The smARTrack™ Feeding System is a novel gastric tube and monitoring device. It was developed to overcome the complications associated with enteral nutrition in mechanically ventilated patients. After closely monitoring 20 mechanically ventilated patients for a cumulative period of 57 days, this is the first document description of the distribution of gastro-esophageal reflux in critically ill mechanically ventilated patients.
One of our main findings shows that GER occurs three times per hour of mechanical ventilation. Reflux above the LES occurred 4072 times or an average of 204 events per patient (range 40-570). We have also recorded three common clinical scenarios that were associated with a high risk of reflux. These include patient position-change, enteral fluid bolus, tracheal suction and migration of the feeding tube tip during ongoing use.
Patient position change:
The mechanically ventilated patient moves spontaneously in bed and is very often passively moved by the nursing and medical teams. Lateral rotation is done during washing, wound treatment, bedding and to prevent pressure sores. Vertical downward movement of the head of the bed occurs for various procedures such as central line placement, washing or bedding.
These events may create a gravitation gradient that promotes GER, thus raising the probability of regurgitation of gastric content and its' aspiration. In 827 (average 41) events of position change, there were 300 (40%) reflux events, within 5 minutes. In order to prevent this sequence the patients should be treated with their torso raised to 30 degrees at least. Another reflux preventing mechanism might be to open the gastric tube to drain whenever the head of the bed is lowered to the supine position.
Enteral fluid bolus:
Fluid boluses of 50-60 ml are given by syringe to the GFT for delivery of various medications and nutrition. This procedure is usually done by the nurse as a rapid push, unaware of the steep rise in gastric pressure. Because of the positive pressure gradient, gastric content is refluxed to the esophagus. In 151 events (average 8) of enteral Fluid Boluses, 35 reflux events occurred within 5 minutes (23%). A method to prevent this surge of gastric pressure may be to reduce bolus volume or avoid syringe boluses altogether and to deliver the fluid or medication by slow enteral infusion.
Feeding tube displacement during enteral nutrition administration:
In 5 out of the 20 patients (25%), 7 tube tip displacement events were detected. In all of them, the tip moved proximally to the upper esophagus. Reflux and aspiration may have been prevented by occlusion of the pumps' feeding-set by the system alarm sequence.
Enteral nutrition by a feeding tube is the standard of care for most mechanically ventilated patients in the ICU and elsewhere. The passage of the tube through the esophagus to the stomach opens the LES and promotes gastro-esophageal reflux. Once the LES is passed, there is nothing but gravitation to prevent the fluid from reaching up-to the patients' mouth. When refluxed gastric content reaches the patients' mouth, there is a high risk for tracheal aspiration and as a result, a chance to develop an aspiration pneumonia called VAP. Aspiration of gastric content can occur without obvious evidence of vomiting, particularly in sedated patients or those with poor mental status, and absent gag reflex. The regurgitation is usually silent until signs of respiratory compromise or pneumonia develop. As mentioned before, clinically significant aspiration occurs in up to 88% of ventilated patients with tracheostomies or trans-laryngeal intubation . Aspiration pneumonia adds an average of 7 days of mechanical ventilation, is associated with a very high mortality and an added average healthcare cost of $40,000 . Currently, the best-proven means of reducing the risk of VAP is by elevating the head of the bed, presumably reducing the risk of reflux, regurgitation and aspiration.
Tracheal Suction (TS) is a routine and common procedure in the ICU. A negative pressure of 100-700 mm mercury is applied to the airway for a period of 10-20 seconds, sometimes 2-3 times in a row, causing a fast outward air flow and a quick and significant reduction in thoracic pressure. In many units where a closed suction system is not in use, this procedure is preceded by disconnection from the ventilator, thus reducing airway pressure to zero even before onset of the suction procedure. In the ICU where the study was conducted, a closed suction system is the standard of care. Therefore, mechanical ventilation was continued during the TS procedure, thus delivering air-leak compensation by the ventilator and reducing the pressure drop. Still, TS was very often followed by reflux probably caused by a rapid pressure drop in the chest and a positive pressure gradient from the stomach to the esophagus. In 327 procedures (average 17) of TS performed, reflux occurred within 5 minutes in 211 events (64.5%). The average was 11 reflux events per patient.
To prevent the pressure gradient during TS, it may be suggested to maintain a raised head of the bed, reduce negative suction pressure, and shorten the procedure, to perform it intermittently and to use a closed suction system so that mechanical ventilation is not interrupted.
Tube tip dislocation:
As a result of various procedures, such as patient movement or positioning change, the gastric tube may get dislodged from its correct position and move in, or outwards. The results of these tube movements may be hazardous if the tip has shifted to the upper esophagus or throat, and an aspiration may result.
Our study has several limitations: It is a pilot observational study studying the reflux of patients without comparing our technique to a gold standard methodology. Our technique will have to be compared to other methods such as tracheal detection of pepsin, stable isotopes, or addition of colorant to the enteral nutrition. We have also to consider that many of the detected reflux events may be of non-clinical significance but those of long duration and high volume may be more relevant.