Preoperative fasting and the risk of pulmonary aspiration-a narrative review of historical concepts, physiological effects, and new perspectives

In the early days of anaesthesia, the fasting period for liquids was kept short. By the mid-20th century 'nil by mouth after midnight' had become routine as the principles of the management of 'full stomach' emergencies were extended to include elective healthy patients. Back then, no distinction was made between the withholding of liquids and solids. Towards the end of the last century, recommendations of professional anaesthesiology bodies began to reduce the fasting time of clear liquids to 2 h. This reduction in fasting time was based on the understanding that gastric emptying of clear liquids is rapid, exponential, and proportional to the current filling state of the stomach. Furthermore, there was no evidence of a link between drinking clear liquids and the risk of aspiration. Indeed, most instances of aspiration are caused by failure to identify aspiration risk factors and adjust the anaesthetic technique accordingly. In contrast, long periods of liquid withdrawal cause discomfort and may also lead to serious postoperative complications. Despite this, more than two decades after the introduction of the 2 h limit, patients still fast for a median of up to 12 h before anaesthesia, mainly because of organisational issues. Therefore, some hospitals have decided to allow patients to drink clear liquids within 2 h of induction of anaesthesia. Well-designed clinical trials should investigate whether these concepts are safe in patients scheduled for anaesthesia or procedural sedation, focusing on both aspiration risk and complications of prolonged fasting.

A physiologically-based digital twin for alcohol consumption-predicting real-life drinking responses and long-term plasma PEth

Alcohol consumption is associated with a wide variety of preventable health complications and is a major risk factor for all-cause mortality in the age group 15-47 years. To reduce dangerous drinking behavior, eHealth applications have shown promise. A particularly interesting potential lies in the combination of eHealth apps with mathematical models. However, existing mathematical models do not consider real-life situations, such as combined intake of meals and beverages, and do not connect drinking to clinical markers, such as phosphatidylethanol (PEth). Herein, we present such a model which can simulate real-life situations and connect drinking to long-term markers. The new model can accurately describe both estimation data according to a χ2 -test (187.0 < Tχ2 = 226.4) and independent validation data (70.8 < Tχ2 = 93.5). The model can also be personalized using anthropometric data from a specific individual and can thus be used as a physiologically-based digital twin. This twin is also able to connect short-term consumption of alcohol to the long-term dynamics of PEth levels in the blood, a clinical biomarker of alcohol consumption. Here we illustrate how connecting short-term consumption to long-term markers allows for a new way to determine patient alcohol consumption from measured PEth levels. An additional use case of the twin could include the combined evaluation of patient-reported AUDIT forms and measured PEth levels. Finally, we integrated the new model into an eHealth application, which could help guide individual users or clinicians to help reduce dangerous drinking.

Preoperative Snack Prescription: A Single-Centre Experience in Optimising Preoperative Fasting Time and Enhancing Guideline Adherence

