Fluid Balance

The combination of mouth breathing after transsphenoidal surgery and the lack of oral intake preoperatively means that the pituitary patient commonly experiences early postoperative thirst. Furthermore, anesthetists normally keep their patients well hydrated during surgery, and excretion of this fluid load can result in an episode of polyuria. It is, therefore, important to recognize that neither the thirst nor the polyuria are necessarily a sign of diabetes insipidus (DI).

Although it is essential to monitor fluid balance in patients, 4-h urine outputs and specific gravity measurement are an inadequate way to keep abreast of fluid management. Nevertheless, they are still sometimes misguidedly used by the inexperienced, and the authors have previously seen transient hypotonic poly-uria during the first 12 h misdiagnosed and treated with synthetic vasopressin (dDAVP). The unfortunate patient who has been misdiagnosed has by then had a 12-h iatrogenic water retention and may be hyponatremia He or she then has a second period of a normal physiologic attempt at correction with a second period of high urine output. If truly unfortunate, this, too, will be treated by zealous junior medical staff and a second bolus of dDAVP given. To avoid such problems, a simple and consistent management regimen should be followed:

Patients should be allowed to drink freely. Until they do so, iv fluids can be given according to standard postoperative protocols. One liter of normal saline in 12 h is sufficient.

Once normal drinking has commenced, the rate of saline infusion can be slowed. A careful record of input and output must be kept. Urinary specific gravity, although commonly recorded, is only a vague pointer to posterior pituitary well-being and should be interpreted with caution. A formal diagnosis of DI should only be made after urine and serum osmolality measurements. It is confirmed in the presence of raised plasma osmolarity >287 mosM/kg and urine osmolarity <200 mosM/kg, giving a ratio of urine to plasma of <1.2. If plasma osmolarity is normal, another cause of the polyuria should be sought. Plasma sodium is a useful parameter to review because it can be estimated rapidly . Sodium >146 mmol/L suggests the possibility of DI.

Diagnostic confusion may occur when treatment of hypertension with diuretics is continued perioperatively. These patients need careful assessment by the endocrinologist.

Once established, DI is treated with dDAVP. The correct dose is the smallest required to abolish the polyuria. In the presence of nasal packs, 1-2 ^g as an intramuscular injection up to 12 h is usually sufficient. Once the packs are out, it is easier to give as a nasal spray as the nasal mucosa absorbs from the moment it is free of the packs. Each "puff" is 10 ^g, and one to two puffs every 12 h is usually sufficient. Some patients prefer the oral preparation for long-term maintenance, often because they have been misinformed that the spray must be refrigerated. The only disadvantages are variable absorption and higher cost.

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Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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