Evaluation of risk factors for perforated peptic ulcer

Although a perforated peptic ulcer (PPU) is worsened consequence of peptic ulcer disease (PUD), several clinical features and prognoses are dramatically different. One of the reasons is that symptoms of PPU vary over time and are classified into three phases. The first phase appears within 2 h of onset, and symptoms such as acute abdominal pain, tachycardia and peripheral coldness are typical of this stage. Then, a perforation releases the gastroduodenal contents into peritoneal cavity, causing chemical peritonitis. Severe pain stimulates sympathetic nerves, and tachycardia and peripheral coldness result. Within 2 to 12 h of onset, inflammation extends to the broader area of the peritoneum, and localized pain becomes generalized. After more than 12 h of onset, patients become hemodynamically unstable, and death may be a consequence [1]. As a result, several clinical features, such as diffuse abdominal pain, muscular defense and a change in symptoms are unique for PPU [2]. Therefore, we should distinguish PPU from PUD.

Early detection and rapid intervention are crucial for treating PPU and affecting prognosis of patients. PPU is a rare disease that only occurs in 2% to 10% of patients with PUD [3], therefore PPU is not a top of differential diagnosis of acute abdomen, leading to delay of intervention. In fact, time of intervention is one of the known prognostic values, known as the Boey score. Boey et al. stated that a delay of more than 24 h in diagnosis and management greatly worsened predicted outcomes and increased post-operative complications [4, 5]. And, prognosis itself is poor; A study prior to 1997 reported the mortality rate of PPU as 12% [6], and even a recent review reported mortality rate for PPU ranged from 1.3% to 20% [1]. Possible reasons for high mortality are pan peritonitis and consequences of bacterial infection following PPU. Perforation allows gastric contents into the peritoneal cavity, initiating chemical peritonitis, and if left untreated, bacterial contamination, intra-abdominal abscess formation and sepsis are results of continuous leakage [7]. Another reason for high mortality is delayed treatment. Therefore, misdiagnosis and delay of treatment must be prevented.

Although diagnostic tests are powerful, PPU is still overlooked due to its low incidence. The most effective method for detecting PPU is contrasted CT scan. Existence of intraperitoneal free gas is known as a sign of perforation, and both specificity and accuracy are high. In fact, by utilizing multi-detector CT (MDCT), it is possible to diagnose with accuracy as high as 98% [8] and determine the site of perforation with 86% accuracy [9]. However, from the perspective of medical costs, availability and radiation exposure, we should not perform a CT scan for all patients with acute abdominal pain. Erect chest X-ray and abdominal X-ray are useful tests from the perspectives of convenience and speed, but their clinical significance is in doubt [1, 10]. Misdiagnosis and delayed intervention for more than 24 h are important factors affecting the prognosis of PPU, thus re-evaluation of the prediction factors for PPU will allow us to suspect the disease, conduct a CT scan and diagnose PPU immediately with an appropriate procedure.

The aim of this study was to evaluate the prediction factors and develop a prediction rule for PPU.

A total of 408 patients were included in this study; 136 were case subjects and 272 were control subjects. Tables 1, 2, 3, and 4 shows the results obtained by univariate analyses, and many factors showed statistical significance. Among the significant factors included taking NSAIDs regularly, having a history of PUD and H. pylori infection and showing diffuse abdominal pain with muscular defense.

Table 5 shows the results from the multivariate analyses. Four different models were conducted and significant differences were found for muscular defense and PUD in all models. The data are as follows for the symptom of muscular defense: logistic step-wise model (odd ratio [OR]: 366.2, 95% confidence interval (CI): 61.9–2166.2), conditional step-wise model (OR: 76.6, 95% CI: 13.7–429.6), logistic forced-entry model (OR: 28.4, 95% CI: 11.6–69.6), and conditional forced-entry model (OR: 23.8, 95% CI: 5.70–100.0). The data are as follows for a history of PUD: logistic step-wise model (OR: 7.81, 95% CI: 1.98–30.8), conditional step-wise model (OR: 21.9, 95% CI: 3.92–122.5), logistic forced-entry model (OR: 3.67, 95% CI: 1.47–9.18), and conditional forced-entry model (OR: 6.40, 95% CI: 1.13–36.2). The following seven factors were statistically significant in two to three models: diffuse pain, daily NSAID use, antiplatelet use, back pain, vomiting, platelet count, and hemoglobin concentration. Furthermore, anticoagulant, proton pump inhibitor (PPI) and steroid medications were found as irrelevant to upper gastric perforation in this study.

