Determining gastric contents during general anaesthesia: evaluation of two methods

Gastric emptying evaluation by ultrasound prior colonoscopy: An easy tool following bowel preparation

AIM: To investigate the gastric emptying after bowel preparation to allow general anaesthesia.

METHODS: A prospective, non-comparative, and non-randomized trial was performed and registered on Eudra CT database (2011-002953-80) and on www.trial.gov (NCT01398098). All patients had a validated indication for colonoscopy and a preparation using sodium phosphate (NaP) tablets. The day of the procedure, patients took 4 tablets with 250 mL of water every 15 min, three times. The gastric volume was estimated every 15 min from computed antral surfaces and weight according to the formula of Perlas et al (Anesthesiology, 2009). Colonoscopy was performed within the 6 h following the last intake.

RESULTS: Thirty patients were prospectively included in the study from November 2011 to May 2012. The maximum volume of the antrum was 212 mL, achieved 15 min after the last intake. 24%, 67% and 92% of subjects had an antral volume below 20 mL at 60, 120 and 150 min, respectively. 81% of patients had a Boston score equal to 2 or 3 in each colonic segment. No adverse events leading to treatment discontinuation were reported.

CONCLUSION: Gastric volume evaluation appeared to be a simple and reliable method for the assessment of gastric emptying. Data allow considering the NaP tablets bowel preparation in the morning of the procedure and confirming that gastric emptying is achieved after two hours, allowing general anaesthesia.

Gastric tubes and airway management in patients at risk of aspiration: history, current concepts, and proposal of an algorithm

Rapid sequence induction and intubation (RSII) and awake tracheal intubation are commonly used anesthetic techniques in patients at risk of pulmonary aspiration of gastric or esophageal contents. Some of these patients may have a gastric tube (GT) placed preoperatively. Currently, there are no guidelines regarding which patient should have a GT placed before anesthetic induction. Furthermore, clinicians are not in agreement as to whether to keep a GT in situ, or to partially or completely withdraw it before anesthetic induction. In this review we provide a historical perspective of the use of GTs during anesthetic induction in patients at risk of pulmonary aspiration. Before the introduction of cricoid pressure (CP) in 1961, various techniques were used including RSII combined with a head-up tilt. Sellick initially recommended the withdrawal of the GT before anesthetic induction. He hypothesized that a GT increases the risk of regurgitation and interferes with the compression of the upper esophagus during CP. He later modified his view and emphasized the safety of CP in the presence of a GT. Despite subsequent studies supporting the effectiveness of CP in occluding the esophagus around a GT, Sellick's early view has been perpetuated by investigators who recommend partial or complete withdrawal of the GT. On the basis of available information, we have formulated an algorithm for airway management in patients at risk of aspiration of gastric or esophageal contents. The approach in an individual patient depends on: the procedure; type and severity of the underlying pathology; state of consciousness; likelihood of difficult airway; whether or not the GT is in place; contraindications to the use of RSII or CP. The algorithm calls for the preanesthetic use of a large-bore GT to remove undigested food particles and awake intubation in patients with achalasia, and emptying the pouch by external pressure and avoidance of a GT in patients with Zenker diverticulum. It also stipulates that in patients with gastric distension without predictable airway difficulties, a clinical and imaging assessment will determine the need for a GT and in severe cases an attempt to insert a GT should be made. In the latter cases, the success of placement will indicate whether to use RSII or awake intubation. The GT should not be withdrawn and should be connected to suction during induction. Airway management and the use of GTs in the surgical correction of certain gastrointestinal anomalies in infants and children are discussed.

Examination of accuracy in the assessment of gastric residual volume: a simulated, controlled study

BACKGROUND

Increased gastric content from enteral nutrition intolerance is thought to place patients at risk for pulmonary aspiration. Although considered a questionable practice, blind gastric tube aspiration is the most common approach to measure gastric content. This simulated study evaluated the accuracy of residual volume (RV) assessment via tube aspirations made from known volumes by controlling the syringe pull technique, feeding tube properties, fluid viscosity, and placement of tubes in the fluid.

MATERIALS AND METHODS

This study was conducted in a metrology laboratory. Aspirates were obtained using a force measurement test system to control force of the syringe pull technique using 3 different procedures (slow 10 inches per minute [ipm], intermittent 10 ipm, and fast 40 ipm). Four different feeding tubes, 10 Fr and 18 Fr, each made of polyurethane and polyvinyl chloride, were placed in varying depths of 100 mL of either water or formula. The effect of fluid viscosity was also examined.

RESULTS

Overall, 108 RVs were analyzed using a force measurement test system. Actual content of RV was underestimated 19% on average and varied across tube size and viscosity. Intermittent and slow syringe pull techniques yielded greater aspirate quantities, although neither technique aspirated the full amount of volume available. The 10 Fr feeding tubes yielded larger RVs in more viscous fluid, yet the 18 Fr tubes performed better with fluids of lower viscosity.

CONCLUSIONS

Based on this simulation, RV assessment does not accurately reflect the total volume of the contents available and, therefore, the clinical utility of this assessment should be further investigated.

