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Archived Comments for: Circuit life span in critically ill children on continuous renal replacement treatment: a prospective observational evaluation study

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  1. Factors affecting circuit lifespan in critically ill children: A child is not a small adult

    Jesus Lopez-Herce, Pediatric Intensive Care Unit. Hospital General Universitario Gregorio Marañón. Madrid

    6 October 2008

    We read with interest the comments of Drs Ricci et al (1) on our article “Circuit lifespan in critically ill children on continuous renal replacement treatment: a prospective observational evaluation study” (2).

    We agree with the authors that “children are not equal to adults”. There are important differences between children and adults in their anatomy, physiology, diseases and response to disease and in the treatments given. In fact, it is essential to understand that “the child is not a small adult”. The effects and the efficacy of some techniques and treatments are different in critically ill children and the criteria for treatment in the adult cannot therefore be applied directly. Because of this, studies that analyze the dose, efficacy and limitations of continuous renal replacement therapies (CRRT) in critically ill children are essential.

    When heparin is used as the anticoagulant in CRRT, low doses are usually recommended. This recommendation was based on studies performed in adults; the catheters and filters used in adults are much larger and the blood flow rates are much higher than in children. One of the most important results of our study is that the use of higher doses of heparin in children is associated with a longer duration of the filter without the risk of more hemorrhagic complications. Of course the dose of heparin must be individualized in each patient, evaluating the hemorrhagic risk factors; however, it is not only the risk of hemorrhage due to excessive anticoagulation that must be evaluated in each patient but also the blood loss that occurs due to clotting of the filter, the haemodynamic disturbances that occur on withdrawing and restarting CRRT, and the decrease in dialytic efficacy due to the downtime when changing filters. In addition, studies need to be performed that analyze the duration of the filter in relation to the coagulation studies rather than the dose of heparin.

    One of the fundamental factors in the duration of CRRT in critically ill children, particularly the smallest children, is how well the vascular access functions. Small diameter catheters only permit a low blood flow and become kinked more easily. Hence the importance of using the largest possible catheter for the age of the patient.

    With regard to the dose of hemofiltration, there are no comparative studies in children that have investigated the influence of high-volume hemofiltration on the vital prognosis and on the duration of the filters, and in adults the results are contradictory (3). We generally use a relatively high volume of hemofiltration. In our study, a total effluent flow rate of more than 35 mL/kg/h was associated with a longer filter life, probably due to the use of hemodiafiltration with lower ultrafiltration rates. Although further studies are necessary, in our opinion the use of hemodiafiltration enables adequate solute removal and prolongs filter duration.

    The subject of the effective daily duration of CRRT is an essential determinant of the efficacy of the technique, as indicated by Ricci et al (1), and the frequency of clotting of the filter is one of the fundamental factors that affects this efficacy. However, there are other very important factors that have an influence on the effective daily duration of CRRT, such as the number and qualifications of the medical and nursing staff, which affect not only the maintenance and the duration of the filter but also the speed of change of the circuit and re-initiation of CRRT when filter clotting occurs. The type of machine used for CRRT also has a significant effect. Some CRRT machines have a preassembled circuit that is very quick and easy to mount, and an almost automatic purging system, whereas the circuit in other machines is more complicated and requires greater training of the nursing staff, and purging is slower and has to be performed almost manually, prolonging the time during which CRRT is interrupted; this can prevent reinitiation of the treatment in some circumstances, such as during the night shift in some hospitals, when the number of nurses available is more limited.

    Finally, Ricci et al (1) indicate that a problem with frequent interruptions of CRRT is the forced interruption of parenteral feeding, leading to an insufficient calorie delivery. In our opinion, this should not occur. In our hospital, a very high percentage of critically ill children with CRRT are fed enterally and this is maintained at the same rate during the periods in which CRRT is interrupted due to filter clotting (4). In those patients requiring parenteral nutrition, this is also maintained when the CRRT circuit clots. In order to prevent dangerous increases in the potassium concentration if the interruption in the CRRT becomes prolonged, it is recommendable not to administer potassium in the parenteral nutrition, or to do this at low doses. During CRRT, the blood electrolyte concentrations are very easy to control by modifying their concentration in the dialysis and replacement fluids.

    Finally, we agree with Ricci et al (1) that randomized studies are necessary to determine the most suitable characteristics of CRRT in children. As the number of critically ill children requiring these techniques is not very high, it is essential to design multicenter studies in order to answer these questions.

    Jesús López-Herce and Jimena del Castillo

    1.Ricci Z, Guzzo I, Picca S, Picardo S. Circuit lifespan during continuous renal replacement therapy: children and adults are not equal. Crit Care 2008;12:178

    2.Del Castillo J, López-Herce J, Cidoncha E, Urbano J, Mencía S, Santiago MJ, Bellón JM. Circuit life span in critically ill children on continuous renal replacement treatment: a prospective observational evaluation study. Crit Care 2008;12:R93.

    3.VA/NIH Acute Renal Failure Trial Network, Palevsky PM, Zhang JH, O'Connor TZ, Chertow GM, Crowley ST, Choudhury D, Finkel K, Kellum JA, Paganini E, Schein RM, Smith MW, Swanson KM, Thompson BT, Vijayan A, Watnick S, Star RA, Peduzzi P. Intensity of Renal Support in Critically Ill Patients with Acute Kidney Injury. N Engl J Med 2008; 359:7-20.

    4.López-Herce J, Sánchez C, Carrillo A, Mencía S, Santiago Mª J, Bustinza A, Vigil D. Transpyloric enteral nutrition in the critically ill child with renal failure. Intensive Care Med 2006; 32:1599-605.

    Competing interests

    We have not any competing interest