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Anaesthetic FRCA Primary - eLFH Obstetrics > eLFH - Physiological changes during Pregnancy > Flashcards

eLFH - Physiological changes during Pregnancy Flashcards

1
Q

Usual weight gain during pregnancy

A

10 to 20 kg

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2
Q

Recommended weight gain for women with normal pre-pregnancy BMI

A

11.5 to 16 kg

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3
Q

Cause of weight gain during pregnancy

A

Foetal growth
Placenta
Amniotic fluid
Uterus
Breasts
Fat
Blood
Extravascular extracellular fluid

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4
Q

Cause of aortocaval compression

A

Weight of gravid uterus compress great vessels against lumbar vertebral bodies

(IVC > Aorta)

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5
Q

Consequence of aortocaval compression

A

IVC obstruction causes fall in venous return to heart leading to drop in maternal cardiac output and BP

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6
Q

Common alternative name for aortocaval compression

A

Supine hypotension

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7
Q

Symptoms of aortocaval compression

A

Dizzy
Nausea

Therefore women usually learn to avoid this position

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8
Q

Consequence if aortic compression predominates aortocaval compression

A

Maternal BP (measured above level of compression) will be normal or raised

However blood supply to uterus and fetoplacental unit (originates below level of compression) reduces and compromises foetus without maternal hypotension

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9
Q

Azygous venous system

A

Internal vertebral venous plexus around spinal cord

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10
Q

Consequence of IVC compression on azygous venous system

A

Azygous venous system becomes dilated with IVC compression

Causes engorgement of veins within the spinal canal

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11
Q

Degree of tilt to left side required to reliably avoid aortocaval compression

A

15 degrees is the compromise
Realistically need 30 degrees

Full left lateral position impractical for obstetric procedures

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12
Q

Gestation from which left lateral tilt is required

A

20 weeks onwards

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13
Q

Approximate uterine blood flow at term

A

700 ml/min

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14
Q

Blood supply to the uterus

A
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15
Q

Graph of changes to heart rate, stroke volume and cardiac output during pregnancy with weeks gestation

A
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16
Q

Why does cardiac output increase further during labour and by how much

A

CO increases by further 40% due to pain

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17
Q

Why does cardiac output increase immediately following delivery

A

Autotransfusion of blood from the uterus

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18
Q

Caution with autotransfusion of blood from uterus

A

If high risk of fluid overload then can precipitate this from point of delivery to around 48 hours after

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19
Q

Volume of blood autotransfused from uterus to mother as uterus contracts

A

~ 500 ml

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20
Q

Average resting heart rate during pregnancy

A

85 bpm

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21
Q

Changes to blood pressure during pregnancy

A

Systolic and diastolic pressure fall (diastolic more so than systolic) and then increases back to pre-pregnancy BP by term

