Article, Cardiology

Association between body mass index and clinical outcomes of patients after cardiac arrest and resuscitation: A meta-analysis

a b s t r a c t

Background: Obesity as one of the risk factors for cardiovascular diseases increases mortality in general popula- tion. Several clinical studies investigated clinical outcomes in patients with different body mass index (BMI) after cardiac arrest . Controversial data regarding BMI on clinical outcomes in those patients exist in those studies. Therefore, we conducted a meta-analysis to evaluate the effect of BMI on survival condition and neuro- logical prognosis in those patients.

Methods: We searched Pubmed, Embase, Ovid/Medline and EBM reviews databases for relational studies inves- tigating the association between BMI and clinical outcomes of patients after CA. Seven studies involving 25,035 patients were included in this meta-analysis. Primary outcome was survival condition and secondary outcome was neurological prognosis. Three comparisons were conducted: underweight (BMI b 18.5) versus normal weight (18.5 <= BMI b 25), overweight (25 <= BMI b 30) versus normal weight and obese (BMI >= 30) versus normal weight.

Results: Using normal weight patients as reference, underweight patients had a higher mortality (odds ratio [OR] 1.35; 95% confidence interval [CI] 1.10 to 1.66; P = 0.004; I2 = 17%). Overweight was associated with increased hospital survival (OR 0.80; 95% CI 0.65 to 0.98; P = 0.03; I2 = 62%) and better neurological recovery (OR 0.72; 95% CI 0.61 to 0.85; P b 0.001; I2 = 0%). No significant difference was found in clinical outcomes between obese and normal weight patients.

Conclusions: Low BMI was associated with lower survival rate in CA patients. Overweight was associated with a higher survival rate and better neurological recovery. Clinical outcomes did not differ between obese and normal weight patients. Further studies are needed to explore the underlying mechanisms.

(C) 2018

Introduction

The prevalence of obesity is rapidly increasing worldwide [1]. Obesity has been implicated as one of the major risk factors for car- diovascular diseases. It induces cardiac alterations called obesity cardiomyopathy and increase ventricular electrical irritability,

Abbreviations: BMI, body mass index; CA, cardiac arrest; CAD, coronary artery disease; CHD, coronary heart disease; CI, confidence interval; CPC, Cerebral Performance Category; CPR, cardiopulmonary resuscitation; CVD, cardiovascular disease; ECMO, extracorporeal membrane oxygenation; ECPR, extracorporeal cardiopulmonary resuscitation; ICU, intensive care unit; IHCA, in-hospital cardiac ar- rest; NOS, Newcastle-Ottawa Scale; OHCA, out-of-hospital cardiac arrest; OR, odds ratio; TTM, Targeted temperature management; VF, ventricular fibrillation; VT, ventric- ular tachycardia; WC, waist circumference; WHO, World Health Organization; WHR, waist-to-hip ratio.

* Corresponding author.

E-mail addresses: [email protected], (L. Zhang), [email protected]. (H. Yu).

1 These authors contributed equally to this article.

thus leading to higher mortality rate compared to general popula- tion [2,3]. However, evidence from clinical cohorts indicates an obesity paradox in overweight and obese patients who seem to have a more favorable prognosis in heart failure [4,5], atrial fibrilla- tion [6,7] and cardiovascular disease patients [8,9]. This phenome- non was also observed in critically ill patients and the patients underwent cardiac surgery [10-12].

Patient with Cardiac arrest and cardiopulmonary resuscitation (CPR) generally have poor prognosis [13,14]. The role of obesity in me- diating outcomes for CA and CPR is unknown. Theoretically, it might be more difficult to resuscitate obese patients because of difficulties in pro- viding adequate chest compressions, Ventilation and oxygenation [15]. Recent studies investigated the association between body mass index (BMI) and the prognosis of CA patients. The outcomes, including short and long survival rate, and neurological recovery, were not consistent. Several studies found that overweight or slight obese patients had bet- ter overall survival condition and neurological prognosis [15-17]. How- ever, in one cohort study conducted by Geri et al., obesity was revealed to be independently associated with 30-day mortality [18]. In some other studies, no significant influence of BMI on survival condition

https://doi.org/10.1016/j.ajem.2018.03.079

0735-6757/(C) 2018

was found in patients underwent CA [19-21]. Most of these studies showed that low BMI was associated with lower rate of survival after CA and CPR. However, the impact of obesity on clinical outcomes of pa- tients underwent CA and CPR is still debated.

