The safety and effect of preoperative reduced fasting time by oral clear liquid administration in adult surgery patients: a randomized controlled trial

Abstract

Purpose

Traditionally, 6–8 hours of fasting has been recommended before surgery to prevent respiratory complications. However, recent evidence suggests that intake of clear fluids up to 2 hours before general anesthesia may be safe. This study aimed to evaluate the safety and efficacy of reduced fasting time with clear liquid intake in surgical patients under general anesthesia.

Methods

In this randomized controlled trial, 60 adult patients undergoing elective endoscopic total extraperitoneal plasty under general anesthesia were divided into two groups (n = 30 each). The control group fasted overnight (nothing per oral), while the liquid group was allowed clear fluids until 2 hours before surgery. Gastric content volume and pH were measured after intubation. Thirst and hunger levels were assessed pre- and postoperatively using a visual analogue scale. Postoperative hoarseness, nausea, vomiting, and oxygen saturation were monitored in the recovery room.

Results

The liquid group consumed an average of 520 mL of fluid. No serious respiratory complications were observed in either group. Pre- and postoperative thirst and hunger scores were significantly lower in the liquid group (P < 0.001). Gastric content volume and acidity showed no significant differences between groups, with most patients having negligible volumes (<1 mL).

Conclusion

Permitting clear liquid intake up to 2 hours before general anesthesia is safe and does not increase the risk of respiratory complications. It effectively reduces thirst and hunger, improving patient comfort without compromising safety.

INTRODUCTION

Perioperative pulmonary aspiration and aspiration-induced pneumonitis due to regurgitation of gastric content have been a concern of surgeons and anesthesiologists, as they can result in adverse conditions such as permanent lung injuries or death [1]. Among the factors related to aspiration risks, preoperative fasting time has been thought to be essential, because the volume and acidity of the gastric content, which is closely related to the fasting time, is the main risk factor of pulmonary aspiration [2].

Conventionally, more than 6–8 hours of preoperative nothing per oral (NPO) for gastric emptying had been regarded as the best method to reduce respiratory aspiration of gastric contents. However, several studies have shown that oral intake of water and other clear liquids up to 2 hours before induction of anesthesia does not increase the gastric residual contents or acidity. One of the studies reported that preoperative water intake resulted in a significant decrease in gastric contents compared to patients who followed a standard midnight fasting regimen after surgery [3,4].

Another problem of preoperative long-time fasting is the significant inconvenience that patients experience, including nausea and vomiting, which can result in negative psychological effects. Recent studies show that patients who took fluid until 2 hours before general anesthesia had less nausea or vomiting. Therefore, minimizing the fasting time can attenuate perioperative discomfort and postoperative negative physiologic change [5,6,7].

Before the result of pioneering research is to be accepted and applied broadly, studies should be repeated to prove reproducibility and safety in that population. In Korea, in which almost all surgery cases take the conventional overnight preoperative fasting time as the standard, more randomized controlled trials are needed to keep in line with this research trend attempting to reduce preoperative fasting time.

This study aims to validate the safety and efficacy in terms of satisfaction of the carbohydrate-rich solution to Korean patients, thus providing a global trend to shorten the fasting time in Korea.

METHODS

Ethics statement

This study was approved by the Institutional Review Board of the Jeju National University Hospital in Jeju, Korea (No. JNUH-2021-09-004). All patients were informed, and they agreed to the purpose and procedures of this study at the last visit to the outpatient clinic before the operation.

Study design and participants

It is an open label randomized controlled study of 60 patients who underwent endoscopic total extraperitoneal plasty (TEP). Of these 60 patients, 30 patients used the conventional overnight preoperative fasting time as a control group, and the other 30 patients took fluid until 2 hours before general anesthesia as a treatment group.

All patients who attended this study were older than 18 years, had a unilateral or bilateral hernia, and were scheduled for elective surgery under general anesthesia. Patients who had high body mass index (BMI, ≥35 kg/m²) were excluded. Also, patients with underlying diabetes mellitus were excluded from this study due to possible concerns of delayed gastric emptying. Every patient was admitted a day before the operation and discharged postoperative day 1. Patients with underlying respiratory disease or American Society of Anesthesiologists physical status classes III and IV were excluded from this study. The type of surgery performed on both groups was endoscopic TEP. This study was conducted from April 2022 to October 2022 at Jeju National University Hospital, Korea.

