1. ‘An Eye Opener’: Perils of CTG Misinterpretation. Handbook CTG

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‘An Eye Opener’: Perils of CTG

Misinterpretation

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Lessons from Confidential Enquiries and Medico-legal Cases

Edwin Chandraharan

Introduction

Since its introduction into clinical practice in late 1960s, cardiotocograph (CTG) interpretation was predominantly based on ‘pattern recognition’ by determining various features observed on the CTG trace (e.g. baseline fetal heart rate [FHR], baseline variability, presence of accelerations and decelerations). One of the main reasons for this approach was due to the fact that the CTG was first introduced to clinical practice without any robust randomized controlled clinical trials to confirm its efficacy. Very unfortunately, robust guidelines on how to use this new technology were not published at the time of introduction of CTG into clinical practice. This unfortunate situation resulted in obstetricians in late 1960s and early 1970s reacting to various patterns observed on the CTG trace without understanding the pathophysiological mechanisms behind these observed features. The first recognized guidelines on CTG interpretation were published by the American College of Obstetricians and Gynaecologists (ACOG) in 1979, and subsequent international guidelines on CTG interpretation were published by the International Federation of Gynecology and Obstetrics (FIGO) in 1987 as there weremore than 20 international guidelines at this time on how to interpret the CTG trace.

Lack of understanding of pathophysiology of intrapartum hypoxia as well as randomized controlled trials on CTG resulted in obstetricians merely exerting a panic reaction to observed decelerations, which were initially termed ‘type 1’ and ‘type 2’ decelerations, and this resulted in increased operative interventions (emergency caesarean sections, operative vaginal births) without any significant reduction in cerebral palsy and perinatal deaths.

Effects of CTG Misinterpretation

In 1971, Beard et al. reported that even when significant abnormalities (e.g. late decelerations and complicated baseline bradycardia) were noted on the CTG trace, more than 60 per cent of fetuses had a normal umbilical cord pH (>7.25). Therefore, CTG interpretation purely based on ‘pattern recognition’ resulted in unnecessary caesarean sections. As the false-positive rate of CTG was 60 per cent, out of 100 caesarean sections performed, 60 were potentially unnecessary. However, due to a paucity of knowledge with regard to fetal acid–base balance during labour in the late 1960s and 1970s, it was thought, based on personal opinions of a few senior obstetricians, that if the fetal pH was 7.25 or less, ‘it is considered possible that the fetus was asphyxiated’. Subsequent large observational studies have refuted this erroneous assumption, and it is now well known that the cord arterial pH of less than 7.0 (and not 7.25) is associated with poor perinatal outcomes. Therefore, if a cut-off of 7.0 was used instead of 7.25 by Beard et al. in 1971, it was very likely that the falsepositive rate of CTG would have been over 90 per cent. This implies that, if pattern recognition is used for CTG interpretation without understanding the fetal physiology, 90 out of 100 emergency caesarean sections performed for suspected fetal compromise would be entirely avoidable.

CTG misinterpretation has an adverse impact on the fetuses, their families as well as the society. In 1997, the fourth ‘Confidential Enquiries into Stillbirths and Deaths in Infancy’ (CESDI) reported that more than 50 per cent of intrapartum-related stillbirths were due to ‘grade 3’ substandard care, and, therefore, approximately 400 out of 873stillbirths were potentially avoidable by an alternative management. Lack of knowledge in the interpretation of CTG traces, failure to incorporate the entire clinical picture (meconium, maternal temperature, chorioamnionitis, etc.), delay in intervention even after recognizing an abnormality on the CTG, as well as communication and common sense issues were the key identified areas in cases with substandard care.

The Chief Medical Officer’s report in the United Kingdom in 2006 titled ‘Intrapartum-Related Deaths: 500 Missed Opportunities’ highlighted similar issues relating to substandard care even 10 years after the CESDI report in 1997. This was followed by the National Health Service Litigation Authority’s (NHSLA) report on ‘100 Stillbirth Claims’ in 2009, which highlighted the fact that 34 per cent of stillbirth claims involved CTG misinterpretation.

In addition to poor perinatal outcomes and long-term neurological sequelae, CTG misinterpretation is also associated with significant medico-legal costs. Vincent and Ennis reported issues relating to poor record-keeping and storage of CTG traces as contributory factors.