Therefore, we performed a systematic review and meta-analysis to explore the association between BMI and clinical outcomes in patients after CA and CPR.

Methods

We followed the PRISMA statement for meta-analysis. Ethical ap- proval and patient consent are not required in a meta-analysis.

Literature search strategy

Pubmed, Embase, Ovid/Medline and EBM reviews (EBM Reviews Cochrane Central Register of Controlled Trials and EBM Reviews Cochrane Database of Systematic Reviews) were searched for relational studies investigating the association between BMI and clinical outcomes of patients after CA by the end of September 2017. The search items were: (a) body weight OR BMI OR body mass index OR obesity OR over- weight OR underweight, (b) cardiac arrest OR cardiopulmonary resusci- tation. The combination of (a) and (b) composed the completed search strategy.

Study selection

Studies meeting the eligibility criteria were pooled into the meta- analysis. The inclusion criteria were as follows: (a) adult patients suf- fered CA of any etiology, (b) the patients were divided into different groups according to World Health Organization (WHO) BMI classifica- tion, (c) clinical outcomes should include the survival condition of pa- tients. Studies that used standard WHO BMI classification cutoffs were also included in this meta-analysis, even though the studies did not fur- ther classify for underweight or severe obese patients. We excluded studies such as case reports, reviews, editorials, animal studies, pediatric studies and the studies that did not report BMI classification or out- comes of interest.

Three authors (YM, LZ, and LLH) independently screened the studies fulfilling the eligibility criteria based on title and abstract after eliminat- ing the duplicates. In case of any possible mistakes, three authors to- gether performed a full-text assessment for final inclusion. Another reviewer (HY) would be consulted if disagreements were still remained.

Type of outcome measures

The primary outcome was survival condition (hospital discharge or longer survival condition) of patients underwent CA with different BMI classification. The secondary outcome was neurological recovery. neurological status of patients was described with Cerebral Perfor- mance Category (CPC). CPC is a five-category scale that ranges from good recovery to death and CPC 1-2 was defined as neurological recov- ery [22].

Data extraction

The following characteristics were extracted: authors, journal, year, place of CA, population, study location, conduct time, study design, a full description of the BMI classification used, primary outcomes and secondary outcomes. The data of baseline characteristics of CA patients, such as age, witnessed arrest rate, bystander CPR rate and comorbidities were also extracted. Data extraction was performed in duplicate by 3 re- viewers (YM, LZ and LLH) and then reached consensus.

Heterogeneity analysis

We did analyses on heterogeneity and reported them as the I2-test. Heterogeneity was classified into none, low, moderate, and high thresh- olds according to the I2 values of 0-24.9%, 25-49.9%, 50-74.9%, and 75-100% respectively [1]. If there was a high level of heterogeneity, sub- group analysis was conducted to figure out the source of heterogeneity.

Quality assessment

We assessed the quality of all studies included in this meta-analysis by using Newcastle-Ottawa Scale (NOS) [23]. NOS is a scale that evalu- ates bias of individual nonrandomized study via patient selection, com- parability and outcome, ranging from 0 to 9 points. Two authors (YM and LLH) checked quality of the seven studies independently. The study with score b 4, from 4 to 6 and N6 were regarded as low, interme- diate and high quality, respectively.

Statistical analysis

We analyzed the association between BMI and patients’ clinical out- comes, involving survival condition and neurological recovery. The ef- fect estimates of discontinuous variables were reported as odds ratio (OR) with the corresponding 95% confidence interval (CI) and summa- rized by forest plots. All the data were analyzed using Review Manager (RevMan Version 5.3) with a random-effects model regardless of the heterogeneity level. P value b 0.05 in 2-sided t-test was regarded as sta- tistical significance.

