Abstract
The relationship between body mass index and pressure ulcers in critically ill patients is controversial. We aimed to investigate the association between body mass index and pressure ulcers by analysing data from the Medical Information Mart for Intensive Care IV (version 2.0) database. Eligible data (21 835 cases) were extracted from the database (2008‐2019). The association between body mass index and pressure ulcers in critically ill patients was investigated by adjusting multivariate trend analysis, restricted cubic spline analysis, and segmented linear models. Subgroup analyses and sensitivity analyses were used to ensure the stability of the results. Trend analysis and restricted cubic spline analysis showed an approximate U‐shaped correlation between body mass index and the occurrence of pressure ulcers in critically ill patients, with the risk of pressure ulcers decreasing rapidly with increasing body mass index (8.6% decrease per unit) after adjusting for relevant factors; the trend reached its minimum at a body mass index of 27.5 kg/m2, followed by a slow increase in the risk of pressure ulcers with increasing body mass index (1.4% increase per unit). Among the subgroups, the highest overall risk of pressure ulcers and the risk of severe pressure ulcers were significantly higher in the underweight group than in the other subgroups, and the risk associated with the overweight group was the lowest. There is a U‐shaped association between body mass index and pressure ulcers in critically ill patients, and being underweight and obese both increase the risk of pressure ulcers. The risk is highest among underweight patients and lowest among overweight patients (but not patients of normal weight), necessitating targeted prevention strategies for critically ill patients with different body mass indexes.
Keywords: body mass index, critical illness, overweight, pressure ulcer, underweight
1. INTRODUCTION
Pressure ulcers, also known as decubitus ulcers, are caused by long‐term pressure on local tissues; persistent ischemia, hypoxia, and malnutrition result in tissue ulceration and necrosis. Pressure ulcers are a common and difficult complication health care workers face at all levels of care, especially in intensive care units (ICUs), where almost all patients have varying degrees of impaired consciousness or limited mobility, factors that make pressure ulcer prevention and treatment extremely difficult. 1 , 2 Studies have reported that the incidence of pressure ulcers in patients in the ICU ranges from 6.78% to 25.9% and that pressure ulcers are associated with higher mortality rates and a significant increase in health care expenditures, placing a serious burden on both patients and society. 3 , 4 , 5
The correlation between weight and the prognosis of critically ill patients has long been noted, and body mass index (BMI) has been a widely used indicator of weight in the clinical setting, as it calibrates height to more accurately describe the patient's weight. 6 Initially, low weight and obesity were thought to be associated with poorer outcomes in critically ill patients, as low weight predicted malnutrition and excess weight increased the risk of chronic diseases such as hypertension and diabetes, all of which can make treatment of critically ill patients more difficult. 7 However, as the “obesity paradox” has been increasingly identified and confirmed by health care professionals, the relationship between weight and the prognosis of critically ill patients is being re‐examined. 8 , 9 The relationship between pressure ulcers, an important aspect of the prognosis of critically ill patients, and body weight has also been more frequently noted. However, most current studies have small sample sizes, focus more on patients with abnormal BMIs, such as those who are malnourished or obese, and do not completely assess the effect of different BMIs on the incidence of pressure ulcers in critically ill patients; the results among studies vary greatly. 10 , 11 , 12
Therefore, we aimed to further examine the correlation between BMI and pressure ulcers in critically ill patients by retrospectively analysing relevant clinical information in a publicly available database. We hope to provide some theoretical guidance for the prevention and treatment of pressure ulcers in critically ill patients.
2. METHODS
2.1. Data source
This was a retrospective study based on data from an open database, and all study data were obtained from the Medical Information Mart for Intensive Care IV (MIMIC‐IV version 2.0) database released June 12, 2022. As the largest and most widely used database in the critical care field, the MIMIC IV database, provided by Beth Israel Deaconess Medical Center, contains comprehensive medical information on tens of thousands of critically ill patients over the last decade. 13 As all patient identifiable information in the database was de‐identified, the Institutional Review Board at Beth Israel Deaconess Medical Center waived the requirement for informed consent and approved a data‐sharing program. All investigators who obtained access to the database (Cooperative Institutional Training Initiative [CITI] certificate No. 43529529) were approved to use the data for medical research.
