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The fetus may feel pain by 20 weeksDocument Transcript
http://www.thefreelibrary.com/The+fetus+may+feel+pain+from+20+weeks.-a0125831891PAIN IS A SUBJECTIVE Experience. The fetus cannot tell us what it is feeling, and there is no objectivemethod for the direct measurement of pain. To address the question of pain in the fetus, one must useindirect evidence from a variety of sources, and then make an informed guess. This approach is similarto that which we use with animals. We cannot ask animals how they feel, but infer from a variety ofindirect approaches including study of their behavior, anatomy and physiology.CONSCIOUSNESSTo feel pain or suffer discomfort, one needs to be conscious, to be aware. We do not know when, if atall, consciousness starts in the fetus. The biological basis of consciousness is little understood, althoughat least in adult humans, the evidence suggests that it is in some way associated with electrical activityin the cerebral cortex. Susan Greenfield has explained that one should not think of consciousness as anall-or-none phenomenon but rather that it may come on like a dimmer switch. This concept of evolvingconsciousness could apply to the developing fetus, in whom experience is most unlikely to be similar toan adults. Furthermore, the fetus may not have the same physical basis for conscious experience as theolder human.ANATOMYThe most important evidence for fetal pain is anatomical. For the fetus to feel pain, it is necessary forstimuli to travel around the body (nociception). This involves neural connections between peripheralreceptors and the spinal cord spinal cord, the part of the nervous system occupying the hollow interior(vertebral canal) of the series of vertebrae that form the spinal column, technically known as thevertebral column. , upward transmission via the spinal cord to the thalamus, and from there to the outercerebral layers. The development of the human nervous system is a progressive and ascending process,with the cerebral cortex the last region to develop.Connections from the periphery to the spinal cord are formed early, at about eight weeks; C fibers beginto grow into the spinal cord at about 10 weeks. The cerebral cortex starts to form at in weeks, althoughat that stage it is isolated from the rest of the brain. Cortical development starts only at about 17 weeksgestation, but continues until long after birth. From 15 weeks, the cortex is underlain by the subplatezone, a layer of neurones below the cortex that is specific to the fetus. Synapses appear within thecortical plate from mid-gestation. The subplate zone expands considerably between 17 and 20 weeks,while from about 17 weeks, there is a shifting population of connections from the thalamus to thisregion. Thalamic thalamic /tha·lam·ic/ (thah-lam´ik) pertaining to the thalamus. fibres penetrate thecortical plate from 24 to 28 weeks and at this stage the full anatomical pathways necessary fornociception are in place.Assuming that activity in the cerebral cortex or subplate zone is necessary for consciousness, then for
the fetus to be conscious of an external experience these regions need to be connected with incomingnervous activity. This starts to happen at about 16 weeks and puts an early limit on when it is likely thatthe fetus might be aware of anything that is going on in its body or elsewhere.The physiological evidence shows that responses in very preterm babies to visual and other stimuli (lighttouch, pain, pressure, temperature, and joint and muscle position sense) can be seen from as early as 24weeks, and are well developed by 27 weeks.BEHAVIOROne has to be cautious about interpreting behavioral responses in terms of conscious experience, forsome, at least, could be purely reflex. It is well known that animals whose cortexes have been removedfor experimental purposes show a wide range of behavioral responses to noxious stimuli.The fetus starts to make movements in response to being touched from eight weeks, and more complexmovements build up, as detected by real time ultrasound, over the next few weeks. It can respond tosound from 20 weeks and discriminate between different tones from 28 weeks.In preterm babies, who now can be kept alive from 23 weeks, one can observe behavioral responses tovarious clinical interventions. Such babies show a distinct pattern of behavior to painful stimuli, such asa heel prick. This includes a wide range of expressions including screwing up the eyes, opening themouth, as well as clenching clenching (klen´ching),n the nonfunctional, forceful intermittent application of the mandibular teeth against the maxillaryteeth. It can become habitual and cause damage to the periodontium. the hands and limb withdrawal,which an older baby would also show if in pain. Most nurses and mothers looking after preterm babiesare convinced that they are both sentient sentient /sen·ti·ent/ (sen´she-ent) able to feel; sensitive.sen·tientadj.1. Having sense perception; conscious.2. Experiencing sensation or feeling. and feel pain.DOES ONE NEED PREVIOUS EXPERIENCE TO FEEL PAIN?Some argue that the fetus cannot feel pain, because pain is a complex phenomenon affected byprevious experience or other simultaneous occurrences. It is well known, for example, that a soldierwounded in battle often feels nothing at the time. It is also possible to sensitize sen·si·tizev.