Results

Study identification and study characteristics

There were 3014 studies identified according to our research strat- egy from the following databases: PubMed, EMBASE, OVID and EBM re- views. After duplication, 1995 studies were screened by three authors independently. By reviewing title and abstract, 1979 studies were ex- cluded because of inconsistent article type, targeted patients and inter- ventions. Sixteen studies with full-text were further assessed for eligibility and nine studies were excluded because of undefined BMI classification, no original data of interested clinical outcomes or irrele- vant studies. Finally, seven studies were included in our meta-analysis [15-21]. The flow diagram of inclusion and exclusion of studies were de- scribed in Fig. 1.

Seven studies were conducted between 1990 and 2015 from United States of America [15,16,20], France [18], Italy [19], Korea [17] and Australia [21]. All seven studies were observational studies. There were four prospective studies [15,16,18,21] and three retrospective studies [17,19,20]. The total number of the patients that involved in this meta-analysis was 25,035. Of the seven studies, three studies [16- 18] included out-of-hospital cardiac arrest (OHCA) patients (n = 1499), two studies included in-hospital cardiac arrest patients (n = 21,437), and two studies included both OHCA and IHCA patients (n = 2099). Three studies [17,18,20] included CA patients who treated with targeted temperature management . One study [19] in- cluded CA patients who treated with extracorporeal cardiopulmonary resuscitation , which is extracorporeal membrane oxygenation life support. In five studies [15,18-21], BMI was classified ac- cording to WHO classification: underweight (BMI b 18.5), normal weight (18.5 <= BMI b 25), overweight (25 <= BMI b 30) and obese (BMI

>= 30). Patients in one study were divided into three groups according to BMI classification: low to normal weight (BMI b 25), overweight and obese [16]. Considering the very small population of low weight co- hort in the study, the low to normal weight group was reckoned to nor- mal weight in this meta-analysis. In the study conducted in Korea [17], BMI was categorized according to WHO classification for Asian

1272 Y. Ma et al. / American Journal of Emergency Medicine 36 (2018) 12701279

population. Study characteristics of the included papers were shown in Table 1. Patients’ baseline characteristics in the involved studies were reported in Table 2.

Quality assessment of included studies

Among the seven studies, six studies scored N6 were considered to be of high quality [15,16,18-21] and one study scored 6 was considered to be of intermediate quality [17]. There were no studies that should be excluded because of low quality. Quality assessment of all studies in- cluded in this meta-analysis was reported in Supplementary Table S1.

Association between BMI and survival condition in patients underwent CA

All seven studies reported survival conditions of patients underwent CA. Three studies reported survival rate at hospital discharge [15,19,20]. The other studies reported longer survival conditions. Geri et al. re- corded 30-day and 1-Year survival rates in OHCA patients, and the out- come of longer survival condition was involved in this meta-analysis. Six studies compared survival conditions between underweight and normal weight groups, and we found that the underweight patients had a lower survival rate (OR 1.35; 95% CI 1.10 to 1.66; P = 0.004; I2

= 17%) (Fig. 2A). There were seven studies that compared survival

condition of patients with normal weight and overweight. This meta- analysis found no significant difference of overall survival condition be- tween these two groups, and there was a high heterogeneity between the seven included studies (OR 0.88; 95% CI 0.72 to 1.07; P = 0.20; I2

= 75%) (Fig. 2B). To determine the source of heterogeneity, we made subgroup analysis. We found that overweight patients had a higher sur- vival rate at hospital discharge (OR 0.80; 95% CI 0.65 to 0.98; P = 0.03; I2

= 62%) (Fig. 3). Considering the heterogeneity of the study population, we did subgroup analysis to investigate the influence of place of CA on survival condition of overweight and normal weight patients. We found that the heterogeneity in studies involved only IHCA patients and only OHCA patients were still marked. We also found that the stud- ies involved both IHCA and OHCA patients showed that overweight pa- tients had a better survival condition compared with normal weight patients (OR 0.79; 95% CI 0.65 to 0.96; P = 0.02; I2 = 0%) (Fig. 4).

