June 2011

E-journal club

 

University of Virginia Health System

Nutrition Support E-Journal Club

June 2011

 

Greetings,

Traditionally, we do not plan traineeship programs for June because our teams generally take time for vacations, “staycations,” and otherwise prepare the body, mind and spirit for the arrival of new resident physicians, fellows and dietetic interns in the near future.  In view of the need to cover for staff that was away, we decided to postpone our June journal club.  We reviewed two articles in July, but decided to post them separately so they will be easier to read and find.

June Citation:

Metheny NA, Stewart BJ, McClave SA.  Relationship between feeding tube site and respiratory outcomes.  JPEN J Parenter Enteral Nutr. 2011 May;35(3):346-55.

Summary: 

This was a retrospective analysis of 428 critically ill, mechanically ventilated patients from 2 prior studies that investigated the association between feeding site and by the simplified Clinical Pulmonary Infection Score (surrogate for pneumonia) and the presence of pepsin in tracheal secretions (proxy for aspiration). Feeding site was designated by physicians and initially confirmed by radiography. Each patient participated in the study for 3 consecutive days, and the simplified Clinical Pulmonary Infection Score was calculated on the fourth day.  The investigators statistically controlled for 4 clinical variables: severity of illness, level of sedation, degree of backrest elevation and use of gastric suction.

Inclusion and Exclusion Criteria were:

Inclusion criteria:

Age ≥18 years, admission to 1 of the 5 ICUs at the study site, continuous tube feedings, and mechanical ventilation.

Exclusion criteria:

Pneumonia present before tube feeding started and use of a gastrostomy or jejunostomy tube.

 

Major Results reported by authors:

The percentage of pepsin detected in tracheal secretions (aspiration proxy) was 11.6% lower than gastric feedings when feeding tubes were in the first portion of the duodenum, 13.2% lower when in the second/third portions of the duodenum, and 18.0% lower when in the fourth portion of the duodenum and beyond (all significant at p < 0.001).  The simplified CPIS score > 6 (possible pneumonia) was not significantly different between gastric and duodenal feeding, but a CPIS score > 6 occurred significantly less often when feedings were introduced at or beyond the second portion of the duodenum (p = 0.02).  Feeding beyond the second portion of the duodenum remained significantly associated with a CPIS > 6, even after statistical control for severity of illness, sedation, degree of backrest elevation and use of gastric suction.

 

Author’s Conclusions:

The authors concluded that their findings “support feeding critically ill patients with numerous risk factors for aspiration in the mid-duodenum and beyond to reduce the risk of aspiration and associated pneumonia.  Diverting the level of feedings is one component of a multi-tiered strategy (including HOB elevation to at least 30 degrees when possible and using gastric suction during small bowel feedings), to decrease the risk of aspiration and ultimately to decrease the risk of pneumonia.”

 

Evaluation:

The major aspect that must be considered when evaluating the results is that it is a retrospective, observational study.  Observational studies can only document associations, and should never be used to suggest cause and effect.  There is no possible way to statistically control for the myriad of factors that influence outcomes in the ICU population, which is why the primary role of observational studies is to form theories that must then be tested in randomized studies. 

This particular study statistically controlled for only 4 factors thought to have a possible influence on pneumonia.  There was no control for other factors known to have an influence on pneumonia incidence, such as how often patients were turned, adequacy of oral care, subglottic secretion drainage, or need for transfusions, to name just a few.  In an unblinded, non-randomized study there are any number of differences between patient groups that can occur which influence pneumonia.  Although the authors reported that there was no significant difference in the degree of backrest elevation between the groups they report that the mean backrest elevation of the gastric group was 26.2 +/- 13 while the mean backrest of the group fed into the 4th portion of the duodenum or beyond was 38.6 +/- 11.  This difference in backrest elevation is certainly a clinically significant difference, and illustrates not only that the gastric fed group did not have appropriate backrest elevation while the small bowel fed group did, but also indicates that these groups were not cared for in the same manner.  An additional difference between the groups was that patients fed in the distal bowel had a significantly greater percentage of patients receiving gastric suction (28.4 fed in D1, 35.3 fed in D2-D3, and 46.9% fed in D4 or beyond).  It would be reasonable to expect that there were other ways in which these groups were treated differently.

