Over the last decade, our understanding of the impact of acute kidney injury and disorders of fluid balance on outcomes in children across disease processes and age spectrum has become clear. Seminal multicenter longitudinal studies in critically ill children, congenital heart disease, and neonatal populations have solidified the association of AKI and disorders of fluid balance with adverse outcomes [1,2,3,4,5]. Unfortunately, there remains no definitive treatment for AKI. In the absence of established AKI therapeutics, the care of these patients has shifted toward strategies aimed at the prevention and/or mitigation of AKI.

In this context there has been a renewed interest in understanding the impact of the most commonly prescribed medication in medicine, intravenous fluids, on outcomes and as a potentially modifiable risk factor to improve outcomes in critically ill patients. Intravenous fluid management is a cornerstone of the management of critically ill patients. Virtually every critically ill child receives intravenous fluids and frequently receives very large volumes. Despite these drugs being used nearly ubiquitously, there remains a lack of clear understanding of the optim

al fluid management strategy. There is an ongoing evolution in our understanding and practices regarding intravenous fluids in critically ill patients. This includes understanding the importance of early fluid resuscitation in critical illness [6] and the phases of fluid management in critical illness [7]. More recently, isotonic fluids have been favored as “maintenance” fluids in efforts to prevent hospital-acquired hyponatremia. Over time, the paradigm of how we manage intravenous fluids has evolved to better understand the impact of volume, timing, and tonicity of intravenous fluid choices [8]. In recent years there has been increasing interest in understanding the impact of intravenous fluid composition (balanced electrolyte solutions vs. 0.9% saline) and associated electrolyte abnormalities (acidosis, dyschloremias) with adverse outcomes.

In the article “Hyperchloremia and association with acute kidney injury in critically ill children,” Ginter et al. report on the impact of hyperchloremia on outcomes in a single-center retrospective study of critically ill children [9]. The authors demonstrate that hyperchloremia is independently associated with AKI in critically ill children after adjusting for severity of illness, renal angina index, change in the serum chloride, and fluid balance. Their single-center study importantly evaluated the chloride load as well as the change in the serum chloride. The patients with hyperchloremia received a larger volume of fluid, a higher chloride load, and had a greater increase in chloride. Furthermore, the utilization of balanced electrolyte solutions was relatively uncommon (5% plasmalyte and 12% Ringer’s lactate). This study adds to the existing literature (Table 1) by further understanding the potentially deleterious impact of utilizing solutions with supraphysiologic chloride content on outcomes in critically ill children.

Table 1 Studies evaluating the impact of intravenous fluid composition and hyperchloremia in critically ill children
Full size table

In interpreting the current study and the existing literature on the topic, it is important to highlight the difficulty of fully understanding the impact of serum chloride levels and chloride loads in critically ill patients. Is the serum chloride the chicken or the egg? Is hyperchloremia merely a reflection of the tubular injury that has occurred because of the etiology of the AKI? Does hyperchloremia represent an exposure to a detrimental internal milieu that in turn causes AKI? Serum chloride likely reflects both the chloride load administered as well as the body’s ability to manage that load and maintain a normal chloride level. Patients with AKI frequently receive more resuscitation fluids and thus chloride load when the overwhelming amount of intravenous fluids (> 80–90%) administered is 0.9% saline as is the case in this study. In future studies urinary biomarkers, fluid management algorithms, and ultimately trials will help us to further tease out whether hyperchloremia is the chicken or egg as it is related to AKI.

As we move forward in research, we will also need to further refine our understanding of the timing and dose of chloride administration on outcomes. As an example, resuscitation fluids that are rapidly administered likely have a very different impact than slow continuous fluids. Logically, the clinical impact of a rapid infusion of 60 mL/kg of 0.9% saline with a pH of 5 is a very different type of chloride load than that same 60 mL/kg delivered over 18 h while being mixed with D5W medication carriers regardless of the chloride content of the fluid. This is highlighted by the recent study evaluating the detrimental impact 0.9% saline has on the endothelial health of patients [17]. Separately, the optimal way to manage these patients may depend upon the patient’s serum chloride. Patients initially with hypochloremia may need hyperchloremic fluids, and patients with hyperchloremia may need hypochloremic fluids. As with any drug prescribed in critically ill children, the provision of intravenous fluids likely needs to be individualized and evaluated on a daily basis.

In summary, there is a complex interplay between the tubular function of the kidneys, the chloride load given to critically children, and the resultant serum chloride. Serum chloride may be a biomarker for AKI or a reflection of the chloride load which in turn may be a risk factor for the development of AKI. Future studies should help to discern these important differences and help answer the question of chicken (modifiable risk factor) or the egg (biomarker for AKI). In the meantime, clinically, patients should be given fluids thoughtfully with an individualized approach and with consideration of their kidney function.