Children's outcomes and parents' preferences for the induction and maintenance of anaesthesia for day-case surgery

Focal points

Clinical and economic choices in anaesthesia for day surgery: a prospective randomised controlled trial

We compared the cost-effectiveness of general anaesthetic agents in adult and paediatric day surgery populations. We randomly assigned 1063 adult and 322 paediatric elective patients to one of four (adult) or two (paediatric) anaesthesia groups. Total costs were calculated from individual patient resource use to 7 days post discharge. Incremental cost-effectiveness ratios were expressed as cost per episode of postoperative nausea and vomiting (PONV) avoided. In adults, variable secondary care costs were higher for propofol induction and propofol maintenance (propofol/propofol; p < 0.01) than other groups and lower in propofol induction and isoflurane maintenance (propofol/isoflurane; p < 0.01). In both studies, predischarge PONV was higher if sevoflurane/sevoflurane (p < 0.01) was used compared with use of propofol for induction. In both studies, there was no difference in postdischarge outcomes at Day 7. Sevoflurane/sevoflurane was more costly with higher PONV rates in both studies. In adults, the cost per extra episode of PONV avoided was pound 296 (propofol/propofol vs. propofol/ sevoflurane) and pound 333 (propofol/sevoflurane vs. propofol/isoflurane).

Anaesthesia for day case surgery: a survey of adult clinical practice in the UK

BACKGROUND AND OBJECTIVE

In October 2000, we conducted a national postal survey of consultant day case anaesthetists in the UK to explore the range and variation in the practice of anaesthetizing a patient for day case surgery (paediatrics, urology and orthopaedics). The survey was carried out as part of a larger study that comprised a major two-centre randomized controlled trial designed to investigate the costs and outcome of several anaesthetic techniques during day care surgery in paediatric and adult patients (cost-effectiveness study of anaesthesia in day case surgery). We report the findings of this national survey of adult urology and orthopaedic day case anaesthetic practice in the UK.

METHODS

The survey used a structured postal questionnaire and collected data on the duration of the surgical procedure; the use of premedication; the anaesthetic agents used for induction and maintenance; the fresh gas flows used for anaesthesia; the use of antiemetics; and the administration of local anaesthesia and analgesia.

RESULTS

The overall response rate for the survey was 74% (63% for urology, 67% for orthopaedics). The survey indicated the following practice in adult urology and adult orthopaedic day case surgery: 6 and 12% used premedication; propofol was the preferred induction agent (96 and 97%) and isoflurane the preferred maintenance agent (56 and 58%); 32 and 41% used prophylactic antiemetics; 86 and 93% used a laryngeal mask.

CONCLUSIONS

This survey identifies the variation in current clinical practice in adult day surgery anaesthesia in the UK and discusses this variation in the context of current published evidence.

Propofol and halothane versus sevoflurane in paediatric day-case surgery: induction and recovery characteristics

BACKGROUND

The aim of this study was to compare the induction and recovery characteristics associated with propofol induction and halothane maintenance with sevoflurane anaesthesia in paediatric day surgery.

METHODS

In total, 322 children were assigned randomly to i.v. propofol induction and halothane/nitrous oxide maintenance or sevoflurane/nitrous oxide alone. The patients' age, sex, and type of surgery were recorded, as were the times required for anaesthetic induction, maintenance, recovery and time to discharge home. Postoperative nausea and vomiting, and the incidence of adverse events during induction and recovery were also noted.

RESULTS

No significant differences were detected in age, sex, type of surgery performed or intraoperative opioid administration. Excitatory movement was more common during induction with sevoflurane. The mean time required for induction with propofol was 3.1 min compared with 5 min in the sevoflurane group (P<0.001). The recovery time was shorter in the sevoflurane group compared with propofol/halothane (23.2 vs 26.4 min, P<0.002). The incidence of delirium in recovery was greater in the sevoflurane group (P<0.001). There was no difference between groups in the time spent on the postoperative ward before discharge home. On the postoperative ward the incidence of both nausea and vomiting was significantly higher in the sevoflurane group (P=0.034). Five children were admitted to hospital overnight, none for anaesthetic reasons.

CONCLUSIONS

The increased incidence of adverse events during induction, postoperative nausea and vomiting and postoperative delirium in the sevoflurane group suggests that sevoflurane is not ideal as a sole agent for paediatric day case anaesthesia.

Anaesthesia for day case surgery: a survey of paediatric clinical practice in the UK

BACKGROUND AND OBJECTIVE

In October 2000, we conducted a national postal survey of day case consultant anaesthetists in the UK to explore the range and variation in practice of anaesthetizing a patient for day case surgery (paediatrics, urology and orthopaedics). This paper reports the findings of this national survey of paediatric day case anaesthetic practice carried out as part of a major two-centre randomized controlled trial designed to investigate the costs and outcome of several anaesthetic techniques during day care surgery in paediatric and adult patients (cost-effectiveness study of anaesthesia in day case surgery).

METHODS

The survey used a structured postal questionnaire and collected data on the duration of surgical procedure; the use of premedication; the anaesthetic agents used for induction and maintenance; the fresh gas flow rates used for general anaesthesia; the use of antiemetics; and the administration of local anaesthesia and analgesia.

RESULTS

The overall response rate for the survey was 74 and 63% for the paediatric section of the survey. Respondents indicated that 19% used premedication, 63% used propofol for induction, 54% used isoflurane for maintenance, 24% used prophylactic antiemetics and 85%, used a laryngeal mask. The findings of this national survey are discussed and compared with published evidence.

CONCLUSIONS

This survey identifies the variation in clinical practice in paediatric day surgery anaesthesia in the UK.

Anaesthetic agents in adult day case surgery

This study reports a review of all comparative published studies of adult day case anaesthesia in the English language up to December 2000. Ten databases were searched using appropriate keywords and data were extracted in a standardized fashion. One hundred-and-one published studies were examined. Recovery measurements were grouped as early, intermediate, late, psychomotor and adverse effects. With respect to induction of anaesthesia, propofol was superior to methohexital, etomidate and thiopental, but equal to sevoflurane and desflurane. Desflurane and sevoflurane were both superior to thiopental. There was no detectable difference between sevoflurane and isoflurane. With respect to the maintenance of anaesthesia, isoflurane and halothane were the worst. There were no significant differences between propofol, desflurane, sevoflurane and enflurane. Propofol is the induction agent of choice in day case patients. The use of a propofol infusion and avoidance of nitrous oxide may help to reduce postoperative nausea and vomiting.

Anaesthetic agents in paediatric day case surgery: do they affect outcome?

