Acute kidney injury (AKI) may complicate many medical conditions, although it usually arises in hospitalized patients. The term “acute kidney injury,” has generally replaced the term “acute renal failure” because it is a more accurate descriptor of kidney dysfunction that may lead to significant morbidity or mortality in the absence of complete renal failure. AKI is not a rare medical condition, with as many as 5% of hospitalized patients having some degree of it. With respect to obstetric patients, however, AKI has become an uncommon complication of pregnancy in developed countries, where it complicates approximately 1 per 10,000 pregnancies. In three successive 10-year periods between 1958 and 1987, Stratta et al. reported ongoing decreases in AKI requiring emergency renal dialysis, falling from a rate of 1 in 3000 gestations in 1958 to 1 in 15,000 in 1987. They documented 81 cases of AKI in pregnancy, of which 11.6% experienced irreversible renal damage, most of which resulted from complications of either severe preeclampsia or eclampsia. Possible explanations for this downward trend include ready availability of prenatal care and legalization of medical abortions. However, in underdeveloped countries, AKI remains a frequent complication of pregnancy, with attendant maternal mortality surpassing 50%. In these nations, AKI has a bimodal distribution, with peaks in the first and third trimesters, presumably reflective of the persistence of illegal abortions, the lack of access to quality prenatal care, as well as preeclampsia/eclampsia. A report of 569 cases of AKI in pregnancy in India showed that the most frequent gestational complication leading to AKI was septic abortion, accounting for 50% of cases.
RENAL ANATOMY AND FUNCTION DURING PREGNANCY
An understanding of the changes that normally occur in renal architecture, function, and blood flow is essential for proper assessment and management of renal disease in the pregnant patient (Table 13-1).
TABLE 13-1Renal Changes in Normal Pregnancy ||Download (.pdf) TABLE 13-1 Renal Changes in Normal Pregnancy
|Alteration ||Change ||Clinical relevance |
|Increased renal size ||Renal length about 1 cm greater ||Postpartum decrease in size should not be mistaken for parenchymal loss |
|Dilation of pelvis, calyces, and ureters ||Resembles hydronephrosis on ultrasound or IVP ||Not to be mistaken for obstructive uropathy, increased rates of upper tract infections |
|Increased renal hemodynamics ||Increased GFR and renal plasma flow ||Decreased serum creatinine and BUN; increased excretion of amino acids, protein, and glucose |
|Changes in acid-base metabolism ||Renal bicarbonate threshold decreases ||Serum bicarbonate level lower by 4-5 mEq/L |
|Renal water handling ||Osmoregulation altered with decreased osmotic thresholds for AVP release, and thirst ||Serum osmolality decreases 10 mOsm/L during normal gestation |
There is a marked increase in kidney size during pregnancy, primarily due to increases in renal vascular volume, as well as the capacity of the collecting system. Hormonal ...