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:
Hydration status/fluid balance/urine output
Presence of intercurrent illness eg UTI
Causes of excess fluid loss eg gastro, surgical drains
Past history of DI with similar episode
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:
Intranasal solution - 100 micrograms/mL
Intranasal spray (10 micrograms/spray)
Parenteral (IM/IM) - 4 micrograms/ml - used
rarely
Oral - 200 micrograms/tablets (roughly 10 micrograms
intranasal is approximately equivalent
to 200 micrograms orally)
Administration - principles
For infants (<1 yr old) - discuss with endocrinologist on
call
Under 2 yrs, dose is usually 2 - 5 micrograms
intranasal
From 2 yrs oand over, dose similarly to adult dose (5 - 10
micrograms/day)
Dosage effect is all or nothing - in general, the dose
determines the duration of action NOT the degree of response.
Oral dose has slower onset/offset of action, therefore NOT
useful in acute situation
Nasal administration is operator dependent - also need to
consider effectiveness if probs with nasal mucosa eg intercurrent
URTI, hayfever, post operatively
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;
- Serum sodium is >145mmol/L (reference range 135 -
145mmol/L)
- Urine output exceeds 4ml/kg/hr (calculated 6 hourly)
- 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
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.
Ensure most recent serum sodium result is above 145 mmol/L
prior to administration of Desmopressin.
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
All urine specific gravity checked and documented
Strict fluid balance chart with output totalled 6
hourly.
Patient weighed daily
Complications of management
Hyponatraemia
Hypernatraemia
Fluid overload
Inform the managing team (usually endocrine/specialties
registrar or endocrinologist on-call) if:
Urine output > 4mls/kg/hr for two consecutive hours - may
need repeat serum sodium
If desmopressin due and there has been inadequate urine
output there may need to reduce/omit the dose
If serum electrolytes are not within normal range
If child is exhibiting signs and symptoms of dehydration or
fluid overload
Desmopressin Administration Checklist (Children's Neuroscience
Centre)