Objectives Preoperative fasting plays a pivotal role in adequately preparing patients for anaesthesia and surgical procedures. However, it is imperative to consider not only the medical aspects but also patients' overall comfort, as this can significantly contribute to improved surgical outcome. The primary objective of this quality improvement project (QIP) is to provide healthcare professionals, including anaesthetists, surgeons, nurses, and stakeholders with information regarding insights required to embrace the concept of preoperative snack prescription as a strategy for enhancing patient-centred care. Methods This QIP was conducted in the vascular surgery department of a district general hospital in Wales, United Kingdom. A prospective analysis was conducted in two cycles, i.e., the pre-intervention group (PrIG) and post-intervention group (PoIG), with preoperative snacks such as biscuits, chips, or cakes, being prescribed to the PoIG. A total of 40 patients who met the inclusion criteria were enrolled in this study, with 20 patients participating in each cycle. The timing of preoperative meals, i.e., the closest preoperative breakfast, lunch, or dinner, preoperative snacks (for the PoIG), anaesthesia commencement, and surgical commencement were collected. Data analysis was performed using IBM SPSS Statistics for Windows, Version 26.0 (Released 2019; IBM Corp., Armonk, New York, United States), in conjunction with Microsoft Excel (Microsoft Corporation, Redmond, Washington, United States). Results In our QIP, the PrIG and PoIG comprised 40% (8 out of 20) and 35% (7 out of 20) female patients, respectively, with mean ages of 74 years (range, 61-86 years) and 61.3 years (range, 36-81 years). Within the PrIG, the mean duration from the preoperative meal to anaesthesia and surgery commencement was 17.8 hours (range, 14.6-22.5 hours) and 18.5 hours (range, 16.0-23.3 hours), respectively. In the PoIG, following the initiation of preoperative snack prescription, the mean time intervals between preoperative snack prescription and anaesthesia and surgery commencement were 10.9 hours (range, 6.5-16.0 hours) and 12.0 hours (range, 7.5-16.5 hours), respectively. Conclusions In summary, our QIP has successfully integrated preoperative snack prescription into the local hospital's preoperative care policy, prioritising the balance between patient safety and comfort. Based on our single-centre experience, we observed a significant reduction in the time interval between preoperative fasting and the initiation of anaesthesia, decreasing from 18.3 hours to 10.9 hours post-implementation of preoperative snacks. This QIP holds relevance for healthcare professionals as it underscores the benefits of shorter fasting periods, which contribute to heightened patient satisfaction and comfort.

Comparison of Gastric Emptying Time after the Ingestion of Whisky with Isocalorically Adjusted Glucose Solution

Previous studies have shown that the liquid gastric emptying mainly depended on energy content, regardless of compositional differences. But the gastric emptying of alcoholic beverages remains unclear. Therefore, we performed the present study to compare gastric emptying times between whisky mixed with water and glucose solution with uniform energy contents and volumes. As a crossover study, 10 healthy male volunteers ingested one of 3 test solutions with a uniform volume of 150 ml, i.e., whisky with water-containing whisky 30 ml (67 kcal), sugar water containing glucose 16.8 g (67 kcal), and water (0 kcal), and the gastric emptying time of each beverage was then assessed by ultrasound measurements of the gastric antral cross-sectional area. The gastric emptying pattern of whisky with water was faster than that of isocaloric sugar water, but slower than that of water. Each antral cross-sectional area 20, 30, and 40 min after the ingestion of sugar water was significantly larger than that of whisky with water. Antral cross-sectional areas 10 and 20 min after the ingestion of water were significantly smaller than those of whisky with water. In conclusion, the gastric emptying time of whisky would be faster than that of isocaloric glucose solution and slower than that of water. Unlike the other beverages, the gastric emptying time of alcohol drinks does not purely depend on the energy content because alcohol itself has no calorie before absorption. This study is registered with the University Hospital Medical Information Network (UMIN) Clinical Trials Registry (UMIN000034443).

Application of In Vivo Imaging Techniques and Diagnostic Tools in Oral Drug Delivery Research

Drug absorption following oral administration is determined by complex and dynamic interactions between gastrointestinal (GI) physiology, the drug, and its formulation. Since many of these interactions are not fully understood, the COST action on “Understanding Gastrointestinal Absorption-related Processes (UNGAP)” was initiated in 2017, with the aim to improve the current comprehension of intestinal drug absorption and foster future developments in this field. In this regard, in vivo techniques used for the characterization of human GI physiology and the intraluminal behavior of orally administered dosage forms in the GI tract are fundamental to gaining deeper mechanistic understanding of the interplay between human GI physiology and drug product performance. In this review, the potential applications, advantages, and limitations of the most important in vivo techniques relevant to oral biopharmaceutics are presented from the perspectives of different research fields.

