Association of Red Cell Index and Hospital Mortality in Chronic Obstructive Pulmonary Disease Patients Admitted to the Intensive Care Unit: A Retrospective Cohort Study

Figures & data

Figure 1 Flowchart of participant selection.

Abbreviations: ICU, intensive care unit; COPD, chronic obstructive pulmonary disease; RCI, red cell index.

Table 1 Baseline and Clinical Characteristics of the Study Population

Variables	Total (n = 821)	RCI<1.18 (n = 274)	1.18≤RCI<2.62 (n = 273)	RCI≥2.62 (n = 274)	p
Male, n (%)	462 (56.3)	133 (48.5)	158 (57.9)	171 (62.4)	0.004
Age, year	71.1 ± 10.6	69.9 ± 10.2	70.9 ± 10.6	72.4 ± 11.0	0.024
Medicare	469 (57.1)	150 (54.7)	149 (54.6)	170 (62)	0.39
White, n (%)	570 (69.4)	199 (72.6)	188 (68.9)	183 (66.8)	0.258
HR, bpm	85.9 ± 15.1	85.1 ± 13.9	83.0 ± 14.0	89.6 ± 16.6	<0.001
RR, bpm	19.8 ± 3.8	19.0 ± 3.3	19.5 ± 3.6	20.9 ± 4.2	< 0.001
SBP, mmHg	114.2 ± 14.0	112.6 ± 12.1	113.9 ± 13.1	116.0±16.3	0.018
DBP, mmHg	61.1 ± 10.3	58.3 ± 8.4	61.0 ± 10.9	64.1 ± 10.8	< 0.001
MBP, mmHg,	76.7 ± 9.6	74.4 ± 7.7	76.9 ± 10.0	78.7 ± 10.4	< 0.001
SpO2, %	96.3 ± 2.5	96.8 ± 2.0	96.5 ± 2.6	95.5 ± 2.6	< 0.001
Hematocrit, %	29.2 ± 6.5	26.7 ± 4.7	29.4 ± 6.2	31.6 ± 7.4	< 0.001
Anion gap, mmol/L	13.0 ± 3.9	12.5 ± 3.7	12.7 ± 3.9	13.7 ± 4.0	< 0.001
RBC,10^12/L	3.4 ± 0.7	3.2 ± 0.5	3.5 ± 0.6	3.6 ± 0.8	< 0.001
Hb, g/L	10.2 ± 1.9	9.5 ± 1.4	10.2 ± 1.8	10.7 ± 2.2	< 0.001
PLT, 10^9/L	178.2 ± 85.5	215.9 ± 95.1	176.2 ± 70.4	142.7 ± 72.5	< 0.001
Lym, 10^9/L	1.7 ± 8.4	3.3 ± 14.3	1.3 ± 0.6	0.6 ± 0.4	< 0.001
Bicarbonate, mmol/L	21.8 ± 5.0	21.5 ± 4.4	22.0 ± 4.7	21.8 ± 5.7	0.518
Chloride, mmol/L	100.5 ± 6.2	101.3 ± 5.4	101.0 ± 6.0	99.2 ± 6.9	< 0.001
Glucose, mg/dL	121.1 ± 42.5	119.6 ± 37.5	120.9 ± 40.7	122.6 ± 48.6	0.714
Sodium, mmol/L	136.8 ± 4.9	136.9 ± 4.2	136.9 ± 4.5	136.6 ± 5.9	0.672
Potassium, mmol/L	4.1 ± 0.6	4.2 ± 0.6	4.1 ± 0.6	3.9 ± 0.6	< 0.001
ALT, IU/L	24.5 (14.0, 55.8)	22.0 (14.0, 42.0)	26.0 (14.0, 56.0)	27.0 (15.0, 77.5)	0.216
AST, IU/L	35.0 (22.0, 77.5)	35.0 (19.0, 57.5)	37.0 (24.0, 87.2)	35.5 (22.0, 90.2)	0.373
BUN, mg/dL	19.0 (13.0, 30.0)	17.0 (12.0, 28.0)	18.0 (13.0, 27.0)	24.0 (15.0, 36.0)	< 0.001
Scr, mg/dL	0.9 (0.7, 1.4)	0.9 (0.7, 1.4)	0.9 (0.7, 1.3)	1.0 (0.7, 1.5)	0.182
Myocardial infarct, n (%)	241 (29.4)	84 (30.7)	97 (35.5)	60 (21.9)	0.002
Congestive heart failure, n (%)	374 (45.6)	130 (47.4)	117 (42.9)	127 (46.4)	0.531
Peripheral vascular disease, n (%)	146 (17.8)	44 (16.1)	60 (22)	42 (15.3)	0.083
Cerebrovascular disease, n (%)	115 (14.0)	47 (17.2)	33 (12.1)	35 (12.8)	0.18
Mild liver disease, n (%)	67 (8.2)	20 (7.3)	11 (4)	36 (13.1)	< 0.001
Severe liver disease, n (%)	34 (4.1)	3 (1.1)	5 (1.8)	26 (9.5)	< 0.001
Diabetes, n (%)	304 (37.0)	122 (44.5)	101 (37)	81 (29.6)	0.001
Renal disease, n (%)	220 (26.8)	73 (26.6)	75 (27.5)	72 (26.3)	0.949
Malignant cancer, n (%)	105 (12.8)	26 (9.5)	20 (7.3)	59 (21.5)	< 0.001
SAPSII	41.8 ± 13.4	41.4 ± 13.2	39.7 ± 12.1	44.3 ± 14.5	< 0.001
OASIS	35.5 ± 8.8	34.7 ± 8.8	34.2 ± 7.9	37.5 ± 9.2	< 0.001
SOFA	4.3 ± 2.5	4.2 ± 2.2	4.1 ± 2.2	4.5 ± 2.8	0.347
Mechanical ventilation, n (%)	467 (60.2)	170 (64.9)	158 (61.5)	139 (54.1)	0.037
Length of hospital stay	8.9 (5.8, 15.4)	9.0 (5.9, 14.0)	8.7 (5.6, 15.7)	9.8 (5.9, 16.0)	0.494
Hospital mortality, n (%)	124 (15.1)	25 (9.1)	29 (10.6)	70 (25.5)	< 0.001