Three studies only involved the patients who received TTM and other studies involved all of the CA patients. We did subgroup analysis and found that the heterogeneity were still high. Analysis of studies involved all CA patients regardless of treatments showed a higher survival rate in overweight patients (OR 0.77; 95% CI 0.64 to 0.93; P = 0.007; I2 = 68%) (Fig. 5). There was no significant difference of survival rate between obese and normal weight patients (OR 0.90; 95% CI 0.74 to 1.10; P = 0.31; I2 = 67%) (Fig. 2C). In subgroup analysis regarding the heteroge- neity of study population, we found that the studies involved only

Image of Fig. 1

Fig. 1. PRISMA flow diagram.

IHCA patients revealed a higher survival rate in obese patients com- pared with normal weight patients (OR 0.80; 95% CI 0.73 to 0.87; P b 0.00001; I2 = 0%). Heterogeneity was still marked between studies in- volved only OHCA patients. No difference was found in studies involved both IHCA and OHCA patients (Fig. 6). There was no difference between obese and normal weight patients who received TTM in survival condi- tions (OR 1.22; 95% CI 0.61 to 2.44; P = 0.57; I2 = 73%). Studies that re- gardless of treatments showed that obese patients had a higher survival rate compared with normal weight patients (OR 0.80; 95% CI 0.74 to 0.86; P b 0.00001; I2 = 0%) (Fig. 7).

Association between BMI and neurological outcomes in patients underwent CA

There were five studies that reported neurological recovery condi- tions of patients underwent CA. Of the five studies, four studies [16,17,19,20] reported discharge rate with neurological recovery (CPC 1-2) or poor neurological outcome (CPC 3-5) and one study [21] re- ported neurological recovery at 6th-month. Meta-analysis of four stud- ies showed no significant difference of neurological outcome between underweight and normal weight patients (OR 0.94; 95% CI 0.58 to 1.53; P = 0.82; I2 = 11%) (Fig. 8A). Of note, there was a significant better neurological outcome in overweight patients compared with normal weight patients (OR 0.72; 95% CI 0.61 to 0.85; P b 0.001; I2 = 0%) (Fig. 8B). We did not find the difference of neurological outcome be- tween obese and normal weight patients (OR 0.86; 95% CI 0.69 to 1.07; P = 0.17; I2 = 0%) (Fig. 8C).

Sensitivity analysis

After excluding the study conducted by Bunch et al. that did not re- port a further classification of underweight and normal weight patients, survival condition and neurological outcome of those patients did not change (Supplementary Fig. S1). We also did sensitivity analysis to eval- uate whether excluding the study conducted by Jung et al. that involved non-standard WHO BMI classification and of intermediate quality

would change the overall conclusions. Of note, there was a significant increase of survival condition of overweight patients compared with normal weight patients (OR 0.81; 95% CI 0.68 to 0.95; P = 0.009; I2 = 60%) (Supplementary Fig. S2). This meta-analysis involved one study that included 21,237 patients, which may play the most important role in the outcomes. After excluded the study by Jain et al., no signifi- cant differences were found in survival conditions between different groups (Supplementary Fig. S3). We excluded the study by Testori et al., the only study that reported CPC at 6th month, and we found no significant difference of neurological outcome of patients at hospital dis- charge (Supplementary Fig. S4).

Discussion

To the best of our knowledge, this systemic review and meta- analysis is the first one that revealed the significant relationship be- tween BMI and clinical outcomes of patients underwent CA. Using nor- mal weight as the reference, we found that underweight was associated with lower survival rate. Of note, we also found that overweight pa- tients had a higher survival rate at hospital discharge and better neuro- logical outcome at hospital discharge. Survival rate and neurological prognosis did not differ between obese and normal weight patients after CA and CPR.

