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General obstetrics > Pregnancy physiology > Flashcards

Pregnancy physiology Flashcards

1
Q

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

What implications do these have anaesthetically>

A
  • 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.
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2
Q

Respiratory:
What are the mechanical changes associated with pregnancy?

What remains unchanged?

A

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
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3
Q

Respiratory:

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

A

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

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4
Q

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

What are the consequences of these changes during maternal apnoea?

A

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.
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5
Q

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

A

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.

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6
Q

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

How does supine maternal position affect cardiac output?

A

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.
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7
Q

Cardiovascular:

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

A

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)
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8
Q

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

A
  • 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.
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9
Q

Cardiovascular:
What normal changes in pregnancy mimic heart disease?

What are concerning symptoms?

A

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
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10
Q

Cardiovascular:

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

A
  • 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
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11
Q

Cardiovascular:

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

What are the consequences of this effect?

A

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.

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12
Q

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?

A
  • 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.
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13
Q

Haematological:

What changes occur to:

  1. Platelets
  2. White cells
A
  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.
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14
Q

Haematological:

What changes occur to:

  1. Platelets
  2. White cells
A
  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.
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15
Q

Haematological:

What changes occur in the coagulation system during pregnancy?

A

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.

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16
Q

Thyroid:

What changes occur in thyroid metabolism during pregnancy?

A
  • 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
Q

Adrenal:

What changes in adrenal function and secretion occurs during pregnancy?

A

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
Q

Pituitary:

What changes in pituitary function and secretion occurs during pregnancy?

A
  • 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
Q

Glucose metabolism:

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

A

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
Q

Parathyroid:

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

A

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
Q

Liver:

What changes occur in hepatic metabolism and function during pregnancy?

A

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
Q

GI tract:

What changes in GI tract function occur during pregnancy?

A

Decreased:

  • Lower oesophageal pressure
  • Gastric peristalsis and delayed gastric empyting

Increased small and large bowel transit times.

23
Q

Renal:

What changes in renal function occur during pregnancy?

A
  • 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
Q

Urinary / collecting system:

What changes occur in the urinary collecting system during pregnancy?

A

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
Q

Genital tract:

What changes occur during pregnancy to:

  1. Vagina
  2. Cervix
A
  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.

General obstetrics (34 decks)

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