Editorials

Why do babies cry?

We still know too little about what will ease babies' pain

Paper p   1393

Parents know that babies cry because they are either in pain or distressed. They also know that babies cry to attract their attention so that they can comfort them. Pain is a subjective experience so one cannot prove that a newborn baby is in pain. One can, however, confirm that the baby is exhibiting signs of distress, probably caused by a painful procedure (such as venepuncture). Parents know that a crying baby needs comforting and will hold the infant close. Breast feeding mothers will give their infants the opportunity to breast feed, even if they are not hungry.

The study by Carbajal et al in this week's issue confirms that these actions of mothers are appropriate (p 1393).¹ This is important not because parents are likely to change their behaviour but because it will encourage health professionals to modify their behaviour when caring for newborn infants. Observational studies have shown that many procedures carried out on newborn infants in hospital are likely to result in pain.² More invasive procedures, including surgical interventions, are likely to result in significant pain and distress. The use of interventions, be they pacifiers, sucrose solutions, cuddling, or analgesia, needs to be evidence based. This requires well designed clinical trials using validated pain assessment tools.

The classic observational analysis of an infant in pain was reported by Charles Darwin in 1872. His description of an infant in pain forms the basis of many of today's pain assessment scales: "Infants, when suffering even slight pain or discomfort, utter violent and prolonged screams ... their eyes are firmly closed, so that the skin round them is wrinkled, and the forehead contracted into a frown. The mouth is widely opened with the lips retracted in a peculiar manner, which causes it to assume a squarish form."³ It has taken health professionals 100 years to develop these observations of facial expression and crying, alongside observations of sleep-arousal state and tone-posture-motor activity, into objective pain assessment tools and distress scales for the newborn infant. Such a validated scale was used by Carbajal et al to determine that non-nutritive sucking on a pacifer provided a better analgesic effect during venepuncture than the use of solutions of glucose or sucrose.

Most neonatal pain assessment tools have been developed for use in full term infants.⁴ Few have been developed for premature infants, who may show different responses.⁵ Yet it is preterm infants who are most likely to experience the greatest number of invasive procedures. Also the pharmacokinetics and pharmacodynamics of analgesic agents in premature infants are often different from those in full term infants. ^{6 7}

Clinical trials are needed to determine which interventions are appropriate after different procedures. Randomised controlled trials have shown the value of both topical and local anaesthesia in infants undergoing circumcision. ^{8 9} Similarly, venepuncture has been shown to be more effective and less painful than the use of a lancet (for heel pricks) in newborn infants. ^{10 11} Health professionals involved in the care of the newborn infant have the responsibility to try to ensure changes in clinical practice on the basis of published clinical trials. We cannot avoid all painful procedures in the newborn but we can minimise the pain and distress after such procedures.

Unfortunately there have been few studies on the dose response to analgesic agents such as morphine and paracetamol in relation to postoperative pain in newborn infants (either full term or preterm). There will always be interindividual variation among babies to a standardised painful procedure. We still, however, do not know what dose of morphine will provide sufficient analgesia after major surgery in most newborn infants. The challenge in the next decade is to answer questions like this, alongside the dose and place of mild analgesic agents such as paracetamol and the value of pacifiers in the newborn infant.

Imti Choonara, professor in child health. 

University of Nottingham, Derbyshire Children's Hospital, Derby DE22 3NE

Acknowledgments

IC has research grants from Astra and Chiroscience in the management of pain in children.