Page 2742 - Cote clinical veterinary advisor dogs and cats 4th

1428 Hypernatremia, Correction of

Hypernatremia, Correction of
VetBooks.ir Example patient: 20-kg dog Correction of Severe Hypernatremia

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with serum Na of 194 mEq/L
Consider using multiple fluid types
simultaneously Measure blood pressure;
1-Initial Consider placing central • E.g., D 5W to replace free water if low, support with 0.9%
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steps line for frequent deficit, plus higher Na fluid to NaCl bolus (initial dose
blood monitoring replace ongoing loss, provide
maintenance needs, address 10-20 mL/kg)
dehydration (if present)
2-Review Determine if hypernatremia is acute (<24 h; examples with asterisk, below*) or chronic
history (>24 h; examples with dagger, below†) → If unsure, assume chronic

3-Volemia Assess volume status (can aid in developing
differential diagnosis, pp. 498 and 1237)

Hypovolemic: hypotonic fluid loss Isovolemic: pure H 2O deficit Hypervolemic: often solute gain
• Vomiting/diarrhea*† • Fever *† • Seawater ingestion*
• Renal loss*† • Diabetes insipidus† • Hypertonic saline*
• Diabetes mellitus† • Hypodipsia† • Hyperaldosteronism†

• Address underlying cause whenever possible, e.g., antiemetic drug for vomiting, desmopressin for
4-Ancillary central diabetes insipidus
care
• Unless contraindicated (e.g., severe vomiting), allow access to drinking water (quantify consumption)
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Determine the reduction in serum Na required to reach upper reference Na (typically 155 mEq/L):
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5-Calculate Patient serum Na – Upper reference Na +
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goal +
• Example: 194 mEq/L – 155 mEq/L = 39 mEq/L is necessary reduction in serum Na
Determine total body water (TBW): body weight (kg) ¥ 0.6 = TBW (in kg and in liters because 1 L = 1 kg)
6-Calculate TBW
• Example: 20 kg ¥ 0.6 = 12 kg (=12 L) is TBW
• Exact selection depends on a variety of factors. Often, hypovolemic animals are treated with 0.45% saline or
7-Choose fluid LRS while isovolemic and hypervolemic animals are treated with D 5 W
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type • Fluid Na content: D 5 W = 0 mEq/L; 0.45% saline = 77 mEq/L; LRS = 130 mEq/L; Normosol-R = 140 mEq/L;
0.9% NaCL= 154 mEq/L
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Determine the change in serum Na expected by 1 L infusion fluids: (fluids [Na ] – Patient [Na ])/((TBW) + 1)
8-Calculate • Example: (0 mEq/L – 194 mEq/L)/(12 L (calculated in step 6) +1) = (–194/13) = –14.9 mEq/L is the expected
expected change + +
change in serum Na caused by infusion of 1 L D 5 W in patient with serum Na = 194 mEq/L
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Determine the fluid dose required to achieve target Na : reduction required / reduction achieved by 1 L
9-Calculate fluid
dose • Example: 39 (as calculated in step 5) /14.9 (as calculated in step 8) = 2.62 L of fluid is the dose required
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to achieve the target reduction in serum Na
• Acute hypernatremia: rates of up to 2 mEq/h are allowable
• Chronic hypernatremia or hypernatremia of unknown duration: do not exceed 0.5 mEq/h, or 10-12 mEq/24 h
10-Calculate
time frame • Time required for safe administration = required reduction / maximum rate for correction
• Example (presume chronic): 39 mEq/L (as calculated in step 5) / 0.5 mEq/L/h (maximum safe rate) = 78 h to
achieve target Na +
Total fluid dose/time required for safe administration = Fluid rate of administration, where total fluid dose
11-Calculate was calculated in step 9 and time required for safe administration was determined in step 10
initial fluid rate
• Example: 2620 mL (2.62 L calculated in step 9)/ 78 h (calculated in step 10) = 33 mL/h initial fluid rate
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12-Monitor and • Recheck serum Na q 4-6h to adjust rate so as not to exceed drop of 0.5 mEq/h
• Check other electrolytes at least q 24h as large volumes of fluid can cause aberrations
adjust
• For hypervolemic patients, be watchful for overhydration (loop diuretic may be useful)
Alternative methods: 1) Same as above, but initially only perform calculations for the first 24 h of care. That is, in step 5 instead of targeting the
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eventual goal 155 mEq/L Na , target a serum Na that is 10 to 12 mEq/L lower than the starting Na . In our example case, the 24 h target
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would be 194 – 12 = 182 mEq/L. At the end of 24 h, recheck serum Na and perform calculations again for the next 24 h. 2) Calculation of water
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deficit for freewater replacement (may underestimate deficit); water deficit = 0.6 ¥ body weight (kg) ¥ ([patient Na /normal Na ] – 1). 3) Rule
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of thumb: 3.7 mL/kg/h of D 5 W will reduce serum Na by 1 mEq/L/h
AUTHOR & EDITOR: Leah A. Cohn, DVM, PhD, DACVIM
www.ExpertConsult.com