To make hypersensitive or reactive to an antigen, such as pollen, especially by repeated exposure. theexperience; people who are depressed often feel more pain than at other times. This complexity of theexperience of pain in adults is not controversial. However, while suffering in adults can be affected byactivity in other parts of the brain, this does not prove that in a naive being, such as the fetus, there canbe no experience of pain. The fact that the sensation of pain can be affected by previous experiencedoes not entail the conclusion that previous experience is necessary to feel pain. Such an argumentwould suggest that a newborn baby could not feel pain either. The view that to experience pain it isnecessary to have experienced pain previously is self defeating: it would mean that there could never bea first experience of pain.SELF CONSCIOUSNESSIt has also been suggested that consciousness implies self consciousness, and as the fetus is not selfconscious it cannot be conscious either. However, consciousness does not necessarily imply selfconsciousness in the adult sense. All that is needed for the fetus to feel pain is that it has a simpleawareness of what is going on in itself. It does not need the more complex understanding that it itself isdifferent from the outside world.STRESS RESPONSESRecent research has concentrated on the stress responses of the fetus to various interventions, just asneonatal research did in the previous decade. It is important to clarify the relevance of this work to adiscussion of pain. Stress responses, defined as an activation of specific hormonal and neurotransmittersystems, do not provide a direct index of pain. Although stress hormones are usually increased when asubject is experiencing pain, there are many other situations which are not painful, such as exercise,which also can increase their levels. Furthermore, production and release of stress hormones such ascortisol cortisol (kôr`tĭsôl) or hydrocortisone, steroid hormone that in humans is the major circulatinghormone of the cortex, or outer layer, of the adrenal gland. can be mediated by the hypothalamus,without involvement of the cortex or other higher brain regions involved in sentience sen·tiencen.1. The quality or state of being sentient; consciousness.2. Feeling as distinguished from perception or thought.Noun 1. .There is now evidence that the human fetus can mount substantial stress responses. These have beenshown both by examining stress hormone levels in the blood before and after invasive procedures andby examining the redistribution of blood flow within the fetus. Some of these responses have beenfound from as early as i6 weeks. What then is the use of measuring stress responses? In consideringstress responses in relation to the question of fetal pain, the "null hypothesis null hypothesis,
n theoretical assumption that a given therapy will have results not statistically different from anothertreatment.null hypothesis,n " is of relevance: if there were no change in stress hormone levels, it would be very unlikely that thefetus was experiencing pain. Stress responses can also be used to give some sort of index, thoughimperfect, of the degree of trauma involved and further determine the effect of analgesiaanalgesia /an·al·ge·sia/ (an?al-je´ze-ah)1. absence of sensibility to pain.2. the relief of pain without loss of consciousness. or anesthesia. It was the demonstration of stressresponses in the newborn during surgery that precipitated the change in attitude in the medical andnursing care of newborn infants. We must emphasize, however, with both the fetus and the newborn,that a stress response, in itself, does not tell us directly what the baby is feeling.CLINICAL IMPLICATIONSThe fetus is still often currently treated as though it feels nothing and is given no analgesia or anesthesiafor potentially painful interventions. This is similar to the way in which newborn babies used to betreated until research compared neonates undergoing cardiac surgery who received deep anesthesiawith those given a lighter regimen of halothane halothane /hal·o·thane/ (hal´o-than) an inhalationalanesthetic used for induction and maintenance of general anesthesia.hal·o·thanen. and morphine. The first-mentioned group had a much better postoperative outcome in terms ofinfection and mortality than the latter. Now such pain relief is routinely given to babies, not just foropen surgery but for more minor procedures. However it is possible that opiate drugs may have longterm adverse effects, and research is needed to determine their risk-benefit ratio for differentinterventions, both in the fetus and in the neonate neonate /neo·nate/ (ne´o-nat) newborn infant.ne·o·naten.A neonatal infant.