Pregnancy and Labor Epidural Effects on Gastric Emptying: A Prospective Comparative Study

BACKGROUND

The lack of reliable data on gastric emptying of solid food during labor has led to some discrepancies between current guidelines regarding fasting for solid food in the parturient. This prospective comparative study aimed to test the hypothesis that the gastric emptying rate of a light meal would be reduced in parturients receiving epidural analgesia and with no labor analgesia compared with nonpregnant and pregnant women.

METHODS

Ten subjects were enrolled and tested in each group: nonpregnant women, term pregnant women, parturients with no labor analgesia, and parturients with epidural labor analgesia. After a first ultrasound examination was performed to ensure an empty stomach, each subject ingested a light meal (125 g yogurt; 120 kcal) within 5 min. Then ultrasound measurements of the antral area were performed at 15, 60, 90, and 120 min. The rate of gastric emptying at 90 min was calculated as [(antral area90 min / antral area15 min) - 1] × 100, and half-time to gastric emptying was also determined. For the Parturient-Epidural group, the test meal was ingested within the first hour after the induction of epidural analgesia.

RESULTS

The median (interquartile range) rate of gastric emptying at 90 min was 52% (46 to 61), 45% (31 to 56), 7% (5 to 10), and 31% (17 to 39) for nonpregnant women, pregnant women, parturients without labor analgesia, and parturients with labor epidural analgesia, respectively (P < 0.0001). The rate of gastric emptying at 90 min was statistically significant and lower in the Parturient-Epidural group than in the Nonpregnant and Pregnant Control groups. In addition, the rate of gastric emptying at 90 min was statistically significant and lower in the Parturient-No-Epidural group than in the Parturient-Epidural group.

CONCLUSIONS

Gastric emptying in parturients after a light meal was delayed, and labor epidural analgesia seems not to worsen but facilitates gastric emptying. This should be taken into consideration when allowing women in labor to consume a light meal.

EDITOR’S PERSPECTIVE

Ultrasound imaging for assessing functions of the GI tract

OBJECTIVE

In the following review we outline how ultrasound can be used to measure physiological processes in the gastrointestinal tract.

APPROACH

We have investigated the potential of ultrasound in assessing gastrointestinal physiology including original research regarding both basic methodology and clinical applications.

MAIN RESULTS

Our main findings show the use of ultrasound to study esophageal motility, measure volume and contractility of the stomach, assess motility, wall thickness, and perfusion of the small bowel, and evaluate wall vascularization and diameters of the large bowel.

SIGNIFICANCE

Ultrasound is a widely accessible technology that can be used for both scientific and clinical purposes. Being radiation-free and user friendly, the examination can be frequently repeated enabling longitudinal studies. Furthermore, it does not influence normal GI physiology, thus being useful to estimate motility and subtle changes in physiology. Accordingly, ultrasound scanning and physiological measurements may make a big difference for the scientist and the doctor; and for the patients who receive an efficient work-up.

Evaluation of Gastric Emptying Time of a Rice-Based Meal Using Serial Sonography

The aim of this prospective study was to evaluate the gastric emptying time of a rice-based meal by serial ultrasonography of the stomach. After baseline ultrasonographic assessment of ten fasted healthy volunteers, volunteers ingested standardized 420 g, 536 kcal rice-based meal (bibimbap), and serial evaluations were performed every hour until the stomach became empty. At baseline, all the participants had an empty stomach. The average time of complete gastric emptying of the rice-based meal was 5.8 ± 0.8 h (95% confidence interval (CI), 5.0 h to 6.5 h). Since the first postintake cross-sectional area (CSA) measurement, a decrease was observed, and CSA was maintained until postprandial 3–4 h (P > 0.05). It declined rapidly 4 h after meal intake (P=0.031), reaching the nadir at approximately 6 h after meal intake. The gastric CSA and hunger score showed a positive correlation (correlation r = 0.616, P < 0). The rice-based meal is emptied after 5.8 ± 0.8 h on average in healthy volunteers. Based on our results, 6.5 h (upper limit of CI) of fasting after the ingestion of a rice-based meal would be a safe preoperative fasting time, and this is in accordance with the current guidelines for preoperative fasting.

