Andrew Stephen, MD
Background
Acute kidney injury(AKI) is a readily measurable and objective outcome for surgical critical care and trauma patients. Next to mortality it is one of the most important outcomes. It is also considered a “patient centered outcome” as AKI can result in massive lifestyle changes(need for ongoing renal replacement therapy) for patients that survive the ICU stay.
Occurrence of AKI in critically ill patients is associated with negative short-term and long-term outcomes.
Short-term:
-fluid overload and decreased cardiopulmonary function
-increased difficulty weaning the ventilator
-reduces likelihood of being able to achieve fascial closure in open abdomen patients
-metabolic acidosis, electrolyte derangements
-need for renal replacement(RRT)
Long-term:
-development of chronic kidney disease(CKD)
-development of end stage renal disease(ESRD)
-increases mortality
Etiologies
Sepsis and hypotension are the most common causes of AKI in SICU patients. Patients with baseline cardiovascular disease and CKD are more prone to develop AKI. An episode in the OR or ER of MAP < 65 mm for as short as a period of 5 minutes can cause AKI in the elderly or in those with cardiovascular disease or CKD.
Previously AKI was thought to result mainly from a renal blood flow(RBF) deficit but recently understanding has shifted to it being more of an inflammatory mediated process.
Objective measures of AKI
Just over 10 years ago RIFLE and AKIN criteria were developed to improve recognition of AKI and so that the degree of injury could be objectively described. Using one of these systems is helpful in communicating to consultants or in sign-outs.
RIFLE
Risk-rise in Cr x 1.5 from baseline, GFR decrease > 25% or UOP < 0.5 mL/kg/h for 6 hours
Injury-Cr x 2, GFR decrease > 50%, UOP < 0.5 mL/kg/h for 12 hours
Failure-Cr x 3, GFR decrease > 75%, UOP < 0.3 mL/kg/h for 24 hours
Loss-loss of renal function > 4 weeks
End stage renal disease-need for renal replacement > 3 months
A review of RIFLE and AKIN: The RIFLE and AKIN classifications for acute kidney injury: a critical and comprehensive review. Lopes JA, Jorge S. Clin Kidney J. 2013 Feb;6(1):8-14.
Importance of reviewing the anesthesia record, ER course, history
One should always review the history leading up to the patient’s admission to the SICU. Creatinine is not an accurate marker of current volume status. Low UOP and creatinine elevation may be a result of events that occurred in the OR or ER: hypotension, blood loss. It is also common to receive orthopedic spine patients among others from the OR with low UOP who are hypovolemic and need prompt resuscitation to avert AKI. Determining volume status remains an inexact art and asking Ken Lynch or an attending their thoughts is often worthwhile.
Managing electrolyte derangements and metabolic acidosis
Hyperkalemia and metabolic acidosis are the most common electrolyte and acid/base derangements. Hyperkalemia can usually be managed medically for some time with insulin, dextrose, NaHCO3, and calcium gluconate. Kayexelate should be avoided as it has been associated with bowel ischemia and surgical patients often have an ileus. Acidosis may be temporized to delay RRT with D5W NaHCO3. One review of NaHCO3 and a 2018 trial it is based on.
Sodium bicarbonate therapy for patients with severe metabolic acidaemia in the intensive care unit (BICAR-ICU): a multicentre, open-label, randomised controlled, phase 3 trial. Jaber S, Paugam C, Futier E, Lefrant JY, Lasocki S, Lescot T, Pottecher J, Demoule A, Ferrandière M, Asehnoune K, Dellamonica J, Velly L, Abback PS, de Jong A, Brunot V, Belafia F, Roquilly A, Chanques G, Muller L, Constantin JM, Bertet H, Klouche K, Molinari N, Jung B; BICAR-ICU Study Group. Lancet. 2018 Jul 7;392(10141):31-40.
Obtaining access for RRT
The internal jugular location is preferred then femoral. A key part of placement is making a big enough incision in the skin to allow the dilator and catheter to pass through, otherwise the wire may get bent.
A video of a femoral catheter placement: https://www.youtube.com/watch?v=oIx7zPJHlwU
Timing, modes of RRT
Timing of initiating RRT remains an incredibly controversial topic. Most recently in an RCT of patients with septic shock and the failure level of RIFLE, RRT within 12 hours was compared to waiting 48 hours to start RRT. No mortality difference was noted. A significant number of patients in the delayed group never received RRT. It may be worth giving patients some time then.
In the SICU continuous modes of RRT are more commonly used due to hemodynamic concerns. The Deranged Physiology blog has a review.
Adjusting, reviewing medication orders
Medication orders should be reviewed daily on rounds and adjustments made for GFR changes. Enoxaparin may need to be changed to heparin for VTE prophylaxis to reduce bleeding risk. Antibiotic dosing often needs to be adjusted.