2.2. Data extraction
All critically ill patients who were admitted to the ICU for the first time and treated for at least 24 h were included in this study. Exclusion criteria were as follows: (1) aged <18 years; or (2) a lack of BMI records or significant abnormalities in BMI (<15 kg/m2 or >55 kg/m2).
All eligible data of critically ill patients were extracted from the MIMIC IV (v2.0) database using structured query language: (1) basic information such as gender, age, race, BMI, length of ICU stay, in‐hospital death information, and information related to pressure ulcers; (2) comorbidities and procedures such as anaemia, tumour, sepsis, diabetes, heart failure, peripheral vascular disease, trauma scoring system (first recorded value within 24 h of admission to the ICU, including the Simplified Acute Physiology Score II [SAPSII], Charlson index, and Barden score); (3) special treatment, including vasoactive drugs, mechanical ventilation, and renal replacement therapy; and (4) the first recorded values within 24 h of ICU admission for red blood cells, haemoglobin, white blood cells, platelets, creatinine, urea nitrogen, and blood glucose. All patients were divided into pressure ulcer and no pressure ulcer groups according to whether pressure ulcers occurred in the ICU. Patients were classified into the underweight group (BMI < 18.5 kg/m2), normal weight group (18.5 kg/m2 ≤ BMI < 25 kg/m2), overweight group (25 kg/m2 ≤ BMI < 30 kg/m2), and obese group (BMI ≥ 30 kg/m2) according to the World Health Organization BMI classification. The primary study outcome was the occurrence of pressure ulcers, and the secondary study outcome was the severity of pressure ulcers. Grade 3, grade 4, and unstageable pressure ulcers were defined as severe.
2.3. Statistical analysis
Statistical analyses were performed using R software (4.2.0). As all continuous data in this study were not normally distributed (Kolmogorov–Smirnov test), the measurement data were expressed as median (quartiles) (M[QR]). The Mann–Whitney U test was used for comparisons between groups, and the count data were expressed as frequency (rate) (chi‐square test).
Trend analysis was first performed on patients with different BMI subgroups, with pressure ulcers as an outcome indicator, and odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. Using restricted cubic spline analysis, we plotted smoothed curves to verify trends and to explore the linear/non‐linear relationship between BMI and pressure ulcers in critically ill patients; segmented linear models were used to quantify this association and to assess the stability of the results (multivariate adjustment). Subsequently, subgroup analyses were used to examine whether the association between BMI and pressure ulcers was equally present in the anaemia, oncology, sepsis, diabetes, heart failure, peripheral vascular disease, trauma, surgery, and orthopaedic treatment subgroups and the correlation between BMI and the incidence and severity of pressure ulcers in patients of different age groups. In all analyses, P values <0.05 were considered statistically significant.
2.4. Sensitivity analysis
As grade 1 pressure ulcers are usually reversible, some studies use grade 2 and above pressure ulcers as the study outcome. 14 , 15 Therefore, grade 2 and above pressure ulcers were studied as the primary outcome in our sensitivity analyses to assess the stability of the results. In addition, there were some patients with incomplete pressure ulcer data, such as pressure ulcer grading without a record of the site of the ulcer. These were not identified as pressure ulcers in the beginning of the study because it was not possible to determine whether this was because of missing data, incorrect recording, or other errors. In the sensitivity analysis, this group of patients was reclassified into the pressure ulcer group to assess the stability of the results.
3. RESULTS
3.1. Baseline characteristics
A total of 21 835 critically ill patients were included in this study and classified by BMI into the underweight group, normal weight group, overweight group, and obese group. A flow chart of the study cohort selection is shown in Figure 1, baseline characteristics of the included patients are shown in Table 1. The overall pressure ulcer incidence rate was 8.44%, and patients in the pressure ulcer group had higher ICU length of stay and mortality rates than those in the no pressure ulcer group, as shown in supplementary Table 1.
FIGURE 1.
Study flow chart. BMI, body mass index; ICU, intensive care unit; MIMIC‐IV, Medical Information Mart for Intensive Care IV.
TABLE 1.
