ORIGINAL ARTICLE – ADULT CARDIAC
Interactive CardioVascular and Thoracic Surgery 18 (2014) 706–712 doi:10.1093/icvts/ivu023 Advance Access publication 23 February 2014
Time from cardiac catheterization to cardiac surgery: a risk factor for acute kidney injury?† Berk Özkaynaka,*, Nihan Kayalara, Funda Gümüşb, Cihan Yücela, Bülent Merta, Kamil Boyacıoglua and Vedat Erentug˘ a a b
̇ Department of Cardiovascular Surgery, Ba gcılar Training and Research Hospital, Istanbul, Turkey ̇ Department of Anesthesiology, Bagcılar Training and Research Hospital, Istanbul, Turkey
̇ * Corresponding author. Bagcılar Egitim ve Araştırma Hastanesi, Kalp ve Damar Cerrahisi Klinigi, Merkez Mh. 6. Sk. Bagcılar, 342000 Istanbul. Tel: +90-533-6439901; fax: +90-212-4404242; e-mail: [email protected] (B. Özkaynak). Received 5 September 2013; received in revised form 19 January 2014; accepted 29 January 2014
Abstract OBJECTIVES: Acute kidney injury can occur after cardiac catheterization and cardiac surgery. The negative effects of the contrast media and cardiopulmonary bypass on renal function may be additive when performed in close succession. The results in the literature are, however, conflicting. METHODS: Preoperative, operative, perioperative and postoperative variables of 573 consecutive adult patients who underwent cardiac surgery on cardiopulmonary bypass were collected prospectively. Acute kidney injury (AKI) was defined according to the Acute Kidney Injury Network criteria based on changes in serum creatinine level within 48 h of surgery. RESULTS: Acute kidney injury was detected in 233 patients (41%). In a multivariate analysis, older age (P = 0.01), longer cardiopulmonary bypass time (P = 0.003), lower preoperative haematocrit level (P = 0.02) and higher body mass index (P = 0.001) were found to be independently associated with development of acute kidney injury. Analysis of the time from cardiac catheterization to surgery by logistic regression modelling did not show any significant change in the risk of acute kidney injury. Risk related to time from catheterization to surgery was not increased even in the patients with elevated preprocedural creatinine levels (>106 μmol l−1; P = 0.23), left ventricular dysfunction (ejection fraction 5 days (n = 288). The 0 and 1 day group (Group A) was selected to identify higherrisk patients who required emergency surgery. Contrast-induced AKI is typically defined as reaching a peak up to 5 days after the catheterization [6]. The 5-day interval was selected to include this peak (Group B).
Statistical analysis Statistical analysis was performed with the IBM® SPSS® Statistics 20.0 software (IBM, Corp., Chicago, IL, USA). Patient characteristics were summarized as frequencies, proportions, or percentages, or means and standard deviations. Independent samples t-test was used for a bivariate analysis of variables with normal distribution between groups. Wilcoxon’s rank-sum test (Mann–Whitney U-test) was used for bivariate comparison of data with nonnormal distribution. Pearson χ 2 and Fisher’s exact χ 2 tests were used to compare categorical variables. A multivariate stepwise logistic regression model was used to assess the risk of development of AKI according to the timing of cardiac catheterization in
relation to the date of the operation. A second stepwise logistic regression model assessed the effect of demographic and perioperative variables on development of AKI. Variables with bivariate significance (P < 0.05) were entered into the regression model. The odds ratio (OR) and 95% confidence interval (CI) for each variable were reported. The c-statistic was calculated to evaluate model discrimination. The Hosmer–Lemeshow test for lack of fit was used for the final model selection. A P-value of 106 μmol l−1) (P = 0.03) than Groups A and B combined. This is probably related to the longer preparation time for surgery in these patients and the intentional delay for patients in a stable condition after recent MI and LVD. Operative and postoperative data for each group are given in Table 2.
Primary outcomes AKI was detected in 233 patients (41%). Eight patients (1%) required haemodialysis postoperatively, 6 (75%) of whom died during the early postoperative period. There was no significant difference between the patients with and those without AKI in relation to the time from catheterization to surgery (P = 0.09). Although the incidence of AKI was slightly higher in Group C, this difference was not statistically significant (P = 0.67). The effect of time between cardiac catheterization and cardiac operation on postoperative AKI was further examined by separate logistic regression models of periods in 0–1, 0–2, 0–4, 0–6, 0–10 days and 0 to ≥11 days before the operation (Table 3). There was a very slight increased risk of developing AKI in 0–2 days but none of the time periods was found to be statistically significant. The risk of developing AKI seems to be neither reduced nor increased by increasing time from catheterization to operation. Furthermore, there was no significant relation in the time from catheterization to operation and AKI in patients with elevated preprocedural creatinine levels (>106 μmol l−1, P = 0.23), LVD (ejection fraction [EF] 106 μmol l−1)
General (n = 573)
Group A (n = 69)
Group B (n = 216)
Group C (n = 288)
P-value
59.3 ± 11
57.9 ± 11.4
59.6 ± 10.3
59.4 ± 11.4
0.54
163 (28) 410 (72) 28 ± 4.6 312 (55) 211 (37) 298 (52) 276 (48) 216 (38) 124 (22) 51 (9) 21 (4) 153 (27) 55 (10) 1.8 ± 1.8
20 (29) 49 (71) 29 ± 4.5 42 (61) 23 (33) 38 (55) 41 (59) 31 (45) 18 (26) 5 (7) 0 24 (35) 4 (6) 2.2 ± 1.9
56 (26) 160 (74) 28 ± 4.3 116 (54) 77 (36) 120 (56) 103 (48) 89 (41) 43 (20) 19 (9) 6 (3) 43 (20) 13 (6) 1.9 ± 2.2
87 (30) 201 (70) 28 ± 4.8 154 (54) 111 (39) 140 (49) 133 (46) 96 (33) 63 (22) 27 (9) 15 (5) 86 (30) 38 (13) 1.6 ± 1.5
0.57
129 (23) 290 (51) 133 (23) 21 (4) 39 ± 4.8 45 (8)
9 (13) 30 (44) 21 (30) 9 (13) 40 ± 3.9 6 (9)
59 (27) 110 (51) 44 (20) 3 (1) 40 ± 4.8 9 (4)
61 (21) 150 (52) 68 (24) 9 (3) 39 ± 4.9 30 (10)
0.02 0.52 0.65 0.26 0.14 0.08 0.55 0.85 0.08 0.005 0.01 0.01 0.0001
0.008 0.03
Bold characters are used to express P– values that are statistically significant (< 0.05). Data are number of patients (%) or mean ± SD. NYHA: New York Heart Association; SD: standard deviation.
