Abstract
This study was to clarify the connection between extrinsic factors and the risk of perioperative pressure injuries (PIs) through the case–control approach, which involved making the intrinsic factors of the patients in the control group with no PIs consistent with those of the case group with PIs. We collected samples from a teaching hospital in Taiwan. We found a total of 132 patients deemed to have developed perioperative PIs. Using 1:2 frequency matching, we matched these cases with patients who had not developed PIs by gender, age, and BMI. Binary logistic regression analysis of the odds ratios of the extrinsic factors and PI risk revealed that the independent variables with statistical significance included duration of anaesthesia 3 h, amount of blood loss, use of electric blankets, diastolic blood pressure below 60 mmHg during surgery, and oxyhemoglobin saturation by pulse oximetry (SPO2) below 93% during surgery. Emphasis should be placed on cooperation among the medical team during surgery, less use of electric blankets, control over the duration of anaesthesia and blood loss, continuous monitoring of the patient during surgery for any emergencies, and the maintenance of patient diastolic blood pressure and blood oxygen levels to reduce the risk of PIs.
Keywords: electric blankets, extrinsic factor, perioperative, pressure injury, pressure‐relieving devices
1. INTRODUCTION
Pressure injuries (PIs) not only consume medical resources but also tend to weaken patients. 1 They are thus an important topic in the field of global healthcare. The risk of PIs among inpatients varies with the nursing environment, and the operating room is considered one of the most dangerous environments for PI development. Indeed, at least one out of every ten surgical patients develop perioperative PIs and Scott et al. suggested that over 25% of the PIs in hospitals are caused by surgery. 2 , 3 Most PIs can be prevented; therefore, to promote healthcare quality and reduce social costs and the mental and economic burdens faced by patients, the prevention of perioperative PIs is an important challenge to overcome. 4 PIs develop when capillaries are blocked or when muscle tissues lack a blood supply. Muscle tissue around the skin that has been under pressure for long periods of time oxygen and nutrients, thus resulting in damage that could potentially be irreversible. 5 , 6
Researchers have identified various causes of PIs among surgical patients. Shafipour et al. conducted a meta‐analysis involving 2540 female surgical patients that presented a PI incidence rate of 12.8% and 3632 male surgical patients that presented a PI incidence rate of 10.1%, thereby revealing that the incidence rate of PIs is higher among female surgical patients than among male surgical patients. 7 Age‐related deterioration in skin elasticity and local circulation reduce tissue tolerance to hypoxia, so age is also a crucial risk factor of PIs. 8 Obesity can cause microvascular dysfunction and diseases, which affect lymphatic drainage and cause lymphedema and circulation‐related skin changes, which can promote the development of PIs. 9 Furthermore, smoking can cause systemic atherosclerosis as well as peripheral vasoconstriction, which reduces blood flow and oxygen perfusion in the skin. 10 Although anaemia is not the only intrinsic factor of PI occurrence, research has shown that low haemoglobin can cause the body to lack the number of red blood cells required to supply oxygen to tissues. Changes in the oxygen dissociation curve can cause local tissue hypoxia, which in turn facilitates the development of PIs. 10 Haemoglobin levels below 10 g/dL, in particular, affect tissue oxygenation and make it difficult for wounds to heal. 11
Regarding comorbidities, diabetes causes glycosylated vessels, which reduce blood perfusion and lead to skin ischemia. 10 Heart diseases are often accompanied by decreased cardiac output or oxygenation, which causes hypotension, poor blood perfusion, and local peripheral ischemia, as well as delayed reperfusion of the ischemic tissue and impaired lymphatic drainage. These factors all lower tissue tolerance and the thresholds of PI occurrence. Congestive heart failure, in particular, causes oedema or dehydration, which may lead to structural changes in the skin and promote the development of PIs. 12 Generally speaking, strokes are caused by cerebrovascular atherosclerosis, so poor perfusion and the side effects of anticoagulants may facilitate the development of PIs. 10 Long‐term dialysis patients have poor peripheral blood flow, which can indirectly influence the development of PIs. 13 The Physical Status Classification System developed by the American Society of Anesthesiologists (ASA) is used to assess whether anaesthesia and analgesia pose a risk to patients. Patients with a higher ASA classification are more likely to develop comorbidities or even die after receiving treatment, anaesthesia, or analgesia. Research has shown that ASA classification is a crucial predictor of PI occurrence among surgical patients. 14 , 15
Perioperative PI development is caused by interactions among multiple intrinsic and extrinsic factors. The primary intrinsic causes of PIs among surgical patients are uncontrollable factors, whereas extrinsic factors are controllable. 16 Less research has been conducted on perioperative PIs; most existing studies are focused on inpatients in general wards. We, therefore, employed a case–control approach and strived to make the intrinsic factors of the patients in the control group with no PIs consistent with those of the case group with PIs. Our aims were to clarify the connection between extrinsic factors and the risk of perioperative PIs and propose effective preventive and improvement measures to prevent perioperative PI occurrence.
