Introduction:
Physiological hyperventilation and dyspnoea in pregnancy is well-established and mild dyspnoea begins in the first or second trimester. We report the case of a 35-year-old female with severe physiological hyperventilation of pregnancy from 18 weeks’ gestation until delivery.
Case:
A 35-year-old (G4P3) presented at 18 weeks’ gestation with profound dyspnoea, presyncope, upper limb paraesthesia and limited exercise tolerance to 20m.
Examination revealed tachypnoea at 24 breaths per minute, increased work of breathing and ability to speak in short sentences. Oxygen saturations were 100% on room air, blood pressure was 116/66mmHg and pulse rate 80 beats per minute.
Arterial blood gas demonstrated a chronic respiratory alkalosis with partial metabolic compensation. Extensive brain, cardiac and pulmonary investigations were unremarkable.
Discussion
Hyperventilation and dyspnoea occur during pregnancy secondary to physiological adaptations. Respiratory rate increases approximately 40% towards the end of the third trimester. (1) Importantly, this increase is associated with a higher tidal volume, while respiratory rate remains unchanged. (2) Our patient had a persistent and sustained tachypnoea ranging from 22-26 breaths per minute from 18 weeks’ gestation to term.
Progesterone-induced hyperventilation is considered a key driver in increasing ventilation during pregnancy to meet metabolic demands. (3) Progesterone increases the sensitivity of the respiratory centre to carbon dioxide via an estrogen-dependent progesterone-receptor mediated facilitation of central neural mechanisms, independent of hydrogen and the respiratory chemoreflexes. (4, 5)
Hyperventilation with respiratory alkalosis is secondary to more complex interactions than simply hormonal-induced changes in setting of a complex interplay between acid-base
balance, wakefulness drives breathe, increased metabolism and decreased cerebral blood flow. (4) This in combination with this case demonstrates while there has been advances in the understanding of respiratory adaptations in pregnancy, the complete underlying pathophysiology is not entirely clear.
Conclusion:
This case highlights a rare case of severe tachypnoea and dyspnoea secondary to exaggerated physiological hyperventilation in pregnancy. Since physiological dyspnoea in pregnancy remains a diagnosis of exclusion, it remains vital to ensure underlying pathological dyspnoea is excluded.