Serum bicarbonate level improves specificity of Berlin Sleep Questionnaire for obstructive sleep apnea

Figures & data

Figure 1. OSAS severity – HCO3 ANOVA.

Figure 2. The predictive value of serum HCO3 in identifying OSAS patients (ROC curve) (AUC: 0.925).

Figure 3. The value of serum HCO3 levels in identifying severe OSAS patients (ROC curve), (AUC: 0.857).

Table 1. Descriptive characteristics of patients.

	Number (n)	Percentage
Gender
Male	193	63.7
Female	110	36.3
Smoking
No	114	61.3
Yes	72	38.7
Alcohol
No	169	90.9
Yes	17	9.1
Obesity
No	65	34.9
Yes	121	65.1
Hypertension
No	104	56.5
Yes	80	43.5
Berlin Sleep Questionnaire
Low risk	85	28.1
High risk	218	71.9
Excessive daytime sleepiness
No	128	42.2
Yes	175	57.8
OSAS
No	81	26.7
Yes	222	73.3
OSAS severity
Mild	46	15.2
Moderate	52	17.2
Severe	124	40.9

Table 2. Comparison of demographic features and arterial blood gas values between patients with or without OSAS.

OSAS		Number (n)	Mean	±Standard deviation	p
AHI	No	81	2.41	1.949	.001
	Yes	222	38.12	24.416
Weight (kg)	No	18	80.00	12.414	.009
	Yes	168	89.49	14.641
Wiest circumference (cm)	No	17	99.94	11.443	.013
	Yes	160	108.27	13.088
BMI	No	18	28.59	4.643	.005
	Yes	168	32.92	6.237
Height (cm)	No	18	166.78	10.762	.56
	Yes	168	165.41	9.373
Epworth Sleepiness Scale	No	81	5.40	4.338	.001
	Yes	222	11.38	4.926
HCO3 (mEq/L)	No	81	23.978	0.821	.001
	Yes	222	25.910	1.226
PaCO2 (mmHg)	No	81	39.27	4.437	.669
	Yes	222	39.54	5.059
PaO2 (mmHg)	No	80	88.49	9.181	.030
	Yes	216	85.73	9.873
Ph	No	81	7.406	0.038	.105
	Yes	222	7.414	0.360
Age (year)	No	81	44.77	12.727	.002
	Yes	222	49.80	12.370

OSAS: obstructive sleep apnea syndrome; AHI: apnea hypopnea index; BMI: body mass index; AHI: apnea hypopnea index.

Table 3. Predictors of OSAS (binary logistic regression analysis).

	B	S.E.	Wald	Df	Sig.	Exp(B)	95% CI for EXP(B)
							Min	Max
Berlin Sleep Questionnaire	2.473	1.266	3.815	1	0.049	11.85	0.99	141.73
Excessive daytime sleepiness	−0.362	1.301	0.077	1	0.781	0.69	0.05	8.90
Weight (kg)	0.070	0.085	0.672	1	0.412	1.07	0.90	1.26
BMI	−0.013	0.191	0.005	1	0.946	0.98	0.67	1.43
Neck circumference (cm)	−0.144	0.223	0.414	1	0.520	0.86	0.55	1.34
PaO2 (mmHg)	−0.077	0.096	0.649	1	0.421	0.92	0.76	1.11
HCO3 (mEq/L)	2.606	0.729	12.775	1	0.001	13.54	3.24	56.56
Age (year)	0.045	0.043	1.078	1	0.299	1.04	0.96	1.13
Coefficient	–58.382	21.444	7.412	1	0.006	0.00

Variables included: Berlin sleep questionnaire, excessive daytime sleepiness, weight. BMI: body mass index, neck circumference; PaO2: partial arterial oxygen pressure; HCO3: bicarbonate, age.

Table 4. OSAS severity–HCO₃ ANOVA.

	N	Mean	Std. deviation	95% Confidence interval for mean
				Lower bound	Upper bound
Simple snoring	81	23.978	8.219	23.796	24.160
Mild OSAS	46	25.002	8.301	24.756	25.249
Moderate OSAS	52	25.681	1.0542	25.387	25.974
Severe OSAS	124	26.343	1.2123	26.127	26.558

OSAS: obstructive sleep apnea syndrome.

Table 5. The predictive value of Berlin Sleep Questionnaire in identification of OSAS or severe OSAS patients and combination with HCO3 cut off values.

	All patients		Patients with a HCO3 cutoff >24.95		All patients		Patients with a HCO3 cutoff > 25.45
	OSAS		OSAS		Severe OSAS		Severe OSAS
BSQ	No	Yes	No	Yes	No	Yes	No	Yes
Low risk	68	17	4	13	83	2	4	2
	80.0%	20.0%	23.5%	76.5%	97.6%	2.4%	66.7%	33.3%
High risk	13	205	3	174	97	122	38	105
	6.0%	94.0%	1.7%	98.3%	44.5%	55.5%	26.6%	73.4%
Total	81	222	7	187	180	124	42	107
	26.7%	73.3%	3.6%	96.4%	59.4%	40.6%	28.2%	71.8%
Sensitivity of BSQ (%)	92.3		93.04		98.3		98.1
Specificity (%)	83.9		57.1		46.1		9.5
Positive predictive value (%)	94		98.3		55.5		73.4
Negative predictive value (%)	80		23.5		97.6		66.7

OSAS: Obstructive sleep apnea; BSQ: Berlin Sleep Questionnaire; HCO3: bicarbonate.