Patient characteristics.
| Variables | Total (n = 21 835) | Underweight (n = 592) | Normal weight (n = 6362) | Overweight (n = 7403) | Obese (n = 7478) |
|---|---|---|---|---|---|
| Age (years) | 66 (55, 76) | 69 (57, 80) | 68 (56, 79) | 67 (56, 77) | 64 (54, 72) |
| Ethnicity, n (%) | |||||
| Caucasian | 14 860 (68.1) | 403 (68.1) | 4224 (66.4) | 5109 (69) | 5124 (68.5) |
| Black | 1608 (7.4) | 57 (9.6) | 465 (7.3) | 475 (6.4) | 611 (8.2) |
| Other | 5367 (24.6) | 132 (22.3) | 1673 (26.3) | 1819 (24.6) | 1743 (23.3) |
| Sex (male), n (%) | 13 350 (61.1) | 249 (42.1) | 3667 (57.6) | 4971 (67.1) | 4463 (59.7) |
| LOS in ICU (days) | 2.8 (1.5, 5.5) | 3.1 (1.7, 5.8) | 2.8 (1.6, 5.5) | 2.6 (1.5, 5.2) | 2.8 (1.5, 5.9) |
| ICU mortality | 2750 (12.6) | 129 (21.8) | 916 (14.4) | 845 (11.4) | 860 (11.5) |
| Scoring scale | |||||
| SAPSII | 36 (28, 45) | 38 (29, 48) | 36 (28, 46) | 35 (28, 45) | 36 (27, 45) |
| Charlson index | 5 (4, 7) | 6 (4, 8) | 5 (4, 7) | 5 (4, 7) | 5 (4, 7) |
| Braden score | 15 (14, 17) | 14 (13, 16) | 15 (14, 17) | 15 (14, 17) | 15 (14, 17) |
| Complications | |||||
| Peripheral vascular disease, n (%) | 8313 (38.1) | 225 (38) | 2445 (38.4) | 2817 (38.1) | 2826 (37.8) |
| Anemias, n (%) | 10 205 (46.7) | 323 (54.6) | 3100 (48.7) | 3413 (46.1) | 3369 (45.1) |
| Neoplasms, n (%) | 3587 (16.4) | 162 (27.4) | 1195 (18.8) | 1201 (16.2) | 1029 (13.8) |
| Diabetes, n (%) | 6508 (29.8) | 94 (15.9) | 1326 (20.8) | 2029 (27.4) | 3059 (40.9) |
| Heart failure, n (%) | 5736 (26.3) | 148 (25) | 1617 (25.4) | 1868 (25.2) | 2103 (28.1) |
| Sepsis, n (%) | 13 000 (59.5) | 356 (60.1) | 3787 (59.5) | 4333 (58.5) | 4524 (60.5) |
| Trauma, n (%) | 839 (3.8) | 23 (3.9) | 309 (4.9) | 261 (3.5) | 246 (3.3) |
| Surgery, n (%) | 11 439 (52.4) | 207 (35) | 3105 (48.8) | 4051 (54.7) | 4076 (54.5) |
| Orthopaedic, n (%) | 858 (3.9) | 36 (6.1) | 289 (4.5) | 261 (3.5) | 272 (3.6) |
| Treatment modality | |||||
| Vasopressor use, n (%) | 11 713 (53.6) | 271 (45.8) | 3270 (51.4) | 4027 (54.4) | 4145 (55.4) |
| Mechanical ventilation, n (%) | 12 626 (57.8) | 307 (51.9) | 3572 (56.1) | 4227 (57.1) | 4520 (60.4) |
| Renal replacement therapy, n (%) | 1490 (6.8) | 29 (4.9) | 352 (5.5) | 477 (6.4) | 632 (8.5) |
| Vital signs | |||||
| Temperature (°C) | 36.8 (36.6, 37.1) | 36.8 (36.5, 37) | 36.8 (36.5, 37.1) | 36.8 (36.6, 37.1) | 36.8 (36.6, 37.1) |
| Heart rate (beats/min) | 82.9 (74.6, 93.7) | 84.8 (75.9, 95.7) | 82.7 (74.3, 93.9) | 82.4 (74.2, 92.9) | 83.4 (75.3, 94.4) |
| Respiratory rate (beats/min) | 18.4 (16.4, 20.9) | 18.7 (16.4, 21.7) | 18.1 (16.1, 20.7) | 18.2 (16.3, 20.8) | 18.8 (16.9, 21.2) |
| MAP (mmHg) | 75.8 (70.6, 82.3) | 76.1 (70.6, 82.9) | 75.6 (70.2, 82.3) | 75.7 (70.7, 82) | 76 (70.8, 82.6) |
| SpO2 (%) | 97.5 (96.1, 98.7) | 98 (96.4, 99.1) | 97.9 (96.5, 99) | 97.6 (96.2, 98.6) | 97.1 (95.8, 98.3) |
| Laboratory tests | |||||
| Red blood cell (109/L) | 3.7 (3.2, 4.3) | 3.5 (3, 4) | 3.6 (3.1, 4.1) | 3.7 (3.2, 4.3) | 3.8 (3.2, 4.4) |
