#109: Cold Chill-dren! What to do with the Hypothermic Infant

May 8, 2024 | By Sam Masur

Audio

Summary:

All is not frost, we’re back to talk through the Hypothermic Infant with Dr. Sriram Ramgopal (Pediatric Emergency Medicine, Lurie Children’s Hospital). How do we know if the baby is septic or is just two blankets short of euthermia? Dr. Ramgopal walks us through the latest research, a differential diagnosis, who needs an infectious workup,  and how much more we have to learn!

Hypothermic Infant Pearls

1. Although 36.0C and 36.5C are different cutoffs for hypothermia used around the world, 36.0C seems to be the consensus definition for most doctors in the USA
2. The premature baby with difficulty feeding is the most common infant to present hypothermic, and this baby will do great. However, if these infants have an infection, they are at the highest risk for poor outcomes, and so they all get worked up for infection
3. If the baby is hypothermic at the pediatrician’s office and the emergency room, that’s considered sustained hypothermia and should be worked up
4. Infants older than 7 days are more likely to be sick if they present with hypothermia
5. There are no inflammatory markers that rule out sepsis in the hypothermic infant
6. HSV testing should be done for patients less than 14 days old

Hypothermic Infant Notes 

Definition

Hypothermia in infancy does not carry a strict definition. The WHO defines hypothermia in neonates as less than 36.5C. However, the Goldstein Criteria for SIRS (Systemic Inflammatory Response Syndrome) [Goldstein, 2005] uses less than 36.0C. Therefore, 36.0C and 36.5C are the most commonly used definitions, but Dr. Ramgopal recommends using 36.0C, which seems to be the consensus amongst surveyed physicians (Ramgopal, 2023).

Differential Diagnosis

Sepsis

Invasive bacterial infection (bacterial meningitis or bacteremia), serious bacterial infection (IBI criteria + UTI), or viral infection such as HSV can all lead to hypothermia. It is not clear why the inflammatory cascade causes hypothermia instead of fever. Although less common, mortality is higher in those infants with SBI who present with hypothermia compared to fever. 

Environmental

Small infants have a difficult time adapting to colder environments. The smaller the baby, the less fat they carry, and so they have a harder time maintaining homeostasis.

Hyperbilirubinemia

Hyperbilirubinemia is also associated with hypothermia. There are theories that hypothermia is a neuroprotective mechanism.

Disturbance of Temperature Regulation/Prematurity

Most common result of most workups for hypothermia. No one really knows why, but infants have a difficult time regulating their temperature at such a young age. This is most common in premature infants.

Less Common:

• Congenital pyloric stenosis: babies who lose nutrition lose even more fat, and then are unable to regulate their temperature
• Congenital cardiac disease: similar physiology with inability to maintain fat and nutrition
• Remainder can be found from Graves et al in Pediatrics, 2022  

Workup

Which babies need testing?

Currently there are no algorithms based on reliable data, unlike the febrile infant. Many pieces of the history and physical have not shown to be reliable in large predictive models of hypothermic infants. This is the topic of lots of upcoming research! Clinical gestalt is also quite challenging to use in these cases because all hypothermic infants will be slightly clamped down, bradycardic, and cool with decreased feeding. While awaiting further research, Dr. Ramgopal recommends working up the following infants:

• Infants greater than 1 week old. The older the infant (chronologically), the higher risk of serious bacterial infection
• Poor perfusion, bradycardia, and decreased feeding/lethargy are all red flags for infection, especially in the febrile infant. Although they haven’t been shown to be statistically significant in the large prediction models for hypothermic infants, working these patients up makes us sleep better at night.
• Apneic spells or difficulty breathing
• Repeated temperature instability. I.e. no improvement despite bundling, thereby requiring the warmer. If the patient was seen at the pediatrician’s office, referred into the ED and is still hypothermic, this counts as persistent hypothermia!
• Always, if you think the baby is sick, send the workup!

As for who NOT to workup, Dr. Ramgopal recommends avoiding testing on:

• Infant with temp 36.0-36.5C, whose recheck temperature is normal again 30 minutes later
• Infant who was referred in for hypothermia, but not hypothermic when you receive them. If they can feed and maintain temps for 2-3 hours, does not need further workup

The truth is the premature baby with difficulty feeding is the most common infant to present hypothermic. This infant will also do excellent with warmth, calories, and support. However, if these infants have an infection, they are at the highest risk for poor outcomes. Therefore, without enough data to exclude infection, most of these infants undergo the workup below.

Tests to Order

Dr. Ramgopal recommends ordering a sepsis workup for the initial testing using the febrile infant guidelines. He also recommends ordering blood sugar, especially since many of these babies are not feeding well, and bilirubin since hyperbilirubinemia is associated with hypothermia.

Check out episode 33 on the Febrile Infant for a reminder of the sepsis workup! This workup includes blood culture, urinalysis, urine culture, CBC, and procalcitonin.  However, we do not have any data for hypothermic infants (yet!) to suggest negative inflammatory markers rule out serious or invasive bacterial infection. 

HSV testing: Dr. Ramgopal recommends ordering HSV testing in infants < 2 weeks old. This includes blood PCR, spinal fluid, and surface swabs.

As for the lumbar puncture, there are also no clear consensus guidelines. However, it should be done on ill appearing infants and those undergoing HSV testing, which likely includes the majority of the patients getting worked up.

Empiric Treatment

If you send the blood culture, urine culture, and/or LP, Dr. Ramgopal recommends ordering empiric antimicrobials. Please check out the febrile infant guidelines for appropriate empiric antimicrobials per age (AAP 2021).

Prevalence and Disparities

Hypothermia infants occur approximately 10-25% as frequently as fever, and more common in premature babies. There has yet to be research into disparities associated with hypothermic infants. However, Dr. Ramgopal acknowledges that hypothermia is more prevalent in premature infants, which we know carries significant health disparities.

Links

• Check out upcoming research, including on Hypothermic Infants through the Pediatric Emergency Medicine Collaborative Research Committee (PEM CRC) 
• Apply for research grants at The Gerber Foundation

Goal

Listeners will explain the differential diagnosis, workup, and management for infants with hypothermia to improve both outpatient and inpatient care. 

Learning Objectives

After listening to this episode listeners will…  

1. Recall the definition of neonatal hypothermia. 
2. Be familiar with the differential diagnosis for hypothermia in infants.
3. Recognize the risk of infection in hypothermic infants. 
4. Describe the workup for the hypothermic infant.
5. Learn about which hypothermic infants to send a lab based workup on.

Disclosures

Dr Ramgopal  reports no relevant financial disclosures. The Cribsiders report no relevant financial disclosures. 

Citation

Masur S, Ramgopal S, Kelly J, Chiu C, Berk J. “#109: Cold Chill-dren! What to do with the Hypothermic Infant”. The Cribsiders Pediatric Podcast. https:/www.thecribsiders.com/ May 8, 2024.