Among the patients with unilateral or bilateral inguinal hernias in the clinic, those who agreed and met the criteria of our study were registered. Once the registered patients were admitted the day before the operation, they were randomized by the medical research coordinator in Jeju National University Hospital using the block randomization method with sealed envelopes, and a carbohydrate-rich solution (12.6 g/100 mL carbohydrates, 50 kcal/100 mL, 260 mOsm; no-NPO; Daesang Wellife) was provided to the patients of treatment group. The treatment group patients were allowed to drink it from midnight to 2 hours before surgery without limitation of amount. The feelings of thirst and hunger were measured right before the patients went to the operating room and in the recovery room after surgery by using the visual analogue scale (VAS) which had scales from 0 to 10. Every postoperative patient in the recovery room was evaluated by the Aldrete score, 9–10/10 was required to move to the general ward. In our study, patients were interviewed after meeting the criteria of ward out. All studied patients were 2/2 of state of consciousness.

All surgical procedures were performed under general anesthesia and a nasogastric tube was inserted after intubation. After the injection of anesthesia and muscle relaxant, one of our study members assisted the anesthesiologist during intubation to cope with the possible risk of gastric-content regurgitation by holding a suction device. Once the intubation was complete, a team member inserted the nasogastric tube and aspirated all gastric contents through the nasogastric tube, to the greatest extent. After aspiration, the volume and acidity were measured by a pH measuring device (pHTestr, ThermoFisher Scientific) after the surgical procedure, just after intubation. In the recovery room postoperatively, 5 different variables were evaluated: thirst, hunger, hoarseness of voice, nausea, and vomiting. Also, patients were observed as to whether they had any acute respiratory symptoms such as vigorous cough or dyspnea, or desaturation.

Statistical analyses

As a basis for the calculation, 2-tails, effect size large (d = 0.8), power of 0.8, and α-error of 0.05 were used to determine a sample size of the 2 independent groups using the Cohen method, and 26 patients were set in both groups, and 3.9 patients were added with an expected dropout rate of 15%; a total of 30 patients (29.9) were finally put in both groups.

Statistical evaluation between the 2 groups was performed using the Mann-Whitney U-test. The Wilcoxon rank-sum test was used to compare the difference between the 2 groups. In all statistical analyses, the level of significance adopted was 5% (P < 0.05).

RESULTS

The ingredients of the oral carbohydrate-rich solution which was used in this study are shown (Table 1). The mean age was not different in the control group and treatment group (58.9 ± 15.9 years and 59.7 ± 15.6 years, P = 0.894). In both groups, there were 28 male patients and 2 female patients. The BMI did not show a significant difference in these 2 groups (control, 24.4 ± 3.55 kg/m² vs. treatment, 24.3 ± 2.92 kg/m²; P = 0.905). Hospital stay was the same at 3 days in all 60 studied patients. There were no significant complications or unexpected events among all patients during the hospital stay. The operation time was not different in both groups (control, 38.1 ± 12.7 minutes vs. treatment, 39.8 ± 11.1 minutes; P = 0.583). The fasting time was significantly different; 746 ± 137 minutes in the control group and 238 ± 103 minutes in the treatment group (P < 0.001). The average solution volume that the treatment group patients were administered until 2 hours before general anesthesia was 520 mL (± 255 mL) (Table 2).

Table 1. Ingredient of the oral carbohydrate-rich solution.

The solution was provided for the treatment group up to 2 hours before induction of general anesthesia.

Table 2. Patients' characteristics.

Values are presented as number only, mean ± standard deviation, or number (ratio).

BMI, body mass index.

There were no significant differences in characteristics between the 2 groups, except the preoperative fasting time. The average solution volume that the treatment group patients administered was 520 mL.

Preoperative thirst was significantly lower in the treatment group (VAS score: control, 3.97 ± 2.03 vs. treatment, 1.47 ± 2.10; P < 0.001), and preoperative hunger also showed a statistically significant difference, which was lower in the treatment group (control, 3.23 ± 2.18 vs. treatment, 1.41 ± 1.72; P < 0.001). Postoperative thirst was lower in the treatment group (control, 4.50 ± 2.13 vs. treatment, 2.37 ± 1.92; P < 0.001). Postoperative hunger showed the tendency to be lower in the treatment group, but it was not statistically different (control, 1.53 ± 2.42 vs. treatment, 1.30 ± 1.92; P = 0.078) (Fig. 1).