| Haemoglobin (g/L) | 11.1 (9.5, 12.8) | 10.5 (9, 12.1) | 10.9 (9.3, 12.5) | 11.2 (9.6, 13) | 11.4 (9.6, 13.1) |
| White blood cell (109/L) | 10 (7.3, 14.1) | 10 (6.9, 14.1) | 9.7 (6.9, 13.6) | 9.9 (7.2, 13.9) | 10.4 (7.6, 14.6) |
| Platelet (109/L) | 192 (143, 251) | 217.5 (156.8, 303) | 192 (138, 254) | 187 (139, 245) | 196 (149, 251) |
| Urea nitrogen (mg/dL) | 18 (13, 27) | 19 (13, 31) | 17 (12, 27) | 18 (13, 26) | 19 (14, 29) |
| Creatinine (mg/dL) | 0.9 (0.7, 1.3) | 0.8 (0.6, 1.2) | 0.9 (0.7, 1.2) | 0.9 (0.7, 1.3) | 1 (0.8, 1.4) |
| Glucose (mg/dL) | 124 (105, 154) | 118 (98, 150) | 121 (101, 148) | 123 (105, 151) | 129 (109, 163) |
Abbreviations: ICU, intensive care unit; LOS, length of stay; MAP, mean airway pressure; SAPSII, simplified acute physiology score II; SPO2, oxygen saturation.
3.2. Trend analysis of BMI and pressure ulcers
Setting the underweight group as the reference variable for trend analysis showed the P for trend <0.001, suggesting a linear relationship between BMI and pressure ulcer occurrence. The OR (95% CI) for the normal weight group, overweight group and obese group were 0.585 (0.453‐0.756), 0.469 (0.355‐0.596), and 0.505 (0.390‐0.654), respectively, after multivariate adjustment; this suggests a decreasing and then increasing relationship between the risk of pressure ulcers and increasing BMI (Table 2).
TABLE 2.
Odds ratios and 95% confidence intervals for pressure ulcers according to BMI classification.
| Adjust | Classification of body mass index (kg/m2) | ||||
|---|---|---|---|---|---|
| Underweight | Normal weight | Overweight | Obese | P value for trend | |
| <18.5 | 18.5 to <25 | 25 to <30 | ≥30 | ||
| Non‐adjust | 1.00 | 0.498 (0.395‐0.628) | 0.385 (0.305‐0.486) | 0.461 (0.366‐0.581) | <0.001 |
| Adjust1 | 1.00 | 0.499 (0.395‐0.631) | 0.392 (0.309‐0.496) | 0.492 (0.390‐0.621) | 0.001 |
| Adjust2 | 1.00 | 0.530 (0.415‐0.678) | 0.433 (0.338‐0.555) | 0.505 (0.395‐0.647) | <0.001 |
| Adjust3 | 1.00 | 0.502 (0.391‐0.644) | 0.389 (0.302‐0.501) | 0.436 (0.341‐0.564) | <0.001 |
| Adjust4 | 1.00 | 0.564 (0.437‐0.726) | 0.440 (0.340‐0.568) | 0.483 (0.374‐0.624) | <0.001 |
| Adjust5 | 1.00 | 0.585 (0.453‐0.756) | 0.469 (0.355‐0.596) | 0.505 (0.390‐0.654) | <0.001 |
Note: Adjust1 was adjusted for demographic information, including age, sex, and ethnicity; Adjust2 was additionally adjusted for complications including peripheral vascular disease, anemias, neoplasms, diabetes, heart failure, sepsis, trauma, surgery and orthopaedic issues; Adjust3 was additionally adjusted for treatment modality, including vasopressor use, mechanical ventilation, and renal replacement therapy; Adjust4 was additionally adjusted for the scoring system, including the Simplified Acute Physiology Score II, Charlson comorbidity index, and Braden score; Adjust5 was additionally adjusted for laboratory tests, including red blood cell, haemoglobin, white blood cell, platelet, urea nitrogen, creatinine, and glucose.