2. MATERIAL AND METHOD
2.1. Design and participants
We collected samples using purposive sampling. The samples for the case and control groups were chosen from the patients of a teaching hospital in Taiwan during the 36‐month period from January 1, 2019, to December 31, 2021.
We first searched the PI reporting subsystem of the hospital's internal Adverse Event Reporting System and found 132 patients that had been deemed to have developed perioperative PIs by the healthcare quality department. All of the patients had received general anaesthesia. Using 1:2 frequency matching, we then matched these cases with patients who had also received general anaesthesia during the same time period but had not developed PIs by gender, age (60 years old or > 60 years old), and BMI (<19 kg/m2, > 40 kg/m2, or 19‐40 kg/m2) for retrospective medical record analysis.
2.2. Sample size
We determined the number of samples needed for this study using G‐power to perform the power analysis of the binary logistic regression analysis. For 80% power, α value of 0.05, and estimated relative risk of 3, we estimated that we needed at least 365 samples, which is why we employed 1:2 frequency matching.
2.3. Data collection
The intrinsic factors contributing to PIs among surgical patients include gender, age, BMI, smoking, HB <10 g/dL, comorbidities (diabetes, cardiovascular diseases, stroke, and regular dialysis), and ASA classification. Research has proven that patients over the age of 60 are more likely to develop PIs, 17 so we used 60 years old as the demarcation point. Ness et al. pointed out that underweight and obese individuals are at greater risk of PIs than those with a normal weight. 18 We, therefore, divided the patients into three BMI groups: underweight (BMI <19 kg/m2), normal weight (BMI 19‐40 kg/m2), and obese (BMI > 40 kg/m2). Patients with low haemoglobin (HB <10 g/dL) may have already had nutritional anaemia before their surgery, which can affect the elasticity of their skin. 19 The ASA Physical Status Classification System divides patients into five classifications based on whether anaesthesia and analgesia pose a risk to them. A higher ASA classification indicates a higher likelihood of comorbidities or even death after the patients receive treatment, anaesthesia, or analgesia. Eberhardt et al. specified that an ASA classification of 3 or higher is a factor that can trigger perioperative PI development. 20 We, therefore, divided the patients into two groups by ASA classification: 3 and < 3.
The extrinsic factors contributing to PIs among surgical patients included surgical type, patient positioning, duration of anaesthesia, amount of blood loss, use of pressure‐relieving devices (gel pads, water cushions, heel troughs, prone position foam pads, and axillary rolls), use of thermoregulation devices (the Bair Hugger, electric blankets, and heating lamps), and special perioperative circumstances (body temperature above 37°C, diastolic blood pressure below 60 mmHg, and oxyhemoglobin saturation by pulse oximetry (SPO2) below 93%).