The other major factor that limits conclusions drawn from this study is the use of CPIS score as a surrogate for pneumonia.  CPIS score has been criticized as having low diagnostic accuracy when compared with quantitative cultures of bronchoalveolar lavage fluid (1-3).  Certainly, in this study, the CPIS would appear to be an over-sensitive marker of true clinical pneumonia incidence due to the very high pneumonia incidence suggested by the CPIS score.  Considering that the investigators excluded patients with pre-existing pneumonia, and that the CPIS score was calculated on day 4, the 46.4% incidence of pneumonia in the gastric fed group and 40.2% in the D1 fed group is an extraordinarily high incidence of nosocomial pneumonia (especially within 4 days). 

Other limitations of this study include the use of nonvalidated measures to re-verify tube position (volume, appearance and pH of aspirates—it was not stated how many patients were on PPIs in each group), only a small number of patients (n=32) were fed into the distal small bowel compared to those fed into the stomach (n=209) or D1 (n=102), and the fact that this study involved 2 cohorts of patients separated by 3-6 years allowing for potential changes in practice, protocols and medications in an ICU setting to influence outcomes (4,5). 

It is also interesting to note that 6% of patients experienced spontaneous tube migration from the small bowel back into the stomach and 3% of gastric tubes ended up in the small bowel.  The displacement of feeding tubes was determined by an x-ray that was obtained for reasons other than for a tube check, and not all patients had routine radiographs of tube position, therefore it is highly probable that a higher percentage of tube migration occurred than was reported.

Our Take Home messages:

1.    Observational studies should not be used to make cause and effect or practice statements.

2.    There is a need for an adequately powered randomized study of the influence of small bowel feedings with or without gastric suction on the development of clinical pneumonia incidence and overall outcomes.

 

References:

  1. Schurink CA, van Nieuwenhoven CA, Jacobs JA, et al. Clinical Pulmonary Infection Score for ventilator-associated pneumonia: accuracy and interobserver variability. Intensive Care Med. 2004;30:217-224.
  2. Fartoukh M, Maitre B, Honore S, Cerf C, Zahar JR, Brun-Buisson C. Diagnosing pneumonia during mechanical ventilation: the Clinical Pulmonary Infection Score revisited. Am J Respir Crit Care Med. 2003;168:173-179.
  3. Luyt CE, Chastre J, Fagon JY. Value of the Clinical Pulmonary Infection Score for the identification and management of ventilator-associated pneumonia. Intensive Care Med. 2004;30:844-852.
  4. Metheny NA, Clouse RE, Chang YH, et al.  Tracheobronchial aspiration of gastric contents in critically ill tube-fed patients: frequency, outcomes, and risk factors.  Crit Care Med 2006;34(4):1007-1015.
  5. Metheny NA, Davis-Jackson J, Stewart BJ.  Effectiveness of an aspiration risk-reduction protocol.  Nurs Res. 2010;59(1):18-25.

Other News on the UVAHS GI Nutrition Website:

 --Check out our new, “Nutrition Support Blog” and “ Resources for the Nutrition Support Clinician.”

--Fall webinar dates and topics now posted; registration to open soon

--Latest Practical Gastroenterology article:

Krenitsky J, Rosner M.  Nutritional Support for Patients with Acute Kidney Injury: How Much Protein is Enough or Too Much?  Practical Gastroenterology 2011; XXXV(6): 28-42.

 

Joe Krenitsky MS, RD

Carol Rees Parrish MS, RD

PS – Please feel free to forward on to friends and colleagues