CTG Fetal monitoring Flashcards
Fetal circulation
Maternal Uterine Artery > flows across the myometrium > into the intervillous space > into the fetus along the umbilical vein > chorionic villus > along the umibilical artery > chorionic villus > intervillous space > myometrium > into the maternal circulation
SA node
primary pacemaker
typically has the faster rate and output in terms of electrical activity
sits in the right artrium
both sympathetic and parasympathetic nerve endings which are part of the autonomic nervous system
SNS
Fright or flight response increases heart rate cardiac output and blood pressure this is acheived through the release of adrenaline and noradrenaline
Parasympathic nervious system
reduces heart rate
cardiact output
blood pressure
action of acetylcholine on the sa node
acetylcholine
membrane stablising agent
acts like a local anaesthetic targeted very specifically on the SA node
the major nerve pathe of the PNS is the vagus nerve
Fetal basline heart rate
CNS & pns balance with each other that generates the normal baseline variability
normal basline variability therefore represents a balance/well oxygenated CNS
presented on a CTG is the most import maker of the fetal wellbeing
catecholamines
helps the body meet physiological stressors by increase the heart rate
fetus - increases cardiac output - resulting in additional blood directed to the placenta to increase oxgyen uptake.
Catecholmaines include dopamine adrenaline noradrenaline they act as hormones or neurotransmitter the adrenal gland produces: adrenaline (80%) noradrenaline (20%) which are released inot the blood stream
adrenaline
released fro mteh adrenal gland
predominantly acts on beta receptors
noradrenaline
released from the adrendal gland
works primarily on the sympathetIc neurone
baroreceptors
are ograns that are senstive to strecth or pressure
situated in the carotied artery, arch of the aorta and the brain stem
Role to protect the fetal brain against excesses in pressure
- fetal hypertension and hypotension are both potentially dangerous to the fragile fetal brain
fetus hypertension - reflex response from the baroceceptiors can directly stimulate the vaus nerve - release acetylochline to the SA node - cause a rapid drop in the FHR and cardiac output, reduces blood pressure to correct the hypertension
fetus hypotension - barorecteptors trigger the CRC to withdraw vagus nerve stimulation and/or increases sympathetic stimulation - relsuts in an increase in the fetal heartr rate and cardiac output to corrent the hypotension
Chemoreceptors
- are organs that are sensitive to changes in blood chemistry
- situated in the carotid artery, arch of the aorta and in the brain stem
- high metablic rate
- resulted in high O2 requirements
- are sensitve to falling o2 levels
if o2 levels fall gradual or there is a greater need for o2
- chemoreceptors tiggers the cardio regulatory centre
- the cardio regulator centre increases the sympathic nervous sytem stimulation
- catecholamines are released from the SA node
- results in increased fetal HR and cardiac output
is aimed to direceting more blood to the placenta in an attempt to increase fetal O2
chemoreceptors are also invoived in the gensis of FHR deceleration.
- an abrupt fall in fetal O2 leads to chemoreceptor stimulation of the vagus nerve (pneumogstric nerve) is the tenth cranial nerve controls heart lungs and digestive tract - stimulates the release of acetycholine and a repid fall in the FHR
“the chemoreflex respone is likey to be the key contributor to variable deceleration”
fetus releases catecholamines
releases catecholaines into the intervascualr compartment from the adrenal glands
results in peripheral vasoconstriction
increases blood pressure
redirects blood, oxygen, nutrients away from the gut and the peripheral vasculature to the organs vital for heart rate control and ultimately survival
vital organs are the brain heart and adrenal glands
increase oxygen demands being placed on fetus
becomes increaseingly sympathetically dominant increases cardiac output maintains adequate oxygen delivery explains baseline tachycardia absent of baseline variabitlity
baseline fetal hr of 180 outcome no variabiles
outcome:
very high cirulating catecholamines
tachy cardia
tachypnoea
likely vocal
therfore resulting in a good apgars score
will require SCN as they have used most of their reserves to maintain perfusion of their vital organs
matenal hypotension _ factors that can affect the maternal transport of 02 and nutrient rich blood to the placenta
maternal low bp- reduced organ perfusion
- less blood flow through the maternal uterine arteries
- less o2 available tothe fetus
Maternal low bp - can lead to acute fetal hypoxia
main common causes:
supine hypotension - the fetus weight compresses the inferior vena cava
diminishes the return of blood to the right atrium
reduces cardiac output
epidural or spinal anaesthesia - occasionally results in maternal
hypotension resulting in a prolonges
deceleration or fetal bradycardia
