Carbon monoxide poisoning during pregnancy

Objective 

To present a case of carbon monoxide poisoning during pregnancy and to discuss the maternal and fetal effects of carbon monoxide

Methods 

A 32-year-old pregnant woman was admitted to Başkent University Ankara Hospital as she had a syncope due to carbon monoxide poisoning at the 15th week of her pregnancy. Her initial evaluation and treatment as well as the perinatal follow-up is presented.

Results 

The patient’s physical examination was unremarkable at the emergency department. Oxygen was applied with mask immediately and laboratory analyses were performed. Carboxyhemoglobin (CO-Hb) level was 31%. Complete blood count and liver and renal function tests had normal results. She was hospitalized and followed at the intensive care unit. Sonography revealed a fetal heart rate of 160/min. After several hours, she was referred to another hospital for hyperbaric oxygen therapy. The case was discussed at the perinatology council and it was concluded that her CO-Hb level was higher than 15% and this might have caused fetal hypoxia leading to death or severe neurological sequelae. Structural screening was normal as well as cranial anatomy in the detailed ultrasonography which was performed at the 20th week of gestation. Fetal magnetic resonance imaging was performed at the 23th week of gestation and was reported to be normal. The patient and her husband opted for continuing the pregnancy.
The patient delivered vaginally a healthy male infant weighing 2,930 g at the 39th week of gestation in May 2014. The Apgar scores at 1 and 5 min were 8 and 9 respectively. Blood gas analyses revealed to be normal. Lactate level (3.6 mmol/L) was higher than the upper limit.

Conclusion

CO poisoning during pregnancy causes maternal then fetal tissue hypoxia primarily by binding to hemoglobin. It has a higher affinity for fetal hemoglobin thus its transplacental passage may cause fetal harm, predominantly in the brain. Hyperbaric oxygen therapy may reduce the risk to the fetus.
Acute maternal CO poisoning is associated with a maternal mortality between 19 and 24% and a fetal mortality between 36 and 67%. In the literature, some predictors about fetal outcome are defined, such as severity of maternal involvement, gestational week at which the poisoning occurred. Placental CO diffusion capacity increases with gestational age and in proportion to fetal weight. Anatomical malformations, especially skeletal abnormalities such as limb malformations are more frequent if intoxication occurs in early gestation. During the late gestation, fetal brain seems to be more sensitive to CO leading to anoxic encephalopathy. However, involvement at any stage of pregnancy may cause functional defects in psychomotor and mental development. In our case, the newborn did not have any symptoms attributable to CO exposure, but 3 months of age is too early to tell about his psychmotor and mental development.

Keywords

Pregnancy, carbon monoxide, poisoning