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Evidence-Based Strategies for Common Clinical Questions

June 2019

“But I left the window cracked open!” The Dangers of Non-Moving Vehicles             

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Column Editor: Rupal Gupta, MD | Medical Director, Operation Breakthrough Clinic | General Academic Pediatrics | Assistant Professor, UMKC School of Medicine

Author:  James Odum, MD | Chief Resident, Children's Mercy Kansas City

Providing anticipatory guidance on car safety has been a foundational component to scripted discussions during well checks for decades. We spend time talking about car seat safety, the proper use of restraints as children grow and develop, and the importance of teaching adolescents the dangers of distracted driving. During summer months, many of us throw in a casual reminder to not leave a child unattended in a parked car. We know that a small child in a hot car is an unsafe combination, and it is painful to see reports on the local news where a child has suffered injury because this seemingly obvious rule-of-thumb escaped the consideration of their caregiver in that moment. Why do these events occur, and how can we provide guidance that will resonate more with parents during the many well visits they attend? 

Since 1998, between 30 to 60 children have died annually from pediatric vehicular hyperthermia (PVH) in the United States.1 Seventy-three percent of PVH fatalities between 1995 and 2002 were attributed to the child being left in the car. The other 27% of cases involved children who were playing outside and later were found locked inside the family’s car, or in an abandoned car in the neighborhood—78% of such victims were boys and almost half were between the ages of 2 and 3 years of age.2 The issue goes beyond parents’ own diligence in taking children out of parked cars. Parents also need to know they should not leave a car unlocked—even on their own property, and they should teach children never to enter a car without a trusted adult.  

What do we know about children who passed away from PVH after being left in the vehicle? In a quarter of these cases, the caregiver chose to leave the child in the car, but about half of cases involved children who were accidentally forgotten.2 The most common theme in review of these cases was the distraction due to change in a caregiver’s normal routine. Some cases involved a parent who meant to take a child to daycare, but drove to work based on their normal routine and forgot that a child was in the backseat. Another common example in these cases involved additional pressures surrounding the chaos of large family gatherings near holidays, especially the Fourth of July. This is particularly of value in our communities because the South (36%) and Midwest (33%) are the two regions most affected by PVH fatalities in the United States. 

While anecdotal examples share valuable stories to families, providers can also teach the thermodynamic concepts behind children overheating in cars. Consider the following questions:   

1) How high can a temperature reach inside a dark sedan if the outside ambient temperature is 98.2oF?
2) What if the windows in that car are left down by approximately 8 inches (halfway down)? 

Under outdoor temperatures of 98.2oF, internal car temperatures range from 124-153oF. The second question addresses the common misconception that lowering windows to allow for air movement negates much of the risk for PVH. If that car’s windows had been left down halfway, the car would still reach 104oF. If the window is left only 25% down in order to prevent a young child from climbing out, the temperature inside the car reaches approximately 120oF. Thus, lowering windows can decrease the temperature relative to the maximum inside the car, but these internal temperatures are still far too high for a young child to tolerate.3  

It may surprise a caregiver to learn that the internal temperature of a parked vehicle can be so much higher than the outside temperature. While the car is parked, direct solar radiation causes a greenhouse phenomenon where longwave radiation becomes trapped inside the vehicle. This causes a continued rise in internal temperatures.4 Even for an outside temperature of 72oF, the internal temperature of a vehicle can reach 117oF within an hour. Eighty percent of this temperature increase occurs in the first 30 minutes of the car being parked.5 All seasons, not just summer, can pose risk to children for PVH.  

Children are especially susceptible to PVH because, as compared to adults, they have a higher surface area to mass ratio, which increases their exposure to external heat sources relative to their weight. They are also less efficient at evaporative cooling through sweat production, and thus have a propensity for a quicker rise in core temperature.4 Young children are also less developmentally capable at performing the behavioral adaptations needed to counteract increasing core temperatures, such as independently finding water or moving to a cooler location.6 Because caregivers cannot control all these factors, they should take preventative measures to avoid excessive heat exposure in young children, including not overdressing young children, and ensuring adequate hydration for them during hot, humid periods.  

We are all aware that cars are dangerous, primarily in the form of high-speed collisions. We are also aware that exposure to sources of elevated temperatures can cause permanent disability or death in the common forms of scalding bath water or summer heat exposure in young athletes. By raising awareness of the risks of excessive heat exposure in parked cars, we can help dispel the notion that neglectful parents are the sole contributors to pediatric deaths secondary to PVH. Whether it is the well-intentioned parent who parks an unlocked car in the driveway while simultaneously encouraging their children to be outside and active, or the caregivers who are distracted by the many conflicting priorities on a daily basis, all should be aware that their children are not immune from the potential of experiencing PVH at times when they are unsupervised or forgotten.

References 

1. Heatstroke Deaths of Children in Vehicles. Null J. http://noheatstroke.org. Updated 20 April 2019. Accessed 9 May 2019. 

2. Heat-Related Deaths to Young Children in Parked Cars: An Analysis of 171 Fatalities in the United States, 1995-2002. Guard A, Gallagher SS. Injury Prevention 2005; 11:33-37. 

3. Heat Stress in Motor Vehicles: A Problem in Infancy. King K, Negus K, Vance JC. Pediatrics 1981; 68:579-582. 

4. Evaluating the Impact of Solar Radiation on Pediatric Heat Balance within Enclosed, Hot Vehicles. Vanos JK, Middel A, Poletti MN, Selover NJ. Temperature 2018; 5(3):276-292.   

5. Heat Stress From Enclosed Vehicles: Moderate Ambient Temperatures Cause Significant Temperature Rise in Enclosed Vehicles. McLaren C, Null J, Quinn J. Pediatrics 2005; 116:e109-112.  

6. Heat-Related Illness in Children in an Era of Extreme Temperatures. Mangus CW, Canares TL. Peds in Review 2019; 40(3):97-107.