Outcomes of The Association Between Body Mass Index and Clinical Outcomes in Acute Lung Injury

BMIThere were no significant demographic differences between the 825 included patients and the 288 patients excluded for lack of BMI data. Among the study population, we found no significant differences in gender or severity of illness between the BMI groups. There were significant differences in age, ALI risk factor, and tidal volume on day 3 (Table 1). Age steadily decreased as BMI increased; severely obese patients had a median age of 54.7 years, compared to 61.5 years in the normal-weight group and 64.7 years in the underweight group (p < 0.001). Obese patients also had different risk factors for ALI (p < 0.05) than normal-weight patients, although in all groups sepsis from a suspected pulmonary source was the most common risk factor. Ventilator tidal volume (milliliter per kilogram of predicted body weight) on day 3 increased steadily as BMI increased (p 40 kg/m2). Unadjusted median hospital and ICU LOS and duration of mechanical ventilation were not significantly different between BMI groups.

After adjusting for age, chronic health points, acute physiology score, and risk factor for ALI, there was no statistically significant difference in mortality between any BMI category and normal-weight patients (Fig 1). We did, however, find a significantly longer adjusted hospital LOS in severely obese patients, who remained in the hospital an average of 10.5 days (95% confidence interval [CI], 4.8 to 16.2 days; p < 0.001) longer than normal-weight patients (Fig 2). This difference markedly increased in the severely obese group when the analysis was restricted to survivors, who had a mean adjusted stay 14.3 days longer than normal-weight patients (95% CI, 7.1 to 21.6 days; p < 0.001). Surviving severely obese patients also had a significantly longer ICU LOS and duration of mechanical ventilation compared to surviving normal-weight patients (mean adjusted increase, 5.6 days; 95% CI, 1.3 to 9.8 days; p = 0.01; and mean adjusted increase, 4.1 days; 95% CI, 0.4 to 7.7 days, respectively; p = 0.03). Age did not modify the association of BMI with hospital LOS, ICU LOS, or duration of mechanical ventilation (Table 2). Morbidity analysis repeated with log transformation of the LOS and duration of mechanical ventilation variables demonstrated a similar pattern in the severely obese patients (data not shown). People may be slim together with remedies of Canadian Health&Care Mall.

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Severely obese patients were also more likely to require a higher level of care on discharge from the hospital (Table 3). With home as the reference discharge disposition, severely obese patients were significantly more likely to be discharged to a rehabilitation facility (odds ratio [OR] 6.0; 95% CI, 1.8 to 20.2) or an SNF (OR, 4.3; 95% CI, 1.5 to 12.5) than normal-weight patients. There was no difference in the discharge patterns to other hospitals or to LTACs.

Fig1

Figure 1. OR of death in each BMI category compared to normal-weight patients, after adjusting for age, acute physiology score, chronic health points, and etiology of ALI. There was no statistically significant difference in mortality between any BMI category and normal-weight patients. Error bars show 95% CI.

Fig2

Figure 2. Mean difference in duration of hospital LOS, ICU LOS, and mechanical ventilation (Mech. Vent.), in days, in each BMI category compared to normal-weight patients. After adjusting for age, acute physiology score, chronic health points, and etiology of ALI, severely obese patients had longer hospital LOS than normal-weight patients. This association was magnified when analyses were restricted to survivors, who also had significantly longer ICU LOS and duration of mechanical ventilation than normal-weight patients. Error bars show 95% CI.

Table 1—Baseline Characteristics by BMI Category

Characteristics Underweight, BMI < 18.5 kg/m2 (n = 50) Normal Weight, BMI 18.5 to 24.9 kg/m2 (n = 301) Overweight,BMI 25 to 29.9 kg/m2 (n = 237) Obese,BMI 30 to 39.9 kg/m2 (n = 183) Severely Obese, BMI > 40 kg/m2 (n = 54) p Value
Age, yr 64.7 ± 18.4 61.5 ± 18.1 58.9 ± 17.4 57.0 ± 15.9 54.7 ± 13.9 < 0.001t
Male gender 28 (56.0) 195 (64.8) 157 (66.2) 116 (63.4) 26 (48.1) 0.35{
Acute physiology score 82.3 ± 31.5 74.9 ± 29.2 74.9 ± 30.0 70.3 ± 29.8 75.0 ± 35.1 0.07t
Chronic health points 3.3 ± 6.1 2.9 ± 6.0 2.5 ± 5.4 2.4 ± 5.3 1.4 ± 3.6 0.05t
Risk factors
Trauma 2 (4.0) 11 (3.7) 27(11.4) 18 (9.8) 1 (1.9) 0.09{
Sepsis 44 (88.0) 254 (84.4) 168 (70.9) 121 (66.1) 44 (81.5) < 0.001{
Pulmonary, No. 25 141 98 67 25
Extrapulmonary, No. 19 113 70 54 19
Other 4 (8.0) 36 (12.0) 42 (17.7) 44 (24.0) 9 (16.7) 0.001{
Day 3 tidal volume§ 8.9 ± 2.6 9.9 ± 2.4 10.4 ± 2.7 10.5 ± 2.6 11.4 ± 2.5 < 0.001t
Admission source
Home 37 (74.0) 228 (75.7) 185 (78.1) 145 (79.2) 43 (79.6) 0.85{
Hospital 1 (2.0) 28 (9.3) 21 (8.9) 15 (82.0) 8 (14.8) 0.24{
SNF/other 12 (24.0) 45 (15.0) 31 (13.1) 23 (12.6) 3 (5.6) 0.09{
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Table 2—Unadjusted Outcomes Among All Patients and Survivors

