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Flashcards in Pregnancy physiology Deck (25)
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1

Respiratory:
What are the upper respiratory tract changes associated with pregnancy?

What implications do these have anaesthetically>

- Hyperaemia and oedema of nasopharynx mucosa with mucus hypersecretion secondary to increased oestrogen.
- Pregnant women more difficult to intubate due to increased Mallampati score, tendency to bleed during ET tube placement.

2

Respiratory:
What are the mechanical changes associated with pregnancy?

What remains unchanged?

Increased:
- Subcostal angle
- Transverse diameter of chest
- Chest circumference

- Level of diaphragm progressively rises by 4 cm.
- Diaphragmatic movement increases by 1-2 cm due to progesterone, so diaphragmatic effort and negative inspiratory pressure is increased.

Unchanged:
- Respiratory muscle function.
- Max inspiratory and expiratory pressures

3

Respiratory:
What are the changes in lung volume and pulmonary function associated with pregnancy?

Elevated diaphragm results in:
- Reduced total lung capacity
- Reduced function residual capacity (expiratory reserve volume and residual volume)

Forced expiratory volume in 1 second (FEV1) remains stable

4

Respiratory:
What are the changes in gas exchange associated with pregnancy?

What are the consequences of these changes during maternal apnoea?

Pregnancy is a state of chronic respiratory alkalosis/hyperventilation.
- Tidal volume increases 30-50% by 8 weeks.
- Respiratory rate (RR) remains stable.
- Minute ventilation increases (TV x RR) --> 50-70% increase in alveolar ventilation.
- Increased alveolar oxygen (PaO2)
- Decreased arterial CO2: facilitates CO2 transfer between fetus and mother.
- Partial renal compensation for respiratory alkalosis (increased renal bicarb secretion) leading to decreased serum bicarb levels.
- Arterial pH increased to 7.4-7.45
- Oxygen consumption increased 20-40%; triples during labour/contraction.

Apnoea results in:
- Rapid hypoxia and hypercapnia
- Respiratory acidosis
- Due to reduced FRC and increased oxygen consumption leading to lower maternal oxygen reserve.

5

Cardiovascular:
What are the changes to the positioning of the heart that during pregnancy?
What consequence does this have for diagnosing cardiomegaly?

Heart is displaced upwards and to the left and rotated along its long axis.

Increased cardiac silhouette on CXR.

Cardiomegaly should be diagnosed with ECHO in pregnancy rather than CXR.

6

Cardiovascular:
What are the changes in cardiac output (CO) that occur during pregnancy?

How does supine maternal position affect cardiac output?

CO increases by 40% due to:
- Increased stroke volume 10-20%(increased ventricular muscle mass/contractility and increased end diastolic volume/dilation of ventricle)
- Increased HR by 15-20 beats/17%.

Maternal supine position:
- CO reduced by 25%
- Gravid uterus compresses the IVC and reduces venous return subsequently SV and CO.

7

Cardiovascular:
What changes in blood pressure, systemic vascular resistance and venous pressure occur during pregnancy?

Blood pressure decreases by 20% due to decreased in systemic vascular resistance:
- Begins at 8 weeks gestation and nadir midpregnancy with progressive rise in BP again towards term.
- Progesterone and nitric oxide mediated smooth muscle relaxation.
- Pulmonary vascular resistance decreases.

Venous pressure in lower limbs rises progressively leading to:
- Oedema
- Haemorrhoids
- Varicose veins
- Increased risk of DVT (venous stasis)

8

Cardiovascular:
What changes in central haemodynamic pressures occur during pregnancy?
What are the consequences?

- Colloidal oncotic pressure decreases significantly
- Central venous pressure and pulmonary capillary wedge pressure do not increase.
- Relative COP : PCWP difference of 30% results in increased propensity to develop pulmonary oedema if there is increased capillary permeability or elevated cardiac preload.

9

Cardiovascular:
What normal changes in pregnancy mimic heart disease?

What are concerning symptoms?

Pregnancy-related dyspnoea:
- Affects 75% women
- Onset before 20 weeks.
- Not progressive, does not affect ADLs or occur at rest.