It has been demonstrated that obesity is one of the risk factors for coronary heart disease and cardiovascular disease . In gen- eral population, there was a significant relationship between obesity and increased overall mortality [24,25]. Body shape may influence on chest compression depth and then interact with CPR quality. Further- more, study conducted by Holmberg et al. showed that patients with ex- treme obesity have difficulty in pre-hospital emergency tracheal intubation [26]. These may lead to high mortality in obese patients. Con- versely, Flegal et al. reported that overweight population was related to lower mortality compared with normal weight population [27]. Besides, increased evidence indicated an obesity paradox in patients with heart failure [4,5], atrial fibrillation [7] and coronary artery disease [6]. A large cohort study conducted in 730 Intensive care units

Table 1

Characteristics of included studies.

Authors Journal

Place of CA & treatment

Population

Study location

Study period

Study design

BMI

classification

Primary outcomes

Secondary outcomes

Guillaume Resuscitation (2016)

OHCA

818

France

2005-2012

Prospective

Underweight: BMI b 18.5

30-day survival rate

Geri

+TTM

observational

Normal weight: BMI 18.5-25

1-year survival rate

study

Overweight: BMI 25-30

Obese: BMI N 30

Eunmi Gil Plos One (2017)

IHCA

200

Italy

2004-2013

Retrospective

Underweight: BMI b 18.5

Hospital survival

Good neurologic

+ECMO

observational

Normal weight: BMI 18.5-24.9

outcomes at

study

Overweight: BMI 25-29.9

Obese: BMI >= 30

discharge

Renuka Circ Cardiovasc Qual

IHCA

21,237

USA

2006-2007

Database

Underweight: BMI b 18.5

Hospital survival

ROSC

Jain Outcomes (2010)

(GWTG-R(R))

Normal weight: BMI 18.5-24.9

Post-resuscitation

Prospective

Overweight: BMI 25-29.9

survival

observational

study

Obese: BMI 30-34.9

Morbidly obese: BM >= 35

Yong Hun American Journal of

OHCA

468

Korea

2008-2015

Retrospective

Underweight: BMI b 18.5

6-month mortality

Neurological

Jung Emergency Medicine

+TTM

observational

Normal: BMI 18.5-22.9

outcomes at hospital

(2017)

study

Overweight: BMI 23.0-27.4

discharge

Obese: BMI >= 27.5

Marion Resuscitation (2014)

OHCA

184

USA

2007-2012

Retrospective

Underweight: BMI b 18.5

Hospital survival

Leary

+IHCA+

observational

Normal weight: BMI 18.5-24.9

Neurological

TTM

study

Overweight: BMI 25-29.9

Obese: BMI >= 30

recovery at hospital

discharge

Christoph Resuscitation (2011)

OHCA

1915

Australia

1992-2007

Prospective

Underweight: BMI <= 18.5

6-month survival

Neurological

Testori

+IHCA

observational

Normal weight: BMI 18.5-24.9

rate

recovery at 6-month

study

Overweight: BMI 25-29.9

Obese: BMI >= 30

CA, cardiac arrest; BMI, body mass index; OHCA, out-of-hospital cardiac arrest; IHCA, in-hospital cardiac arrest; TTM, targeted temperature management; ECMO, extracorporeal membrane oxygenation; CPC, cerebral performance category; ICD, Implantable cardioverter defibrillator; ROSC, return of spontaneous circulation.

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Y. Ma et al. / American Journal of Emergency Medicine 36 (2018) 12701279

Table 2

Characteristics of patients in the included studies.

