Acute renal failure after burn injury

　　1. Shock

　　Hypovolemic shock after burn injury is the main cause of acute renal failure. During shock, the decrease in glomerular arterial blood pressure or serum sodium stimulates the juxtaglomerular apparatus, producing a large amount of renin and angiotensin II, causing vasoconstriction of renal vessels, ischemia and hypoxia of the kidneys, a decrease in glomerular filtration rate, and oliguria or anuria.

　　2. Toxic substances

　　Toxic substances produced during severe burns and sepsis, including free hemoglobin, myoglobin, and bacterial toxins, can directly or indirectly exacerbate renal damage.

　　3. Antibiotics

　　Aminoglycoside antibiotics, polymyxin B, and sulfonamide drugs can cause nephrotoxic reactions.

　　4. Other causes

　　Dehydration caused by severe diarrhea, thermal wind therapy, and stress-induced diabetes is not corrected in time. The pre-renal failure can be precipitated by the large-scale application of vasoconstrictors or diuretics before the blood volume is replenished during the shock phase. Elderly patients and those with kidney disease before the injury may develop renal failure.

　　The complications of acute renal failure after burn injury are similar to those of acute renal failure, mainly including the following:

　　1. Infection is one of the most common and severe complications, especially common in this disease.

　　2. Cardiovascular complications include arrhythmias, heart failure, pericarditis, and hypertension.

　　3. Neurological complications include headache, drowsiness, muscle twitching, coma, epilepsy, and are related to the retention of toxins in the body, water intoxication, electrolyte imbalance, and acid-base imbalance.

　　4. Gastrointestinal complications are manifested as anorexia, nausea, vomiting, abdominal distension, hematemesis, or hematochezia, and bleeding is often caused by erosion of the gastrointestinal mucosa or stress ulcers.

　　5. Hematological complications, due to the rapid decline in renal function, can lead to a decrease in erythropoietin, causing anemia, but most cases are not severe. A few cases may have a tendency to bleed due to a decrease in coagulation factors.

　　6. Electrolyte imbalance and metabolic acidosis can lead to hyperkalemia, hyponatremia, and severe acidosis, which are one of the most dangerous complications of acute renal failure.

　　During polyuria, the patient's daily urine output can reach 3000-5000ml. Due to the excretion of a large amount of water and electrolytes, dehydration, hypokalemia, hyponatremia, and other conditions may occur. If not supplemented in time, the patient may die from severe dehydration and electrolyte imbalance.

　　During the recovery period, serum urea nitrogen and creatinine levels return to normal, uremic symptoms subside, renal tubular epithelial cells regenerate and repair, most patients can completely recover renal function, and a few patients may have varying degrees of renal dysfunction.

　　1. Oliguria

　　After sufficient blood volume and water replacement, oliguria still occurs, and oliguria should be differentiated between pre-renal and post-renal conditions.

　　2. Low urine specific gravity

　　Fixed at 1.010～1.018, urine sediment contains granular casts, epithelial cell fragments, red blood cells, and white blood cells.

　　3. Azotemia

　　Urea nitrogen/blood urea nitrogen＜14:1, creatinine/blood creatinine＜10:1, blood urea nitrogen/blood creatinine＜10:1.

　　4. The measurement of free water clearance

　　The normal value of free water clearance is negative, the closer to zero, the more severe the renal dysfunction, free water clearance is more sensitive than blood chemistry tests (BUN, Cr) and is helpful for early diagnosis.

　　5. Filtration sodium excretion fraction FENa

　　When renal insufficiency is functional, renal tubules can reabsorb sodium ions in large quantities, FENa decreases; whereas in tubular organic changes, the ability to reabsorb sodium ions is significantly reduced, FENa increases, so FENa can be used to predict the ability of renal tubules to reabsorb sodium. Note: UNa urine sodium (mmol); Pna plasma sodium (mmol); Cr creatinine clearance; PCr plasma creatinine (mg/dl); V urine volume (L); GFR glomerular filtration rate; UCr urine creatinine (mg/dl); FENa normal value 1～3.

　　FENa＜1 suggests renal insufficiency is pre-renal or functional, FENa＞3 suggests acute tubular damage, renal insufficiency is renal or organic. When renal insufficiency is functional, renal tubules can reabsorb sodium ions in large quantities, FENa decreases; whereas in tubular organic changes, the ability to reabsorb sodium ions is significantly reduced, FENa increases, so FENa can be used to predict the ability of renal tubules to reabsorb sodium. Note: UNa urine sodium (mmol); Pna plasma sodium (mmol); Cr creatinine clearance; PCr plasma creatinine (mg/dl); V urine volume (L); GFR glomerular filtration rate; UCr urine creatinine (mg/dl); FENa normal value 1～3.

