Sodium bicarbonate as a single dose antacid in obstetric anaesthesia

Gastric pH and volumes were measured in 84 women who had general anaesthesia for emergency Caesarean section. Forty-eight received only 20 ml 8.4% sodium bicarbonate immediately before induction of anaesthesia and 36 ranitidine 150 mg 6-hourly during labour in combination with NaHCO3. Gastric pH was less than 2.5 in four women who received only bicarbonate. All aspirates from the ranitidine plus bicarbonate group had a pH greater than 2.5. Mean volumes of gastric content aspirated were 87 (SD 87.4) and 60 (SD 46.3) ml for the bicarbonate alone and bicarbonate plus ranitidine series respectively. These differences were not significant. Twenty millilitres of 8.4% NaHCO3 cannot be recommended as a single dose antacid for emergency Caesarean section. Ranitidine plus bicarbonate is considered a reliable antacid regimen to ensure elevation of gastric pH to safe levels.     

Combination treatment with ranitidine and sodium bicarbonate prior to obstetric anaesthesia

The gastric pH and volume were measured in 175 patients undergoing elective, and 313 undergoing emergency, obstetric procedures. Ranitidine 150 mg was administered orally every 6 hours in labour and at least 2 hours before elective Caesarean section. Patients received 20 ml of 8.4% sodium bicarbonate orally immediately prior to induction of anaesthesia. The combination of ranitidine and sodium bicarbonate produced marked alkalinisation of gastric contents (mean pH 8.9). The administration of sodium bicarbonate pre-operatively in patients who received ranitidine less than 2 hours before operation led to satisfactory elevation of gastric pH. Only four patients had a gastric pH less than 2.5, one patient refused any medication, two received only ranitidine and one patient had a long interval from administration of bicarbonate to aspiration of gastric contents. Gastric volumes were high in labouring patients (mean 84 ml) despite administration of ranitidine. The effectiveness of sodium bicarbonate as a single dose antacid therapy prior to obstetric anaesthesia requires further study.     

USE OF I.M. RANITIDINE FOR THE PROPHYLAXIS OF ASPIRATION PNEUMONITIS IN OBSTETRICS

Twenty patients who underwent elective Caesarean section receivedranitidine 150 mg by mouth 8–14 h, and 50 mg i.m. 90 min,before surgery. Intraoperative gastric aspiration resulted incontents with a pH > 2.5 and volume < 25 ml in all patients(mean pH 6.5 (SD 0.8); mean volume 9.0 (SD 7.2) ml). Sixty patientsin labour, who received ranitidine 50 mg i.m. 6-hourly, underwentemergency surgery. Half of this group received, in addition,a single preinduction dose of either 15 or 30 ml of sodium citrate0.3 mol litre^-1. A further 30 patients who remained unmedicatedduring labour and required emergency surgery received a preinductiondose of 15 or 30 ml of sodium citrate 0.3 mol litre^-1 alone.Ranitidine medication resulted in a mean aspirated gastric volumeof 31.4 (26.6) ml and pH of 5.3 (2.1); five of 30 patients hada pH < 2.5. The addition of sodium citrate 0.3 mol litre^-1resulted in gastric pH > 2.5 in all patients and a mean gastricvolume of 43.2 (38.3) ml. The group who received only sodiumcitrate 0.3 mol litre^-1 had a mean pH of 5.3 (1.1) and a meanvolume 122.7 (98.2) ml.     

A comparison of omeprazole and ranitidine for prophylaxis against aspiration pneumonitis in emergency Caesarean section

One hundred and sixty-two Chinese women undergoing emergency Caesarean section were allocated at random on admission to the labour ward to receive one of three regimens for orally administered chemoprophylaxis against acid aspiration: ranitidine 150 mg 6 hourly with sodium citrate at induction of anaesthesia, omeprazole 40 mg 12 hourly with sodium citrate, or omeprazole 40 mg 12 hourly alone. Intragastric pH and volume were measured immediately after induction of anaesthesia. Ten patients (17%) in the omeprazole-only group, three (6%) in the omeprazole and citrate group and one (2%) in the ranitidine group had an intragastric pH less than 2.5 and volume greater than 25 ml (p less than 0.05). The use of sodium citrate resulted in higher intragastric pH but larger intragastric volumes (p less than 0.05). The sodium citrate and ranitidine regimen was the most cost-effective among the three.     

