Poliuria post-obstructiva. Análisis fisiopatológico de un caso / Post-obstructive polyuria. Pathophysiological analysis of a case

The relief of the impediment to urinary flow is the treatment of acute kidney failure due to urinary tract obstruction. However, there is a risk of inducing massive polyuria, which can be self-limited or produce severe contraction of the intravascular volume with pre-renal acute kidney failure and alterations in the internal environment. Polyuria, urine output > 3 L/d or > 200 mL/min for more than 2 hours, can have multiple causes, and can be classified as osmotic, aqueous or mixed. Post-obstructive polyuria obeys different pathogenic mechanisms, which overlap and vary during a patient's evolution. Initially, there is a decrease in vasoconstrictor factors and an increase in renal blood flow, which, added to the excess of urea accumulated, will cause intense osmotic diuresis (osmotic polyuria due to urea). Added to these factors are the positive sodium and water balance during acute renal failure, plus the contributions of crystalloid solutions to replace diuresis (ionic osmotic polyuria). Finally, there may be tubular dysfunction and decreased solutes in the renal medullary interstitium, adding resistance to the action of vasopressin. The latter causes a loss of free water (mixed polyuria). We present the case of a patient with post-obstructive polyuria where, by analyzing the clinical symptoms and laboratory alterations, it was possible to interpret the mechanisms of polyuria and administer appropriate treatment for the pathogenic mechanism.

Enfoque práctico para el diagnóstico y tratamiento de los estados poliúricos en pacientes con injuria cerebral aguda / Diagnosis and therapy of polyuric states in patients with acute cerebral injury

In patients with acute cerebral injury, polyuric states can potentially trigger, maintain and aggravate the primary neurological damage, due to hypovolemia, arterial hypotension and alterations of osmolarity. The true incidence of the condition in this population is unknown. A widely validated definition of polyuric state is lacking and its etiology is multifactorial. There are two principal classes of polyuria: a) aqueous polyuria with diabetes insipidus as the main cause; and b) osmotic polyuria in which sodium, glucose or ureaplay the main role. Polyuric states are in close association with disorders of water and sodium metabolism and with alterations in acid-base balance. A detailed analysis of the history, clinical picture and simple laboratory determinations in blood and urine, are required for an adequate assessment of these polyuric states. The problem must be faced with pathophysiological reasoning and a systematic and sequential approach, because each disorder needs a specific therapy.