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Fluid, diuretic and nutrition management in children having cardiac surgery

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This guideline applies to all children in paediatric cardiology ( ward 23B )

Pre-operative Management

  • Nil By Mouth (NBM)
    • Infants < 6/12 should be nil by mouth (milk or solids) for 4 hours.
    • Infants > 6/12 should be nil by mouth (milk or solids) for 6 hours.
    • All infants and children can have clear fluids up to 2 hours pre-op.
    • Infants with shunts and cyanotic infants and children (sats≤ 80%), especially with Hct > 0.55 should be offered clear fluids up to 2 hours preop, and IV fluids if NBM >4 hours.
  • All children should have diuretics withheld on day of surgery.
  • All infants with duct-dependant systemic blood flow (eg hypoplastic left heart or coarctation and VSD) should be NBM from birth and on total parenteral nutrition (TPN) until surgery to minimise the risk of necrotising enterocolitis (NEC).

Early Postoperative status

  • Bypass surgery causes a significant 'stress' response in particular in neonates and infants. This results in fluid and salt retention by the kidneys.
  • On Day 2 post-op most infants and children are still 5 - 10% up on their pre-op weight. Daily weighs are usually the best method of determining fluid balance on the ward.
  • Unlike gastrointestinal surgery or sepsis, there are not usually any ongoing losses so they do not require extra fluid input; in fact they need to be fluid and salt restricted.
  • Within 72 hours the stress response has usually settled, unless the infant/child has ongoing low cardiac output, and their weight should be back to pre-op levels.
  • Certain cardiac conditions predispose to fluid retention and post-op pleural effusion over the first month after surgery. These children require fluid restriction to continue beyond the initial few days (see Fluid retention risk examples in Table 3).

Table 1 - Standard IV Maintenance Fluid (see Starship Clinical Guideline IV Fluids)

Indication Prescription Use
 >4 weeks corrected age 
0.9% sodium chloride + 5% glucose 1000mL bag 0.9% sodium chloride + 5% glucose 
0.9% sodium chloride + 5% glucose + 20 - 40mmol/L potassium chloride 1000mL bag 0.9% sodium chloride + 5% glucose and add 20mL of 10mmol/10mL potassium chloride*
< 4 weeks corrected age 
0.9% sodium chloride + 10% glucose 1000mL bag 0.9% sodium chloride + 5% glucose and add 100mL 50% glucose 
0.9% sodium chloride + 10% glucose +/- 20 mmol/L potassium chloride  1000mL bag 0.9% sodium chloride + 5% glucose and add 100mL 50% glucose and 20mL of 10mmol/10mL potassium chloride* 

*Potassium is only added to fluids after serum potassium and creatinine levels have been reviewed.

NB:  Standard IV maintenance fluids apply to cardiac children in paediatric cardiology (ward 23B) with the following exceptions:

  • Children less than 6 months after cardiopulmonary bypass: omit potassium chloride on the day of operation 
  • Children in whom the arterial or venous potassium is greater than 5mmol/L: omit potassium chloride
  • Newborn infants on the day of birth receive 10% glucose and do not need any added sodium chloride/potassium chloride. These are added on day two (2).
  • See Starship Clinical Guideline IV Fluids for exclusions and cautions

Table 2 - IV fluid maintenance rates (mls/hr)

To calculate standard IV fluid rate for children using 4/2/1 rule
Weight Hourly fluid allowance
For first 10kg 4mL/kg/hr
For weight 10-20kg 2mL/kg/hr
All additional weight over 20kg 1mL/kg/hr
Adult allowance Approx 100mls/hr
To calculate IV fluid rate of 70% = multiply the standard rate by 0.7 to obtain 70%
For example:
37kg child (4x10) + (2x10) + (1x17) = 40 + 20 + 17 = 77mL/hr.
70% is 77 x 0.7 = 54mL/hr (this is the IV maintenance rate for this child)

Diuretic use and serum electrolyte monitoring

Common diuretics used in Paediatric cardiology


  • loop diuretic, potassium wasting
  • 1 mg/kg/dose IV or oral up to Q6 hrly
  • IV much more potent than oral form.
  • more potent if child has not had frusemide preoperatively
  • usually give with amiloride or spironolactone to reduce potassium loss (unless ACE inhibitor given)

Medicine information see: ( (


  • Potassium sparing, weak diuretic
  • Usual dose: 0.2 mg/kg/day orally
  • Takes 24-48 hours to have an effect
  • can cause hyponatraemia with frusemide at times
  • stop if ACE inhibitor is at full dose (as can cause hyperkalaemia)

Medicine information see; ( (


  • Potassium sparing, potent
  • Usual dose: 0.5 - 1mg/kg/dose twice daily (Elixir). Tablet: round off to 12.5mg or 25mg
  • Takes 24-48 hours to have an effect
  • use in children not infants
  • useful in hepatic congestion
  • caution : when used in conjunction with ACE inhibitor ( increases serum potassium), or in renal impairment

