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Critically ill patients have an increased risk for aspirating oropharyngeal secretions and regurgitated gastric contents. For those who are tube-fed, aspiration of gastric contents is of greater concern.
While witnessed large-volume aspirations occur occasionally, small-volume clinically silent aspirations are far more common. For example, a laboratory study identified frequent microaspirations in approximately half of a large population of critically ill, mechanically ventilated patients who were receiving tube feedings.1
In the same study, risk for pneumonia was about 4 times greater in patients identified as frequent aspirators. Because no bedside tests are currently available to detect microaspirations, efforts to prevent or minimize aspiration take on added importance.
There is evidence that a sustained supine position (zero-degree head-of-bed elevation) increases gastroesophageal reflux and the probability for aspiration; for example, using a radioactive-labeled formula, endobronchial counts were higher when patients were lying flat in bed (zero degree) compared to when they were in a semirecumbent (45-degree) position.2
Thus, elevating the head of the bed to an angle of 30 to 45 degrees, unless contraindicated, is recommended for patients at high risk for aspiration pneumonia (eg, a patient receiving mechanical ventilation and/or one who has a feeding tube in place).3,4
Although effectiveness of the reverse Trendelenberg position in minimizing aspiration has not been studied, it is likely to produce similar results to an elevated backrest position.4
Sedation causes reduced cough and gag reflexes and can interfere with the patient’s ability to handle oropharyngeal secretions and refluxed gastric contents; in addition, sedation may slow gastric emptying.5,6 To reduce the risk for aspiration, it is prudent to use the smallest effective level of sedation.
Expert panels recommend that correct feeding-tube placement be verified at regular intervals to minimize the risk for aspiration.3,4,7 If feedings are administered at the wrong site (such as the esophagus, or even the stomach of a patient who requires small-bowel feedings), the risk for aspiration is increased.8
It is not uncommon for feeding tubes to become malpositioned during routine use. For example, in a study of 201 critically ill patients, it was found that the distal tips of 24 of 116 feeding tubes originally positioned in the small bowel were displaced upward into the gastrointestinal tract (23 into the stomach and 1 into the esophagus).9
Tube-fed patients who experience frequent regurgitation and aspiration of gastric contents are at increased risk for poor respiratory outcomes.1
Guidelines developed jointly by the Society of Critical Care Medicine and the American Society for Parenteral and Enteral Nutrition recommend that patients be monitored for tolerance to enteral feedings by noting abdominal distention, complaints of abdominal pain, observing for passage of flatus and stool, and monitoring gastric residual volumes.10
Because gastric distention predisposes to regurgitation, it is recommended that gastric residual volumes (GRVs) be measured every 4 hours in critically ill patients.4 Practice varies widely in regard to GRVs; however, 200 ml and 250 ml are frequently cited values for initial concern.11,12
In a study of 206 critically ill patients, 2 or more GRVs of at least 200 ml and 1 or more GRVs of at least 250 ml were found significantly more often in patients who experienced frequent aspiration.11 Prokinetics are sometimes advocated to improve gastric emptying when GRVs exceed a stipulated value. Several sources recommend that feedings be stopped when GRVs exceed 500 ml.4,7
In a study of gastrointestinal (GI) symptoms in critically ill patients, investigators found that those with 2 or more simultaneous GI symptoms (such as high gastric aspirate volume, absent or abnormal bowel sounds, vomiting/regurgitation, diarrhea, bowel distension, and gastrointestinal bleeding) were less likely to have successful enteral feedings than those with fewer than 2 GI symptoms (84% vs 12.2%, respectively, p < .001).13
Although bedside assessments for GI function such as GRVs and abdominal girth are difficult to evaluate,14-16 they are frequently used in combination to provide an estimate of GI tolerance to enteral feedings. Small bowel feeding with the tube’s ports situated at or below the Ligament of Treitz is strongly recommended for patients with persistent intolerance to gastric feedings and documented aspiration.7
An expert panel has concluded that no recommendation can be made regarding the best type of formula delivery method (continuous or intermittent).3 Also, no guidelines exist for bolus feedings.
On the basis of logic, however, administering an entire 4-hour volume of formula over a period of a few minutes is more likely to predispose to regurgitation of gastric contents than is the steady administration of the same volume over a period of 4 hours.
Continuous feedings are used in most critical care units. Supportive of this action is a small study of neurologically impaired adult patients; aspiration was observed more frequently in those with intermittent feedings (3 of 17) than in those who received continuous feedings (1 of 17).17
It is possible that the bolus method of feeding may decrease the lower esophageal pressure and thus predispose patients to reflux and aspiration.18 Other researchers reported that adult burn patients who received continuous tube feedings had less stool frequency and less time required to reach nutritional goals than did intermittently fed patients.19
Tracheal intubation interferes with overall swallowing physiology.20 Thus, it is reasonable to expect some degree of swallowing impairment when patients are initially extubated.
A systematic literature review found that recently extubated patients were at increased risk for swallowing difficulties; more than 20% of the patients in many of the reviewed studies experienced dysphagia.21
A persistent low cuff pressure (< 20 cm H2O) predisposes patients to pneumonia, presumably by predisposing to aspiration of oropharyngeal secretions and/or refluxed gastric contents.22 To minimize aspiration of secretions pooled above the endotracheal tube’s cuff, hypopharyngeal suctioning should be performed before deflating the cuff.3
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