Heart surgery is unique in that it involves extracorporeal circulation and lowering the patient's body temperature to induce peripheral vasoconstriction and reduce the blood supply to peripheral tissues, which increases the risk of PIs. 21 During orthopaedic and neurosurgical spine surgery, patients are placed in a prone position, which alters the body's centre of gravity and applies pressure and shear forces to the face, chest, anterior superior iliac spine, and knees. These body parts have less adipose tissue, which increases the chance of PIs. 22
Research has established a strong connection between patient positioning during surgery and PI occurrence 15 Shaw et al. discovered that patients placed in a prone or lateral position during surgery were more likely to develop PIs than those placed in a supine position. 23 PIs are possible even when the duration of surgery is 1.5 to 2 h, but the Minnesota Hospital Association only considers durations over 3 h to be a high‐risk factor for PIs. 24 Increased blood loss during surgery decreases cardiac output and blood pressure. Diastolic blood pressure below 60 mmHg, in particular, alters the hemodynamics and impedes tissue perfusion, which affects tissue tolerance to pressure. 25
In addition, heating devices may be used during surgery to maintain the patient body temperature, but excessive perspiration leads to moisture on the skin, which weakens the skin's natural barrier. 26 For every 1°C increase in body temperature, metabolism rates and oxygen consumption increase by 10%, and the fixed positions necessary for surgery mean continued tissue compression. These factors increase the oxygen demand and metabolic waste of cells. Thus, the use of thermoregulation devices and body temperatures above 37°C can both increase the chance of skin damage. 27
In this study, the hospital used the Bair Hugger, electric blankets, humidifiers, and heating lamps to regulate patient body temperatures during surgery. Next, static pressure‐relieving devices are mostly used in operating rooms. These devices are generally pads made of gel, water, foam, or a mix of these materials and mainly distribute localised pressure to a larger body surface area to regulate or redistribute pressure. 28 In this study, the hospital used pressure‐relieving devices such as gel pads, water cushions, heel troughs, prone position foam pads, and axillary rolls to reduce the risk of PIs among surgical patients. Pulse oximeters are used in the operating room to measure tissue oxygen saturation. 29 Oxygen saturation levels below 93% indicate inadequate oxygenation and perfusion in the body, which means that normal tissue cell functions cannot be maintained, and this is of utmost importance to tissue damage. 30
2.4. Ethical considerations
The study is a sub‐project of a large‐scale research project; some of the results have already been published. 31 Data collection began after gaining approval from the institutional review board, Office of Human Research at Taipei Medical University—Joint Institutional Review Board (Approval Number: N202106059).
2.5. Data analysis
To reduce the differences in the intrinsic factors, we adopted 1:2 frequency matching to match the patients in the PI case group with those in the control group by gender, age, and BMI. We then performed chi‐square tests to compare the intrinsic and extrinsic factors of the two groups and used binary logistic regression to calculate the odds ratios (ORs) and 95% confidence intervals of the extrinsic factors and PI risk. The statistical analyses were performed using SPSS 19 (SPSS Inc., Chicago, IL, USA) with P values less than 0.05 indicating statistical significance.
3. RESULTS
3.1. Analysis of intrinsic factors in the PI case group and control group
Table 1 presents the distributions of the intrinsic factors, including gender, age, BMI, smoking, HB, comorbidities, and ASA classification, in the case group and the control group. The preliminary findings of chi‐square tests indicated no significant differences between the intrinsic factors of the two groups.
TABLE 1.
