Obstetrics

Hyperbaric oxygen therapy in carbon monoxide poisoning in pregnancy: Maternal and fetal outcome

a b s t r a c t

Objective: Closer monitoring and treatment is vital for pregnant Carbon monoxide poisoning cases due to fetal poisoning component. Permanent damage can occur in both the mother and the baby. It may cause stillbirth even though no serious clinical symptoms occur in the mother. Hyperbaric oxygen (HBO) treatment is advised for all pregnant patients regardless of their clinical symptoms. Pregnant CO poisoning patients that received HBO treatment and their fetal status were evaluated in this study.

Methods: Pregnant patients poisoned with CO treated in the same hyperbaric clinic were evaluated. Pregnant pa- tients that received HBO treatment in a multiplace chamber were evaluated in terms of clinical status, demo- graphic structure, laboratory tests, fetal effects and progress of the fetus until birth and 6 months postpartum. Results: A total number of 32 pregnant cases were treated. COHb values were over 20% (min 6.9- max 40.2) in 23 patients, 11 patients had a history of syncope. All patients took HBO treatment under 2.4 ATA pressure for 120 min. 3 patients received more than 1 session of HBO treatments due to fetal stress; all other cases took 1 ses- sion of HBO treatment. No spontaneous abortus occurred in early follow-ups; only 4 babies were born prema- turely. 2 of the babies were lost in the early phases after birth, due to causes non-related to CO poisoning complications (cyanotic heart disease, necrotising enterocolitis). No significant difference were observed in the comparison of laboratory results of Patients with syncope and of those who did not have syncope and compar- ison of patients with COHb value higher than 20% and patients with COHb value lower than 20% (p > 0.05).

Conclusion: HBO is not advisable for pregnant patients except for CO poisoning. In this study it is observed that HBO treatment under 2.4 ATA pressure for 120 min has no harmful effects on the mother and the fetus. It is ob- served that continuation of HBO treatment in the cases with fetal distress findings has beneficial effects. COHb levels and syncope were shown to have no significant effect on clinical symptoms and on blood tests.

(C) 2021

  1. Introduction

carbon monoxide poisoning still cause a significant degree of mortality and morbidity in many countries. Abnormal levels of accumulation of this colorless, odorless and tasteless gas cause symptoms of poisoning. A wide range of symptoms like headache, flu-like symptoms can be seen and they may vary up to coma and death. Diagnosis can be difficult due to the fact that clinical symp- toms vary depending on the severity of the poisoning [1,2]. CO in- hibits not only heme containing hemoglobin and myoglobin but also cytochrome oxidase and cytochrome p450. Studies have indi- cated that CO cause lipid peroxidation and free radical formation. It causes defects on highly oxygen depending cerebral and cardiac organs [3]. Hyperbaric Oxygen (HBO) treatment is a treatment mo- dality that has been used effectively for CO poisoning for years. It is

* Corresponding author at: Necmettin Erbakan University, Meram Faculty of Medicine, Department of Underwater and Hyperbaric Medicine, Meram, 42080 Konya, Turkey.

E-mail address: arsabdullah@gmail.com.

applied as continuous or intermittent breathing of oxygen under pressures higher than 1 absolute atmospheres. HBO treatment ele- vates partial oxygen pressure independent of hemoglobin, avoids lipid peroxidation and facilitates delivery of oxygen to tissues by shifting oxyhemoglobin dissociation curve to the right. Blood elimi- nation time of CO is significantly lower with HBO when compared to normobaric Oxygen treatment. Cerebral oxidative damage and late neurological symptoms were shown to be avoided with HBO treatment [4-6].