Evaluating ranitidine, pantoprazole and placebo on gastric pH in elective surgery

Background and Aim:

Concern about the grim nature of postoperative acid aspiration syndrome grew among the anesthesiologist over the years warranting the need for pre-emptive intervention. The aim of the study is to compare the effects of preoperative oral ranitidine versus pantoprazole given in regulating gastric pH in elective surgery.

Methods:

This prospective, parallel group, controlled, randomized, single-blind study was conducted at a tertiary care postgraduate teaching institute at Kolkata, involving 120 participants of either sex, aged 18-60 years of American Society of Anesthesiologists physical status I and II, who were scheduled for elective surgery under general anesthesia lasting for more than 2 h. The participants were divided into three groups. In group A (n=40) participants received placebo tablet, in group B (n=40) participants received ranitidine tablet while in group C (n=40), participants received pantoprazole tablet and their gastric pH estimated serially.

Results:

The participants in the three groups were comparable in terms of age, sex, body weight, duration of surgery and type of surgery distribution. In regard to changes in gastric pH trends, there was no statistically significant difference between serial pH values in group A (Friedman test; P>0.05) and group C participants. (P>0.05). However, the mean preoperative gastric pH values (7.140±.7652) were significantly lower than mean pH values (7.253±.7514) after 2 h postoperatively in group B participants (P<0.05).

Conclusion:

From the observations and analyses of the present study, it can be inferred that ranitidine is more effective than pantoprazole to raise the gastric pH for prevention of aspiration pneumonitis.

A single dose of intravenous esomeprazole decreases gastric secretion in healthy volunteers

BACKGROUND

Data suggest that esomeprazole decreases gastric secretion.

AIMS

To assess the effect of a single i.v. esomeprazole dose on gastric secretion volume 3 h after drug administration, as a primary endpoint, and to evaluate, as secondary endpoints, the reduction 1 and 5 h after dosing; time when the gastric pH was <2.5 and esomeprazole's safety.

METHODS

In all, 23 healthy Helicobacter pylori-negative volunteers (10 men, 13 women, mean age 28.2 +/- 6) participated in this single-centre, randomized, double-blind, placebo-controlled, 2-way, single-dose cross-over study. In different sessions, volunteers received i.v. either esomeprazole 40 mg or placebo. An inserted double-lumen nasogastric tube perfused and aspirated gastric liquid. Mechanical fractioned aspiration measured secretion volume; aliquot spectrophotometry assessed gastric secretion volume lost to the duodenum.

RESULTS

Three hours post-i.v. esomeprazole, average gastric secretion decreased by 77.6% (vs. baseline) compared to placebo. Values 1 and 5 h after dosing were 73.5% and 74.5%. Five hours after esomeprazole, the gastric pH was <2.5 3.9% of the time and 73.3% after placebo (P < 0.002). Esomeprazole was well-tolerated. No serious adverse events occurred.

CONCLUSIONS

Intravenous esomeprazole decreases gastric secretions. The potential clinical impact in averting bronchoaspiration during anaesthesia induction and in intensive care patients should be investigated in further studies.

Fasting from midnight – the history behind the dogma

The purpose of this chapter is to review historical fasting guidelines and how the dogma of fasting from midnight arose and came to be challenged by randomized clinical trials of preoperative clear liquids versus overnight fast. Medical and anaesthesia textbooks and journals from the 19th and 20th centuries were consulted, and the results of clinical trials and the reaction to them are reviewed. The dogma appeared to result from extrapolation of pulmonary aspiration risk in 'full-stomach' emergency cases to healthy elective cases. This was reinforced when 25 mL in the stomach, present in half of all healthy fasting patients, was used as a surrogate marker for high risk of aspiration. Subsequent large-scale studies showed the risk to be minimal. Meta-analysis of randomized clinical trials demonstrated the safety of clear oral liquids until 2 hr preoperatively in healthy patients undergoing elective surgery. Reaction was cautious but led to eventual acceptance of evidence-based fasting guidelines.

Comparison of preoperative gastric contents and serum gastrin concentrations in pregnant and nonpregnant women

STUDY OBJECTIVE

The aim of this study was to compare the volume and the pH level of preoperative gastric contents and serum gastrin concentrations between pregnant and nonpregnant women.

DESIGN

This prospective controlled study was conducted in a single blind manner.

PATIENTS

One hundred pregnant women scheduled for elective cesarean delivery (pregnant group) and 100 nonpregnant women who underwent gynecologic surgery (nonpregnant group) were enrolled.

INTERVENTIONS

Gastric content was aspirated gently with 14-F multiorificed nasogastric tube before the induction of anesthesia.

MEASUREMENTS

The volume and the pH level of the aspirated gastric contents were measured, and serum gastrin concentration was measured by the double antibody gastrin method.

MAIN RESULTS

The gastric volume in the pregnant group was greater than in the nonpregnant group (0.49 +/- 0.4 vs 0.24 +/- 0.2 mL/kg, P < .05). The gastric pH level in the pregnant group was lower than in the nonpregnant group (2.4 +/- 1.4 vs 3.0 +/- 1.9, P < .05). The number of patients at risk was 45 (45.5%) in the pregnant group and 16 (16.7%) in the nonpregnant group (P < .05). The serum gastrin levels of the 2 groups were not significantly different (32.1 +/- 12.3 vs 28.2 +/- 8.3 pg/mL). The preoperative anxiety level of the pregnant group was higher than in the nonpregnant group (4.4 +/- 2.1 vs 3.8 +/- 2.2, P < .05).

