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

Gastroesophageal reflux and aspiration of gastric contents in anesthetic practice

General anesthesia may predispose patients to aspiration of gastroesophageal contents because of depression of protective reflexes during loss of consciousness. In addition, some patients may be at increased risk of pulmonary aspiration because of retention of gastric contents caused by pain, inadequate starvation, or gastrointestinal pathology resulting in reduced gastric emptying and gastroesophageal reflux. Despite increasing knowledge of the problems associated with aspiration, the relatively small incidence and associated mortality rates in the perioperative period do not appear to have changed markedly over the last few decades. In this review article, the physiological factors associated with an increased risk of gastroesophageal reflux and aspiration are considered together with some of the methods that are used to prevent aspiration. In particular, preoperative starvation, the use of drugs designed to increase gastric pH, recent developments in airway devices, and appropriate application of cricoid pressure are critically appraised.

Preoperative fluid restrictions: hospital policy and clinical practice

This study examined the practice of preoperative fluid restrictions and the influence of the hospital 'nil by mouth' policy on clinical practice. Structured interviews were used to assess the knowledge of nurses and anaesthetists relating to current hospital policy, their attitudes to fluid fasting and the constituents of clear fluids. The interval between the last intake of fluid and the induction of anaesthesia was measured in 90 adult patients to determine actual periods of fasting. It was found that most patients on the same operating list commenced fasting simultaneously with little or no attempt made to individualize the timing which contributed to prolonged periods without fluids, ranging from 3 hours 30 minutes to 17 hours and 45 minutes. Only 30% of nurses were aware of the hospital policy compared with 75% of anaesthetists. The evidence from this study demonstrated that the hospital policy was not reflected in clinical practice which continued to be based on tradition.

Anesthesia for office endoscopy

A trend is emerging in the United States whereby surgical procedures are gradually migrating to less complex environments. The demands of cost containment, pressures to limit unnecessary time delays, and desires for increased control have all conspired to promote ambulatory surgicenters, minor procedure center, and office surgical suites. Concomitant with this shift is a differing attitude toward anesthesia, with an increasing number of procedures using alternatives to general anesthesia, such as regional blocks and conscious sedation.

Changing preoperative fasting policies. Impact of a national consensus

BACKGROUND

Liberalisation of preoperative fasting rules has been discussed and recommended in the anaesthesia literature in recent years. In Norway, a national consensus on this issue was reached in 1993. The aim of the present study was to investigate whether a national consensus on fasting recommendations led to a change in fasting policies in Norwegian anaesthesia departments.

METHODS

A questionnaire on preoperative fasting routines was sent to all Norwegian anaesthesia departments in 1993 and repeated in 1996.

RESULTS

Written local guidelines for preoperative fasting were present in 85% of the institutions in both surveys. Of the hospitals, 69% had changed their local guidelines after the national consensus. In 1996 more hospitals allowed less than 6 h fasting for clear liquids in children (93% versus 71% in 1993; P < 0.005). A similar tendency was noted in adults (79% versus 63% in 1993; P = 0.1). In contradiction to the national guidelines, 31% of the departments reported that they allowed less than 6 h fasting after a light breakfast in the morning of surgery in 1996. The corresponding number for 1993 was 21% (ns).

CONCLUSION

The new, consensus-based national fasting guidelines have been associated with a change towards more liberal fasting policies in Norwegian departments of anaesthesia. However, as not all local changes were supported by the national consensus, other sources of information were used when local policies were decided.

Perioperative thirst: a patient perspective

Many institutions continue to require surgery patients to take nothing by mouth after midnight despite current research that supports allowing most patients to drink fluids up to 3 hours before surgery. This study of 50 elective surgery patients describes their perceptions of discomfort caused by thirst. Results show that thirst caused significantly more discomfort to the patient than not being able to eat or sleep or worrying about the surgery itself. Given these results, nurses are urged to work within their institutions to change the current practice regarding preoperative fluid restriction.

Fasting before and after ambulatory surgery

During the last decade, questions about the length of time patients were required to fast before elective operations, as well as when they should resume oral fluids after an outpatient operation, became important issues in anesthesia and surgical practice. This review analyzes reasons for the traditional fasting guidelines and presents recent evidence that has caused rethinking in the guidelines. Current recommendations regarding both the presurgical fasting guidelines and fluid intake requirements for discharge after outpatient surgery are outlined.

Day ophthalmic surgery: aspects of perioperative care

At Flinders Medical Centre in Adelaide, eye surgery under local anaesthesia (peribulbar block) has been carried out in the day ophthalmic surgery unit since 1987. In a subset of 536 patients, 112 patients required additional anaesthesia (supplementary retrobulbar block or regional muscle infiltration) to achieve full ocular paresis, and 10 patients required intraoperative supplementation of anaesthesia because of discomfort. Six patients had their surgery postponed (one had a retrobulbar haemorrhage and five became anxious after the procedure commenced). Sedation was rarely required and there were no adverse effects of the anaesthetic on surgical procedures or patients' vision. The authors conclude that peribulbar block provides satisfactory anaesthesia and that day ophthalmic surgery is safe and effective.

