Slide the plastic over the animal's head. Slip a rope noose over the muzzle, pull it closed, and secure it with the plastic underneath. Do the same with another noose at the back of the head. With its eyes covered the animal will calm down considerably. Make sure that the plastic does not obstruct the nostrils.
Monitoring is difficult.
Breathing can be monitored by holding a hand over a nostril. The sensitivity of the ears provides a relative indication of the depth of immobilization. It is not possible to find a vein reliably and easily in a hippopotamus. The tail vein is the only possibility for collecting blood, but it is normally difficult or even impossible to lift the tail. Antidotes and emergency drugs should be administered IM in the perineal area close to the vagina or anus.