Table 2: Operative, perioperative and postoperative variables General (n = 573) Operation CABG 462 (81) Valve 49 (9) Combined 39 (7) Other 23 (4) Cross-clamp time (min) 64 ± 33 CPB time (min) 102 ± 44 Lowest haematocrit on CPB 24 ± 3.8 Lowest mean arterial pressure on CPB 51 ± 5 Perioperative fluid and blood product transfusion Total replacement (ml) 3314 ± 1700 Colloid (ml) 568 ± 470 Packed red blood cells (units) 0.6 ± 0.9 Fresh frozen plasma (units) 1.4 ± 1.1 Whole blood (units) 0.7 ± 0.7 Perioperative inotrope 244 (43) Acute kidney injury 233 (41) Intra-aortic balloon pump 9 (2) Atrial fibrillation 103 (18) Time on ventilator (h) 10 ± 13 Total drainage (ml) 557 ± 303 Intensive care unit stay (days) 4±4 Length of hospital stay (days) 5±4
Group A (n = 69)
Group B (n = 216)
Group C (n = 288)
P-value
63 (91) 2 (3) 3 (4) 1 (1) 61 ± 35 97 ± 42 24 ± 3.8 52 ± 6
175 (81) 16 (7) 13 (6) 12 (6) 62 ± 30 99 ± 43 25 ± 3.4 51 ± 5
224 (78) 31 (11) 23 (8) 10 (4) 66 ± 35 104 ± 44 24 ± 4.1 50 ± 5
0.13
0.27 0.29 0.18 0.04
3259 ± 746 454 ± 451 0.6 ± 0.8 1.8 ± 0.8 0.9 ± 0.5 30 (43) 28 (41) 1 (1) 8 (12) 10 ± 9 542 ± 270 4±4 5±4
3246 ± 710 538 ± 455 0.5 ± 0.9 1.5 ± 1.3 0.7 ± 0.6 82 (38) 83 (38) 2 (1) 31 (14) 9±7 593 ± 332 3±3 4±3
3378 ± 2293 621 ± 481 0.7 ± 1 1.3 ± 1.1 0.7 ± 0.8 132 (46) 122 (43) 6 (3) 64 (22) 11 ± 17 533 ± 286 4±5 6±5
0.66 0.01 0.02 0.009 0.12 0.22 0.67 0.58 0.02 0.33 0.08 0.03 0.03
Bold characters are used to express P– values that are statistically significant (< 0.05). Data are number of patients (%) or mean ± SD. CABG: coronary artery bypass graft surgery; CPB: cardiopulmonary bypass; SD: standard deviation.
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Table 3: Logistic regression analysis of the risk of development of AKI after cardiac surgery in relation to the time between cardiac catheterization and surgery B
χ2
C
Number of cases (%)
OR
95% CI
P-value
0 0–1 0–2 0–4 0–6 0–10 0 to ≥11 Overall daysa
0.03 0.03 0.29 0.09 0.03 0.03 0.27 0.001
0.004 0.004 0.29 0.03 0.003 0.003 0.31 0.007
0.5 0.503 0.53 0.51 0.502 0.502 0.51 0.54
49 (9) 60 (10) 95 (17) 117 (20) 86 (15) 146 (26) 573 (100)
1.03 0.97 1.33 1.09 1.03 1.03 1.31 1.001
0.41–2.56 0.33–2.79 0.47–3.78 0.41–2.92 0.39–2.71 0.38–2.78 0.51–3.39 0.99–1.006
0.95 0.95 0.59 0.86 0.95 0.95 0.58 0.79
ORIGINAL ARTICLE
Time (days)
a Hosmer–Lemeshow, χ 2 = 9.45, degrees of freedom = 8, P = 0.31. Bold characters are used to express P– values that are statistically significant (< 0.05). AKI: acute kidney injury; C: c-statistic; CI: confidence interval; OR: odds ratio.
Table 4: Bivariate analysis of the variables associated with development of AKI
Age Sex Female Male Body mass index (kg m−2) Hypertension Diabetes mellitus Hyperlipidaemia Smoker Family history Chronic obstructive pulmonary disease Peripheral arterial disease Left ventricular dysfunction EuroSCORE II (% mortality risk) Time from angiography to operation (days) Emergency surgery Operation CABG Valve Combined Other Preoperative creatinine level ≤106 μmol l−1 Preoperative creatinine level >106 μmol l−1 Preoperative haematocrit Cross-clamp time (min) CPB time (min) Lowest haematocrit on CPB Lowest mean arterial pressure on CPB Perioperative blood drainage Perioperative fluid and blood product transfusion Colloid (ml) Packed red blood cells (units) Fresh frozen plasma (units) Whole blood (units) Perioperative inotrope Intra-aortic balloon pump Time on ventilator (h) Total drainage (ml) Intensive care unit stay (days) Mortality
No AKI (n = 340)
AKI (n = 233)
P-value
58 ± 11.1
61.1 ± 10.7
0.001
94 (28) 246 (72) 27.5 ± 4.5 177 (52) 123 (36) 181 (53) 166 (49) 133 (39) 67 (20) 33 (10) 38 (11) 1.7 ± 1.9 11 ± 38 41 (12)
69 (30) 164 (70) 28.8 ± 4.7 135 (58) 88 (38) 117 (50) 111 (48) 83 (36) 57 (25) 18 (8) 17 (7) 1.9 ± 1.7 12 ± 24 24 (10)
0.67
276 (81) 32 (9) 20 (6) 12 (4) 317 (93) 23 (7) 40 ± 4.7 61 ± 30 96 ± 37 25 ± 4 51 ± 5 540 ± 171
186 (80) 17 (7) 19 (8) 11 (5) 211 (91) 22 (9) 39 ± 4.8 69 ± 36 110 ± 51 24 ± 4 50 ± 5 580 ± 240
0.51
521 ± 444 0.5 ± 0.9 1.4 ± 0.9 0.7 ± 0.5 141 (42) 3 (1) 9 ± 10 531 ± 279 3±3 7 (2)
641 ± 499 0.7 ± 1.1 1.5 ± 1.4 0.8 ± 0.9 103 (44) 6 (3) 12 ± 16 594 ± 333 8±5 18 (8)
0.007* 0.001 0.45 0.29 0.49 0.11 0.0001* 0.06* 0.0001* 0.001
Bold characters are used to express P– values that are statistically significant (< 0.05). Data are number of patients (%) or mean ± SD. *Mann–Whitney U-test. CPB: cardiopulmonary bypass; SD: standard deviation.