The more recent NHSLA’s ‘10 Years of Maternity Claims’ report highlighted the medico-legal implications of CTG misinterpretation, which contributed not only to claims arising from cerebral palsy and stillbirths but also to complications arising out of emergency caesarean sections. Failure to recognize an abnormal CTG, failure to incorporate clinical picture, failure in communication and injudicious use of oxytocin infusion were highlighted as key contributory factors to medico-legal claims. The overall cost of medico-legal claims was over three billion pounds.

The issues relating to CTG misinterpretation are not unique to the United Kingdom. Recent publications from Norway have suggested that substandard care is common in birth asphyxia cases, and human error is the most common contributory factor. Similar publications from Sweden have highlighted that injudicious use of oxytocin in labour was associated with approximately 70 per cent of all medico-legal claims. The author’s own medico-legal practice, analysis of the CTG trace as well as management of labour suggested that approximately 70 per cent of all cases of cerebral palsy and perinatal mortality were potentially avoidable by an alternative management.

In addition, poor CTG interpretation may lead to an unnecessary intrapartum operative intervention such as fetal scalp blood sampling (FBS), operative vaginal delivery aswell as an emergency caesarean section, all of which are associated with potentially serious maternal and fetal complications.

In June 2016, the Royal College of Obstetricians and Gynaecologists published ‘Each Baby Counts: key messages from 2015’. There were 921 reported cases in 2015 comprising of 119 intrapartum deaths, 147 early neonatal deaths and 655 babies with severe brain injury in the UK.

CTG Interpretation: What Is the Problem?

One of the main drawbacks of CTG is that it was introduced into clinical practice without any robust randomized controlled trials. Due to the lack of knowledge of fetal physiology in the 1960s when the CTG technology was developing, obstetricians who worked with the technology very unfortunately reacted to various patterns that were observed on the CTG trace since no proper guidelines as to how to use the technology were made available to the practitioners! Although several attempts were made by obstetricians working with the technology to produce an acceptable methodology of CTG classification, the first robust guidelines were only produced in 1979 by ACOG.

This was followed by the production of CTG guidelines by FIGO in 1987 to have a consensus in view of several different guidelines in use around the world, each adopting different features and classification systems at that time.

The initial panic attacks caused by the ‘decelerations’ observed on the CTG trace resulted in an exponential increase in operative vaginal births as well as emergency caesarean sections without any significant reductions in cerebral palsy or perinatal deaths. Obstetricians in 1960s and early 1970s were indeed very surprised to observe babies being born in a very good condition with vigorous crying when obstetricians had thought that they were experiencing ‘asphyxia’ based on the observed decelerations onthe CTG trace. Professor Richard Beard’s study in 1971 caused further confusion among obstetricians when he demonstrated that even when severe abnormalities were noted on the CTG trace, approximately 60 per cent of neonates were born with a normal acid–base balance (arterial umbilical cord pH >7.25).This led to some obstetricians introducing a test called FBS, which was developed by Erich Saling in Germany in 1962 as an alternative to a Pinard’s stethoscope. FBS was never validated as an additional or adjunctive test to the CTG prior to its introduction into clinical practice. It was merely introduced as a ‘knee-jerk reaction’ in response to Beard’s publication to reduce the false-positive rate of CTG so as to avoid unnecessary caesarean sections.

Such decelerations that were reflex responses of a fetus to a hypoxic or mechanical stress in labour in order to protect the myocardium as well as changes secondary to increased systemic blood pressure during umbilical cord compression were thought to be ‘pathological’. This erroneous assumption without a deeper understanding of fetal physiology resulted in such classifications as ‘type 1’ and ‘type 2’ decelerations, leading to further panic attacks among obstetricians and an increase in unnecessary intrapartum operative interventions. Conversely, a failure to appreciate the significance of abnormalities observed on the CTG trace resulted in intrapartum stillbirths, hypoxicischaemic encephalopathy (HIE) and its long-term sequelae such as cerebral palsy and learning difficulties, as well as early neonatal deaths.

The vast majority of current guidelines on CTG interpretation are purely based on ‘pattern recognition’, and some of these guidelines force obstetricians to perform an FBS for a ‘pathological’ CTG despite current evidence from the Cochrane Database of Systematic Reviews confirming that FBS, unlike what was believed by some senior obstetricians in the past, neither reduces operative interventions nor improves long-term perinatal outcomes. In contrast, FBS may be associated with potentially serious fetal complications (including severe haemorrhage, sepsis and leakage of cerebrospinal fluid) and may in fact delay delivery by up to 18 minutes.

