Past Papers · SAQ
Applied Respiratory Physiology — Pregnancy
2023A Q18
Exam questionExplain the respiratory changes that occur at term in pregnancy.
CICMWrecks answer
Master answer
Respiratory Changes In Pregnancy
Anatomical
- Diaphragm ascends ~4cm due to foetus
- AP and lateral diameters of thorax increase 2~3cm due to relaxin effect on chest
wall - Thoracic circumference increases 5~7cm (AP and lateral diameters increased 2~3cm)
- Airway dilatation → decreased resistance (35%) and increased deadspace (45%)
- Increased cardiac output, intravascular volume, and decreased oncotic pressure
- Increased plasma volume → increased pulmonary blood volume → decreased compliance
- Venous engorgement → Upper airway oedema
Mechanical
- Lung volume changes occur from 20 weeks
- TLV decreases 5% from baseline
- FRC decreased 20% due to both ERV and RV
- Significant postural change in FRC of 70%
- Progesterone → increased sensitivity to CO2 → Minute ventilation increases 50%
- TV increases (25%)
- RR increases
- Results in hypocarbia and compensated respiratory alkalosis
- pCO2 ~ 26-32mmHg
- HCO3 ~ 18-20mmol/l
- Further increase in MV during contractions
- Inspiratory capacity increased by 10%
- Closing capacity unchanged
- Increased O2 consumption during labour (60%)
After birth
- FRC and RV return to normal within 48 hours
- TV returns to normal within 5 days
Sakurai 2016
Past papers