Paediatrics
Neonate
Up to 4/52
Infant
Up to 1-12/12
Child
Up to 16yrs
Airway
Best maintained in neutral position.
Jaw thrust very effective Actual size of airway small – increased resistance to flow.
Nasal resistance represents up to 50% of total airway resistance.
Obligate nasal breathers up to 6 months.
Tongue large.
Prone to partial obstruction esp GA, Down’s - with increased work of breathing.
Epiglottis
Long, floppy, U-shaped.
Larynx
Higher and more anterior – C3.
Narrowest at cricoid.
Cylindrical shaped glottis.
Trachea
Shorter length.
Main bronchi at equal angles and more acute to trachea.
RS
Alveoli
10% adult level at birth. Number & size increase until age 8 when lung growth due to increase in alveolar size. Lung volume disproportionately small compared to body size.
Mechanics respiration
Resistance ↑ as narrowed airways up to age 8.
Ribs horizontal, intercostal muscles poorly developed and diaphragm flatter and less efficient. Lower % type I muscle fibres.
Ventilation therefore diaphragmatic and rate dependent.
Chest wall very compliant, leads to in-drawing during respiration & reduction in FRC during GA. (Lungs relatively stiff at birth but compliance increases rapidly first few weeks).
FRC & TLC relatively small; increase with age.
Closing volume may exceed FRC in normal breathing leading to airway closure and atelectasis. WOB and oxygenation improved with CPAP.
Oxygen consumption
High in neonates (6-8ml/kg/min) and infants.
Sats curve shifted left by fetal Hb.
Alveolar ventilation
Tidal volume fixed (6-7ml/kg) – increase rate needed to increase minute ventilation.
Ratio of alveolar ventilation to FRC high (5:1) in neonates – FRC less efficient buffer to changes in partial pressures of gases. Reduced stimulation to hypoxia in neonates.
Volatile agents
↑ metabolic rate and alveolar MV mean more rapid induction and emergence ??? ↑ CO → ↑ induction time.
Profound respiratory depressants so IPPV in neonates.
Post-op apnoea
More common in ex-premature babies, peak at 44 weeks post conceptual age, but up to 60 weeks.
Increased incidence with haematocrit <30%, temp <34.
Incidence reduced with caffeine on induction.
Age Resp rate (/min)
0 30 –35
2 25-35
5 25-30
12 20-25
RR = 30 – (age/2)
CVS
Cardiac output
Resting CO high in neonate (CI 200ml/kg/min).
Rate dependent – limited ability to increase stroke volume in response to increased preload.
Ventricles small, reduced contractile mass and poor compliance.
Also tolerates increases in afterload poorly.
Arterial blood pressure lowest in neonate with ↓SVR, increases to keep pace with perfusion demands.
Systolic BP over 1yr = 80 + (age x 2)
ECG
Right axis deviation, inverted T V1 – V4 normal, reflects relatively reduced mass of LV.
age 0-1 - 110-160 HR
1-2 - 100-150
2-5 - 95-140
5-12 - 80-120
Autonomic to heart
Parasympathetic tone predominates in infants. Bradycardia easily with hypoxia, vagal manouvres.
Blood
Total blood volume small - 90ml/kg neonate; 80 ml/kg child; 70 adult.
HbF predominates first 2-3 months of life, then HbA production stimulated & replaces HbF by 4 months.
Hb initially high (18) then low (10-12) in infancy.
Vit K dependent clotting factors reduced first 2 months.
Transfuse after 15% blood loss.
Fluid requirements
Increased fluid requirements in neonates – high metabolic rate, ↑surface area:body wt ratio, ↓renal concentrating ability. GFR low in newborn, adult values at 2 years.
Neonates
- Glucose solutions (10%) with added Na (3mmol/kg/day) and K (2mmol/kg/day).
- Intra-operatively can add 25mls 50% dextrose to 500mls of Hartmanns to make a 2.5% dextrose/Hartmanns solution.
4ml/kg/h up to 10kg
2 next 10 kg
1 for each subsequent kg
Avoid hypotonic solutions. Use 0.45% saline/5% dextrose post-operatively as maintenance
Replace intra-operative losses with Hartmanns
Age TBW ECF
Neonate 80% 45%
2 year 60% 35%
CNS
Myelination
Incomplete till 2nd year. Physiological response to painful stimuli, although efferents not well developed in neonates.
Brain
Growth rapid, double in size in 6 months.
Spinal cord
Ends lower border L5 in newborn, L3 by 8 years.
MAC
Neonates as adult.
Peaks at 1 yr ↑50%.
Declines to adult levels by puberty.
GI
Decreased lower oesophageal sphincter tone in infants.
Abdomen more protuberant.
Liver
Reduced metabolic enzymes at birth, matured by 3/12.
Protein binding increases with age.
Biliruben metabolism inefficient.
Carbohydrate reserves low.
Temperature regulation
↑ heat loss.
Large surface area : body weight ratio.
Minimal SC fat with poor insulation.
Limited vasoconstrictor response.
Unable to shiver.
Non shivering thermogenesis by metabolism in brown fat → ↑O2 consumption.