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22
Q

Gestation at which BP is at its lowest

A

20 weeks

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23
Q

Cause for drop in BP during pregnancy

A

Fall in systemic vascular resistance

MAP = CO x SVR

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24
Q

Spirometry trace of non-pregnant vs pregnant adult

A
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25
Lung volumes which are increased in pregnancy
Tidal volume Respiratory rate Minute ventilation
26
Lung volumes which are reduced in pregnancy
Functional residual capacity Expiratory reserve volume Residual volume Total lung capacity
27
Why does pregnancy cause faster fall i PaO2 during apnoea
Reduced FRC Higher oxygen demands
28
Recommended pre-oxygenation method for pregnancy GA
3 minutes tidal breathing
29
Why does end tidal oxygen concentration rise faster in pregnant women
Higher minute ventilation in pregnancy
30
When does PaCO2 decrease during pregnancy and implication
Early in pregnancy Often lower PaCO2 present in women anaesthetised for termination of pregnancy or ectopic pregnancy
31
Changes to ventilator settings for term LSCS under GA
Slightly higher RR and VT Targeting lower EtCO2 / PaCO2 of 4.1
32
Alveolar gas equation
33
Why does PaO2 rise as PaCO2 falls during pregnancy
Alveolar partial pressure O2 increases as per alveolar gas equation Therefore higher diffusion gradient into arterial blood
34
Cause for more difficult intubation in pregnancy
Mucosa more vascular and oedematous Subtly alters laryngoscopy views
35
Reason to avoid nasal intubation, NG tube or suction to nose during pregnancy
Increased vascularity of mucosa increases chance of haemorrhage
36
Changes to contents of chest during pregnancy
Diaphragm and chest contents displaced cephalad as pregnancy advances AP diameter of chest increases to accommodate this
37
Changes to carina during pregnancy
Carina displaced cephalad as pregnancy advances Therefore shorter distance from teeth to carina and higher chance of endobronchial intubation
38
Changes to heart during pregnancy
Heart is enlarged and pulmonary vessel engorgement
39
ECG changes during pregnancy
Left axis shift T wave inversion in V2
40
GI changes during pregnancy
Gastro-oesophageal reflux
41
Reasons for increased gastro-oesophageal reflux during pregnancy
Lower oesophageal sphincter tone reduced After 20 weeks reflux promoted by gravid uterus Increased gastric contents volume
42
Changes to gastric contents during pregnancy
pH falls (3.0 -> 2.4) Volume increases (0.24 -> 0.49 ml/kg)
43
Risks of GA which are increased in pregnancy
Gastric contents aspiration Hypoxaemia Death (Due to GI changes and reduced time for airway manipulation)
44
Methods to reduce risks from GI changes
Reduce gastric acidity RSI
45
Gestation from which all pregnant women should have RSI and considered high risk of aspiration
All women over 16 - 18 weeks should have RSI Prior to 16 weeks gestation, if there are no other risk factors, then RSI is not mandatory
46
How soon after delivery is RSI still mandatory for GA
Withing 48 hours of delivery RSI is mandatory After 48 hours, risk of gastric contents returns to pre-pregnancy levels
47
Haematological changes in pregnancy
Plasma volume rises RBC volume increases Hypercoagulability
48
Why does Hb concentration fall during pregnancy
RBC volume increase to compensate for blood loss at delivery, but not as much as plasma volume increases, therefore [Hb] falls
49
Lower limit of normal Hb concentration for pregnant women
110
50
Cause of hypercoagulability in pregnancy and therefore raised VTE risk
Raised plasma levels of: - Fibrinogen - Factor VII - Factor X - Factor XII Decreased fibrinolysis
51
Neurological changes in pregnancy with implication on anaesthesia
Reduced doses of drugs are required to induce and maintain general and regional anaesthesia MAC for inhaled agents typically reduced by ~30% From late first trimester onwards local anaesthetic dose typically reduced by ~30% for regional anaesthesia Induction dose for IV agents also reduced
52
Renal changes in pregnancy
Rise in: - GFR - Kidney size - Urinary collecting system size - Glycosuria - Proteinuria
53
Amount GFR rises in pregnancy
50-70% increase
54
Cause for increased glycosuria in pregnancy
Rise in GFR can overwhelm capacity for tubular re-absorption of glucose
55
Why are UTIs and pyelonephritis more common in pregnancy
Dilated urinary collecting system (renal pelvis + calyces + ureters) leads to tendency of urine stasis Also increased glycosuria
56
Upper limit of normal proteinuria level in pregnancy
300 mg/24 hr collection
57
Changes to plasma albumin concentration in pregnancy
Albumin concentration falls in early pregnancy and is then static up to term
58
Mean urea concentration in pregnancy
3.3 mmol/L
59
Mean creatinine concentration in pregnancy
51 micromol/L
60
Hormones which change in pregnancy
Progesterone Human chorionic gonadotrophin (hCG) Human placental lactogen (hPL) Aldosterone
61
Progesterone changes in pregnancy
Concentration rises to a peak near term Falls just before term - may contribute to initiation of labour Progesterone responsible for many of the physiological changes of pregnancy Vital for maintenance of pregnancy
62
Alternate name for hPL (human placental lactogen)
Chorionic somatomammotrophin
63
hPL features
Peptide hormone Structure and function similar to growth hormone
64
Consequence of raised hPL
Causes impaired glucose tolerance due to insulin resistance
65
Aldosterone changes in pregnancy
Aldosterone secretion from adrenal cortex increases Results in Na+ and water retention
66
Metabolic changes in pregnancy
Rise in maternal basal metabolic rate Also contributes to increased oxygen consumption
67
hCG features
Peptide hormone Produced by embryo and later by placenta
68
Role of hCG in pregnancy
Maintain the corpus luteum and hence maintain progesterone production Possible has a role in the altered immune system in pregnancy

Anaesthetic FRCA Primary - eLFH Obstetrics (6 decks)

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