Should NPO Be the Rule Before Cath? Reexamining Pre-Procedure Routines

There are many tests and procedures in medicine, and specifically in cardiology, that require patients to take nothing by mouth (NPO) for several hours before the procedure. NPO has been the standard of care for cardiac cath since its inception, because of the associated vomiting that was common with the first generation of radio contrast materials that were almost toxic. However, over the decades, the contrast media and the cath procedure itself have become very safe. It is rare to have a patient undergo a diagnostic cath with an adverse event like vomiting, hypotension (contrast-related) or arrhythmia [right coronary artery (RCA)-induced ventricular tachycardia (VT) or heart block] when using any of the modern contrast media used today. However, the pre-procedure orders for cardiac cath still state, “NPO after midnight.” Should this remain our practice? “Let the patient eat,” said Dr. John Bittl from Ocala, Florida, when asked about his pre-cath routine. He continued, “It’s time to eliminate the NPO order before invasive and interventional procedures, because 1) there is no hydration protocol that maintains euvolemia better than the homeostatic mechanisms of the body; 2) there is no compelling evidence that fasting makes PSA (procedural sedation and anesthesia, also called "conscious sedation") safer; and 3) there is only about a 0.1% risk of needing emergency surgery for percutaneous coronary interventions (PCIs). In our program, for the past 13 years, we have not required patients to fast. We do not decrease insulin doses. We have avoided intravascular volume depletion, hyperglycemia (which may contribute to acute kidney injury with contrast), and osmotic diuresis. We have decreased the number of hungry, disgruntled patients who complain to nurses. Patient and nurse satisfaction is therefore very high. Eliminating the NPO order is a radical idea, but it is something that every interventional program should consider.” Dr. Kirk Garratt of Lenox Hill Hospital, New York City disagreed. “Interesting idea, John, but I have to point out the obvious — one aspiration event and you’re toast! In addition, you’re in violation of a ‘thousand’ guideline statements. In NYC, for better or worse, [I believe] this will keep patients fasting.” I agree with Dr. Bittl’s answer to Dr. Garrett’s fear of lawyers. “It is curious to justify medical practice on fear of litigation in lieu of evidence.” Dr. Bittl supports this approach with a review of the evidence surrounding the NPO practice. “The scientific evidence for fasting for conscious sedation is very weak. The American Society of Anesthesia guidelines discuss this extensively and have concluded that there is no strong relation between fasting, gastric volume, or risk of aspiration. In any case, the patients at highest risk for nausea and vomiting are those who present with ST-elevation myocardial infarction (STEMI), who are not fasting anyway. “In the general cath lab population, fasting increases the risk of intravascular volume depletion, hyperglycemia in the diabetic patients, and subsequent risk of acute kidney injury (AKI). Using the legal threat, what is the greater risk: AKI or aspiration? As pointed out, the recommendations vary quite a bit. It’s hard to say that there is a standard.” Dr. Bittl provided me with two overviews on the subject. Brady et al¹ who addressed preoperative fasting for adults to prevent perioperative complications. They found that recent guidelines have recommended a shift in fasting policy from the standard ‘NPO from midnight’ approach to more relaxed policies, which permit a period of restricted fluid intake up to a few hours before surgery. Brady et al systematically reviewed the literature on different preoperative fasting regimens (duration, type and volume of intake permitted) on perioperative complications and patient wellbeing (including aspiration, regurgitation and related morbidity, thirst, hunger, pain, nausea, vomiting, and anxiety) in different adult populations. The review examined randomized, controlled trials that compared the effect on postoperative complications of different preoperative fasting regimens on adults. Thirty-eight randomized comparisons (made within 22 trials) were identified. Most were based on ‘healthy’ adult participants who were not considered to be at increased risk of regurgitation or aspiration during anesthesia. Few trials reported the incidence of aspiration/regurgitation or related morbidity, but relied on indirect measures of patient safety, i.e., intra-operative gastric volume and pH. There was no evidence that the volume or pH of participants’ gastric contents differed significantly depending on whether the groups were permitted a shortened preoperative fluid fast or continued a standard fast. Participants given a drink of water preoperatively were found to have a significantly lower volume of gastric contents than the groups that followed a standard fasting regimen. This difference was modest and clinically insignificant. There was no indication that the volume of fluid permitted during the preoperative period (i.e., low or high) resulted in a difference in outcomes from those participants that followed a standard fast. Few trials specifically investigated the preoperative fasting regimen for patient populations considered to be at increased risk during anesthesia of regurgitation, aspiration and related morbidity. Brady et al’s conclusions were that there was no evidence that a shortened fluid fast increased the risk of aspiration, regurgitation or related morbidity compared with the standard NPO after midnight policy. Interestingly, permitting patients to drink water preoperatively resulted in significantly lower gastric volumes. In another study further supporting Dr. Bittl’s view, Soreide et al² reviewed pre-operative fasting guidelines and found that in general, clear fluids are allowed up to 2 hours before anesthesia, and light meals up to 6 hours. The same recommendations apply for children and pregnant women not in labor. Based on the available literature, their task force produced new consensus-based Scandinavian guidelines for pre-operative fasting. Soreide et al emphasized that it remains to be seen to what extent the new liberalized fasting routines should apply to patients with functional dyspepsia or systematic diseases such as diabetes mellitus. Controversial areas still include the effect of fasting in emergency patients, women in labor and in association with procedures done under ‘deep sedation’. Soreide et al concluded that more research on the effect of various fasting regimes in subpopulations of patients is needed to provide evidence-based pre-operative fasting guidelines. Where does this leave us now? Clinicians should be encouraged to appraise this evidence for themselves and when necessary, adjust their standard fasting policies (NPO from midnight) for patients that are not considered ‘at-risk’ during anesthesia, particularly for those receiving moderate conscious sedation as used in the cath lab. I agree with Dr. Bittl. At least let patients have their morning coffee.

References

1. Brady M, Kinn S, Stuart P. Preoperative fasting for adults to prevent perioperative complications. Cochrane Database Syst Rev 2003;(4):CD004423. 2. Soreide E, Eriksson LI, Hirlekar G, et al. Pre-operative fasting guidelines: an update. Acta Anaesthesiol Scand 2005;49:1041-1047.

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