Ranitidine prophylaxis before anaesthesia in early pregnancy

Forty patients presenting for vaginal termination of pregnancy, divided randomly into four groups, received either no medication, sodium citrate 30 ml orally, ranitidine 150 mg orally or ranitidine 50 mg intravenously. During the procedure, gastric contents were removed by orogastric tube for volume and pH measurements. Ranitidine, orally and intravenously, significantly increased gastric pH and reduced gastric volume. In the control group only one pH was greater than 2.5. Sodium citrate raised the pH above 2.5 in 6 out of 10 patients. Fasting patients in the first months of pregnancy may be at risk of developing Mendelson's syndrome. Ranitidine is very effective in increasing gastric pH and at the same time reducing gastric volume in such patients.     

Comparison of the effect of two dose schedules of oral omeprazole with oral ranitidine on gastric aspirate pH and volume in patients undergoing elective surgery

We have compared gastric aspirate pH and volume at induction of anaesthesia in 222 patients who had received either omeprazole or ranitidine before elective operations. Omeprazole was given orally either as 40 mg on the evening before and 40 mg on the morning of surgery or as 80 mg on the morning of surgery. Ranitidine 150 mg was given orally on the evening before surgery and 2 h before anaesthesia. Treatment success was defined as aspirate pH > or = 2.5 and volume < 25 ml at induction of anaesthesia. Treatment was successful in 84% (95% confidence interval (CI) 73-91%) of patients in the omeprazole 40 + 40 mg group, 84% (95% CI 73-91%) in the ranitidine group and 73% (95% CI 61-83%) in the omeprazole 80 mg group. There were no statistically significant differences between the groups. Twelve patients in the omeprazole 80 mg group had gastric pH < 2.5 and four had volume > 25 ml. Only three patients had a gastric pH < 2.5 in the omeprazole 40 + 40 mg group and none had volume > 25 ml, which compared well with the ranitidine group. Omeprazole, given as 40 mg in the evening and 40 mg on the morning of operation, has a potential role for use in patients at risk for aspiration during general anaesthesia.      

Ranitidine as an antacid before elective Caesarean section

In a preliminary study, 20 women in labour received ranitidine 50 mg intravenously. No significant changes were seen in the height, frequency or amplitude of uterine contractions or in fetal heart rate or pattern. No neonatal problems attributable to ranitidine were found. Ranitidine crossed the placenta, the mean fetal-maternal ratio being 0.9. Levels in the infants 12 hours following delivery were all very low. Ranitidine 150 mg orally was given to 80 healthy women undergoing elective Caesarean section at varying times from 75 to 510 minutes pre-operatively. From 2 to 6 hours following ingestion, the pH of gastric contents was greater than 2.5 in all but one patient. The mean volume aspirated (8 ml) was significantly lower than in a control group receiving magnesium trisilicate (mean volume 30 ml). Neonatal assessment included Apgar scoring, neurobehavioural examination, feeding progress, measurement of acidity and culture of gastric aspirates. No significant differences between groups were found. Blood levels indicated that the oral drug is readily absorbed by the parturient and that a smaller proportion is transferred to the fetus, mean fetal-maternal ratio at delivery being 0.38.     

Antacid therapy for emergency Caesarean section

One hundred patients undergoing emergency Caesarean section were treated with cimetidine 200 mg intramuscularly when the decision was made to deliver the patient by Caesarean section and, preceding general anaesthesia, 30 ml of 0.3 M sodium citrate was administered orally. No routine antacid therapy was employed during labour. No patient had a gastric aspirate pH of less than 2.7, and only one of less than 3. The regimen is simple and effective, and treats only those patients at risk of acid aspiration.     

