reliable predictor of AKI after cardiac surgery and found that highest sensitivity and specificity was reached by the lowest DO2 indexed on CPB.


  Conclusion Top


Optimizing DO2 to tissues during CPB by increasing either hematocrit or pump flow is most important in preventing AKI; in addition, VCO2 level has no role. Also NGAL is an early and sensitive biomarker that can diagnose and predict the severity of AKI before serum creatinine is elevated.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Seitz S, Rauh M, Gloeckler M, Cesnjevar R, Dittrich S, Koch AM. Cystatin C and neutrophil gelatinase-associated lipocalin: biomarkers for acute kidney injury after congenital heart surgery. Swiss Med Wkly 2013; 143:w13744.  Back to cited text no. 1
    
2.
Pallone TL, Zhang Z, Rhinehart K. Physiology of the renal medullary microcirculation. Am J Physiol Renal Physiol 2003; 284 (2):F253–F266.  Back to cited text no. 2
    
3.
Deen WM, Lazzara MJ, Myers BD. Structural determinants of glomerular permeability. Am J Physiol Renal Physiol 2001; 281 (4):F579–F596.  Back to cited text no. 3
    
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Riou B. Troponin: important in severe trauma and a first step in the biological marker revolution. Anesthesiology 2004; 101 (6):1259–1260.  Back to cited text no. 4
    
5.
Schiffl H, Lang SM. Update on biomarkers of acute kidney injury: moving closer to clinical impact? Mol Diagn Ther 2012; 16 (4):199–207.  Back to cited text no. 5
    
6.
Matsui K, Kamijo-Ikemori A, Sugaya T, Yasuda T, Kimura K. Usefulness of urinary biomarkers in early detection of acute kidney injury after cardiac surgery in adults. Circ J 2012; 76 (1):213–220.  Back to cited text no. 6
    
7.
Paarmann H, Charitos EL, Beichar EA, Heinze H, Schon J, Berggreen A, Heringlake M. Duration of cardiopulmonary bypass is an important confounder when using biomarkers for early diagnosis of acute kidney injury in cardiac surgical patients. Appl Cardiopulmonary Pathophysiol 2013; 17:284–297.  Back to cited text no. 7
    
8.
Delcroix G, Gillain N, Moonen M, Radermacher L, Damas F, Minon JM, Fraipont V NGAL usefulness in the intensive care unit three hours after cardiac surgery. ISRN Nephrol 2013; 2013:865164.  Back to cited text no. 8
    
9.
Koyner JL, Bennett MR, Worcester EM, Ma Q, Raman J, Jeevanandam V et al. Urinary cystatin C as an early biomarker of acute kidney injury following adult cardiothoracic surgery. Kidney Int 2008; 74 (8):1059–1069.  Back to cited text no. 9
    
10.
Haase M, Bellomo R, Devarajan P, Schlattmann P, Haase-Fielitz A. Accuracy of neutrophil gelatinase-associated lipocalin (NGAL) in diagnosis and prognosis in acute kidney injury: a systematic review and meta-analysis. Am J Kidney Dis 2009; 54 (6):1012–1024.  Back to cited text no. 10
    
11.
Ranucci M, De Toffol B, Isgrò G, Romitti F, Conti D, Vicentini M. Hyperlactatemia during cardiopulmonary bypass: determinants and impact on postoperative outcome. Crit Care 2006; 10 (6):R167.  Back to cited text no. 11
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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Abstract
Introduction
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Patients and methods
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