Abstract
Background
Postoperative pneumonia is a main adverse event that causes increased postoperative morbidity and prolonged length of hospital stay leading to high postoperative mortality. Continuous positive airway pressure (CPAP) is a type of non-invasive ventilation for the delivery of a positive airway pressure during respiration. In this study, we evaluated the impact of postoperative prophylactic CPAP on prevention of pneumonia in patients after open visceral surgery.
Methods
In this observational cohort study, we compared the rates of postoperative pneumonia in patients who underwent open major visceral surgery from January 2018 till August 2020 in the study and control group. The study group had postoperative prophylactic sessions of CPAP for 15 min, 3–5 times a day and a repeated spirometer training was also performed in the general surgical ward. The control group received only the postoperative spirometer training as a prophylactic measure against postoperative pneumonia.
The chi-square test was used to measure the relationships between categorical variables, and a binary regression analysis determined the correlation between independent and dependent variables.
Results
A total of 258 patients met the inclusion criteria who had open visceral surgery for various clinical illnesses.
There were 146 men (56.6%) and 112 women with a mean age of 68.62 years. As many as 142 patients received prophylactic CPAP and they were grouped into the study group, whereas 116 patients without prophylactic CPAP were placed in the control group.
Overall, the rate of postoperative pneumonia was significantly less in the study group (5.6% vs. 25.9% in the control group; p-value < 0.0001), which could be confirmed by the regression analysis (OR 0.118, CI 95% 0.047–0.295, p < 0.001).
Conclusion
Postoperative intermittent CPAP after open visceral surgery can be performed in a general surgical ward. Our study showed a significant association with a low rate of postoperative pneumonia, especially in high-risk patients. This leads to a significantly shorter postoperative hospital stay especially in high-risk patients after upper gastrointestinal surgery.
Trial registration number
DRKS00028988, 04.05.2022, retrospectively registered.
Keywords: Postoperative pneumonia , Abdominal surgery, Risk reduction, CPAP
Introduction
The rate of postoperative pulmonary complications (PPC) following open abdominal surgery remains as high as 40% (PPC) [1]. Consequently, this high rate of PPC leads to high postoperative morbidity and mortality. The risk of postoperative re-admission to ICU or endotracheal re-intubation for mechanical ventilation increases by postoperative pneumonia and respiratory failure, which prolongs hospital stay with added risk of nosocomial infections and high postoperative mortality [2]. Arozullah et al. has also reported an increased postoperative mortality of 27% in patients with postoperative respiratory failure [1].
Most PPC are triggered by atelectasis, which leads to a reversible loss of functional lung tissue caused by an alveolar collapse [3]. Midline laparotomy can reduce pulmonary function as low as 50% of the preoperative value in comparison [4-6]. This reduction is more distinctive after upper abdominal laparotomy compared to lower abdominal laparotomy [7].
The perioperative causes of the respiratory insufficiency following atelectasis are well described. The primary reason is the reduced movement of the diaphragm during ventilation causing a more thoracic breathing with a markedly decreased tidal volume, finally causing a collapse of small airways [6-8]. The triggering mechanism is postoperative abdominal pain when patients tend to have shallow breathing which eventually leads to basal alveolar collapse.
Additionally, general anesthesia can cause reduced functional residual capacity by anesthetic agents [9], thus increasing the risk of peri- and postoperative atelectasis [10]. This effect can last for several days and can be aggravated by surgical trauma or pain [9]. Besides these anesthesiologic factors, the combination with technical and individual risk factors increases the rate of postoperative pneumonia.
Literature has shown a host of clinical trials and attempts to reduce the rates of PPC [11-13]. Besides sufficient pain management, respiratory physiotherapy plays a major role in the routine recovery of surgical patients. However, in their Cochrane review in 2009, Guimarães et al. showed no evidence for the commonly used spirometry for PPC prevention in upper abdominal surgery [14].
Continuous positive airway pressure (CPAP) is a non-invasive ventilation (NIV) technique using a high-pressure gas source delivering a constant positive pressure to the airways within in- and expiration [15]. This positive pressure antagonizes the pulmonal restrictive pattern and prevents the collapse of the small airways.