Medicine information see; ( (


  • loop diuretic
  • potent in oral form
  • 1 mg bumetanide = 40mg Frusemide IV
  • useful if frusemide resistance seems to have developed
  • better oral absorption than frusemide

Medicine information see; ( (

Monitoring of serum electrolytes

  • daily whilst on IV frusemide, every 2 - 3 days thereafter
  • where electrolytes are significantly outside of the normal range, discuss with the senior medical staff

Potassium (K+) 

  • Most K+ is intracellular so the plasma K+ may not reflect total body stores 
  • Early post op: K+ is often required to balance frusemide until amiloride and spironolactone takes effect
  • Aim for K+ ≥ 4.0
  • Potassium chloride supplements may be given orally (1-2mmol/kg/day)
  • IV K+ is used frequently in the PICU, but rarely and with extreme caution in Ward 23B.
  • For this drug guideline - CTRL + click to follow link: what link

Sodium (Na+)

  • Serum Na+ is a useful index of body water. Low serum Na+ usually reflects increase in body free water, not low total body Na+ (however this is not true if the child is on loop diuretics). Treatment is water restriction, as well as reduced diuretics ( to control it) and avoid giving Na+ if possible. Assessment of the cause may require measurement of urinary sodium, although this is unreliable if the child is on diuretics.
  • High sodium usually indicates free water deficit for which the treatment is increased intravenous or enteral water.

Calculating daily fluid input & diuretic use in infants/children after cardiac surgery

Factors to consider when calculating fluid and diuretic use:

  1. Preoperative
    - presence of congestive cardiac failure or renal failure or other syndrome medical condition
    - use of preoperative diuretics
  2. Intraoperative
    - underlying diagnosis and ventricular function
    - potential for fluid retention
    - operative difficulty / complications
    - resultant physiology : single or two ventricle repair ? complex physiology ?
    - potential for fluid retention - see Table 3: Fluid retention risk
  3. Postoperative recovery / measurements
    - daily weight
    - renal function
    - evidence of fluid retention

Table 3: Fluid retention risk post cardiac surgery

Standard risk - Arterial switch
- Conduit Replacement
- AV Canal (balanced)
- Tetralogy with pulmonary valve preservation
- Elective mitral or aortic valve surgery
High risk - Arch repair or Norwood
- Shunt or PA band palliation
- Bidirectional Glenn or Fontan
- AV Canal (unbalanced)
- Tetralogy with Pulmonary Outflow Patch or severe cyanosis preop (restrictive RV)
- Semi-acute valve or VSD with significant preop congestive failure
- Impaired post operative ventricular function
NB: The ward consultant will clarify whether the patient is considered high risk for fluid retention

Table 4: Guideline for post-operative fluid and diuretic regimen for cardiac infant/child

- Calculate IV maintenance rate = standard IV rate x 0.7 (see Table 2: IV fluid maintenance)
- Once taking enteral fluid, maintenance includes both IV and oral intake
- Enteral feeding should be started as soon as possible (as soon as child clinically stable) as per the PICU enteral feeding guidelines
- Fluids should be charted as mls/kg/day
- Daily fluid balance may be misleading with a daily weight comparison to the preoperative weight more useful at determining fluid status
Day of operation Pre-op: for neonate check if recent use of aminoglycosides. 
No diuretics on day of operation
NBM as per Starship nil by mouth guideline
Post-op:   Bypass case - IV maintenance 50% of standard rate (including infusions)
                   Non-bypass - IV maintenance 70% of standard rate (including infusions)
Day 1
Post op in PICU
IV maintenance at 50% of standard rate
IV diuretics: frusemide once to twice daily + oral amiloride daily(if K+ normal)
Transition from IV to enteral fluids if possible
Day 2  IV maintenance if still ventilated at 70% of standard rate
Start and grade up enteral feeds if possible
"Standard Risk"
Start and grade up enteral feeds
Consider transition to oral diuretics 1 - 2 x daily if:
- absorbing feeds
- no evidence of CHF
- weight back towards preop weight
"High Risk"
IV diuretics 1 - 2 x daily
Start enteral feeds as per PICU enteral feed guideline
Day 3 to 4  IV maintenance if still ventilated at 70% of standard rate
"Standard Risk"
Increase fluid to 70% to 90% of standard rate once extubated and absorbing enteral feed
Transition to oral diuretics if
- absorbing feeds
- no evidence of CHF
- weight back towards preop weight
"High Risk"
Stay on IV diuretics if weight still > 5% above pre-operative weight
Continue to titrate up enteral feeds as per PICU enteral feed guideline
Day 5 to 6 "Standard Risk"
Grade up to full enteral feeds as tolerated
Consider reducing oral diuretic to daily or stopping once taking full feeds
"High Risk"
Transition from IV to oral diuretics
90% - 100% of standard rate as enteral feeds
Day 7 to 10 "Standard Risk"
- Standard risk neonates & small infants should be on full breast feeds or 150 ml/kg/day by day 7 post operation
- Many infants and children with complete repairs can have diuretics stopped by time of discharge
- Weight gain prior to discharge is not critical where there is a good biventricular repair, normal work of breathing and infant is achieving full enteral feeds
- Weight gain can be followed in the community once discharged
"High Risk"
- High risk infants may take longer to reach full enteral feeds.
- Use smaller steps and continue BD diuretics for longer.
- Usually on at least daily diuretics at discharge
- Consider energy supplementation once infant is tolerating 120 mls/kg/day enteral volumes (involve dietitian)
 Day 10 to 14 Children undergoing a Fontan Operation need to remain fluid restricted through the 2nd week postop until drains are out (i.e. 70-90% of standard fluids).
- Aim for weight about 5% less than preop weight
- use IV diuretics or oral bumetanide if necessary. 
 > 14 Days - Occasionally infants and children will remain fluid restricted for prolonged periods i.e severe ventricular dysfunction, persistent heart failure, late presenters, and severe pre-operative cyanosis. These infants and children may be relatively resistent to diuretics.
- Single ventricle neonates may not cope with more than 130 ml/kg/day of fluid so supplements are required to achieve adequate nutritional intake
- These children will need dietitian input to achieve adequate caloric intake with concentrated fluids and energy supplementation
- Referral to community dietition at discharge

