This study outlines the etiology, associated presenting signs and symptoms, and outcomes of surgically managed peritonitis in a tertiary care center in central Malawi. The most common etiologies of peritonitis were appendicitis and volvulus. Abdominal rigidity, generalized peritonitis (versus localized), hypotension, tachycardia and anemia were significantly associated with mortality. The overall mortality rate was 15%. Ultrasound was specific but not sensitive in diagnosing appendicitis.
There are several similarities between our findings and those from other African countries. Appendicitis was the most common cause of peritonitis in our series (21%) and in studies on acute abdomen from Ghana (43.1%), Nigeria (40.3%) and Ethiopia (24.5%)[[3, 5, 6]]. One important distinction is that our study included patients with peritonitis defined as rigidity, guarding, or rebound tenderness, while these other studies included all patients with acute abdomen. Nega (2009) was the only investigator to report specific symptoms and reported guarding in only 39% of his patients, and though tenderness was present in 78% this was not specifically peritoneal tenderness.
Our mortality rate (15%) was similar to reported rates from Ethiopia (4.9-15.3%)[5, 7]. A report from the 1960s in England also had a similar mortality rate of 20%, though this study included only patients with generalized peritonitis . Interestingly, we found no correlation between the duration of symptoms and mortality, while Kotiso et al. noted 7.6% mortality rate in patients with symptoms of 2 days or less, compared with 25% among those with symptoms over 2 days in duration . Though it is unclear why we did not observe a similar trend, one hypothesis is that our population had more "survivor bias" with the sickest dying prior to presentation; this bias is noted in a variety of epidemiologic studies from developing countries [[9–11]].
We found a significant correlation between outcome and several presenting signs and laboratory values. Generalized peritonitis (versus localized) was correlated with mortality. This is likely because localized peritonitis was most commonly seen in appendicitis which had a low mortality rate, whereas all cases of perforated peptic ulcer (with a high mortality rate) had generalized peritonitis (data not shown). We also found that hypotension, tachycardia, and anemia were associated with increased mortality. Several of these factors are also predictive of mortality in other surgical emergencies including traumatic injuries and necrotizing soft tissue infections [12, 13]. Triage and care of patients with peritonitis might therefore be improved by using predictive tools similar to those applied to other acute surgical conditions such as trauma and necrotizing soft tissue infections.
Surgical diseases leading to peritonitis have a geographic variability. For example, in developed countries diverticulitis is a common cause of peritonitis, while we did not observe any cases of diverticulitis in our series . Additionally, we noted variation even within Africa, as several studies from Ethiopia report gallbladder pathology including gangrenous cholecystitis and gallbladder empyema whereas in our study there was no gallbladder pathology [7, 14].
The specificity of ultrasound (1.0) among those suspected of having appendicitis was similar to a that reported in a meta-analysis of ultrasound for appendicitis in adults (0.93), however our calculated sensitivity was considerably lower than the meta-analysis (0.50 versus 0.83) . One potential explanation of why we observed a lower than expected sensitivity is the selection bias in our study related to including only patients with peritonitis, as it may be that appendicitis is more difficult to diagnose when peritonitis is present due to patient intolerance of the examination or less reliable ultrasound findings late in the disease process. An alternative explanation is that the test is operator-dependent and the ultrasonographers are not experienced or adequately trained to diagnose appendicitis. Regardless inability to diagnose appendicitis by ultrasound in patients with peritonitis did not sway the clinician away from surgical intervention. In this study, the sensitivity and specificity of ultrasound to detect free fluid and/or abscess was 0.82 and 0.83. Interpretation of this is limited without intra-operative quantification of fluid volume, as prior studies suggest a minimum of 100 mL to over 500 mL of fluid is necessary for an ultrasound to reveal fluid .
This retrospective study was not able to examine the utility of plain films in the management of peritonitis because patients often keep their radiographs upon discharge. Our analysis also showed association between preoperative factors and outcome, but this observational study does not prove causality. Future research should aim to determine if correction of factors associated with mortality (such as fluid resuscitation to correct tachycardia and/or hypotension) might improve outcomes. The generalizability of this study is also limited to adult patients at a tertiary care setting, as we did not include patients admitted to the pediatric ward or patients managed in district hospitals or health centers. Lastly, the definition of peritonitis, though standardized, assumes that all health care providers are adept at assessing the abdominal exam for guarding, rebound tenderness, and rigidity.