Both the numbers of children undergoing day case surgery and the type of procedures performed in this way are increasing. This expansion will only be beneficial if anaesthesia and surgery are provided with minimal post-operative morbidity e.g. postoperative delirium or nausea and vomiting. The choice of anaesthetic technique is considered critical to optimizing the service provided to patients and for this reason much research has addressed this question. This review considers the effect of anaesthetic technique on postoperative outcome in paediatric day case surgery. The outcome measures reviewed by this article are induction of anaesthesia, effects on the cardiovascular system, recovery from anaesthesia and postoperative nausea and vomiting. In each section both quantitative and qualitative outcome measures are discussed. Comparisons are made between sevoflurane and halothane, sevoflurane and propofol, propofol and halothane, desflurane and halothane and the presence or absence of nitrous oxide.

The new neuromuscular blocking agents: do they offer any advantages?

The pharmacodynamics and pharmacokinetics of the two most recent aminosteroid neuromuscular blocking drugs to become available, rapacuronium bromide (Org 9487) and rocuronium bromide are reviewed. Two new classes of drug with neuromuscular blocking properties, the bis-tetrahydroisoquinolinium chlorofumarates and the tropinyl diester derivatives are introduced. Comparisons between these drugs and mivacurium and cisatracurium are made. Rapacuronium 1.5 mg kg(-1) (ED95 1 mg kg(-1)), produces maximal neuromuscular block in 54 s. Time to recovery of the train-of-four ratio to 0.7 is achieved within 20 min after neostigmiine 0.05 mg kg(-1) given at 2 min. The plasma clearance of rapacuronium is 7-8 ml kg(-1) min(-1). Rapacuronium undergoes hepatic metabolism: no prolongation of effect has been reported after a single bolus or a short infusion in patients with hepatic or renal failure. Org 9488 is the 3-desacetyl metabolite of rapacuronium, which has neuromuscular blocking properties. Its much lower clearance (1.28 ml kg(-1) min(-1)) and plasma equilibration constant (0.105 min(-1)) may limit the prolonged use of rapacuronium. Rocuronium given at 2xED95 produces maximal neuromuscular block in 1 min. Spontaneous recovery of the train-of-four ratio to 0.7 takes over 40 min. Rocuronium has a plasma clearance of 4 ml kg(-1) min(-1). Its pharmacodynamics are altered in hepatic and renal disease. A number of anaphylactoid reactions to rocuronium have been reported recently. The bis-tetrahydroisoquinolinium chlorofumarate GW280430A has an ED95 of 0.19 mg kg(-1). Given at three times this dose, onset of neuromuscular block occurs within 100 s; the duration of block is 8-9 min. Following a 2 h infusion, the recovery index does not seem to be increased. Early studies suggest that this drug has no adverse cardiovascular or respiratory side-effects. The tropinyl diester derivative G-1-64 will produce 80-90% neuromuscular block in less than 2 min using 3xED80. Ninety per cent recovery of the first twitch of the train-of-four occurs after 5-7 min using one ED80. A recovery index of less than 2 min has been reported in rats. All the tropinyl diesters appear to produce vagal block.

A survey of epidural technique and accidental dural puncture rates among obstetric anaesthetists

Five hundred UK obstetric anaesthetists were surveyed to investigate retrospectively the relationship between experience, rotation of the epidural needle within the epidural space, choice of loss-of-resistance agent and accidental dural puncture (ADP) rate. Responses were received from 390 (78%) of the members surveyed. Anaesthetists with more than 15 years' experience are more likely to perform an epidural with the patient in the lateral position (P < 0.001), use loss-of-resistance to air to detect the epidural space (P < 0.001) and rotate the epidural needle after identifying the epidural space (P = 0.001) when compared to those of less experience. A reduced inadvertent dural puncture rate was found to be associated with increased frequency of performing the procedure (P = 0.012), greater experience of the practitioner (P = 0.049) and non-rotation of the epidural needle (P = 0.023). There are three components that can alter from case to case; patient positioning, loss-of-resistance agent and needle rotation. Loss-of-resistance agent and patient positioning in isolation did not significantly influence ADP rate. This study suggests that the combination of practising lateral patient positioning, loss-of-resistance to saline and non-rotation of the epidural needle significantly reduces ADP rate (P = 0.035).

Inhalational versus intravenous induction. A survey of emergency anaesthetic practice in the United Kingdom

A survey was constructed to ascertain the views of The Royal College of Anaesthetists tutors regarding the acceptability of inhalational induction with sevoflurane for emergency anaesthesia. A questionnaire was sent to all tutors asking them to indicate their preferred choice of anaesthetic technique, and whether they believed inhalation induction with sevoflurane to be acceptable, in each of four scenarios: acute epiglottis; bleeding after tonsillectomy; appendicitis; and laparotomy in the shocked patient. Two hundred and sixty-two (89%) completed questionnaires were received from 294 college tutors. We have shown that the majority of The Royal College of Anaesthetists tutors would use sevoflurane for patients with an acutely compromised airway. One in four college tutors would accept the use of sevoflurane for a shocked patient for laparotomy. Anaesthetists who manage critically ill patients with an inhalational induction should be reassured by the fact, that a significant proportion of their colleagues would find this technique acceptable.

Apolipoprotein A-I in bile inhibits cholesterol crystallization and modifies transcellular lipid transfer through cultured human gall-bladder epithelial cells

BACKGROUND

Apolipoprotein A-I (Apo A-I), conventionally purified by several steps including organic solvent-delipidation from plasma, inhibits cholesterol crystallization in bile. To observe a significant effect in vitro, however, supraphysiological concentrations above 100 microg/mL are required. For this reason, this protein has not been considered to play a physiological role in vivo. In the present study, we examined the cholesterol crystal growth-inhibiting effect of biliary Apo A-I at its physiological concentration, the modification of transcellular transfer of biliary lipids through cultured human gall-bladder epithelial cells (GBEC) by Apo A-I at its physiological concentration and the binding and secretion of Apo A-I by GBEC.

METHODS AND RESULTS

We purified biliary Apo A-I to near homogeneity using immobilized artificial membrane chromatography. At 5 microg/mL, biliary Apo A-I reduced cholesterol crystal mass by 50%, whereas plasma-derived, solvent-delipidated Apo A-I had no effect. Using an antibody-capture enzyme-linked immunosorbent assay, we found reduced Apo A-I concentrations in bile samples from gallstone patients when compared with bile samples from gallstone-free controls (medians, 2.35 and 9.4 microg/mL, respectively). In a GBEC line, Apo A-I (5 microg/mL) enhanced transfer of phospholipid and cholesterol from the mucosal to the serosal side of cell monolayers by approximately 50%. These cells appear to bind Apo A-I reversibly in a dose- and time-dependent manner, compatible with receptor-type binding. Cultured human gall-bladder epithelial cells also showed basal secretion of Apo A-I, which was greatly increased by exposure to model bile solutions.