Notes: Continuous variables are presented as mean ± SD or median (quartile), while categorical variables are presented as absolute numbers (percentages).

Abbreviations: RCI, red cell index; HR, heart rate; RR, respiratory rate; SBP, systolic blood pressure; DBP, diastolic blood pressure; MBP, mean blood pressure; SpO2, pulse oximetry derived oxygen saturation; RBC, red blood cell; Hb hemoglobin; Lym, Lymphocytes, PLT, platelets; ALT, alanine transaminase; AST, aspartate transferase; BUN, blood urea nitrogen; Scr, serum creatinine; SAPS II, simplified acute physiology score II; OASIS, oxford acute severity of illness score; SOFA, sequential organ failure assessment.

Table 2 Univariate Analysis of Risk Factor Associated with Hospital Mortality in Patients with COPD

Variable	OR (95% CI)	P
Gender (Male vs female)	0.64 (0.43–0.94)	0.021
Age, year	1.04 (1.02–1.06)	<0.001
Race
Non-white	Ref
Other	3.1 (1.43–6.73)	0.004
White	1.4 (0.67–2.9)	0.369
RCI	1.05 (1.02–1.07)	<0.001
HR	1.03 (1.02–1.05)	<0.001
RR	1.14 (1.08–1.19)	<0.001
SBP	0.98 (0.96–0.99)	0.008
DBP	0.99 (0.98–1.01)	0.552
MBP	0.99 (0.97–1.01)	0.199
Hematocrit	0.97 (0.95–1)	0.098
SpO2	0.86 (0.8–0.93)	<0.001
Anion gap	1.14 (1.09–1.2)	<0.001
Bicarbonate	0.92 (0.89–0.96)	<0.001
Glucose	1 (0.99–1)	0.387
BUN	1.02 (1.01–1.03)	<0.001
Scr	1.28 (1.12–1.48)	<0.001
Sodium	0.98 (0.95–1.02)	0.431
Potassium	0.74 (0.54–1.02)	0.063
Chloride	0.95 (0.93–0.98)	0.002
ALT	1 (1–1)	0.003
AST	1 (1–1)	0.001
Myocardial infarction (Yes vs No)	1.12 (0.74–1.7)	0.578
Congestive heart failure (Yes vs No)	1.55 (1.06–2.28)	0.025
Cerebrovascular disease (Yes vs No)	2.3 (1.44–3.67)	0.001
Peripheral vascular disease (Yes vs No)	1.06 (0.65–1.74)	0.809
Renal disease (Yes vs No)	1.31 (0.86–1.98)	0.205
Liver disease (Yes vs No)	2.48 (1.43–4.28)	0.001
Diabetes (Yes vs No)	0.49 (0.32–0.76)	0.002
Malignant cancer (Yes vs No)	1.49 (0.88–2.51)	0.136
SAPSII	1.06 (1.05–1.08)	<0.001
OASIS	1.11 (1.08–1.13)	<0.001
SOFA	1.18 (1.09–1.27)	<0.001
Mechanical ventilation (Yes vs No)	1.56 (1.04–2.35)	0.032

