Suero literally means "serum" or refers to the fluid in a medical IV drip. It's a perfect example of the song's central metaphor: comparing heartbreak to a medical emergency.
In the lyrics, Daddy Yankee pleads, “Un suero de cariño es lo que me toca” (An IV drip of affection is what I need). He uses this dramatic, medical imagery to express how desperately he needs his partner's love, as if it were the only medicine that could save his life.
Daddy Yankee takes the idea of being 'lovesick' to a whole new level in 'Llamado De Emergencia'! This isn't just a sad song about a breakup; it's a full-blown medical drama. He makes an emergency call for his ex to come back because he is literally dying without her. He tells her, 'Ven y sana mi dolor / Tienes la cura de este amor' (Come and heal my pain / You have the cure for this love). He says no doctors or aspirin can help him, because she has the 'formula secreta' (secret formula) to fix his heart.
The medical details get more and more intense. He says he can barely feel his heartbeat, 'Casi no siento mis pálpitos', and needs a paramedic to give him an 'electroshock' of her warmth. He even asks for 'respiración boca a boca' (mouth-to-mouth resuscitation) and suggests the stretcher can be their bed! It's a desperate and dramatic plea, describing a world where without her, 'las espinas son las que florecen' (it's the thorns that blossom). He needs her to come back fast, because his 'signos vitales van disminuyendo' (vital signs are diminishing).