CONCLUSIONS

Apolipoprotein A-I in bile, thus, has both a direct effect on cholesterol crystal formation and enhances lipid removal from gall-bladder bile by GBEC. This effect may be specific and receptor mediated. These observations support two separate roles for human biliary Apo A-I and suggest that this protein may be important in preventing the formation of cholesterol crystals (the initial step in gallstone formation) in supersaturated bile.

Diffusion behavior of lipid vesicles in entangled polymer solutions

Dynamic light scattering was used to follow the tracer diffusion of phospholipid/cholesterol vesicles in aqueous polyacrylamide solutions and compared with the diffusive behavior of polystyrene (PS) latex spheres of comparable diameters. Over the range of the matrix concentration examined (Cp = 0.1-10 mg/ml), the diffusivities of the PS spheres and the large multilamellar vesicles exhibited the Stokes-Einstein (SE) relation, while the diffusivity of the unilamellar vesicles did not follow the increase of the solution's viscosity caused by the presence of the matrix molecules. The difference between the diffusion behaviors of unilamellar vesicles and hard PS spheres of similar size is possibly due to the flexibility of the lipid bilayer of the vesicles. The unilamellar vesicles are capable of changing their shape to move through the entangled polymer solution so that the hindrance to their diffusion due to the presence of the polymer chains is reduced, while the rigid PS spheres have little flexibility and they encounter greater resistance. The multilamellar vesicles are less flexible, thus their diffusion is similar to the hard PS spheres of similar diameter.

Effect of NSAIDs on gallbladder bile composition

Secretion of gallbladder mucin is an important step in gallstone pathogenesis. Previous studies have demonstrated that aspirin and other nonsteroidal antiinflammatory drugs (NSAIDs) can both inhibit gallbladder mucin secretion and prevent gallstone formation in animal models of cholesterol gallstone disease. The present study was performed to determine if chronic NSAID use was associated with a reduction in the mucin content or affected the lipid components of human gallbladder bile. Four groups of patients were identified retrospectively from a cohort of 230 morbidly obese patients who underwent gastric bypass surgery. The index group consisted of 18 patients who were found to have gallstones at gastric bypass surgery and had a history of chronic NSAID use. Three other patient groups were identified from the cohort by matching this index population for sex, race, and age according to the following criteria: (1) patients with gallstones who had not utilized NSAIDs, (2) patients without gallstones but with chronic NSAID use, and (3) patients without gallstones and without a history of NSAID use. Gallbladder bile was obtained from all patients by direct aspiration from the gallbladder at the time of surgery. Patients with gallstones had a significantly (P < 0.02) greater concentration of gallbladder mucin in their gallbladder bile compared to patients without gallstones (0.897 +/- 0.226 vs 0.173 +/- 0.039 mg/ml). Among gallstone patients, gallbladder mucin was reduced in those patients with a history of chronic NSAID use (1.18 +/- 0.43 vs 0.74 +/- 0.19 mg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Hypercalcemia decreases bile flow and increases biliary calcium in the prairie dog

BACKGROUND

Biliary calcium is known to play an important role in the pathogenesis of gallstones. Calcium salts are present in all pigment gallstones and are also present in the core of most, if not all, cholesterol gallstones.

METHODS

The effects of acute hypercalcemia on bile flow and biliary calcium secretion were examined in 22 prairie dogs during intravenous taurocholate infusion (0, 1.0, 2.25, and 4.5 mumol/kg/min).

RESULTS

Bile flow was linearly correlated with bile acid output in both control (y = 7.62x + 13.5, r = 0.98) and hypercalcemic (y = 7.00x + 10.4, r = 0.96) animals. At lower bile acid outputs (< 3.0 mumol/kg/min), biliary ionized calcium output per increment bile acid output was significantly increased in hypercalcemic animals (0.016 versus 0.011 mumol Ca++ mumol taurocholate, p < 0.001). Bile ionized calcium concentrations approximated Gibbs-Donnan predicted values only at low bile flow rate.

CONCLUSIONS

Hypercalcemia decreases bile flow and increases biliary ionized calcium concentration in the prairie dog. These effects favor the precipitation of calcium salts in bile.

Premicellar taurocholate enhances calcium uptake from all regions of rat small intestine

BACKGROUND/AIMS

The specific components of bile, which is necessary for normal calcium absorption, are unknown. We have previously shown that Ca2+ is bound with high affinity by premicellar taurocholate. The current studies examined the effects of taurocholate on intestinal calcium transport.

METHODS

Intestinal Ca2+ uptakes were measured from proximal, mid, and distal small intestinal segments perfused with solutions containing 45CaCl2 (0.1-1 mmol/L), taurocholate (0-10 mmol/L), trihydroxymethylaminomethane buffer (pH 7), phenolsulfonpthalein (nonabsorbable marker), and NaCl (total ionic strength, 0.16 mol/L) for four randomized perfusion periods. In other studies, the proximal small intestine was divided into two equal segments and perfused with either 45CaCl2 or 45CaCl2 plus taurocholate (2.5-5 mmol/L). Calcium absorption was measured from the difference in uptake and calcium concentration retained in mucosa. Finally, effects of taurocholate on Ca2+ uptake across isolated brush border membrane vesicles were measured.

RESULTS

Premicellar taurocholate produced an approximately 1.7-2-fold enhancement (P < 0.01) in Ca2+ uptake in all regions, with lesser contributions from micellar taurocholate. These effects resulted in a net increase in calcium absorption. Premicellar taurocholate also significantly increased calcium uptake across brush border vesicles.

CONCLUSIONS

Premicellar taurocholate significantly enhances calcium uptake into, and absorption across, enterocytes. The mechanisms remain to be experimentally verified.

Evidence that bile salts are important for iron absorption

The role of bile salts in intestinal Fe absorption has not previously been defined. We have recently shown that bile salts having cholanic ring 7 alpha-OH and/or 12 alpha-OH groups bind Fe2+ with high affinity at premicellar concentrations and also produce a two-to threefold enhancement in Fe2+ uptake from perfused intestinal segments in vivo. However, the physiological relevance of these observations for Fe2+ absorption was not known. To study this, we examined the effects of a single dose of taurocholate (TC) administered with 59Fe-FeSO4 in reversing iron malabsorption induced by bile duct ligation. Fe absorption from three 0.5-mg doses of 59Fe-FeSO4 was measured from five groups of six adult Sprague-Dawley rats each: group 1, before and after bile duct ligation and subsequent administration of 59Fe-FeSO4 + TC test dose; group 2, before and after bile duct ligation followed by a third dose of Fe alone; group 3, before and after bile duct ligation followed by a third dose of Fe+taurodehydrocholate (TDHC); group 4, sham laparotomy; and group 5, nonoperated controls where Fe absorption was measured from three doses of 59Fe-FeSO4 at the same time intervals as group 1. Absorption was measured, using whole body counting, after achievement of steady-state counts after each Fe dose. Mean percentage absorption from dose 1 (baseline) was 35.33 +/- 4.6% (SE). No significant differences between any groups were noted. In nonoperated controls (group 4), Fe absorption was virtually identical after all three doses. Also, hematocrit did not change in any of the 30 animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Gallbladder mucin, arachidonic acid, and bile lipids in patients who develop gallstones during weight reduction

BACKGROUND

Arachidonic acid (AA) and hydrophobic bile salts (BS) stimulate gallbladder mucin (GBM) secretion, which is thought to be an essential step in gallstone pathogenesis. The present study was performed to evaluate the relationship between AA, BS, and GBM in patients who develop gallstones following weight reduction.