CO is the most common cause of the household poisonings [7]. Preg- nant CO poisoning cases have special importance among other cases; the fetus may be more affected than the mother to CO exposure. Fetal poisoning can be more severe due to fetal hemoglobin’s higher affinity to CO. Fetal COHb starts to rise later than the mother’s and reaches its peak over a longer period of time. CO levels are thought to be 10-15% higher in fetal blood. Fetal COHb elimination time is longer than the mother. It may cause stillbirth even though no serious complications are observed in the mother [8]. It is important to evaluate all pregnant CO poisoning cases for HBO treatment [8,9]. Studies with large series

https://doi.org/10.1016/j.ajem.2021.01.007

0735-6757/(C) 2021

of cases and studies about the treatment pressure, duration and number of sessions are very limited in the literature. Pregnant CO poisoning cases treated with HBO treatment are evaluated in this study.

Table 1

Demographic features.

n (%)

  1. Materials and method

Pregnant CO poisoning cases treated with HBO treatment between the dates January 2016-March 2019 were evaluated in this study. Local ethical committee approval was adopted. Patients were treated

Mean Age 25.09 +- 7.26 (min17- max 40)

Gestational Week 23.18 +- 8.50 (min 8- max35)

Immigrant Patient 6 (18.75%)

gestational diabetes 4 (12.50%)

Preeclampsia 0

Education

None 14 (43.75%)

in a multiplace chamber with a chamber attendant. Patients were trans-

Primary School

4 (12.50%)

ferred for HBO treatment right after the diagnosis in the emergency de-

Junior High School

6 (18.75%)

partment or peripheral centers. Poisonings related only to CO exposure

at homes or in work environment were included in the study. Patients stayed in the multiplace chamber with a chamber attendant for

High Scholl

University Gravity

1

7 (21.87%)

1 (3.12%)

12 (37.50%)

120 mins; the sessions consist of compression to 45 ft depth (2.4 ATA)

2

6 (18.75%)

in 15 min, breathing 100% oxygen in three periods of 25 min and

3

5 (15.62%)

5 min of air-breaks between the oxygen periods and 20 min of decom-

pression (Fig. 1). Patients took normobaric oxygen treatment with 100%

4

5

Parity

6 (18.75%)

3 (9.37%)

FiO2 for 24 h following HBO treatment. Patients were monitored in the

1

14 (43.75%)

intensive care unit until total clinical recovery, with a minimum follow-

2

5 (15.62%)

up time of 48 h. HBO treatment was continued if maternal and fetal

3

6 (18.75%)

symptoms persist.

Sociodemographic features of the patients, clinical status due to CO

4

5

6 (18.75%)

1 (3.12%)

poisoning of the mother and their laboratory results, fetus related data

were evaluated. Birth information of the fetuses, pre and postnatal health problems were questioned. Data about the ongoing pregnancy and birth was followed after the patient was discharged from the hospi- tal following HBO treatment. Data of the mother and fetus was collected 6 months postpartum from national medical record system and through phone calls of the patient. SPSS 18.0 statistics programme was used in the comparison of patient data. Definitive statistics were documented as mean value and standard deviation for continual numeric variables, as numbers and percentage (%) for categoric variables. Student t-test was used for group comparisons. Results were presented in tables and graphics.

  1. Results

32 pregnant patients with CO poisoning were treated in the study. 1 of the patients had 2 episodes of poisoning in different times of the same pregnancy. Sociodemographic data of the patients is presented in Table 1.

Vast majority of the patients (28 patients, 87.5%) had an education level of junior high school or lower. 4 of the patients (12.5%) had

gestational diabetes, none of the patients had preeclampsia. 3 patients were poisoned at work; 29 of the patients were poisoned by stoves at home or in the tents they live. In 30 of the cases other people in the same environment were poisoned too.

