Intro to obstetrics Flashcards
What is the first stage of labour?
- for prim 8hrs, multiparous 5hrs
- latent phase
- regular contractions < 10mins apart but minimal pain
- membranes may remain intact initially
- cervice dilates to 3-4 cm
- active phase
- ongoing dilation of the cervix by 0.5 - 1cm/hr
- assoc/w increasing pain on contractions
- foetal head descends into pelvis and neck flexes
What is the second stage of labour?
- From fully dilated to birth
- Should last <2hrs in nulliparous woman
- 1hr in multiparous woman
- if longer than this - consider instrumental delivery
- contractions are strong, sustained and occur at less than 5 minute intervals
- associated with the need to push
- baby’s head is visible
What is the third stage of labour?
- delivery of placenta and membranes
- usually less than 5 minutes
- midwife continues controlled cord traction and suprapubic compression to help with expulsive contractions
What is failure to progress?
- When the active phase has continued for 4hrs
- epidural may be requested at this point
- intervention usually takes the form of an infusion of syntocinon
How many vertebrae are there?
24 total
- 7 cervical
- 12 thoracic
- 5 lumbar
- 3-5 fused vertebrae form the sacrum and coccyx
Where does the spinal cord finish?
L1/2
Where does the dural sac finish?
S2 - continues as the filium terminale
Where do spinal nerves exit in relation to their associated vertebral body?
Spinal nerves exit BELOW their associated vertebral body (ie L4 nerve root leabes inferiorly to L4 vertebral body)
EXCEPT for in cervical region - 8 nerves but only 7 verebral bodies - so the nerves are numbered according to the bertebra below except C8 which exists between C7 and T1
Where does the anterior spinal ligament run from?
From occiput cranially to sacrum caudally - attached to the intervertebral discs at each level
Where does the posterior spinal ligament run?
Runs cranially to caudally, attaching to each vertebrae and disc
Where does the ligamentum flavum run from?
From C2 to S1 connecting the laminae of the vertebral discs
Does it cause pain to pierce the spinal ligaments or the ligamentum flavum?
No, they have no sensory innervation
What are the boundaries of the epidural space?
Anteriorly
- posterior longitudinal ligament and vertebral bodies
Posteriorly
- ligamentum flavum
Superiorly
- fusion of spinal and periosteal dural layers at foramen magnum
Inferiorly
- sacrococcygeal membrane
Laterally
- pedicles and intervertebral foramina
What changes in the central and peripheral nervous system happen during pregnancy?
- MAC reduced by 30% for inhalational agents
- onset and depth of anaesthesia increased
- decreased volume of epidural space and compensatory reduction in CSF production
What effects on MAP happen in pregnancy?
Falls in the first trimester due to effects of progesterone on vascular smooth muscle - causes peripheral vasodilation and reduced SVR
MAP increases gradually from 24 weeks and regains pre-preggo levels at term. The increase in SV is maintained due to aortocaval compression - increases HR.
How is uteroplacental perfusion maintained despite reduced BP?
- increased cardiac output
- renin-angiotension-aldosterone system activated to increase salt and water retention and increase plasma volume
- increased pre-load due to increased blood volume which increases stroke volume to maintain CO
What does pregnancy do to CVP and pulmonary capillary wedge pressure?
No effects on these
How much is blood volume increased at 34 weeks pregnancy?
40-50%
What effect can pregnancy have on the ECG?
Increased ventricular wall mass with corresponding left axis deviation of up to 20°
Heart dilates and flow murmurs are common
When does aorto-caval compression begin?
20 weeks gestation.
Gravid uterus compresses the abdominal viscera and vessels. At term compression of both IVC and abdominal aorta occurs and CO may reduce as much as 30% when supine.
How are pregnant women able to maintain BP despite aorto-caval compression?
They compensate by increasing CO and SVR through an increase in sympathetic tone.
Regional anaesthesia can create profound hypotension because this sympathetic tone is removed.
What happens to coagulation in pregnancy?
Pregnancy is a prothrombotic state due to increased production of clotting factors and reduced fibrinolysis and antithrombotic components such as protein C and S.
What happens to platelets in pregnancy?
Overall count usually normal but relative amounts may be much less due to haemodilutional effects.
Patients with pre-eclampsia should have platelet countchecked incase of HELLP syndrome.
How does pregnancy affect FRC?
Reduced from 20 weeks onwards as the diaphragm is pushed upwards.
FRC reduced by up to 30% when supine.
What happens to alveolar dead space in pregnancy?
Reduced as increased CO improves perfusion of lung units.
What alters the response to CO2 in pregnancy?
Progesterone
What happens to CO2 production in pregnancy?
Increased due to enhanced metabolism and combined output from mother and foetus.
How is the increased demand of O2 and CO2 production matched in pregnancy?
Minute ventilation increases due to an increase in tidal volume.
This means that PaCO2 is reduced to 4kPa at term despite RR remaining normal.
What happens to blood pH in pregnancy?
It will remain within normal limits despite the increased minute ventilation + reduced PaCO2 due to an increased renal secretion of bicarbonate.
What would aggressive hyperventilation in pregnancy do?
It negates the effect of increased renal bicarbonate secretion and will result in respiratory alkalosis which impairs maternal-foetal O2 exchange.
Why is the obstetric airway more difficult?
- tissue oedema and swelling affect the larynx and arytenoids
- fat/breast tissue
What are the hepatic effects of pregnancy?
- LFTs are usually slightly lower than pre-preggo levels
- ALP may be slightly higher due to production of ALP by placenta
- reduction of plasma cholinesterases (meaning more sensitivity to suxamethonium), especially if pre-eclamptic or liver disease
What are the GI SEs of pregnancy?
- GORD from 20 weeks
- stomach and bowel compressed by the uterus
- relaxation of lower oesophageal sphincter
- during labour gastric emptying is delayed
- enhanced by opioids regardless of route of admin
- after 12 weeks - assume all pregnant women to have full stomachs
What are the renal SEs of pregnancy?
- salt and water retention due to aldosterone
- causes volume expansion
- increases volume of distribution
- renal blood flow increases as much as 50% at term
- therefore filtration rate also increases to 150ml/min
- the increased levels of filtrate exceed the ability of the renal tubules to reabsorb all solutes hence glycosuria and proteinuria more likely
