J Clin Med Res

Journal of Clinical Medicine Research, ISSN 1918-3003 print, 1918-3011 online, Open Access

Article copyright, the authors; Journal compilation copyright, J Clin Med Res and Elmer Press Inc

Journal website http://www.jocmr.org

Original Article

Volume 11, Number 10, October 2019, pages 696-702

Is Bedside End-Tidal CO₂ Measurement a Screening Tool to Exclude Pulmonary Embolism in Emergency Department?

Figure 1. Comparison of ETCO₂, D-dimer and Wells scores of the PE and non-PE groups. ETCO₂: end-tidal carbon dioxide; PE: pulmonary embolism.

Figure 2. ROC analyses for ETCO₂, Wells score, and D-dimer level for diagnosing PE. PE: pulmonary embolism; ETCO₂: end-tidal carbon dioxide; ROC: receiver operating characteristic.

**Table 1.** Clinical and Demographical Characteristics of Patients
	PE, mean ± SD/n (%)	Non-PE, mean ± SD/n (%)	P
PE: pulmonary embolism; HT: hypertension; DM: diabetes mellitus; CAD: coronary artery disease; CHF: chronic heart failure; DVT: deep vein thrombosis; CVA: cerebrovascular accident.
Age	66.3 ± 18.6	66 ± 14.9	0.920
Female	32 (64)	22 (44)	0.045
Male	18 (36)	28 (56)
Comorbidity
HT	29 (58)	23 (460)	0.230
DM	16 (32)	13 (26)	0.509
CAD	10 (20)	13 (26)	0.476
CHF	10 (20)	8 (16)	0.603
DVT	11 (22)	6 (12)	0.183
Malignancy	7 (14)	9 (18)	0.585
CVA	6 (12)	2 (4)	0.269
Admission symptom
Dyspnea	25 (50)	28 (56)	0.224
Chest pain	22 (44)	18 (36)
Hemoptysis	2 (4)	0
Palpitation	1 (2)	4 (8)
Intubation status
Yes	0	2 (4)	0.153
No	50 (100)	48 (96)
Blood pressure
Hypertensive	8 (16)	4 (8)	0.062
Normotensive	38 (76)	34 (68)
Hypotensive	4 (8)	12 (24)
Pulse rate
> 120	8 (16)	14 (28)	0.350
100 - 120	29 (58)	25 (50)
< 100	13 (26)	11 (22)
Respiratory rate
> 20	22 (44)	29 (58)	0.359
12 - 20	26 (52)	19 (38)
< 12	2 (4)	2 (4)
Body temperature
Hyperthermia	10 (20)	4 (8)	0.084
Normothermia	40 (80)	46 (92)
Blood gas analysis
pH	7.41 ± 0.08	7.42 ± 0.07	0.448
pO₂	62.15 ± 10.49	67.85 ± 10.20	0.007
pCO₂	33.46 ± 6.22	32.70 ± 6.85	0.559
HCO₃	20.65 ± 3.65	21.43 ± 3.88	0.308
Outcome
Admitted	20 (40)	50 (100)	< 0.001
Discharged	30 (60)	0

Table 1. Clinical and Demographical Characteristics of Patients

PE, mean ± SD/n (%)

Non-PE, mean ± SD/n (%)

PE: pulmonary embolism; HT: hypertension; DM: diabetes mellitus; CAD: coronary artery disease; CHF: chronic heart failure; DVT: deep vein thrombosis; CVA: cerebrovascular accident.

Age

66.3 ± 18.6

66 ± 14.9

0.920

Female

32 (64)

22 (44)

0.045

Male

18 (36)

28 (56)

Comorbidity

29 (58)

23 (460)

0.230

16 (32)

13 (26)

0.509

CAD

10 (20)

13 (26)

0.476

CHF

10 (20)

8 (16)

0.603

DVT

11 (22)

6 (12)

0.183

Malignancy

7 (14)

9 (18)

0.585

CVA

6 (12)

2 (4)

0.269

Admission symptom

Dyspnea

25 (50)

28 (56)

0.224

Chest pain

22 (44)

18 (36)

Hemoptysis

2 (4)

Palpitation

1 (2)

4 (8)

Intubation status

Yes

2 (4)

0.153

50 (100)

48 (96)

Blood pressure

Hypertensive

8 (16)

4 (8)

0.062

Normotensive

38 (76)

34 (68)

Hypotensive

4 (8)

12 (24)

Pulse rate

> 120

8 (16)

14 (28)

0.350

100 - 120

29 (58)

25 (50)

< 100

13 (26)

11 (22)

Respiratory rate

> 20

22 (44)

29 (58)

0.359

12 - 20

26 (52)

19 (38)

< 12

2 (4)

Body temperature

Hyperthermia

10 (20)

4 (8)

0.084

Normothermia

40 (80)

46 (92)

