Severity of Hypoxic Ischemic Encephalopathy and Neurological Pupil Index in Neonates

BACKGROUND:

A newborn baby diagnosed with Hypoxic ischemic encephalopathy (HIE) needs frequent assessment of brain function which includes assessment of pupils in the eyes. However the traditional penlight does not provide a standard measurement and is not very accurate , as it varies based on interpretation of the observer. A new hand-held, non-contact device known as the automated "pupillometer", not only provides a safe, reliable, accurate measurement of the pupil size, but also provides additional information like Neurological Pupil Index (NPi). This value is used to assess the brain function in adults and older children, but the significance of the same has not been studied in a newborn population.

METHODOLOGY:

An Informed consent will be obtained prior to enrolment of the infant in the study. Neurological examination and pupillary assessment will be done at 5 different timepoints: - first at admission(baseline), followed by 24 hours, 48 hours and 72 hours of life, and once prior to discharge. Measurements will be done in both eyes and lesser score of the two will be considered for analysis. Outcome measures including EEG (which is continuous) and MRI (done on day 5 per unit protocol) will be documented and collated for analysis. This is an observational study and the measurement of NPi will not alter the treatment protocol.

The device has been approved by Health Canada for use across all patient population. This device poses no new risks and is safe to use, as it is a non-contact device and is relatively easy to use. Aseptic precautions will be followed when the device is used.

ANALYSIS:

SAMPLE SIZE CONSIDERATIONS:

This is a novel study, with no pre-existing literature. Hence, an initial small scale pilot study will be undertaken with a convenient sample size of all moderate to severe HIE within a year, with anticipation of 70% recruitment. An estimated sample size of 20-25 will help estimate the effect size, variability of NPi, explore relationship between NPi & indicators of severity of HIE and further refine study design & sample size calculation

STATISTICAL ANALYSIS:

Primary outcome:

The primary outcome (abnormal EEG pattern) will be a categorical variable (Yes/No type) The relationship between NPi and the primary outcome will be analysed using logistic regression model and expressed as Odds ratio with 95% confidence intervals.

Secondary outcome:

The secondary outcome (a composite measure of factors which indicate risk for severe HIE (including occurrence of seizure during admission, abnormal MRI finding or persistent feeding difficulty) will be assessed using logistic regression A Receiver-Operator Characteristic curve analysis will evaluate the diagnostic accuracy of NPi in predicting clinical severity of HIE indicating sensitivity & specificity. Any novel threshold values which can predict the cut-off for abnormal EEG pattern, or risk of severe HIE using other indicators will be identified with AUC >0.7

Inclusion criteria

• Neonates ≥35 weeks of GA, with Hypoxic ischemic encephalopathy admitted to neonatal neuro-intensive care unit at Alberta children's hospital, Calgary will be included in the study

Exclusion criteria

• Infants with chromosomal abnormalities/ syndromic associations
• Infants with ocular / orbital injuries or structural anomalies of the eye obscuring the pupillometry measurement
• Infants with inadequate pupillometry data / EEG data