In this study, gastric ultrasound was employed to quantitatively and qualitatively evaluate gastric contents in two cohorts of spinal surgery patients who were administered varying doses of oral carbohydrates. Gastric emptying was observed, and a comparative analysis was conducted between the two patient groups on the protocol with respect to blood glucose levels, thirst and hunger sensations, anxiety levels, and length of stay. In this study, 100 patients undergoing spinal surgery were enrolled, and the experimental findings demonstrated that both group A and group B achieved fasting sinus levels within 120 minutes after consuming a carbohydrate beverage (i.e., prior to surgery), with no significant difference in emptying rate (P > 0.05). The risk of reflux aspiration was deemed low enough to permit routine anesthesia induction. When we compared postoperative hunger, thirst, anxiety, postoperative nausea and vomiting (PONV), and hospitalization duration between group A and group B, Group B was superior in postoperative hunger and thirst. The data obtained from this study can serve as a valuable foundation for optimizing the Enhanced Recovery After Surgery (ERAS) protocol.
The preferred method for assessing gastric emptying by many researchers is gastric ultrasound [36, 37]. Gastric ultrasound scans the changes in the cross-sectional area of the gastric antrum at various time points to determine gastric emptying [38]. In this study, the CSA after 120 minutes of carbohydrate intake (T4) was 3.36 ± 1.03 cm2 in group A and 3.64 ± 1.00 cm2 in group B, both of which closely resembled the CSA during fasting (Tm moment), indicating that oral administration of less than 400 ml of carbohydrate 2 h before surgery is safe. Previous studies have demonstrated that patients undergoing surgery under general anesthesia who consumed 400 ml of carbohydrates 2 h preoperatively and underwent gastric ultrasound examination at 120 min did not show an increased risk of aspiration[11, 18], which aligns with our findings. In a previous investigation involving cesarean section patients [36], the median CSA in right lateral recumbency during fasting was 4.35 cm2 (IQR 3.4–5.6), which was not different from the median CSA in right lateral recumbency at 120 min, 4.55 cm2 (IQR 3.8–6.5) (P > 0.05). Considering that pregnant individuals may be more susceptible to aspiration due to alterations in gastric physiology caused by an enlarged uterus and hormonal changes [39], these results further support our findings. In a study conducted by Jeong et al. [40], the gastric emptying of patients who underwent midnight fasting was compared to those who received preoperative oral carbohydrates. The ultrasonographic CSA at 120 minutes after oral carbohydrate intake was found to be 7.97 ± 3.62 cm2, similar to the CSA of patients who fasted at midnight during the same period. Furthermore, our findings align with previous studies in terms of the risk of regurgitation aspiration. Notably, this study observed larger CSA at 120 minutes after oral intake than other studies, suggesting a potential predisposing factor for delayed gastric emptying in elderly patients [41]. However, this aspect was not investigated within our study; therefore, further preoperative risk assessment should be conducted regarding drinking regimens in elderly patients.
Previous studies have demonstrated a linear correlation between GV and the cross-sectional area of the gastric sinus, enabling us to accurately calculate GV using cross-CSA, for a more precise assessment of aspiration risk [42]. In our study, both group A and group B exhibited a return to fasting state GV at 120 min, with similar speeds (P > 0.05). When we evaluated the aspiration risk in patients who had not emptied their stomachs, we found that the GV was less than 0.8 ml/kg, indicating a very low risk. These findings suggest that after oral administration of 400 ml and 200 ml carbohydrate solutions, the patients' GV essentially returned to predrinking levels within two hours. Another experimental study comparing maltodextrin with another carbohydrate solution in healthy adults demonstrated safe reduction of GV to fasting baseline levels for 2 hours, which suggests that anesthesia induction can be performed safely with a low risk of reflux and aspiration 2 h after oral carbohydrate intake [43]. Another study demonstrated that the GV measured in the immediate preoperative period was comparable between the 2-hour preoperative oral carbohydrate group and the fasting group, with no significant difference [44]. This further supports the feasibility of administering oral carbohydrates 2 hours before surgery. Song et al. investigated gastric emptying in children who consumed carbohydrates preoperatively and found no significant difference in GV between them and patients who fasted for 8 hours prior to surgery [37]. In a study utilizing gamma-photography, complete emptying of the stomach occurred at 90 minutes after consuming a drink containing 12.0% carbohydrates, administered 4 hours before surgery. The present study revealed that at 90 minutes postconsumption, both groups A and B had higher GV than the baseline fasting levels (P < 0.05), indicating an inappropriate state for anesthesia induction. These discrepancies may be attributed to differences in research equipment, formulation of the carbohydrate fluid, and the populations themselves [45]. Shin et al. [46] discovered a statistically significant difference in gastric capacity measured at 120 minutes between the first and second stages of total knee arthroplasty (TKA) in elderly patients, the latter stage showing greater capacity. This difference may be attributed to the presence of postoperative stress-induced inflammatory factors after the initial TKA, as well as chronic postoperative pain, which affects gastric emptying prior to the TKA. Considering that our study focused on a single operation and that spinal surgery-related stress and pain have less impact on gastric emptying than a second-stage surgery shortly after the similar first stage of TKA, our findings suggest that successful gastric emptying can be achieved at 120 minutes following preoperative consumption of 400 ml and 200 ml carbohydrates, indicating the safety and reliability of commencing surgery at this time point.
