Pressure Injury Risk Factors in Patients Undergoing General Anesthesia Surgeries

Pressure injuries, formerly known as pressure ulcers, are damage to the skin and underlying tissues primarily caused by prolonged local pressure disrupting blood circulation, often over bony areas.^1,2 In 2016, the term pressure ulcer was changed to pressure injury by the National Pressure Injury Advisory Panel because not all such injuries lead to visible tissue damage or ulceration.³ In addition to physical discomfort, pressure injuries lead to an increased risk of infection, extended postoperative recovery period, and longer hospitalization period, all of which are detrimental to patients’ quality of life.⁴ Additionally, they are associated with an economic burden, and medical expenses and pressure on health care systems are increasing.⁵ This burden is particularly noteworthy when the global pressure injury incidence rate of 7.8% to 13.5%⁶ and surgery-related injury rate of 12.0% to 24.7% are considered.^7,8

Pressure injuries are harmful to patients and a major problem that exhausts medical resources. In one study, US hospital-acquired pressure injuries were associated with an average cost of $10 708 per patient, with the total annual cost being approximately $26.8 billion.⁹ Another study estimated that the total cost of treating pressure injuries in the United States was $11.0 billion per year.¹⁰ The cost associated with pressure injuries in Australian public hospitals was $9.11 billion (US) in 2020.¹¹ Early identification of the signs of pressure injury may help minimize the associated economic burden and enable the adoption of effective measures for improving patient quality of life.

Patients with postoperative pressure injuries experience discomfort due to their surgical wounds and pain due to the injury itself. In addition to basic nursing care, these patients require close monitoring, which places a considerable burden on health care workers. Thus, identifying the causes of pressure injuries in patients undergoing surgery is crucial for its prevention. Most studies on pressure injury causes in surgical patients have primarily included age, body mass index (BMI), preoperative Braden scale score, surgery duration, American Society of Anesthesiologists (ASA) physical classification, and surgical position as study variables.^12-14 In general, patients receiving general anesthesia are required to fast before their surgery. Prolonged fasting may cause various degrees of dehydration,¹⁵ leading to a decrease in blood sugar levels and lipolysis of body fats, which can contribute to pressure injury.¹⁶ Furthermore, ancillary warmers (eg, electric blankets), which are commonly used in surgery to maintain patients’ body temperature during the procedure, increase the risk of pressure injury¹⁷; layering of such warmers increases the pressure on patients’ skin and tissues. In addition, the vasoconstriction activities of vasopressors used intraoperatively may interfere with hemostatic effects and skin perfusion, which increases the incidence rate of pressure injury.¹⁸ The aforementioned variables require in-depth investigation. Thus, in the current study, the authors explored the characteristics of patients with pressure injuries who underwent surgery under general anesthesia and those of the surgeries performed on these patients. In addition, the authors investigated possible correlations between patient characteristics, surgical characteristics, and pressure injury risk.

Study Design

In this retrospective study, data were collected from patients who underwent surgery from January 1, 2018, through December 31, 2018. Pressure injuries that develop ≥72 hours postoperatively can be attributed to the nursing care patients receive.¹⁹ Therefore, observational data related to the signs of pressure injury during surgery and at 3 days after the procedure were used in this study. This study was approved by the institutional review board of the study hospital (approval number: IRB2021032). Because of the retrospective nature of the study, obtaining patient consent was not required.

Settings and Participants

This study included patients who underwent surgery under general anesthesia at a regional teaching hospital in southern Taiwan. The inclusion criteria were as follows: age >18 years and receiving general endotracheal anesthesia, general anesthesia with a laryngeal mask, or epidural anesthesia. Outpatients, patients receiving intravenous general anesthesia, patients with any pre-existing pressure injury, and patients with any medical device-related pressure injury were excluded from this study. A literature review revealed that the minimum surgical duration for the development of pressure injury is 135 to 158.67 minutes^13,20; therefore, patients receiving intravenous general anesthesia were excluded. Patients who received epidural anesthesia were included in this study because anesthetics can be administered through a catheter to maintain continuous anesthesia in these cases.

Data Collection Tools

Data on patient risk factors were collected by reviewing recent studies.^12,21,22 The risk factors associated with surgical pressure injuries in the studies included age; sex; BMI; preoperative Braden scale score; anemia; intraoperative body temperature; intraoperative blood pressure; comorbidities, such as diabetes, hypertension, and heart disease; and smoking status. Regarding surgical risk factors, data on surgery duration, fasting duration, intraoperative ancillary warmer use, vasopressor use and type, general anesthesia type, ASA physical classification, intraoperative blood loss volume, surgical position, and other factors possibly associated with pressure injury were collected for analysis.

Data Collection

Data were extracted from paper-based medical records (on-site review) and the hospital’s surgery and nursing information systems. The data were anonymized and entered into a spreadsheet (Excel, Microsoft Corp).