Mean COHb of the patients on admission was 24.9 +- 8.8 (min 6.9- max 40.2). In 23 cases (69.9%) COHb levels were higher than 20. 11 of the cases (33.3%) had syncope. 9 patients (27.2%) had troponin ele- vation, 4 patients (12.1%) had creatin kinase elevation, 5 patients (15.1%) had CK-MB elevation, 9 patients (27.2%) had lactate eleva- tion, 8 patients (24.2%) had LDH elevation, 4 patients (12.1%) amy- lase elevation, 16 patients (48.4%) had WBC count elevation. 22 patients (66.6%) had a drop in HCO3 levels (Table 2). Mean time until HBO treatment after poisoning was 5.424 +- 2.88 h (1-15). All patients were either conscious or confused; none of the patients were comatose or intubated. 13 patients (39.39%) were transferred from different cities for HBO treatment and 100% oxygen was applied via a reservoir mask during the transport. 27 patients (84.4%) had 1 session, 3 patients (9.3%) had 2 sessions, 1 patient (3.1%) had 3 ses- sions of HBO treatment; the patient who had 2 episodes of poisoning

Image of Fig. 1

Fig. 1. hyperbaric oxygen therapy profile.

Table 2

CO intoxication and HBOT data.

COHb (%)

24.9 +- 8.8 (min 6.9- max 40.2)

COHb > %20

20 (69.6%)

COHb < %20

13 (30.4%)

Syncope

Number of HBOT Sessions

11 (33.3%)

1 session

27 (81.8%)

2 sessions

5 (15.2%)

3 sessions

1 (3.0%)

Time until HBOT (Hours) 5.42 +- 2.88 (min 1- max 15)

Transfer from a different city 13 (39.39%) Intoxication location

Home 29 (87.9%)

Work 4 (12.1%)

Table 4

Blood tests definitive analysis (results). Descriptive statistics

N

Minimum

Maximum

Mean

Std. Deviation

COHb

33

6.9

40.2

24.86

8.80

Lactate

33

0.85

5.10

1.75

0.86

HCO3

33

16.0

24.3

20.34

2.35

Troponin I

33

0.00

1.41

0.11

0.287

LDH

33

110

345

211.97

51.87

CK

33

23

553

88.77

100.30

CK-MB

33

3.5

45.0

19.04

9.06

ALT

33

6

27

11.68

4.69

AST

33

10

36

20.13

5.77

Amylase

33

39

162

71.28

27.59

WBC

33

5460

22,100

11,125.48

3666.48

PLT

33

109,000

339,000

223,935.48

63,565.68

in 15 days had 2 sessions of HBO in the first poisoning and 1 session of HBO in the second one. Patients took 100% oxygen with a non-breather bag mask for 24 h following the HBO treatment. Patients were moni- tored at least for 48 h and discharged after clinical recovery.

No miscarriages happened in the follow-ups; 4 patients had prema-

Table 5

Statistical comparison.

Blood tests

ture births (32-34. weeks). 2 babies died after birth. One of the babies died due to congenital cyanotic heart disease diagnosed before the CO poisoning. The other baby was born from a twin pregnancy at 33rd week with a birth weight of 1800 g and with respiratory distress; he was intubated and monitored in the newborn intensive care unit (ICU). The baby was lost after necrotising enterocolitis and rectal bleed- ing. Other follow-up babies were born term and with normal birth weights. 22 patients (68.75%) had vaginal birth, 10 patients (31.25%) had C-sections. No congenital abnormalities or developmental problems were recorded in babies except the 2 babies lost after birth. No significant difference was observed when blood tests (Troponin, CK, CK-MB, HCO3, AST, ALT, amylase, lactate, WBC) of patients with COHb values over 20 and under 20 are compared (p > 0.05). No signif- icant difference in terms of blood tests was observed when patients with syncope were compared to those who did not have syncope (p > 0.05). (See Tables 3-5.)

  1. Discussion

Closer evaluation and treatment is vital for pregnant CO poisoning cases due to fetal poisoning component. It is difficult to diagnose mild poisonings due to common symptoms like headache, vertigo, fatigue and dizziness [1,10,11].

