Prolonged pre-catheterization fasting: do the risks outweigh the benefits?

Having patients fast prior to surgeries or procedures dates back to the mid-nineteenth century. In 1946, Mendelson retrospectively examined the cases of 44,016 pregnant women given anesthesia and found 66 cases of aspiration (0.15%) with two deaths. He recommended “withholding oral nutrition during delivery to prevent aspiration” and this recommendation evolved over time to the current guidance to take ‘nil per os (NPO) after midnight’ (1,2). Even with additional investigation, the historical precedent has remained deeply intertwined in clinical practice. The current 2017 guidelines from the American Society of Anesthesiologists (ASA) are similar to the 1999 ASA practice guidelines and recommend no clear liquids within 2 hours, no light meals within 6 hours, and no heavy meals within 8 hours prior to elective procedures utilizing moderate sedation (3,4). Recommendations for cardiac catheterization procedures were provided in a 2021 expert consensus document from the Society of Cardiovascular Angiography and Interventions (SCAI) (5). The SCAI expert consensus generally reflects the 2017 ASA recommendations, though they are careful to note that these cutoffs may be “too stringent” for the cardiac catheterization laboratory. Similarly, a Scientific Statement From the American Heart Association on Evidence-Based Practices in the Cardiac Catheterization Laboratory notes that the evidence to support NPO practice is ‘limited’, that the incidence of emesis with iso-osmolar or hypo-osmolar contrast agents is low and that there is no compelling evidence to suggest that fasting will make procedures requiring conscious sedation any safer (6).

The number of studies directly evaluating pre-cardiac catheterization fasting is limited, with a 2021 systematic review identifying nine studies, none of them randomized controlled trials (RCT), with the majority being deemed poor quality (7). Since then, three studies, including the present study, have addressed this important question. The COROnary angiography Non-Fasting (CORO-NF) study was a single-center, prospective, pragmatic study that compared 150 patients in the “conventional protocol phase” (NPO for at least 6 hours prior to angiography) to 150 patients in the “experimental phase” (reducing minimum fasting duration to 2 hours). Results showed that fasting time was reduced from 821±357 to 230±146 minutes with an increase in patient satisfaction. There were no aspiration-related adverse events in either of the 2 groups (8). The second study randomized 197 inpatients undergoing cardiac catheterization to a ‘heart-healthy diet’ group that could eat a specified diet until the scheduled procedure or to a fasting group that had nothing by mouth after midnight. Results showed that the heart-healthy diet group had significantly more satisfaction than the fasting group without any cases of aspiration, intubation, or hypoglycemia in either group (9).

The third study was the Comparison Between Fasting and No Fasting Before Interventional Coronary Intervention on the Occurrence of Adverse Events (TONIC trial), which is a single-center, prospective, single-blind randomized non-inferiority trial with patients randomized to a fasting or nonfasting group, stratified by insulin-dependent diabetes (10). Adult patients were included if they had a planned elective or semi-urgent coronary angiography or percutaneous coronary intervention (PCI). Notable exclusion criteria were coronary emergencies, hemodynamic instability, and patients undergoing a concurrent noncoronary procedure. Patients randomized to the nonfasting group were allowed to eat and drink at their convenience while patients in the fasting group were instructed to fast for at least 6 hours prior to the procedure for solids and liquids, which was their routine practice. Fasting times were calculated from the last food intake, documented by unblinded ward staff, to the procedure start time. The primary outcome was a composite of vasovagal reaction, hypoglycemia, and isolated nausea and/or vomiting that occurred up to four hours post-procedurally. Secondary outcomes measured contrast-associated acute kidney injury (CA-AKI) with creatinine measured on day 3, aspiration pneumonia within seven days, patient satisfaction from a survey, and procedural complications. Both per-protocol and modified intention-to-treat (mITT) analyses were performed.

The study randomized 755 patients with 379 and 376 in the fasting and nonfasting groups, respectively. The population was typical for a cardiac catheterization laboratory study with 75% being male with a mean age of 68 years. Comorbidities were prevalent with 23% being current smokers or past smokers, 29% being diabetic, 72% having hypertension, and 58% having dyslipidemia. The vast majority of procedures were elective (94%) with 70% only involving coronary angiography and 30% including a PCI. The average procedure time was 28 minutes with a median of 50 cc of iso-osmolar contrast iodixanol (Visipaque 320) used in both groups.

The median fasting times were 15 (14 to 18) hours and 3 (2 to 6) hours for both solids and liquids in the fasting and nonfasting groups, respectively. Roughly 20% of patients in the nonfasting group fasted more than 6 hours for both solids and liquids, with 18% reporting fasting for personal convenience. The primary endpoint occurred in 30 of 365 (8.2%) nonfasting patients vs. 37 of 374 (9.9%) fasting patients, supporting non-inferiority with absolute differences in the primary outcome favoring the nonfasting group of −1.7% and −2.1% in mITT and per-protocol analysis, respectively. The composite absolute difference was largely driven by differences in vagal reactions. Secondary outcomes showed similar rates of CA-AKI, 2% and 4% in the fasting and nonfasting groups (P=0.08), respectively. Two patients had an aspiration event with aspiration pneumonia. Overall patient satisfaction was similar across groups but nonfasting patients reported feeling less hungry and less thirsty and a majority of patients would prefer a nonfasting strategy in a future coronary procedure, 71% and 87% in the fasting and nonfasting groups, respectively. Subgroup analysis of the nonfasting group that divided patients into two groups based on fasting time did not show significant differences except for less hypoglycemia in the <3 hours of fasting subset.