Heart auscultation:
- 1st heart sound louder with exaggerated splitting
- 3rd heart sound due to rapid diastolic filling (90%)
- 90% have ESM

Other normal findings:
- Relative sinus tachycardia
- Peripheral oedema
- Ectopic beats

Concerning symptoms:
- Haemoptysis
- Syncope
- Chest pain with exertion
- Progressive orthopnoea
- PND

10

Cardiovascular:

What normal ECG changes would you expect to find with pregnancy?

- Atrial and ventricular ectopic beats.
- Left axis shift
- Small Q-wave and T-wave inversion in lead III
- ST depression and T-wave inversion in inferior and lateral leads

11

Cardiovascular:

What effect does labour and the immediate puerperium have on maternal cardiovascular function?

What are the consequences of this effect?

Uterine contraction causes auto-transfusion of 300-500 mL leading to even greater increase in CO (12%; 50% above prepregnancy level).

Max CO reached 10-30 mins after delivery (60-80% above pregnancy) but returns to prelabour baseline after 1 hour.

Women with cardiovascular compromise most at risk of pulmonary oedema during second stage of labour and the immediate puerperium.

12

Haematological:

Describe the changes that lead to a physiological anaemia in pregnancy.

What happens in the puerperium?

What are the associated changes in iron metabolism?

- Increase in blood volume 40-50%.
- Increase in red cell mass by 30% (400-450 mL).
- Red cell mass increase relatively slow than plasma volume expansion leading to physiological anaemia.

In the puerperium:
- Blood volume decreases after delivery.
- Diuresis occurs leading to decreased plasma volume.
- Less of a decrease in haematocrit.

Increased iron requirements approx 1000 mg.
- 300 mg to fetus
- 500 mg to RBC mass
- 200 mg for normal daily iron losses.

13

Haematological:

What changes occur to:
1. Platelets
2. White cells

1. Platelets:
- Mild decrease in Plt count.
- Plt function increased
- Gestation thrombocytopenia affects 8%; counts between 70-150 and not associated with increased complications; normalises 1-2 weeks postpartum.

2. White cells:
- Increases progressively
- Can be 20-30 during labour.
- Not a reliable marker of infection during labour.
- Normalises 1-2 weeks postpartum.

14

Haematological:

What changes occur to:
1. Platelets
2. White cells

1. Platelets:
- Mild decrease in Plt count.
- Plt function increased
- Gestation thrombocytopenia affects 8%; counts between 70-150 and not associated with increased complications; normalises 1-2 weeks postpartum.

2. White cells:
- Increases progressively
- Can be 20-30 during labour.
- Not a reliable marker of infection during labour.
- Normalises 1-2 weeks postpartum.

15

Haematological:

What changes occur in the coagulation system during pregnancy?

Hypercoagulability to minimise peripartum haemorrhage through:
- Increased venous stasis
- Changes in coagulation cascade
- Vessel wall injury

Changes in coagulation cascade:
- Increase in procoagulants: fibrinogen (factor I), factor VII, VIII, IX, X.
- Decrease in inhibitors of coagulation: decreased Protein-S and anti-thrombin.
- Decrease in fibrinolytic activity: decreased plasminogen activator inhibitor-1 (PAI-1), and increase in PAI-2 by 25x.

Changes also increase risk of VTE 5 x.

PT, APTT and thrombin time are unchanged.

16

Thyroid:

What changes occur in thyroid metabolism during pregnancy?

- Thyroid binding globulin production from liver increases.
- Subsequent increase in total T4 and T3 to compensate.

Biochemical hyperthyroidism: can occur in early pregnancy has hCG has TSH-like activity leading to increased T4 and suppressed TSH levels.

TSH increases during 2nd and 3rd trimesters with reduction in T4 and T3.

Pregnancy is a relatively iodine deficiency state because:
- Increased iodine requirements for fetus.
- Increased renal iodine loss due to increased GFR and decreased renal tubular reabsorption.
- Reflexive 3 x increased absorption of iodine by thyroid; hypertrophy may occur if pre-existing dietary insufficiency.

17

Adrenal:

What changes in adrenal function and secretion occurs during pregnancy?

