Understanding Acute Kidney Injury (AKI Made Easy)

foreign [Music] deterioration in the function of the kidneys is known as an acute kidney injury sometimes also called acute renal failure to measure this reduction in kidney function glomerular filtration rate or GFR is normally used which is a measurement of how well the kidneys are filtering the blood the functional unit of the kidney that actually does this is the nephron made up of the glomerulus which is a modified capillary and as blood passes through it the waste is filtered into the Bowman's capsule GFR is the volume filtered through the glomerulus into the Bowman's capsule and

through the Nephron in a given unit of time the filtrate passes along through the proximal convoluted tubule Loop of henle distal convoluted tubule and the distal collecting duct undergoing secretion and reabsorption as it travels ultimately it forms urine and collects into the renal pelvis and passes into the bladder through the ureter to directly measure this process is difficult we instead use creatinine clearance to estimate the GFR creatinine is a normal breakdown product of creatine released from muscle tissue and this is freely filtered by the glomerulus and is not reabsorbed so fits the kind of substance

we need however creatinine is secreted into the filtrate by the peritubular capillaries so it does tend to overestimate the GFR slightly the cockcraft Gult formula is a famous formula used to estimate the creatinine clearance and therefore GFR taking into account age Mass gender and the serum creatinine but more recently other formulas such as the modification of diet in renal disease study group formula have become more widely used the causes of acute kidney injury are broken down into three main types pre-renal intrinsic and posterenal pre-renal causes are primarily involved with a reduction in blood perfusion to

the kidney such as during periods of hypovolemia which could come from GI losses like vomiting or diarrhea or even hemorrhages or Burns hypotension is another cause which can itself be caused by hypovolemia as well as cardiogenic causes distributive causes like sepsis or anaphylaxis or obstructive causes like a pulmonary embolism renal artery stenosis or an aortic dissection may also interrupt blood flow to the kidneys intrinsic causes affect components of the Nephron directly the glomerulus generates a pressure gradient by having relative afferent vasodilation and efferent vasoconstriction non-steroidal anti-inflammatories can cause vasoconstriction of the afferent arterial and ACE

inhibitors or Angiotensin receptor blockers can cause efferent vasodilation both of which can reduce the pressure gradient and therefore reduce GFR acute tubular necrosis is when epithelial cells of the tubular system die which can actually be caused by pre-renal injury so pre-renal injury can later cause an intrinsic injury Rhabdomyolysis and hemolysis can also cause this due to release of myoglobin which injures the renal tubular cells antibiotics like aminoglycosides and Vancomycin can also cause it as can contrast from radiological studies acute interstitial nephritis is inflammation of the interstitium of the kidney it can be caused by medication

like antibiotics including penicillins proton pump inhibitors and non-steroidal anti-inflammatories can also cause it as can some immune diseases like lupus another cause of intrinsic Aki glomerular diseases like anti-glomerular basement membrane disease also known as good pastures disease or post-infection glomerulonephritis vascular conditions like thrombosis or embolic events can also cause intrinsic Aki post renal causes are causes beyond the kidney due to obstruction of the passage of urine this could be from outside the urinary system pressing in such as benign prostatic hypotrophy or an extrinsic tumor or it could be from within the urinary system itself such

as strictures or intrinsic tumors renal Stones could also cause an Aki however this would generally be affecting one kidney and therefore is more Uncommon there are no specific signs and symptoms of an acute kidney injury although there may be signs of the underlying cause such as the presence of vomiting and diarrhea in cases caused by gastrointestinal losses urine production May provide a clue including looking at the pattern and time scale of the reduction in urine production alongside this there can be General symptoms of lethargy nausea and even delirium patients may present as being hypovolemic but

on the other side can also present with fluid overload in which case there may be a reduction in cardiac output that is causing the reduced renal function the definition of Aki has been proposed as an increase in serum creatinine by 26 micromoles per liter in 48 hours an increase in creatinine by 1.5 times the Baseline in seven days or urine production of less than 0.5 milliliters per kilogram per hour for more than six hours as each of these would generally indicate a reduction in GFR Aki is actually fairly common with some studies quoting five percent

of all hospital patients at some point during their admission suffering an Aki in most cases it is first identified by a blood test showing raised serum creatinine and this test should also include electrolytes as reduced kidney function can predispose to electrolyte imbalances a high urea to creatinine ratio tends to suggest a pre-renal cause urine studies can also be done including a urine dip which could identify proteinuria or microscopic hematuria and urinalysis including microscopy looking for castes which are small tube-shaped particles casts made up of brown or black pigment May indicate acute tubular necrosis made from

necrosed epithelial cells while red blood cell casts May indicate glomerulonephritis and white blood cell casts May indicate acute interstitial nephritis urinary concentrations of electrolytes creatinine and urea can also help differentiate the primary cause however electrolyte concentrations can often be altered by diuretic use Imaging can include an ultrasound which may help to identify any structural abnormalities as could a CT scan for some cases particularly intrinsic causes a kidney biopsy may be needed for a diagnosis the treatment depends on severity and on the underlying cause in most cases intravenous fluids are given to promote renal perfusion but

one of the main exceptions being in times where the patient is fluid overloaded offending medication should be reviewed on a risk benefit basis and the pneumonic dam for diuretics ACE inhibitors or Angiotensin receptor blockers and antibiotics metformin and non-steroidal anti-inflammatories can help remember some of these metformin is included because it is excreted by the kidneys and can predispose to acidosis again in some cases nephrotoxic medication may need to be continued such as in fluid overload secondary to heart failure where the diuretics may actually end up increasing renal function if electrolyte imbalances are present then they

should also be corrected for example hypokalemia with calcium gluconate to stabilize The myocardium and reduce the risk of arrhythmia alongside insulin and dextrose to reduce potassium levels while maintaining blood glucose in obstructive causes this should generally be relieved by a catheter if the obstruction is a bladder Outlet obstruction urine output alongside fluid intake should be measured with daily weights and renal replacement therapy where the function of the kidney is replaced such as hemodialysis is indicated in some cases such as severe acidosis or hyperkalemia drug intoxications or in cases refractory to medical treatment