[Analgesia with opioids in the paediatric patient.]

Opioids have been used for analgesia in nearly all civilizations. In paediatrics their use has become widely accepted for combating severe pain, especially postoperative pain and tumour pain. Receptors in the central nervous system are the best known sites of action of opioids, but the existence of peripheral receptors is also probable. The action depends on whether the opioid is more agonist or antagonist and on the peculiarities of physiology in childhood: in the small child a hyperdynamic blood circulation makes resorption faster, and in newborn and premature infants distribution and excretion are influenced by the different composition of the body and the immaturity of liver and kidney. The best known opioid is morphine, and it is the reference substance with which all other opioids are compared. Fentanyl has been used even for the smallest ventilated prematures in recent times, as it is easy to manage and has an early onset of action. Its depressant action on the respiratory centre is an advantage when attempts of spontaneous breathing make mechanical ventilation difficult. Obstinate constipation is the disadvantage of both morphine and fentanyl, and an exacerbation of hyperbilirubinaemia has been seen with fentanyl. Nalbuphine causes a lower degree of respiratory depression. The newer opioids alfentanil and sufentanil have already been used for the relief of paediatric postoperative pain and during mechanical ventilation, but no special advantages of their use are reported. Meperidine has been favoured especially for postoperative pain, although it appears to have no advantages over morphine. Its active metabolite normeperidine may accumulate and cause seizures; meperidine should not be used in prematures or in children with renal dysfunction. There are few publications on the use of piritramide in paediatric pain. Tramadol is widely used for emergencies, as it has the least sedative action; but it has disadvantages in causing nausea and vomiting. Codeine is widely used for its antitussive action. While the necessity of good analgesia for even the smallest infant cannot be overstated, the opioid used must be carefully selected with reference to the age of the child and the pain to be controlled.