The rate of gastric emptying at each stage was determined based on the GV, and gastric emptying did not occur at a constant rate in either group. Interestingly, in group A, gastric emptying reached its top speed between the initiation of oral intake and 30 minutes, whereas in group B the peak rate was between 30 and 60 minutes after oral intake. These findings suggest that carbohydrate emptying does not solely follow a pattern of initial rapid and subsequent slow rates. Nygren et al. [45] conducted a comparative study on the rate of gastric emptying for water and carbohydrates, revealing that within the first 60 minutes after consuming 400 ml of liquid, water emptied from the stomach at a faster rate than carbohydrates; however, both groups reached similar levels of emptying after 90 minutes. This phenomenon can be attributed to various factors related to the nature of the liquid, including dosage and state. It has also been suggested that peak gastric emptying occurs within 30 minutes following oral intake of liquids, followed by a decrease in rate. This observation can be explained by the rapid passage through the gastric curvature facilitated by physiological structures upon initial entry into the stomach [47]. In this study, the rate of gastric emptying in group A was significantly higher than that in group B in the first 30 min after oral administration of carbohydrates, while from 30–120 min, gastric emptying in group B was faster (P < 0.05), indicating that a carbohydrate volume of 400 ml outperformed a volume of 200 ml in terms of the overall gastric emptying rate. Wong et al. [48] assessed the impact on gastric emptying when patients were orally administered either 300 ml or 50 ml of water and found that the former not only did not delay gastric emptying but also resulted in a significantly shorter half-time for gastric emptying compared to the latter. The rate of gastric emptying is influenced by both the quantity of food intake and the energy content of liquids, a larger volume and higher energy of liquids exerting a greater impact on the work rate of the duodenum and the speed of gastric emptying compared to smaller volumes of liquids [49, 50].
Achieving optimal gastric emptying while meeting energy requirements is a crucial aspect of ERAS, and the rate of gastric emptying is influenced by the preoperative number of individuals with delayed gastric emptying. The gastric emptying number ratio reflects the final preoperative gastric emptying number of patients. In this study, patients in groups A and B exhibited gastric emptying rates of 92% and 88%, respectively. Importantly, nonemptying patients did not demonstrate a high risk of reflux aspiration, highlighting the efficacy of preoperative carbohydrate utilization in ERAS. Garg et al. [51] discussed gastric emptying in children after 8 ml/kg of pure fruit juice and 8 h of fasting before the operation. Significant gastric emptying was observed 120 min after taking pure fruit juice, to an even more complete level than that after 8 h of fasting. This suggested that carbohydrates can promote gastric emptying, 71.8% of their patients achieving complete gastric emptying. Although some patients did not achieve complete emptying, their associated risks remained below the threshold. Carbohydrates do not significantly affect gastric emptying, and the change in total liquid volume consumed (less than 400 ml) does not have significantly affect the gastric emptying rate. This effect may be attributed to the faster emptying rate observed with larger liquid doses, as mentioned earlier. Therefore, considering the absence of significant differences in gastric emptying rates between the two groups, a 400 ml carbohydrate drink (as in group B) would provide enough energy and ensure safe anesthesia induction.