Fig. 1. Comparison of visual analogue scale (VAS) scores for thirst and hunger before and after surgery. Thirst shows significantly lower in the treatment group preoperatively (3.97 ± 2.03 vs. 1.47 ± 2.10, P < 0.001) and postoperatively (4.50 ± 2.13 vs. 2.37 ± 1.92, P < 0.001). Hunger shows significantly lower in the treatment group preoperatively (3.23 ± 2.18 vs. 1.41 ± 1.72, P < 0.001) and tendency to be lower postoperatively (1.53 ± 2.42 vs. 0.63 ± 1.30, P = 0.078). ^*P < 0.05.

The volume of gastric contents was only measurable for 4 patients in the control group and 2 patients in the treatment group. The measured volumes were not significantly different between the groups (control, 13.1 ± 9.80 mL vs. treatment, 16.5 ± 4.95 mL; P = 0.682). It was less than 1 mL in all other patients of both groups. Acidity was not significantly different (control, 3.52 ± 1.09 and treatment, 5.25 ± 2.99; P = 0.322) (Fig. 2).

Fig. 2. Intraoperative findings of gastric contents and acidity which were measured by aspiration through the nasogastric tube immediately after intubation. The volume of gastric contents was only measurable for 4 patients in the control group and 2 patients in the treatment group, not showing differences between the 2 groups (13.1 ± 9.80 mL vs. 16.5 ± 4.95 mL, P = 0.682). The volume of gastric contents was less than 1 mL in all other patients of both groups. The acidity of gastric contents was also not significantly different (3.52 ± 1.09 and 5.25 ± 2.99, P = 0.322).

Postoperative hoarseness was observed in no patient in the control group and 1 patient in the treatment group, which was fully recovered before discharge. One patient in the control group and 2 patients in the treatment group complained of mild nausea, but no one had vomiting in both groups. Oxygen saturation which was measured in the recovery room postoperatively did not show a difference in both groups (control, 99.9 ± 0.365% vs. treatment, 99.9 ± 0.548%; P = 0.782). None of the patients in both groups had acute serious pulmonary complications such as desaturation or dyspnea during the entire postoperative period (Table 3).

Table 3. Postoperative patients' signs.

Values are presented as number only or mean ± standard deviation.

SpO₂, peripheral capillary oxygen saturation.

The 2 groups had no significant differences in the signs that were measured in the recovery room postoperatively.

DISCUSSION

Pulmonary aspiration and aspiration-induced pneumonitis is one of the serious complications in surgery under general anesthesia and, traditionally, preoperative fasting has been regarded as the safest method to prevent the risk of aspiration of stomach contents during anesthesia. Six to 8 hours of fasting is generally accepted to achieve the prevention of aspiration [8].

However, recent studies have reported that a long duration of fasting before surgery causes a significant inconvenience to patients, and intake of water or other clear fluid up to 2 hours before induction of anesthesia does not increase aspirated pulmonary complications induced by regurgitation of gastric contents [2,9]. Physiologically, T1/2 of normal gastric emptying of solid food is more than 2 hours. In contrast, it is less than 1 hour in clear liquid [10,11]. Under this physiologic difference in gastric emptying time for solid and liquid, some groups have reported that the oral intake of clear liquids up to 2 hours before induction of anesthesia does not increase the gastric residual contents to cause aspiration [7]. Brady et al. [5] showed no difference in intraoperative gastric volume between the unlimited volume of clear fluid and the fasted group. Our study showed similar results objectively by measuring the amount of gastric contents immediately after induction of general anesthesia. The residual gastric fluid volume over 1 mL was able to be aspirated through a nasogastric tube in 4 of 30 patients in the control group and 2 of 30 patients in the treatment group who took the carbohydrate-rich solution up to 2 hours before surgery, and there was no statistical difference in the control group and treatment group.

Some studies reported the metabolic benefits of improved insulin sensitivity and reduced postoperative insulin resistance by reducing fasting time using preoperative carbohydrate-rich solutions [12,13]. However, we did not measure these with the characteristics of our study, which were the short time to return to diet and the relatively short hospital stay. Instead, we focused more on comparing complications and convenience between the 2 groups.