METHODS

Eleven patients who underwent gastric bypass, developed symptomatic gallstones, and then underwent cholecystectomy were evaluated. Gallbladder bile was obtained for analysis during each procedure. Matched patients who did not develop gallstones following gastric bypass served as controls.

RESULTS

GBM increased in every patient who developed stones (mean increase: 5000%). The largest increase was observed soon after gastric bypass, and this declined curvilinearly with time. Gallbladder bile cholesterol was initially elevated but then rapidly declined before increasing back to pregastric bypass levels after weight loss was complete. No significant changes in phosphatidylcholine molecular species (including AA) or BS composition were observed following weight reduction. Concentrations of cholesterol, phospholipids, and changes in [AA] over time were each a linear function of [BS]. No relationship between GBM and any of these bile constituents was apparent.

CONCLUSIONS

These observations strongly suggest that increases in GBM, which occur with gallstone formation in humans, are not the result of alterations in biliary AA or BS composition.

Gallstones in patients with morbid obesity. Relationship to body weight, weight loss and gallbladder bile cholesterol solubility

Gallstones are common in obesity, and in individuals undergoing weight reduction. However, the relationships between body weight, weight reduction, gallbladder bile composition and gallstone formation are not well understood. The present studies were conducted on a cohort of 230 morbidly obese individuals presenting for bariatric surgery. Mean body weight ranged from 90-235.4 kg (mean: 136.2 kg). Body mass index (BMI) ranged from 35.4-94.7 kg/m2. Thirty-two patients (14%) had undergone prior cholecystectomy and 48 (21%) were found to have gallstones by intraoperative ultrasonography. No significant relationship was observed between gallstone prevalence and body weight. Following bariatric surgery weight loss averaged 1.57 kg/week over six months. Absolute weight loss ranged from 13.6-81.3 kg. Symptomatic gallstones requiring cholecystectomy developed in 15/150 patients (10%) over two years of follow-up. In contrast, ultrasonography detected asymptomatic gallstones in 34/92 patients (37%) six months following bariatric surgery. No relationship existed between the amount of weight lost and gallstone formation. Gallbladder bile cholesterol solubility remained constant throughout the entire weight range present in this population. No significant difference in cholesterol solubility was present between persons presenting for bariatric surgery and patients who developed symptomatic gallstones and underwent cholecystectomy following weight reduction. We conclude that gallstones are common in patients with severe obesity both before and following bariatric surgery. However, weight loss per se does not appear to be the major determinant of gallstone formation in persons who weigh in excess of 100 kg.

Cultured human gallbladder epithelia. Methods and partial characterization of a carcinoma-derived model

BACKGROUND

Gallstone disease remains a leading cause of morbidity and mortality in humans. Despite extensive research into the physiology of the gallbladder, little is known about mucosal events that precede and contribute to stone formation. Here, we describe and partially characterize a cultured epithelial model of human gallbladder mucosa.

EXPERIMENTAL DESIGN

Cells originally obtained from a well-differentiated gallbladder mucosal carcinoma were cultured in modified Eagle's minimum media (supplemented with fetal calf serum and antibiotics) on polycarbonate supporting matrices.

RESULTS

Cell cultures were observed to come to confluence with 6 to 9 days. Light and transmission electron microscopy demonstrated the resultant epithelia to be predominantly one cell thick, to be polar in orientation, and to have apical villi. Epithelia exhibited cytokeratin markers consistent with their epithelia origin, functionally acidified the mucosal bathing solutions, and secreted mucin. Further experiments demonstrated transepithelial potential differences, mucosal-to-serosal transfer of sodium which could be inhibited with amiloride and 4-acetamido-4'-isothiocyanatostilbene-2-2'-disulfonic acid, and paracellular movement of neutral molecular probes inversely related to size.

CONCLUSIONS

This culture model of human gallbladder mucosal carcinoma cells exhibits parameters consistent with native gallbladder and may offer a convenient new research tool for the study of the pathophysiology of gallstone formation.

Calcium in human gallbladder bile

Biliary calcium is believed to be of great importance in gallstone pathogenesis. These studies were therefore performed to determine if quantitative and/or qualitative differences in calcium are present in gallbladder bile from patients with and without gallstones. Bile was obtained by direct gallbladder aspiration from 68 obese patients undergoing elective gastric bypass surgery. Forty-five patients had no evidence of gallstones or sludge, 18 had cholesterol gallstones, and five had black pigment stones. Gallbladder bile was also obtained from 27 nonobese patients undergoing elective cholecystectomy (19 cholesterol; eight black pigment gallstones). For all patients, total calcium ranged from 1.50 to 16.44 mmol/L (mean: 6.05 +/- 0.31 mmol/L); free Ca++ ion ranged from 0.53 to 2.83 mmol/L (mean: 1.28 +/- 0.05 mmol/L). Considerable overlap was observed between obese and nonobese subjects and between patients with and without gallstones. For all patient groups, calcium, Ca++, and bound calcium increased linearly with increasing concentrations of bile salt. No significant differences in the slopes of these relationships were observed with obesity or gallstones. In contrast, free Ca++ ion was greater in gallbladder bile from gallstone patient groups throughout the entire range of bile salt. We hypothesize that this observed increase in Ca++ resulted from increased Gibbs-Donnan forces and excess gallbladder mucin present within the gallbladder bile of patients with gallstones.

In vivo studies of biliary ceftriaxone excretion and solubility in guinea pig hepatic bile

Ceftriaxone (CFTX), a third-generation cephalosporin, has occasionally been reported to produce biliary sludge composed of its calcium salt. We performed studies in guinea pigs to (1) investigate the hepatic route of CFTX excretion, (2) determine ceftriaione's effects on bile flow and composition, and (3) quantify the solubility and metastability of the calcium salt as a function of administered dose. Our results show that even at high doses ceftriaxone has only minimal effects on bile flow and biliary electrolyte secretion, either alone or in combination with bile salt (taurocholate) infusion. A significant increase in total calcium concentration was observed without change in free Ca2+ concentration, this is compatible with formation of a soluble calcium salt of ceftriaxone, as previously demonstrated in vitro. Ion products of Ca2+ and ceftriaxone as high as 3.5 times the solubility product constant without crystal formation were observed, confirming the presence of a metastable state for the calcium salt of ceftriaxone in the living animal. Biliary excretion of ceftriaxone inhibited excretion of indocyanine green, suggesting that ceftriaxone and indocyanine green share a common anionic excretory pathway in this species.