3.3. Restricted cubic spline analysis of BMI and pressure ulcers
Restricted cubic spline analysis showed an approximate U‐shaped correlation between BMI and the development of pressure ulcers in critically ill patients, with the risk of pressure ulcers decreasing rapidly with increasing BMI after adjusting for relevant factors; the risk reached a minimum at BMI = 27.5 kg/m2, followed by a slow increase in the risk of pressure ulcers with increasing BMI (Figure 2). To further quantify this correlation, segmented linear regression model analysis was applied. After adjusting for all factors, the results showed that the risk of pressure ulcers increased by 8.6% for every 1 unit decrease in BMI when BMI was less than the inflection point (BMI = 27.5 kg/m2), while the risk of pressure ulcers increased by 1.4% for every 1 unit increase in BMI when BMI was greater than the inflection point (Table 3).
FIGURE 2.
Association between body mass index and the risk of pressure ulcers in critically ill patients (non‐adjust [A] and after‐adjust [B]). CI, confidence interval; OR, odds ratio.
TABLE 3.
Piecewise two‐line models for the association between BMI and pressure ulcers.
| Change point of BMI (kg/m2) | OR below change point (95% CI) | P value | OR above change point (95% CI) | P value | |
|---|---|---|---|---|---|
| Non‐adjust | 26.9 | 0.893 (0.872‐0.915) | <0.001 | 1.033 (1.021‐1.045) | <0.001 |
| Adjust1 | 26.7 | 0.892 (0.869‐0.915) | <0.001 | 1.037 (1.025‐1.049) | <0.001 |
| Adjust2 | 26.9 | 0.901 (0.878‐0. 925) | <0.001 | 1.022 (1.010‐1.035) | <0.001 |
| Adjust3 | 27.3 | 0.903 (0.881‐0.926) | <0.001 | 1.020 (1.007‐1.034) | 0.002 |
| Adjust4 | 27.5 | 0.916 (0.894‐0.939) | <0.001 | 1.017 (1.003‐1.031) | 0.015 |
| Adjust5 | 27.5 | 0.922 (0.899‐0.945) | <0.001 | 1.016 (1.002‐1.030) | 0.024 |
Note: Adjust1 was adjusted for demographic information, including age, sex, and ethnicity; Adjust2 was additionally adjusted for complications including peripheral vascular disease, anemias, neoplasms, diabetes, heart failure, sepsis, trauma, surgery, and orthopaedic issues; Adjust3 was additionally adjusted for treatment modality, including vasopressor use, mechanical ventilation, and renal replacement therapy; Adjust4 was additionally adjusted for the scoring system, including Simplified Acute Physiology Score‐II, Charlson comorbidity index, and Braden score; Adjust5 was additionally adjusted for laboratory tests, including red blood cell, haemoglobin, white blood cell, platelet, urea nitrogen, creatinine, and glucose.
Abbreviations: BMI, body mass index; CI, confidence interval; OR, odds ratio.
3.4. Association between BMI and pressure ulcers in different subgroups
The same curvilinear correlation was observed in all subgroups, with the risk of pressure ulcers decreasing and then increasing with increasing BMI, but the correlation was not statistically significant in the renal replacement therapy subgroup (P = 0.051) (Figure 3). In the different age subgroups, the incidence of pressure ulcers and severe pressure ulcers increased with increasing age. The incidence of pressure ulcers and severe pressure ulcers in the underweight group was the highest of all age groups. The incidence of pressure ulcers and severe pressure ulcers in the normal weight group, overweight group, and obese group generally tended to decrease and then increase, whereas the overweight group had the lowest incidence of pressure ulcers and severe pressure ulcers. Pressure ulcers were mainly concentrated in the pressure‐prone areas when lying down, such as the coccyx, buttocks, heel, and sacrum. Caudal pressure ulcers had the highest incidence among all pressure ulcer sites and were particularly pronounced in the underweight group; the incidence of ulcers on the buttocks was second, and they were more likely to occur in obese patients (Figure 4).