CONCLUSIONS

We confirmed that pregnant women have much greater and more acidic gastric contents than the nonpregnant patients preoperatively, and it is not because of serum gastrin concentration.

The effect of intravenous pantoprazole and ranitidine for improving preoperative gastric fluid properties in adults undergoing elective surgery

We studied pantoprazole, a new potent and fast-acting proton pump inhibitor. Its effects on preoperative gastric fluid volume and pH have not yet been determined. In this randomized, controlled trial, we examined the effects of preoperative IV pantoprazole or ranitidine on gastric pH and volume. Ninety patients (ASA status I and II, scheduled for elective surgery) were studied. One hour before surgery, patients in Group I (n = 30) were given IV saline 5 mL, those in Group II (n = 30) were given 40 mg of pantoprazole IV, and those in Group III (n = 30) were given 50 mg of ranitidine IV. A nasogastric tube was inserted immediately after anesthesia induction. Gastric contents were aspirated, and volume and pH were recorded. The pH values determined in Group I were 3.73 +/- 0.82; in Group II, they were 5.30 +/- 1.84; and in Group III, they were 4.80 +/- 1.40. There was no statistical difference between Groups 2 and 3, but there was a significant difference between Group I and Groups 2 and 3 (P < 0.0005). The volume of the gastric contents was 28.67 +/- 10.98 mL in Group I, 15.20 +/- 15.52 mL in Group II, and 7.77 +/- 11.17 mL in Group III. There was no statistical difference between Groups 2 and 3, but there was a statistically significant difference between Group I and Groups 2 and 3 (P < 0.0005). The proportion of patients considered "at risk" of significant lung injury should aspiration occur was 20% of Group I, 10% of Group II, and 3.3% of Group III. When statistically evaluated, there was no difference among groups. We concluded that the administration of IV pantoprazole and ranitidine 1 h before surgery is effective in reducing gastric pH and volume.

IMPLICATIONS

This randomized, controlled trial examined the effects of preoperative IV pantoprazole or ranitidine on gastric pH and volume. We concluded that IV pantoprazole and ranitidine, given 1 h before surgery, are effective in reducing gastric pH and volume.

Pre-operative oral erythromycin reduces residual gastric volume and acidity

We investigated whether low-dose erythromycin (200 mg) given as an oral premedicant altered the residual gastric volume and its acidity in fasted patients at induction of anaesthesia in a single-blinded study. Sixty patients were allocated randomly to receive either an erythromycin tablet (200 mg) or nothing with 10 ml water 3 h before induction of anaesthesia, and another 60 patients 1 h before induction of anaesthesia. Oral erythromycin significantly reduced residual gastric volume when it was given approximately 3 h (P<0.05; 95% CI for median difference: 0.1-17 ml) or 1 h (P<0.0005; 95% CI for median difference: 6-24 ml) before induction of anaesthesia. Erythromycin significantly reduced gastric acidity when it was given 1 h before induction of anaesthesia (P<0.02; 95% CI for median pH difference: 0.1-1.7). In contrast, when given 3 h before induction of anaesthesia, erythromycin did not significantly alter acidity.

A comparison of rabeprazole, lansoprazole, and ranitidine for improving preoperative gastric fluid property in adults undergoing elective surgery

Acid aspiration syndrome at the induction of anesthesia is still a potentially life-threatening complication. Its severity is affected by both pH and volume of the gastric juice that is aspirated. We compared the effects of rabeprazole (a new proton pump inhibitor), lansoprazole, and ranitidine on gastric fluid properties in a prospective, randomized, double-blinded fashion in 180 adult patients undergoing elective surgery. Patients were divided into six groups (n = 30 in each) according to their premedication. Patients in each group received placebo-rabeprazole (PLA-RAB), rabeprazole-placebo (RAB-PLA), rabeprazole-rabeprazole (RAB-RAB), lansoprazole-lansoprazole (LAN-LAN), placebo-ranitidine (PLA-RAN), or placebo-placebo (PLA-PLA) for the first-second medication. Each dose of the study drug was 20 mg for rabeprazole, 30 mg for lansoprazole, and 150 mg for ranitidine. The first medication was given orally at 9:00 PM on the day before surgery and the second at 5:30 AM on the day of surgery. Each patient fasted overnight and took the drug with 20 mL of water. After tracheal intubation, gastric fluid was aspirated via an orogastric tube, and the volume and pH of the aspirate was measured. Preoperative gastric fluid acidity and volume were improved by the study drugs in the following order: PLA-RAN (pH 5.3, volume 0.10 mL/kg), RAB-RAB, LAN-LAN, PLA-RAB, and RAB-PLA (pH 3.8, volume 0.22 mL/kg). The proportion of patients at risk of acid aspiration syndrome according to the traditional criteria (pH < 2.5 and volume > 0.4 mL/kg) was minimized in Groups RAB-RAB and PLA-RAN (0%). We concluded that a single morning dose of ranitidine rather than two doses (bedtime and morning) of rabeprazole was the most effective premedicant to control gastric fluid properties and to minimize the risk of aspiration pneumonitis.

