When a person has heat stroke, it's a good idea to put a cold bottle of water under your armpit as a temporary measure until you get to the hospital.
ーWhen a person has heat stroke, it's a good idea to put a cold bottle of water under your armpit as a temporary measure until you get to the hospital.
「熱中症になったら、病院に着くまで応急処置として脇の下に冷たいボトルの水を当てるといいよ」
to have heat stroke で「熱中症になる」
to put a cold bottle of water under one's armpit で「脇の下に冷たい水のボトルをあてる」
temporary measure で「応急処置」
to get to the hospital で「病院に着く」
ご参考まで！
カナダ 