CO is the most common cause of the household poisonings among Developing countries [7]. Poisoning cases in western countries are mostly due to exposures to the burning of carbon based fuels in engines [4]. Usage of coal and wood burning stoves elevates the number of CO poisoning cases in winter [12]. It is easier to diagnose when more than one member of the residents of the house develop similar symptoms. In this study 87.5% of the patients were poisoned with at least another person in the same household. Poor housing accommodations of recent immigrants, without adequate heat sources or ventilation, may have put

Table 3

Pregnancy follow up after CO intoxication.

Premature birth

4 (12.50%)

Birth method

Vaginal birth

22 (68.75%)

C-section

10 (32.25%)

Babies with abnormalities 2 (6.25%)

Hospitalisation in the newborn ICU 4 (12.50%) Baby sex

Female 13 (39.4%)

Male 20 (60.6%)

Syncope +/ Syncope – p > 0.05

COHb > %20/COHb<20 p > 0.05

them more at risk for carbon monoxide poisoning. In our study 7 of the patients (21.87%) were immigrants and citizens of another country. 87.5% of the patients had junior high school or lower level of education. Only 2 patients were graduated from high school and 2 had university education. Using coal and wood stoves or unsuitable heating systems is a determinant of Lower socioeconomic status and the definition matches our study group [8,12]. None of the patients reported prior CO poisoning. One patient had two episodes of CO poisoning in the work environment in the same pregnancy; within 15 days. The patient was poisoned again 15 days following the first episode, even though she was informed about the poisoning and prevention methods. CO poison- ing should be considered in differential diagnosis in patients using stoves, especially in winter months [1,13].

Reported Maternal mortality is 19-24%, fetal mortality is 36-67%; depending on the gestational age and the degree of the maternal poi- soning [9,11]. CO diffusion gets higher as the gestational age and fetal weight increase [14]. Fetal death is possible even though maternal poi- soning is mild [14,15]. CO half-life is 2 h for the mother whereas it is 7 h for the fetus. This is why HBO is recommended to be applied for longer durations for pregnant CO poisoning cases [8]. In this study 10 patients had syncope; all patients had dizziness, fatigue and headache symp- toms. None of the patients were comatose or intubated. But some of the patients had elevations of cardiac, muscle and blood gas levels in the blood due to hypoxia (Table 2). Mean time until HBO treatment after poisoning was 5.42 +- 2.88 h (1-17). One of the patients was treated with HBO more than 10 h after poisoning; all other patients re- ceived the treatment in 10 h or shorter. It was aimed to minimize the maternal and fetal exposure time by applying HBO treatment as soon as possible. No maternal or fetal deaths due to poisoning occurred in our study. Early intervention with HBO treatment and normobaric 100% oxygen lead to good results in early phases of CO poisoning, but 4 premature births and 2 fetal deaths occurred in natal phase.

CO poisoning is reported in the literature to elevate rates of prema-

ture births and teratogenic effects [7,16-18]. Preterm delivery, hypoxic ischemic encephalopathy, hypotonia, cerebral palsy, areflexia, persis- tent seizures, microcephaly, cardiomegaly, limb malformations are the reported fetal morbidities [9]. In our study in the follow-up after HBO treatment, 4 babies were prematurely born (32-34. weeks). 4 babies were hospitalized in the newborn ICU and 2 babies died. One of these babies was lost due to congenital cyanotic heart disease diagnosed

prior to poisoning; the other baby was born prematurely at 33rd week from a twin pregnancy and hospitalized in the newborn ICU due to re- spiratory failure. He later died due to acute respiratory distress syn- drome (ARDS), necrotising enterocolitis and Rectal bleeding. The other twin survived and had no health problems. The immigrant mother had no prior pregnancy check-ups and was reported to apply the hospi- tal only for CO poisoning related symptoms. Thus there is no clear infor- mation about the development of the baby. Other babies in the study had no birth related problems or symptoms requiring hospital admis- sions in the follow-up. Lack of early miscarriages in the study group shows the efficacy of the treatment. No teratogenical effects was ob- served in this study. C-section rate is 31.25%; which is similar to C-section rates in our country [19].

