A Prospective Investigation of Pleth Variability Index (PVI) as a Dynamic Parameter of Fluid Responsiveness in Children

Background: Hypovolemia is a frequent cause of circulatory failure in anesthetized and
critically ill children. Fluid boluses are the first line of treatment aimed at optimizing
stroke volume and ultimately improving oxygen delivery. A patient whose stroke volume
significantly increases as a result of a fluid bolus is deemed 'fluid responsive'.
Traditional parameters of circulatory status (e.g. blood pressure, heart rate, central venous
pressure) have been shown to be ineffective at predicting fluid responsiveness. Dynamic
parameters of fluid responsiveness, such as pulse pressure variation (PPV) and stroke volume
variation (SVV), reflect hemodynamic changes secondary to intermittent positive pressure
ventilation. These indices have proven to be superior to the traditional static measures of
circulatory status in predicting fluid responsiveness. Furthermore, the use of these dynamic
parameters in a goal-directed fashion has been shown to improve outcome in high risk, adult
surgical patients. As such, there is increasing interest in using dynamic parameters to guide
fluid resuscitation in mechanically ventilated infants and children. Unfortunately, there is
a paucity of literature examining the validity of these dynamic parameters in children. The
need for arterial vascular access, which is less common in small children, has also limited
the ability to investigate these parameters. Recently, a non-invasive dynamic parameter has
been developed examining the plethysmographic waveform from a pulse oximeter. The pleth
variability index (PVI) represents the dynamic changes in hemodynamic performance that occur
during the respiratory cycle. Studies of PVI in adults have shown it to be a reliable
predictor of fluid responsiveness. However, conclusive data in children are lacking.

Hypothesis: This study is designed to investigate the ability of PVI to non-invasively
predict fluid responsiveness in mechanically ventilated children. The hypothesis is that a
higher PVI will predict significant stroke volume increases in response to a fluid bolus in
mechanically ventilated children.

Methods: The study population will consist of 20 children undergoing cardiac catheterization
who will have normal (non-shunted) physiology at the conclusion of the procedure, ages 1-12
years. All subjects will receive a PVI measurement as well as a stroke volume measurement via
transthoracic echocardiography. Subsequent volume expansion will be achieved with an
intravenous bolus of 10 mL/kg of isotonic crystalloid (normal saline) administered over 10
minutes. After completion of the bolus, an additional PVI measurement and stroke volume
measurement will be obtained.

Significance: Hypovolemia is a significant cause of harm in anesthetized and critically ill
infants and children. In order to successfully resuscitate these patients, we must gain a
better understanding of how to optimize cardiac output and oxygen delivery. A non-invasive
monitor which indicates stroke volume responsiveness has the potential to better guide fluid
resuscitation and improve outcomes.

Inclusion Criteria:

- Children undergoing cardiac catheterization who will have normal (non-shunted)
physiology at the conclusion of the procedure.

Exclusion Criteria:

- Patients with additional congenital heart abnormalities, cardiac arrhythmias,
ventricular dysfunction, and known pulmonary disease.