Outcomes Underweight, BMI < 18.5 kg/m2 (n = 50) Normal Weight, BMI 18.5 to 24.9 kg/m2 (n = 301) Overweight,BMI 25 to 29.9 kg/m2 (n = 237) Obese,BMI 30 to 39.9 kg/m2 (n = 183) Severely Obese, BMI > 40 kg/m2 (n = 54) p Value
Mortality 22 (44) 122 (40.5) 87 (36.7) 58 (31.7) 14 (25.9) 0.01t
Hospital LOS, d
All patients 18.2 ± 15.3 19.4 ± 17.2 21.8 ± 17.4 19.0 ± 17.1 29.8 ± 41.3 0.28J
Survivors 24.9 ± 17.0 21.6 ± 18.1 24.6 ± 17.5 21.5 ± 18.0 35.6 ± 45.7 0.34
ICU LOS, d
All patients 10.8 ± 11.1 11.8 ± 13.1 13.5 ± 13.0 10.7 ± 9.4 15.3 ± 14.7 0.23J
Survivors 13.7 ± 13.3 12.1 ± 13.2 14.3 ± 13.1 11.3 ± 9.7 17.7 ± 14.9 0.22
Duration of mechanical ventilation, d
All patients 9.2 ± 10.9 8.7 ± 10.7 10.4 ± 11.5 8.3 ± 8.4 10.8 ± 12.7 0.13J
Survivors 11.8 ± 13.4 8.2 ± 9.8 10.4 ± 12.0 8.5 ± 8.8 12.2 ± 12.8 0.24
Discharge disposition in survivors
Home 0 11(6.1) 10 (6.7) 5 (4.0) 3 (7.5) 0.76t
Rehabilitation 16 (57.1) 69 (38.5) 58 (38.7) 44 (35.2) 19 (47.5) 0.54t
SNF 5 (17.9) 14 (7.8) 14 (9.3) 5 (4.0) 3 (7.5) 0.10t
Hospital 2(7.1) 20(11.2) 21 (14.0) 14(11.2) 9 (22.5) 0.14t
LTAC 0 6(3.4) 3 (2.0) 3 (2.4) 0 0.52t
Other 5 (17.9) 59 (33.0) 44 (29.3) 54 (43.2) 6(15.0) 0.55t

Table 3—Adjusted Discharge Disposition Outcomes Among Survivors

Variables Underweight, BMI < 18.5 kg/m2 (n = 28) Normal Weight, BMI 18.5 to 24.9 kg/m2 (n = 179) Overweight,BMI 25 to 29.9 kg/m2 (n = 150) Obese,BMI 30 to 39.9 kg/m2 (n = 125) Severely Obese, BMI > 40 kg/m2 (n = 40)
Hospital N/A 1.0 (reference) 1.4 (0.5-3.8; 0.48) 0.7 (0.2-2.1; 0.51) 2.7 (0.5-14.6; 0.24)
Rehabilitation 1.6 (0.3-9.2; 0.62) 1.0 (reference) 1.4 (0.6-3.0; 0.45) 0.9 (0.4-2.0; 0.76) 6.0 (1.8-20.2; 0.004)
SNF 2.0 (0.6—6.2; 0.24) 1.0 (reference) 1.2 (0.7-2.1; 0.57) 0.9(0.5-1.6; 0.74) 4.3 (1.5-12.5; 0.008)
LTAC 2.9 (0.6-12.7; 0.17) 1.0 (reference) 1.4 (0.5-3.5; 0.52) 0.5 (0.2-1.7; 0.28) 2.6 (0.5-14.0; 0.26)
Other N/A 1.0 (reference) 0.6 (0.1-2.6; 0.48) 0.5 (0.1-2.4; 0.42) N/A
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