You should ask the nurse: • What the trend is in urine output—has it been gradually decreasing, or suddenly stopped? If the latter, have they checked if the urinary catheter is blocked by flushing it? This is a rapidly reversible cause of poor urinary output. • What the observations are for the patient. Ask for the heart rate, blood pressure, respiratory rate, oxygen saturations, and temperature, so you can get an idea of how unwell the patient is. This will help you prioritize how soon you need to see the patient. Healthy adults have a urine output of about 1 mL/kg/hour. Oliguria refers to a reduced urine output and is defined variously as <400 mL/day, <0.5 mL/kg/hour, or <30 mL/hour. Anuria refers to the complete absence of urine output. Decreased urine output should be taken very seriously as it may be the first (and only) sign of impending acute renal failure. Untreated, patients may die from hyperkalaemia, profound acidosis, or pulmonary oedema due to the kidneys not performing their usual physiological role. Normal urine output requires: • adequate blood supply to the kidneys • functioning kidneys, and • flow of urine from the kidneys, down the ureters, into the bladder, and out via the urethra. Pathology affecting any of these requirements can result in poor urine output, which is why the differential diagnosis for poor urinary output is often classified as shown in Figure 22.1. In practice, as a junior doctor you want to diagnose and treat the prerenal and postrenal causes. If you come to the conclusion that it is a renal cause (by exclusion), call the renal physicians for an expert opinion. This is crucial in determining the diagnosis: • Adequate intake? Remember that an adult of average size will require about 3 L of fluid intake per 24 hours (30–50 mL/kg/day). Febrile patients will require an extra 500 mL for every 1 °C above 37.0 °C to compensate for increased loss of fluids from evaporation and increased respiratory rate.
Abnormal Cardiac Autonomic Regulation in Mice Lacking ASIC3