Statistical Analysis

SPSS v20 (IBM Corp) was used for data analysis. Descriptive statistics were used to describe the distribution of patient and surgical characteristics, namely age, sex, BMI, preoperative Braden scale score, preoperative hemoglobin level, preoperative hematocrit, intraoperative body temperature, intraoperative blood pressure, comorbidities (eg, diabetes, hypertension, and heart disease), smoking status, surgery duration, fasting duration, anesthesia duration, ancillary warmer use, vasopressor use and type, anesthesia type, ASA physical classification, intraoperative blood loss volume, and surgical position. Continuous variables are presented as numbers, percentages, means, and standard deviations. Logistic regression was performed to identify correlations between patient and surgical characteristics and factors influencing this correlation.

This study included 11 231 postoperative patients (men, 55.6%; mean age, 57.0 ± 17.5years). The risk factors for pressure injury are summarized in Table 1; missing values are indicated with an em dash (—). The patients’ mean BMI, preoperative Braden scale score, hemoglobin level, and hematocrit were 25.1 ± 4.5 kg/m², 21.9 ± 1.8, 13.4 ± 14.2 g/dL, and 39.2 ± 6.6%, respectively. The minimum and maximum intraoperative body temperatures were 35.2°C ± 0.9°C and 35.8℃ ± 0.7°C, respectively. The minimum intraoperative diastolic blood pressure was 51.7 ± 9.7 mm Hg, and the frequency of intraoperative diastolic blood pressure of <60 mm Hg was 9.7 ± 12.8; the mean duration of intraoperative diastolic blood pressure of <60 mm Hg was 48.3 ± 64.2 minutes. The intraoperative diastolic blood pressure was <60 mm Hg in 8629 patients (76.8%). Of the included patients, 2364 (21.0%) were smokers. Regarding comorbidities, 4223 patients (37.6%) had hypertension, 2444 (21.8%) had diabetes, and 1073 (9.6%) had heart disease. The mean surgery duration, fasting duration, and blood loss volume were 109.1 ± 22.7 minutes, 657.0 ± 213.2 minutes, and 110.5 ± 258.1 mL, respectively. Intraoperative ancillary warmers and vasopressors were used in 3817 (34.0%) and 5527 (49.2%) patients, respectively. Most patients (n = 7093; 63.2%) received general endotracheal anesthesia. The most common surgical position was the supine position (n = 6707; 59.7%). In total, 7643 patients (68.1%) had an ASA physical classification of II.

Of the included patients, 250 developed postoperative pressure injuries. The following data apply to these 250 patients: most were men (56.8%; mean age, 63.08 ± 15.863 years), and 131 (52.4%) were aged ≥65 years. The mean BMI was 25.197 ± 5.756 kg/m², and 134 patients (53.6%) had a BMI of ≥24 kg/m². Not all patients undergoing surgery required a preoperative Braden scale score, and only 193 patients were checked. The mean preoperative Braden scale score of the 193 patients was 21.62 ± 2.007, and the score was 19 to 23 for 178 patients (92.2%). The mean hemoglobin level and hematocrit were 12.771 ± 2.3024 g/dL and 38.174% ± 5.945%, respectively. The mean minimum and maximum intraoperative body temperatures were 34.384℃ ± 1.821°C and 35.733℃ ± 0.806°C, respectively; most patients had a body temperature of <36℃. The mean minimum diastolic blood pressure was 47.21 ± 7.348 mm Hg, and 228 (91.2%) patients had diastolic blood pressure of <60 mm Hg. Among these 250 patients, 57 (22.8%) smoked, 124 (49.6%) had hypertension, 77 (30.8%) had diabetes, and 35 (14.0%) had heart disease (Table 2). The mean duration of surgery was 140.2 ± 125.4 minutes; this duration was ≤120 minutes in 137 (54.8%) patients. The mean fasting duration was 660.6 ± 234.2 minutes, and this duration was >480 minutes in 205 (82.0%) patients. The mean volume of blood loss was 433.8 ± 623.0 mL, and this volume was >500 mL in 61 (24.4%) patients. Ancillary warmers and vasopressors were used in 117 (46.8%) and 205 (83.7%) patients, respectively. A total of 161 patients (64.4%) received general endotracheal anesthesia, and 166 (66.4%) patients had an ASA physical classification of II. The supine position was the most common surgical position (n = 104; 41.6%; Table 3).

The distribution of the classification and location of postoperative pressure injuries is presented in Table 4. The same patient may develop postoperative pressure injuries in different parts of the body. The total number of pressure injuries was 369. The locations are listed with corresponding frequencies: coccyx, 83 (22.5%); chest, 62 (16.8%); and gluteus, 44 (11.9%). Regarding classification of International Pressure Injury Classification System, 248 patients (99.2%) had class 1 pressure injuries and 2 patients (0.8%) had class 2 pressure injuries. In these 2 patients, pressure injuries developed in the inguinal area.

