Renal response to mechanical ventilation in patients with chronic hypercapnia

Flow diagrams for the diagnosis of acid-base disorders

This article discusses flow diagrams and tables intended to provide a systematic approach to the rapid laboratory differential diagnosis of acid-base disorders in the emergency department.

Urinary sodium and chloride during renal salt retention

One hundred ten episodes of renal salt retention (urinary sodium and/or chloride less than 10 mEq/L) were studied retrospectively to determine the significance of discordance of urinary sodium from chloride. In 16 episodes the urinary sodium exceeded chloride by at least 15 mEq/L. This disparity was associated with the necessity for urinary excretion of substantial quantities of poorly reabsorbed anions (penicillin, ketones, or diatrizoate), a rapidly falling serum bicarbonate level (due to resolving metabolic or developing respiratory alkalosis), or substantial renal insufficiency (serum creatinine greater than 3 mg/dL). In 14 of 110 episodes, urinary chloride exceeded urinary sodium by at least 15 mEq/L. These patients were more often oliguric and had a higher mean serum chloride than patients without this dissociation. In patients with oliguria, hyponatremia, or metabolic alkalosis, measurement of urinary sodium or chloride alone will, in a substantial number of cases, fail to detect renal salt retention. When evidence is sought for renal salt retention, both urinary sodium and chloride should be determined.

Renal response to short-term hypocapnia in man

This study examines the renal response to moderate hyperventilation in healthy man. Eight men hyperventilated for 26 hr (PaCO2 approximately 30 to 32 mm Hg) in normoxia (barometric pressure, PB approximately 740 mm Hg) and hypobaric hypoxia (PB approximately530 mm Hg). Anaerobic samples of arterial blood and urine were studied at two-hour intervals. Plasma [HCO3-] fell with time during sustained hypocapnia and after 26 hr was reduced 2.5 mEq/liter, with plasma pH compensated approximately 60%. Statistically significant changes in renal H+ handling were observed within the initial 2 hr of hyperventilation and were evident over the first 12 hr. Over 26 hr, mean total HCO3-excretion in hypocapnia was 10.2 mEq above control and mean total acid excretion (UVTA + UVNH4+) was 17.5 mEq below control. An increased urinary excretion of cations, especially sodium, accompanied the decrease in acid excretion. Plasma lactic acid accumulation was negligible. We conclude that renal mechanisms contribute significantly and relatively quickly to plasma pH compensation during the early phase of adaptation to hypocapnia in man.