Related Experiment Video
Updated: Jul 4, 2026
A Preterm Rat Model for Pain Studies
Published on: February 9, 2024
Changes in physiological and behavioural pain indicators over time in preterm and term infants at risk for neurologic
Sharyn Gibbins1, Bonnie Stevens, Patrick McGrath
1Interdisciplinary Research, NICU, Sunnybrook Health Sciences Centre, Canada. sharyn.gibbins@sunnybrook.ca
Insights
Infant pain responses, including facial actions and heart rate, generally decreased by 6 months of age compared to the neonatal period. Some differences in cry responses were noted between neurological impairment risk groups.
Area of Science:
- Neonatal care
- Developmental pediatrics
- Pain research
Background:
- Approximately 10% of Neonatal Intensive Care Unit (NICU) infants face risks for Neurological Impairment (NI).
- Limited understanding exists regarding how NI risk influences pain responses over time.
Purpose of the Study:
- To compare physiological and behavioral pain responses in infants with varying NI risks.
- Assess pain responses during the neonatal period (Session 1) and at 6 months of age (Session 2).
Main Methods:
- Prospective observational study of 149 infants across high, moderate, and mild NI risk cohorts.
- Pain responses (physiological and behavioral) recorded during heel lance (NICU) and immunization (6 months).
- Measured heart rate, oxygen saturation, facial actions, and cry characteristics.
Main Results:
- Overall, infants exhibited diminished facial activity and altered physiological responses (lower heart rate, higher oxygen saturation) at 6 months compared to the neonatal period.
- Infants at high NI risk showed significant changes in specific facial actions between sessions.
- Cry characteristics varied, with higher pitch in moderate NI risk infants during the neonatal period and longer cry duration in high NI risk infants.
Conclusions:
- Infant pain responses tend to be less intense at 6 months compared to the neonatal period.
- Specific differences in cry responses were observed among infants based on their neurological impairment risk levels.
- Further research is needed to understand the reasons behind these session and cohort-specific differences in pain responses.
Background:
Approximately 10% of infants admitted to a Neonatal Intensive Care Unit (NICU) are at risk for Neurological Impairment (NI). While we have limited knowledge on the influence of NI risk on pain responses, we have no knowledge of how these responses change over time.
Objective:
To compare physiological and behavioural pain responses of infants at three levels of NI risk during the NICU neonatal period (Session 1) and at 6 months of age (Session 2).
Design/Methods:
Prospective observational design with 149 preterm and term infants at high (Cohort A, n=54), moderate (Cohort B, n=45) and mild (Cohort C, n=50) risks for NI from 3 Canadian tertiary level NICUs. Infants were observed in the NICU during 3 standardized phases of a heel lance: baseline, stick and return-to-baseline. At 6 months, infants were observed during the same three phases during an intramuscular immunization injection. Physiological (heart rate, oxygen saturation) and behavioural (9 facial actions, cry) responses were continuously recorded.
Results:
A significant interaction of Phase by Session was found with less total facial activity observed during Session 2 (all p values<0.04). A significant interaction for Session by Cohort was found, showing that infants in Cohort A had significantly more change from baseline-to-stick phase for brow bulge, eye squeeze, nasolabial furrow and open lips between sessions with less facial actions demonstrated at Session 2 (all p<0.02). There were significantly lower mean and minimum heart rate (all p<0.02) and higher minimum and maximum oxygen saturation (p<0.04) at Session 2. Significantly higher mean and minimum fundamental cry frequencies (pitch) in Cohort B (p<0.04) were found in Session 1. Cohort A had significantly longer cry durations, but no significant differences in cry dysphonation.
Conclusions:
Behavioural and physiological infant pain responses were generally diminished at 6 months of age compared to those in the neonatal period with some differences between NI risk groups in cry responses. Future exploration into the explanation for these differences between sessions and cohorts is warranted.