0.002 0.17 0.69 0.48 0.78 0.39 0.17 0.41 0.12 0.04 0.09* 0.51
0.24 0.006 0.005 0.0001 0.007 0.004* 0.03
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Table 5: surgery
Multivariate analysis of the demographic and perioperative variables associated with development of AKI after cardiac
Age (years) CPB time (min) Body mass index (kg m−2) Preoperative haematocrit Constant
B
χ 2 (Wald)
OR
95% CI
P-value
0.022 0.007 0.066 −0.045 −2.463
6.62 8.63 11.17 5.43 4.64
1.022 1.007 1.068 0.956 0.085
1.005–1.039 1.002–1.011 1.028–1.11 0.920–0.993
0.01 0.003 0.001 0.02 0.03
Bold characters are used to express P– values that are statistically significant (< 0.05). c-statistic for the model = 0.658, Hosmer–Lemeshow χ 2 = 13.24, degrees of freedom = 8, P = 0.104. AKI: acute kidney injury; CI: confidence interval; CPB: cardiopulmonary bypass.
during CPB was significantly associated with AKI (P = 0.006). The longer durations of cross-clamp and CPB and the lower minimum mean arterial pressure during CPB were found to be significantly related to the development of postoperative AKI (P = 0.005, P = 0.0001 and P = 0.004, respectively). Multivariate analysis of the variables with bivariate significance showed older age (P = 0.01), longer CPB time (P = 0.003), higher body mass index (BMI, kg m−2; P = 0.001) and lower preoperative haematocrit (P = 0.02) to be independently associated with development of AKI (Table 5; c-statistic = 0.658, Hosmer–Lemeshow χ 2 = 13.24, degrees of freedom = 8, P = 0.104). Although increased amounts of colloid infusion and packed red blood cell (PRBC) transfusion, lower haematocrit levels on CPB, excess perioperative blood drainage, longer cross-clamp time and lower mean arterial pressure on CPB were noted in the bivariate analysis, none of these variables was found to be significantly associated with development of AKI in the logistic regression model. Overall postoperative hospital mortality was 4.4%. Mortality was not significantly different between the three groups of time from catheterization (P = 0.15); however, it was significantly increased in the patients with AKI (P = 0.001). Bivariate analysis of the variables age (P = 0.001), diabetes mellitus (P = 0.04), elevated preoperative creatinine levels (>106 μmol l−1; P < 0.0001), longer cross-clamp (P < 0.0001) and CPB times (P < 0.0001), presence of AKI (P = 0.001), lowest haematocrit level measured on CPB (P = 0.01), increased amounts of perioperative blood drainage (P = 0.004) and PRBC transfusion (P < 0.0001) and total perioperative colloid infusion (P = 0.008) showed significant associations of these factors with mortality. However, in the multivariate logistic regression analysis, elevated preoperative creatinine levels (>106 μmol l−1) were associated with a more than 5-fold increase in mortality (OR, 5.39; 95% CI, 1.99–14.63; P = 0.001) followed by almost a 3-fold increase in the presence of AKI (OR, 2.96; 95% CI, 1.14–7.69; P = 0.03). Other independent predictors for mortality were presence of diabetes mellitus (OR, 2.74; 95% CI, 1.11–6.78; P = 0.03), increasing amounts of perioperative PRBC transfusion (OR, 1.68; 95% CI, 1.24–2.28; P = 0.001) and older age (OR, 1.06; 95% CI, 1.01–1.11; P = 0.02) (c-statistic = 0.844, Hosmer–Lemeshow χ 2 = 6.56, degrees of freedom = 8, P = 0.59).
DISCUSSION Our study showed that the time between cardiac catheterization and cardiac surgery was not a significant risk factor for the
occurrence of AKI. Even after extensive statistical analysis, there was no significant correlation between any of the groups, according to the time between cardiac catheterization and operation, and the development of AKI. There are contradicting reports regarding the association between AKI and the time between angiography and cardiac surgery. Del Duca et al. [10] concluded that cardiac catheterization performed within 5 days before the operation is a significant risk factor for acute renal failure after cardiac surgery. Medalion et al. [11] also suggested that CABG should be delayed by at least 5 days in patients who receive a high contrast dose. Their results showed that an operation performed within 24 h of catheterization was an independent predictor of postoperative acute renal failure [11]. Similar to Hennessy et al. [12], Ranucci et al. [13] reported that surgery performed on the same day as angiography is a risk factor for acute renal failure. However, in those reports, patients who underwent surgery close to the time of angiography and developed acute renal failure had more preoperative risk factors for postoperative acute renal failure. In contrast, in the present study, Group C included more patients with elevated preoperative creatinine levels and other risk factors for postoperative acute renal failure as a result of our institutional policy of delaying surgery in these patients. There are other studies supporting our results. Ko et al. [14] noted that the time interval between coronary angiogram and cardiac surgery did not affect the risk of AKI after cardiac surgery. Brown et al. [15] suggested that same-day angiography may be safe in a select population of valve surgery patients. Greason et al. [16] further supported these findings and concluded that in select patients with a low risk of AKI, same-day angiography was not associated with increased morbidity, AKI or death. In the present study, we performed separate regression analysis comparing various ranges of time intervals and overall days to explore the effect of time from catheterization to operation on the development of postoperative AKI; however, there was no significant risk of developing AKI, even at 10 days. In most studies, age, LVD, diabetes mellitus, peripheral vascular disease, preoperative use of an intra-aortic balloon pump, chronic obstructive pulmonary disease, emergency surgery and elevated preoperative creatinine levels are commonly associated with increased risk of AKI [2, 10, 12, 14, 17–19]. In the present study, age, BMI, preoperative haematocrit and CPB time were among the factors significantly associated with AKI. Although an elevated preoperative creatinine level (>106 μmol l−1) was not significantly associated with AKI in our patient group, it was significantly associated with mortality.
B. Özkaynak et al. / Interactive CardioVascular and Thoracic Surgery
Funding Results of routine laboratory tests were used for this retrospective study. Therefore no budget was necessary. Conflict of interest: The authors have no relevant financial or non-financial relationship to disclose.