Gastric fluid volume and pH in elective surgical patients: triple prophylaxis is not superior to ranitidine alone

The effect of oral ranitidine alone was compared with sequentially administered ranitidine, metoclopramide, and sodium citrate on gastric fluid volume and pH in 196 healthy, elective surgical inpatients, each of whom was randomly assigned to one of four groups. Patients in all groups received oral ranitidine 150 mg 2-3 hr before the scheduled time of surgery. Those in Group 1 also received oral metoclopramide 10 mg one hour before surgery, and sodium citrate 0.3 M 30 ml on call to the operating room; Group 2 received sodium citrate but no metoclopramide; Group 3 received metoclopramide but no sodium citrate; Group 4 received ranitidine alone. Following induction of anaesthesia a #18 Salem sump tube was passed into the stomach and all available gastric fluid was aspirated. Volumes were recorded and pH measured. In all groups mean pH was greater than 5.8, although at least one patient in each group had pH less than 2.5. Mean volumes were significantly greater in patients who received citrate (Groups 1 and 2: 22 and 19 ml) than in those in those who did not (Groups 3 and 4: 10 and 8 ml). One patient in Group 2 and one in Group 3 had pH less than 2.5 with volume greater than 25 ml. Our results do not demonstrate any advantage of double or triple prophylaxis over ranitidine alone. The practical difficulty of correctly administering two or even three medications, each at different but exact preoperative intervals, is emphasized.     

A comparison of the effects of omeprazole and ranitidine on gastric secretion in women undergoing elective Caesarean section

This study compares the efficacy of omeprazole and ranitidine at reducing gastric secretion in obstetric patients. Sixty-five women scheduled to undergo elective Caesarean section under general anaesthesia were randomly allocated to receive either omeprazole 40 mg or ranitidine 150 mg orally at 2200 hours the night before and at 0600 hours on the morning of surgery. Intragastric pH and volume were measured immediately after induction of anaesthesia and on completion of surgery. All patients had gastric aspirates less than 25 ml. None of the omeprazole group had an aspirate of pH less than 3.5. Six patients (19%) in the ranitidine group had aspirates of pH less than 3.5, a significant difference from the omeprazole group (p less than 0.05). Of these six, two (6%) had aspirates of pH less than 2.5. Hence this study showed that omeprazole was more effective and consistent than ranitidine at maintaining gastric pH greater than 3.5.     

Intraoperative, direct and continuous measurement of stomach pH following pretreatment with ranitidine or sodium citrate

We carried out continuous direct pH measurements of gastric fluid in 49 female patients pretreated with 300 mg ranitidine by mouth on the evening prior to surgery and 150 mg by mouth before the operation. A further 51 women were pretreated with 30 ml sodium citrate shortly before admission to the operating room. Twenty patients received 30 ml sodium citrate via a separate gastric tube after the first pH measurement; 22 were given no premedication. In 95% of cases, 30 ml sodium citrate was found to increase the pH to over 3.5 within 5 min; a failure rate of 5% can therefore be expected. This can be explained mainly by the failure of sodium citrate to mix thoroughly with the gastric fluid. Pretreatment with ranitidine increased the pH to over 4.0 in every case, and the pH on extubation was still over 4.0 even after delayed pH on extubation was still over 4.0 even after delayed or prolonged operations. We recommend that 30 ml sodium citrate be given shortly before the beginning of emergency obstetric operations. However, we prefer ranitidine for elective operations in patients at risk for aspiration because it increases of the gastric fluid pH to at least 4.0 in every case.     

