How to read a CTG - GM Flashcards
what is cardiotocography
used to monitor fetal HR and uterine contractions
most commonly used in the third trimester
the two transducers of CTG
one record fetal HR using US
the other monitors contractions of the uterus by measuring tension of the maternal abdominal wall (providing an indirect indication of intrauterine pressure)
DR C BRAVADO
DR - define risk
C - contractions
BRa - baseline rate
V - variability
A - accelerations
D - decelerations
O - overall impression
risk factors that may influence interpretation of a CTG
gestational diabetes
hypertension
asthma
multiple gestation
post date gestation
previous CS
intrauterine growth restriction
premature rupture of membranes
congenital malformations
oxytocin induction/augmentation of labour
pre-eclampsia
absense of prenatal care
smoking
drug abuse
contractions
- record number of contractions in a 10 minute period
individual contractions are seen as peaks on the uterine activity monitor
each big square is equal to 1 minute
baseline rate of foetal heart
average HR of the fetus in a 10-minute window
ignore accelerations or decelerations
normal baseline foetal heart rate
110-160 bpm
fetal tahcycardia
baseline HR greater than 160
causes include
- fetal hypoxia
- chorioamnionitis
- hyperthyroidsim
- fetal or maternal anaemia
- fetal tachyarrythmia
fetal bradycardia
baseline HR less than 110
when might fetal bradycardia be normal
it is common to have a baseline HR of 100-120 during
- postdate gestation
- occipul posterior or transverse presentations
severe prolonged tachycardia
less than 80 bpm for more than 3 minutes
indicates severe hypoxia
causes include
- prolonged cord compression
- cord prolapse
- epidural and spinal anaesthesia
- maternal seixures
- rapid fetal descent
variability
variation in fetal HR from one beat to the next
a healthy fetus will constantly be adapting its heart rate in response to changes in its environment
normal level of variability
5-25 bpm
indicates intact neurological system in the fetus
categories of variability
reassuring, non-reassuring, abnormal
non reassuring variability
less than 5 bpm for between 30-50 minutes
more than 25 bpm for 15-25 minutes
abnormal variability
less than 5bpm for more than 50 minutes
more than 25 bpm for more than 25 minutes
sinusoidal
causes of reduced variability
fetal sleeping: most common cause, should last no longer than 40 minutes
fetal acidosis (due to hypoxia): more likley if late decelerations are also present
fetal tachycardia
drugs: opiates, benzodiazepines, methyldopa, and magnesium sulphate
prematurity: variability is lower at earlier gestations (< 28 weeks)
congenital heart abnormalities
accelerations
an abrupt increase in baseline fetal heart rate of greater than 15 bpm for greater than 15 seconds
presence of accelerations is reassuring
accelerations occuring alongside uterine contractions is a sign of a healthy fetus
absent accelerations
with an otherwise normal CTG, this is of uncertain significance
decelerations
abrupt decrease in a baseline fetal heart rate of greater than 15 bpm for greater than 15 seconds
cause of decelerations
in response to hypoxic stress, the fetus reduces its heart rate to preserve myocardial oxygenation and perfusion.
unlike an adult, a fetus cannot increase its respiration depth and rate
types of decelerations
early deceleration
variable deceleration
late deceleration
prolonged deceleration
sinusoidal pattern
early decelerations
start when uterine contractions begin and stop when uterine contractions stop
considered physiological
are early decelerations pathological
they are physiological and not pathological
why do early decelerations occur
due to increased fetal intracranial pressure caused increased vagal tone
will quickly resolve once the contraction ends and intracranial pressure reduces
variable deceleration
rapid fall in baseline fetal heart rate with a variable recovery phase
may not have any relationship to uterine contractions
variable decelerations are seen in
often seen during labour and in pateints with reduced amniotic fluid volume
what causes variable deceleration
umbilical cord compression
initially there is compression on the umbilical vein which causes acceleration, the compression on the umbilical artery which causes deceleration, then pressure on the cord is reduced causing another acceleration
shoulders of deceleration
the accelerations that occur before and after a variable deceleration
indicate that the fetus is not yet hypoxic and is ada[ting to the reduced blood flow
variable decelerations without shoulders
more worrying as it suggests the fetus is hypoxic
late deceleration
begin at the peak of uterine contraction and recover after the contraction ends
are late decelerations worrying
yes
indicates there is insufficient blood flow to the uterus and placenta
blood flow to the fetus is significantly reduced causing fetal hypoxia and acidosis
causes of reduced uteroplacental blood flow include
maternal hypotension
pre-eclampsia
uterine hyperstimulation
prolonged deceleration
deceleration that lasts more than 2 minutes
non-reasurraing deceleration
between 2-3 minutes
abnormal deceleration
longer than 3 minutes
sinusoidal pattern
sinusoidal CTG pattern is rare
very concerning, associated with high rates of fetal morbidity and mortality
characteristics of a sinusoidal CTG pattern
- a smooth, regular, wave like pattern
- frequency of around 2-5 cycles a minute
- stable baseline rate around 120-160bpm
- no beat to beat variability
a sinusoidal CTG pattern usually indicates
severe fetal hypoxia
severe fetal anaemia
fetal/maternal heamorrhage
what qualitites should a reassuring CTG have
baseline fetal heart rate: 110-160bpm
baseline variability: 5-25bpm
decelerations: none or early, variable decelerations with no concerning characteristic for less than 90 minutes
