Background

Diabetes insipidus (DI) is an uncommon condition with either relative or absolute lack of anti-diuretic hormone (ADH) leading to inability to concentrate the urine and subsequent polyuria/polydypsia and potentially fluid and electrolyte imbalance. This can be seen in a variety of conditions in the paediatric population, most commonly in patients post neurosurgery or with cerebral malformations.

Assessment

Consideration should be given to:

1. Hydration status/fluid balance/urine output
2. Presence of intercurrent illness eg UTI 
3. Causes of excess fluid loss eg gastro, surgical drains
4. Past history of DI with similar episode
5. Change in weight as marker of fluid status

Baseline investigations should include urea and electrolytes, full ward test of urine and paired serum and urine osmolality.

Diabetes insipidus is present when the serum osmolality is raised (>295milliOsmol/kg) with inappropriately dilute urine (urine osmolality < 700milliOsmol/kg). The serum sodium is often elevated due to excess free water losses.

Management

(1) Rehydration

After assessment of level of dehydration and ongoing losses, adequate rehydration therapy should be commenced. If the serum Na is > 150mmol/L, rehydration should occur over 48 hours (see hypernatraemia guideline).
If Na >170mmol/L, contact ICU.

(2) Desmopressin administration

Discussion with the endocrinologist on call is advised prior to the commencement of Desmopressintherapy  

Desmopressin (DDAVP, trade name: Minirin^(R)) acts on the distal tubules and collecting ducts of the kidney to increase water reabsorption, as a long acting analog of anti-diuretic hormone (ADH).

There are several formulations available:

1. Intranasal solution - 100 micrograms/mL
2. Intranasal spray (10 micrograms/spray) 
3. Parenteral (IM/IM) - 4 micrograms/ml - used rarely  
4. Oral - 200 micrograms/tablets (roughly 10 micrograms intranasal is approximately equivalent to 200 micrograms orally)

Administration - principles

1. For infants (<1 yr old) - discuss with endocrinologist on call
2. Under 2 yrs, dose is usually  2 - 5 micrograms intranasal 
3. From 2 yrs oand over, dose similarly to adult dose (5 - 10 micrograms/day)
4. Dosage effect is all or nothing - in general, the dose determines the duration of action NOT the degree of response.
5. Oral dose has slower onset/offset of action, therefore NOT useful in acute situation
6. Nasal administration is operator dependent - also need to consider effectiveness if probs with nasal mucosa eg intercurrent URTI, hayfever, post operatively
7. Careful fluid balance needs to be maintained to prevent fluid overload/hyponatraemia.

Criteria for Desmopressin Administration
At RCH, Desmopressin should be administered by two accredited Registered Nurses or parents, who are competent and confident, ensuring the following 3 criteria have been achieved;

1. Serum sodium is >145mmol/L (reference range 135 - 145mmol/L)
2. Urine output exceeds 4ml/kg/hr (calculated 6 hourly)
3. Urine specific gravity is 1.005 or less (dilute urine output)

N.B. If desmopressin has been prescribed and the child does not meet all 3 criteria then consult with senior staff (often Endocrine / Neurosurgery fellow or consultant) prior to administration of desmopressin to prevent fluid overload and hyponatraemic seizures.

Ongoing management of patients on Desmopressin - general principles

1. At a minimum, daily serum electrolytes and osmolality and daily urine osmolality are required until stable - consider more frequent electrolytes if hypernatraemic or concerns about fluid state or the child is fasting for theatre or a procedure.
2. Ensure most recent serum sodium result is above 145 mmol/L prior to administration of Desmopressin.
3. Need to have 1 - 2 hrs of diuresis (greater than 4ml/kg/hour) prior to administration of next dose to allow free water clearance and avoid hyponatraemia
4. All urine specific gravity checked and documented
5. Strict fluid balance chart with output totalled 6 hourly.
6. Patient weighed daily

Complications of management

1. Hyponatraemia
2. Hypernatraemia
3. Fluid overload

Inform the managing team (usually endocrine/specialties registrar or endocrinologist on-call) if:

1. Urine output > 4mls/kg/hr for two consecutive hours - may need repeat serum sodium
2. If desmopressin due and there has been inadequate urine output there may need to reduce/omit the dose 
3. If serum electrolytes are not within normal range
4. If child is exhibiting signs and symptoms of dehydration or fluid overload

Desmopressin Administration Checklist (Children's Neuroscience Centre)