Underlying considerations
Crystalloid or colloid fluids or blood are available for volume replacement.
The distribution of different fluids through the main compartments within the body (in decreasing volume: intracellular, interstitial and intravascular) is determined by constituents of the fluid. In general, the large molecules in colloids ensure that a greater proportion of the volume given as colloid will be retained in the intravascular space, the compartment where fluid resuscitation is directed. Blood is retained best in the intravascular space. The ability of the osmotically active particles of colloid to remain intravascular, and retain intravascular fluid volume, is varied. The complex starches used in heta- or pentastarch remain in the vascular space for a prolonged period. The gelatin derivatives of Gelofusine or Haemaccel of other colloids do so for only a few hours. Albumin will exchange readily with the albumin in the interstitial fluid, but remains in the intravascular space for more than 24 hours in health. Albumin loss to the tissue fluid will be enhanced where the endothelial barrier function is degraded by endothelial inflammation.
Again with crystalloids, distribution is determined by the constituents. The sodium and chloride of normal saline will ensure that it is localised more to the whole extracellular compartment (where sodium is the main osmotically active particle), and so when given intravenously, only a minor part will remain in the intravascular compartment as the majority of extracellular fluid is tissue fluid. This is in contrast to the distribution of 5% glucose, which after the metabolism of the glucose is effectively free water, which then disperses through all the fluid compartments of the body and so even less is retained intravascularly.
Those who support colloid resuscitation emphasis the importance of oncotic pressure in maintaining intravascular volume and tissue perfusion. Those who favour crystalloids
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respond that as the endothelium becomes leakier in ill patients, the colloid will also leak and serve to retain fluid in the tissues. To equal the increase of intravascular volume produced by a colloid, approximately three to five times as much crystalloid must be given.
Colloids are in general more expensive than crystalloids, and of the colloids, human albumin solution (HAS) is the most expensive and most restricted in availability.
Anaphylactic reactions are commoner with the colloids and more so with the gelatine-based colloids. Transmission of viral infections is a concern with the use of HAS.
Most of the fluids used in resuscitation are (close to) isotonic. Hypertonic solutions, particularly hypertonic saline has been used to resuscitate patients usually following blood loss. Experience in paediatrics is not extensive, but certainly some reports are favourable. An underlying concept is that smaller volumes of hypertonic solutions may adequately resuscitate the intravascular volume, without excess tissue oedema.
Further details on the composition of fluids can be found in Appendix B.
If blood is needed, it may be given after full cross-match which takes about 1 hour to perform. In more urgent situations type-specific non-cross-matched blood (which is ABO rhesus compatible but has a higher incidence of transfusion reactions) should be requested.
It takes about 15 minutes to prepare. In dire emergencies O-negative blood must be given.
Fluids should be warmed if this can be done without delay. Isotonic electrolyte solution should be kept available in a warmed cabinet. Further details on the management of shock in trauma, burns and diabetes can be found in Chapters 15, 20 and Appendix B.
Clinical considerations
Many trials contrasting fluid resuscitation regimens have been carried out, though few have been in paediatrics. None have produced a definitive answer. A recent Cochrane analysis suggesting that use of albumin increased mortality provoked considerable debate in the literature but there were few paediatric trials included and many of the studies were not done in the emergency situation. A further Cochrane review found no evidence that any colloid solution was more effective than any other, though neither was there a demonstrable benefit to albumin resuscitation
Furthermore, although all forms of shock are often treated as one, there is no reason to expect all forms of shock to respond to treatment in the same way, as their underlying biology differs.
Although the debate is often described as “crystalloid versus colloid”, within each group there are important differences between individual crystalloids and individual colloids.
Where the electrolytes or tonicity are disturbed, the immediate concern is to reverse shock or disturbances of perfusion. Chronic disturbances of electrolytes or tonicity should be corrected more slowly (over 24–48 hours) as compensatory mechanisms will have developed. Over rapid correction is likely to contribute to morbidity.The fluid used will depend on the disturbance of electrolytes.
Clinical decisions
The clinical decisions which must be made are essentially: When should we give fluid;
how much fluid should we give, and which fluid should we give?
When should we give fluid?
Fluids should be given where perfusion is compromised. Assessment of perfusion is difficult, and relies on assessment of organ function – urine output, mentation, peripheral perfusion. In a retrospective review of children with septic shock, early administration of large volumes of fluid (>40 ml/kg in the first hour) was associated with better outcome than smaller volume resuscitation encouraging a vigorous approach in
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septicaemia. In contrast, where shock is caused by penetrating trauma requiring definitive surgical management, maximal fluid resuscitation may be best delayed until operation as improving perfusion without improving oxygen-carrying capacity as well results in a worse outcome.
How much fluid should we give?
Administration of fluid should be guided by the response. Smaller volumes may be judged by their effect on the feature (for example peripheral perfusion) which provoked the administration of the fluid bearing in mind the caveats in Chapter 3 on the interpretation of these signs. If large volumes are needed, resuscitation is best guided by measurement of cardiac filling pressures and therefore patients requiring large volume resuscitation need prompt paediatric intensive care advice and timely transfer.
Which fluid should we give?
No definitive answer can be given. Where small volumes of fluid are used it may not matter. When larger volumes of fluid are used it must be more important.
In acute collapse, a smaller volume of colloid is needed than crystalloid to produce a given increase in intravascular volume, and so more rapid correction of haemodynamic derangement may be possible with colloid if it is readily available.
When larger volumes of fluid are used, the choice of fluid becomes more important. As the circulating volume of a child is approximately 80 ml/kg, if more than 40 ml/kg of fluid is used over a short time, one half of the child’s circulating volume will have been given.
If much more fluid transfusion is needed, significant haemodilution may result, and consideration should be given to using blood for fluid resuscitation with measurements of the central venous pressure (effectively cardiac preload) to guide fluid resuscitation.
Where large volumes are used human albumin solution is generally preferred in paediatric practice although most adult patients are resuscitated with synthetic colloids, crystalloid, or hypertonic solutions.
IN CONCLUSION
There is no definitive evidence demonstrating which fluid is best for resuscitation.
Other important questions – how much and when should fluids be used also remain to be answered. Clinical trials will be needed to answer these questions, though they are likely to be difficult to perform. Whilst awaiting more clinical trials, fluid resuscitation guided by a knowledge of the pathophysiology underlying the disease, and of the different roles of the different fluids will remain optimal management.
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CHAPTER
I 11 I
The child with an abnormal pulse rate or rhythm
INTRODUCTION
Most tachyarrhythmias in children are caused by a re-entrant congenital conduction pathway abnormality but some are secondary to poisoning or metabolic disturbance, follow cardiac surgery or occur in the course of cardiomyopathy. In tachyarrhythmias the rate is fast but the rhythm largely regular.
Most bradyarrhythmias are secondary to hypoxia and shock and are pre-terminal events although a few follow conduction pathway damage during cardiac surgery. The rate is slow and the rhythm usually irregular.
Children with congenital conduction pathway abnormalities will present in one of two ways. If they are able to communicate effectively, i.e the older child, they will present early, usually in good condition, with a perception of palpitations. If they are unable to communicate, i.e the younger child and infants, they will present later with poor feeding or even shock if their parent has not noticed the abnormal heart rate.
Those with other causes of tachyarrhythmias, such as poisoning, may present with additional symptoms, depending on the cause and progress of the underlying problem.
Children with bradyarrhythmias will almost always be in severe and pre-terminal respiratory failure or shock on presentation.
This chapter will provide the student with an approach to the assessment, resuscitation and emergency management of children with abnormal pulse rate or rhythm.