INFLUENCE OF PREOPERATIVE GASTRIC ASPIRATION ON THE VOLUME AND pH OF GASTRIC CONTENTS IN OBSTETRIC PATIENTS UNDERGOING CAESAREAN SECTION

Aspiration of gastric contents, the most common anaestheticcause of maternal mortality, is decreased by emptying of thestomach and the use of antacids and H₂-receptor antagonists.One hundred and eighty-three mothers presenting for emergencyCaesaren section were allocated to three groups. In group 1,the stomach was emptied before operation via an orogastric tubeand thereafter 30 ml of sodium citrate 0.3 mol litre^–1was ingested 5–15 min before induction of general anaesthesia(our usual practice). Group 2 received only 30 ml of sodiumcitrate 0.3 mol litre^–1. Group 3 received ranitidine 50mg i.v. before operation, 5–15 min before induction ofanaesthesia, in addition to sodium citrate. Our results showthat preoperative gastric emptying with an orogastric tube followedby sodium citrate is preferred if anaesthesia should be induced15–20 min later. However, the use of ranitidine and sodiumcitrate is preferred at subsequent times. Although our datashow that preoperative gastric emptying decreased the mean intragastricvolumes before Caesarean section, the number of patients atrisk of acid aspiration was not reduced. In view of these findingsand the unpleasantness of orogastric intubation, we suggestthat routine preoperative gastric aspiration via an orogastrictube is not justified, although the manoeuvre should still beused following a recent meal.     

Ranitidine and single-dose antacid therapy as prophylaxis against acid aspiration syndrome in obstetric practice

The efficacy of the non-particulate antacid 0.3 M sodium citrate in single and multiple dose regimes was investigated in 156 obstetric patients, both emergency and elective, who required operative delivery under general anaesthesia. Failure of either of these regimes to elevate the intragastric pH consistently to an acceptable level (greater than 3) led to investigation of a regime combining the histamine H2-receptor antagonist, ranitidine, and a single pre-anaesthetic dose of 0.3 M sodium citrate in a further 170 patients. Satisfactory pH values (greater than 3) were achieved in all patients studied. The results from the first 99 cases were analysed statistically by comparison with the multiple dose sodium citrate regime and showed a very significant improvement in the ranitidine group for intragastric pH and volume. No untoward side-effects were discovered in either mother or baby and the 6-hourly administration of ranitidine, which was easily complied with, had no effect on the progress of labour or operative delivery rate.     

Use of cimetidine as an oral antacid in obstetric anesthesia

The H2-receptor antagonist, cimetidine, was used instead of magnesium trisilicate BPC as routine antacid therapy before both elective and emergency obstetric anesthesia. Two trials of its efficacy in increasing intragastric pH and decreasing the volume of gastric contents in parturients are reported. In the first trial, 400 mg of cimetidine given orally to patients being delivered by elective cesarean section effectively decreased gastric acidity, providing induction of anesthesia occurred 90-150 min after its administration. Of 62 patients requiring emergency anesthesia during active labor and who had been treated with 200 mg of cimetidine orally at 2-h intervals, 80% had gastric contents with a pH higher than 2.5. Failure to decrease gastric acidity to this level was mainly due to anesthesia being required within 60 min of the loading dose, but it also was considered that inaccurate timing of repeat doses and possibly delay in uptake due to gastric stasis by narcotic analgesia played a part. In trial 2 the same cimetidine regimen plus a 15-ml oral dose of 0.3 M sodium citrate given 10 min before induction of anesthesia was studied. All 72 women delivered by elective cesarean section had a low volume of gastric contents with pH greater than 2.5. Only 4% of 135 patients requiring emergency anesthesia had gastric aspirates the pH of which was less than 2.5. The volume (97 +/- 8.4 ml) of gastric contents removed from the latter patients were considered to still pose a hazard at induction of general anesthesia. No maternal or infant side effects related to cimetidine therapy were noted.     

