Blood pressure in Danish children during general anaesthesia: Hypotension in a paediatric population observational (HIPPO) study.

---

Prospective observational multicentre assessing blood pressure in 726 Danish children aged 0-12 years during general anaesthesia, measured by oscillometry or invasively (excluding premature infants and children having cardiothoracic surgery).

• Primary outcome measured was Mean Arterial Pressure (MAP):
  • Not measured at any point during anaesthesia in 81 patients (11%), predominantly in the youngest age groups.
  • A pre-induction blood pressure was also more likely to be missing in the youngest patients.
  • Overall, MAP was lower in the youngest age groups.
  • The largest variation in MAP was seen in infants.

 

• Secondary outcomes measured:
  • Lowest MAP
    • For infants, the median of lowest MAP was 47 mmHg (IQR 38-58 mmHg).
    • For 12 year olds, this increased to 51 mmHg (IQR 46-58 mmHg).
  • MAP threshold for intervention
    • Highly variable, for example:
      • Infants – threshold ranged from 25 to 45 mmHg
      • 7 year olds – threshold ranged from 50 to 70 mmHg
    • Type of intervention to increase blood pressure
      • 32 patients (4.4%) received one or more intervention:
        • one or more fluid bolus (n=20)
        • vasoactive drugs (n=29)

Limitations of this study:

• No standardisation of method to measure BP, size of appropriate cuff, site of measurement.
• Anaesthesia depth, analgesics given and level of anxiety prior to induction were not assessed.
• Organ specific outcomes (e.g. kidney dysfunction) were not assessed and were beyond this study’s scope.

 

Comments:

Reference values for blood pressure are derived from population-based studies in healthy, non-anaesthetised children, and there is a lack of consensus on clear definitions of hypotension. This likely contributes to the observed large variation in trigger values for intervention.

Previous studies have shown flow velocity in the middle cerebral artery (measured via transcranial Doppler) to reduce if MAP decreased >20% in infants <6 months and >40% in infants >6 months. Further, another study demonstrated that cerebral saturations (near-infrared spectrometry) dropped significantly if MAP was lowered below absolute values of 35 mmHg in patients <6 months and 43 mmHg in patients ≥6 months. The youngest patients are likely to be more vulnerable to variations in MAP given immature cerebral autoregulation. However, as in this study, this group had the largest variations of blood pressure observed, as well as being more likely to not have any blood pressure measured at all.

Measurement of blood pressure is recommended during every general anaesthetic and in children of all ages to reduce risk of detrimental effects of hypotension or large variations in blood pressure. Occult cerebral hypoperfusion under general anaesthesia is of course multifactorial, and a clear threshold at which hypotension may contribute remains unclear. Thus, in each individual patient, several factors in addition to blood pressure need to be addressed to reduce the risk of neuro-morbidity.

 

Reviewed by Dr Natalie Akl