IMPLICATIONS

Acid aspiration syndrome at the induction of anesthesia is rare but still a potentially life-threatening complication. We compared rabeprazole, lansoprazole, and ranitidine for reduction of preoperative gastric fluid acidity and volume in elective surgery and found that a combination of bedtime and morning doses of rabeprazole, or a morning dose of ranitidine, similarly minimized the variables. In adult patients who are at risk of aspirating gastric contents, improvement of gastric fluid environment by rabeprazole can reasonably be anticipated to provide protection against pneumonitis should regurgitation and aspiration of gastric contents occur.

Cisapride does not alter gastric volume or pH in patients undergoing ambulatory surgery

PURPOSE

To evaluate the efficacy of 20 mg cisapride p.o. in reducing residual gastric volume and pH in adult ambulatory surgical patients.

METHODS

Using a prospective randomised double-blind controlled design, we administered either 20 mg cisapride p.o. or placebo preoperatively to 64 ASA 1-2 ambulatory surgical patients. Following induction of anesthesia we measured volume and pH of residual gastric contents, using blind aspiration through an orogastric tube. Parametric data were analysed using unpaired, one tail Students' t test. Non-parametric data were analysed using Fishers Exact test and Chi square analysis. Statistical significance was accepted at the probability level of < 0.05.

RESULTS

Residual gastric volumes were similar in the two groups (19.5 +/- 23.8, 23.9 +/- 24.4 ml), in the cisapride and placebo groups respectively, P=0.24). Data shown are mean (+/- SD). The proportions of patients with a residual gastric volume exceeding 0.4 ml x kg(-1) were similar in the two groups (4 of 28, and 8 of 23 patients in the cisapride and placebo groups respectively, P=0.09). The pH of the residual gastric contents were similar in the cisapride and placebo groups (1.6 +/- 0.5, 1.4 +/- 0.5, respectively, P=0.26). The proportions of patients with pH < 2.5 was also similar in the cisapride and placebo groups (21 of 25, and 20 of 21 patients respectively, P=0.2).

CONCLUSIONS

Preoperative administration of 20 mg cisapride p.o. to patients scheduled for outpatient surgery does not alter either the volume or the pH of gastric contents. Its use in this setting is of no apparent clinical benefit.

Effect of preoperative paracetamol on gastric volumes and pH in children

The effect preoperative paracetamol elixir has on gastric contents is unknown. Children presenting for elective adenotonsillectomy were randomized to receive either paracetamol elixir (40 mg x kg(-1)) 90 min before surgery or paracetamol suppositories (40 mg x kg(-1)) intraoperatively. Following induction of anaesthesia a 16 Fr multiple-oriface orogastric tube was passed into the stomach and measure taken of the residual gastric volume and pH. The children had a mean age of 8.5 years (SD 3.2) with a weight of 35 kg (SD 16.5). Children given elixir (n=41) had a mean residual gastric volume of 0.083 ml x kg(-1) (95% CI; 0.006, 1.24) and a pH of 1.83 (95% CI; 0.75, 4.49), while those given suppositories (n=40) had a mean residual gastric volume of 0.083 ml x kg(-1)(95% CI; 0.008, 0.9) and a pH of 2.07 (95% CI; 0.84, 5.12). There was no significant difference between these two groups. Paracetamol elixir is rapidly absorbed in the gastrointestinal system of children and preoperative administration has no effect on gastric contents. Given paracetamol's slow equilibration rate constant from the central to the effect compartment, children may be given this medication preoperatively for routine surgical procedures.

A comparison of the volume and pH of gastric contents of obese and lean surgical patients

Obese surgical patients are typically considered to be more likely than lean patients to possess high-volume and low-pH (HVLP) gastric contents after a standard preoperative fast, based on a study of a population predominately consisting of patients receiving intramuscular preoperative sedation. We revisited this issue in a study population of 256 fasted surgical patients, of which 232 received no preoperative antacid or gastric prokinetic drug. Immediately after endotracheal intubation, an 18-French sump tube was placed, and gastric contents were withdrawn. Subjects' gastric contents were defined as HVLP if they exhibited a combination of a volume > 25 mL and a pH < 2.5. Obesity was defined as a body mass index > 30. Among nonmedicated obese patients, the proportion with HVLP gastric contents was 20 of 75 (26.6%). The proportion of lean patients with HVLP gastric contents was 66 of 157 (42.0%). The difference between the HVLP proportions for these two groups was found to be significant (P < 0.05) using chi 2 analysis. Obesity seems to be associated with a significantly decreased risk of HVLP gastric contents among surgical patients with no history of gastroesophageal pathology after a normal interval of preoperative fasting.

IMPLICATIONS

Previous studies have shown that obese surgical patients have a greater volume of acidic stomach contents than lean patients, despite a routine preoperative fast. We have reexamined this issue and found that among otherwise healthy, fasted, obese surgical patients, there is a lower incidence of combined high-volume, low-pH stomach contents compared with lean patients.