Cortisol:
- Cortisol levels increased x 3
- Cortisol binding globulin increased.
- Blunted exogenous corticosteroid suppression

Increased levels of:
- Angiotensin II
- Renin
- Aldosterone.

Urinary catecholamines, metaneprhines and vanyillylmandelic acid unaffected.

18

Pituitary:

What changes in pituitary function and secretion occurs during pregnancy?

- Anterior pituitary volume increases progressively up to 35%. Involution postpartum slower if breastfeeding.

Prolactin:
- Secretion increased 10x and normalises 2 weeks postpartum unless breastfeeding.
- 1st trimester secretion due to oestrogen and progesterone.

LH and FSH:
- Undetectable due to high oestrogen and progesterone.

Growth hormone:
- Unchanged
- Placental secretion of human placental lactogen which closely resembles GH.

ADH:
- Unchanged
- Break down of ADH increased due to placental secretion of cystine amninopeptidase.

Pituitary ACTH secretion unchanged.
Placenta secretes ACTH and CRH.

19

Glucose metabolism:

What changes regarding glucose metabolism and insulin sensitivity occur during pregnancy?

Insulin:
- Sensitivity increases in 1st trimester then decreases in 2nd and 3rd trimesters. Insulin resistance mediated by secretion of anti-insulin hormones from placenta (hPL, glucagon and cortisol).
- Secretion doubles

Result:
- Lower fasting glucose level
- High post-prandial gluclose level

Pre-existing diabetes:
- Increased insulin requirements
- Increased risk of ketoacidosis.

Glycosuria:
- Renal tubular threshold for glucose falls leading to increased glycosuria in pregnancy.
- Not a reliable marker for IGT or GDM.

20

Parathyroid:

What changes occur in calcium metabolism and vitamin D requirements during pregnancy?

Calcium:
- Demand is increased
- Urinary loss is increased
- Increased Vit-D mediated gut absorption.

Increased vitamin-D requirements 50-100%.

Fall in albumin leads to:
- Fall in total calcium
- Unaffected free ionised calcium.

21

Liver:

What changes occur in hepatic metabolism and function during pregnancy?

Increased hepatic metabolism.

Decreased total serum protein due to fall in serum albumin 20-40%.

Increased production of :
- Fibrinogen
- Caeruloplasmin
- Transferrin
- TBG and cortisol binding globulin

Liver enzymes:
- ALP increased 2-4 x but due to increased secretion by placenta.
- Upper limit of ALT and AST reduced <30.

Unchanged:
- Bilirubin

22

GI tract:

What changes in GI tract function occur during pregnancy?

Decreased:
- Lower oesophageal pressure
- Gastric peristalsis and delayed gastric empyting

Increased small and large bowel transit times.

23

Renal:

What changes in renal function occur during pregnancy?

- Increase in renal plasma flow 60-80% by 2nd trimester; decreases slightly in 3rd trimester but still >50% of pre-pregnancy.

- Increased GFR, CrCl increased by 50%
- Decreased serum urea and Cr as a result.

- Increased protein excretion.
- Increased sodium retention leading to water retention and oedema.

Increased renal secretion of:
- Vitamin D
- EPO
- Renin

24

Urinary / collecting system:

What changes occur in the urinary collecting system during pregnancy?

Significant dilatation of ureters right > left side due to:
- Progesterone effect causing ureteral smooth muscle relaxation
- Compression of ureters by uterus or iliac vessels.

Microscopic haematuria in absence of proteinuria, infection or renal impairment secondary to bleeding from small venules in dilated collecting systems.

25

Genital tract:

What changes occur during pregnancy to:
1. Vagina
2. Cervix

1. Vagina:
- Bluish discolouration due to increased vascularity and hyperaemia.
- Decreased pH due to increased oestradiol and glycogen levels which are metabolised by lactobacilli into lactic acid.
- Vulval varicosities due to progesterone-mediated increase in venous distensibility, increased circulating volume and mechanical effect of uterus.
- Vaginal epithelium and muscle thickens but connective tissue underlying epithelium relaxes.

2. Cervix:
- Hormone mediated change in collagen structure and glycosaminoglycans soften and dilate cervix; following delivery this is repaired.
- Copious thicker and more acidic cervical mucus mediated by progesterone.