Distributions and chi‐square analysis of intrinsic factors of pressure injuries (PIs) among surgical patients
| Intrinsic factor | All | Case group | Control group | P |
|---|---|---|---|---|
| N = 396 | n = 132 | n = 264 | ||
| N (%) | n (%) | n (%) | ||
| Gender | 1.000 | |||
| Male | 282 (71.2) | 94 (71.2) | 188 (71.2) | |
| Female | 114 (28.8) | 38 (28.8) | 76 (28.8) | |
| Age | 1.000 | |||
| ≤60 years old | 165 (41.7) | 55 (41.7) | 110 (41.7) | |
| >60 years old | 231 (58.3) | 77 (58.3) | 154 (58.3) | |
| BMI | 1.000 | |||
| <19 kg/m2 | 78 (19.7) | 26 (19.7) | 52 (19.7) | |
| >40 kg/m2 | 12 (3.0) | 4 (3.0) | 8 (3.0) | |
| 19 to 40 kg/m2 | 306 (77.3) | 102 (77.3) | 204 (77.3) | |
| Smoking | 0.076 | |||
| Yes | 118 (29.8) | 44 (33.3) | 74 (28.0) | |
| No | 231 (58.3) | 78 (59.1) | 153 (58.0) | |
| Quit for more than 1 year | 50 (12.6) | 10 (7.6) | 40 (15.2) | |
| HB <10 g/dL | 0.474 | |||
| Yes | 357 (90.2) | 117 (88.6) | 240 (90.9) | |
| No | 39 (9.8) | 15 (11.4) | 24 (9.1) | |
| Comorbidities (multiple conditions possible) | ||||
| Diabetes | 98 (24.7) | 40 (30.3) | 58 (22.0) | 0.070 |
| Cardiovascular diseases | 177 (44.7) | 81 (61.4) | 138 (52.3) | 0.086 |
| Stroke | 48 (12.1) | 16 (12.1) | 32 (12.1) | 1.000 |
| Regular dialysis | 17 (4.3) | 5 (3.8) | 12 (4.5) | 0.726 |
| ASA classification | 0.607 | |||
| <3 | 309 (78.0) | 101 (76.5) | 208 (78.8) | |
| ≥3 | 87 (22.0) | 31 (23.5) | 56 (21.2) | |
Abbreviations: ASA, American Society of Anesthesiologists; BMI, body mass index; HB, haemoglobin.
3.2. Pressure injuries in patients during surgery and distribution of characteristics
Table 2 shows the grades of PIs as well as the sizes and locations of PIs among surgical patients. The majority of patients were in Stage 2. The average area of PIs was 48.9 (107.6) cm2, and no significant differences were found in the area of PIs at different stages. PIs occurred most commonly on the upper body, and there was a significant difference in the location of PIs at different stages (P < 0.001).
TABLE 2.
Grades of pressure injuries (PIs) as well as sizes and locations of PIs among surgical patients
| Intrinsic factor | Case group | Stage 1 PIs | Stage 2 PIs | Unstageable or suspected deep tissue injuries | P |
|---|---|---|---|---|---|
| n = 132 | n = 45 | n = 86 | n = 1 | ||
| Area of PI (length × width cm2), Mean (SD) | 48.9 (107.6) | 40.1 (46.0) | 54.1 (129.0) | 0.1 (−) | 0.704 a |
| Location of PI, n (%) | <0.001 b | ||||
| Head | 4 (3.0) | 2 (4.4) | 2 (2.3) | 0 | |
| Shoulders or upper limbs | 6 (4.5) | 1 (2.2) | 5 (5.8) | 0 | |
| Torso | 50 (37.9) | 2 (4.4) | 47 (54.7) | 1 (100) | |
| Back | 9 (6.8) | 5 (11.1) | 4 (4.7) | 0 | |
| Greater trochanter or iliac crest | 4 (3.0) | 0 | 4 (4.7) | 0 | |
| Sacrum or ischium | 53 (40.3) | 32 (71.2) | 21 (24.4) | 0 | |
| Heel bone in foot or ankle | 6 (4.5) | 3 (6.7) | 3 (3.4) | 0 |
One‐way ANOVA.
Chi‐square analysis.
3.3. Analysis of extrinsic factors in the PI case group and control group
The preliminary findings of chi‐square tests in Table 3 revealed significant differences between the case group and the control group in the duration of anaesthesia (P < 0.001), amount of blood loss (P < 0.001), the use of gel pads (P = 0.003) and water cushions (P = 0.032) in pressure‐relieving devices, the use of electric blankets (P < 0.001) in thermoregulation devices, and body temperature above 37°C (P = 0.020), diastolic blood pressure below 60 mmHg (P < 0.001), and SPO2 below 93% (P = 0.003) in special perioperative circumstances. No significant differences were found between the two groups in the remaining extrinsic factors.
TABLE 3.