It is recommended to continue HBO treatment in case poisoning ef- fects persist in the mother or the fetus [6,12,20]. In this study 4 of the 32 patients received 2, 1 patient had 3 sessions and 1 patient had a total of 3 sessions with a 15 day gap. HBO treatment was continued in these pa- tients because fetal stress was observed in the fetal USG held after the session. 13 patients (39.4%) were referred from different clinics so im- mediate HBO therapy was held in order not to lose time; this is why all of the patients could not be evaluated with USG for fetal distress, prior to HBO. Patients took 3 periods of oxygen treatment daily under

2.4 ATA pressure; each oxygen period was 25 min (Fig. 1). HBO is re- ported to have a possibility of causing abnormalities in the fetus [21,22]. None of the babies in this study had abnormalities after birth;

2 babies were lost due to causes non-related to HBO treatment. Elkharrat et al. treated pregnant patients under 2 ATA pressure for 90 min and reported that lower treatment pressures may decrease the teratogenic effects of HBO treatment [11]. In other studies, treatments were held in different pressures and durations and no teratogenic ef- fects were reported [11,23,24]. In our study patients were treated with 120 min sessions consisting of 3 oxygen periods of 25 min, under 2.4 ATA. No problems occurred in the follow-ups of the patients. The treat- ment applied seems to be a safe method.

Applicable safe HBO therapy methods were defined in the literature. The Weaver protocol recommends application of 3 HBO sessions within 24 h [5]. These protocols are considered to be safe in terms of late-onset Neurological sequelae occurrence and morbidity. But there is no specific treatment protocol defined for pregnant carbon monoxide poisoning cases. In this study 1 session of HBO therapy was applied followed by 24 h of normobaric 100% oxygen treatment in order to avoid possible harmful effects of HBO therapy. Ongoing elimination of CO from both the mother and the fetus, minimization of the hypoxic damage, lipid peroxidation and mitochondrial damage due to the poisoning was aimed. 100% oxygen treatment with a mask was applied after HBO due to longer half-life of fetal COHb and due to the fact that fetal COHb can not be determined [6,8]. Pulmonary oxygen toxicity (absorp- tion atelectasis, acute tracheobronchitis, ARDS) was not observed in pa- tients during normobaric oxygen treatment. The normobaric oxygen treatment we applied seems to be safe since pulmonary oxygen toxicity usually occurs after continuous oxygen treatment longer than 3 days [25].

Some studies state an indication for HBO treatment for pregnant CO poisoning cases if COHb levels are higher than 20%; whereas the latest EUBS statement advises HBO treatment for all pregnant cases [8,12,26,27]. Kopelman et al., described a case of carbon monoxide poi- soning where the Carboxyhemoglobin level was only 6.9% two hours after the exposure; although the mother had mild symptoms, the baby was more severely affected for 6 days after the exposure [28]. Norman et al. reported that values over 48% is a negative prognostic parameter in most cases [7]. In this study mean COHb levels on admission was

24.9 +- 8.8% (min 6.9-max 40.2). tissue hypoxia due to blockage of blood oxygen transport leads to muscle, heart and liver enzyme eleva- tions. Syncope due to drop of oxygen because of the poisoning is re- ported as one of the indications for HBO treatment. Norman et al. reported worse Fetal outcomes for pregnant CO poisonings with coma

or Altered consciousness. In our study 11 patients had syncope. No dif- ference in terms of Blood parameters (troponin, CK and others) were detected between the patients who had syncope and those who did not (p < 0.05). Even though existence of syncope and COHb levels over 20% are reported as indication parameters for HBO treatment no difference in blood parameters was observed. COHb begins to de- crease as soon as the patient is removed from the toxic environment and starts to breath clean air or oxygen. COHb levels may drop until the patients is transferred to hospital for the initial evaluation. Half- life of carboxyhemoglobin is around 5 h on room air, 90 min on high flow oxygen, and less than 30 min with HBO [5,6]. This is why we rec- ommend HBO treatment for all pregnant CO poisoning cases regardless of the COHb levels and the existence of syncope.