Prolonged preoperative water fasting may result in dehydration, hypoglycemia, and reduced insulin sensitivity in patients. The intake of preoperative carbohydrates has been shown to decrease the occurrence of complications [52, 53]. It is crucial to control perioperative blood glucose levels, as traditional water fasting can lead to postoperative hypoglycemia, causing symptoms such as malaise and syncope that can impede patient recovery. Furthermore, both fasting and surgical stress responses can promote muscle catabolism and trigger the release of stress hormones, leading to insulin resistance and hyperglycemia [54, 55]. This was also observed by Rajan et al. [56]: patients who did not receive carbohydrates exhibited higher intraoperative glucose values than those who received carbohydrates two hours before surgery. Elevated glucose is detrimental to wound healing and increases the risk of wound infection, particularly in major surgeries [57]. Preoperative oral carbohydrate intake aims to minimize fluctuations in blood glucose levels, enhance postoperative hypoglycemia management, and reduce glycemic variability and insulin resistance, potentially shortening hospital stays [55, 58, 59]. However, it has been suggested that the association between preoperative carbohydrate loading and insulin resistance may only be significant if high doses of carbohydrates are administered [60], or they may have no effect at all [61]. In this study, we compared fasting and postsurgery blood glucose concentrations between groups at the same time points. The observed changes were not statistically significant, indicating minimal differences in the impact of orally administered carbohydrates with varying doses on patients' blood glucose levels. The blood glucose concentration after surgery was significantly higher than the fasting level in both groups, but it remained within the safe range. Therefore, preoperative carbohydrate loading effectively stabilizes postoperative blood glucose levels and reduces the incidence of postoperative hypoglycemia, thus promoting recovery. Diabetic patients were excluded from this study due to their special dietary requirements and the potential presence of gastroparesis [62]. Further studies are needed to investigate whether diabetic patients can benefit from preoperative carbohydrate intake.
In recent years, many scholars have reached a consensus that preoperative carbohydrate intake can ease patients' subjective discomfort and reduce the incidence of thirst, hunger, anxiety, and fatigue compared to fasting [63, 64]. In this study, we observed postoperative complications in both groups after administering varying doses of carbohydrates to patients undergoing spinal surgery. In the comparison of hunger and thirst scores in this study, we found that group A had less discomfort caused by hunger and thirst than group B, though the two groups had no significant difference in anxiety scores. Previous studies have suggested that preoperative administration of carbohydrates reduces anxiety scores [65] due to their ability to raise the serotonin concentration within the body [66]. In addition to the properties of the liquid, anxiety may also be influenced by individual differences within the population, surgical procedure type and duration, and factors such as preoperative drug administration. In this study, the two groups had similar anxiety scores, but consuming carbohydrates 2 hours before surgery significantly reduced patient anxiety when compared to traditional water fasting. Importantly, we did not conduct a controlled experiment with patients on traditional water fasting this time but only compared patients who consumed different doses of carbohydrates 2 hours before surgery because many studies have demonstrated the advantages of shortening the water fast in reducing postoperative complications. Preoperative carbohydrate intake has reduced the incidence of nausea and vomiting after several elective surgeries [67, 68], which may be explained by the improvement of gastric emptying and the reduction of stress response. For the particular surgical position of spine surgery, this may increase the risk of postoperative nausea and vomiting. In our study, there was no significant difference in the incidence of nausea and vomiting between the 400 ml and 200 ml groups, and both groups showed a lower incidence than seen under traditional water fasting. Additionally, preoperative consumption of carbohydrates has been associated with shorter hospital stays, which strongly correlate with patients' subjective well-being and may advance the time to discharge when the patient's postoperative recovery improves, such as through a reduction in insulin resistance and surgical stress and stabilization of glucose metabolism and gastrointestinal function [69, 70]. Before major invasive surgery, such as orthopedic surgery, intake of carbohydrates also reduces postoperative protein loss and enhances muscle strength and weight recovery [71]. Consistent with these findings, our results demonstrated no significant difference in hospitalization duration between the two groups, indicating that both interventions can be incorporated into an ERAS protocol, promoting functional recovery and shortening hospital stays. Carbohydrate loading in both groups improved the incidence of postoperative complications and alleviated discomfort, ultimately facilitating patients' postoperative recovery. These outcomes provide a solid foundation for implementing the ERAS program. Our findings suggest that 400 ml of carbohydrates can be a better way to reduce the patients' postoperative thirst and hunger, and it performed better at promoting postoperative recovery.