Authors Age (Mean) Male sex (%) Witnessed arrest (%) Bystander CPR (%) VF/VT (%)

Underweight

Normal weight

Overweight

Obese

Underweight

Normal weight

Overweight

Obese

Underweight

Normal weight

Overweight

Obese

Underweight

Normal weight

Overweight

Obese

Underweight

Normal weight

Overweight

Obese

T. Jared

67.3

62

61

73

81

81

75

82

92

59

41

46

100

100

100

Bunch

Guillaume

60.9

58

58.7

62.4

70.2

44.4

68.2

73.7

88.8

81.5

84.9

90.1

52.6

18.5

40.6

45.2

54.3

33.3

53.6

56.3

Geri

Eunmi Gil

36.5

63.5

62

65

50

65.3

60.4

33.3

28.6

33.9

18.9

13.3

Renuka

67.4

68.6

66.9

62.5

51.4

59.6

63

54.8

15.4

19.7

22.4

22.8

Jain

Yong Hun

64

60

59

59.5

35.6

68.4

73

71.1

84.4

73

78.3

76.3

51.1

49

51.9

44.7

Jung

Marion

58

58

65

60

38

69

59

47

25

18

32

29

Leary

Christoph

57

58

60

58

30

68

72

60

97

96

97

94

16

23

25

20

46

59

66

57

Testori

Authors DM (%) CAD/MI (%) Dyslipidemia (%) Hypertention (%)

Underweight

Normal weight

Overweight

Obese

Underweight

Normal weight

Overweight

Obese

Underweight

Normal weight

Overweight

Obese

Underweight

Normal weight

Overweight

Obese

T. Jared Bunch

12

16

30

73

82

80

31

34

38

Guillaume Geri

18.3

0

9.8

16.9

29.3

14.8

16.4

25.4

44.5

18.5

23.9

40.3

Eunmi Gil

35.7

50

43.4

40

0

16.9

11.3

6.7

0

13.6

17

20

28.6

46.6

50.9

53.3

Renuka Jain

18.2

21.8

26.8

38.9

11.3

14.4

15.5

15.3

Yong Hun Jung

Marion Leary

Christoph

3

12

18

22

3

25

30

28

Testori

CPR, cardiopulmonary resuscitation; VF, ventricular fibrillation; VT, ventricular tachycardia. DM, diabetes mellitus; CAD, coronary artery disease; MI, myocardial infarction.

A

B

Fig. 2. Forest plots showing the association between BMI and survival condition in patients after CA. A. Underweight vs. Normal weight. B. Overweight vs. Normal weight. C. Obese vs. Normal weight. CI, confidence interval.

demonstrated that overweight was associated with greater survival in critical ill patients [10]. Recently, a meta-analysis involved 557,720 pa- tients revealed that obesity is associated with lower risks in patients after cardiac surgery [12]. Consistently, our meta-analysis also found that overweight patients underwent CA apparently had a favorable short-term survival condition and neurological prognosis. Does obesity actually improve clinical outcomes or existing confounding factors leads to those conclusions need to be further discussed.

Obesity paradox in patients after CA and CPR was observed in our meta-analysis. Better understanding of this phenomenon could help identifying the patients with higher risk. There are several potential ex- planations for obesity paradox in patients underwent CA. There is an in- consistency distribution of comorbidities in different BMI classification groups in studies involved in this meta-analysis and obese patients al- ways have comorbidities, such as diabetes, coronary artery disease (CAD), dyslipidemia and hypertension [15,18,21]. Thus, obese patients may have more chances to get medication therapies than normal weight patients. In addition, compared to low or normal weight pa- tients, obese patients may have greater metabolic reserves, less cachexia and increased muscle mass, resulting in better Clinical prognosis [9]. Be- sides, patients with obstructive Sleep apnea (OSA) are exposed to

intermittent hypoxia, leading to brain Ischemic preconditioning. A study conducted by Aleos et al. showed that patients with OSA had higher unadjusted survival rates, and better adjusted neurological out- comes at discharge [28]. There is a strong relationship between obesity and OSA and obese patients with OSA might benefit from this ischemic preconditioning protection. On the other hand, patients with low-BMI were more likely to develop cachexia or chronic diseases, leading to high mortality. Previous study demonstrated that confounding by smoking is one of the biases in BMI-mortality analysis in patients with cardiovascular diseases [29]. However, a study reported that smokers had a higher survival rate at hospital discharge among patients after CA [30], which seemed paradoxical to the previous studies. Neverthe- less, among the included studies, only one study recorded the smoking status of patients in different BMI groups. Notably, BMI value as the only measurement for obesity is insufficient. Waist-to-hip ratio (WHR) and waist circumference (WC) as measures of central obese are better indi- cators for predicating mortality with low measurement error and high precision [31,32]. A cross section survey for US population revealed that people with central obese had higher mortality risk compared with a man with similar BMI but no central obese, indicating central obesity defined by WHR was more effective to predict clinical outcomes

Fig. 3. Subgroup analysis of hospital survival rate and longer survival condition in patients after CA. CI, confidence interval.

