This cross-sectional study involved 133 patients aged over 80 undergoing nasal feeding. We measured the pepsin level in saliva as a simple indicator of GERD to investigate factors related to GERD in these patients. We found that factors independently related to a relatively high level of pepsin in saliva were diabetes (OR: 2.67; 95%CI: 1.225–5.819, P = 0.013) and nasal feeding methods (OR: 2.475; 95%CI: 1.183–5.180, P = 0.016).
Invasive tests for GERD diagnosis are difficult and even impossible in very elderly patients, such as those included here, so we used pepsin level as an indicator of GERD. Due to a lack of a gold standard for normal pepsin level in elderly people, the patients were divided into two groups according to the median pepsin level. Previous studies have suggested that the concentration of pepsin in saliva samples changes at different time periods [18, 24]; however, there is still no consensus on the optimal collection time [18, 20, 21]. Hayat et al. [18] used a PPI test to determine pepsin, and suggested that the positive detection rate and concentration 1 h after a meal are higher than during the fasting state in the morning, therefore, they recommended collecting saliva samples 1 h after meal. However, Na et al. [24] believed that the concentration of pepsin upon waking was higher than 1 h after a meal when GERD symptoms occur. To resolve this difference, we collected the patient's samples during fasting in the morning and 1 h after lunch. The results showed that the pepsin levels in the morning and 1 h after lunch were highly positively correlated, with no significant difference. This difference with the previous studies might be because of the differences in the populations. In elderly patients with nasal feeding, the concentration of pepsin accumulated in the mouth and throat likely remained relatively stable due to decreased activity, increased time in bed, and decreased saliva secretion. Therefore, we speculate that the pepsin content in the saliva of elderly patients with nasal feeding is basically stable throughout the day and responds to reflux.
Age was not independently related to increased salivary pepsin in this study. However, other studies on different age groups have suggested that age does have an influence GERD. In a previous study, prevalence was significantly higher in subjects aged more than 50 years [10]. Another study [3] indicated that increased age was associated with the prevalence of GERD, and the mechanisms of increased GERD disease in older patients intensified the underlying diseases, disturbed esophageal motility, and decreased salivary secretion. However, there are few studies concerning patients aged ≥ 80 years. In our study, age was not a risk factor because there was no significant difference in the degree of underlying diseases and physiological functions of the patients aged ≥ 80 years. In other words, when patients are aged ≥ 80 years, their condition is complex, which attenuates or disperses the effects of age.
According to a previous study, diabetic patients are more prone to GERD [25]. This is in agreement with the results of this study which found that diabetes was related to higher levels of pepsin in the saliva. Hyperglycemia affects autonomic function and gastrointestinal hormone secretion, resulting in insufficient gastric motility in patients [3, 6, 26]. Insufficient gastric motility is one pathogenic mechanism of GERD. In addition, obesity is an important risk factor for GERD, and obesity and type 2 diabetes are closely associated [25]. This suggests that patients with a history of diabetes should be specifically concerned with the presence of GERD during medical and nursing care.
Feeding method was also shown to be related to a higher level of pepsin in saliva. It has been reported that the use of a stomach tube with a small outer diameter can reduce the occurrence of complications, such as reflux [27]. However, the results of this study showed that the outer diameter of the gastric tube was not a factor affecting the content of pepsin. Perhaps the sample size of this study was too small, and the diameters of the two gastric tubes were not remarkably different. Therefore, we could not reach a similar conclusion. Previous studies in Chinese have suggested that a nasal feeding pump can inject liquid food into the stomach at a constant rate and slowly, which is superior to syringe injection in preventing intestinal nutrition complications. The results of our study also showed a high risk of high concentrations of pepsin in the saliva of syringe-fed patients. We hypothesize that because syringe feeding injects food into the stomach quickly, causing a rapid increase in the pressure applied to stomach, this leads to increased risk of GERD. In contrast, using a nasal feeding pump not only reduces the pressure of the food on the lower esophageal sphincter, but also slows down the rate of blood glucose in the patient.
There were several limitations in this study. First, the sample size was not very large, and we did not compare the results with a healthy control group. Second, due to the gold standard diagnostic method for GERD being invasive and not suitable for patients aged 80 and over, we could only choose the level of pepsin in saliva to indicate GERD. As the level of pepsin that indicates GERD has not been agreed we cannot definitely say that the patients in the ≥ 7.75 ug/ml pepsin group had GERD. Third, this was a cross-sectional study and lacked follow-up data. Fourth, the patients included in this study were all male, and the results might not apply to female patients. Finally, only the use of non-steroidal anti-inflammatory drugs (NSAID), aspirin and anticholinergic drugs on the level of pepsin were analyzed. Other drugs with potential effects were not included in the analysis. These may cause some bias to the results.