FIGURE 3.
Association between body mass index and the risk of pressure ulcers among critically ill patients in various subgroups. CI, confidence interval; OR, odds ratio.
FIGURE 4.
Incidence of pressure ulcers (A) and severe pressure ulcers (B) and the site of pressure ulcers (C) among different groups.
3.5. Sensitivity analysis
After excluding grade 1 pressure ulcers, BMI showed the same approximate U‐shaped correlation with pressure ulcers after adjusting for multiple factors. In contrast, the inclusion of patients with missing pressure ulcer data in the pressure ulcer group for sensitivity analysis showed that the results of the analysis, including trend analysis and segmented linear models, were consistent with previous results. The risk of pressure ulcers decreased and then increased with increasing BMI, with an inflection point at a BMI of 27.5 kg/m2 (supplementary materials).
4. DISCUSSION
In this study, we found an approximate U‐shaped correlation between BMI and pressure ulcers in critically ill patients, with both underweight status and obesity increasing the risk of pressure ulcers. The lowest risk of pressure ulcers was at a BMI of 27.5 kg/m2 after adjusting for multiple factors. A segmented linear regression model showed that the risk of pressure ulcers in critically ill patients showed a more pronounced change with BMI before the inflection point (BMI < 27.5 kg/m2). This association of BMI with pressure ulcers in critically ill patients was consistent across all subgroups, except the renal replacement therapy subgroup, and across age strata. Advanced age and underweight status were associated with higher rates of pressure ulcers and severe pressure ulcers in critically ill patients, and the lowest rates of pressure ulcers were found among overweight patients rather than patients of normal weight.
Similar to the findings of other studies, we found that underweight status contributed to a significantly higher incidence of pressure ulcers in critically ill patients. Labeau et al. analysed data from 1117 ICUs and found that underweight status was independently associated with ICU‐acquired pressure ulcers as an important influencing factor. 16 Kottner et al. reported the results of a German pressure ulcer survey in which underweight patients had a significantly higher incidence of pressure ulcers in the sacral and sciatic regions than did normal weight or obese patients. The incidence of pressure ulcers in prone areas such as the sacrum and sciatic ridge was significantly higher among underweight patients than in normal weight or obese patients, which is consistent with the results of this study. 11 Insufficient weight is often a result of poor nutrition, especially in a state of high consumption and acute gastrointestinal injury because of severe disease, and the nutritional status is often difficult to improve or deteriorates even further. 17 Nutritional status plays a pivotal role in the development of pressure ulcers, as malnutrition leads to a decrease in subcutaneous fat, muscle atrophy, and abnormal endocrine metabolism, causing the vulnerable area of adipose tissue to bear a greater local load. The resulting tissue deformation further causes blood, lymphoid, and other microcirculation disorders, leading to structural and functional cellular damage, and eventually pressure ulcers develop. 18 , 19 Moreover, tissue repair is extremely dependent on nutrient supply, and malnutrition makes it difficult for pressure ulcer wounds to heal and more likely to develop into severe pressure ulcers; this is consistent with the findings of our study. 20
Although less pronounced than underweight status, obesity in this study posed a higher risk of pressure ulcers. Similarly, Ness et al. published an analysis in 2018 that included bedside audit information from 377 hospitals. They indicated that morbid obesity was an independent and significant risk factor for pressure ulcer development. 10 Drake et al. suggested in an earlier study that BMI over 40 was independently associated with pressure ulcers, and patients with a BMI over 40 had a risk of pressure ulcers two times that of patients of other weights after adjustment for the Braden score. 21 Obesity has many localised effects on pressure load. Although extra subcutaneous fat can provide better subcutaneous cushioning, reduce the degree of local tissue deformation, and prevent the occurrence of pressure ulcers, greater weight leads to an increase in pressure load and increases the risk of pressure ulcers. 22 Biomechanical modelling shows that with an increase in BMI, the protective effect of fat on tissue deformation is gradually offset by the increased pressure load caused by higher body weight, and the risk of pressure ulcers gradually increases. 23 The large body weight of obese patients, especially morbidly obese patients, creates greater local stress and makes turning care extremely difficult, though this is mitigated to some extent by adequate medical staffing in the ICU. 24 In addition, obese patients often have a higher prevalence of diabetes, and the resulting impaired peripheral circulation may contribute to the development of pressure ulcers. 25