CPAP is commonly used in cardiogenic lung edema, exacerbations of chronic obstructive pulmonary disease, or hypoxemic respiratory failure [16], as well as in critically ill patients, as a part of all NIV techniques in intensive or intermediate care units. However, CPAP can also be adopted in general wards by specially trained staff [17, 18]. Data from postoperative patients after thoracic surgery showed an effective reduction in the need of re-intubation and acute respiratory failure [18].
The aim of this study is to evaluate the role of prophylactic postoperative CPAP in general surgical wards in preventing or minimizing postoperative pneumonia after open major visceral surgery.
Methods
In this study, we retrospectively included all patients undergoing open major visceral surgery from January 2018 to August 2020 in the Department of Surgery at Hospital Reinbek St. Adolf-Stift, a secondary care hospital in northern Germany. In 2017, the prophylactic CPAP treatment, which previously was routinely performed only in the ICU, was established for prophylactic use and treatment in the general surgical wards of the hospital. We included all patients with laparotomies with a postoperative prophylactic use of CPAP in a general surgical ward, in addition to the routinely used spirometer (Fig. 1). Patients without laparotomy and those, with missing data were excluded from the study. Patients treated without CPAP as a prophylactic procedure or those, receiving CPAP after diagnosis of a pneumonia were grouped in the control group.
Fig. 1.
Study flow diagram describing the inclusion of patients between January 2018 and August 2020 and the intervention by CPAP in a general surgical ward with the main outcome “occurrence of a postoperative pneumonia”
The additional usage of CPAP treatment depended on the patient’s perioperative risk according to the established Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) score [19]. This score includes patient’s age, preoperative SpO2, previous respiratory infections, location of incision, and the duration and urgency of the procedure to calculate the risk score. Depending on the items, a score ranging from 0 to 123 points was calculated and result in three risk groups: low risk: < 26; intermediate risk: 26–44; high risk: ≥ 45.
All patients received a repeated spirometer training to prevent postoperative pneumonia. Additionally, Patients with an ARISCAT score of more than 30 points were selected for the prophylactic CPAP treatment. If used, the CPAP treatment was performed 3 to 5 times a day for 15 to 20 min, depending on the cardiorespiratory status of the patient. The procedure was monitored by nurses who were trained to use CPAP equipment by experienced doctors.
CPAP was administered as followed: A continuous airflow of 12–14 l/min was applied via a gas mixer (Dräger Oxymixer High Flow, Dräger, Germany) on a tube system through a positive end-expiratory pressure (PEEP) valve (PEEP-Ventil, Dahlhausen, Germany). The PEEP was set to 5 cm H20 and administered via a face mask (Dahlhausen, Germany) at the patient’s end. No additional oxygen was used (Fig. 2).
Fig. 2.
Dummy with CPAP mask including a PEEP-valve. CPAP, continuous positive airway pressure; PEEP, positive end-expiratory pressure
The described setting allowed the application of low-level CPAP only, without any form of pressure support or other assisted or mandatory ventilation features. If a patient needed non-invasive ventilation, other devices and settings (intermediate/intensive care) were used.
Major open abdominal surgery was defined as all visceral resections such as gastrectomy, esophagectomy, hemicolectomy, all intra-abdominal infections, or intraabdominal perforations or obstructions treated by laparotomy. All patients treated by minimally invasive procedures or without intraabdominal procedures were excluded. Additionally, all gynecological patients were excluded as these patients were treated in a separate department following other structured perioperative pathways. Patients who refused CPAP therapy were placed into the control group and received only spirometer training to prevent postoperative pneumonia.
Patients’ demographics, preoperative medical conditions, body mass index (BMI), the American Society of Anesthesiologists (ASA) classification of physical health, clinical diagnosis, surgical approach and procedure, length of surgery and hospital stay, complications according to Dindo-Clavien’s classification [20], and mortality were extracted from the clinical archiving system at a single time point. The use of a nasogastric tube was based on the decision by the treating surgeon and not primarily by the usage of a CPAP treatment. This dataset was then collated with laboratory results. Postoperative morbidity was defined as a complication occurring within the same hospital stay [20]. As the occurrence of a postoperative pneumonia within the same postoperative stay was the primary outcome, we adopted the definition of nosocomial pneumonia proposed by the German Robert-Koch-Institute. There, postoperative pneumonia is defined as a pathological radiological image such as infiltration in x-ray or CT-scan and clinical presentations in combination with systemic inflammation marked by elevated leucocytes or fever postoperatively within the same hospital stay [21]. Additional confirmation of the microbial infection using, for example, broncho-alveolar lavage, was not used routinely as its not mandatory for the diagnosis of a nosocomial pneumonia. As the first cases of the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) infection, causing COVID-19 disease, occurred within the study period in Germany [22], we reviewed the medical records for any other perioperative infections as well.
