Physiology of 2nd Stage

Question 1

Describe the 2nd stage of labour

Answer 1

• Full dilation to birth
• Strong contractions every 2-3 minutes lasting 1 minute
• Foetus descends down birth canal

Question 2

Name some of the features of the second stage of labour

Answer 2

• Increase contraction intensity
• Membrane rupture?
• Pressure of foetal head on sacral/ obsturator nerve
• Increased perspiration
• Stretch receptors stimulated
• Anus everted and patulous (open and spread out)
• Bulging of perineal region
• Dilated and distended vulva
• Rapid contractions with no interval
• Crowning
• Delivery

Question 3

What are the primary and secondary powers?

Answer 3

Primary power = involuntary (contraction, retraction, relaxation)
Secondary power = urge to push

Question 4

Describe crowning

Answer 4

Vulva stretches and encircles the largest diameter of the foetal head

Question 5

What can delay labour?

Answer 5

Full bladder

Question 6

What cardiovascular changes occur in the mother during 2nd stage?

Answer 6

• CO 40-50% up to 100%
• Compression of aorta and iliac arteries
• CO shifts to head and upper extremities
• BP increases by 30/25mmHg (during contraction) or 10/5mmHg (between contractions)
• Steady increase in PR to 100bpm

Question 7

Why does cardiac output increase?

Answer 7

Increase in catecholamines resulting from pain

Question 8

Give some reasons that pulse rate may increase

Answer 8

• Dehydration
• Anxiety
• Pain
• Some drugs

Question 9

What is the most accurate period of assessment for vital signs?

Answer 9

Between contractions

Question 10

What respiratory changes occur in the mother during 2nd stage?

Answer 10

• Increase in metabolism increases oxygen demand = increased RR
• PP of carbon dioxide decreases (32mmHg to 22mmHg)
• Hyperventilation common - leads to decreased PP of carbon dioxide
• Opposite effect occurs in excessive shallow breathing
• Excessive/prolonged maternal pushing causes decrease in oxygen

Question 11

What gastrointestinal changes occur in the mother during 2nd stage?

Answer 11

• Decreased motility and absorption in active phase
• Delayed emptying time
• Exaggerated after narcotic intake
• Nausea and vomiting
• Dehydration, dry lips and mouth due to breathing deeply

Question 12

What renal changes occur in the mother during 2nd stage?

Answer 12

• Full bladder may be masked by intensity of contractions and pressure of presenting parts
• May cause delayed progress/ trauma
• Diaphoresis (excessive sweating)
• Increased water loss through perspiration

Question 13

What haematopoietic changes occur in the mother during 2nd stage?

Answer 13

• 500ml (usual loss)
• 1000ml (lost in CS)
• Compensated by hypervolemia
• Slight decrease in coagulation time
• Increased plasma fibrinogen levels
• Decreased leucocyte levels as labour progresses

Question 14

What fluid and electrolyte changes occur in the mother during 2nd stage?

Answer 14

• Decrease in plasma Na and Cl levels due to decreased GI tract absorption, panting and diaphoresis
• Polyuria is common
• Analgesia may affect foetal electrolyte balance

Question 15

What should be monitored in 2nd stage?

Answer 15

• Uterine contractions
• Cervical dilation
• Descent of presenting part
• Maternal wellbeing
• Foetal wellbeing