The Significance of a Serum Creatinine in Defining Renal Function in Seriously Injured and Septic Patients

Abstract

Most current analyses of multiple organ failure after injury use the serum creatinine (SCr) as a surrogate for defining renal insufficiency (RI) or renal failure (RF). This study correlates SCr with glomerular filtration rate, renal perfusion, and renal excretion in injured and septic patients. The 289 injured patients were in shock for an average of 32 minutes and received an average of 13.9 transfusions by the end of the operation. The 34 septic patients were in shock for an average of 23 minutes and received 8.4 crystalloid during operation. The renal studies included (SCr), inulin clearance (CIn), and creatinine clearance (CCr), renal plasma flow (CPAH), renal blood flow, and the clearance of sodium (CNa++), osmolar clearance (COsm), and urine output. All clearance studies followed the classic methodologies described by Homer Smith, including weight-guided leading dose, steady-state serum levels, and urine collections made exactly 15 minutes after serum collections. The average SCr in 289 trauma and septic patients was 1.23 mg/dL and 1.3 mg/dL, respectively. The average CCr was 106 mL/min and 103 mL/min, whereas the average CIn was 96 mL/min and 95 mL/min, respectively. The CIn correlated (p<0.0005) with CCr in all patients, whereas the CIn was lower than CCr due to the tubular excretion of creatinine. For the group of patients with RI (CIn between 10 and 30 mL/min) and nonoliguric RF (CIn<10 mL/min), the average CCr was 3.1. Other values in this subgroup included an average CCr 23.6 mL/min, CIn 14.6 mL/min, CPAH 69.9 mL/min, renal blood flow 138 mL/min, CNa 0.7 mL/min, COsm 1.5 mL/min, and urine output 1.4 mL/min. Although nephrectomy in 15 of 36 patients with renal injury or death in 21 patients was associated with a higher SCr, the relationship between SCr and renal function studies remained the same as with survivors and patients without renal injury. The best SCr value for defining RI was 2.4 mg/dL and for RF was 3.1 mg/dL. Based on these findings, one can recommend that when SCr data are extracted from large trauma registries, the definition of RI should be inferred when the SCr exceeds 2.4 mg/dL, and RF should be diagnosed when the SCr exceeds 3.1 mg/dL.