Distributions and chi‐square analysis of extrinsic factors of pressure injuries (PIs) among surgical patients
| Extrinsic factor | N = 296 | Case group | Control group | P |
|---|---|---|---|---|
| n = 132 | n = 164 | |||
| All | N (%) | n (%) | n (%) | |
| Surgical type | ||||
| Cardiovascular surgery | 7 (1.8) | 1 (0.8) | 6 (2.3) | 0.281 |
| Orthopaedic surgery | 51 (12.9) | 16 (12.1) | 35 (13.3) | 0.750 |
| Neurosurgery | 166 (41.9) | 61 (46.2) | 105 (39.8) | 0.221 |
| Patient positioning | 0.916 | |||
| Supine position | 217 (54.9) | 73 (55.3) | 144 (54.5) | |
| Lateral position | 35 (8.8) | 8 (6.1) | 27 (10.2) | |
| Prone position | 128 (32.3) | 49 (37.1) | 79 (29.9) | |
| Other | 16 (4.0) | 2 (1.5) | 14 (5.3) | |
| Duration of anaesthesia | <0.001 | |||
| ≥3 h | 286 (72.2) | 123 (93.2) | 163 (61.7) | |
| <3 h | 110 (27.8) | 9 (6.8) | 101 (38.3) | |
| Amount of blood loss | <0.001 | |||
| ≤100 mL | 227 (57.3) | 39 (29.5) | 188 (71.2) | |
| 101 to 500 mL | 104 (26.3) | 45 (34.1) | 59 (22.3) | |
| 501 to 999 mL | 28 (7.1) | 19 (14.4) | 9 (3.4) | |
| ≥1000 mL | 37 (9.3) | 2 9 (22.0) | 8 (3.0) | |
| Use of pressure‐relieving devices (multiple choices possible) | ||||
| Gel pads | 27 (6.8) | 16 (12.1) | 11 (4.2) | 0.003 |
| Water cushions | 39 (9.8) | 19 (14.4) | 20 (7.6) | 0.032 |
| Heel troughs | 8 (2.0) | 4 (3.0) | 4 (1.5) | 0.312 |
| Prone‐position foam pads | 24 (6.1) | 7 (5.3) | 17 (6.4) | 0.655 |
| Axillary rolls | 44 (11.1) | 19 (14.4) | 25 (9.5) | 0.142 |
| Use of thermoregulation devices (multiple choices possible) | ||||
| Bair Hugger | 395 (99.7) | 131 (99.2) | 264 (100) | 0.157 |
| Electric blankets | 35 (8.8) | 29 (22.0) | 6 (2.3) | <0.001 |
| Humidifiers | 395 (99.7) | 132 (100) | 263 (99.6) | 0.479 |
| Heating lamps | 10 (2.5) | 5 (3.8) | 5 (1.9) | 0.257 |
| Special perioperative circumstances (multiple conditions possible) | ||||
| Body temperature above 37°C | 106 (26.8) | 45 (34.1) | 61 (23.1) | 0.020 |
| Diastolic blood pressure below 60 mmHg | 290 (73.2) | 126 (95.5) | 164 (62.1) | <0.001 |
| SPO2 below 93% | 27 (6.8) | 16 (12.1) | 11 (4.2) | 0.003 |
Abbreviation: SPO2, pulse oximetry.
3.4. Influence of extrinsic factors on the risk of PIs
The results in Table 4 show that the extrinsic factors that reached statistical significance included duration of anaesthesia (B = 1.07, OR = 2.9, P = 0.013), amount of blood loss 101 to 500 mL (B = 0.80, OR = 2.23, P = 0.012), amount of blood loss 501 to 999 mL (B = 1.63, OR = 5.09, P = 0.001), amount of blood loss 1000 mL (B = 2.28, OR = 9.81, P < 0.001), use of electric blankets (B = 2.10, OR = 8.14, P < 0.001), diastolic blood pressure below 60 mmHg during surgery (B = 2.09, OR = 8.09, P < 0.001), and SPO2 below 93% during surgery (B = 1.26, OR = 3.54, P = 0.016). This means that these extrinsic factors are the primary risk factors of PI occurrence. Thus, the model accurately explains 79.5% of the overall risk of PIs during surgery.
