SELECTED GEN MED FROM PAEDIATRIC BASICS COURSE 2018 (10)

Question 1

SpO2 and pCO2 TARGETS WITH MECHANICAL VENTILATION?

Answer 1

Mechanical ventilation can easily cause lung injury and _circulatory impairmen_t, so adequate, rather than normal targets are set:

• For SpO2 of 88-92%
• For pCO2, virtually any elevation is tolerated provided pH remains >7.2, unless specifically targeting normocapnoea, eg in head injury

Question 2

DESIRABLE VENTILATOR PARAMETERS TO AVOID VILI (IN CHILDREN)

Answer 2

• FiO2 not >50%
• Plateau pressure (ie inspiratory pressure plus PEEP) not >30cmH2O
• Tidal volumes not >6-8ml/kg
• Sufficient PEEP to stop marginal alveoli cyclically opening and closing (causing ‘atelectotrauma’): generally 5 - 10cm H2O

Question 3

HOW HIGH FLOW NASAL PRONG OXYGEN THERAPY (HFNPO2) WORKS

Answer 3

HFNPO2 uses warm, humidified gases delivered at very high flow rates (> 1L/kg/m) to support respiration by:

• Increasing FiO2
• Generating CPAP to splint the airways open (typically 2-4cm H20)
• Reducing nasopharyngeal deadspace

Question 4

THE PATHO-PHYSIOLOGY OF ARDS AND PNEUMONIA AND HOW TO VENTILATE IT

Answer 4

• The principle problem in ARDS and pneumonia is patchy alveolar collapse and consolidation, producing 3 different sets of alveoli to ventilate:
  
  • A relatively _n_ormal subset, which get most of the TV and risk over-distention
  • A marginal subset, which repeatedly open and close, sustaining atelectotrauma
  • A fully _co_llapsed subset, through which the blood shunts, causing hypoxia.
• The usual ventilation strategy is to use high PEEP to splint marginal alveoli open, and low TV to reduce barotrauma (accepting hypercarbia)

Question 5

THE PATHO-PHYSIOLOGY OF ASTHMA AND HOW TO VENTILATE IT

Answer 5

• The principle problem in asthma is high small airways resistance, the alveoli beyond are relatively normal
• The usual ventilation strategy is to:
  
  • use volume controlled ventilation and accept the high airway pressures that result, understanding they are not seen by the alveoli.
  • Use slow resp rates and ratio changes to prolong expiratory times.

Question 6

WHAT IS PROPOFOL INFUSION SYNDROME?

Answer 6

• Prolonged use of high dose propofol for ICU sedation is associated with Propofol Infusion Syndrome: life threatening metabolic acidosis, rhabdomyolysis, cardiac arrhythmia & failure.

Question 7

SVT IN CHILDREN

Answer 7

Sinus tachycardia at up to 200bpm is seen in small children due to fever, pain etc, but narrow complex tachycardia >220 is likely SVT, especially if

• rapid onset/offset
• fixed rate

Management

1. oxygen
2. Vagal manoeuvre
   
   1. facial ice pack for toddlers
   2. straw blowing for older children
3. Adenosine 100/200/300 mcg/kg rapidly*
4. Sync Cardioversion if compromised, at 0.5/1/2 J/kg
5. Amiodarone or Esmolol if cardioversion fails

* perhaps using a 3 way tap and 2nd flush syringe

Question 8

SODIUM METABOLISM AND HYPONATREMIA

Answer 8

Na is the principle extracellular cation, and the key determinant of ECF volume and tonicity.

• Na is actively absorbed by the gut, and excreted via the kidneys (Renin-Angiotensin-Aldosterone system) and sweat.
• Hyponatremia (<135) causes neurological dysfunction, with confusion, seizures and cerebral oedema, and may be due to either:
  
  • water overload, via
    
    • excess intake/IVT, or
    • excess retention due to cardiac/renal failure, SIADH etc.
  • sodium deficit, due to
    
    • diarrhoea
    • diuretics
    • sweating.

Management:

Address the cause, and:

• If water overload: fluid restriction and diuretics
• If sodium deficit: rehydrate with NS, and if still low, consider hypertonic.

Question 9

RAPID CORRECTION OF HYPO OR HYPERNATREMIA

Answer 9

• Rapid correction of hyponatremia is dangerous, due to the risk of osmotic demyelination: start with NS initially, and only consider hypertonic slowly, later.
• Rapid correction of hypernatremia is dangerous, due to the risk of cerebral oedema, seizures and subdural haemorrhage: start with NS initially, and only consider hypotonic slowly, later.

Question 10

HYPERGLYCAEMIA AND PSEUDO-HYPONATREMIA

Answer 10

• High serum glucose levels draw water out of the cells and into the ECF, causing a ‘dilutional hyponatremia’, which should not be primarily treated as it is not caused by Na derangement.
• It may be a causal factor in the cerebral oedema of DKA treatment,
• As a rough guide, each rise in BSL of 10mmol/l causes a dilutional fall in Serum Sodium of 3mmol/l.