Fluids

1. Choice of intravenous fluid. After restoration of the circulating volume, the main residual fluid deficit is within the intracellular compartment. Historically, relatively hypotonic solutions were recommended, but a failure of plasma sodium concentration to rise during treatment has been linked with the development of cerebral oedema (see below). Most authors would therefore now recommend using isotonic (0.9 per cent) saline for the first few hours before changing to a more hypotonic solution, such as 0.45 per cent saline. 0.18 per cent saline is no longer recommended. In practice, the fluid type is usually changed once the blood glucose concentration has fallen to around 1015 mmol/L, but if this occurs very early during treatment, there is a possibility of giving too little sodium. In this situation, isotonic saline should be continued simultaneously with sufficient dextrose to avert hypoglycaemia during the latter stages of treatment. During such combination therapy, care should be taken to ensure that overall fluid volume is appropriate.

2. Volume of fluid. The volume of fluid to be replaced is based on the clinical assessment of the deficit plus maintenance fluid requirements, with the proviso that ongoing losses are also replaced. Clinical assessment of the degree of dehydration cannot be precise, and it is important not to over-estimate the degree of dehydration. The rate at which the fluids are given is an area of contention. It has been standard practice to give initial fluid rapidly initially, and then slow down the rate. However, since the rapid infusion of large volumes of fluid has been proposed as one risk factor for the development of cerebral oedema, once the circulating blood volume has been restored, it is reasonable to correct the remaining fluid deficit slowly and evenly over the next 24 or even 36 or 48 h. Furthermore, slow rehydration has been used successfully in adults with diabetic ketoacidosis and, paradoxically, it may lead to more rapid restoration of acid/base balance.

3. Practicalities of fluid administration.

• It is essential that all fluids administered are documented carefully, particularly the fluid that is given in the initial phase of therapy and during transfer to the ward; this is where most errors occur.

• By this stage, the circulating volume should have been restored. If not, give a further 10 mL/kg 0.9 per cent saline or 4.5 per cent albumin over 30 min.

• Otherwise, once circulating blood volume has been restored, calculate fluid requirements as follows:

requirement = maintenance + deficit [deficit (litres) = % dehydration x body weight (kg)]

• To avoid over-zealous fluid replacement, which may be a risk factor for cerebral oedema, never assess dehydration as more than 10 per cent. Include the volume of fluid that may have been given during resuscitation.

Age Maintenance values

Add maintenance and deficit and give the total volume evenly over the next 24 hours. i.e.

, maintenance + deficit hourly rate =-24-

Example:

A 20 kg 6 year old boy who is 10 per cent dehydrated will require 10 per cent x 20 kg = 2000 mL deficit plus 60 mL x 20 kg = 1200 mL maintenance

• It may be preferable (although there is no definite evidence) to lengthen the period of rehydration to 48 h in very young children or those who are very hyperosmolar with high plasma sodium levels or very high blood glucose levels. Discuss this with a senior clinician.

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