We also found that overweight, critically ill patients had the lowest risk of developing pressure ulcers. Although the idea that “moderate obesity” has a protective effect on critically ill patients is increasingly accepted by critical care providers, there is a lack of sufficient research findings to support this in the area of pressure ulcers. 9 , 26 The mechanisms involved are not fully understood, but they may be related to several aspects. First, overweight patients have higher nutritional reserves compared with underweight and normal‐weight patients, which is more conducive to maintaining the nutritional supply of all tissues and organs and the stability of endocrine metabolic function in a state of high disease consumption; these patients also have a lower risk of developing diabetes and cardiovascular disease compared with obese patients. 8 Second, overweight individuals have thicker subcutaneous fat than individuals with a normal weight and underweight individuals, and a lower body weight than obese individuals, which enables them to effectively cushion the pressure load caused by body weight and minimise tissue distortion, leading to a lower risk of pressure ulcers. 2 , 23
It has been noted that about a third of grade 1 pressure ulcers in critically ill patients progress to more severe types, so stage 1 pressure ulcers were included in this study. 27 However, because most grade 1 pressure ulcers have superficial and reversible damage, they were not considered pressure ulcers in another part of this study. 14 , 15 We recalculated the sensitivity analysis after excluding stage 1 pressure ulcers, and the results were consistent with the inclusion of stage 1 pressure ulcers, suggesting good stability of the results.
The present study did have some limitations. First, although the sample size was large, retrospective studies have inherent limitations, including selection bias and missing data, and even if sensitivity analysis is interpreted to some extent, results still need further validation by a multicenter prospective study. Second, because the data used in the analysis were from an open database and detailed individual records were not available, the analysis assumed a static clinical environment in terms of pressure ulcer prevention interventions, equipment, and medical staff knowledge, which may have affected the results. In addition, BMI provides a summary measure of the overall nutritional status, but does not consider the distribution of muscle and body fat. As a risk factor for pressure ulcers, BMI should be considered more comprehensively in conjunction with other risk factors in practical clinical work.
4.1. Conclusion
There is an approximate U‐shaped association between BMI and pressure ulcers in critically ill patients, with both underweight status and obesity increasing the risk of pressure ulcers in these patients. Underweight patients have the highest risk of pressure ulcers, and overweight (but not normal weight) patients have the lowest risk, necessitating development of targeted prevention strategies for critically ill patients with different BMIs.
AUTHOR CONTRIBUTIONS
Jianhua Wu and Fujin Chen designed the study. Fujin Chen extracted the data from the MIMIC‐IV database. Fujin Chen, Jianhua Wu, and Bukao Ni analysed the data and drafted the manuscript. Xiaobo Wang provided critical revision of the manuscript for important intellectual content. Yujie Pan, Jianhua Wu and Bukao Ni reviewed and improved the paper. All authors read and approved the manuscript.
FUNDING INFORMATION
None.
CONFLICT OF INTEREST STATEMENT
The authors declare that they have no competing interests.
ETHICS STATEMENT
The Institutional Review Board at the Beth Israel Deaconess Medical Center approved the use of MIMIC‐IV for research purposes and waived the requirement for informed consent. The author Fujin Chen obtained the certificate (certificate number: 43529529) and permission to use the MIMIC‐ IV database after completing a web‐based course. The study was designed and conducted in accordance with relevant guidelines and regulations (Declaration of Helsinki).
Supporting information
Data S1. Supporting information.
ACKNOWLEDGEMENTS
Not applicable.
Chen F, Wang X, Pan Y, Ni B, Wu J. The paradox of obesity in pressure ulcers of critically ill patients. Int Wound J. 2023;20(7):2753‐2763. doi: 10.1111/iwj.14152
DATA AVAILABILITY STATEMENT
The datasets analysed during the current study are available in the Medical Information Mart for Intensive Care IV database (MIMIC‐IV version 2.0) repository. https://physionet.org/content/mimiciv/2.0/
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data S1. Supporting information.
Data Availability Statement
The datasets analysed during the current study are available in the Medical Information Mart for Intensive Care IV database (MIMIC‐IV version 2.0) repository. https://physionet.org/content/mimiciv/2.0/