A consecutive series of 188 esophageal cancer patients who underwent esophagectomy from April 2012 to March 2016 in The University of Tokyo Hospital were enrolled. We previously reported the incidence of postoperative pneumonia as 20% (21 out of 105 patients) from 2009 to 2012 in a patient cohort without preoperative oral hygiene care; this cohort was used as a historical control (13). All of the current study participants received preoperative oral hygiene care from dentists and perioperative bacteriological studies were performed routinely as standard perioperative care. The clinico-pathological characteristics and the surgical procedures of the 105 previous and 188 current patients are shown in Table 1.
(Table 1 to be located here)
This was an interventional study with a prospectively accumulated cohort of esophageal cancer patients undergoing esophagectomy after preoperative oral hygiene care. The primary clinical endpoint was the incidence of postoperative pneumonia. The secondary study endpoint was the impact of oral hygiene care on bacteria in the oral cavity and other sites adjacent to the airway. Data obtained from the perioperative bacteriological cultures and oral bacterial counts were analyzed to evaluate oral hygiene care’s effectiveness in both clinical and non-clinical terms.
Oral hygiene care
Patients visited dentists as outpatients and screening for dental disease was done by dental pantomography. Tooth extraction was performed when severe dental disease was noted. Buccal swab samples were retrieved for quantitative bacterial analysis as described in the subsequent section. After these steps, patients were given detailed instructions on tooth-brushing techniques and advised to perform tooth brushing at least three times a day. No subsequent care was given by dentists except on occasions such as follow-up visits after tooth extraction.
Perioperative culture studies
Culture specimens were collected at the sites and timings reported below and sent immediately to the laboratory. Bacteriological studies were performed in exactly the same way as those in our previous study (13). The culture specimens were (A) dental plaque and (B) tongue coating immediately before surgery; (C) gastric juice from the gastric conduit immediately before anastomosis; (D) sputum obtained by endotracheal suction during the operation; (E) gastric juice from the nasogastric tube on the first or the second postoperative day; (F) sputum obtained by endotracheal suction within three days after surgery.
Quantitative measurement of oral bacteria.
Quantitative measurement of oral bacteria was begun in March 2013. Buccal swabs were done with cotton swab sticks from the 5th tooth (or, if missing, from any other tooth) and the tongue coating. These swab samples were processed using a Bacterial Counter (Panasonic Healthcare Co., Ltd., Tokyo, Japan) according to the manufacturer’s instructions. This device measures the dielectrophoretic impedance in the aqueous medium washing the cotton swab to quantify the amount of microbes trapped in the cotton swab (14,15). If possible, this quantification of the oral cavity microbial load was repeated three times for each patient: the first and the second samples were retrieved before and immediately after oral hygiene care, and the third was retrieved in the early hours of the day the surgery was performed. (The first and the second samplings, however, had to be abandoned in January 2015 when the medical staff collecting these specimens retired.) Increases or decreases in the bacterial load detected in the three types of specimens and their association with the incidence of postoperative pneumonia were the subjects of the analysis.
Diagnostic criteria of postoperative pneumonia
The diagnosis of pneumonia was made in accordance with the Japanese Respiratory Society’s Guidelines for Hospital Acquired Pneumonia in Adults. This diagnosis was contingent on the presence of pulmonary infiltrates in the standard chest radiography and at least two of the three criteria (a) pyrexia (>38.0 degrees), (b) leukocytosis (>12,000/mm3) or leukocytopenia (<4000/mm3), and (c) purulent airway exudates. All cases of pneumonia diagnosed by the above diagnostic criteria occurring within 14 days after the operation were retrospectively defined as postoperative pneumonia . These criteria are identical to those of our previous study.
Proportional differences were tested by Fisher’s exact test. Student’s t-test was used to compare group differences. Association of the oral bacterial count to the incidence of pneumonia was verified by logistic regression analysis. A value of P<0.05 was regarded as statistically significant. All analyses were performed using JMP Pro software version 14.0.0 (SAS Institute Inc., Cary, NC, USA).