Changes in gallbladder bile composition following gallstone formation and weight reduction

Changes in gallbladder bile composition that occurred in patients who developed gallstones during weight reduction were evaluated. Bile was sampled directly from the gallbladder in 11 morbidly obese patients with no gallstones at the time of gastric bypass surgery and after gallstones had formed at cholecystectomy. Bile salt concentration ([BS]) increased significantly from a mean of 82.7-157.7 mmol/L (P less than 0.05). The concentration of cholesterol in gallbladder bile increased slightly and cholesterol saturation declined slightly with weight reduction and gallstone formation. Gallbladder mucin concentration increased 18-fold from a mean of 62 to 1110 micrograms/mL (P less than 0.001). Both free [Ca2+] and total calcium [Ca] increased 40% from mean values of 1.12 and 5.05 mmol/L at gastric bypass to 1.86 and 8.60 mmol/L after gallstone formation (P less than 0.05). The increase in [Ca2+] observed after gallstone formation was much greater than anticipated from changes in [BS] alone. This excess [Ca2+] in gallbladder bile increased curvilinearly with increasing mucin concentration. These results show that both gallbladder mucin and [Ca2+] increase with gallstone formation in humans and that mucin may modulate [Ca2+] in gallbladder bile.

Convective movement of Ca2+ across guinea pig gallbladder epithelium

Recently, much interest has developed in biliary calcium because of its importance in the pathogenesis and composition of gallstones. While much progress has been made in understanding the thermodynamic factors that control biliary calcium concentrations, little is known about the kinetic factors that control the movement of calcium across the gallbladder epithelium. These studies measure guinea pig gallbladder epithelial permeability to Ca2+ during in vivo convective water movement across the membrane. Water movement, ranging from -15.2 (absorption) to 6.3 microliters.min-1.cm-2 (water entry), was induced by placing hypotonic, isotonic, and hypertonic solutions into the gallbladder lumen. Calcium movement was found to be directly and linearly related to water flow, indicating that Ca2+ moved with the convective water flow, presumably across paracellular channels. The slope of this relationship (0.602), representing the concentration of calcium in the fluid translocated across the gallbladder epithelium, was only about half that of plasma or luminal contents, indicating that calcium movement across the membrane was restricted. The mean sieving coefficient (1 - r) of guinea pig gallbladder, calculated from this slope, was approximately 0.5, indicating that the epithelium is only moderately permeable to Ca2+. The results suggest that intraluminal chelation of Ca2+ for the possible prevention and/or treatment of calcium-containing gallstones is a potentially feasible therapeutic modality.

High-affinity binding is essential for enhancement of intestinal Fe2+ and Ca2+ uptake by bile salts

Both calcium and iron are bound with high affinity by premicellar bile salts having cholanic ring 7-OH and/or 12-OH groups, forming soluble cation-bile salt complexes. The authors of the current study recently showed that premicellar taurocholate markedly enhances intestinal iron and calcium uptake. However, the relationship of high-affinity binding to the observed uptake enhancement was unknown. In the current study, this relationship was examined by studying taurodehydrocholate (TDHC) binding and intestinal uptake of both cations. Ca2+ binding was measured by noting depression of [Ca2+] activity in solutions containing constant total Ca concentrations (1 mmol/L) and varying [TDHC] (0.5-50 mmol/L). Fe2+ binding was assessed by equilibrium dialysis studies of 59FeSO4 (0.179-1.79 mmol/L) and TDHC (0.5-50 mmol/L). Effects of TDHC on intestinal Fe2+ and Ca2+ uptake were measured in isolated perfused intestinal segments in vivo in seven and eight Sprague-Dawley rats, respectively. TDHC, lacking ring OH groups, did not bind either cation with high affinity and had no effect on their intestinal uptake. These results suggest that high-affinity binding is essential for bile salt-induced enhancement of intestinal Fe2+ and Ca2+ uptake.

Canine bile contains anticrystallization factors that inhibit precipitation of calcium carbonate

Previous studies have strongly suggested that human bile contains a substance(s) that interferes with the precipitation of calcium phosphate and carbonate from solution. These studies, however, did not distinguish between calcium binding by biliary constituents resulting in decreased calcium carbonate saturation (alterations in solution thermodynamics) and true inhibition of calcium salt precipitation by kinetic factors. Because our recent studies have shown that canine common duct bile is always supersaturated with calcium carbonate (thermodynamically at risk for precipitation), we hypothesized that it must contain kinetic factors that inhibit formation and/or growth of calcium carbonate crystals. Effects of canine bile, bovine albumin and the bile salt taurocholate on calcium carbonate precipitation were studied in highly supersaturated solutions of calcium carbonate that spontaneously undergo rapid precipitation. Measured free ionized calcium concentrations, [Ca++], and calculated calcium carbonate saturation indices were compared in test solutions and controls to evaluate the thermodynamic effects of test solutions on the degree of saturation in the assay system. It is shown that addition of only 0.2 ml of normal canine gallbladder bile to the assay system (a 1:101 dilution of biliary components) abolished precipitation. A lesser inhibitory effect (a decrease in the rate of precipitation) was observed when gallbladder bile was diluted but was lost after 10-fold dilution. Canine common duct bile caused a decrease in the rate of precipitation similar to diluted gallbladder bile. In contrast, sodium taurocholate (250 mmol/L), the major bile salt in the dog, and albumin (1.5 gm/L), the most abundant protein in bile, had only a minimal inhibitory effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Gallstone formation after rapid weight loss: a prospective study in patients undergoing gastric bypass surgery for treatment of morbid obesity

The present study evaluated the incidence of gallstone formation in 105 morbidly obese patients undergoing rapid weight loss after proximal gastric bypass surgery. Intraoperative ultrasonography demonstrated gallstones in 20 (19%) and gallbladder sludge in four (4%) patients. Eighty-one patients had a normal gallbladder ultrasound. After bariatric surgery, these patients were followed prospectively with periodic gallbladder ultrasound examinations. At 6 months, gallstones had developed in 36% and gallbladder sludge in 13% of patients. These percentages remained relatively constant at 12 and 18 months. Body weight declined rapidly after surgery from a mean of 132.3 kg to 95.5, 87.0, and 84.0 kg at 6, 12, and 18 months, respectively. Gallstones developed significantly more often in the white race, and in women. No significant differences in age, body weight, percent ideal body weight, percent weight loss, or percent of excess body weight lost existed between patients who developed gallstones or sludge and those who did not. Patients who developed gallbladder sludge had less cholesterol and lower cholesterol saturation (1.25 +/- 0.42) in their gallbladder bile than persons who developed gallstones (2.00 +/- 0.79). Forty percent (13/32) of patients who developed gallstones became symptomatic; nine (28%) underwent elective cholecystectomy. An attempt to prevent gallstone formation during rapid weight loss appears warranted.