REFERENCES [1] Bove T, Calabro MG, Landoni G, Aletti G, Marino G, Crescenzi G et al. The incidence and risk of acute renal failure after cardiac surgery. J Cardiothorac Vasc Anesth 2004;18:442–5. [2] Rosner MH, Okusa MD. Acute kidney injury associated with cardiac surgery. Clin J Am Soc Nephrol 2006;1:19–32. [3] Kelly AM, Dwamena B, Cronin P, Bernstein SJ, Carlos RC. Meta-analysis: effectiveness of drugs for preventing contrast-induced nephropathy. Ann Intern Med 2008;148:284–94. [4] Hillis LD, Smith PK, Anderson JL, Bittl JA, Bridges CR, Byrne JG et al. 2011 ACCF/AHA guideline for coronary artery bypass graft surgery: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation 2011;124:e652–735. [5] Sudarsky D, Nikolsky E. Contrast-induced nephropathy in interventional cardiology. Int J Nephrol Renovasc Dis 2011;4:85–99. [6] McCullough PA. Contrast-induced acute kidney injury. J Am Coll Cardiol 2008;51:1419–28. [7] Mehran R, Aymong ED, Nikolsky E, Lasic Z, Iakovou I, Fahy M et al. A simple risk score for prediction of contrast-induced nephropathy after percutaneous coronary intervention: development and initial validation. J Am Coll Cardiol 2004;44:1393–9. [8] Nashef SA, Roques F, Sharples LD, Nilsson J, Smith C, Goldstone AG et al. EuroSCORE II. Eur J Cardiothorac Surg 2012;41:734–45. [9] Mehta RL, Kellum JA, Shah SV, Molitoris BA, Ronco C, Warnock DG et al. Acute kidney injury network: report of an initiative to improve outcomes in acute kidney injury. Crit Care 2007;11:R31. [10] Del Duca D, Iqbal S, Rahme E, Goldberg P, de Varennes B. Renal failure after cardiac surgery: timing of cardiac catheterization and other perioperative risk factors. Ann Thorac Surg 2007;84:1264–71. [11] Medalion B, Cohen H, Assli A, Vaknin Assa H, Farkash A, Snir E et al. The effect of cardiac angiography timing, contrast media dose, and preoperative renal function on acute renal failure after coronary artery bypass grafting. J Thorac Cardiovasc Surg 2010;139:1539–44. [12] Hennessy SA, LaPar DJ, Stukenborg GJ, Stone ML, Mlynarek RA, Kern JA et al. Cardiac catheterization within 24 hours of valve surgery is significantly associated with acute renal failure. J Thorac Cardiovasc Surg 2010;140:1011–7. [13] Ranucci M, Ballotta A, Kunkl A, De Benedetti D, Kandil H, Conti D et al. Influence of the timing of cardiac catheterization and the amount of contrast media on acute renal failure after cardiac surgery. Am J Cardiol 2008; 101:1112–8. [14] Ko B, Garcia S, Mithani S, Tholakanahalli V, Adabag S. Risk of acute kidney injury in patients who undergo coronary angiography and cardiac surgery in close succession. Eur Heart J 2012;33:2065–70. [15] Brown ML, Holmes DR, Tajik AJ, Sarano ME, Schaff HV. Safety of same-day coronary angiography in patients undergoing elective valvular heart surgery. Mayo Clin Proc 2007;82:572–4. [16] Greason KL, Englberger L, Suri RM, Park SJ, Rihal CS, Pislaru SV et al. Safety of same-day coronary angiography in patients undergoing elective aortic valve replacement. Ann Thorac Surg 2011;91:1791–6. [17] Kramer RS, Quinn RD, Groom RC, Braxton JH, Malenka DJ, Kellet MA et al. Same admission cardiac catheterization and cardiac surgery: is there an increased incidence of acute kidney injury? Ann Thorac Surg 2010;90:1418–24. [18] Kumar AB, Suneja M, Bayman EO, Weide GD, Tarasi M. Association between postoperative acute kidney injury and duration of cardiopulmonary bypass: a meta-analysis. J Cardiothorac Vasc Anesth 2012;26:64–9. [19] Mehta RH, Honeycutt E, Patel UD, Lopes RD, Williams JB, Shaw LK et al. Relationship of the time interval between cardiac catheterization and elective coronary artery bypass surgery with postprocedural acute kidney injury. Circulation 2011;124:S149–55.
ORIGINAL ARTICLE
The main limitation of this study is its retrospective observational design. Our study cohort included patients with various risks and different types of operations, reflecting our daily clinical experience. However, patients with prominent chronic kidney failure and those receiving preoperative dialysis were excluded to express a new renal insult. Furthermore, widely accepted and sensitive AKI network criteria have been used to define AKI. High-risk patients with elevated creatinine levels are managed— complying with the guidelines—through proper hydration, discontinuation of nephrotoxic agents and optimization of renal functions before the operation. These patients had a longer time interval between catheterization and operation and were predominantly present in Group C. This bias in our study may be an advantage, since our practice filters out the high-risk patients. Consequently, the low- and medium-risk patients could be studied to obtain clearer evidence on the effect of time between catheterization and operation. Another limitation is the lack of data on the volumes of contrast used for the catheterizations, which were not recorded. However, note that all the patients received the same type of contrast agent, the lowest possible amounts of contrast were used and no excess use was reported in any of the patients. Since the quantity and type of contrast used did not vary, it is possible that these were not influential factors in this study. This study has important clinical implications and can guide surgeons on the timing of surgery after cardiac catheterization. First, in emergency and urgent cases, surgery can be performed safely with appropriate precautions, and it should not be delayed to decrease the risk of postoperative renal dysfunction. These precautions should include optimization of preoperative haematocrit levels; maintenance of adequate haematocrit and mean arterial pressure during CPB and use of meticulous surgical techniques to minimize the duration of CPB, perioperative bleeding and requirements for blood transfusion. Even in elderly patients, patients with LVD and patients with increased creatinine level, the timing between angiography and surgery was not found to be a risk factor for AKI, and early surgery can be recommended in clinically unstable patients. Secondly, since Group C included a greater number of patients with increased risk of AKI, optimizing renal functions preoperatively in stable patients may be an appropriate strategy. Although the guideline recommends withholding surgery only in patients with chronic renal dysfunction, we believe that it would also be useful to withhold the intervention for the optimization of renal functions in high-risk patients ( particularly in older patients and in those with high BMI and low preoperative haematocrit levels) and in patients undergoing CPB of a possibly longer duration. In conclusion, our results do not support the a priori hypothesis of the additive risk of cardiac catheterization and CPB on the development of postoperative AKI, when these procedures are performed in close succession. According to various reports, the axiomatic concept of the ‘recovery period’ of the kidneys after exposure to contrast is widely accepted and further insults on the functional reserve of the kidneys should be avoided in this interim period of 10 days. However, our results showed that surgery may be considered ‘safe’ on any day after catheterization, if influential factors other than time are accounted for when planning cardiac surgery, in order to prevent postoperative renal complications.