Statistical analyses were performed using IBM SPSS Statistics Version 25 (IBM Co., Armonk, NY, USA). All linear variables were listed as means with standard deviation. Categorical variables were arranged as numbers with percentages. Chi-square test or Fisher’s exact test was used to determine relationships between categorical variables depending on group size. Mann–Whitney U test was used to measure the probability of difference between two sets of data. Logistic regression was applied to confirm the potential correlation between postoperative pneumonia and CPAP treatment. A p-value < 0.05 was considered statistically significant.
This study was approved by the Ethics Committee of the Medical Association Schleswig–Holstein, has been registered at the German Clinical Trial Register (DRKS00028988), and was conducted in accordance with the Declaration of Helsinki.
The data in this study are reported in concordance with the STrengthening the Reporting of OBservational studies in Epidemiology (STROBE) criteria [23].
Results
During the study period, 7394 surgical procedures were performed. Out of these, 268 patients were treated by laparotomy due to various reasons. After excluding 10 patients due to missing data, 258 fulfilled the inclusion criteria to receive repeated spirometer training. Of these, 142 patients (55%) were treated with additional postoperative prophylactic CPAP treatment in a general surgical ward and, consequently, they were grouped into the study group. On the other hand, 116 (45%) patients did not receive prophylactic CPAP treatment and served as a control group.
In total, there were 146 (56.6%) men and 112 (43.4%) women with a mean age of 68.62 years and a mean BMI of 26.17 kg/m2. The data showed no relevant differences between the patients’ characteristics in both groups apart from a higher prevalence of pulmonary comorbidities in the control group. Of 45 patients with previous pulmonary comorbidities, chronic-obstructive pulmonary disease was the most common (40%), whereas obstructive sleep apnea was rarely reported (4.4%). No perioperative infection with the SARS-CoV-2 virus was reported in the study cohort. The surgical characteristics such as indications for surgery and surgical approaches differed between both groups. In upper gastrointestinal surgery, prophylactic CPAP was used more frequently. As shown in Table 1, the ARISCAT score was higher in the study group, and thus, more patients with an intermediate or high risk were reported in this group.
Table 1.
The demographic and clinical characteristics of patients in the control and study group in the study (N = 258)
| Features | Total | Control group n = 116 |
Study group n = 142 |
p-value |
|---|---|---|---|---|
| Age, M ± SD [years] | 68.62 ± 13.20 | 67.69 ± 14.07 | 69.37 ± 12.45 | 0.413a |
| Sex, N (%) | 0.054b | |||
| Male | 146 (56.6) | 58 (50.0) | 88 (62.0) | |
| Female | 112 (43.4) | 58 (50.0) | 54 (38.0) | |
| ASA classification, N (%) | 0.945b | |||
| ASA 1 | 8 (3.1) | 4 (3.4) | 4 (2.8) | |
| ASA 2 | 97 (37.6) | 45 (38.8) | 52 (36.6) | |
| ASA 3 | 120 (46.5) | 53 (45.7) | 67 (47.2) | |
| ASA 4 | 33 (12.8) | 14 (12.1) | 19 (13.4) | |
| BMI, M ± SD [kg/m2] | 26.17 ± 5.23 | 26.15 ± 5.34 | 26.19 ± 5.15 | 0.918a |
| Smoking, N (%) | 59 (22.9) | 27 (23.3) | 32 (22.5) | 0.888b |
| Medical history, N (%) | ||||
| Pulmonary | 45 (17.4) | 27 (23.8) | 18 (12.7) | 0.026b |
| Renal | 29 (11.2) | 16 (13.8) | 13 (9.2) | 0.241b |
| Cardiac | 130 (50.4) | 54 (46.6) | 76 (53.5) | 0.265b |
| Diabetes | 47 (18.2) | 19 (16.4) | 28 (19.7) | 0.489b |
| Indications for surgery, N (%) | < 0.001b | |||