The TONIC study expands the knowledge base around fasting for cardiac catheterization laboratory procedures but several important limitations must be kept in mind. First, only 18% and 22% of patients in the fasting and nonfasting groups, respectively, received conscious sedation with midazolam and less than 5% received pain medication with morphine. This utilization of conscious sedation is unlikely to reflect general practice as an international survey reported that conscious sedation during cardiac catheterization was used by 92% of cardiologists in North America and 38% in other countries (11). This difference in the use of sedation may or may not make a difference in outcomes however as the use of conscious sedation with benzodiazepine and analgesics was not shown to increase risks of pulmonary aspiration in a systematic review of fasting and perioperative complications (12,13). Second, while the study randomized 755 patients, this represents only 34% of potentially eligible individuals during the study period. Without information on the patients who were excluded and/or the reasons for exclusion, there is potential for selection bias. Third, while there was inclusion of higher-risk patients with left main disease, chronic total occlusion, and rotational atherectomy, only 30% of patients underwent PCI (14). Fourth, even though the median fasting duration in the nonfasting group was 3 hours, 20% of patients had fasting times greater than 6 hours. Lastly, while the interventional cardiologists in this study are to be congratulated on using a median of only 50 cc per patient, that is significantly lower than the average amount of contrast used, especially with PCI (15).

In summary, several conclusions are apparent on pre-cardiac catheterization fasting from the available studies. First, the length of fasting in clinical practice using the current guidelines is prolonged; fasting times in the conventional groups in the TONIC study and the CORO-NF study were 15 and 13.7 hours, respectively. Second, patient satisfaction is higher in groups with less time spent fasting. Third, aspiration is very rare with two reported cases in the TONIC study (0.3%) and none in the CORO-NF study. Even in the highest-risk patients who require emergent catheterization due to ST-elevation myocardial infarction and/or cardiogenic shock, aspiration is so rare that it is not included as a reported endpoint in any of the clinical studies. Lastly, data on the effect of fasting on CA-AKI is inconsistent although there is a signal in some of the trials that prolonged fasting may increase the incidence. In one study of 146 patients undergoing coronary angiography who were at high risk of CA-AKI, multivariate analysis showed that hemoglobin, the time that the patient was fasting and contrast volume were associated with the development of CA-AKI (16). Interestingly, there was a highly significant interaction between the amount of intravenous fluids, NPO time and contrast volume and changes in post-procedure creatinine suggesting that the dangers of fasting in regards to CA-AKI might vary depending on clinical factors such as hydration state and amount of contrast used.

Two studies that are either waiting to be published (CHOW NOW trial) or completed (SCOFF trial) will provide more information. CHOW NOW (Can We Safely Have Our Patients Eat With Cardiac Catherization – Nix or Allo) (17) randomized 599 cardiac catheterization patients to standard fasting (nothing by mouth after midnight with clear liquids up to 2 hours before the procedure) versus nonfasting (no restriction on oral intake). The primary composite outcome was a composite of CA-AKI, periprocedure hypotension, aspiration pneumonia, nausea/vomiting, hypoglycemia, and hyperglycemia and did not differ between groups (11.3% vs. 9.8%; P=0.65). The SCOFF trial is an investigator-initiated, multicenter, randomized trial in which patients will be randomized 1:1 to fasting (6 h solid food and 2 h clear liquids) or to no fasting. The primary outcome will be a composite of hypotension, hyperglycemia, hypoglycemia, and aspiration pneumonia. Secondary outcomes will include patient satisfaction, CA-AKI, new intensive care admission, new non-invasive or invasive ventilation requirement post-procedure, and 30-day mortality and readmission (18).

Further studies are needed to determine whether there are patient groups in which the risk of aspiration is higher and thus NPO times might need to be more stringent. Potential subgroups at higher risk would be patients with heart failure, obesity, arrhythmias or hemodynamic instability, patients undergoing femoral access who must remain on their back for longer periods of time, or patients with delayed gastric emptying times (e.g., diabetics). Another group of patients potentially at higher risk are those taking glucagon-like peptide-1 (GLP-1) receptor agonists, which can cause delayed gastric emptying and are associated with nausea and vomiting, and thus theoretically could increase the risk of aspiration. The ASA Task Force on Preoperative Fasting noted the lack of data and recommended that patients on daily dosing hold GLP-1 agonists on the day of the procedure and patients on weekly dosing hold GLP-1 agonists a week prior to the procedure/surgery (19).

While more RCTs are needed to determine the optimal length of fasting before coronary procedures, it is clear that clinical practice needs to evolve to keep pace with current risks. New technologies, and in particular, the development of nonionic contrast media, have made nausea and vomiting very rare in the cardiac catheterization laboratory (20). The persistence of prolonged fasting times is likely due to clinical inertia and is a relic of the tradition of making all procedural patients NPO at midnight. And while aspiration is now very rare and studies have not shown any benefits of prolonged fasting or substantive reduction in periprocedural complications, there is evidence of potential harms with prolonged fasting including increased insulin resistance, increased length of hospital stay, risk of delirium, and CA-AKI (16,21-23). Just as we have adopted new medications and treatments in the Cardiac Catheterization Laboratory, pre-cardiac catheterization fasting protocols must evolve for our patient’s benefit.

Acknowledgments

Funding: None.

Footnote

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