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Interactive CardioVascular and Thoracic Surgery 18 (2014) 706–712 doi:10.1093/icvts/ivu023 Advance Access publication 23 February 2014
Time from cardiac catheterization to cardiac surgery: a risk factor for acute kidney injury?† Berk Özkaynaka,*, Nihan Kayalara, Funda Gümüşb, Cihan Yücela, Bülent Merta, Kamil Boyacıoglua and Vedat Erentug˘ a a b
̇ Department of Cardiovascular Surgery, Ba gcılar Training and Research Hospital, Istanbul, Turkey ̇ Department of Anesthesiology, Bagcılar Training and Research Hospital, Istanbul, Turkey
̇ * Corresponding author. Bagcılar Egitim ve Araştırma Hastanesi, Kalp ve Damar Cerrahisi Klinigi, Merkez Mh. 6. Sk. Bagcılar, 342000 Istanbul. Tel: +90-533-6439901; fax: +90-212-4404242; e-mail: [email protected] (B. Özkaynak). Received 5 September 2013; received in revised form 19 January 2014; accepted 29 January 2014
Abstract OBJECTIVES: Acute kidney injury can occur after cardiac catheterization and cardiac surgery. The negative effects of the contrast media and cardiopulmonary bypass on renal function may be additive when performed in close succession. The results in the literature are, however, conflicting. METHODS: Preoperative, operative, perioperative and postoperative variables of 573 consecutive adult patients who underwent cardiac surgery on cardiopulmonary bypass were collected prospectively. Acute kidney injury (AKI) was defined according to the Acute Kidney Injury Network criteria based on changes in serum creatinine level within 48 h of surgery. RESULTS: Acute kidney injury was detected in 233 patients (41%). In a multivariate analysis, older age (P = 0.01), longer cardiopulmonary bypass time (P = 0.003), lower preoperative haematocrit level (P = 0.02) and higher body mass index (P = 0.001) were found to be independently associated with development of acute kidney injury. Analysis of the time from cardiac catheterization to surgery by logistic regression modelling did not show any significant change in the risk of acute kidney injury. Risk related to time from catheterization to surgery was not increased even in the patients with elevated preprocedural creatinine levels (>106 μmol l−1; P = 0.23), left ventricular dysfunction (ejection fraction 5 days (n = 288). The 0 and 1 day group (Group A) was selected to identify higherrisk patients who required emergency surgery. Contrast-induced AKI is typically defined as reaching a peak up to 5 days after the catheterization [6]. The 5-day interval was selected to include this peak (Group B).
Statistical analysis Statistical analysis was performed with the IBM® SPSS® Statistics 20.0 software (IBM, Corp., Chicago, IL, USA). Patient characteristics were summarized as frequencies, proportions, or percentages, or means and standard deviations. Independent samples t-test was used for a bivariate analysis of variables with normal distribution between groups. Wilcoxon’s rank-sum test (Mann–Whitney U-test) was used for bivariate comparison of data with nonnormal distribution. Pearson χ 2 and Fisher’s exact χ 2 tests were used to compare categorical variables. A multivariate stepwise logistic regression model was used to assess the risk of development of AKI according to the timing of cardiac catheterization in
relation to the date of the operation. A second stepwise logistic regression model assessed the effect of demographic and perioperative variables on development of AKI. Variables with bivariate significance (P < 0.05) were entered into the regression model. The odds ratio (OR) and 95% confidence interval (CI) for each variable were reported. The c-statistic was calculated to evaluate model discrimination. The Hosmer–Lemeshow test for lack of fit was used for the final model selection. A P-value of 106 μmol l−1) (P = 0.03) than Groups A and B combined. This is probably related to the longer preparation time for surgery in these patients and the intentional delay for patients in a stable condition after recent MI and LVD. Operative and postoperative data for each group are given in Table 2.
Primary outcomes AKI was detected in 233 patients (41%). Eight patients (1%) required haemodialysis postoperatively, 6 (75%) of whom died during the early postoperative period. There was no significant difference between the patients with and those without AKI in relation to the time from catheterization to surgery (P = 0.09). Although the incidence of AKI was slightly higher in Group C, this difference was not statistically significant (P = 0.67). The effect of time between cardiac catheterization and cardiac operation on postoperative AKI was further examined by separate logistic regression models of periods in 0–1, 0–2, 0–4, 0–6, 0–10 days and 0 to ≥11 days before the operation (Table 3). There was a very slight increased risk of developing AKI in 0–2 days but none of the time periods was found to be statistically significant. The risk of developing AKI seems to be neither reduced nor increased by increasing time from catheterization to operation. Furthermore, there was no significant relation in the time from catheterization to operation and AKI in patients with elevated preprocedural creatinine levels (>106 μmol l−1, P = 0.23), LVD (ejection fraction [EF] 106 μmol l−1)
General (n = 573)
Group A (n = 69)
Group B (n = 216)
Group C (n = 288)
P-value
59.3 ± 11
57.9 ± 11.4
59.6 ± 10.3
59.4 ± 11.4
0.54
163 (28) 410 (72) 28 ± 4.6 312 (55) 211 (37) 298 (52) 276 (48) 216 (38) 124 (22) 51 (9) 21 (4) 153 (27) 55 (10) 1.8 ± 1.8
20 (29) 49 (71) 29 ± 4.5 42 (61) 23 (33) 38 (55) 41 (59) 31 (45) 18 (26) 5 (7) 0 24 (35) 4 (6) 2.2 ± 1.9
56 (26) 160 (74) 28 ± 4.3 116 (54) 77 (36) 120 (56) 103 (48) 89 (41) 43 (20) 19 (9) 6 (3) 43 (20) 13 (6) 1.9 ± 2.2
87 (30) 201 (70) 28 ± 4.8 154 (54) 111 (39) 140 (49) 133 (46) 96 (33) 63 (22) 27 (9) 15 (5) 86 (30) 38 (13) 1.6 ± 1.5
0.57
129 (23) 290 (51) 133 (23) 21 (4) 39 ± 4.8 45 (8)
9 (13) 30 (44) 21 (30) 9 (13) 40 ± 3.9 6 (9)
59 (27) 110 (51) 44 (20) 3 (1) 40 ± 4.8 9 (4)
61 (21) 150 (52) 68 (24) 9 (3) 39 ± 4.9 30 (10)
0.02 0.52 0.65 0.26 0.14 0.08 0.55 0.85 0.08 0.005 0.01 0.01 0.0001
0.008 0.03
Bold characters are used to express P– values that are statistically significant (< 0.05). Data are number of patients (%) or mean ± SD. NYHA: New York Heart Association; SD: standard deviation.