| Gastric pathology | 41 (15.9) | 12 (10.3) | 29 (20.4) | |
| Esophageal pathology | 23 (8.9) | 5 (4.3) | 18 (12.7) | |
| Pancreatic pathology | 49 (19.0) | 6 (5.2) | 43 (30.3) | |
| Colorectal pathology | 140 (54.3) | 90 (77.6) | 50 (35.2) | |
| Liver pathology | 5 (1.9) | 3 (2.6) | 2 (1.4) | |
| Type of lesion, N (%) | 0.001b | |||
| Malignant | 143 (55.4) | 52 (44.8) | 91 (64.1) | |
| Benign | 115 (44.6) | 64 (55.2) | 51 (35.9) | |
| Surgical approach, N (%) | < 0.001b | |||
| Median laparotomy | 138 (53.5) | 78 (67.2) | 60 (42.3) | |
| Transverse laparotomy | 101 (39.1) | 32 (27.6) | 69 (48.6) | |
| Other | 19 (7.4) | 6 (5.2) | 13 (9.2) | |
| Nasogastric tube, N (%) | 203 (78.7) | 76 (65.5) | 127 (89.4) | < 0.001b |
| Peridural anesthesia, N (%) | 108 (41.9) | 27 (23.3) | 81 (57.0) | < 0.001b |
| Emergency procedure, N (%) | 49 (19.0) | 28 (24.1) | 21 (14.8) | 0.079b |
| ARISCAT-Score, M ± SD | 38.47 ± 11.71 | 34.45 ± 11.93 | 41.76 ± 10.47 | < 0.001a |
| Low risk, N (%) | 37 (14.3) | 27 (23.3) | 10 (7.0) | |
| Intermediate risk, N (%) | 150 (58.1) | 68 (58.6) | 82 (57.7) | |
| High risk, N (%) | 71 (27.5) | 21 (18.1) | 50 (35.2) | |
M, mean
SD, standard deviation
ASA, American Society of Anesthesiologists
BMI, body mass index
ARISCAT, Assess Respiratory Risk in Surgical Patients in Catalonia
aMann-Whitney U test.
bChi-square test.
Overall, 38 patients were diagnosed with postoperative pneumonia, including 8 patients in the study and 30 in the control group. The rate of postoperative pneumonia in the study group was significantly less than in the control group (5.6% vs. 25.9%; p-value < 0.0001).
Of these 38 patients, 9 (23.7%) needed treatment in an intensive care unit. Only one patient in the study group needed treatment in an ICU; whereas all other patients in the study group were treated by antibiotics in the general surgical ward. Six patients, all without prophylactic CPAP therapy, died due to pneumonia and respiratory insufficiency (5.2% vs. 0% in the study group; p = 0.006). Of these 6 patients, 4 have had no previous pulmonary comorbidity as a potential risk factor.
The overall rate of postoperative complications according to Dindo-Clavien and also the rate of anastomotic leakage between both groups did not differ (Table 2). Focusing on elective procedures, the rate of postoperative major complications was 18.2% and 17.4% in the control and study group respectively (p = 0.877).
Table 2.
A comparison of surgical outcomes between the study and control groups within the first 30 days after surgery (N = 258)
| Features | Control group n = 116 |
Study group n = 142 |
p-value |
|---|---|---|---|
| Postoperative complication according to DC | 0.717a | ||
| Grade 0 | 65 (56.0) | 92 (64.8) | |
| Grade 1 | 8 (6.9) | 5 (3.5) | |
| Grade 2 | 13 (11.2) | 15 (10.6) | |
| Grade 3 | 17 (14.7) | 17 (12.0) | |
| Grade 4 | 3 (2.6) | 3 (2.1) | |
| Grade 5 | 10 (8.6) | 10 (7.0) | |
| Major complication DC ≥ 3b | 30 (25.9) | 30 (21.1) | 0.370a |
| Anastomotic leakage | 4(3.4) | 3 (2.1) | 0.704b |
| Postoperative vomiting | 20 (17.2) | 15 (10.6) | 0.085b |
| Pneumonia | 30 (25.9) | 8 (5.6) | < 0.0001b |
| Length of stay (mean ± SD), days | 11.49 ± 8.58 | 13.23 ± 9.30 | 0.002c |
DC, Dindo-Clavien classification
SD, standard deviation
aChi-Square-test
bFischer’s exact test
cMann-Whitney-U-test
Values are reported as number (%) except where otherwise specified
The association of the prophylactic CPAP treatment with the occurrence of a postoperative pneumonia could be proven in the logistic regression analysis (OR 0.118, CI 95% 0.047–0.295, p < 0.001) (Table 3).
