Menu Search Donate
clinical guideline banner

Diabetes Insipidus -post-neurosurgical management of acute

This document is only valid for the day on which it is accessed. Please read our disclaimer.

Objective

Management guideline specifically for new onset or transient diabetes insipidus (DI) following neurosurgery in Starship Children's Hospital

Introduction

  • A Paediatric Endocrinologist must be consulted in all children with post neurosurgical diabetes insipidus (DI)
  • Acute DI may develop after injury or surgery to the hypothalamic-pituitary region
  • For established DI or treatment of DI due to chemotherapy, brain death or other aetiologies, see other guidelines

Key management principles

  1. Mild-moderate hypernatraemia (Na <155 mmol/l) is the intended target range.
    Avoid vascular compromise
    It is relatively easy to treat hypernatraemia > target range
    Acute hyponatraemia is life-threatening and must be actively avoided
      
  2. DI is not life threatening unless the following occurs:
    The child is prevented from drinking when severely thirsty 
    The child has an impaired thirst mechanism (hypodipsia/adipsia)
    The child is unable to access water when they need to, e.g. very young or altered level of consciousness 
    The child is over treated with AVP analogues (DDAVP etc).
      
  3. The tri-phasic response is relatively common 
    This is immediate DI (hours to days), a variable period of SIADH (days), followed by permanent DI
    Avoid over-treatment with AVP analogues until DI is permanent
      
  4. A number of factors can complicate peri-operative fluid balance:
    Fluids: 
    Large volumes of saline or other isotonic fluids result in obligate diuresis (mimicking DI).
    Mannitol or similar osmotic agents also lead to large volume urine output.
    Endocrine:
    Cortisol and T4 deficiency can result in reduced free water excretion, with DI unmasked by hormone replacement (including dexamethasone).

All patients at high risk of DI should be seen by Endocrinology pre-op for pituitary function assessment

Management of DI requires close co-ordination of Neurosurgical and Endocrinology care.

If steroid cover required see Starship guideline on stress steroids or in emergencies call Endocrinology 021 974804.

Monitoring requirements

  • Pre-op: weight and accurate fluid input and output
  • Intra-op: Frequent (hourly) serum sodium (Na) monitoring and accurate fluid input and output
  • Post-op: Care is most appropriately performed in the ICU or the IOU 26A
    Daily weight and accurate fluid input and output
    Ongoing iSTAT or blood gas Na monitoring (hourly or as required)
    12 hourly serum electrolytes, urea, creatinine, osmolality and urine Na, K, creatinine and osmolality (Biochem)

Management key points

  • All patients should have their own DI management plan documented pre-op
  • 0.9% saline is the fluid of choice, avoid hypotonic fluids
  • No treatment of DI with DDAVP or infusion, unless serum Na >155mmol/l and cannot maintain fluid status (oral or IV)
  • If ongoing DI then each dose of DDAVP must be earned in the acute phase

For the purposes of these guidelines, DI can be assumed to be present if:

  • Urine volume persistently >4 ml/kg/hr in absence of mannitol or diuretics
  • Urine is dilute, i.e. specific gravity (Sg) <1.005 and/or urine osmolality <200 mOsm/kg
  • Serum sodium concentration is elevated (>145 mmol/l)
  • An awake patient should be thirsty!! Beware of patients with an impaired thirst mechanism.

Hypernatremia and hyponatraemia during DI management

Hypernatraemia

  • If serum Na rises above 145 mmol/l, check urine output and specific gravity (USg)
  • If the serum Na continues to rise and exceeds 155mmol/l increase fluid intake appropriately.
    Let the thirsty child drink.
    IVF (0.9% saline) should be increased in children unable to drink.
  • Discuss possible use of an AVP infusion or stat dose of DDAVP with an Endocrinologist (avoid DDAVP in the first 48 hours).