Technical position on milk and its derivatives in adult health and disease from the Asociación Mexicana de Gastroenterología and the Asociación Mexicana de Gerontología y Geriatría

Milk is a liquid food that possesses an important quantity of highly bioavailable macronutrients. In addition, it is readily accessible, as well as relatively inexpensive. Given that the knowledge of physicians about nutrition and food composition is deficient, in general, many of the dietary interventions recommended in diverse clinical settings lack a scientific basis. The aim of the present review was to produce a technical opinion that serves as a frame of reference to best sustain recommendations for consuming milk and dairy products as daily nutrition in the adult and older adult. The effects of milk and dairy products during the pediatric stage are not addressed in the present work. The Asociación Mexicana de Gastroenterología and the Asociación Mexicana de Gerontología y Geriatría jointly discussed and analyzed topics dealing with the legal designation of milk, the classification and nutritional profile of cow's milk, its nutritional characteristics, its consumption in the adult, intolerance to cow's milk, and associations of milk consumption with digestive tract alterations and other conditions. Finally, certain aspects of milk consumption in the older adult and its relation to overall health are briefly discussed.

Radiologic assessment of gastric emptying of water-soluble contrast media: New data security from a longitudinal study

BACKGROUND AND OBJECTIVES

Practice guidelines for preoperative fasting have not clearly established the fasting time needed after oral administration of water-soluble contrast media. The aim of this study was to determine the time required for the gastric emptying during the water-soluble contrast media in patients with acute abdominal pain.

METHODS

This prospective longitudinal study included sixty-eight patients older than 18 years of age with acute abdominal pain, who required a water-soluble contrast media enhanced abdominal computed tomography study. Plain radiographs were obtained hourly until complete the gastric emptying. Patients with probable bowel obstruction were not included in the study.

RESULTS

A total of 31 (45,6%), 54 (79,4%), and 64 (94,1%) patients achieved a complete gastric clearance of barium in 1, 2 and 3 hours, respectively. All patients achieved complete emptying of water-soluble contrast media within 6 hours. Gastric emptying time was not associated with gender (P=0,44), body mass index (P=.35), fasting time prior to water-soluble contrast media intake (P=0,12), administration of opioids in the emergency room (P=0,7), and the presence of comorbidities (P=0,36).

CONCLUSION

Ninety-four percent of the patients with acute abdominal pain achieved complete gastric emptying within 3hours after the administration of water-soluble contrast media. All of them achieved complete gastric emptying within 6hours. The results suggested 6hours after oral intake of the contrast media is enough to complete transit of water-soluble contrast media through the stomach and avoid unnecessary risks.

Indirect vs direct assessment of gastric emptying: A randomized crossover trial comparing C-isotope breath analysis and MRI

BACKGROUND

Indirect methods to assess gastric emptying (GE), such as ¹³ C breath tests (BT), are commonly used. However, BT usually use a sampling time of 4+ hours. The current study aims to assess the validity of BT for four liquid meals differing in physicochemical properties. To this aim, we compared them to MRI GE-measurements.

METHODS

Fifteen healthy males (age 22.6 ± 2.4 years, BMI 22.6 ± 1.8 kg/m² ) participated in a randomized 2 × 2 crossover experiment. Test foods were liquid meals, which were either thin/thick and 100/500 kcal, labeled with 100 mg of ¹³ C-octanoate. GE was measured with MRI and assessed by ¹³ C recovery from breath. Participants were scanned every 10 minutes and at six time points breath samples were collected up to t = 90 minutes. Two curves were fitted to the data to estimate emptying halftime (t_{50 Ghoos} and t_{50 Bluck} ). T₅₀ times were ranked per participant and compared between methods.