TABLE 4.
Logistic regression analysis results of pressure injury (PI)‐related factors
| Independent variable | B | OR (95% CI) | Wald's χ2 | P |
|---|---|---|---|---|
| Duration of anaesthesia | ||||
| ≥3 h | 1.07 | 2.91 (1.26‐6.72) | 6.23 | .013 |
| <3 h | Ref. | |||
| Amount of blood loss | ||||
| ≤100 mL | Ref. | |||
| 101 to 500 mL | 0.80 | 2.23 (1.19‐4.19) | 6.27 | .012 |
| 501 to 999 mL | 1.63 | 5.09 (1.87‐13.87) | 10.15 | .001 |
| ≥1000 mL | 2.28 | 9.81 (3.87‐24.89) | 19.09 | <.001 |
| Use of pressure‐relieving devices | ||||
| Gel pads | 0.66 | 1.94 (0.66‐5.71) | 1.45 | .229 |
| Water cushions | 0.52 | 1.68 (0.70‐4.04) | 1.70 | .247 |
| Use of thermoregulation devices | ||||
| Electric blankets | 2.10 | 8.14 (3.03‐21.86) | 17.27 | <.001 |
| Special perioperative circumstances | ||||
| Body temperature above 37°C | 0.12 | 1.12 (0.61‐2.05) | 0.14 | .709 |
| Diastolic blood pressure below 60 mmHg | 2.09 | 8.09 (3.19‐20.54) | 19.33 | <.001 |
| SPO2 below 93% | 1.26 | 3.54 (1.26‐9.94) | 5.76 | .016 |
Abbreviations: 95% CI, 95% confidence interval; OR, odds ratio; SPO2, pulse oximetry.
4. DISCUSSION
This study found that with no differences between the intrinsic factors of the PI case group and the control group, surgical patients under anaesthesia for 3 h or more were at greater risk of PIs. Surgical patients that lost 101 to 500 mL, 501 to 999 mL, or 1000 mL of blood during surgery were at greater risk of PIs than those that lost 100 mL of blood. Patients using electric blankets or displaying diastolic blood pressure below 60 mmHg or SPO2 below 93% during surgery were also at greater risk of PIs.
Early studies indicated that the duration of pressure is not a crucial factor of PIs; the tolerance of the patient's body to pressure plays a more important role. Specifically, patients subject to intrinsic factors of PIs have poor tolerance to pressure caused by the bed mattress during surgery. 15 , 32 At present, most researchers believe that undergoing surgery for more than 3 h is a risk factor of PIs. 33 , 34 The proportion of patients developing PIs also increases as the duration of the surgery lengthens. 35 Pressure damage usually begins to develop during surgery in the muscles and subcutaneous tissue and then progresses towards the dermis and epidermis. PIs occur in body tissue that has been continuously under pressure for 3 h without relief. The Minnesota Hospital Association associates a prolonged surgery (3 h and longer) with a greater risk of pressure injuries. 24 The results of this study also indicated the following: no differences existed between the PI case group and the control group, the regression coefficient was significantly positive in terms of the duration of anaesthesia, and patients who had been under anaesthesia for 3 h or more were at greater risk of PIs.
Increased blood loss during surgery lowers arterial pressure and decreases blood volume, which stimulates the sympathoadrenal system, causes massive catecholamine secretion, and induces peripheral vasoconstriction to increase venous return. The haemoglobin in the blood provides tissues with oxygen and nutrients; thus, when blood pressure is low and the blood flow in blood vessels decreases, the skin does not receive adequate oxygen and nutrients, which facilitates the development of PIs. 36 In this study, the regression coefficient results show that in terms of the amount of blood loss, the regression coefficients of 101 to 500 mL, 501 to 999 mL, and 1000 mL were all significantly positive. For special perioperative circumstances, the regression coefficient of diastolic blood pressure below 60 mmHg was significantly positive. The results of this study also show that blood loss and diastolic blood pressure < 60 mmHg are risk factors of PIs.
