Formal assessment of the newborn baby is important: to allow documentation of the neonate’s general state of wellbeing; as a prognostic exercise, to identify neonates at risk and focus medical attention on them; possibly as a means of following progress over time; and as a research tool for determining the effects of various interventions or conditions on neonatal outcome (e.g. drug therapy, anaesthetic techniques, epidemiological factors). Various methods have been described; as far as obstetric anaesthesia is concerned, the important ones are those that focus on the neonate’s gross physiological status at or shortly after birth, and those that assess its neurobehaviour.
Problems and special considerations
The easier the system for assessment (and therefore the more attractive it is to busy clinicians), the less its ability to discern subtle differences, and thus the less useful it is as a tool, especially when the effects being studied are likely to be small (e.g. a possible difference in the effects of two similar drugs in labour). Conversely, tiny differences revealed by very sensitive measurements may be of uncertain significance clinically. In addition, factors that might ordinarily be prognostic may be susceptible to the actions of anaesthetic agents - for example, ketamine may be associated with falsely high scores when using systems that rely heavily on muscle tone.
Methods of assessment
Measures of overall physiological status
• Time to sustained respiration (TSR). The time between delivery and sustained spontaneous ventilation is a very crude indicator of neonatal wellbeing, but it does indicate babies that need special attention and attempts to quantify the degree of impairment. It does not distinguish between babies who are slow to breathe unsupported for different reasons (e.g. drugs, congenital defects), and is best suited to birth asphyxia. It is rarely performed routinely.
• Apgar score. Described by the American anaesthesiologist Virginia Apgar in 1953, the system comprises five variables, each scoring 0-2 (Table 158.1). The Apgar score is now a standard tool and is recorded routinely after virtually all deliveries. It is usually performed at 1 and 5 minutes after birth, although it may be repeated thereafter. A modified system, ‘Apgar minus colour’ (maximum of 8), has been suggested but is rarely used.
• Umbilical cord blood gas analysis at delivery is a reflection of the metabolic status of the fetus and the adequacy of fetal oxygenation in the immediate peripartum period.
Table 158.1 Apgar scoring system
|
0 |
1 |
2 |
|
|
Heart rate |
Absent |
< 100 |
> 100 |
|
Respiratory effort |
Nil |
Weak cry |
Strong cry |
|
Muscle tone |
Limp |
Poor tone |
Good tone |
|
Reflex irritability |
Nil |
Some movement |
Strong withdrawal |
|
Colour |
Blue/pale |
Pink body/blue extremities |
Pink |
The Royal College of Obstetricians and Gynaecologists (RCOG) recommends the measurement of cord blood gases in all neonates delivered by caesarean section or by instrumental delivery for fetal distress, or where there have been concerns over fetal wellbeing during labour.
Tests of neurobehavioural status
The following tests are sometimes referred to eponymously:
• Neurobehavioural assessment score (NBAS). Developed in 1973 by the American paediatrician Brazelton, the NBAS is the most commonly used of the detailed neurobehavioural assessment systems. It takes 45-60 minutes and requires trained staff to perform it.
• Early neonatal neurobehavioural scale (ENNS). Developed in 1974 by the American anaesthetist Scanlon, the ENNS is less complicated than the NBAS and therefore quicker to perform (about 5-10 minutes). It examines wakefulness, tone and the response to various stimuli, including the presence or absence of neonatal reflexes.
• Neurological and adaptive capacity score (NACS). Developed in 1982 by the paediatrician Amiel-Tison and anaesthetic colleagues in San Francisco, the NACS takes about 5 minutes to perform and is a relatively crude measure, mainly examining neonatal tone. It has been claimed that the NACS can distinguish between the effects of asphyxia and those of drugs, although this has been challenged. It has, however, been widely used in obstetric anaesthetic studies because of its ease of use.
Effects of anaesthetic drugs
In general, the more gross an effect, the easier it is to show it; thus, for example, maternal pethidine can readily be demonstrated to suppress neonatal condition at birth and affect neurobehaviour and feeding for 1-2 days postpartum, by using relatively crude scoring systems. However, more subtle tools such as the NBAS are required to investigate smaller effects, and their significance may be disputed. Finally, the difficulty in conducting randomised studies, and the inadequate size of most studies that have looked at measures of neonatal assessment in depth, mean that no clear conclusions can be drawn in many cases. However, the overall effects of maternal anaesthetic and analgesic drugs on the neonate can be summarised:
• Systemic drugs. Impairment is seen depending on the dosage and the test used: the more sensitive the assessment system, the greater the effect. Thus effects on alertness and responsiveness may be detected by using the NBAS and ENNS before respiratory depression is seen. Some effects of pethidine are apparent 24-48 hours postpartum, and subtle differences, for example in feeding, may persist for up to 6 weeks.
• Regional anaesthesia. Lidocaine was suspected of impairing the ENNS in the 1970s (the ‘alert but floppy baby’) but this was not substantiated subsequently. There is no hard evidence of impairment after regional anaesthesia or analgesia for labour or caesarean section with various local anaesthetics or opioids. Although some studies have claimed to find differences, the difficulty of using adequate controls and conflicting results from other studies make these uncertain.
Hypotension lasting less than 2-3 minutes has not been associated with demonstrable effects, although Apgar score, acid-base profiles and crude neurobehavioural scores have been found to be affected if hypotension is prolonged. The place of regional anaesthesia when the fetus is compromised is still debated by anaesthetists and others, most anaesthetists supporting its use.
• General anaesthesia. The effects of general anaesthesia have been greater than those of regional anaesthetic techniques in most studies. Low concentrations of volatile agents are thought to have little effect.
Key points
• The more complex the method used to assess the neonate’s state, the more subtle the changes found.
• Anaesthetic and analgesic drugs have all been implicated in affecting neurobehaviour to some degree; this is generally agreed for systemic opioids and general anaesthesia but less certain for regional anaesthetic techniques, as long as hypotension is mild and limited.
• In terms of neonatal neurobehaviour, regional anaesthesia for delivery of the severely compromised fetus is thought by most anaesthetists to have advantages over general anaesthesia, but this is still disputed.
Further reading
Littleford J. Effects on the fetus and newborn of maternal analgesia and anesthesia: a review. Can J Anesth 2004; 51: 586-609.
Reynolds F. Labour analgesia and the baby: good news is no news. Int J Obstet Anesth 2011; 20: 38-50.