Effects of single-dose oral ranitidine and sodium citrate on gastric pH during and after general anaesthesia

The effects on gastric pH of the H₂-receptor antagonist ranitidine (R) with 0.3 molar (M) sodium citrate (SC) as an oral effervescent and those of plain SC were studied in 25 patients scheduled for elective surgery. Following induction of general anaesthesia, the gastric contents were evacuated via a nasogastric tube, and a pH electrode was placed in the stomach. Then, eight patients received R 300 mg plus SC dose (Group R300), ten received R 150 mg plus SC dose (Group R150), and seven received 50 ml SC alone (Group SC). The drugs were administered orally in a double-blind fashion, and the gastric pH was recorded continuously over a period of 24 hr. Mean (range) baseline pH values were 1.2 (0.8–1.8), 1.3 (1.0–1.8), and 1.2 (0.9–1.6) in the R300, R150, and SC groups, respectively (P = NS among groups). These values increased to 7.0 (6.2–7.5), 6.9 (6.3–7.3), and 4.9 (1.9–7.3), respectively, at emergence from anaesthesia (P < 0.05 for R300 vs SC and R150 vs SC). Two minutes after administration of R300 and R150, a mean (range) gastric pH of 6.8 (5.8–7.5), and 5.6 (1.2–7.0), respectively, was reached, and remained above 2.5 for 14 hr (P = NS). Plain SC increased the gastric pH within two minutes to a mean of 6.8 (6.7–7.0), and maintained it above 2.5 for six hours (P < 0.05 for R300 vs SC at 8, 10, 12, and 14 hr after induction). We conclude that both the combination of R plus SC, and SC alone are rapidly effective in neutralizing gastric acid when administered orally after induction of anaesthesia. However, the effectiveness of plain SC is shorter-lived, and if maintenance of gastric pH above 2.5 for longer than six hours is needed, the R plus SC combination should be administered.     

Ranitidine suspension or famotidine resoriblette and gastric fluid volume and pH

We studied the effect of two new formulations of H₂-receptor antagonists on gastric fluid pH and volume. Forty-five healthy, elective adult in-patients in three study groups, 15 in each, were premedicated using oral diazepam 10 mg with 100 ml of a dose of water soluble suspension of ranitidine 300 mg with sodium citrate/bicarbonate, or a resoriblette of famotidine 40 mg, or placebo. Gastric fluid samples were obtained by blind aspiration after anaesthesia induction, 50–70 min from premedication, and again 90 min from premedication. After a mean period of 60 min from ingestion the patients medicated with H₂-antagonists had higher gastric juice pH than those in the control group (1.5 (1.1–6.3), median (range)) (P < 0.0001) for ranitidine (6.8 (4.1–7.8)), P< 0.01 for famotidine (3.9 (1.5–7.6)); P < 0.05 ranitidine vs famotidine). Recovered volumes were similar for the groups (median 3–4 ml, range 0–50 ml). None of the H₂ patients had pH < 3.5 and volume ≥0.3 ml · kg^?1 (P<0.05 vs placebo). In second aspirations, taken 90 min from premedication, the group differences from control in pH persisted. Famotidine patients had the lowest volumes (P < 0.05 vs controls); yet one famotidine patient had a pH < 2.5 and volume ≥ 0.3 ml · kg^?1. It is concluded that, at the moment of oral anxiolytic premedication, ranitidine-buffer suspension effectively reduced gastric juice acidity, whereas famotidine resoriblette failed to increase reliably gastric pH in 50–90 min.     