Premicellar taurocholate enhances ferrous iron uptake from all regions of rat small intestine

Inorganic iron is virtually insoluble at the pH of small intestinal contents. This severe solubility limitation has been partly overcome by intraluminal substances that bind and solubilize iron, thus increasing availability for absorption. While several dietary ligands capable of solubilizing Fe2+ in intestinal lumen have been described, an endogenous binding ligand has not been previously described. It has recently been shown that certain trihydroxy bile acids (taurocholate and glycocholate) show high-affinity premicellar and low-affinity micellar Fe(2+)-binding properties, resulting in the formation of soluble Fe(2+)-bile salt complexes. It was hypothesized that this binding would increase the intraluminal pool of soluble iron, increase delivery of soluble iron to mucosal carriers, and thus enhance intestinal Fe2+ uptake. As a first step toward testing this hypothesis, the effect of taurocholate on Fe2+ uptake from all regions of in vivo rat small intestine is reported. It is shown that taurocholate, at premicellar concentrations, produces a marked, stepwise increase in Fe2+ uptake from all regions of small bowel, with little further increase above the critical micellar concentration. Enhancement of intestinal Fe2+ uptake is a newly described effect, and potential physiological function, of premicellar bile salts.

Recovery of bile secretion following orthotopic liver transplantation

Recovery of hepatic function following orthotopic liver transplantation includes the ability to produce 'adequate' bile. What constitutes adequate bile flow, however, has not previously been defined. The present study was undertaken to characterize biliary water and electrolyte secretion following hepatic transplantation. Bile was sampled from nine liver transplant recipients for 15-25 consecutive days during chronic t-tube biliary drainage. Liver biopsies and t-tube cholangiograms were unremarkable in all patients. During the first post-operative day mean bile flow, bile salt concentration, [BS], and bile salt output (BSO) were 60.0 microliters/min, 6.8 mM and 0.41 mumol/min, respectively. [BS] increased over days 1-5 and then plateaued at 12.2 mM over days 6-25 post-transplant. BSO and bile flow increased over days 1-12 before achieving steady-state values of 4.52 mumol/min and 334.7 microliters/min, respectively. In each patient bile flow increased linearly with increasing BSO. Choleretic index (CI), varied from 36.9-77.1 microliters/mumol (mean: 50.7 +/- 8.8). The y-intercept for this relationship ranged from 52.4-156.9 microliters/min (mean: 95.9 +/- 81.8). Only primary bile salts (82% cholate and 17% chenodeoxycholate), were observed in the bile of each patient. Biliary electrolyte concentrations were similar to that observed in plasma. Each was relatively unaffected by changes in bile flow and BSO. Electrolyte outputs increased linearly with respect to both BSO and bile flow. We conclude that recovery of bile secretion following orthotopic liver transplantation occurs gradually over a 10-12 day period and is strongly dependent upon bile salt secretion.

Pathogenesis of ceftriaxone-associated biliary sludge. In vitro studies of calcium-ceftriaxone binding and solubility

Ceftriaxone, a semisynthetic third-generation cephalosporin, has recently been associated with biliary sludge formation. Analysis of the biliary concretions induced by this agent shows a calcium salt of ceftriaxone. The present in vitro studies were undertaken to provide insight into the pathogenesis of ceftriaxone-associated biliary sludge formation by evaluating possible interactions that may exist between calcium, bile salts, and ceftriaxone. Ceftriaxone possessed high calcium-binding affinity. The formation constant for the calcium ceftriaxone salt at 37 degrees C was about 157.3 L/mol; stoichiometry of the salt was 1:1, i.e., calcium ceftriaxone. The calcium-binding property of ceftriaxone was observed to be additive to that of taurocholate in mixed taurocholate-ceftriaxone solutions. Although the solubility product constant for calcium ceftriaxone was only 1.62 x 10(-6) mol/L2, marked metastability was observed; neither visible nor microscopic precipitates developed until the [Ca2+] x [ceftriaxone] ion product exceeded the solubility product constant by a factor of 10.4. Metastability of the calcium ceftriaxone salt was also observed in human gallbladder bile in vitro. Estimates of human biliary calcium ceftriaxone solubility in vivo were than calculated from previously-reported values for biliary [Ca2+], [ceftriaxone], and from the solubility product constant as defined in this study. Calculated saturation indices for calcium-ceftriaxone in human bile generally increased (corresponding to a decrease in solubility) with increasing ceftriaxone dose. At doses less than or equal to 1 g, saturation index was well within the metastable range of this calcium-salt. However, at doses greater than or equal to 2 g, the saturation index surpassed the metastable limit. Under these conditions, precipitation of ceftriaxone could occur. It was concluded that the development of ceftriaxone-induced biliary sludge is a solubility problem that occurs in patients receiving high-dose treatment (greater than or equal to 2 g). This study proposes that the risk of developing ceftriaxone-associated biliary "pseudolithiasis" increases with increasing ceftriaxone dose and in patients with impaired gallbladder emptying.

Human gallbladder mucosal function. Effect of concentration and acidification of bile on cholesterol and calcium solubility

The most recognized function of the human gallbladder is to store bile. However, this organ is not a static reservoir. It actively modifies bile by two processes: concentration and acidification. This study was designed to simultaneously evaluate the relationship between these two physiological processes in the normal human gallbladder and to define their effects on biliary cholesterol and calcium solubility. Bile was sampled directly from the gallbladder of 78 morbidly obese patients undergoing elective gastric bypass procedures. All had negative results of intra-operative ultrasound examinations for sludge and gallstones, normal liver function tests, and no history of hepatobiliary disease. Bile salt concentrations, an indirect index of concentration by the gallbladder, ranged from 15.1-272.8 mmol/L. As [bile salt] increased, [Na+], [K+], free [Ca2+], [cholesterol], [phospholipid], and [total lipid] increased linearly; [Cl-1] decreased linearly. Molar percent cholesterol decreased from 17.2% in dilute bile to 10.1% in fully concentrated bile, suggesting that cholesterol was absorbed by the gallbladder. As bile was concentrated, cholesterol saturation index decreased curvilinearly from a maximum of 3.7 in dilute bile to 1.0-1.5 in concentrated bile. Concentration of gallbladder bile was accompanied by progressive acidification. Bile pH decreased linearly with increasing [bile salt]; [CO3(2-)] decreased curvilinearly. Despite increasing [Ca2+], CaCO3 saturation index decreased curvilinearly with increasing [bile salt] from a maximum of 3.62 in dilute bile to a minimum of 0.12 in concentrated and acidified bile. CaCO3 saturation index also decreased exponentially with decreasing pH. This study concludes that concentration of bile enhances cholesterol solubility while acidification enhances calcium salt solubility. By increasing the solubilities of these two species, gallbladder mucosal function may play a key role in preventing gallstone formation.