Table 3.
The results of the logistic regression analysis of the occurrence of a postoperative pneumonia (N = 258). (Nagelkerkes R2 0.176)
| Variable | Coeff | S.E | Wald | Sig | OR | 95% CI |
|---|---|---|---|---|---|---|
| Sex | 0.456 | 0.389 | 1.375 | 0.241 | 1.578 | 0.736–3.385 |
| Obesity | − 0.009 | 0.480 | 0.000 | 0.985 | 0.991 | 0.38–2.540 |
| Prophylactic CPAP | − 2.138 | 0.468 | 20.884 | < 0.001 | 0.118 | 0.047–0.295 |
| Use of peridural anesthesia | 0.726 | 0.417 | 3.026 | 0.082 | 2.067 | 0.912–4.685 |
| Constant | − 1.461 | 0.336 | 18.881 | < 0.001 | 0.232 |
The subgroup analysis (Table 4) of organ-specific impact of CPAP treatment showed less postoperative pneumonia in upper gastrointestinal surgery such as esophageal (p = 0.003), gastric (p = 0.011), and pancreatic resections (p < 0.0001). Due to the small number of cases, liver surgery was excluded from this subgroup analysis.
Table 4.
An organ-specific subgroup analysis in our study (N = 258)
| Features | Control group n = 116 |
Study group n = 142 |
p-value |
|---|---|---|---|
| Colorectal (N = 140) | 90 (77.6) | 50 (35.2) | |
| Pneumonia | 15 (12.9) | 3 (2.1) | 0.112c |
| Length of hospital stay, M ± SD [days] | 10.46 ± 6.86 | 15.18 ± 12.62 | 0.002b |
| Esophagus (N = 23) | 5 (4.3) | 18 (12.7) | |
| Pneumonia | 4 (4.3) | 1 (0.7) | 0.003c |
| Length of hospital stay, M ± SD [days] | 21,80 ± 14.53 | 15.17 ± 9.81 | 0.202b |
| Gastric (N = 41) | 12 (10.3) | 29 (20.4) | |
| Pneumonia | 6 (5.2) | 3 (2.1) | 0.011c |
| Length of hospital stay, M ± SD [days] | 12.50 ± 7,67 | 10.93 ± 4.91 | 0942.b |
| Pancreas (N = 49) | 6 (5.2) | 43 (30.3) | |
| Pneumonia | 4 (3.4) | 1 (0.7) | < 0.0001c |
| Length of hospital stay, M ± SD [days] | 18.83 ± 18.65 | 11.60 ± 5.95 | 0.540b |
aChi-Square-test
bMann-Whitney-U-test
cFisher’s exact test
M, mean
SD, standard deviation
Values are reported as number (%), except where otherwise specified
In our study, the use of prophylactic CPAP treatment was associated with a short hospital stay in patients with upper gastrointestinal surgery. Following this subgroup analysis, colorectal patients with CPAP treatment stayed longer (p = 0.002) than others. The rates of pneumonia in these patients were six times less following CPAP treatment in comparison to the control group (2.1% vs. 12.9%; p = 0.112). The prolonged stay in colorectal patients using prophylactic CPAP can be attributed to a high rate of emergency procedures (30.7% of all colorectal resections).
According to the ARISCAT score, also high-risk patients showed a significant lower rate of postoperative pneumonia after prophylactic CPAP treatment (OR 0.026, 95% CI 0.005–0.136, p < 0.0001) (Table 5).
Table 5.