Figure 1 shows ROCs of the four models. The AUCs for each model are as follows: logistic forced-entry method: 0.97 (95% CI: 0.95–0.99), logistic step-wise model: 0.92 (95% CI: 0.89–0.95), conditional forced-entry model: 0.97 (CI: 0.95–0.99), and conditional step-wise method: 0.98 (95% CI: 0.96–0.99). The AUCs of all models were high enough to confirm the results.

Our prediction models exhibited many different predicted risk factors for PPU and outcomes of the AUCs verified their significance. Some were similar to the known prediction factors of PUD, but some were different.

Some similarity among prediction factors of PUD and PPU was reconfirmed though our study. According to prior studies, the following factors increased the OR for PUD: NSAID use (OR: 4.85), antiplatelet drug use (OR: 1.68) and H. pylori infection (OR: 18.1) [11, 12]. Furthermore, PUD is known to present nausea, hematemesis, and loss of appetite and is often seen in patients with gastroesophageal reflux disease (GERD) and a previous history of ulcer. In addition, when symptoms such as persisting radiating back pain and sudden rapidly exacerbating multiple abdominal pains were associated, potential complications, including perforation, were suggested [13]. As well, in our PPU study, the above factors were shared prediction factors for perforation. We hypothesized that patients with GERD and/or a previous history of ulcer were susceptible to gastric complications by nature, but even without the nature of susceptibility, NSAIDs or antiplatelet drugs alone could penetrate the gastric mucous membrane by inhibiting cyclooxygenase-1 (COX-1). We concluded that symptoms such as nausea, hematemesis, loss of appetite, radiating and multiple pains resulted from a wide range of mucous damage and stimulation of the nerves distributed throughout the peritoneum and mesentery [14].

There were some differences in the prediction factors between PUD and PPU. For one, anticoagulants were thought of as a prediction factor for PUD, increasing the OR to 1.98 [15], but anticoagulants did not increase the risk of PPU in our study. Certainly, in molecular biological point of view, coagulation is a defense mechanism that can protect gastric mucous membrane, and by the use of anticoagulants, homeostasis of reproductive process can be disrupted. However, in clinical setting, by the perspective of our findings we consider that anticoagulants alone do not cause significant influence on biological setting. We hypothesized that the insignificance of anticoagulant drugs was due to their mechanism. Unlike Cox-1 inhibitors, anticoagulants are medications which inhibit the productions of fibrin at the end of the blood coagulation reaction [16]_; they may promote the bleeding risk, but may not cause damage to the gastric mucous membrane. In addition, vomiting is a symptom often seen in patients with PUD and with esophageal perforation [17], but a reduction in vomiting was statistically significant in PPU subjects. We hypothesized that continuous leakage reduced the gastric contents, leading to less vomiting as a physical symptom. Finally, an increase in platelet count was statistically significant in PPU, and could be used as a prediction factor. Platelets are component of blood, necessary to arrest bleeding, thus thrombocytopenia is known cause of bleeding. In our PPU study, however, platelet counts were significantly increased. We presumed that peritonitis caused inflammation and perforation stimulated platelet aggregation; reactive thrombocytosis is a phenomenon seen in the PPU patients.

There are some limitations in our study. Our study is a research at a single institution and targets only one ethic group. Thus, generalization of our outcome into different ethnicity might be difficult and these could be a selection bias. Moreover, there are some missing data because initial encounter with patients and diagnostic process are conducted by different doctors each time. For example, it could be an interesting research by comparing X-ray and CT scan to patients with abdominal pain. Since X-ray is not gold standard for diagnosing acute abdomen, thus unperformed each case, we could not gather enough data for X-ray. Furthermore, there may be a group of false negative. Some outpatients with abdominal disturbance may not be taken CT scan, and may not be diagnosed as PPU. However in our hospital, CT scan is available 24 h every day, every year, so that barrier for taken CT scan is very low. In addition to the low barrier, board certificated radiologists are within reach at all times, false negative is limited. Moreover, the phenomenon which some variables are significant in multivariate analyses but not significant in univariate analysis is mainly coming from confounding factors. In addition, the effect of unbalanced sample size, the influence of missing data and an extremely large within-group variation, relative to between-group variation are other variables, contributing to the discrepancy.

In this study, out of many categories from past medical histories, including physical findings, medications, and laboratory data, prediction factors for upper gastrointestinal perforation were extracted. In the clinical setting, even though perforation is a rare disease, when the patients present with muscular defense and PUD history, a physician should take abdominal CT scan without any hesitation for diagnosing PPU.