Osteopenia of Prematurity
- Introduction
- Diagnosis of metabolic bone disease
- Considerations and recommendations for enteral feeding
- What this means for very premature babies.
- Length of supplementation.
Introduction
This can be a significant problem for very premature babies and there is some suggestion that hypophosphataemia prolongs the need for ventilatory support. Some very premature babies have very "thin" bones on their x-rays.
Diagnosis of metabolic bone disease
- biochemical tests of osteopenia of prematurity are not definitive
- serum Phosphate: suspicious if <1.5, likely if < 1.1 mmol/L
- the alkaline phosphatase (ALP) is more elevated than usual for preterm babies. Levels above 600 or 800 IU/L are quoted. However, the ALP only rises high if there is bone turnover. If the condition is very severe the ALP may not be very high
- the calcium level may be normal, elevated or even low
- a bone x-ray will show very poor mineralisation and as the infants grow can show changes of rickets or fractures
- an abnormal Ca++ : PO4 ratio in the urine. In normal infants it is less than 1.0 (both measured in mmol/L))
Conversion factors (One of the problems with this area is that the USA, and many books, work in mg, while Australia and Europe use mmol/L)
| Ca++ | 1 mmol = 40 mg |
| PO4- | 1 mmol = 31 mg |
| Mg++ | 1 mmol = 24 mg |
Considerations and recommendations for enteral feeding
|
Fetal retention rates per day in mid to third trimester |
Human Milk per 100ml. Approx |
FM85 per 5g |
HM 100ml + 5g FM85 |
Fortified EBM @ 180 ml/kg/d the baby gets about |
Recommended per 150 ml/kg/d (Probably needs to be at top end) |
|
|
Ca |
2.3 to 3.0 mmol/kg 90 – 120 mg/kg |
0.75 mmol (30 mg) |
1.3 mmol (51 mg) |
2.0 mmol (81 mg) |
3.6 mmol (146 mg) |
3.0 to 5.7 mmol (120 – 230 mg) |
|
PO4 |
1.9 to 2.4 mmol/kg 60 - 75 mg/kg |
0.5 mmol (15 mg) |
(34 mg) |
1.6 mmol (49 mg) |
2.9 mmol (88 mg) |
1.9 to 4.5 mmol (60 – 140 mg) |
|
Mg |
0.10 to 0.14 mmol/kg 2.4 – 3.4 mg/kg |
0.15 mmol (3.5 mg) |
0.08 mmol (2.0 mg) |
0.23 mmol (5.5 mg) |
0.4 mmol (9.9 mg) |
0.33 to 0.63 mmol (7.9 to 15 mg) |
Remember that not all the minerals given are absorbed and retained. Retention rates for enteral nutrition vary but are about 50-60% for calcium, 70-80% for phosphorus and 50% for magnesium.
What this means for very premature babies
Premature infants fed with fortified EBM at 150 ml/kg/day, or more, should be getting just about enough calcium and phosphate. However, they need to be monitored and may still need supplementing. Fortification of feeds should start as early as possible – as soon as they are tolerating 120 ml/kg.
Vitamin D about 500 IU/day is required. Pentavite provides 405 units per day. Larger doses have no increased benefit.
Extra phosphate supplementation. If a baby needs supplementation then a solution of phosphate 0.8 mmol/ml is made by dissolving one tablet of Sandoz phosphate in 20 ml water.
Begin supplementation with 3 mmol/kg/day in 3 divided doses (i.e. 1 mmol/kg/dose tds). The dose should then be titrated against the blood phosphate level over the following weeks. Stop phosphate supplements if the serum phosphate is >1.8 mmol/L
Monitoring. "bone bloods" should be monitored every two weeks in very premature babies unless they are found to be phosphate depleted and if supplements are given they should be measured every week.
Length of supplementation
No one really knows how long to go on supplementing with phosphate. However it is worth considering that the babies are still growing fast up to and beyond "term".
Updated 06/02/2010
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