Acid aspiration prophylaxis for emergency Caesarean section

Over a 3.5 year period, 384 patients requiring emergency Caesarean section under general anaesthesia received at random one of six acid aspiration prophylaxis regimens as soon as the decision was made for surgery. In the first phase of the study, sodium citrate administered orally 0.3 M, 30 ml (group C, n = 120) was compared with metoclopramide 10 mg administered intravenously and sodium citrate (group MC, n = 65). In the second phase, all patients received sodium citrate, and either intravenous administration of ranitidine 50 mg (group RC, n = 50), omeprazole 40 mg (group OC, n = 50), ranitidine 50 mg with metoclopramide 10 mg (group RMC, n = 50) or omeprazole 40 mg with metoclopramide 10 mg (group OMC, n = 49). Gastric contents were aspirated using a 16 FG Salem sump tube and acidity measured with a pH meter. Non-parametric tests were used for comparisons. There was no difference in gastric volume or pH between groups C and MC, or among OC, RC, OMC and RMC. After pooling the data, median (range) gastric volume in groups C and MC (55 (0-360) ml) was greater than in groups OMC and RMC (40 (3-270) ml, p < 0.05). Median (range) pH was lower in groups C and MC (4.97 (0.76-6.99)) than in groups OC, RC, OMC and RMC (5.76 (1.11-7.5), p < 0.001). The proportion of patients with pH < 3.5 and volume > 25 ml in the C and MC groups (43/185) was greater than that in the OC, RC, OMC and RMC groups (18/199, p < 0.001). Ranitidine and omeprazole administered intravenously were equally effective adjuncts to sodium citrate in reducing gastric acidity for emergency Caesarean section. Compared with sodium citrate alone, the addition of either ranitidine, omeprazole or metoclopramide alone did not reduce gastric volume while small reductions in gastric volume were seen with the addition of metoclopramide and either ranitidine or omeprazole.

A comparison of lansoprazole, omeprazole, and ranitidine for reducing preoperative gastric secretion in adult patients undergoing elective surgery

Acid aspiration syndrome of induction of anesthesia is a life-threatening complication whose severity is affected by both pH and volume of the aspirated gastric juice. We compared the effects of two proton pump inhibitors (PPIs), lansoprazole and omeprazole, and an H2 blocker, ranitidine, on gastric secretion in a prospective, randomized, double-blind fashion in 200 adult patients of ASA physical status I undergoing elective surgery. The patients were divided into eight groups (n = 25 each) according to their premedication. The patients received lansoprazole-lansoprazole (Group L-L), lansoprazole-placebo (Group L-P), placebo-lansoprazole (Group P-L), omeprazole-omeprazole (Group O-O), omeprazole-placebo (Group O-P), placebo-omeprazole (Group P-O), placebo-ranitidine (Group P-R), or placebo-placebo (Group P-P), as the first and second medications. The dose of the study drug was 30 mg for lansoprazole, 150 mg for ranitidine, and 80 mg for omeprazole. The first medication was administered orally at 9:00 PM on the night before surgery and the second at 5:30 AM in the morning on the day of the surgery. Each patient fasted overnight and took the drug with 20 mL of water. After tracheal intubation, gastric fluid was aspirated via an orogastric tube and the volume and pH of the aspirate were measured. The pH of the aspirated gastric fluid was higher in Groups P-R, L-L, P-L, O-O, and O-P than in Group P-P (P < 0.05). The volume of the gastric contents was similar in Groups P-0 and P-P, and the other groups had smaller gastric volume than Group P-P (P < 0.05). Gastric fluid from patients in Group P-R was the least acidic (pH 6.1 +/- 1.2) and had the least volume (0.09 +/- 0.06 mL/kg). Group L-L was comparable with Group P-R in both pH and volume, whereas Groups P-L and O-O were similar to Group P-R only in volume. The proportion of patients at risk according to the traditional criteria (pH < 2.5 and volume 0.4 mL/kg) was significantly lower in Groups L-L (0%), P-L (4%), O-O (4%), and P-R (0%) than in Group P-P (48%) (P < 0.05). We concluded that two consecutive doses of lansoprazole or a morning dose of ranitidine seemed to be the most effective preanesthetic medication for reducing gastric acidity and volume.

A comparison of intravenous ranitidine and omeprazole on gastric volume and pH in women undergoing emergency caesarean section

We have compared the effect of intravenously administered omeprazole and ranitidine on gastric contents in a double-blind study in 80 consecutive women undergoing emergency Caesarean section. When the decision to perform emergency Caesarean section was made, patients were randomly assigned to receive either ranitidine 50 mg or omeprazole 40 mg intravenously. The volume and pH of the gastric contents were measured immediately after tracheal intubation and again before extubation. The gastric pH was found to be higher after omeprazole than after ranitidine immediately after intubation (5.89 +/- 1.46 and 5.21 +/- 1.36 respectively) (P < 0.05) and before extubation (5.97 +/- 1.38 and 5.32 +/- 1.24 respectively) (P < 0.05). However, the gastric volumes were comparable in both the groups. The number of patients with gastric volume > 25 ml and pH < 2.5 were 3 (7.5%) in the ranitidine group and 1 (2.5%) in the omeprazole group after intubation and none in either of the groups before extubation. We conclude that omeprazole 40 mg iv administered at the time of the decision to operate, results in higher gastric pH than ranitidine in obstetric patients undergoing emergency Caesarean section.