Postoperative pneumonia as calculated by the grouped ARISCAT-score (N = 258)
| Overall population | Control group n = 116 |
Study group n = 142 |
p-value | OR | 95% CI | |
|---|---|---|---|---|---|---|
| Low/intermediate, N | 187 | 95 | 92 | |||
| Pneumonia, N (%) | 23 (13.8) | 17 (14.7) | 6 (4.2) | 0.025a | 0.320 | 0.120–0.853 |
| High, N | 71 | 21 | 50 | |||
| Pneumonia, N (%) | 15 (20.3) | 13 (61.9) | 2 (3.8) | < 0.0001a | 0.026 | 0.005–0.136 |
OR, Odd’s ratio
CI, confidence interval
aFisher’s exact test
Discussion
This study showed an association between a low rate of postoperative pneumonia with the intermitted application of prophylactic CPAP treatment in a general surgical ward after open major visceral gastrointestinal surgery. In particular, the patients with a high risk of PPC, according to the ARISCAT-Score, had a significantly lower odd ratio for postoperative pneumonia (OR 0.026, 95% CI 0.005–0.136, p < 0.0001) following the prophylactic CPAP treatment. Our study endorses the prophylactic role of CPAP in preventing PPC and thus reducing the overall morbidity and mortality of patients with resultant better clinical outcomes.
In our study, prophylactic CPAP treatment was administered more frequently to patients with upper abdominal surgery. This might be due to the known high risk for PPC after upper abdominal surgery, reported to be as high as 60% [24]. Several techniques have been attempted to reduce the high rate of PPC by optimizing inspiration and by recruiting pulmonary tissue, thereby increasing tidal volume. Roukema et al. showed a reduction in PPC rate from 60% to 19% by using perioperative breathing exercises alone [24]. The impact of perioperative use of incentive spirometry as an additional tool, as also performed in our cohort, in preventing PPC in upper abdominal surgery was also analyzed in a systematic review [25].The investigators were not able to find a significant improvement by using the incentive spirometry. On the other hand, Katsura et al. reported outright benefits of the preoperative-focused respiratory muscle training [26]. However, PPC were not considered the primary or secondary endpoint outcomes in the studies selected in the systematic review. The application of intermitting prophylactic CPAP modality works on the premise that this technique could be used in all general wards as established in our center. Therefore, our CPAP system is incredibly simple and has no possibility for pressure support and no possibility of instituting typical non-invasive ventilation. As the core element of the used system is the prevention of alveolar collapse by providing a continuous positive pressure with a low PEEP, the easier the system the better can it be implemented in a general ward. Of course, this causes the need for transfer of patients to an intermediate or intensive care unit in case of respiratory failure.
Several studies have evaluated the use of postoperative CPAP as a treatment in hypoxemia. Squadrone et al. have reported a reduced rate of PPC for re-intubation in hypoxemia after major surgery using postoperative CPAP treatment [27]. Nevertheless, its use as a standard treatment of hypoxemia, a consensus conference recommends the use of CPAP as an noninvasive ventilation in an ICU or in a system with high-level clinical monitoring and with immediate possibility of invasive ventilation, if necessary [28]. This narrative of its use in high-level care units was supported by the findings of Antonelli et al., who observed a higher rate of intubation in patients with hypoxemia in patients with postoperative sepsis than because of other factors [29].
In contrast, Plant et al. showed the feasibility of simple noninvasive ventilation in cases with exacerbated COPD in general wards [30].
The prophylactic use of the CPAP technique is not commonly established and, at the moment, upper gastrointestinal surgery is considered a relative contraindication to CPAP treatment in the German Guidelines for non-invasive mechanical ventilation [31]. This might be due to the potentially increased risk for anastomotic leakage by the positive pressure. Our data showed an equally low rate of postoperative anastomotic leakage of around 3% within both groups (p = 0.704). Our data shows that this technique is feasible in a general surgical ward with a low risk and safe clinical outcome in patients following gastrointestinal surgery.
Different studies in multiple surgical fields have reported their experiences with the prophylactic use of postoperative CPAP treatment [32-34].