Fasting guidelines in different countries

Abstention from food and drink prior to anaesthesia remains a cornerstone in safe practice. Despite the lack of scientific support, previous guidelines, similar for fluids and solids, have for more than three decades more often than not recommended "nil by mouth" ("nothing-per-os"; "NPO" in the US) after midnight or a fixed duration of time. Based on an increased number of studies of relevance to the duration of preoperative fasting, reviews on this subject concerning both adults (1) and children (2) and a large number of editorials (3-7), have recently been published. Since there may be a discrepancy between conclusions based on scientific studies and the current routine practice-this presentation is intended to survey the current recommendations in different countries and how they relate to publications on the subject. Opinions are mainly derived from officers of associations linked to The World Federation for Anaesthesiologists (WFSA) and from current literature.

Preoperative gastric emptying. Effects of anxiety and oral carbohydrate administration

BACKGROUND

Overnight fasting is routine before elective surgery. This may not be the optimal way to prepare for surgical stress, however, because intravenous carbohydrate supplementation instead of fasting has recently been shown to reduce postoperative insulin resistance. In the current study, gastric emptying of a carbohydrate-rich drink was investigated before elective surgery and in a control situation.

METHODS

Twelve patients scheduled for elective surgery were randomly given 400 mL of either a carbohydrate-rich drink (285 mOsm/kg, 12.0% carbohydrates, n = 6) or water 4 hours before being anesthetized. Gastric emptying was measured (gamma camera, 99Tcm). Each patient repeated the protocol postoperatively as a control. All values were presented as the mean +/- SEM by means of a nonparametric statistical evaluation.

RESULTS

Despite the increased anxiety experienced by patients before surgery (p < 0.005), gastric emptying did not differ between the experimental and control situations. Initially, water emptied more rapidly than carbohydrate. However, after 90 minutes, the stomach was emptied regardless of the solution administered (3.2 +/- 1.1% [mean +/- SEM] remaining in the stomach in the carbohydrate group versus 2.3 +/- 1.2% remaining in the stomach in the water group).

CONCLUSIONS

Preoperative anxiety does not prolong gastric emptying. The stomach had been emptied 90 minutes after ingestion of both the carbohydrate-rick drink and water, thereby indicating the possibility of allowing an intake of iso-osmolar carbohydrate-rich fluids before surgery.

Gastric fluid volume and pH after nizatidine in adults undergoing elective surgery: influence of timing and dose

We conducted a prospective, randomized, double-blind study to investigate the effect of oral nizatidine (150-600 mg), a new potent H2 antagonist, on preoperative gastric fluid pH and volume in adults undergoing elective surgery. One hundred and seventy-five healthy adults (21-68 yr) were randomly allocated to seven treatment groups (n = 25); Placebo was administered at 21:00 and 06:30 the night before and on the day of surgery, respectively (0/0: control); nizatidine 150 mg at 21:00 and placebo at 06:30 (150/0); placebo at 21:00 and nizatidine 150 mg at 06:30 (0/150); nizatidine 150 mg at 21:00 and 06:30 (150/150); nizatidine 300 mg at 21:00 and placebo at 06:30 (300/0); placebo at 21:00 and nizatidine 300 mg at 06:30 (0/300); and nizatidine 300 mg at 21:00 and 06:30 (300/300). Each patient fasted overnight and took the drug and/or placebo with 20 ml water. After induction of anaesthesia, the pH and volume of gastric fluid obtained through an orogastric tube were measured. The mean pH of 0/150, 150/150, 300/0, 0/300, and 300/300 groups was higher than that of the control group (P < 0.05). Gastric volume in these groups was smaller than in the control (P < 0.05). The 150/0 group failed to decrease gastric fluid volume and increase pH. In the 300/0 group, the gastric pH was lower than other regimens which effectively decreased gastric acidity (P < 0.05). The number of patients with a pH < 2.5 and a volume > 0.4 ml.kg-1 in the 0/150, 150/150, 0/300, and 300/300 groups (0%) was less than in the control group (16%) (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Modification of the diuretic and natriuretic effects of a dopamine infusion by fluid loading in preoperative cardiac surgical patients

An intravenous infusion of dopamine at 2.5 microgram/kg/min was administered for 40 minutes to anesthetized cardiac surgical patients, and their renal function was measured. Five patients had the usual preoperative regimen of reduced fluid intake for the night and morning before surgery (nonhydrated), and five patients received normal saline, 2 mL/kg/hr intravenously, for 6 hours before anesthesia (hydrated). Renal function (measured by urine output, sodium excretion, free water clearance, and fractional excretion of sodium) was similar immediately before starting the dopamine infusion. All four variables were significantly higher in the hydrated group after 10 minutes; this difference becoming maximal after 40 minutes. Twenty minutes after stopping the dopamine infusion, renal function was similar in the two groups. This study indicates that preoperatively fluid-restricted patients demonstrate powerful salt and water conservation with reduced natriuretic and diuretic responses to a low-dose dopamine infusion when compared with hydrated patients. Patients with adequate fluid loading and intravascular volume will demonstrate a marked natriuresis and diuresis in response to low-dose dopamine infusion.

The effect of pre-operative oral fluids on morbidity following anaesthesia for minor surgery

Postoperative morbidity and serum osmolality were studied in 46 patients who were encouraged to drink water until 3 h pre-operatively and 49 receiving the normal fasting regimen prior to minor surgery. There was significantly less thirst in the postoperative period in those patients allowed to drink and subjectively better recovery than after previous anaesthesia. There was no morbidity from ingestion of up to 11 of water 2.5 h pre-operatively. Although there was only a moderate improvement in postoperative recovery we feel that allowing patients to drink water pre-operatively improves patient comfort, especially since patients may have to fast for much longer than guidelines recommend, simply because of the traditional organisation of operating lists.

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.