Acid aspiration prophylaxis in elective biliary surgery. A comparison of omeprazole and famotidine using manually aided gastric aspiration

We have compared the effects of single oral doses of omeprazole 40 mg, famotidine 40 mg or placebo on gastric secretion in 45 non-obese patients the night before elective biliary surgery. After stable anaesthesia had been established, a Salem orogastric tube was introduced and gastric contents were aspirated by a blinded observer. The volume and pH were noted. After the abdomen was opened aspiration was repeated but on this occasion with the surgeon's manual assistance. We found that the initial aspirate volume underestimated total gastric volume by an average (SD) of 7.1 (6.6) ml. Famotidine, but not omeprazole, produced a significant decrease in gastric volume and acidity. Patients were considered to be at risk if pH < 2.5 and volume > 0.4 ml.kg-1. Three patients in the omeprazole group, three in the placebo group and none in the famotidine group came into this category. We conclude that a single oral dose of omeprazole 40 mg given the night before surgery does not afford adequate prophylaxis for acid aspiration syndrome.

Sugarless gum chewing before surgery does not increase gastric fluid volume or acidity

Patients occasionally arrive in the operating suite chewing gum despite instructions to avoid oral intake for a specific number of hours before surgery. Some anaesthetists are hesitant to proceed with these patients fearing an increase in gastric volume and acidity. This study was undertaken to determine if gum chewing increased gastric volume and acidity. Seventy seven patients were recruited and informed consent obtained. Thirty-one patients who fasted overnight were randomly assigned either to serve as control (Group 1) or to chew sugarless gum prior to anaesthesia (Group 2). The remaining 46 patients fasted overnight but were given sugarless gum and allowed to chew it until immediately before induction of anaesthesia if they desired (Group 3). Volume and pH of gastric content were determined immediately after induction of anaesthesia and tracheal intubation. Results revealed mean values (range) of gastric volume for Group 1-26 ml (9-60), Group 2-40 ml (5-93), and Group 3-28 ml (4-65). Mean values for pH (range) were Group 1-1.8 (1.0-4.6), Group 2-1.6 (1.3-1.9), Group 3-1.7 (1.0-4.4). There was no difference between groups in terms of gastric volume or pH. In addition, there was no relationship between gastric content and the length of time from gum discard to induction or the length of time gum was chewed. In conclusion, the data suggest that induction of anaesthesia is safe and surgery does not need to be delayed if a patient arrives in the OR chewing sugarless gum.

Gastric pH and volume after oral fluids in the postpartum patient

The aim of this study was to investigate the relationship between preoperative oral fluids and gastric pH and volume in women undergoing sterilization between one and five days postpartum. Fifty postpartum patients received 150 ml water approximately two to three hours before surgery while 50 postpartum and 50 non-pregnant women were fasted from midnight. After induction of anaesthesia, gastric contents were aspirated using a Salem sump tube and the gastric pH and volume were measured. There were no differences in intragastric pH and volume, median (range), among the postpartum fasted group, 1.19 (0.74-4.57), 22 (1-78) ml, postpartum water group 1.18 (0.70-6.4), 25.5 (3-66) ml and the non-pregnant group 1.27 (0.51-6.63), 25 (3-69) ml. There was no correlation between postpartum interval, 60 (12-120) hr, and intragastric pH or volume. It is concluded that oral water may be given safely two to three hours preoperatively to patients more than one day postpartum. Intragastric volume and acidity were not increased and the findings in postpartum patients were similar to those found in non-pregnant patients.

Acid aspiration prophylaxis in morbidly obese patients: famotidine vs. ranitidine

Famotidine and ranitidine were compared as agents for the prevention of acid aspiration syndrome in 32 morbidly obese patients undergoing vertical banded gastroplasty. Single-dose oral famotidine or double-dose oral ranitidine were administered on a random basis before surgery. Gastric contents were aspirated through a gastric tube, manually aided by the surgeon with the abdomen open. Mean (SD) gastric volumes were 13.8 ml (6.7) and 12.1 ml (13.0) for the famotidine and ranitidine groups, respectively. Mean (SD) gastric pH values were 6.2 (1.5) and 6.8 (1.5), respectively. There were no significant differences between the groups and no patient was considered 'at risk' (pH less than 2.5 and gastric volume greater than 25 ml). We conclude that single-dose oral famotidine and double-dose oral ranitidine are equally effective for preventing acid aspiration syndrome in morbidly obese patients.

Gastric fluid volume and pH in elective patients following unrestricted oral fluid until three hours before surgery

This clinical study was designed to assess the results of new preoperative fasting guidelines in which patients are instructed that they must not eat any solid food after midnight, but that they may drink unrestricted amounts of clear fluid until three hours before their scheduled time of surgery. We studied 199 healthy, elective surgical inpatients aged 18-70 yr to determine whether there was any correlation between the ingestion interval or the volume of fluid ingested, with the volume and pH of residual gastric fluid at induction of anaesthesia. Pregnant patients, and those with gastric disorders or who were taking medications that affect gastric motility or secretion, were excluded. Either no premedication was given, or oral diazepam 5-15 mg was given 90 min preoperatively. Of the 199 patients, 105 ingested 50-1200 ml on the morning of surgery. The ingestion-induction interval was less than three hours in 12 patients whose actual surgery time was ahead of schedule. The remaining 94 patients did not drink because they were scheduled for surgery before 11:00 (n = 51), they did not want to drink (n = 24), or they were advised not to drink by their nurse or surgeon (n = 16). Following induction of anaesthesia, gastric fluid was aspirated through a #18 Salem sump orogastric tube, the volume was recorded and pH was measured with a calibrated pH meter. Patients were divided retrospectively into four groups (in three of which patients ingested fluid) according to the ingestion-induction interval (1.3-3.0 hr, 3.1-5.0 hr, 5.1-8.0 hr, and nothing by mouth after midnight).(ABSTRACT TRUNCATED AT 250 WORDS)

