How to assess sun and heat tolerance in vulnerable populations, including older adults, young children, and individuals with cardiovascular disease, kidney disease, or taking medications such as diuretics, beta-blockers, and certain antidepressants, during a physical exam?

Assessing Sun and Heat Tolerance During Physical Examination

Assessment of sun and heat tolerance during physical examination should focus on identifying specific risk factors that impair thermoregulation rather than performing standardized heat tolerance testing, as most individuals have adequate thermoregulatory capacity when modifiable risk factors are controlled.

History-Based Risk Stratification

Medication Review

• Systematically review medications that impair thermoregulation or hydration status, including beta-blockers, phenothiazines (which adversely impact thermoregulation), and diuretics (which increase dehydration potential and reduce volume-dependent cardiac output) 1
• Identify anticholinergic drugs, dopamine-reuptake inhibitors for ADHD, and certain antidepressants that affect hydration or thermoregulation 1

Chronic Medical Conditions

• Document conditions that decrease exercise-heat tolerance: diabetes insipidus, type 2 diabetes mellitus, obesity (BMI ≥85th percentile), juvenile hyperthyroidism (Graves disease), cystic fibrosis, cardiovascular disease, and kidney disease 1
• Any chronic condition adversely affecting water-electrolyte balance or thermoregulation warrants heightened concern 1
• Consider sickle cell trait as a contributing risk factor for vascular dysfunction and exertional collapse during heat stress 1

Recent Illness Assessment

• Current or recent illness significantly increases heat-illness risk, particularly illnesses involving gastrointestinal distress (vomiting, diarrhea) or fever, due to negative residual effects on hydration status and temperature regulation 1

Acclimatization and Fitness Status

• Assess heat acclimatization status, as lack of acclimatization is a major modifiable risk factor 1
• Evaluate baseline fitness level and recent physical activity patterns 1
• Document sleep/rest patterns, as inadequate rest increases heat-illness risk 1

Physical Examination Components

Hydration Status Assessment

• Evaluate current hydration status through clinical signs: assess mucous membranes, skin turgor, and orthostatic vital signs 1
• Recognize that dehydration further reduces volume-dependent cardiac output, particularly critical in elderly patients 1

Body Composition

• Document obesity or overweight status (BMI ≥85th percentile for age in children), as this significantly decreases exercise-heat tolerance 1

Cardiovascular Assessment

• Evaluate baseline cardiovascular function, particularly in elderly patients and those with known cardiovascular disease, as these populations have reduced thermoregulatory capacity 1

Age-Specific Considerations

Children and Adolescents

• Recent evidence indicates that healthy, well-hydrated children aged 9-12 years have similar thermoregulatory capacity as adults when exposed to equal relative intensity exercise and environmental conditions 1
• Focus assessment on modifiable risk factors rather than assuming inherent heat intolerance 1

Older Adults

• Thermoregulatory capacity is significantly reduced in elderly populations due to medications, reduced physiological adaptability, and comorbidities 1, 2, 3
• Assess for polypharmacy and multiple chronic conditions that compound heat-illness risk 3

Documentation of Risk Factor Burden

Create a cumulative risk profile by documenting:

• Number of concurrent risk factors present 1
• Environmental conditions anticipated (temperature, humidity) 1
• Planned activity intensity and duration 1
• Access to fluids and shade during activities 1

When Formal Heat Tolerance Testing May Be Indicated

• Consider formal heat tolerance testing 8-12 weeks after a previous heat stroke episode to detect possible residual injury in thermoregulatory capacity 4
• The heat tolerance test (120 minutes exposure to 40°C and 40% relative humidity while walking at 5 km/h) can differentiate between temporary and permanent heat susceptibility 5
• However, for routine clinical practice, history-based risk stratification is more practical and sufficient than formal testing 1

Critical Clinical Pitfalls

• Do not assume children have inherently poor heat tolerance—recent evidence refutes this when children are adequately hydrated and acclimatized 1
• Recognize that multiple risk factors compound exponentially; even moderate environmental conditions become dangerous with multiple risk factors present 1
• Never underestimate the impact of medications on thermoregulation, particularly in elderly patients on beta-blockers, diuretics, or phenothiazines 1
• Previous heat stroke does not necessarily indicate permanent heat intolerance if prompt cooling was provided 1