Polymerase Chain Reaction (PCR) and Cultivation of the Peritoneal Fluid at Operation for Appendicitis and Postoperative Enteral Antibiotic Treatment (PACPAT)

Aim The primary aim is to investigate whether it is possible to determine if there are bacteria in the patient's peritoneal fluid either from PCR (polymerase chain reaction) or cultivation within 24 hours in patients undergoing surgery for acute appendicitis.

The secondary purpose is to investigate whether oral administered postoperative antibiotic treatment is non-inferior to prior standard intravenous administration therapy focusing on wound infection and intra-abdominal abscess.

The clinical issues

Previous studies from our department have shown that both over- and under treatment with antibiotics in patients operated for acute appendicitis is reality. It has not previously been possible to control the treatment based on the result of peritoneal fluid culture, because the final response to conventional cultivation is first available after a 3-4 days. The PCR (polymerase chain reaction) technique allows diagnostics within hours.

The second problem is that conventional postoperative antibiotic treatment is most often the only reason for the patient to remain hospitalized for at least 3 days. With oral antibiotic treatment the patient can be treated at home.

Hypotheses

• In case of acute appendicitis surgery, it is possible to determine the presence of bacteria in the peritoneal fluid by PCR or culture within 24 hours, and that the final response to D + R after a further 3 days of culture is consistent with this.
• Oral postoperative antibiotic therapy is non-inferior to traditional intravenous administration in complicated appendicitis.

Background Acute appendicitis surgery is one of the most frequent operations with a lifetime risk of approximately 9%.

Appendicitis can be classified as uncomplicated (phlegmonous) or complicated (gangrenous, perforated or peri appendicular abscess) based on perioperative findings. Perioperative antibiotics prophylaxis is administered to all patients, who are operated for acute appendicitis, whether there is complicated or uncomplicated appendicitis due to prevent complications. The complications are primarily wound infection or intra-abdominal abscess. In complicated appendicitis treatment continues for three days after surgery. The antibiotic treatment targets both aerobic and anaerobic intestinal bacteria. Several antibiotic regimens have been found to be equivalent. In our department, cefuroxime and metronidazole as intravenous administration are used as standard.

It is the surgeon who alone determine whether an appendicitis is complicated by the findings under the surgery. A previous study conducted in the ward showed that in 42% of the cases where the surgeon assessed that the appendix was perforated, no bacterial growth could be detected by growing on perioperatively retrieved peritoneal fluid, while in 18% of cases where the histology showed simply phlegmonous appendicitis, there was a positive culture result. Therefore, there is a risk of both under- and over treatment, which is inappropriate for many reasons, including increased resistance development. Therefore, a more evidence-based approach to postoperative antibiotic treatment after surgery for acute appendicitis is needed.

A prerequisite to organize a more appropriate antibiotic treatment will be the ability to obtain a reliable culture result from peritoneal fluid within 24 hours. Conventional cultivation can be problematic because not all bacteria will show growth within this time. PCR could be a better method and an alternative to ordinary culture.

If it is found that it is possible within 24 hours after the operation to determine whether there is growth of bacteria in the peritoneal fluid, it will be possible to let this determine if continued postoperative treatment are needed regardless of the operative findings, thus reducing the risk of under- or overtreatment.

Another important clinical question is whether antibiotics should be given intravenous or oral. Oral treatment will be convenient for both the patient and the health care system, as the patient will then be able to be treated at home. A previous retrospective Danish study has shown that oral antibiotic treatment is equivalent to intravenous treatment and that the hospitalization time can be reduced by an average of 61 hours. Oral treatment has been introduced in some Danish hospitals.

Method The study design is a prospective cohort/feasibility and non-inferior study, which includes a total of 100 patients older than 18 who undergo an appendectomy due to acute appendicitis.

When diagnostic laparoscopy is performed and appendicitis is recognized, 10 ml of peritoneal fluid is extracted for examination by special equipment approved for this purpose. In the absence of peritoneal fluid, the surgeon will rinse with 20 ml of sterile saline corresponding to the peri appendicular area. The peritoneal fluid is then sent for PCR, culture and resistance determination.

When these procedures are performed usual antibiotic treatment in the form of 3 g of cefuroxime and 1.5 g of metronidazole are administered intravenously and the operation is performed according to usual guidelines.

If there is a complicated appendicitis (assessed preoperatively), oral antibiotic treatment in the form of 875 mg amoxicillin / 125mg clavulanic acid + 500mg metronidazole x 3 daily for 3 days are prescribed. The treatment will be independent to the result of PCR determination and the culture on the peritoneal fluid.

The sample containing the peritoneal fluid is sent to the microbiological department, where they make the cultivation and resistance determination as well as the PCR. Growth is observed on the cultures at 12, 24 and 36 hours and the final result with resistance determination after 3 days. The type of bacteria in the samples are recorded. Follow-up is done 30 days postoperative, where the patient is contacted by telephone for postoperative complications. Complications for appendicitis are typically intraabdominal abscess and wound infection, and therefore special attention will be given to these. Wound infections are defined by the Centers for Disease Control and Prevention (CDC) surgical site infections (SSI). These and any other complications are also recorded according to the Clavien Dindo classification (CD).

The part of the study that deals with the PCR and culture on the peritoneal fluid is a descriptive study to investigate whether the PCR technique can be introduced into the daily clinic. The technique has not previously been tested anywhere and therefore it is not possible to make any strength calculation on the sensitivity and specificity of the PCR method relative to the result of the final culture. From our previous studies it is known that at least one third of the patients will be classified as having a complicated appendicitis. The inclusion of 100 patients will in our opinion be enough to be able to calculate sensitivity and specificity with acceptable safety limits, which can be indicative of further studies.

The other part of the study concerns the change of antibiotic treatment from intravenous to oral treatment. The basis for assessing this will be the frequency of any infectious complications compared to the frequencies present in the literature. Wound infections by the laparoscopic technique is about 3% and intra-abdominal abscess is about 7.5%. The investigators will continuously record the frequency of these complications, and if deviations from the above occur a detailed review of each case will be made and a decision on whether this part of the project can continue or not. The results will also be indicative of whether a randomized trial will be necessary.

Project feasibility All methods are tested. The method of taken samples from the peritoneal fluid is tested in another study at the department. The study itself is a feasibility study to see if it is safe and possible to use these methods in the clinic. For these reasons, a pilot study is not necessary.

Limitation The exclusion criteria are a limitation. Especially the age limit of 18 years courses that the generalizability to patients under 18 is not possible. It is a problem because there is a lot of patients with appendicitis under the age of 18.

It is also a limitation that the study only includes 100 patients. The reason for this is that the study is a feasibility study and therefore believed 100 patients is enough to conclude if further studies are needed.

Expected clinical impact The results could be of great importance for future treatment. If it is possible to get an answer of the presence of bacteria in the peritoneal fluid within 24 hours, it is possible to target the antibiotic treatment to the right patients. This is important for the single patient but also important for the society because the use of antibiotic leads to development of antibiotic resistant bacteria and therefore it is important to avoid unnecessary use of antibiotic. Since appendicitis is a very frequent disease, research in this area is of great importance as it involves a high number of patients and thus a large amount of antibiotics. Especially because it is shown that the surgeons overestimate the number of patients with complicated appendicitis.

In addition to this the oral treatment has the impact that most patients can be treated with antibiotics at home. This will have a positive impact for both patient and society.