Rodrigue et al. reported bias in the transfer of pregnant CO poisoning cases to HBO centers. They stated closer evaluation should be consid- ered due to teratogenic risks of HBO treatment, difficulties in transfer of an unstable pregnant case and due to the fact that most centers have monoplace chambers. They noted that an emergency C-section can be considered for pregnancies over 26th week if there is no HBO treatment center available in the hospital [17]. The number of HBO cen- ters are limited worldwide and they are usually located in big cities. Since this patient group is usually from the lower socioeconomic level and since the number of centers is limited, patient transfer is necessary in most of the cases. In this study 13 patients (39,4%) were transferred from different cities. A high percentage of the patients were transferred from different cities and 3 patients needed more than 1 session of HBO treatments. Pregnant patients should be referred to the closest HBO center regardless of their gestational time due to the fact that fetal COHb has a longer half-time and due to complications of poisoning. In this study no problems occurred during patient transfer.

To date there a few large studies in the literature about HBO treat- ment for pregnant CO poisoning cases. Elkharrat et al. used HBO treat- ment for 44 pregnant CO poisoning cases and reported 6 miscarriages and 34 term and normal births. The study stated that HBO treatment can be used safely and effectively for pregnant cases [11]. In the study of Koren et al. 38 infants were followed; 2 fetal deaths and 1 cerebral palsy was reported in 5 heavily poisoned pregnant cases. The other 2 cases underwent HBO treatment and gave birth to healthy babies [24]. In a study of 412 infants, babies were evaluated in terms of psychomotor development on the 8th day, 1st year and 6th year. No significant differ- ence in psychomotor development, height and weight parameters was detected between babies that took HBO and those who did not [29]. They stated that HBO treatment can be safely applied on infants. This study supports previous data about the safety of HBO treatment.

As stated, patients were treated with an attendant nurse inside the chamber. Patients were informed about the middle ear equalization techniques and in case of the occurrence of pain due to ear or sinus squeezing during compression phase, compression was stopped and patients were brought to treatment depth with a slow descent. So we had no patients who withdrew treatment due to barotrauma. Blood pressure and blood glucose determination in case the patient have a problem were the parameters performed inside the chamber. No hypo- glycemic episodes were observed in this study. Previous studies imple- ment the efficacy of HBO treatment pressures above 2 ATA, and suggest the use of highest applicable pressure [5,6]. 2.4 ATA is a safe treatment pressure for oxygen toxicity and so higher pressures were not consid- ered for pregnant cases in order to avoid seizures due to oxygen toxicity. No oxygen toxicity or Epileptic seizures occurred in the patients.

The limitations of this study are the retrospective nature of the study, the absence of a control group and the short follow-up period of the babies.

  1. Conclusion

Pregnant CO poisoning cases remain to be an emergency causing morbidity and mortality. Primary treatment approach for all cases

-pregnant or not- is removal of patient from the toxic environment, breathing 100% oxygen and supportive medication. HBO treatment is recommended for pregnant CO poisoning cases although the number of studies about the subject is limited. In this study patients treated with HBO treatment are evaluated and maternal and fetal results are re- ported. It is observed that 3 periods of 25 min HBO treatment under 2.4 ATA showed no negative effects on the mother or the fetus and it can be applied safely. In cases with persisting fetal distress HBO was continued and good outcomes were obtained. The study has no control group thus it should be supported with studies with larger patient groups and Hy- perbaric oxygen therapy should be considered in all pregnant CO poi- soning cases.

Declaration of competing interest

The author declared that there is no conflict of interest with this presentation.

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