Pain in the Neonate: The Effects of Anesthesia

Over the past 20 years, advances in patient monitoring and anesthetic techniques coupled with a better understanding of the pathophysiology underlying neonatal disease states have made a great impact on the practice of neonatal anesthesia. Nevertheless, whether anesthesia is necessary in neonates and what constitutes adequate anesthesia for neonates are still major concerns among parents, health care professionals, and the public. For the anesthesiologist, the issue of adequate anesthesia is paramount to providing quality medical care. Yet Lippmann et al. (1976) wrote that in surgery for patent ductus arteriosus (PDA), "anesthetic or analgesic agents in our experience are unnecessary," and in a recent article Gauntlett (1987) stated that only 85 percent of anesthetists responding to a survey believed that newborns perceived pain. For some anesthesiologists the rationale of withholding anesthesia is still based on the notion that infants requiring surgery are too ill to withstand the significant cardiovascular and respiratory depressant effects of anesthesia. For others, the knowledge that neonatal cortical connections and nerve myelination are incomplete, coupled with the neonate's primitive reflex (decorticate posturing) in response to pain, allow them to rationalize that operative procedures in neonates can be performed without the benefit of anesthesia. The issue of pain management, however, is not limited to the operating room. In a survey of intensive care nurses, 59 percent of the responders believed that newborns did not perceive pain in a manner similar to adults, but 77 percent believed that pain medications were underutilized (Franke et al., 1986). Thus, it appears that pain management for newborns is frequently not undertaken or is inadequately administered. experience associated with actual or potential tissue damage or described in terms of such damage," then pain becomes a subjective phenomenon, and its occurrence in newborns may be impossible to determine. Anatomic, physiologic, and neuroendocrine data compiled over recent years, however, suggest that neonates do indeed perceive pain (nociception). Nociceptive pathways and anatomic substrates for pain transmission appear to be present in neonates, and with growth and development during infancy and childhood there are further refinements of the sensory modalities and intracortical connections. Anand et al. have recently reviewed this information, and consequently it will not be further discussed (Anand and Hickey, 1987; Anand et al., 1989). A schematic view of the developmental changes occurring in the central nervous system as they relate to pain perception is presented in Figure 1. For health care providers involved in the care of sick newborns, the neonate's perception of nociception appears intuitively obvious. Invasive procedures such as heel lancing (Harpin and Rutter, 1983; Owens and Toot, 1984), circumcision (Williamson and Williamson, 1983), and intramuscular injections evoke such characteristic behavioral (facial grimacing, crying) (Porter et al., 1986; Grunau and Craig, 1987) and sympathetic responses (tachycardia, hypertension, palmar sweating) (Raju et al., 1980; Harpin and Rutter, 1982; Kelly and Finer, 1984; Marshall et al., 1984), that it is difficult to believe that the neonate is not feeling pain. Because it appears intuitively obvious that nociception is a real phenomenon in the neonate, the remainder of this paper will deal with two physiologic manifestations of nociception: the cardiovascular response and the neuroendocrine response. The modulating effects that anesthetics have on these two physiologic responses will also be addressed.