Ajuste aplicando el diseño de tres niveles

Guidelines and training

This thesis has shown that a very important aspect of effective and safe use of ST-analysis of

the fetal ECG is adherence to the STAN® _{clinical guidelines (Appendix A).}22 _{Several studies}

in this thesis showed that in practice obstetric caregivers often fail to follow these guidelines. This may lead to inadequate decisions regarding whether or not to intervene for suspected

General discussion | 159

additional techniques such as FBS, in addition to ST-analysis, inconsistent adherence to these guidelines may also lead to incorrect decisions to perform or to refrain from performing FBS. More strict interpretation of both CTG and ST-waveform according to the guidelines may further prevent cases with adverse neonatal outcome and guide efficient use of FBS, aimed at specific situations that need additional fetal information, without redundant invasiveness.

Even when STAN® _{guidelines are consistently followed, still half of cases with adverse}

outcome being monitored by ST-analysis of the fetal ECG were identified too late, not allowing for earlier intervention. On the other hand, compared to monitoring by CTG only, WKH UDWH RI µIDOVH-QHJDWLYH¶ FDVHV LQ ZKLFK WKHUH ZHUH QR LQGLFDWLRQV WR LQWHUYHQH EDVHG RQ guidelines and the trial protocol, is much lower when a more comprehensive strategy of monitoring by ST-analysis of the fetal ECG is used, instead of monitoring by CTG only. Since the information provided by ST-analysis can only be judged when the CTG is correctly classified, CTG interpretation should (still) be continuously trained, not only in a formal but also in an informal clinical setting. Training should emphasize on the (timely) recognition of in specific (pre)terminal CTG patterns, since in 40% of cases with adverse outcome the latter

trace, as incorporated in the STAN® _{guidelines, is reason to perform an intervention.}

Overall, monitoring by ST-analysis of the fetal ECG has shown to be a cost-effective strategy, as compared to monitoring by CTG only. Additional costs for training, which is required for effective and safe implementation of ST-analysis of the fetal ECG, may at first sight be

considered as a disadvantage. However, the increased use of the STAN® _{method has already}

led to training of labour ward personnel in an informal clinical setting, which in the future may limit the need for official training sessions and thereby additional costs.

Fetal blood sampling

Myocardial anaerobic metabolism and glycogenolysis underlie a rise in T/QRS ratio of the fetal ECG, whereas accumulation of CO2 and a subsequent increase in free hydrogen ions underlie an acidotic pH obtained at FBS. This means that the information provided by ST- analysis seems more valuable, because it probably better reflects the metabolic fetal compensation to hypoxia. A low pH obtained at FBS is dominated by the respiratory component of fetal acidosis, which is part of normal labour. Despite the fact that the results of both ST-analysis of the fetal ECG and FBS are based on different mechanisms, in some situations their combined use may be necessary to timely identify a compromised fetus.

Although in our trial, as well as in the mentioned meta-analysis,18 _{the incidence of FBS was}

significantly lower in the ST-analysis group, still in 10.6% of deliveries FBS was performed

in addition to ST-information (Table 1).14-18 _{Recommended situations in which FBS should be}

performed in addition to ST-analysis of the fetal ECG are outlined in the most recent STAN®

clinical guidelines.22 _{However, in our trial 40% of FBS in addition to ST-analysis was not}

performed according these guidelines. Moreover, in this group there were only three cases with metabolic acidosis at birth, which had also been identified by significant ST-events before the moment of FBS. This may indicate that consequent obstetrical management

according to the STAN® guidelines will yield an even lower FBS rate in women monitored by ST-analysis of the fetal ECG.

A strategy of monitoring by CTG plus ST-analysis will not completely rule out the use of FBS. However, the substantial decrease in the need to perform FBS, compared to CTG only, is a favourable outcome, since FBS has several drawbacks. It provides only intermittent information and the decision to perform FBS is based on a subjective interpretation of the CTG. Furthermore, performance of FBS requires expertise, is invasive, often fails and is time-

consuming.23-25 _{The latter may even cause a serious delay in delivery, especially during the}

second stage of labour, when FBS is performed to check the significance of CTG and ST- changes.

Recently, measurement of lactate instead of pH in fetal scalp blood has been introduced as a biochemical marker of hypoxia. With respect to operative deliveries or neonatal outcome no

differences with pH have been found, but the success rate in lactate sampling was higher.26

Definition of neonatal outcome

A general problem of studies on intrapartum fetal monitoring is the definition of a clinically

relevant outcome measure. Although it may be discussed whether long-term adverse

outcomes are of greatest interest and importance, the choice for a marker of adverse outcome also heavily depends on its prevalence. Since cases with perinatal mortality, cerebral palsy and even encephalopathy are rare, most studies primarily focus on short-term neonatal outcomes, such as perinatal asphyxia. Moreover, it is known that a poor condition at birth is

associated with the development of neurological problems and long-term adverse outcome.27-

29

Defining neonatal asphyxia is complicated. Often its biochemical derivative metabolic acidosis is used, which is the combined presence of both a low umbilical cord-artery pH and base deficit (BD). BD is a calculated value from the measured values pH and pCO2 in umbilical cord blood. This calculation is highly influenced by the choice of fetal fluid compartment (whole blood or extracellular fluid). Moreover, algorithms for calculation of BD

vary with different brands of blood gas analysing devices.30-32 _{Due to the lack of good}

evidence on the association of either algorithm with neonatal outcome, there is no consensus regarding which algorithm should be used. This creates clinical difficulties with respect to the definition of acidosis. This is clearly illustrated by our trial, in which the incidence of metabolic acidosis according to the BD in blood was much higher than the incidence of metabolic acidosis according to the BD in extracellular fluid. When cord blood gases are used as outcomes, (in)comparability of study results is also a problem. This is illustrated by the five trials comparing monitoring by ST-analysis of the fetal ECG to CTG only (Table 1). In four of these trials metabolic acidosis was analysed according to pH and BD in the

extracellular fluid,14,15,17 _{whereas in one trial pH and BD in blood was used.}16 _{Because of the}

use of different algorithms for calculation of BD, a straight comparison of the results of these

General discussion | 161

the trial of Ojala from blood to extracellular fluid,16 leads to different study results with a

(non-significant) decrease instead of an increase in the rate of metabolic acidosis.33

7RRYHUFRPHWKHSUREOHPRIGLIIHUHQWDOJRULWKPVWREHXVHGIRUµDUWLILFLDO¶FDOFXODWLRQRI%' the directly determined parameter lactate may be used instead. Lactate alone, preferably adjusted for gestational age, or in combination with pH, has been shown to be a satisfactory

alternative for BD as an indicator for fetal condition at birth.34,35

Another problem with respect to neonatal acid-base status, concerns the collection of umbilical cord blood. Although parameters measured in the umbilical cord artery correlate best with the fetal tissue oxygenation and acid-base status, it is recommended to obtain blood from both the umbilical cord artery and vein. In this way it is possible to identify the origin of a sample and insight is provided into the cause and duration of hypoxia and the quantity of an acid-base shift. However, in clinical practice often sampling of the umbilical cord is forgotten or only one sample is available. The latter is then likely to be the (less-informative) venous sample, because the vein is larger and contains more blood than the arteries, especially in case of asphyxia. Furthermore, the timing of cord blood clamping influences acid-base values. Delayed clamping (> 30 seconds after birth) of the umbilical cord leads to a rapid decrease in PaCO2, which results in a falsely high BD, thereby affecting the measured values of cord

blood acid-base parameters.36