The results of the logistic regression evaluating the effects of age, hypertension, diabetes, heart disease, intraoperative diastolic blood pressure, vasopressor use and type, surgery duration, hemoglobin level, hematocrit, ASA physical classification, ancillary warmer use, preoperative Braden scale score, blood loss volume, minimum intraoperative body temperature, and surgical position on postoperative pressure injury risk are shown in Table 5. The results reveal the following risk factors: age of ≥65 years; intraoperative diastolic blood pressure of <60 mm Hg for a total duration of >30 minutes; intraoperative dopamine, norepinephrine, or epinephrine use; surgery duration of >120 minutes; ASA physical classification of III or greater; blood loss volume of >500 mL; minimum intraoperative body temperature of ≤35°C; and supine and prone surgical positions.

Few studies on pressure injuries in surgical patients have focused on fasting duration, ancillary warmer use, or intraoperative vasopressor use and type. Therefore, these variables were included in the present study. The correlation between vasopressor use and postoperative pressure injury varied markedly with the type of vasopressor used (ie, dopamine, norepinephrine, or epinephrine). The findings indicate that the patients were susceptible to pressure injury because of changes in their hemodynamics due to the use of anesthesia, which resulted in reduced tissue perfusion and cellular hypoxia. The use of dopamine, norepinephrine, or epinephrine correlated with the development of pressure injury. Although Celik et al demonstrated that vasopressor use is associated with pressure injuries, the types of vasopressors investigated in their study were not specified; thus, a comparison of their study with the current study is not possible.²³ Dong et al revealed a strong correlation between dopamine use and pressure injury, which corroborates the findings of the current study.²⁴ Conversely, Tura et al reported no prominent associations between vasopressor use and pressure injury.²⁵ Because the vasopressor types used in their study were not specified, further comparison and analysis were not possible.

In the current study, the use of auxiliary warmers did not correlate with the development of pressure injury; this finding is consistent with those of Kandemir et al²⁶ but not with those of Weng et al.¹⁷ However, Weng et al¹⁷ did not report the temperature settings of the warmers, and therefore, the difference in results cannot be analyzed. Moreover, the mean surgery duration in the pressure injury group in the aforementioned study was >3 hours, which is longer than that in the current study. Patients’ skin is at an elevated temperature after prolonged maintenance of the supine position, which increases the incidence of pressure injury. Therefore, appropriate temperature settings are essential. Surgical drapes not only place additional weight on patients but also increase their skin temperature, thus increasing the risk of pressure injury.

In the current study, no significant correlation was identified between fasting duration (>8 hours) and pressure injury risk, which is consistent with findings reported by Xiong et al.¹⁶ Data regarding fasting duration were collected from nursing records in the current study; however, the actual fasting durations might have been longer than those recorded. Furthermore, when fasting, the patients received rehydration solutions to prevent hypoglycemia. Few studies have assessed this variable, and therefore, it may present a direction for future research. Actual fasting data should be used to investigate the correlation between the use of supplemental fluids and blood sugar administered to patients during the fasting period and the risk of pressure injury.

The finding of the current study that an age of ≥65 years is a risk factor for pressure injuries indicates that older patients are more susceptible to such injuries, which is consistent with the findings of several studies.^13,14,27 Older patients are likely to develop pressure injuries because of their reduced skin and muscle mass, which compromises the skin repair mechanism. No significant correlation was identified between BMI and pressure injury risk; this finding is consistent with those of Celik et al²³ and Cemile and Sayin.²⁸ In the current study, most patients with pressure injuries had a BMI of ≥24 kg/m². Therefore, intraoperative preventive measures are required for patients who are overweight.

Preoperative Braden scale score did not correlate with pressure injury risk in this study, which corroborates the findings of Ma et al.²⁹ Most patients in the current study had preoperative Braden scale scores of 19 to 23, which indicates that pressure injuries can develop regardless of whether a person has a favorable skin condition. Nonetheless, adequate preventive measures can be used in conjunction with the risk assessment scale to identify high-risk patients as early as possible and appropriately use silicone foam dressings or fat pads to prevent pressure injuries.

No significant correlation was identified between anemia and postoperative pressure injury risk; this finding is similar to those reported by Celik et al.²³ By contrast, Tura et al²⁵ identified a strong correlation between preoperative hemoglobin levels and postoperative pressure injury risk. The mean hemoglobin level of the patients in that study might have been lower than that (normal range) of the patients in the current study and that of those in Celik et al.²³ Moreover, few patients with malnutrition were included in the current study. Further studies are required to investigate the correlations among anemia, nutrition, and pressure injury risk.