Biliary calcium and gallstone formation

The purpose of this paper is to present a brief overview of the current status of the field of biliary calcium and the role of calcium in the formation and maturation of gallstones. The study of free Ca+(+) ions in bile by electrochemical potentiometric measurements using Ca+(+)-selective ion-exchange electrodes is a relatively new field, but much progress has been made in the past few years. Using this powerful analytical tool, new concepts and findings have arisen in almost every aspect of biliary calcium. Although the current symposium is targeted primarily toward cholesterol gallstones, there are several areas in which understanding of biliary calcium may significantly contribute to a better understanding of the pathogenesis of cholesterol, as well as "pigment" (calcium salt), gallstones. Five broad areas are considered in relation to biliary calcium: (a) physiology (calcium entry into bile), (b) biophysics (the regulation of biliary free [Ca+(+)] as related to Gibbs-Donnan equilibria, (c) physical chemistry (the physicochemical state of calcium in bile, (d) thermodynamics (calcium solubility in bile), and (e) kinetics (pronucleating and antinucleating factors and metastable states). With more specific reference to cholesterol stones, consideration is also made of (a) the calcium salt "seed" hypothesis in cholesterol stone pathogenesis; (b) the interactions of Ca+(+) with phospholipid-cholesterol vesicles, with consideration of possible structural requirements and (c) thermodynamic and kinetic factors as related to peripheral or "eggshell" calcification of existing cholesterol stones.

Premicellar taurocholate avidly binds ferrous (Fe++) iron: a potential physiologic role for bile salts in iron absorption

Two of the major divalent cations in human physiology, Ca++ and Fe++, are poorly soluble at the pH of intestinal contents, and active "uphill" transport mechanisms exist for both ions in proximal small intestine. We have recently demonstrated significant binding of Ca++ to both premicellar and micellar bile salts and have postulated that high-affinity premicellar binding involves interposition of Ca++ between terminal carboxyl (COO-) and 7-OH or 12-OH groups of the steroid ring. The present studies were made to determine whether such binding extends to other divalent cations, and specifically to Fe++, which, like Ca++, has a hydrated diameter of 6 A. Equilibrium dialysis studies of sodium taurocholate were made at 25 degrees C with solutions containing 0.5 to 150 mmol/L taurocholate and 0.018 to 1.8 mmol/L iron 59-labeled FeSO4 at pH 3.0 to 6.3 and a total ionic strength of 0.15 mol/L. In control (saline dialysand) cells, [Fe++] was virtually equal in dialysands and dialysates within 5 hours. In sharp contrast, taurocholate-containing dialysands showed significantly higher counts than dialysates, indicating Fe++ binding to taurocholate, independent of pH and Fe concentration. After correction for taurocholate-induced Gibbs-Donnan effects across the membrane, the apparent taurocholate affinity constant (K'f) for Fe++ in micellar solutions (5 to 150 mmol/L) was essentially constant at about 3.1 (mol/L)-1, then increased dramatically below the critical micellar concentration to greater than 100 (mol/L)-1 at [taurocholate] = 0.5 mmol/L. The hyperbolic rise in K'f below the critical micellar concentration is similar to that which we have previously reported for Ca++, indicating significant high-affinity binding of Fe++ to premicellar taurocholate anions and low-affinity binding to micellar anions. It is postulated that Fe++ binding, particularly by premicellar bile salts, may play an important physiologic role in increasing iron solubility within the intestinal lumen, thus increasing iron absorption. The possible role of bile salts in increasing divalent cation solubility and absorption from the intestine is a new field of bile acid research.

Biliary calcium secretion in the dog occurs primarily by passive convection and diffusion and is linked to bile flow

Despite the importance of biliary calcium in the pathogenesis of gallstones, little is known about the sites or modes of entry of calcium into bile. We here examine the mechanisms of calcium entry into canine bile by comparing the entry of calcium, over a wide range of bile flows (2.4 to 38.0 microliters/kg per minute), with that of potassium, a small ion that is passively distributed throughout the biliary tract and that is also subject to alteration by Gibbs-Donnan forces. It is shown that (1) the concentrations of free ionized calcium, [Ca++], increases in an apparently linear fashion with increasing total bile salt concentration at low bile flow, whereas the rise in [Ca++] is strongly blunted at high rates of flow; (2) the entry of both calcium and potassium into bile is tightly linked to bile flow; and (3) calcium outputs are linearly related to potassium outputs with an intercept at the origin. These results indicate that the canaliculus is permeable to Ca++ ions, and that Ca++ enters bile primarily by passive convection and diffusion. Calcium entry is thus tightly linked to the water flux generated by bile salt secretion. Such passive entry and distribution indicate that calcium will always be present in bile and that possible therapeutic reduction of biliary [Ca++] for treatment, and possibly prevention of calcium-containing gallstones, will require sustained chelation of calcium within the lumen of the biliary tract.

Binding of calcium by organic anions, determined by perturbation of the equilibrium solubility of [14C]calcium oxalate

Confirmation is needed of the reported binding of calcium ions (Ca2+) by bile salts, which is believed to decrease the activity of free calcium ions [Ca2+] available for precipitation of insoluble calcium salts of organic anions in pigment gallstones. We report a new method to determine the association constants (K'f) of calcium for organic anions, from the perturbation by the added anion of the equilibrium solubilization of calcium [14C]oxalate monohydrate crystals (CaOx*). CaOx* crystals were prepared by stepwise conversion of [14C]oxalic acid to its K+ and Ca2+ salts. Structure and purity were confirmed by X-ray diffraction of the crystals. CaOx* was incubated (37 degrees C, under N2) in 0.15 M NaCl in CO2-free deionized H2O at pH 6.3. Dissolution of CaOx*, estimated by radioassay of the 0.22-micron Millipore filtrate, attained equilibrium at 3 days, with K'sp = [Ca2+] * [Ox=] = 2.34 X 10(-8) M2, calculated using known affinity constants for the soluble complexes of NaOx- (K'NaOx = 3.215 M-1) and CaOx (K'CaOx = 195.0 M-1). Keeping total [Na+] = 0.15 M, we added anions that formed soluble complexes with Ca2+. This decreased free [Ca2+], causing more CaOx* to dissolve in amounts related to the concentration of added anion and its K'f for Ca2+. With this method, K'f values for citrate, malonate and malate were similar to the values we determined with the Ca2+ ion electrode, and to published values obtained with the Ca2+ ion electrode and other methods. The sensitivity of the CaOx method permits determination of K'f values with small quantities and low concentrations of the anions and calcium.