Table 2: Operative, perioperative and postoperative variables General (n = 573) Operation CABG 462 (81) Valve 49 (9) Combined 39 (7) Other 23 (4) Cross-clamp time (min) 64 ± 33 CPB time (min) 102 ± 44 Lowest haematocrit on CPB 24 ± 3.8 Lowest mean arterial pressure on CPB 51 ± 5 Perioperative fluid and blood product transfusion Total replacement (ml) 3314 ± 1700 Colloid (ml) 568 ± 470 Packed red blood cells (units) 0.6 ± 0.9 Fresh frozen plasma (units) 1.4 ± 1.1 Whole blood (units) 0.7 ± 0.7 Perioperative inotrope 244 (43) Acute kidney injury 233 (41) Intra-aortic balloon pump 9 (2) Atrial fibrillation 103 (18) Time on ventilator (h) 10 ± 13 Total drainage (ml) 557 ± 303 Intensive care unit stay (days) 4±4 Length of hospital stay (days) 5±4
Group A (n = 69)
Group B (n = 216)
Group C (n = 288)
P-value
63 (91) 2 (3) 3 (4) 1 (1) 61 ± 35 97 ± 42 24 ± 3.8 52 ± 6
175 (81) 16 (7) 13 (6) 12 (6) 62 ± 30 99 ± 43 25 ± 3.4 51 ± 5
224 (78) 31 (11) 23 (8) 10 (4) 66 ± 35 104 ± 44 24 ± 4.1 50 ± 5
0.13
0.27 0.29 0.18 0.04
3259 ± 746 454 ± 451 0.6 ± 0.8 1.8 ± 0.8 0.9 ± 0.5 30 (43) 28 (41) 1 (1) 8 (12) 10 ± 9 542 ± 270 4±4 5±4
3246 ± 710 538 ± 455 0.5 ± 0.9 1.5 ± 1.3 0.7 ± 0.6 82 (38) 83 (38) 2 (1) 31 (14) 9±7 593 ± 332 3±3 4±3
3378 ± 2293 621 ± 481 0.7 ± 1 1.3 ± 1.1 0.7 ± 0.8 132 (46) 122 (43) 6 (3) 64 (22) 11 ± 17 533 ± 286 4±5 6±5
0.66 0.01 0.02 0.009 0.12 0.22 0.67 0.58 0.02 0.33 0.08 0.03 0.03
Bold characters are used to express P– values that are statistically significant (< 0.05). Data are number of patients (%) or mean ± SD. CABG: coronary artery bypass graft surgery; CPB: cardiopulmonary bypass; SD: standard deviation.
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Table 3: Logistic regression analysis of the risk of development of AKI after cardiac surgery in relation to the time between cardiac catheterization and surgery B
χ2
C
Number of cases (%)
OR
95% CI
P-value
0 0–1 0–2 0–4 0–6 0–10 0 to ≥11 Overall daysa
0.03 0.03 0.29 0.09 0.03 0.03 0.27 0.001
0.004 0.004 0.29 0.03 0.003 0.003 0.31 0.007
0.5 0.503 0.53 0.51 0.502 0.502 0.51 0.54
49 (9) 60 (10) 95 (17) 117 (20) 86 (15) 146 (26) 573 (100)
1.03 0.97 1.33 1.09 1.03 1.03 1.31 1.001
0.41–2.56 0.33–2.79 0.47–3.78 0.41–2.92 0.39–2.71 0.38–2.78 0.51–3.39 0.99–1.006
0.95 0.95 0.59 0.86 0.95 0.95 0.58 0.79
ORIGINAL ARTICLE
Time (days)
a Hosmer–Lemeshow, χ 2 = 9.45, degrees of freedom = 8, P = 0.31. Bold characters are used to express P– values that are statistically significant (< 0.05). AKI: acute kidney injury; C: c-statistic; CI: confidence interval; OR: odds ratio.
Table 4: Bivariate analysis of the variables associated with development of AKI
Age Sex Female Male Body mass index (kg m−2) Hypertension Diabetes mellitus Hyperlipidaemia Smoker Family history Chronic obstructive pulmonary disease Peripheral arterial disease Left ventricular dysfunction EuroSCORE II (% mortality risk) Time from angiography to operation (days) Emergency surgery Operation CABG Valve Combined Other Preoperative creatinine level ≤106 μmol l−1 Preoperative creatinine level >106 μmol l−1 Preoperative haematocrit Cross-clamp time (min) CPB time (min) Lowest haematocrit on CPB Lowest mean arterial pressure on CPB Perioperative blood drainage Perioperative fluid and blood product transfusion Colloid (ml) Packed red blood cells (units) Fresh frozen plasma (units) Whole blood (units) Perioperative inotrope Intra-aortic balloon pump Time on ventilator (h) Total drainage (ml) Intensive care unit stay (days) Mortality
No AKI (n = 340)
AKI (n = 233)
P-value
58 ± 11.1
61.1 ± 10.7
0.001
94 (28) 246 (72) 27.5 ± 4.5 177 (52) 123 (36) 181 (53) 166 (49) 133 (39) 67 (20) 33 (10) 38 (11) 1.7 ± 1.9 11 ± 38 41 (12)
69 (30) 164 (70) 28.8 ± 4.7 135 (58) 88 (38) 117 (50) 111 (48) 83 (36) 57 (25) 18 (8) 17 (7) 1.9 ± 1.7 12 ± 24 24 (10)
0.67
276 (81) 32 (9) 20 (6) 12 (4) 317 (93) 23 (7) 40 ± 4.7 61 ± 30 96 ± 37 25 ± 4 51 ± 5 540 ± 171
186 (80) 17 (7) 19 (8) 11 (5) 211 (91) 22 (9) 39 ± 4.8 69 ± 36 110 ± 51 24 ± 4 50 ± 5 580 ± 240
0.51
521 ± 444 0.5 ± 0.9 1.4 ± 0.9 0.7 ± 0.5 141 (42) 3 (1) 9 ± 10 531 ± 279 3±3 7 (2)
641 ± 499 0.7 ± 1.1 1.5 ± 1.4 0.8 ± 0.9 103 (44) 6 (3) 12 ± 16 594 ± 333 8±5 18 (8)
0.007* 0.001 0.45 0.29 0.49 0.11 0.0001* 0.06* 0.0001* 0.001
Bold characters are used to express P– values that are statistically significant (< 0.05). Data are number of patients (%) or mean ± SD. *Mann–Whitney U-test. CPB: cardiopulmonary bypass; SD: standard deviation.