The current study revealed correlations of pressure injury risk with hypothermia and intraoperative diastolic blood pressure of <60 mm Hg; these findings are similar to those of Celik et al²³ and Karahan et al,³⁰ indicating that the temperature of the operating room should be properly maintained during surgery. Patient body temperature and blood pressure should be monitored to prevent increased metabolic load and oxygen consumption, which may result in tissue ischemia and cell death, leading to pressure injury. The multivariate analysis revealed no correlations between comorbidities and pressure injury risk; this finding contradicts that of a meta-analysis conducted by Haisley et al.²¹ The difference in findings might be because the sample size of patients with comorbidities was smaller in the current study than that of the earlier study. Protective measures should be adopted in surgery for patients with comorbidities.

In this study, surgery duration of >120 minutes, ASA physical classification of III or greater, and blood loss volume of >500 mL were strongly correlated with pressure injury risk; this finding is consistent with those of Haisley et al²¹ and Aloweni et al.²⁷ A surgery duration of >120 minutes was associated with a pressure injury risk that was 1.687 times higher than that seen in patients whose surgery duration was ≤120 minutes. Patients with higher ASA physical classifications were also more likely to develop pressure injuries. The volume of intraoperative blood loss may vary across surgery types; this should be considered in future studies investigating the correlation between intraoperative blood loss and pressure injury risk.

A supine or prone surgical position was strongly correlated with postoperative pressure injury risk; this finding is consistent with those of several other studies.^16,24,31 Pressure points vary across surgical positions, and pressure injuries may develop in the absence of appropriate preventive measures. In the current study, most patients were in the prone position during surgery; thus, most pressure injuries developed in the chest and iliac crest areas. The second most common position was the lateral position; in patients who underwent surgery in the lateral position, most pressure injuries developed on the iliac crest. The skin and tissue over bony prominences are susceptible to pressure injuries because of the lack of fat tissues. Thus, in this study, patients who were underweight exhibited the highest incidence of postoperative pressure injuries. Therefore, preventive measures should be adopted for surgical patients who are underweight and those who must be in the prone or lateral position during surgery. Furthermore, depending on surgeons’ preferences, various ancillary equipment may be used intraoperatively when patients assume the prone position. The use of such devices as bow frames, spine frames, chest rolls, and variations of bow frames may affect the incidence of pressure injuries.

This study has several limitations. Notably, 22.8% of the included patients did not have Braden scale scores. However, most of the scores that were obtained indicated low risk, and therefore, even if the missing values indicated high risk, the overall risk landscape would remain largely the same. The missing data were missing completely at random (MCAR), meaning the absence of the data was not influenced by any observed or hidden variables. Although unaddressed missing data may pose statistical challenges, the MCAR nature of these missing data adds a degree of confidence to the analysis.³³ The authors focused primarily on diastolic blood pressure and therefore were unable to obtain insights related to systolic blood pressure. Additionally, the study was undertaken at a single center, and these results may not be generalizable to patients in different types of institutions.

The study identified age, surgery duration, intraoperative diastolic blood pressure, vasopressor use, ASA physical classification, minimum intraoperative body temperature, blood loss volume, and surgical position as pressure injury risk factors. To mitigate these risks, it is imperative for surgical teams to implement a comprehensive approach that encompasses monitoring patient age and medical history, controlling the duration of surgery to alleviate pressure, regulating diastolic blood pressure, selecting vasopressors with caution to ensure their effective and safe use, adhering to ASA guidelines for managing high-risk patients, maintaining an optimal intraoperative body temperature, minimizing blood loss, and employing appropriate surgical positions and devices designed to relieve pressure.

Additionally, implementing regular repositioning protocols and using pressure-reducing devices can help prevent pressure injuries during the perioperative period. Proper education and training for health care staff on pressure injury prevention and management are crucial to ensuring optimal outcomes for patients.

Special thanks to Ditmanson Medical Foundation Chia-Yi Christian Hospital for providing study data.

Affiliations: ¹Department of Nursing, Ditmanson Medical Foundation Chia-Yi Christian Hospital, Taiwan; ²Department of Nursing, Chang Gung University of Science and Technology, Chia-Yi Campus, Taiwan; ³Chronic Diseases and Health Promotion Research Center, Chang Gung University of Science and Technology, Chia-Yi Campus, Taiwan; ⁴School of Nursing, Chung Shan Medical University, Taiwan.

Disclosure: The authors disclose no financial or other conflicts of interest.

Correspondence: Tsui-Hua Hsu, Department of Nursing, Chang Gung University of Science and Technology, Chia-Yi Campus, No. 2, Sec. W., Jiapu Rd., Puzi City, Chiayi County 613, Taiwan; thhsu@mail.cgust.edu.tw

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