　　The mortality rate of acute renal failure after burn is relatively high, and the focus of prevention is to prevent the occurrence of complications:

　　1. Pay attention to infection, which is the most common complication of the disease, and strict monitoring and preventive measures against infection should be taken.

　　2. Actively correct water, electrolyte, and acid-base balance disorders, provide timely and correct anti-shock treatment, prevent insufficient effective blood volume, and relieve renal vessel constriction to avoid the occurrence of renal ARF.

　　3. For severe soft tissue crush injuries and accidental transfusion of incompatible blood, while treating the primary disease, 250ml of sodium bicarbonate solution should be used to alkalinize urine, and mannitol should be applied to prevent hemoglobin, myoglobin from blocking renal tubules or other renal toxins from damaging renal tubular epithelial cells.

　　4. Before surgery that affects renal blood flow, it is necessary to expand blood volume, and mannitol or furosemide (Lasix) should be used during and after the operation to protect renal function. The dosage of mannitol should not exceed 100g. Furosemide 1-3g/d can transform oliguric acute renal failure (ARF) into non-oliguric ARF. Dopamine 0.5~2ug/(kg·min) can dilate renal vessels to increase glomerular filtration rate and renal plasma flow.

　　5. When oliguria occurs, fluid replacement tests can be applied, which can distinguish between prerenal and renal ARF, and may also prevent the progression of prerenal ARF to renal ARF.

　　For patients with moderate to severe burns, appropriate examinations should be carried out as follows:

　　1. Urine examination:Urine output is reduced, urine volume ≤17ml/h or

　　2. Azotemia:Blood urea nitrogen and creatinine increase, but azotemia cannot be used as a sole diagnostic criterion, because even in patients with normal renal function who have massive gastrointestinal bleeding, blood urea nitrogen can also increase, and blood creatinine increases. Blood urea nitrogen/blood creatinine ≤10 is an important diagnostic indicator. In addition, urine/blood urea <15 (normal urine urea 200-600mmol/24h, urine/blood urea >20), and urine/blood creatinine ≤10 also has diagnostic significance.

　　3. Blood examination:Red blood cells and hemoglobin decrease, white blood cells increase, platelets decrease, blood potassium, magnesium, and phosphorus increase, blood sodium is normal or slightly decreased, blood calcium decreases, and carbon dioxide binding capacity also decreases.

　　4. Urinary sodium:is quantitative >30mmol/L.

　　Fractional excretion of sodium (FENa) measurement, this method has certain significance for the etiology, and values greater than 1 indicate acute tubular necrosis, non-oliguric acute tubular necrosis, and urinary tract obstruction, and the value

　　5. Measurement of pure water clearance:This method is helpful for early diagnosis.

　　Pure water clearance = urine volume (1 hour) (1 - urine osmolality/blood osmolality)

　　The normal value is -30, the larger the negative value, the better the renal function; the closer to 0, the more severe the renal function.

　　-25～-30 indicates that renal function has begun to change.

　　-25～-15 indicates mild to moderate renal damage.

　　-15～0 indicates severe renal damage.

　　The diet for acute renal failure after burn should be low in salt, low in fat, high in quality low protein, low in phosphorus, high in calcium, and high in calories.

　　1. Supply high-quality protein:For patients with acute renal failure, it is necessary to limit the intake of protein, which can reduce nitrogen retention in the blood, alleviate the burden on the kidneys, and thus delay the progression of chronic renal function failure. Generally, the protein intake is recommended to be 0.4-0.6g/kg body weight per day, and high-quality protein should be chosen, such as animal proteins such as eggs, milk, lean meat, etc., which contain a high proportion of essential amino acids and produce less nitrogenous substances after decomposition in the body. Plant proteins such as soy products, corn, flour, rice, etc., contain fewer essential amino acids and more non-essential amino acids, with low biological value, hence known as "low-quality protein", and appropriate limitations should be imposed. There are also certain requirements for protein intake for patients with nephrotic syndrome, neither strictly controlling the protein intake nor emphasizing high-protein diet excessively, because sustained low plasma protein levels can lead to decreased resistance, easy infection, recurrent edema, and aggravation of the condition, while high-protein diet can cause increased glomerular filtration, which over time can promote glomerulosclerosis. Currently, it is advocated that for patients with nephrotic syndrome with normal renal function, the daily protein intake should be 1g/kg body weight, and high-quality protein should be the main choice.

