Validation of Minimally Invasive Ultrasound Indicator Dilution Technique in Critically Ill Children

Validation of a Novel, Minimally Invasive Ultrasound Indicator Dilution Technique for Measuring Cardiac Index in Critically Ill Children

A novel method to measure cardiac index based on ultrasound indicator dilution technology (UIDT) has been developed by Transonic Systems Inc. (Ithaca, NY, USA). The method overcomes many of the limitations that have plagued the existing techniques used to measure cardiac index in critically ill children.

In the proposed investigation, the investigators hope to validate a novel application of an existing technology in critically ill infants and children. The primary aim of this study is to determine the accuracy of cardiac index measured by UIDT when compared to the gold-standard Fick technique. The primary hypothesis is that the average of three consecutive measurements of cardiac index by UIDT will be accurate when compared to the Fick technique. Secondary aims will be to determine the precision of the measurement, the feasibility of the technique with regards to time required and any complications encountered. An exploratory secondary aim of this study is to determine whether central blood volume (CBV) derived from indicator transit time (ITT) correlates with central venous pressure (CVP) and echocardiography derived measures of preload.

Inclusion Criteria:

• Age: less than 18 years.
• Admission to the CICU (Cardiac Intensive Care Unit) (8S) or MISICU (Medical-Surgical Intensive Care Unit) (7S) of the Children's Hospital Boston.
• Presence of a central venous catheter with its tip in the superior vena cava or a catheter in the pulmonary artery, documented by radiography.
• Requirement for mechanical ventilation via an endotracheal or tracheostomy tube.
• Presence of an arterial catheter.
• Patients must have a two ventricle circulation.

Exclusion Criteria:

• Endotracheal tube leak of greater than 10%.
• A significant air leak around the endotracheal tube makes VO2 impossible to measure.
• Presence of relevant intracardiac shunt.
• Intracardiac shunt will decrease the area under the arterial dilution curve unpredictably, making cardiac index calculations unreliable.
• A patent foramen ovale and a single ventricular septal defect less than or equal to 2mm or an atrial septal defect less than or equal to 3mm will be considered irrelevant for the purposes of this study.
• Previous enrollment in an incompatible research study.
• Current or prior diagnosis of heparin induced thrombocytopenia.
• A small amount of heparin is required to flush the extracorporeal AV (Arteriovenous) loop that is required for the measurements.
• Pneumothorax with ongoing air leak.
• An air leak will invalidate the measurement of VO2.