Blood gas analysis

7.41 ± 0.08

7.42 ± 0.07

0.448

pO₂

62.15 ± 10.49

67.85 ± 10.20

0.007

pCO₂

33.46 ± 6.22

32.70 ± 6.85

0.559

HCO₃

20.65 ± 3.65

21.43 ± 3.88

0.308

Outcome

Admitted

20 (40)

50 (100)

< 0.001

Discharged

30 (60)

**Table 2.** Assessment of the Wells Score
Wells risk score	CT angiography	P
PE: pulmonary embolism; CT: computed tomography.
< 2 (low risk)	9 (18)	23 (46)	> 0.001
2 - 6 (moderate risk)	31 (62)	27 (54)	> 0.001
≥ 7 (high risk)	10 (20)	0	< 0.001

Table 2. Assessment of the Wells Score

Wells risk score

CT angiography

PE, n (%)

Non-PE, n (%)

PE: pulmonary embolism; CT: computed tomography.

< 2 (low risk)

9 (18)

23 (46)

> 0.001

2 - 6 (moderate risk)

31 (62)

27 (54)

> 0.001

≥ 7 (high risk)

10 (20)

< 0.001

**Table 3.** ETCO₂ and D-Dimer Levels
	PE, median (IQR)	Non-PE, median (IQR)	P
ETCO₂: end-tidal carbon dioxide; PE: pulmonary embolism; IQR: interquartile range.
ETCO₂	21 (4)	28.5 (6)	< 0.001
D-dimer	2,091 (2,332)	850.5 (1,152)	< 0.001

Table 3. ETCO₂ and D-Dimer Levels

PE, median (IQR)

Non-PE, median (IQR)

ETCO₂: end-tidal carbon dioxide; PE: pulmonary embolism; IQR: interquartile range.

ETCO₂

21 (4)

28.5 (6)

< 0.001

D-dimer

2,091 (2,332)

850.5 (1,152)

< 0.001

**Table 4.** Comparison of the Sensitivities, Specificities, PPVs, and NPVs of ETCO₂, Wells Score, and D-Dimer Level for Diagnosing PE
	Area	Cut-off	Sensitivity	Specificity	PPV	NPV
PE: pulmonary embolism; ETCO₂: end-tidal carbon dioxide; PPV: positive predictive value; NPV: negative predictive value.
ETCO₂	0.901	34 mm Hg	100%	8%	52.1%	100%
D-dimer	0.730	500 ng/mL	100%	18%	54.9%	100%
Wells score	0.777	4	80%	46%	59.7%	69.7%

Table 4. Comparison of the Sensitivities, Specificities, PPVs, and NPVs of ETCO₂, Wells Score, and D-Dimer Level for Diagnosing PE

Area

Cut-off

Sensitivity

Specificity

PPV

NPV

PE: pulmonary embolism; ETCO₂: end-tidal carbon dioxide; PPV: positive predictive value; NPV: negative predictive value.

ETCO₂

0.901

34 mm Hg

100%

52.1%

100%

D-dimer

0.730

500 ng/mL

100%

18%

54.9%

100%

Wells score

0.777

80%

46%

59.7%

69.7%

**Table 5.** Logistic Regression Analysis for PE
	B	SE	P	Odds ratio	95% CI for odds ratio
PE: pulmonary embolism; ETCO₂: end-tidal carbon dioxide; SE: standard error; CI: confidence interval.
Age	-0.018	0.024	0.458	0.982	0.937	1.030
Sex	0.487	0.710	0.493	1.627	0.405	6.545
pH	4.323	7.249	0.551	75.433	0.000	111,697,648.876
pO₂	-0.086	0.042	0.037	0.917	0.845	0.995
pCO₂	0.036	0.091	0.692	1.037	0.868	1.238
HCO₃	-0.048	0.133	0.717	0.953	0.735	1.236
D-dimer	0.000	0.000	0.092	1.000	1.000	1.001
Wells	2.027	0.720	0.005	7.589	1.850	31.135
ETCO₂	-0.519	0.113	0.000	0.595	0.477	0.743
Constat	-17.017	54.448	0.755	0.000

Table 5. Logistic Regression Analysis for PE

Odds ratio

95% CI for odds ratio

Lower

Upper

PE: pulmonary embolism; ETCO₂: end-tidal carbon dioxide; SE: standard error; CI: confidence interval.

Age

-0.018

0.024

0.458

0.982

0.937

1.030

Sex

0.487

0.710

0.493

1.627

0.405

6.545

4.323

7.249

0.551

75.433

0.000

111,697,648.876

pO₂

-0.086

0.042

0.037

0.917

0.845

0.995

pCO₂

0.036

0.091

0.692

1.037

0.868

1.238

HCO₃

-0.048

0.133

0.717

0.953

0.735

1.236

D-dimer

0.000

0.092

1.000

1.001

Wells

2.027

0.720

0.005

7.589

1.850

31.135

ETCO₂

-0.519

0.113

0.000

0.595

0.477

0.743

Constat

-17.017

54.448

0.755

0.000