0.002 0.17 0.69 0.48 0.78 0.39 0.17 0.41 0.12 0.04 0.09* 0.51
0.24 0.006 0.005 0.0001 0.007 0.004* 0.03
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Table 5: surgery
Multivariate analysis of the demographic and perioperative variables associated with development of AKI after cardiac
Age (years) CPB time (min) Body mass index (kg m−2) Preoperative haematocrit Constant
B
χ 2 (Wald)
OR
95% CI
P-value
0.022 0.007 0.066 −0.045 −2.463
6.62 8.63 11.17 5.43 4.64
1.022 1.007 1.068 0.956 0.085
1.005–1.039 1.002–1.011 1.028–1.11 0.920–0.993
0.01 0.003 0.001 0.02 0.03
Bold characters are used to express P– values that are statistically significant (< 0.05). c-statistic for the model = 0.658, Hosmer–Lemeshow χ 2 = 13.24, degrees of freedom = 8, P = 0.104. AKI: acute kidney injury; CI: confidence interval; CPB: cardiopulmonary bypass.
during CPB was significantly associated with AKI (P = 0.006). The longer durations of cross-clamp and CPB and the lower minimum mean arterial pressure during CPB were found to be significantly related to the development of postoperative AKI (P = 0.005, P = 0.0001 and P = 0.004, respectively). Multivariate analysis of the variables with bivariate significance showed older age (P = 0.01), longer CPB time (P = 0.003), higher body mass index (BMI, kg m−2; P = 0.001) and lower preoperative haematocrit (P = 0.02) to be independently associated with development of AKI (Table 5; c-statistic = 0.658, Hosmer–Lemeshow χ 2 = 13.24, degrees of freedom = 8, P = 0.104). Although increased amounts of colloid infusion and packed red blood cell (PRBC) transfusion, lower haematocrit levels on CPB, excess perioperative blood drainage, longer cross-clamp time and lower mean arterial pressure on CPB were noted in the bivariate analysis, none of these variables was found to be significantly associated with development of AKI in the logistic regression model. Overall postoperative hospital mortality was 4.4%. Mortality was not significantly different between the three groups of time from catheterization (P = 0.15); however, it was significantly increased in the patients with AKI (P = 0.001). Bivariate analysis of the variables age (P = 0.001), diabetes mellitus (P = 0.04), elevated preoperative creatinine levels (>106 μmol l−1; P < 0.0001), longer cross-clamp (P < 0.0001) and CPB times (P < 0.0001), presence of AKI (P = 0.001), lowest haematocrit level measured on CPB (P = 0.01), increased amounts of perioperative blood drainage (P = 0.004) and PRBC transfusion (P < 0.0001) and total perioperative colloid infusion (P = 0.008) showed significant associations of these factors with mortality. However, in the multivariate logistic regression analysis, elevated preoperative creatinine levels (>106 μmol l−1) were associated with a more than 5-fold increase in mortality (OR, 5.39; 95% CI, 1.99–14.63; P = 0.001) followed by almost a 3-fold increase in the presence of AKI (OR, 2.96; 95% CI, 1.14–7.69; P = 0.03). Other independent predictors for mortality were presence of diabetes mellitus (OR, 2.74; 95% CI, 1.11–6.78; P = 0.03), increasing amounts of perioperative PRBC transfusion (OR, 1.68; 95% CI, 1.24–2.28; P = 0.001) and older age (OR, 1.06; 95% CI, 1.01–1.11; P = 0.02) (c-statistic = 0.844, Hosmer–Lemeshow χ 2 = 6.56, degrees of freedom = 8, P = 0.59).
DISCUSSION Our study showed that the time between cardiac catheterization and cardiac surgery was not a significant risk factor for the
occurrence of AKI. Even after extensive statistical analysis, there was no significant correlation between any of the groups, according to the time between cardiac catheterization and operation, and the development of AKI. There are contradicting reports regarding the association between AKI and the time between angiography and cardiac surgery. Del Duca et al. [10] concluded that cardiac catheterization performed within 5 days before the operation is a significant risk factor for acute renal failure after cardiac surgery. Medalion et al. [11] also suggested that CABG should be delayed by at least 5 days in patients who receive a high contrast dose. Their results showed that an operation performed within 24 h of catheterization was an independent predictor of postoperative acute renal failure [11]. Similar to Hennessy et al. [12], Ranucci et al. [13] reported that surgery performed on the same day as angiography is a risk factor for acute renal failure. However, in those reports, patients who underwent surgery close to the time of angiography and developed acute renal failure had more preoperative risk factors for postoperative acute renal failure. In contrast, in the present study, Group C included more patients with elevated preoperative creatinine levels and other risk factors for postoperative acute renal failure as a result of our institutional policy of delaying surgery in these patients. There are other studies supporting our results. Ko et al. [14] noted that the time interval between coronary angiogram and cardiac surgery did not affect the risk of AKI after cardiac surgery. Brown et al. [15] suggested that same-day angiography may be safe in a select population of valve surgery patients. Greason et al. [16] further supported these findings and concluded that in select patients with a low risk of AKI, same-day angiography was not associated with increased morbidity, AKI or death. In the present study, we performed separate regression analysis comparing various ranges of time intervals and overall days to explore the effect of time from catheterization to operation on the development of postoperative AKI; however, there was no significant risk of developing AKI, even at 10 days. In most studies, age, LVD, diabetes mellitus, peripheral vascular disease, preoperative use of an intra-aortic balloon pump, chronic obstructive pulmonary disease, emergency surgery and elevated preoperative creatinine levels are commonly associated with increased risk of AKI [2, 10, 12, 14, 17–19]. In the present study, age, BMI, preoperative haematocrit and CPB time were among the factors significantly associated with AKI. Although an elevated preoperative creatinine level (>106 μmol l−1) was not significantly associated with AKI in our patient group, it was significantly associated with mortality.
B. Özkaynak et al. / Interactive CardioVascular and Thoracic Surgery
Funding Results of routine laboratory tests were used for this retrospective study. Therefore no budget was necessary. Conflict of interest: The authors have no relevant financial or non-financial relationship to disclose.