A recently published study showed promising post-operative results after lung surgery [35]. The study demonstrated a reduced rate of postoperative atelectasis and pneumonia without an increased rate of adverse events using continuous CPAP for 6 h after surgery. The authors used the respiratory failure index to group patients into high- or non-high-risk groups showing the best results of CPAP in high-risk patients. In sharp contrast, we also used the well-established ARISCAT-score [36] system which reported a significantly low rate of PPC in non-high-risk patients. Palleschi et al. also showed a reduction of PPC using an intermitting postoperative CPAP treatment for three days after pulmonary lobectomy [18].
The effects after abdominal surgery were discussed in a Cochrane database analysis in 2014 which found reduced PPC using prophylactic postoperative CPAP treatment [17]. However, the analysis included different studies with a range of CPAP applications in the postoperative period.
There are little data about the intermittent use of CPAP in the postoperative period, which might be due to its less common usage in general surgical wards. In 2001, in their randomized controlled study, Denehy et al. investigated the synergistic effect of adding short postoperative CPAP treatments for 15 or 30 min several times per day to the routine postoperative physiotherapy in upper abdominal surgery [37]. Unfortunately, the authors did not find a significant decrease in PPC in the studied cohort. Additionally, no significant difference was found in another randomized controlled trial by Christensen et al. on a small sample size of 17 patients in each group comparing CPAP with physiotherapy and respiratory muscle training [38]. Notwithstanding, the ever-emerging technological developments in surgery and the use of more advanced equipment with the implementation of enhanced recovery concepts after surgery, reducing the incidence of PPC might play an integral role in reducing the rates of postoperative morbidity and mortality [39].
Although our study showed a significantly lower rate of postoperative pneumonia, the rate of postoperative major complications according to the Dindo-Clavien did not differ significantly between the study and control groups.
This might be contributed to the included procedures. Smit et al. reported an overall rate of infectious complications of 28% with a postoperative pneumonia rate of 9.5% with a lower rate of pancreatic resections included [40]. This is in line with the postoperative pneumonia rate of 10% reported by Squadrone et al. in their CPAP study[27]. In that study, no esophageal resections were included, which are known to have a high risk for postoperative pneumonia of up to 30% [41].
Furthermore, the length of hospital stays and the beneficial effect of CPAP could not be observed in the subgroup of colorectal resections. This might be due to the inclusion of emergency procedures, as these patients were overrepresented in the colorectal subgroup and they were known to have a high risk of postoperative complication rate including PPC.
A deeper analysis of the international literature did not provide sufficient evidence in favor of CPAP technique in lower gastrointestinal surgery as the rate of postoperative pneumonia in elective colorectal surgery is estimated to be approximately as low as 5% [6].
Limitations
There are several limitations of this study. First, this is a retrospective single-center non-randomized cohort study. Second, both groups were comparable in terms of their demographics and medical history, but CPAP treatment was more often used in upper gastrointestinal surgery. This also limited the comparability to the literature, as the reported rates differ between the level of surgical resections. The inclusion of patients in the study group might be biased by the treating physicians, as this procedure was based on the ARISCAT score and the compliance of the patients. Even if the performance of CPAP in a normal ward is safe, as shown in this study, it comes with the flaw of its regular usage, as it depends on the availability of the patient, the devices, and the nurses’ experience. This shortcoming can cause a variability of administration of the CPAP treatment in the study group.
Further research is necessary to identify the optimal patient cohort and the best practice for postoperative intermittent CPAP treatment in abdominal surgery.
Conclusion
This cohort study presents promising results with a low postoperative pneumonia rate using a simple but structured intermittent CPAP ventilation strategy in a general surgical ward. Postoperative pneumonia rates after laparotomies could be reduced significantly, especially in high-risk patients, using the prescribed prophylactic CPAP treatment protocol. This technique is feasible, cost-effective, and easily achievable in general surgical wards.
Authors’ contributions
All authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by Jonas Herzberg and Daniel Merkle. The first draft of the manuscript was written by Jonas Herzberg and Salman Yousuf Guraya and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
Data Availability
The raw data supporting the conclusions of this article will be made available by the authors on reasonable request.
Declarations
Ethical approval
Approved by the Ethics Committee of the Medical Association Schleswig–Holstein (031/22 I).
Informed consent
Not applicable due to the retrospective study design.
Conflict of interest
The authors declare no competing interests.
Footnotes
Publisher's note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Data Availability Statement
The raw data supporting the conclusions of this article will be made available by the authors on reasonable request.