Archived Comments for:
Does sodium bicarbonate infusion really have no effect on the incidence of acute kidney injury after cardiac surgery? A prospective observational trial
Limitations of observational studies in the prevention of cardiac-surgery AKI by sodium bicarbonate
Helmut Schiffl, SRH University of Health Science
5 May 2015
The secondary data reported by Dr Wetz and her colleagues suggest that perioperative sodium bicarbonate (SBIC) infusion may reduce the incidence of post-cardiac surgery (CS) - AKI in low risk patients [1]. This observational study is in contradiction with two recent meta-analyses demonstrating uniformly that SBIC does not reduce the incidence of CS-AKI but – on the contrary - harms these patients [2, 3].
The study design used by the investigators (subset of patients participating in a prospective study and historic controls) is likely to have resulted in selection bias, confounding and raises concerns about internal validity. The authors reduced the number of patients forming the SBIC group from 225 to 174 due to incomplete data, which casts doubts on the claimed “high quality“ of the prospective study. Furthermore both groups were not treated equally. The control group had longer aortic clamp and cardiopulmonary bypass times (recognized intra-operative risk factors), higher free Hb concentrations and received less peri-operative fluid administration. Most importantly, the controls with low risk and controls with high risk for CS-AKI had similar incidences of AKI.
The authors claim that SBIC may prevent CS-AKI by protection from pigment nephropathy. However, there is no proof that SBI reduces pigment nephropathy [4].
The statement of the authors that serum creatinine concentrations on day 10 after surgery indicate persisting or chronic kidney disease is wrong. There are numerous data demonstrating that serum creatinine concentrations indicating partial recovery of renal function after AKI may normalize within 12 months after the initial insult [5].
Whether or not sodium bicarbonate infusion may reduce the incidence of CS-AKI in low risk patients undergoing coronary artery surgery remains doubtful.
Reference List
1. Wetz AJ, Brauer A, Quintel M, Heise D. Does sodium bicarbonate infusion really have no effect on the incidence of acute kidney injury after cardiac surgery? A prospective observational trial. Crit Care. 2015;19:183.
2. Tian ML, Hu Y, Yuan J, Zha Y. Efficacy and safety of perioperative sodium bicarbonate therapy for cardiac surgery-associated acute kidney injury: a meta-analysis. J Cardiovasc Pharmacol. 2015;65:130-136.
3. Tie HT, Luo MZ, Luo MJ, Zhang M, Wu QC, Wan JY. Sodium bicarbonate in the prevention of cardiac surgery-associated acute kidney injury: a systematic review and meta-analysis. Crit Care. 2014;18:517-0517.
4. Schiffl H. Sodium bicarbonate infusion for prevention of acute kidney injury: no evidence for superior benefit, but risk for harm? Int Urol Nephrol. 2015;47:321-326.
5. Schiffl H, Fischer R. Five-year outcomes of severe acute kidney injury requiring renal replacement therapy. Nephrol Dial Transplant. 2008;23:2235-2241.
Critical Care
Limitations of observational studies in the prevention of cardiac-surgery AKI by sodium bicarbonate
5 May 2015
The secondary data reported by Dr Wetz and her colleagues suggest that perioperative sodium bicarbonate (SBIC) infusion may reduce the incidence of post-cardiac surgery (CS) - AKI in low risk patients [1]. This observational study is in contradiction with two recent meta-analyses demonstrating uniformly that SBIC does not reduce the incidence of CS-AKI but – on the contrary - harms these patients [2, 3].
The study design used by the investigators (subset of patients participating in a prospective study and historic controls) is likely to have resulted in selection bias, confounding and raises concerns about internal validity. The authors reduced the number of patients forming the SBIC group from 225 to 174 due to incomplete data, which casts doubts on the claimed “high quality“ of the prospective study. Furthermore both groups were not treated equally. The control group had longer aortic clamp and cardiopulmonary bypass times (recognized intra-operative risk factors), higher free Hb concentrations and received less peri-operative fluid administration. Most importantly, the controls with low risk and controls with high risk for CS-AKI had similar incidences of AKI.
The authors claim that SBIC may prevent CS-AKI by protection from pigment nephropathy. However, there is no proof that SBI reduces pigment nephropathy [4].
The statement of the authors that serum creatinine concentrations on day 10 after surgery indicate persisting or chronic kidney disease is wrong. There are numerous data demonstrating that serum creatinine concentrations indicating partial recovery of renal function after AKI may normalize within 12 months after the initial insult [5].
Whether or not sodium bicarbonate infusion may reduce the incidence of CS-AKI in low risk patients undergoing coronary artery surgery remains doubtful.
Reference List
1. Wetz AJ, Brauer A, Quintel M, Heise D. Does sodium bicarbonate infusion really have no effect on the incidence of acute kidney injury after cardiac surgery? A prospective observational trial. Crit Care. 2015;19:183.
2. Tian ML, Hu Y, Yuan J, Zha Y. Efficacy and safety of perioperative sodium bicarbonate therapy for cardiac surgery-associated acute kidney injury: a meta-analysis. J Cardiovasc Pharmacol. 2015;65:130-136.
3. Tie HT, Luo MZ, Luo MJ, Zhang M, Wu QC, Wan JY. Sodium bicarbonate in the prevention of cardiac surgery-associated acute kidney injury: a systematic review and meta-analysis. Crit Care. 2014;18:517-0517.
4. Schiffl H. Sodium bicarbonate infusion for prevention of acute kidney injury: no evidence for superior benefit, but risk for harm? Int Urol Nephrol. 2015;47:321-326.
5. Schiffl H, Fischer R. Five-year outcomes of severe acute kidney injury requiring renal replacement therapy. Nephrol Dial Transplant. 2008;23:2235-2241.
Competing interests
No competing interests