Interpreting CTG Flashcards
What is CTG?
Cardiotocography (CTG) is used during pregnancy to monitor fetal heart rate and uterine contractions.
It involves the placement of two transducers onto the abdomen. One transducer records the fetal heart rate using ultrasound and the other transducer monitors the contractions of the uterus by measuring the tension of the maternal abdominal wall
What is the structure for interpreting CTG?
DR C BRAVADO:
DR: Define risk
C: Contractions
BRa: Baseline rate
V: Variability
A: Accelerations
D: Decelerations
O: Overall impression
How should you assess contractions on CTG?
record the number of contractions present in a 10 minute period (10 big squares)
Duration: How long do the contractions last?
Intensity: How strong are the contractions (assessed using palpation)?
It is common to have a baseline heart rate of between 100-120 bpm in the following situations:
Postdate gestation
Occiput posterior or transverse presentations
Severe prolonged bradycardia (less than 80 bpm for more than 3 minutes) indicates severe hypoxia.
Causes of prolonged severe bradycardia include:
Prolonged cord compression
Cord prolapse
Epidural and spinal anaesthesia
Maternal seizures
Rapid fetal descent
Baseline variability refers to the variation of fetal heart rate from one beat to the next. Why is this important to assess?
a healthy fetus will constantly be adapting its heart rate in response to changes in its environment.
Normal variability indicates an intact neurological system in the fetus
Normal variability is between 5-25 bpm.
What is a ‘reassuring’ variability?
5 – 25 bpm
What is a ‘non-reassuring’ variability?
less than 5 bpm for between 30-50 minutes
more than 25 bpm for 15-25 minutes
What is an ‘abnormal’ variability?
less than 5 bpm for more than 50 minutes
more than 25 bpm for more than 25 minutes
sinusoidal
What can cause reduced variability?
Fetal sleeping: this should last no longer than 40 minutes (this is the most common cause)
Fetal acidosis (due to hypoxia): more likely if late decelerations are also present
Fetal tachycardia
Drugs: opiates, benzodiazepines, methyldopa and magnesium sulphate
Prematurity: variability is reduced at earlier gestation (<28 weeks)
Congenital heart abnormalities
What are accelerations?
abrupt increase in the baseline fetal heart rate of greater than 15 bpm for greater than 15 seconds
The presence of accelerations is reassuring.
Accelerations occurring alongside uterine contractions is a sign of a healthy fetus.
What are decelerations?
an abrupt decrease in the baseline fetal heart rate of greater than 15 bpm for greater than 15 seconds
Variable decelerations are usually caused by umbilical cord compression. The mechanism is as follows:
- The umbilical vein is often occluded first causing an acceleration of the fetal heart rate in response.
- Then the umbilical artery is occluded causing a subsequent rapid deceleration.
- When pressure on the cord is reduced another acceleration occurs and then the baseline rate returns.
What causes early decelerations?
increased fetal intracranial pressure causing increased vagal tone
resolves at the end of contraction, physiological
What causes late decelerations?
reduced uteroplacental blood flow:
Maternal hypotension
Pre-eclampsia
Uterine hyperstimulation