Abbreviations: OR, odds ratio; CI, confidence interval; Ref, reference; RCI, red cell index; COPD, chronic obstructive pulmonary disease; HR, heart rate; RR, respiratory rate; SBP, systolic blood pressure; DBP, diastolic blood pressure; MBP, mean blood pressure; SpO2, pulse oximetry derived oxygen saturation; ALT, alanine transaminase; AST, aspartate transferase; BUN, blood urea nitrogen; Scr, serum creatinine; SAPS II, simplified acute physiology score II; OASIS, oxford acute severity of illness score; SOFA, sequential organ failure assessment.

Table 3 Relationship Between Red Cell Index and Hospital Mortality in Different Models

Variable	Crude model		Model 1		Model 2		Model 3		Model 4
	OR (95% CI)	p	OR (95% CI)	p	OR (95% CI)	p	OR (95% CI)	p	OR (95% CI)	p
RCI continuous	1.05 (1.02–1.07)	<0.001	1.05 (1.02–1.07)	<0.001	1.04 (1.01–1.06)	0.006	1.03 (1.01–1.06)	0.006	1.03 (1.01–1.06)	0.012
RCI tertiles
RCI<1.18	1(Ref)		1(Ref)		1(Ref)		1(Ref)		1(Ref)
1.18≤RCI<2.62	1.18 (0.67–2.08)	0.557	1.15 (0.64–2.04)	0.642	1.23 (0.67–2.27)	0.509	1.21 (0.64–2.28)	0.55	1.4 (0.73–2.7)	0.31
RCI≥2.62	3.42 (2.09–5.59)	<0.001	3.37 (2.02–5.6)	<0.001	2.55 (1.45–4.49)	0.001	2.41 (1.35–4.3)	0.003	2.33 (1.27–4.27)	0.006
p for trend		<0.001		<0.001		0.001		0.002		0.005

Notes: Crude model was not adjusted. Model 1 was adjusted for gender+ age+ race. Model 2 was adjusted for model 1+ HR+ RR+ SBP+ SpO2 +cerebrovascular disease+ liver disease+ congestive heart failure+ diabetes. Model 3 was adjusted for model 2+ anion gap + chloride + bicarbonate + BUN+ Scr +ALT+AST. Model 4 was adjusted for model3 + SAPSII+OASIS+ SOFA+ mechanical ventilation.

Abbreviations: OR, odds ratio; CI, confidence interval; Ref, reference; RCI, red cell index; HR, heart rate; RR, respiratory rate; SBP, systolic blood pressure; SpO2, pulse oximetry derived oxygen saturation; ALT, alanine transaminase; AST, aspartate transferase; BUN, blood urea nitrogen;Scr, serum creatinine; SAPS II, simplified acute physiology score II; OASIS, oxford acute severity of illness score; SOFA, sequential organ failure assessment.

Figure 2 Forest plot of association between red cell index (RCI) and hospital mortality. Crude: unadjusted; Adjusted: adjusted for gender, age, race, HR, RR, SBP, SpO2, cerebrovascular disease, liver disease, congestive heart failure, diabetes, anion gap, chloride, bicarbonate, BUN, Scr, ALT, AST, APSII, OASIS, SOFA, mechanical ventilation.

Abbreviations: OR, odds ratio; CI, confidence interval; HR, heart rate; RR, respiratory rate; SBP, systolic blood pressure; SpO2, pulse oximetry derived oxygen saturation; BUN, blood urea nitrogen; Scr, serum creatinine; ALT, alanine transaminase; AST, aspartate transferase; SAPS II, simplified acute physiology score II; OASIS, oxford acute severity of illness score; SOFA, sequential organ failure assessment.