Our patient has the flu and reports 5 to 6 loose stools a day. he has experienced an isotonic fluid volume loss. what does "isotonic fluid loss" mean? your patient has the flu and reports 5 to 6 loose stools a day. he has experienced an isotonic fluid volume loss. what does "isotonic fluid loss" mean? water and electrolytes are lost in equal proportions. more water is lost than enters the body. less water is lost than enters the body. no water is lost: the body water content remains the same. water is lost at the same rate as it enters the body.