If a patient has a comparatively minor burn, he will probably start to eat and drink normally when shock is over. He will then be able to adjust his fluid and electrolytes himself without difficulty, so that you can take his drip down at about 48 hours, and start giving him a high protein diet about the third or fourth day. But, if his burn is extensive and he is not drinking for any reason, you will have to control his fluid and electrolyte intake for him. Two things are particularly important at this stage—water and sodium.
Although little plasma will leak from a patient’s burn after 48 hours when shock is over, he will continue to lose fluid by evaporation from its wet surface. In a 30% burn he may lose 2 litres of fluid a day in addition to his loss by other routes. The result is that he can easily become dehydrated, hypernatraemic, wasted, and oliguric. His serum osmolarity will rise and he may die from circulatory failure. So, keep a careful watch on his fluid balance chart, even if he is taking fluids by mouth. Calculate the water loss from his burn from Fig. 58-8. It is based on his surface area. Read this off from Fig. 58-6.
Fig. 58-8 is only a rough guide to the fluid a patient needs. Add it to his daily fluid requirements (scale E in Fig. 58-6), and adjust the fluid you give him in the light of the following factors.
(1) The ambient temperature. He will need more fluid if the weather is hot.
(2) The stage of healing of his burn. His fluid requirements will become less as it heals.
(3) Oedema is not a good guide to his electrolyte and fluid needs, because he can be both oedematous and salt depleted.
(4) His urinary output. Unfortunately, this too is an imperfect guide because a diuretic phase commonly follows the shock phase.
A patient can also lose much sodium from a severe burn. Calculate his sodium loss from Fig. 58-8. To find out how many mmols of sodium there are in the commonly used fluids, consult Fig. A 15-6 in Primary Anaesthesia.
If your laboratory tests are limited, the safest fluid to give him will be 0.18% saline in 5% dextrose for maintenance (for ’shock’ he needs Ringer’s lactate or 0.9% saline). Take care not to overload young children and cause water intoxication as described in the next section.