The xenos are literally Napoleon, masters of maneuver warfare, flanks and divide and conquer tactics. Sometimes, the only way to win the war is to lose the battle (in style).
Jean is completely right, (of course, being swiss he has an innate advantage fighting the french) the #1 killer of medics is tunnel visioning on your patients and ignoring the rapidly crumbling situation in front of you. Learning to rollerbed the closest guy and running away is the best skill you can learn as a medic.