We had 1 patient with postoperative hoarseness in the treatment group. This hoarseness might be from chemical irritation of aspirated gastric contents. However, a temporary hoarseness after endotracheal intubation is one of the most common complications in general anesthesia. It occurs in 14.4% to 50% of patients who undergo endotracheal intubation [14,15,16]. The patient who showed postoperative hoarseness recovered completely by the next day after the operation. This very short-term recovery from the hoarseness can be seen as evidence that this hoarseness could be caused by irritation of endotracheal intubation instead of gastric contents aspiration.

One patient in the control group and 2 patients in the treatment group complained of nausea, but none of the patients in both groups had vomiting postoperatively. In general, the incidence of postoperative nausea and vomiting (PONV) after general anesthesia is up to 30% when inhalational anesthetics are used. Additionally, studies have reported that the incidence of PONV was lower in the carbohydrate-rich solution group than in the fasted group between 12 hours and 24 hours after surgery [17,18]. Based on their results, we interpret that the PONV of our patients is the effect of residual anesthetic gas or narcotics rather than increased gastric residual contents. Our results also did not show evidence of an increase in PONV in the treatment group compared to the control group.

Thirst is a common discomfort in patients immediately after general anesthesia. According to Aroni et al. [19], 75% of patients who fasted for more than 8 hours before general anesthesia felt thirsty in the recovery room. Our results show that providing liquid solutions to patients up to 2 hours before general anesthesia can improve the thirst that immediate postoperative patients suffer from. Additionally, reduced fasting time with liquid solution ameliorates the thirst that patients commonly experience in the morning of the day of surgery. It can be a simple but powerful method to improve the quality of life in patients who need operations under general anesthesia.

There are several possible reasons to reduce postoperative thirst by decreasing the fasting time. First, patients who undergo prolonged preoperative fasting experience a reduction in total body water, leading to a relative state of dehydration. This decrease in plasma volume increases plasma osmolality, stimulating the hypothalamic osmoregulatory center and heightening the sensation of postoperative thirst. In contrast, patients who consume water up to 2 hours before surgery may maintain more stable intravascular volume and plasma osmolality, potentially mitigating postoperative thirst. Second, even when patients receive intravenous fluids perioperatively, prolonged fasting reduces saliva production, which leads to dry mouth and causes a sense of thirst. And the following lack of swallowing reflex and oral stimulation worsens this symptom.

These positive results were also observed in the treatment group in terms of hunger. According to their lower hunger score using an oral carbohydrate-rich solution, we can find that patients achieve better satisfaction during the hospital stay pre- and postoperation. All of the patients who participated in this study did not have any acute respiratory complications such as desaturation, dyspnea, or productive cough and were discharged on the day following surgery.

So far, only a few randomized controlled studies for reduced fasting trials using clear liquid have been conducted in Korea. One of them was for the safety of reduced fasting using a carbohydrate-rich clear solution up to 2 hours before general anesthesia, which was conducted by Chang et al. [6], the first in Korea. Another interesting study was performed by Huh et al. [20] for pediatric patients who underwent minimally invasive pectus excavatum repair. They reported that the pediatric anesthesia emergence delirium and faces pain scale scores were lower in the clear liquid group without an increase in postoperative respiratory complications.

Our study shows better results in the aspect of perioperative satisfaction during the hospital stays in the reduced fasting group. Most of all, we proved the safety of using clear liquid up to 2 hours before general anesthesia by the most objective method that compared the amount of gastric contents directly after induction of general anesthesia in both groups. Furthermore, we excluded diabetic patients from our study to eliminate potential confounding factors, such as PONV, which could be attributed to diabetic gastroparesis.

However, our study still has limitations. It included only patients with pre-peritoneal endoscopic surgery and excluded patients who underwent intraperitoneal surgery manipulating hollow viscera, which possibly could change intestinal motility. The next study will be designed to include patients who received intraperitoneal surgery and compare the postoperative complications in both groups.

In conclusion, reducing the fasting time using clear liquid for surgery patients requiring general anesthesia is safe and effective in providing satisfaction. We hope that this result will help surgeons' confidence in decreasing the preoperative fasting time without concern for possible respiratory complications during surgery with general anesthesia.