Unlimited clear fluid ingestion two hours before surgery in children does not affect volume or pH of stomach contents

To determine the effect on gastric contents of unlimited clear fluid ingestion by children up to two and a half hours and then up to two hours before elective surgery, 228 healthy children (ages two to twelve years) were prospectively studied. During Phase I of this study subjects ingested unrestricted volumes and types of clear fluids up to three hours (control group) or two and a half hours before surgery. After establishment of adequate anaesthesia, gastric fluids were aspirated via an orogastric tube. Gastric volume was measured with a syringe and gastric pH was determined. After determining that there was no adverse effect associated with reducing a clear fluid fast to two and a half hours, Phase II of the study was begun. The methods for Phase II were unchanged except that unlimited clear fluids were permitted up to three hours (control group) or two hours preoperatively. In both Phase I and II, gastric volume and gastric pH were unaffected by reducing the fast to less than three hours. It is concluded that ingestion of unlimited clear fluids up to two hours before elective surgery does not affect gastric contents of healthy children.

Gastric residual volume in infants and children following a 3-hour fast

The effect of a 3-hour versus a 10-hour preoperative fasting interval on the gastric residual volume and gastric pH of pediatric patients was evaluated. Forty-four healthy infants, 1 month to 5 years of age, were randomly assigned to one of two groups. The 3-hour nil per os (NPO) group consisted of 19 infants kept NPO for 3 hours following ingestion of up to 4 ounces of 5% dextrose in water (D5W). The control group consisted of 25 infants who remained NPO an average of 10 hours prior to surgery. Gastric residual volume was calculated using the dye-dilution technique. After the dye marker was injected into the stomach, complete aspiration of the stomach (including the volume of dye marker plus residual gastric contents) was attempted as another method to measure gastric residual volume. There were no significant differences in gastric residual volume between the 3-hour and the 10-hour NPO groups using either the dye-dilution or aspiration methods. However, there were significant differences between the two measuring techniques. Gastric residual volume was significantly greater in volume when measured by the dye-dilution technique than it was when measured by the aspiration technique in both the 10-hour (p less than 0.009) and the 3-hour (p less than 0.0009) NPO groups. Complete aspiration of a known volume of fluid injected through the orogastric tube was not possible in 23 of the 44 (52.4%) infants. Mean gastric pH was less than 2.0 in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Clear fluids three hours before surgery do not affect the gastric fluid contents of children

This prospective, randomized, single-blind study of 121 healthy children aged 2 to 12 yr investigated the effect of clear fluids on gastric contents. Gastric fluid volume and pH were measured immediately following the induction of general anaesthesia and were not significantly affected by the ingestion of unlimited clear fluids up to three hours preoperatively. After a prolonged fast (mean fast 14 hr), gastric fluid volume was 0.39 +/- 0.37 ml.kg-1 and gastric pH was 1.7 +/- 0.4; after unlimited clear fluids (203 +/- 109 ml) up to three hours before surgery gastric fluid volume was 0.34 +/- 0.28 ml.kg-1 and gastric pH was 1.8 +/- 0.7 (mean +/- SD). Gastric fluid volume (ml.kg-1) increased in both the control and study groups as age increased, P less than 0.005. It is concluded that drinking clear fluid up to three hours before scheduled surgery does not have a measurable effect on gastric volume and pH of healthy children of ages 2 to 12 yr.

Occurrence of gastroesophageal reflux on induction of anaesthesia does not correlate with the volume of gastric contents

In an attempt to explain the discrepancy between the high number of patients said to be at risk of aspiration pneumonitis and the low reported incidence of this anaesthetic complication, 100 ASA physical status I-II elective surgical patients were studied. The volume of fluid present in the stomach at the time of induction of anaesthesia was correlated with gastroesophageal reflux (GER) detected by visual inspection of the pharynx and by continuous measurement of upper oesophageal pH. Mean gastric volume was 30 +/- 28 ml (range 0-210 ml). Gastric fluid volume greater than or equal to 0.4 ml.kg-1 at pH less than or equal to 2.5 was present in 46 patients. No GER was detected during induction of anaesthesia in our sample of 100 patients. Furthermore, patient age, duration of preoperative fasting, body mass index, cigarette smoking, alcohol consumption, preoperative anxiety, and a history of preoperative GER were not correlated with significant modifications of gastric volume or pH. We conclude that the low incidence of aspiration pneumonitis in elective surgical patients may be explained in part by the very low risk of GER, despite gastric fluid volumes of more than 0.4 ml.kg-1 in a high proportion of this patient population.