KEY RESULTS

On average, MRI and BT showed similar t₅₀ rankings for the four liquid meals. In comparison to MRI, t_{50 Ghoos} overestimated, while t_{50 Bluck} underestimated GE time_. Moreover, more viscous foods were overestimated. In most participants individual t₅₀ time rankings differed significantly between methods.

CONCLUSIONS & INFERENCES

BT can assess relative emptying differences on group level and collecting breath data for 90 minutes constitutes a lower burden for participants and the research facility. However, BT has severe shortcomings compared to MRI for individual GE assessment. Notably, food matrix effects should be considered when interpreting the results of BT.

Practice Guidelines for Preoperative Fasting and the Use of Pharmacologic Agents to Reduce the Risk of Pulmonary Aspiration: Application to Healthy Patients Undergoing Elective Procedures

Supplemental Digital Content is available in the text.

[Use of ultrasound for gastric volume evaluation after ingestion of different volumes of isotonic solution]

BACKGROUND AND OBJECTIVES

The current preoperative fasting guidelines allow fluid intake up to 2hours before surgery. The aim of this study was to evaluate the gastric volume of volunteers after an overnight fast and compare it with the gastric volume 2hours after ingestion of 200 and 500mL of isotonic solution, by means of ultrasound assessment.

METHOD

Eighty volunteers underwent gastric ultrasound at three times: after 8hours of fasting; 2hours after ingestion of 200mL isotonic saline, followed by the first scan; and on another day, 2hours after ingestion of 500mL of the same solution after an overnight fast. The evaluation was quantitative (antrum area and gastric volume, and the ratio of participants' gastric volume/weight) and qualitative (absence or presence of gastric contents on right lateral decubitus and supine positions. A p-value<0.05 was considered significant).

RESULTS

There was no difference in quantitative variables at measurement times (p>0.05). Five volunteers (6.25%) had a volume/weight over 1.5mL.kg^-1 at fasting and 2hours after ingestion of 200mL and 6 (7.5%) after 500mL. Qualitatively, the presence of gastric fluid occurred in more volunteers after fluid ingestion, especially 500mL (18.7%), although not statistically significant.

CONCLUSION

Ultrasound assessment of gastric volume showed no significant difference, both qualitative and quantitative, 2h after ingestion of 200mL or 500mL of isotonic solution compared to fasting, although gastric fluid content has been identified in more volunteers, especially after ingestion of 500mL isotonic solution.

What is the manner of gastric emptying after ingestion of liquids with differences in the volume under uniform glucose-based energy content?

BACKGROUND & AIMS

We previously demonstrated that the gastric emptying rate of liquids chiefly depended on the total amount of calories (energy content) in a uniform volume. The aim of the present study was to examine the effects of different volumes of liquids with a uniform energy content on gastric emptying.

METHODS

Three types of test solutions were prepared with a uniform amount of calories (200 kcal provided by glucose) and step-wise increments in volume (200 ml, 400 ml, and 600 ml). The gastric volume of each solution was determined by ultrasound measurements of the gastric antral cross-sectional area after their ingestion by 8 healthy volunteers.

RESULTS

The mean gastric volume decreased exponentially to nearly 0 ml 70 min after ingestion in the 200 ml group, 90 min in the 400 ml group, and 100 min in the 600 ml group. Each gastric emptying curve converged with identical slopes on the graph when the points at which the gastric emptying curves of the 200 ml and 400 ml groups reached the zero point on the Y-axis (mean gastric volume) were shifted toward 110 min on the X-axis (time scale).

CONCLUSIONS

The volume of liquid ingested with a uniform glucose-based energy content is a critical determinant of liquid gastric emptying. The gastric emptying time may be predicted following the ingestion of an isocaloric liquid with any volume over a predefined range once a gastric emptying curve following the ingestion of a liquid has been plotted on a graph.

TRIAL REGISTRY NUMBER

UMIN000014930.