Nasogastric Tube Size, Reflux, and Aspiration

Abstract & Commentary

Synopsis: Although no statistically significant differences were found, trends supported more gastro-esophageal reflux and microaspiration with large-bore nasogastric tubes.

Source: Ferrer M, et al. Ann Intern Med 1999;130: 991-994.

To determine whether gastroesophageal reflux and microaspiration can be reduced by the use of small-bore nasogastric (NG) tubes, Ferrer and colleagues conducted a randomized crossover trial in 16 mechanically ventilated patients who had been intubated more than 72 hours in a respiratory ICU. Each patient was first assigned to receive a small (2.85 mm) or large (6.0 mm) bore NG tube. Twenty-four hours after tube insertion, radioactive technetium colloid (1 mL) was instilled through the NG tube. Sequential samples of serum, gastric juice, and pharyngeal and tracheal secretions were obtained before (baseline), and 1, 2, 3, 4, 5, and 17 hours after instillation. These measures were then repeated 72 hours later using the alternate size tube. Results were corrected for decay and expressed as a decimal logarithm of counts per minute per mL. Gastroesophageal reflux was defined as an increase in radioactive counts in pharyngeal aspirates by one log10, compared with baseline. Microaspiration was defined as an increase of more than one log10 in tracheal aspirates. Complete data were obtained in 16 subjects with the large-bore tube, and in 15 subjects with the small-bore tube.

There were differences in mean and cumulative radioactive counts over time. However, mean counts did not differ between the two types of tubes for any type of sample or at any time point. Nevertheless, there was a greater incidence of gastroesophageal reflux and aspiration with large-bore than with small-bore NG tubes. For gastroesophageal reflux, the incidence was 10 of 15 (67%) for small-bore tubes and 13 of 16 (81%) with large-bore tubes (CI, -16.6-44.6 percentage points; P > 0.20). For aspiration, the incidence was three of 15 (20%) for small-bore tubes and five of 16 (31%) for large-bore tubes (CI, -19.4-41.4; P > 0.20). A trend toward greater frequency of aspiration was seen in studies with reflux (eight of 23) as compared with studies without reflux (zero of eight) (P = 0.076). Aspiration was not detected in studies without reflux.

COMMENT BY LESLIE A. HOFFMAN, PhD, RN

Small-bore NG tubes are advocated as a means of reducing gastroesophageal reflux and microaspiration in intubated patients. This recommendation is logical, since reducing the size of the tube may improve closure of the lower esophageal sphincter and, thus, prevent or reduce gastroesophageal reflux. However, because of insufficient evidence, the use of small-bore tubes for prevention of nosocomial pneumonia is not recommended by the CDC (MMWR Morb Mortal Wkly Rep 1997;46[RR-1]:1-79).

Findings of this study indicated no significant difference in radioactive counts in the various samples, or the frequency of gastroesophageal reflux, or microaspiration with the two types of tubes. However, the incidence of gastroesophageal reflux and microaspiration was higher when large-bore NG tubes were used. The study was carefully designed. The sample included patients at high risk for aspiration, i.e., acute respiratory failure (n = 8), neurologic disease (n = 3), cranial trauma (n = 2), cardiac arrest (n = 2), and coma (n = 1). Risk factors were identical, since patients received both types of NG tubes. All patients were positioned in the same manner (semirecumbent), and tube position was confirmed by abdominal radiography. Evidence of aspiration and reflux was carefully documented using radioactive counts from varied sources. However, the sample size was small, raising the potential of a Type II error (insufficient subjects). Also, there was no indication whether the incidence of reflux or aspiration varied dependent on the type of tube that was first inserted (order effect).

The findings of this study indicate that small-bore tubes do not eliminate the risk of gastroesophageal reflux or microaspiration in mechanically ventilated patients. Nevertheless, their use was associated with a lower incidence of these adverse events.

Among patients with nasogastric tubes, trends indicated a greater frequency of aspiration with:

a. small-bore tubes.

b. large-bore tubes.

c. elderly patients.

d. longer duration of intubation.

e. None of the above