　　2. Limit water intake:Acute renal failure patients without oliguria and edema do not need to control their water intake. For patients with edema, the intake of water should mainly be controlled according to the urine output and the degree of edema. Generally speaking, when edema is obvious, the intake of water, in addition to food, should be limited to 500-800ml per day. After urinary tract infection, to avoid and reduce the停留 and reproduction of bacteria in the urinary tract, patients should drink more water and urinate frequently to achieve the purpose of frequent flushing of the bladder and urethra. Patients with urinary tract stones should also drink plenty of water because reduced urine output is one of the main reasons for the formation of urinary tract stones. Drinking plenty of water can dilute the concentration of urinary crystals, avoid excessive urine concentration, reduce precipitation opportunities, and generally require drinking 2400-3000ml of water per day to maintain daily urine output at 2000-2400ml or more. Increased urine output can promote the excretion of small stones, and at the same time, urine dilution can also slow down the growth rate of stones and avoid recurrence of stones after surgery.

　　3. Provide low-salt and low-sodium diets:During the oliguria period, edema is often accompanied, and low-salt, salt-free, or low-sodium diets should be adopted according to the determination of blood sodium levels.

　　4. During hyperkalemia, reduce the potassium content in the diet and avoid foods high in potassium to prevent an increase in exogenous potassium and exacerbate hyperkalemia.High-potassium foods can reduce potassium content by freezing, soaking in water, or discarding the soup.

　　5. If improvement can be achieved in the short term, a low-protein diet should be provided. For those with severe gastrointestinal reactions, intravenous fluid replacement can be administered in the short term, mainly with glucose as the main component.

　　6. During the polyuria period, urine output increases, blood urea nitrogen levels decrease, and appetite improves. Appropriate nutrition can accelerate the body's repair.During the polyuria period, attention should be paid to the supplementation of water and electrolytes, with about 1000 milliliters of water per day. When administering intravenous fluids, the urine output of the previous day should also be calculated. It is important to provide vitamin preparations.

　　7. During the recovery period, blood creatinine and blood urea nitrogen levels gradually decrease, and dietary protein can be gradually increased. Amino acid injections can be administered if necessary.Amino acid injections contain isoleucine, leucine, lysine, methionine, valine, arginine, histidine, etc. It is noteworthy that branched-chain amino acids should account for 40% to 50% of essential amino acids, which is conducive to the synthesis of muscle protein.

　　8. Avoid刺激性 food such as alcohol, coffee, and chili during acute renal failure.

　　The above precautions for acute renal failure need to be emphasized to both patients and their families. In addition, attention should be paid to bed rest, comfortable emotions, and maintaining a cheerful spirit. Early treatment should be carried out as soon as possible for the primary disease that triggers acute renal failure. Acute renal failure patients must be hospitalized for treatment, and the handling of these factors will directly affect the prognosis of acute renal failure.

　　1. Active and effective anti-shock, anti-infection, and wound treatment

　　It is the key to preventing the occurrence of acute renal failure. Early excision of necrotic tissue and covering the wound can prevent the release of antibiotics and infection.

　　2. Energy Supply

　　Burn patients with acute renal failure require 5000KCal of calories per day, which must be achieved through a combination of oral and intravenous nutrition. To reduce fluid intake, concentrated high-calorie intravenous nutrition can be used. The use of a certain amount of essential amino acids for patients with acute renal failure will not increase blood urea nitrogen, on the contrary, with sufficient essential amino acids and calorie supply, it promotes the utilization of endogenous urea, reduces the decomposition of endogenous protein, decreases blood urea nitrogen, and also reduces blood potassium. However, for patients with significantly decreased creatinine clearance rate, the supply of protein should be appropriately controlled.

　　3. Control of Fluid Intake

　　During the treatment process, it is necessary to strictly prevent excessive fluid infusion, measure body weight every day, and accurately estimate the patient's fluid intake.

　　The fluid requirement for adult burn patients with ARF = 500ml + 24-hour urine output + gastrointestinal loss + body surface evaporation loss + additional fluid loss.

　　Additional fluid loss includes 1000ml of water loss from tracheotomy, and an increase of 2000 to 3000ml of water loss when using a hot air blower.

　　4. Dialysis Treatment

　　The commonly used methods are peritoneal dialysis and hemodialysis. Peritoneal dialysis is simple to use, and it is easy to control excessive body fluid with a high osmotic dialysis solution, without the need to restrict diet. However, peritoneal dialysis takes a long time, is not convenient for turning over and wound treatment; there is a significant loss of albumin and amino acids; it is prone to complications such as abdominal and thoracic infections.

　　Hemodialysis requires surgery to create an arteriovenous fistula; blood must be heparinized when passing through the dialyzer, which is relatively complex, but the short dialysis time of hemodialysis is conducive to wound treatment, without the risk of abdominal and thoracic infection, and the effect of hemodialysis is good and fast.

　　Indications for dialysis: ①Serum potassium level higher than 6.5mEq/L; ②Hyponatremia, congestive heart failure, pulmonary edema, cerebral edema, soft tissue edema; ③Blood urea nitrogen greater than 100mg/dl or an increase of 30mg/dl per day; ④Progressive acidosis, CO2-CP＜15mmol/L or blood pH＜7.15.