Bindu et al. pointed out that the average core temperature of a healthy individual is 36.5°C to 37.3°C. During 2 h of surgery, the body can maintain its temperature at 34.5°C to 36°C. 24 However, after 3 to 4 h of surgery, body temperatures may fall below 34.5°C. To maintain patient body temperatures, electric blankets are often used on the operating table. A heat setting above 41°C is significantly correlated with PI occurrence. This is because every increase of 1°C in body temperature raises metabolism rates and oxygen consumption by 10%. Pressure‐related tissue hypoxia combined with increased temperatures will increase the risk of PIs in local tissue. 37 Furthermore, when an electric blanket is placed between a patient and the operating table, the difference between the materials of the electric blanket and the mattress on the operating table means a greater area of contact with the electric blanket. Furthermore, the fibres on the surfaces of electric blankets are longer, which also increases friction and thereby generates heat, increasing the risk of PIs as well. 38 , 39
In this study, in the use of thermoregulation devices, the regression coefficient of the use of electric blankets was significantly positive. The results of this study also confirmed that using electric blankets during surgery increases the risk of PIs and that said risk is 8.14 times higher than the risk of PIs in patients not using electric blankets. However, considering that overly‐low body temperatures in patients during surgery must be prevented and that heating devices such as electric blankets are not recommended, other devices must be developed as a substitute for electric blankets.
PIs are the result of skin or tissue damage caused by insufficient oxygen in local tissue blood due to prolonged pressure or friction on the skin.16 Thus, some researchers believe that inadequate oxygenation can lead to tissue hypoxia and necrosis and increase the risk of PIs. 40 , 41 Karayurt et al. discovered that aside from lower PaO2, patients that developed PIs also presented higher PH values and PaCO2. 42 In this study, the regression coefficient of SPO2 below 93% was significantly positive; we found that patients with SPO2 below 93% during surgery were 3.54 times more likely to develop PIs than those with SPO2 levels equal to or greater than 93%.
In addition, this study discovered that the use of pressure‐relieving devices alone does not lower the risk of PIs. Ebi et al. 4 also pointed out that although pressure‐relieving devices are frequently used in clinical practice to prevent PIs, they should not be considered the primary means of prevention because there is currently no evidence indicating which type of pressure‐relieving device is suitable for each type of surgical patient. 43
As the results of this study show, the prevention of perioperative PI development should not rely on the use of pressure‐relieving devices alone. Emphasis should be placed on cooperation among the medical team during surgery, less use of electric blankets, control over the duration of anaesthesia and blood loss, continuous monitoring of the patient during surgery for any emergencies, and the maintenance of patient diastolic blood pressure and blood oxygen levels to reduce the risk of PIs. This study employed 1:2 frequency matching to reduce the differences in intrinsic factors, enhance the representativeness of the control group, and avoid selection bias. However, the study samples are limited to the surgical patients of a teaching hospital in Taiwan and do not include surgical patients in other hospitals or countries. Therefore, the generalizability of the results may be limited.
5. CONCLUSION
With no differences between the intrinsic factors of the PI case group and the control group, we conducted an analysis of the influence of extrinsic factors on the risk of PIs. We found that surgical patients under anaesthesia for 3 h or more, patients that lost 101 to 500 mL, 501 to 999 mL, or 1000 mL of blood during surgery, patients lying on electric blankets during surgery, and patients displaying diastolic blood pressure below 60 mmHg or SPO2 below 93% during surgery were at greater risk of PIs.
FUNDING INFORMATION
No funding was obtained for this study.
CONFLICT OF INTEREST
The authors declare that they have no conflict of interest.
ETHICS STATEMENT
Ethics approval is applicable.
Weng P‐W, Chang W‐P. Extrinsic factors of pressure injuries in patients during surgery: A frequency matched retrospective study. Int Wound J. 2023;20(6):1934‐1942. doi: 10.1111/iwj.14053
DATA AVAILABILITY STATEMENT
The data analyzed during the current study are available from the corresponding author upon reasonable request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data analyzed during the current study are available from the corresponding author upon reasonable request.