Hyponatremia

  • This is an emergency that typically occurs following excess fluid intake or inappropriate ADH secretion/administration and should be avoided at all costs.
  • Check urine output and specific gravity (USg), consult an Endocrinologist if diagnostic uncertainty.
  • The management of SIADH is fluid restriction.
  • More rarely, hyponatraemia may be due to cerebral salt wasting (CSW). Identification is important as the management is very different to that for SIADH. CSW is associated with clinical intravascular volume depletion, polyuria and high urinary Na levels (usually >80mmol/l)

Severe symptomatic hyponatremia: Emergency only

  • In urgent situations the use of hypertonic saline infusion may be required. Hypertonic saline may be used to correct severe, acute hyponatremia, with the aim being to raise serum Na to 125 mmol/l.
  • The patient should be in a PICU
  • See Formula for Hypertonic Saline below

Formulae

Hypertonic Saline
Consult with the Intensivist or Endocrinologist before the use of hypertonic saline

Na required (mmol) = (125 - measured Na) x 0.6 x body weight (kg)
where
125 = desired serum Na
 0.6 = distribution factor for Na as a fraction of body weight
Use 3% or 5% NaCl as available (normally 1-2 ml/kg of 3%) Then normally IV frusemide about 4 hours after this is given 

Insensible losses
Insensible loss = 17 ml/m2/hour or calculated for weight as follows:

2 kg  1.3 ml/kg/hr
4 kg   1.0 ml/kg/hr
10 kg   0.8 ml/kg/hr 
20 kg  0.6 ml/kg/hr 
40 kg  0.5 ml/kg/hr 

Fractional excretion of sodium
FENa = Urine Na/Urine creat x plasma creat/plasma Na
Interpretation:

  • In health, FENa is <1 %
  • If oliguric, a low FENa suggests there is not excessive ADH action and the patient may be sodium and water depleted.
  • If oliguric, a high FENa suggests excess exogenous or endogenous ADH

ADH replacement for established Central DI

No form of ADH or vasopressin should be used without consulting a Paediatric Endocrinologist

  • ADH administration should only be considered after a reasonable period of observation establishes that DI is persistent.
  • ADH can be replaced using two different formulations with different duration of actions;

Aqueous vasopressin (Pitressin, Parke Davis) by continuous IV infusion

  • Half-life approximately 30 minutes, clinical duration of action 2-3 hours.
  • Very useful in acute situations because short half-life allows accurate titration.

Desmopressin (DDAVP, Ferring) given either intranasally or parenterally (IV, IM,or SC)

  • Half-life approximately 3 hours, clinical duration of action 8-24 hours.
  • Should generally only be used in a stable situation, not in acute post-surgical or post-traumatic DI.

Methods of ADH administration

Aqueous Vasopressin (Pitressin) infusion

Commence aqueous vasopressin infusion at rate of 0.5 mU/kg/hr (or lower if concerned about sensitivity to AVP). See below for method of dilution. Prior to connecting to the patient, flush the line with 10 ml of the solution to prime the plastic line with the peptide.

Starting dose of aqueous vasopressin 0.5 mU/kg/hr
Usual dose range 0.5 to 2.0 mU/kg/hour 

Infusion rate guide - intravenous aqueous vasopressin

 Weight (kg) Infusion rate 
0.5 mU/kg/hr = 0.1 ml/kg/hr 
   mU/hr  ml/hr
 5 2.5  0.5 
10 
20  10 
30  15  
40  20 

Aqueous IV Vasopressin has a half-life of approximately 30 minutes, so a change is reflected 1-3 hours later.

Q2H Na measurements (using the iSTAT) can be used to guide adjustments whilst unstable.