Canine common duct and gallbladder bile contain antinucleating factors that inhibit CaCO3 precipitation

We performed studies involving large incremental additions of calcium to bile to examine the degree of CaCO3 supersaturation that can be achieved in bile, as compared with that in simple NaCl-NaHCO3 solutions. The addition of CaCl2 to bile increased total and free ionized calcium by from four to 12 times their original values and by from two to three times the highest concentrations encountered in bile in vivo. The increase in [Ca++] resulted in fourfold to 12-fold increases in the saturation indexes of bile, with the saturation index reaching as high as 73.4 in a common duct sample. Despite the markedly elevated CaCO3 saturation indexes, evidence of CaCO3 precipitation was not observed in either common duct or gallbladder bile over a 24-hour period. For comparison, calcium added to NaCl-NaHCO3 solutions resulted in the precipitation of CaCO3 within 4 hours if saturation indexes were greater than 12. These results indicate that native bile contains potent antinucleating factors that markedly inhibit CaCO3 precipitation, and they confirm our previous in vivo observations in canine common duct bile.

Absorption of biliary calcium from the canine gallbladder: protection against the formation of calcium-containing gallstones

Calcium salts are the major components of pigment gallstones. The calcium species in bile that is critical for Ca++ precipitation is free ionized calcium, [Ca++]. Factors that regulate biliary [Ca++] in bile are therefore of great importance in the pathogenesis of pigment gallstones. The fate of biliary Ca++ on entry into the gallbladder has not previously been studied. We here report that a minimum of 51.3% +/- 8.8% (SEM) of Ca++ is absorbed from the canine gallbladder on concentration of bile during a 24-hour fast. In addition, there was absorption of least 70.9% +/- 6.2% of Na+, 56.5% +/- 8.6% of K+, and nearly all (greater than 98%) of Cl-. Absorption, neutralization, or both, of HCO3- was also nearly complete (greater than 98%). During concentration of bile by the gallbladder, the concentrations of all biliary cations increased as total bile salt concentration increased, whereas anion concentrations declined. These results are consistent with a Gibbs-Donnan effect induced by impermeable, negatively charged bile salt molecules. Comparison of bile/plasma [Ca++] ratios with those for [K+], a passively distributed ion, was also consistent with, although not proof of, the passive absorption and distribution of Ca++ across the gallbladder epithelium. The absorption of Ca++ by the gallbladder may be a factor in the prevention of pigment gallstones, because it limits free Ca++ ion in bile, and thus decreases the likelihood of precipitation of calcium.

Pancreatic calcification and stone formation: a thermodynamic model of calcium in pancreatic juice

CaCO3 is a major constituent of pancreatic stones, salivary stones, and many pigment gallstones. Elucidation of the physicochemical state of calcium is necessary for definition of calcium solubility in these systems. Pancreatic stones are observed in both humans and cattle, and are approximately 95% CaCO3 (calcite) in both species. Despite its importance, little is known about the physicochemical state of calcium in pancreatic juice. This paper presents an a priori model, based on established physicochemical principles, for the state of calcium in the juice at all levels of secretion. Two postulates of the model are the following: the limiting free [Ca2+] in the juice is governed by the solubility product (K' sp) for CaCO3; if K' sp is exceeded, the juice is supersaturated and precipitation of CaCO3 is thermodynamically possible; total calcium, [Ca], in the juice is the sum of four distinct species: free ionized calcium, Ca2+; calcium-bicarbonate complex, CaHCO3+; calcium carbonate ion-pair, CaCO3(0); and protein-bound calcium, CaProt. Overall equations of the model and graphical corollaries are presented. The model predicts an inverse hyperbolic relationship between [Ca2+] or [Ca] and [HCO3-]. Calcium solubility is maximal at low [HCO3-]; as [HCO3-] increases, both [Ca2+] and [Ca] decline to respective limiting values of approximately 0.015 and 0.15 mM. At low [HCO3-], most of [Ca] is present as Ca2+ and CaProt, whereas at high [HCO3-], most [Ca] is CaHCO3+ and CaCO3(0). Protein, HCO3-, and CO3(2-) ions are thus important buffers for Ca2+ in the juice. The model provides a quantitative framework for further elucidation of calcium lithogenicity in the pancreas, salivary gland, and biliary tract.

Evidence for H+ secretion by the in vivo canine gallbladder

In humans and most other species, a decline in pH of gallbladder contents occurs during the concentration of bile. Recent in vitro studies in rabbit, guinea pig, and Necturus gallbladders have strongly suggested mucosal H+ secretion during sodium reabsorption, presumably representing a Na+/H+ exchange. The present in vivo studies are the first attempt to determine whether H+ secretion by the gallbladder can be demonstrated in the living animal. Gallbladder bile was obtained from 27 anesthetized dogs after 12-24-h fasts; 12 samples of common duct bile were also obtained in 3 dogs during variable taurocholate infusion. In common duct bile, observed ranges were as follows: pH, 7.37-7.85; CO2 partial pressure (PCO2), 21-32 mmHg; total CO2 concentration ([TCO2]), 16.4-41.4 mM; total bile salt concentration ([TBS]), 16-93 mM; and [Na], 153-192 mM. In gallbladder bile, respective ranges were as follows: pH, 5.72-7.29; PCO2, 36-101 mmHg; [TCO2], 1.21-15.5 mM; [TBS], 150-305 mM; and [Na], 199-266 mM. In all samples [Na] was linearly related to [TBS]. Carbon dioxide partial pressure increased from a mean of 27.3 mmHg in common duct bile to greater than 100 mmHg in gallbladder bile at [TBS] = 180 mM, then declined to approximately 36 mmHg as [TBS] increased to greater than 300 mM. Peak PCO2 occurred at pH approximately 6.4-6.6, then declined as pH decreased to approximately 5.7. Bile to plasma PCO2 ratios increased from a mean of 1.08 in common duct samples to greater than 2.0 in gallbladder samples at pH approximately 6.3, then declined to approximately 1.0 in fully concentrated bile. If the high PCO2 values in bile were solely due to tissue CO2 production, a sustained increase in PCO2 throughout Na+ reabsorption might be expected. The results strongly suggest H+ secretion (HCO3- neutralization), as peak PCO2 occurred when [TBS] was only about 180 mM, long before sodium absorption was complete. It is hypothesized that H+ secretion may have important favorable effects on calcium lithogenicity, reducing the likelihood of the formation of CaCO3- containing gallstones.