Acute renal failure in pregnancy

Acute renal failure in pregnancy can be induced by any of the disorders leading to renal failure such as acute tubular necrosis. There are certain conditions associated with pregnancy which vary between the first and second halves of gestation. Early in pregnancy, the most common problems are prerenal disease due to hyperemesis gravidarum or acute tubular necrosis, resulting from a septic abortion. Mild to moderate preeclampsia is not part of this differential diagnosis, since renal function is generally maintained in the normal or near normal range.

THROMBOTIC MICROANGIOPATHY .An important and difficult differential diagnosis is that of acute renal failure in late pregnancy in association with microangiopathic hemolytic anemia and thrombocytopenia. There are three main entities that must be considered: thrombotic thrombocytopenic purpura (TTP); postpartum hemolytic uremic syndrome (HUS); and severe preeclampsia, usually with the HELLP syndrome (hemolysis with a microangiopathic blood smear, elevated liver enzymes, and a low platelet count) .
The distinction between HUS-TTP and severe preeclampsia is important for therapeutic and prognostic reasons. However, the clinical and histologic features are so similar that establishing the correct diagnosis is often difficult. Most important are the history.(eg, preceding proteinuria and hypertension favor preeclampsia) and time of onset.
Preeclampsia typically develops in the third trimester, with only a few percent of cases developing in the postpartum period, usually in the first one to two days.
Thrombotic thrombocytopenic purpura almost always occurs antepartum; many cases begin before 24 weeks but the disease also occurs in the third trimester.
The hemolytic-uremic syndrome is generally a postpartum disease. Symptoms can begin before delivery, but the onset in most cases is delayed for 48 hours or more after delivery (mean about four weeks).

Preeclampsia: Severe preeclampsia, which is much more common than HUS or TTP, is usually preceded by clinical features characteristic of preeclampsia such as hypertension and proteinuria. Renal failure is relatively unusual even with severe cases, unless there is significant bleeding or hemodynamic instability or marked DIC. The renal and extrarenal abnormalities typically resolve spontaneously within the first two weeks postpartum. In some cases, however, preeclampsia begins in the postpartum period without prior proteinuria and may be difficult to initially differentiate from postpartum HUS. Only the subsequent spontaneous recovery will point toward preeclampsia in this setting.
Severe preeclampsia may be associated with a true DIC state with prolongation of the prothrombin and partial thromboplastin times and low levels of clotting factors. These findings, if present, are important diagnostically since they are almost always absent in HUS-TTP in which increased platelet consumption and thrombocytopenia are the primary abnormalities.
Thrombotic thrombocytopenic purpura : TTP is characterized by the pentad of microangiopathic hemolytic anemia, thrombocytopenia, renal insufficiency, fever, and neurologic abnormalities. The degree of renal impairment is often mild, whereas the neurologic involvement, fever, and thrombocytopenia are more striking.

Hemolytic-uremic syndrome : The HUS may follow a normal pregnancy or be preceded by findings indistinguishable from preeclampsia. As noted above, the absence of DIC, onset more than two days after delivery, and/or persistent disease for more than one week are the main findings that differentiate the HUS from preeclampsia.


RENAL CORTICAL NECROSIS: Bilateral renal cortical necrosis (or, in less severe cases, acute tubular necrosis) may be induced during pregnancy by abruptio placentae or other severe complication such as placenta previa, prolonged intrauterine fetal death, or amniotic fluid embolism.
Affected patients typically have one of the above complications of pregnancy and then develop the abrupt onset of oliguria or anuria, frequently accompanied by gross hematuria, flank pain, and hypotension. The triad of anuria, gross hematuria, and flank pain is unusual in the other causes of renal failure in pregnancy.

The diagnosis can usually be established by ultrasonography or CT scanning, which demonstrate hypoechoic or hypodense areas in the renal cortex. Renal biopsy or arteriography also can be performed, but these invasive procedures are not required in most cases. Renal calcifications on plain film of the abdomen also suggests renal cortical necrosis, but this is a late consequence of healing and is not visible for one to two months.
No specific therapy has been shown to be effective in this disorder. Many patients require dialysis, but 20 to 40 percent have partial recovery with a creatinine clearance that stabilizes between 15 and 50 mL/min.

ACUTE PYELONEPHRITIS: Although renal function is generally well maintained during episodes of acute pyelonephritis , some pregnant women can develop acute renal failure. Renal biopsy in this setting may reveal focal microabscesses and recovery after appropriate antimicrobial therapy may be incomplete due to irreversible injury.

ACUTE FATTY LIVER OF PREGNANCY: Acute fatty liver is a rare complication of pregnancy that is associated with acute renal failure in up to 60 percent of cases. The diagnosis should be suspected in a woman with preeclampsia who has hypoglycemia, hypofibrinogenemia, and a prolonged PTT in the absence of abruptio placentae.

URINARY TRACT OBSTRUCTION: Relaxation of uterine smooth muscle and pressure on the ureters by the gravid uterus typically result in mild to moderate dilatation of the collecting systems. This functional hydronephrosis, which tends to be more prominent on the right, is detectable by ultrasonography but is not usually associated with renal dysfunction. Rarely, the degree of obstruction is sufficient to cause renal failure]. The diagnosis can be established in some cases by the normalization of renal function in the lateral recumbent position and its recurrence when supine. In some cases, however, either insertion of a ureteral catheter or delivery of the fetus is required.

Nephrolithiasis: Rarely, acute urinary tract obstruction in pregnancy is induced by a kidney stone. Since this process is unilateral, affected women present with acute flank pain and microscopic or gross hematuria, rather than renal failure.