[33]. Moreover, body fat is also a stronger indicator for mortality [9]. Various measures of obese should be used in further studies to explore the relationship between obese and clinical outcome in patients after CA.

Admittedly, there are some limitations that should be taken into consideration. Firstly, we drew the conclusion that obese did not in- crease mortality and exacerbate neurological prognosis in patients underwent CA. However, there was only one study that involved BMI classification of severe obesity in this meta-analysis. Therefore, there were not sufficient data to perform further analysis to figure out the re- lationship between morbidly obese and clinical outcomes of patients underwent CA. Kitahara et al. revealed that class III obesity was

associated with elevated death due to heart disease compared to normal weight population [34]. Hence, the relationship between severe obesity CA patients and survival condition should be further explored. Secondly, there was a significant difference in baseline characteristics among the included studies, for instance, the location of CA (OHCA, IHCA or both), the use of TTM and the percentage of ventricular fibrillation/ven- tricular tachycardia (VF/VT) rhythm. Sample size in the included studies ranged from 184 to 21,237, and studies with larger sample sizes had more influence on the final outcomes. In addition, follow-up in different studies ranged from six months to five years. Thus, high heterogeneity was observed in survival condition in this meta-analysis. Finally, all of the included studies were observational study. Some important data

Fig. 4. Subgroup analysis of survival condition in overweight and normal weight patients targeting the place of CA. IHCA, in-hospital cardiac arrest; OHCA, out-of-hospital cardiac arrest; CI, confidence interval.

Fig. 5. Subgroup analysis of survival condition in overweight and normal weight patients targeting the treatment. TTM, targeted temperature management; CI, confidence interval.

related to favorable prognostic factors of patients after CA were defi- ciency in some included studies, such as percentage of witnessed arrest and bystander CPR. And there is a lack of risk adjustment for differences in those variable because Individual patient data were not available for meta-analysis.

Conclusions

This meta-analysis investigated the association between BMI and clinical outcomes in patients after CA. With existing limited data, we found that low-BMI was related to lower survival rate and overweight patients had a higher hospital survival rate as well as better neurological recovery. Furthermore, no difference was found in mortality and

neurological outcome between obese and normal weight CA patients. Further studies are needed to explore the underlying mechanisms.

Supplementary data to this article can be found online at https://doi. org/10.1016/j.ajem.2018.03.079.

Competing interests

Declarations of interest: none.

Funding

This study was supported by the National Natural Science Founda- tion of China (No. 81772038).

Fig. 6. Subgroup analysis of survival condition in obese and normal weight patients targeting the place of CA. IHCA, in-hospital cardiac arrest; OHCA, out-of-hospital cardiac arrest; CI, confidence interval.

Fig. 7. Subgroup analysis of survival condition in obese and normal weight patients targeting the treatment. TTM, targeted temperature management; CI, confidence interval.

Image of Fig. 8

Fig. 8. Forest plots showing the association between BMI and neurological outcomes in patients after CA. A. Underweight vs. Normal weight. B. Overweight vs. Normal weight. C. Obese vs. Normal weight. CI, confidence interval.

Authors’ contributions

YM conducted the literature searches, study screen, data extraction, quality assessment, data analysis and manuscript writing. LLH per- formed study screen, data extraction, quality assessment and manu- script writing. LZ conducted study screen and manuscript writing. HY conceived this study and revised the manuscript. BL helped revised this manuscript.

All authors read and approved the final manuscript.

Acknowledgements

We sincerely thank for all authors of all included primary clinical studies.

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