Sensory Case Study 4*

Lost in the Desert

July 13th, AM


Mark, a white, 35-year-old male weighing approximately 70 kilogram (kg) started a three-hour drive across the desert on US 95 from Yuma, Arizona, to Blythe, California. He set out at 7 AM on what was expected to be a very hot July day. He anticipated that it would take him about three hours to reach Blythe—plenty of time to make his 11 AM appointment with Sarah, his fiancée. When he failed to appear by noon, Sarah became concerned and called the highway patrol.


By 12:30 PM, Search and Rescue Officer Maria Arroyo, who was patrolling nearby, reported finding an abandoned car on the side of the road with a damaged radiator that matched Sarah’s description of Mark’s vehicle.  By 1 PM Henry Morningstar, paramedic and a member of the helicopter crew, reported a shirtless, hatless man wandering down a desert wash. The local air temperature was hovering at 105° F in the shade (and there was darned little of that). The relative humidity was less than 5%. The helicopter crewmembers spotted a man staggering on the desert. Mark was still conscious but clearly delirious. Henry also noted that Mark was weak, nauseous, disoriented, and complained of a headache. His blood pressure was quite low—70/50—and he was not sweating despite the oppressive heat. His body temperature was also high—105°. The patient was diagnosed as having heat stroke. The paramedic also noted first degree burns on his face and back.


July 13th, PM


Henry started oral rehydration with an isotonic solution containing electrolytes, glucose, and water.  As Mark recovered in the hospital, he related what happened to him earlier in the day. Since he was a newcomer to desert areas, he saw no need to bring UV A/B sunblock or extra water on his trip from Yuma to Blythe. He waited by the car for a while but then, about 10 AM, as the sun climbed, he saw a large body of water in the distance, possibly, he thought, the Colorado River. The “river” was, in reality, a mirage, as he realized later after he had walked some distance. He then started to become confused and could not find his way back to the highway. Eventually he became very hot and threw away his shirt and hat.


Subsequent Months


After he left the hospital, Mark saw extensive new melanin formation in his skin. Much later Mark noticed some new moles on his shoulders. The moles grew, changed color, and bled.




1.            Given the conditions, what should Henry do to try to save Mark? He must decide very quickly. Mark has very little time left and may not survive the trip by helicopter to the hospital. Gather into your groups and use your textbooks as resources to gather for information about what Henry should do. What has caused Mark’s weakness, nausea, disorientation, headache, and low blood pressure? Why isn’t he sweating?

2.            Why didn’t the paramedic give Mark distilled water rather than an electrolyte/glucose solution?

3.            Why did Mark become disoriented? How would you test your ideas to see if you are right? What does your group think based on the information in the text?

4.            What did Mark do that increased his chance of burns?

5.            What should Mark be concerned with regarding these moles? He talked to dermatologist Dr. Charles Culp about the moles. What tests might Dr. Culp conduct after removing the moles?

6.             Why would Mark’s skin have looked red within the first few hours of his adventure rather than redness developing hours and days later as a result of “sunburn”?

7.            What is (are) the function(s) of the skin?


*adapted from a case study by

David Evans

Natural Sciences, Penn College/PSU



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