Target for infusion:

  • urine output 2 - 4 ml/kg/hr
  • neutral fluid balance
  • maintain serum Na 145 - 155 mmol/l

Overhydration (i.e. too much vasopressin, too much antidiuretic effect):

  • Falling serum sodium with falling or low urine output
  • Positive fluid balance
  • Concentrated urine (USg >1.030 is very concentrated)

The appropriate adjustment is to decrease or cease the vasopressin infusion

Underhydration (i.e. too little vasopressin, not enough antidiuretic effect):

  • Rising serum sodium and high urine output
  • Negative fluid balance
  • Dilute urine (USg <1.005 is very dilute)

The appropriate adjustment is to increase the vasopressin infusion

Dilution of aqueous vasopressin

  • The only available preparation of Pitressin available is extremely concentrated, for use in other clinical situations. Thus it is necessary to dilute this solution 4000 fold prior to use as follows.
  • Note that this is a different dilution to that required for patients having IV aqueous vasopressin during chemotherapy (see separate protocol).
Pitressin (aqueous vasopressin; Parke Davis) 20 units/ml, 1ml ampoules
 Step 1  Take 0.25 ml (5 units) of 20 unit/ml ampoule using a 1 ml syringe
 Step 2 Add to 500 ml bag 0.9 % saline, using a long needle so that the concentrated solution does not stay in the region of the injection port
= 5 000 milliunits (mU) per 500 ml
= 10 mU per ml (SOLUTION A) 
 Step 3 Mix thoroughly 
 Step 4 Take 25ml SOLUTION A (= 250 mU vasopressin) and 25ml 0.9% saline into a 50 ml syringe to make 250 mU per 50 ml = 5 mU/ml 

Intranasal Desmopressin (Minirin)

Desmopressin should only be given after consultation with a Paediatric Endocrinologist. It is generally not suitable for acute post-operative or post-traumatic DI; aqueous vasopressin is preferred due to its much shorter half-life.

A small dose is given initially, since some children will be very sensitive to initial doses and have profound and rapid antidiuresis. There is no harm in giving too little an initial dose, provided that accurate fluid replacement is proceeding.

Method

  • DDAVP is supplied as Minirin, Ferring 100 micrograms/ml, 2.5 ml bottle, with graduated administration tube with marks at 0.05 ml (5 mcg), 0.1 ml (10 mcg), 0.15 ml (15 mcg) and 0.2 ml (20 mcg).
  • Due to the small initial doses used, a 1/10 dilution is generally required.
  • As a guide, the initial doses of DDAVP intranasally are:
    Infants 0.5 to 1 micrograms
    Children 1 to 2.5 micrograms

Subsequent doses and frequency can be adjusted according to response. A further dose may be required when:

  • urine output is > 5 ml/kg/hour for 2 hours, and
  • urine specific gravity <1.005.

For stable DI, once or twice daily doses are normally sufficient.

Oral dosing with the liquid nasal formulation may be indicated (e.g. neonates). DDAVP absorption is decreased orally as compared with the nasal mucosa, so that the oral dose is increased 10-fold.

Neonatal DI

Either chorothiazide or oral DDAVP (use nasal solution 100 mcg/ml), under endocrinologist review.

Chlorothiazide dose is 10mg/kg/dose BD, formula/EBM also diluted 25% with water.

Note that newborns will always have a dilute urine and high urine output, but serum Na remains stable.

Parenteral Desmopressin (Minirin)

Parenteral desmopressin (IV, IM or SC) may be useful in relatively stable patients where there is limited access to the nasal mucosa. The dose to be used is 1/10th the intranasal dose and the duration of action is similar to intranasal DDAVP.

The concentration of parenteral Desmopressin solution is 4 micrograms/ml; dilution of the solution is required.

A guide for the initial dose is:

  • Infants   0.1 micrograms = 0.025 ml
  • Children 0.2 micrograms = 0.05 ml

Did you find this information helpful?

Document Control

  • Date last published: 28 October 2014
  • Document type: Clinical Guideline
  • Services responsible: Paediatric Endocrinology, Paediatric Neurosurgery
  • Author(s): Craig Jefferies, Andrew Law, Natasha Heather
  • Editor: Greg Williams
  • Review frequency: 2 years

More From Starship