Nutritional management post cardiac surgery

  • In the first 5 days after surgery (longer if the situation is complex) the focus is on fluid restriction and energy intake can be restricted as a result. Enteral feeding should be started as early as possible as per the PICU enteral feeding guidelines.
  • In infants, gut absorption is compromised and enteral feeding is started slowly via NG and only increased as absorption allows.
  • Necrotising enterocolitis (NEC) can be a complication of low cardiac output and can develop pre-op or post-op in cardiac infants
  • Expressed breast milk (EBM) is the safest feed for neonates (it contains 0.72kcal/ml).
  • The recommended nutrient intake for a term baby is approximately 108kcal/kg/day
  • For infants with certain conditions requiring an increased cardiac output or with increased respiratory effort, energy requirements may be 120 - 150 kcal/kg/day to achieve growth (i.e. 20% - 50% more than a normal infant).
  • It is therefore important to consider early energy supplementation for infants with single ventricle anatomy, complex cardiac physiology or those with an increased energy requirement due to other causes
    • Consider energy supplementation once infant is tolerating 120mls/kg/day enteral volumes with referral to dietitian

Basic feeding recommendations


To ensure adequate nutritional intake infants need:

  • Careful documentation of breast feeding (see Table 5: breast feeding code below) with NG top ups where necessary
  • Assessment of growth, with weekly measurement of weight, height and head circumference, and documentation of growth on growth chart
  • Early referral to dietitian and lactation consultant
  • For at risk infants - consultation with dietitian for energy supplementation (breastfed) or formula at increased concentration (bottle fed) especially if fluid restricted


  • Whilst on narcotic they have little interest in food - encourage fluids & light snacks.
  • Encourage protein-rich foods once they are off narcotics and starting to mobilise.
  • Involve dietitian for extra calories if they have low BMI preoperatively and/or ongoing protein losses eg. Fontan with chest drain losses.
  • Salty foods are discouraged in 23B.

Table 5: Breastfeeding code

NWH Newborn Unit Breastfeeding Code  
The following 'Breastfeeding Code" is a guide only. Please take into account maternal milk volume, milk ejection reflex and medical condition of the infant when assessing a breastfeed.

Follow the steps below to make a breastfeeding assessment of a preterm/sick or newborn infant and to determine how much supplement will be given.  
1 Use the following scale to score and document the infants breastfeeding ability and whether a supplement/top-up is required:
A. Offered the breast, not interested/sleepy
B. Interested in feeding, however does not latch
C. Latches onto the breast, however comes on and off or falls asleep.
D. Latches, however sucking is uncoordinated or has frequent long pauses.
E. Latches well, long slow rhythmical sucking and swallowing - Short feed.
F. Latches well, long slow rhythmical sucking and swallowing - Long feed. 
Depending on assessment and scoring:
A, B & C requires full supplemental feed.
D & E requires ½ supplemental feed.
F requires no supplemental feed. 
3 Do not supplement the infant who scores an E if the mother is available for another breastfeed. Consider not supplementing the infant who scores a D if the mother is available for another breastfeed. The infant may wake sooner for the next feed.
4 If nasogastric feed is indicated, it is preferable to provide the opportunity for infant to have skin-to-skin contact or nuzzling at the breast. See Assessing Readiness to Feed/Establishing Breastfeeding


  1. Woods, DJ (editor), New Zealand Formulary for Children [Internet]. 2016 [updated 2016 July 1 ; 2016; cited 2016, July 1]. Available from: 
  2. Frusemide (Frusemide-Claris) [New Zealand data sheet] AFT Pharmaceuticals Ltd [updated April 2009]. Available from URL:
  3. Breast feeding Code

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Document Control

  • Date last published: 12 July 2016
  • Document type: Clinical Guideline
  • Services responsible: Paediatric Cardiology
  • Author(s): Kirsten Finucane, Marion Hamer
  • Editor: Marion Hamer
  • Review frequency: 2 years