neonatea newborn animal. .TERMINATION OF PREGNANCYLate terminations may cause pain to the fetus if they involve an invasive procedure, such as surgicaldismemberment. Modification of the technique, such as preparatory occlusion of the umbilical cord,may be appropriate.CHILD BIRTHThe experience of the baby during birth is not usually considered. It is generally assumed that as birth isa natural phenomenon, undergone for thousands of years without pain relief, that it is painless for thebaby. This may not be the case.Failure to provide adequate analgesia for preterm neonates is now considered substandard andunethical practice. There have been similar calls for fetuses to be given analgesia during invasiveprocedures. The opioid agonists, such as fentanyl fentanyl /fen·ta·nyl/ (fen´tah-nil) an opioid analgesic;the citrate salt is used as an adjunct to anesthesia, in the induction and maintenance of anesthesia, incombination with droperidol (or similar agent) as a neuroleptanalgesic, and , are the drugs most widelyused for sedation and analgesia for newborns. We now have evidence that direct fentanyladministration to the fetus can blunt stress responses in utero in utero (in u´ter-o) [L.] within the uterus.in u·ter·oadj.In the uterus.in utero adv. also.Intravenous administration of fentanyl in the mother is unsatisfactory since the rate of transfer acrossthe placenta is slow. Larger doses may cause respiratory depression in the mother. However, not onlydo they cause sedation, they may also have adverse behavioral effects if delivery soon follows, impairingfetal responsiveness. General anesthesia Anesthesia, General DefinitionGeneral anesthesia is the induction of a state of unconsciousness with the absence of pain sensation
over the entire body, through the administration of anesthetic drugs. has significant risks in pregnancy.The potential benefits of analgesia in the fetus need to be balanced against the risk of additionalprocedures and the potential for adverse long term drag effects.CONCLUSIONThere clearly is not enough evidence to be certain if and when the fetus starts to feel pain. By 26 weeks,the full anatomical system for nociception has been formed, an EEG EEG: see electroencephalography. shows activity in the cerebral cortex and the preterm baby of the same gestational age ges·ta·tion·alagen.See estimated gestational age.Gestational ageThe estimated age of a fetus expressed in weeks, calculated from the first day of the last normalmenstrual period. , if delivered, shows a complex range of pain behavior pain behavior,n a joint test during which the patient indicates a particular point in which pain is initially experiencedand/or increases while the practitioner moves the joint through the range of motion. . Some haveconcluded that it is not possible for the fetus to be aware of events before 26 weeks gestation and notto feel pain until considerably later than that. This seems unduly certain, given the available evidence.Before 26 weeks, too little is known about the physical basis of consciousness in the fetus to be surethat it has no awareness. Given the anatomical evidence, it is possible that the fetus can feel pain from20 weeks and is caused distress by interventions from as early as 15 or 16 weeks. This sets limits as tothe earliest stage that analgesia might be considered.It is not possible to measure pain directly in the fetus. Studies of stress responses can be used to give anindex of the degree of trauma induced by different interventions and also the response to analgesia oranesthesia, but they do not indicate what the fetus actually experiences. The assessment of whether orwhen the fetus is likely to feel pain has to be based on an evaluation of the available anatomical andphysiological--evidence. The physical system for nociception is present and functional by 26 weeks and itseems likely that the fetus is capable of feeling pain from this stage. The first neurons to link the cortexwith the rest of the brain are in place from about 16 weeks gestation. Their activation could beassociated with unpleasant conscious experience, even if not pain. Thalamic fibers first penetrate thesubplate zone at about 17 weeks gestation and the cortex at 20 weeks. These issues are important, notonly because of immediate suffering, but also because of possible long term adverse effects of this earlyexperience. Research in these areas is urgently required.The 18th century philosopher, Jeremy Bentham, wrote of animals: "The question is not Can theyreason?, nor, Can they talk?, but Can they suffer?" This caused a change in attitude towards animalsand their treatment that is still continuing today, such that in the UK, even frogs and fishes are required
by Act of Parliament to be protected by anesthesia from possible suffering due to invasive procedures.Why not human beings?This article is based on: Vivette Glover and Nicholas M Fisk Fisk , James 1834-1872.American railroad financier and speculator who attempted in 1869 to corner the gold market with JayGould, leading to Black Friday, a day of nationwide financial panic. , "Fetal pain: implications for researchand practice," British Journal of Obstetrics and Gynaecology Obstetrics and Gynaecology (oftenabbreviated to OB/GYN or O&G) are the two surgical specialties dealing with the female reproductiveorgans, and as such are often combined to form a single medical speciality and postgraduate trainingprogram. , 1999, Vol. 106, No. 9, pp881-6.PROFESSOR VIVETTE GLOVER is director of the Fetal and Neonatal Stress Research Group at ImperialCollege, London.