Pediatrics International (2009) 51, 59–65 doi: 10.1111/j.1442-200X.2008.02654.x © 2008 Japan Pediatric Society The hemodynamic monitoring of cardiac function and the esti- mation of blood volume are fundamental to the control of criti- cally ill children. The measurement of cardiac output is one of the principal elements for estimating a patient’s hemodynamic situation and tissue perfusion, and can help to direct treatment and monitor the clinical course of patients with septic and/or cardiogenic shock. Although several methods exist for measur- ing cardiac output, the most widely used in adults is pulmonary thermodilution using a Swan–Ganz catheter. But this technique is not widely used in children due to the difficulty and risk of complications of inserting a Swan–Ganz catheter into the pulmon- ary artery, particularly in infants. 1,2 The blood volume is esti- mated from indirect clinical parameters (state of hydration, peripheral perfusion, diuresis) and pressure measurements (cen- tral venous pressure [CVP], left atrial pressure, pulmonary capil- lary pressure), assuming a linear relationship between blood volume and the pressure within the cardiac cavities. But there are many situations in the critically ill child (valvular insufficiency, heart failure, pulmonary hypertension, increased intrathoracic pressure etc.) in which there is no satisfactory relationship between the pressures and the blood volume, and hypovolemia may coexist with normal or even elevated venous or pulmonary capillary pressures. The pulse-induced continuous cardiac output (PiCCO) sys- tem is a method for the continuous measurement of cardiac out- put by thermodilution in the femoral artery and analysis of the pulse contour curve. It is less invasive than pulmonary thermodi- lution because it does not require the insertion of a catheter in the pulmonary artery but only a central venous catheter and an arte- rial catheter. Experimental and clinical studies have found a good correlation between cardiac output measured by arterial ther- modilution and by pulmonary thermodilution. 3,4 Apart from the measurement of hemodynamic parameters, arterial thermodilu- tion enables the parameters of intracardiac and intrathoracic blood volume and the extravascular lung water to be calculated. Some experimental studies and studies in adults have indicated that the calculation of the intracardiac volumes by arterial ther- modilution is a more reliable method for estimating blood vol- ume, and that it correlates better with cardiac filling measured by transesophageal echocardiography than pressure measures such Original Article Cardiac output and blood volume parameters using femoral arterial thermodilution Jesús López-Herce, Amaya Bustinza, Luis Sancho, Santiago Mencía, Angel Carrillo, Ramón Moral and Jose María Bellón Pediatric Intensive Care Unit, Gregorio Marañón General University Hospital, Madrid, Spain Abstract Background : The pulse-induced continuous cardiac output (PiCCO) system is a less invasive method than pulmonary thermodilution for the measurement of cardiac output and estimating blood volume parameters. The normal values in children have not been defined. The purpose of the present paper was therefore to evaluate cardiac output and param- eters of blood volume using femoral arterial thermodilution in critically ill children. Methods : A prospective study was performed in 17 critically ill children aged between 2 months and 14 years. Two measurements were taken for each determination of cardiac output, global end diastolic volume (GEDVI), intrathoracic blood volume index (ITBI), extravascular lung water index (ELWI), systolic volume index (SVI), stroke volume vari- ation (SVV), cardiac function index (CFI), left ventricular contractility (dp/dt max), and the systemic vascular resistance index (SVRI). Results : One hundred and seventeen measurements were performed. The mean cardiac index (CI) was 3.5 ± 1.3 L/min per m 2 . The GEDVI (399.7 ± 349.1 mL/m 2 ), ITBI (574.5 ± 212.2 mL/m 2 ) and dp/dt max (804.6 ± 372.1 mmHg/s) were lower than reported in adults, whereas ELWI (18.9 ± 9.3 mL/m 2 ) and CFI (8 ± 2.5 L/min) where higher. The GEDVI, SVI, dp/dt max and CI increased with the weight of the patients whereas the ELWI values decreased. Conclusions : Femoral arterial thermodilution is a suitable technique for the measurement of cardiac output in criti- cally ill children. The intrathoracic and intracardiac volumes are lower than in adults, whereas extrapulmonary water is higher; these values are related to the weight of the patient. Key words cardiac index, cardiac output, children, extravascular lung water , femoral arterial thermodilution technique, intrathoracic blood volume. Correspondence: Jesús López-Herce, PhD MD, Sección de Cuidados Intensivos Pediátricos, Hospital Gregorio Marañón, Dr Castelo 47, 28009 Madrid Spain. Email: pielvi@ya.com Received 23 January 2007; revised 1 December 2007; accepted 7 January 2008; published online 8 July 2008.