Colonoscopy Outcomes by Duration of NPO Status
Colonoscopy is the most frequently performed procedure in the US and indications include evaluation of symptoms, screening, and surveillance. Among the challenges to achieving safe and high quality colonoscopic exams are limited colonoscopy capacity, complexity of patient scheduling, and adequate bowel cleansing. Quality of bowel preparation is improved by administering the purgative agent closer to the time of colonoscopy, a practice widely adopted by the gastroenterology community in the form of split-dose (PM and AM) preparation, so that at least half of the purgative is taken two to six hours prior to the colonoscopy, on the morning of the exam. However, optimizing bowel preparation quality needs to be balanced against potential increased risk of adverse events, in particular, aspiration requiring hospitalization, related to shorter duration of NPO ("nothing by mouth") status prior to colonoscopy. The 2011 American Society of Anesthesiology (ASA) guideline recommends 2 hours of NPO prior to moderate sedation. Adherence to this guideline would permit use of split-dose regimens and reduce procedure cancellations due to patient oral ingestion at intervals greater than 2 hours prior to a procedure.
A systematic review conducted by the Evidence-based Synthesis Program (ESP) Center at the Minneapolis VA Medical Center has evaluated the evidence on the relationship between timing of NPO and the incidence of aspiration and colonoscopy rescheduling. Other outcomes included other anesthesia-related harms, bowel preparation quality, colonoscopy quality measures, resource use, and patient satisfaction.
Hospital- and population-based studies have reported that aspiration incidence requiring hospitalization during colonoscopy with moderate or deep sedation is very low (1 in 1000 or less). However, NPO status was not documented in these studies. No study documenting NPO status found that shorter NPO status prior to colonoscopy increased aspiration risk. Report authors found that shorter time from completion of colonic preparation to colonoscopy (ie, 1 to 6 hours) was associated with greater bowel preparation quality than were intervals of 8 hours or longer. The authors also found that shorter duration of NPO was associated with higher adenoma detection rates. The authors found no direct evidence of the effect of NPO status on colonoscopy rescheduling.
VARIATION IN VA PRACTICE
An informal survey of 55 VA chiefs of anesthesiology in March 2014 found that anesthesiologists across the VHA appear to have differing policies and practices regarding NPO for elective procedures. Possible reasons for not adhering to the ASA guidelines are concerns that laxatives may not be treated similar to ingestion of clear liquids and that the volume of laxative may be larger than that of other clear liquids. Studies that evaluated ingestion of clear liquids up to 2 hours prior to anesthesia administration suggest that this ingestion does not affect stomach volume or pH compared to earlier ingestion. Other reasons for non-adherence of anesthesia providers to the ASA guidelines need to be explored.
LIMITATIONS AND RESEARCH GAPS
Report authors noted that the findings are limited by the lack of information directly addressing the key questions — the effect of NPO status on aspiration and other harms, procedural quality indicators, resource use, rescheduled colonoscopies, and patient satisfaction. In fact, only 5 of 40 included studies reported on aspiration according to NPO status and one reported on rescheduling (the report's co-primary outcomes). The available evidence was largely from studies that evaluated the effect of different regimens on bowel preparation quality. Patients with serious comorbidities were typically excluded. In addition, most studies examining different bowel preparation regimens and NPO status were not adequately powered to detect aspirations requiring hospitalizations or designed to assess rescheduling due to NPO status.
Reported research gaps include studies on: 1) accurate assessment of aspiration requiring hospitalization and other serious anesthesia related adverse events according to NPO status, 2) extent of and reasons for variation in anesthesia NPO status practice and policy, 3) effect of NPO status on procedure rescheduling and patient adherence and satisfaction, and 4) reasons for reduced patient adherence to recommendations for NPO status and bowel preparation. Future studies to close these knowledge gaps could improve care quality.
Shaukat A, Wels J, Malhotra A, Greer N, MacDonald R,Carlyle M, Rutks I, and Wilt TJ. Colonoscopy Outcomes by Duration of NPO Status Prior to Colonoscopy with Moderate or Deep Sedation. VA ESP Project #09-009; 2015.
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