The effect of magnesium trisilicate mixture, metoclopramide and ranitidine on gastric pH, volume and serum gastrin

Eighty women (40 for elective Caesarean section and 40 for elective gynaecological surgery) were randomly assigned to one of five treatment groups and received pre-operatively either no medication; magnesium trisilicate mixture (BP) 30 ml; metoclopramide 10 mg intramuscularly; ranitidine 150 mg orally on the night prior to, and the morning of, surgery; or metoclopramide 10 mg intramuscularly in combination with oral ranitidine 150 mg (the latter again given on the night prior, and the morning, of surgery). The effect of these medications on intragastric pH, volume and serum gastrin-17 was measured. No patient receiving ranitidine had a pH of less than 4. Magnesium trisilicate mixture resulted in the largest intragastric pH change although one woman in this group had a pH of 1.7. The largest intragastric volumes were seen in the patients who had received magnesium trisilicate mixture, whilst the patients who had received metoclopramide in combination with ranitidine had the smallest intragastric volumes. Magnesium trisilicate mixture and metoclopramide resulted in no change in serum gastrin levels. However, in the subjects who had received ranitidine on the night prior to surgery, the fasting serum gastrin was significantly higher (p less than 0.01) than the values in the remaining subjects, the mean (SEM) values being 60.3 (6.3) pg/ml in those not receiving ranitidine and 111.3 (19.5) pg/ml in those who had been given ranitidine.     

The Effect of Sodium Citrate on the pH and the Amount of Gastric Contents Before General Anaesthesia

Sixty patients were prospectively studied with respect to the volume and pH of their gastric contents after allocation to one of three preoperative treatments. All patients received diazepam (Apozepam) 5 mg the night before operation and 10 mg at 06.30 on the morning of operation. One group received sodium citrate solution 50 ml perorally at 06.30, 75-370 min before operation. A second group received water 50 ml perorally at 06.30, 100-405 min before operation. The third group received 50 ml water at 06.30 and 50 ml sodium citrate solution perorally just before admission to the operation theatre, 15-50 min before aspiration. Statistical analysis showed elevated pH and volume of gastric contents in the group receiving water in the morning and sodium citrate solution just before admission to the operating theatre immediately after induction of anaesthesia. There was no statistically significant difference of pH and aspirated volume between the group receiving water and the group receiving sodium citrate at 06.30.     

Dose-response effects of intravenous ranitidine on gastric pH and volume in outpatients

The dose-response effects of intravenous ranitidine given 45 min to 5 h earlier on gastric pH and volume were evaluated in six groups of 25 outpatients, each undergoing elective surgery under general anesthesia. Patients in Group 1 received no ranitidine and served as controls. Patients in Groups 2-6 received ranitidine intravenously in incremental doses of 0.5 mg X kg-1 body weight from 0.5 mg to 2.5 mg (Group 2, 0.5 mg; Group 3, 1.0 mg; Group 4, 1.5 mg; Group 5, 2.0 mg; and Group 6, 2.5 mg). Ninety-six per cent of patients in the control group (Group 1) had gastric pH less than or equal to 2.5 while 36% of the patients had gastric content volumes greater than or equal to 25 ml with pH less than or equal to 2.5. Ranitidine, in incremental doses of 05.-2.5 mg X kg-1 body weight, caused a significant reduction of gastric acidity and volume. The ED50 of ranitidine producing a gastric pH greater than 2.5 was 0.36 mg X kg-1, and the ED95 was 0.98 mg X kg-1 body weight. The ED95 of ranitidine producing a gastric volume less than 25 ml was 1.96 mg X kg-1. At the dose of 1.5 mg X kg-1 of ranitidine, 100% of the patients had gastric contents with pH greater than 2.5. The proportion of patients with volume less than 25 ml was 68% with ranitidine, 0.5 mg X kg-1, and gradually increased to 100% with 2.5 mg X kg-1 body weight.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacologic prevention of Mendelson syndrome. A controlled clinical trial]

This controlled study considers the effect of ranitidine, both alone and in association with metoclopramide, on the acidity and volume of the gastric content of 75 patients requiring caesarean section. Ranitidine, when used alone (50 mg intravenously 30-60 minutes before the operation) significantly reduced (p less than 0.01) the acidity (pH greater than 2.5) and the volume (less than 25 ml) of the gastric content of the patient thus treated. Ranitidine in association with metoclopramide may also reduce the pH and the volume, but did not show any significant statistical differences when compared with the use of ranitidine alone.