Omeprazole for prophylaxis of acid aspiration in elective surgery

The aim of the study was to determine whether a single oral dose of omeprazole 40 mg is effective in increasing the pH of gastric residue above 2.5 at the time of anaesthetic induction in adult patients scheduled for elective gynaecological surgery. The patients were allocated to receive either chlorazepate dipotassium 25 mg alone or omeprazole 40 mg and chlorazepate dipotassium 25 mg on the night before surgery. Gastric volume and pH were measured after induction of anaesthesia. Patients who received omeprazole had a higher mean pH than control patients (p less than 0.001). The pH was less than 3.5 in 50% of patients in the control group, but in only 4.5% of those who received omeprazole (p less than 0.01). Mean (SEM) volume of gastric fluid was 15.2 (2.7) ml in the control group and 9.2 (1.8) ml in the omeprazole group, but the results were not statistically significant. A single dose of 40 mg omeprazole significantly decreased the number of patients at risk of aspiration pneumonitis.

Large volumes of apple juice preoperatively do not affect gastric pH and volume in children

The effect on gastric pH and volume of 0, 6 and 10 ml.kg-1, of apple juice given 2.5 hours before surgery to children aged five to ten years was investigated in this prospective, randomized, single-blind study. Gastric contents were aspirated after induction of anaesthesia, and the volume measured. The pH of the gastric aspirate was then assessed using pH paper. Neither gastric volume nor pH immediately following the induction of general anaesthesia were significantly different among the three groups. Gastric volumes after 0, 6 and 10 ml.kg-1, of juice averaged (mean +/- SD) 0.45 +/- 0.31, 0.66 +/- 0.79 and 0.71 +/- 0.76 ml.kg-1, respectively; gastric pH averaged 1.7 +/- 0.6, 1.7 +/- 0.6 and 1.8 +/- 0.8, respectively. On the basis of questions asked immediately before induction of anaesthesia, patients who drank 6 ml.kg-1 of apple juice had decreased thirst and were less irritable and upset before anaesthesia than those who had not (P less than 0.05). It is concluded that drinking large volumes of clear apple juice 2.5 hours before scheduled surgery does not have a measurable effect on gastric volume and pH and may offer benefits such as improved patient comfort.

Measuring gastric contents during general anaesthesia: evaluation of blind gastric aspiration

Various medications have been reported to decrease gastric content volume and thus risk for pulmonary aspiration. The majority of studies have used blind gastric tube aspiration of stomach contents as the method of measuring the volume of gastric contents. This study evaluated the accuracy of this method by first measuring gastric content volume using blind gastric aspiration and then aspirating residual content in the stomach, using a visually guided flexible fiberoptic gastroscope. Ten obese patients undergoing elective surgery were studied. Gastric contents were collected using a multi-orificed gastric tube and blind aspiration. Immediately after this was completed, residual gastric volume was collected using a visually guided gastroscope. The sum of these two aspirate volumes (true total gastric volume) was statistically compared with the blind aspirate volume. The blind aspirate volume underestimated true total gastric volume by an average of 14.7 ml and was significantly different from true total gastric volume (p less than 0.05). Blind gastric aspiration was thus demonstrated only to approximate true gastric volume. Its use to measure precisely gastric volume cannot, therefore, be recommended.

The effect of preoperative apple juice on gastric contents, thirst, and hunger in children

The effect of 3 ml.kg-1 of apple juice given 2.6 +/- 0.4 hours preoperatively was investigated in 80 healthy children of ages five to ten years in this prospective, randomized, single blind study. The children who drank apple juice preoperatively had decreased gastric volume, thirst, and hunger (p less than 0.05). The gastric volume in the control group was 0.43 +/- 0.46 ml.kg-1 and in the patients who received apple juice the gastric volume was 0.24 +/- 0.31 ml.kg-1. The gastric pH was not significantly different, with the control group's gastric pH being 1.7 +/- 0.6 and the treated group's pH was 2.2 +/- 1.2. Further studies of the effects of different volumes and timing of preoperative clear fluids are indicated in paediatric patients.

Gastric fluid volume, pH, and emptying in elective inpatients. Influences of narcotic-atropine premedication, oral fluid, and ranitidine

One hundred and twenty healthy, elective surgical inpatients were randomly assigned to one of four groups. Between two and three hours before the scheduled time of surgery all patients ingested a marker dye, phenol red, 50 mg in 10 ml water, with placebo tablet alone (Groups 1 and 2), placebo tablet with 150 ml oral fluid (Group 3), or oral ranitidine 150 mg with oral fluid 150 ml (Group 4). Patients in Group 1 received oral diazepam or no premedication, while those in Groups 2, 3, and 4 received IM narcotic and atropine one hour preoperatively. Following induction of anaesthesia the residual gastric fluid was aspirated through a Salem sump tube and its volume, pH, and phenol red content measured. Mean volumes were Group 1: 24 ml; Group 2: 13 ml; Group 3: 17 ml; Group 4: 14 ml. Mean pH values were Group 1: 2.99; Group 2: 3.03; Group 3: 3.44; Group 4: 5.28. The amount of phenol red in the samples indicated at least 90 per cent gastric emptying had occurred in 90 per cent of patients. We conclude that, in healthy patients, 150 ml oral fluid is almost completely emptied from the stomach within two hours of ingestion, even when followed one hour later by narcotic-atropine premedication.