In addition, several publications have highlighted that the interpretation of CTG is fraught with both inter- and intra-observer variations. Therefore, merely classifying CTG traces based on pattern recognition would lead not only to erroneous interpretations but also to unnecessary intrapartum operative interventions as well as delays in intervention.

Therefore, there is an urgent need to go back to basic fetal physiology to understand the pathophysiology behind the features observed on the CTG trace so as to treat the fetus rather than merely classifying the CTG trace into normal, suspicious orpathological. There is an urgent need, first, to appreciate that intrapartum fetal monitoring is all about ensuring that the fetus is not exposed to any significant hypoxic stress, and, second, to differentiate between a fetus that is able to and one that is unable to mount a successful compensatory response to ongoing stress or has exhausted all the means of compensation and hence has begun the process of decompensation. Therefore, features observed on the CTG traces should be used to understand fetal pathophysiology in order to avoid inappropriate interventions.

Midwives and obstetricians caring for women must avoid unnecessary operative interventions during labour while ensuring optimum perinatal outcome by developing a deeper understanding of fetal physiology.

Further Reading

1. Beard RW, Filshie GM, Knight CA, Roberts GM. The significance of the changes in thecontinuous fetal heart rate in the first stage of labour. J Obstet Gynaecol Br Commonw. 1971;78: 865–881.

2. Chauhan SP, Klauser CK, Woodring TC, Sanderson M, Magann EF, Morrison JC. Intrapartum nonreassuring fetal heart rate tracing and prediction of adverse outcomes: int erobserver variability. Am J ObstetGynecol. 2008; 199: 623.e1–623.e5.

3. NHSLA. Study of stillbirth claims. 2009. www.nhsla.com/safety/Documents/NHS%20Litigation%20Authority%20Study%20of%20Stillbirth%

4. NHSLA. Ten years of maternity claims: An analysis of NHS litigation authority data. 2012. www.nhsla.com/safety/Documents/Ten%20Years%20of%20Maternity%20Claims%20- %20An%20Analysis%20of%20the%20NHS%20LA%20Data%20-%20October%202012.pdf

5. Chandraharan E. Fetal compromise: diagnosis and management. In: Obstetric and Intrapartum Emergencies: A Practical Guide to Management. Cambridge University Press, 2012.

6. Chandraharan E, Lowe V, Penna L, Ugwumadu A, Arulkumaran S. Does ‘process based’ training in fetal monitoring improve knowledge of Cardiotocograph (CTG) among midwives and obstetricians? In: Book of Abstracts. Ninth RCOG International Scientific Meeting,Athens, 2011. www.rcog.org.uk/events/rcog-congresses/athens-2011

7. Ayres-de-Campos D, Arteiro D, Costa-Santos C, Bernardes J. Knowledge of adverse neonatal outcome alters clinicians’ interpretation of the intrapartum cardiotocograph. BJOG. 2011; 118(8): 978–984.

8. Chandraharan E. Fetal scalp blood sampling during labour: is it a useful diagnostic test or a historical test that no longer has a place in modern clinical obstetrics? BJOG. 2014; 121(9):1056–1060.

9. Department of Health, UK. On the state of public health: annual report of the Chief Medical Officer 2006. Chapter 6. Intrapartum-Related Deaths: 500 Missed Opportunities.webarchive.nationalarchives.gov.uk/20130107105354/http://www.dh.gov.uk/prod_consum_dh/group

10. CESDI. Fourth Annual Report: Concentrating on Intrapartum Deaths 1994-95. London.Maternal and Child Health Research Consortium, 1997.

11. Ennis M, Vincent CA. Obstetric accidents: a review of 64 cases. BMJ. 1990; 300(6736):1365–1367.

12. Berglund S, Grunewald C, Pettersson H, Cnattingius S. Severe asphyxia due to deliveryrelated malpractice in Sweden 1990–2005. BJOG. 2008; 115(3): 316–323.

13. Andreasen S, Backe B, Øian P. Claims for compensation after alleged birth asphyxia: a nationwide study covering 15 years. Acta Obstet Gynecol Scand. 2014; 93(2): 152–158.

14. Royal College of Obstetricans and Gynaecologists. Each baby Counts: key messages from 2015. London: RCOG2016.