REFERENCES [1] Bove T, Calabro MG, Landoni G, Aletti G, Marino G, Crescenzi G et al. The incidence and risk of acute renal failure after cardiac surgery. J Cardiothorac Vasc Anesth 2004;18:442–5. [2] Rosner MH, Okusa MD. Acute kidney injury associated with cardiac surgery. Clin J Am Soc Nephrol 2006;1:19–32. [3] Kelly AM, Dwamena B, Cronin P, Bernstein SJ, Carlos RC. Meta-analysis: effectiveness of drugs for preventing contrast-induced nephropathy. Ann Intern Med 2008;148:284–94. [4] Hillis LD, Smith PK, Anderson JL, Bittl JA, Bridges CR, Byrne JG et al. 2011 ACCF/AHA guideline for coronary artery bypass graft surgery: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation 2011;124:e652–735. [5] Sudarsky D, Nikolsky E. Contrast-induced nephropathy in interventional cardiology. Int J Nephrol Renovasc Dis 2011;4:85–99. [6] McCullough PA. Contrast-induced acute kidney injury. J Am Coll Cardiol 2008;51:1419–28. [7] Mehran R, Aymong ED, Nikolsky E, Lasic Z, Iakovou I, Fahy M et al. A simple risk score for prediction of contrast-induced nephropathy after percutaneous coronary intervention: development and initial validation. J Am Coll Cardiol 2004;44:1393–9. [8] Nashef SA, Roques F, Sharples LD, Nilsson J, Smith C, Goldstone AG et al. EuroSCORE II. Eur J Cardiothorac Surg 2012;41:734–45. [9] Mehta RL, Kellum JA, Shah SV, Molitoris BA, Ronco C, Warnock DG et al. Acute kidney injury network: report of an initiative to improve outcomes in acute kidney injury. Crit Care 2007;11:R31. [10] Del Duca D, Iqbal S, Rahme E, Goldberg P, de Varennes B. Renal failure after cardiac surgery: timing of cardiac catheterization and other perioperative risk factors. Ann Thorac Surg 2007;84:1264–71. [11] Medalion B, Cohen H, Assli A, Vaknin Assa H, Farkash A, Snir E et al. The effect of cardiac angiography timing, contrast media dose, and preoperative renal function on acute renal failure after coronary artery bypass grafting. J Thorac Cardiovasc Surg 2010;139:1539–44. [12] Hennessy SA, LaPar DJ, Stukenborg GJ, Stone ML, Mlynarek RA, Kern JA et al. Cardiac catheterization within 24 hours of valve surgery is significantly associated with acute renal failure. J Thorac Cardiovasc Surg 2010;140:1011–7. [13] Ranucci M, Ballotta A, Kunkl A, De Benedetti D, Kandil H, Conti D et al. Influence of the timing of cardiac catheterization and the amount of contrast media on acute renal failure after cardiac surgery. Am J Cardiol 2008; 101:1112–8. [14] Ko B, Garcia S, Mithani S, Tholakanahalli V, Adabag S. Risk of acute kidney injury in patients who undergo coronary angiography and cardiac surgery in close succession. Eur Heart J 2012;33:2065–70. [15] Brown ML, Holmes DR, Tajik AJ, Sarano ME, Schaff HV. Safety of same-day coronary angiography in patients undergoing elective valvular heart surgery. Mayo Clin Proc 2007;82:572–4. [16] Greason KL, Englberger L, Suri RM, Park SJ, Rihal CS, Pislaru SV et al. Safety of same-day coronary angiography in patients undergoing elective aortic valve replacement. Ann Thorac Surg 2011;91:1791–6. [17] Kramer RS, Quinn RD, Groom RC, Braxton JH, Malenka DJ, Kellet MA et al. Same admission cardiac catheterization and cardiac surgery: is there an increased incidence of acute kidney injury? Ann Thorac Surg 2010;90:1418–24. [18] Kumar AB, Suneja M, Bayman EO, Weide GD, Tarasi M. Association between postoperative acute kidney injury and duration of cardiopulmonary bypass: a meta-analysis. J Cardiothorac Vasc Anesth 2012;26:64–9. [19] Mehta RH, Honeycutt E, Patel UD, Lopes RD, Williams JB, Shaw LK et al. Relationship of the time interval between cardiac catheterization and elective coronary artery bypass surgery with postprocedural acute kidney injury. Circulation 2011;124:S149–55.
ORIGINAL ARTICLE
The main limitation of this study is its retrospective observational design. Our study cohort included patients with various risks and different types of operations, reflecting our daily clinical experience. However, patients with prominent chronic kidney failure and those receiving preoperative dialysis were excluded to express a new renal insult. Furthermore, widely accepted and sensitive AKI network criteria have been used to define AKI. High-risk patients with elevated creatinine levels are managed— complying with the guidelines—through proper hydration, discontinuation of nephrotoxic agents and optimization of renal functions before the operation. These patients had a longer time interval between catheterization and operation and were predominantly present in Group C. This bias in our study may be an advantage, since our practice filters out the high-risk patients. Consequently, the low- and medium-risk patients could be studied to obtain clearer evidence on the effect of time between catheterization and operation. Another limitation is the lack of data on the volumes of contrast used for the catheterizations, which were not recorded. However, note that all the patients received the same type of contrast agent, the lowest possible amounts of contrast were used and no excess use was reported in any of the patients. Since the quantity and type of contrast used did not vary, it is possible that these were not influential factors in this study. This study has important clinical implications and can guide surgeons on the timing of surgery after cardiac catheterization. First, in emergency and urgent cases, surgery can be performed safely with appropriate precautions, and it should not be delayed to decrease the risk of postoperative renal dysfunction. These precautions should include optimization of preoperative haematocrit levels; maintenance of adequate haematocrit and mean arterial pressure during CPB and use of meticulous surgical techniques to minimize the duration of CPB, perioperative bleeding and requirements for blood transfusion. Even in elderly patients, patients with LVD and patients with increased creatinine level, the timing between angiography and surgery was not found to be a risk factor for AKI, and early surgery can be recommended in clinically unstable patients. Secondly, since Group C included a greater number of patients with increased risk of AKI, optimizing renal functions preoperatively in stable patients may be an appropriate strategy. Although the guideline recommends withholding surgery only in patients with chronic renal dysfunction, we believe that it would also be useful to withhold the intervention for the optimization of renal functions in high-risk patients ( particularly in older patients and in those with high BMI and low preoperative haematocrit levels) and in patients undergoing CPB of a possibly longer duration. In conclusion, our results do not support the a priori hypothesis of the additive risk of cardiac catheterization and CPB on the development of postoperative AKI, when these procedures are performed in close succession. According to various reports, the axiomatic concept of the ‘recovery period’ of the kidneys after exposure to contrast is widely accepted and further insults on the functional reserve of the kidneys should be avoided in this interim period of 10 days. However, our results showed that surgery may be considered ‘safe’ on any day after catheterization, if influential factors other than time are accounted for when planning cardiac surgery, in order to prevent postoperative renal complications.
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