Hyponatraemia after postoperative fluid management in children
*E-mail: o.dearlove{at}man.ac.ukEditor—Most postoperative paediatric surgical patients will be nil by mouth from a few hours to at least a few days or even weeks after the operation and the importance of postoperative fluid and electrolyte balance cannot be stressed strongly enough. We present an audit project for which the local audit committee gave approval. The aims of this study were: (i) to check what types of fluids are being used after operation; (ii) to determine whether electrolyte levels are being checked after operation; and (iii) to determine whether the commonly used fluids cause any fluids and electrolytes derangement.
A retrospective study of 104 patients who underwent appendectomy at Royal Manchester Children's Hospital from September 2004 to March 2005 found that 51 patients (49%) had their electrolytes monitored 24 h after operation, 23 patients (22%) had their electrolytes monitored 3 days after operation and the remainder (34) had no record of electrolytes after operation. The postoperative fluids used were: in 91 patients (87%) 0.45% saline and 5% dextrose, 7 patients (6.7%) Hartmann's solution in addition to the above, and 1 patient (0.96%) total parenteral nutrition in addition to the above fluid. Data were incomplete on three patients.
Of the 51 patients who had their electrolytes checked on the first postoperative day, 16 (32%) had hyponatraemia ranging from 127 to 133 mmol litre–1, 7 (14%) of them <130 mmol litre–1; and 32% of the patients who had their electrolytes checked within a day of surgery had hyponatraemia, 14% severe <130 mmol litre–1.
Between 70% and 80% of a child's body is made up of water which is divided into extracellular fluid (ECF) and intracellular (ICF). The ECF is subdivided into interstitial fluid (ISF) and intravascular fluid (IVF). Although osmolarity of these fluids are similar (ranging 290–320 mosmol litre–1), the electrolyte contents are very different. The ECF contains a high concentration of sodium and the ICF has a high concentration of potassium and magnesium. Fluid moves from one component to another depending on various physiological pressure and osmotic gradients. In illness and injury these fluid shifts may be rapid, with significant clinical consequences.
The ECF volume is controlled by manipulation of its major cation: sodium. The sensors are carotid baroreceptors, atrial stretch receptors and juxtaglomerular apparatus. A reduction in ECF volume causes ADH release, release of atrial natriuretic peptide and activation of renin–angiotensin–aldosterone system. Control of osmolarity is by varying water intake and excretion. A rise in ECF osmolarity triggers sensation of thirst and causes release of ADH. Very sick children may not be able to respond to the sensation of thirst and most of them are kept nil by mouth. The secretion and levels of antidiuretic hormone may be raised in sick children, worsening hyponatraemia.
Dr Cunliffe's editorial on this subject contributes an interesting viewpoint, but as far as we can see it is not evidence based.1 Alder Hey uses a fluid saline 0.18% and dextrose 2.5% which does not have a majority following according to the questionnaire survey2 in the British Journal of Anaesthesia, and we know of no published audit of results of its use. Readers will recognize that this is a recurring issue: a surfeit of opinions without evidence and surveys of what anaesthetists might do or say they do. Our audit stands out as a record of what people did, and not a paper about what they said they could have done.
The Department of Health has also recently renewed an interest in hyponatraemia occurring after operation in children in hospital. In 2003 there was advice from the Royal College of Anaesthetists3 warning of problems of four-and-a-fifth saline (dextrose 4% and saline 0.18%), at which point this hospital switched to half normal saline (dextrose 5% and saline 0.45%) which was the fluid used in our review. The issue is under current review and renewed consultation in 2006. The use of four-and-a fifth saline was described as ‘dangerous and harmful and should never be used’4 in a GMC case. However, we have found one of the recommended solutions for its replacement is also associated with significant hyponatraemia. Doctors expect that if they are told not to use one solution but to use others by outside agencies, there is an evidence base that it is safer. At the present time, this is not the case, nonetheless the authors note that tendentious GMC cases on such things as hyponatraemia will become much easier to prove against doctors when the standard of proof goes down to the civil level of balance of probabilities.
We recommend that fluid and electrolytes should be more vigorously and regularly monitored especially in postoperative surgical patient. Half normal saline, saline 0.45% and dextrose 5%, one of the recommended solutions still can cause hyponatraemia in postoperative children. Thus more research is required to finding more suitable postoperative fluids.
Declaration of Interest
Dr Playfor's article, cited in the Editorial, is also from this Hospital. The data have been presented in the Singapore Surgical Congress 2006.
Manchester, UK
Editor—We would like to thank Dr Dearlove and colleagues for sharing with us the results of their limited audit on fluid management after appendicectomy. It illustrates some of the problems relating to fluid management in children—that hyponatraemia is a common finding in the postoperative period and that there is often a failure to adequately monitor children on i.v. therapy. It is difficult to draw any conclusions from the audit as we are not told if all children were still receiving i.v. fluids at 24 h and 3 days after surgery. Following appendicectomy, i.v. fluids can be discontinued quite quickly.
There is extensive opinion within the literature on which maintenance fluid we should be giving, despite there being little evidence to support it. The choice is between using hypotonic or isotonic solutions. There is a further choice to be made as to whether fluids are given in the volume recommended by Holliday and Segar, or reduced by 20%, 30% or 40% if you believe their formula overestimates requirements.
The question of how to improve the safety of fluid management in children needs to not only address the fluid types that we give, but to look at other issues. We need to give greater priority to teaching the principles of fluid and electrolyte management to both undergraduates and postgraduates. Many cases of fatal hyponatraemia have occurred from children being given the wrong type of fluid for the wrong reason—choosing a hypotonic fluid for resuscitation. The prescribing of i.v. fluids should be as rigorous as the prescribing of drugs. Fluid prescription charts should be redesigned to allow prescribing of different fluids for maintenance, for resuscitation and for replacement of any other losses. Such an important task should not be left to the most junior doctor in a medical team to do without supervision. Children should be accurately weighed and electrolytes monitored before and regularly during any i.v. fluid therapy.
Hyponatraemia can occur following administration of both hypotonic and isotonic maintenance fluids, and so changing over to isotonic maintenance fluid may not be the answer to this problem. Ideally we should monitor plasma sodium and osmolality alongside urinary sodium and osmolality, and tailor the fluids we give according to how much sodium and free water that patient needs.
Although there is a move towards the use of isotonic fluids for maintenance in postoperative children, we do not yet know what new problems this may cause. We do need an evidence base through research to enable better fluid management in children, but this is something which will not appear overnight. In the meantime we still need to treat patients, and audit may have a role to play in helping us to regularly review our practice.
For information, we do not think there is such a fluid as saline 0.18% in dextrose 2.5%. At Alder Hey we have always used saline 0.45% in dextrose 5% as maintenance fluid for our postoperative patients.
Liverpool, UK
*E-mail: Mary.cunliffe{at}rlc.nhs.uk
References
1 Cunliffe M and Potter F. Four and a fifth and all that. Br J Anaesth 2006; 97:274–7
2 Way C, Dhamrait R, Wade A, Walker I. Perioperative fluid therapy in children, a survey of current practice. Br J Anaesth 2006; 97:371–9
3 Possibility of severe overload with hyponatraemia. Available from http://www.rcoa.ac.uk/index.asp?PageID=695&SearchStr=hyponatraemia
4 GMC v Dr Mark Leonard Baxandall. Available from http://www.gmc-uk.org/concerns/decisions/search_database/pcc_baxandall_20040621.asp
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