Results of gastric neutralization with hourly antacids and cimetidine in 320 intubated patients with respiratory failure

Interventions for preventing upper gastrointestinal bleeding in people admitted to intensive care units

BACKGROUND

Upper gastrointestinal (GI) bleeding due to stress ulcers contributes to increased morbidity and mortality in people admitted to intensive care units (ICUs). Stress ulceration refers to GI mucosal injury related to the stress of being critically ill. ICU patients with major bleeding as a result of stress ulceration might have mortality rates approaching 48.5% to 65%. However, the incidence of stress-induced GI bleeding in ICUs has decreased, and not all critically ill patients need prophylaxis. Stress ulcer prophylaxis can result in adverse events such as ventilator-associated pneumonia; therefore, it is necessary to evaluate strategies that safely decrease the incidence of GI bleeding.

OBJECTIVES

To assess the effect and risk-benefit profile of interventions for preventing upper GI bleeding in people admitted to ICUs.

SEARCH METHODS

We searched the following databases up to 23 August 2017, using relevant search terms: MEDLINE; Embase; the Cochrane Central Register of Controlled Trials; Latin American Caribbean Health Sciences Literature; and the Cochrane Upper Gastrointestinal and Pancreatic Disease Group Specialised Register, as published in the Cochrane Library (2017, Issue 8). We searched the reference lists of all included studies and those from relevant systematic reviews and meta-analyses to identify additional studies. We also searched the World Health Organization International Clinical Trials Registry Platform search portal and contacted individual researchers working in this field, as well as organisations and pharmaceutical companies, to identify unpublished and ongoing studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and quasi-RCTs with participants of any age and gender admitted to ICUs for longer than 48 hours. We excluded studies in which participants were admitted to ICUs primarily for the management of GI bleeding and studies that compared different doses, routes, and regimens of one drug in the same class because we were not interested in intraclass effects of drugs.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures as recommended by Cochrane.

MAIN RESULTS

We identified 2292 unique records.We included 129 records reporting on 121 studies, including 12 ongoing studies and two studies awaiting classification.We judged the overall risk of bias of two studies as low. Selection bias was the most relevant risk of bias domain across the included studies, with 78 studies not clearly reporting the method used for random sequence generation. Reporting bias was the domain with least risk of bias, with 12 studies not reporting all outcomes that researchers intended to investigate.Any intervention versus placebo or no prophylaxisIn comparison with placebo, any intervention seems to have a beneficial effect on the occurrence of upper GI bleeding (risk ratio (RR) 0.47, 95% confidence interval (CI) 0.39 to 0.57; moderate certainty of evidence). The use of any intervention reduced the risk of upper GI bleeding by 10% (95% CI -12.0% to -7%). The effect estimate of any intervention versus placebo or no prophylaxis with respect to the occurrence of nosocomial pneumonia, all-cause mortality in the ICU, duration of ICU stay, duration of intubation (all with low certainty of evidence), the number of participants requiring blood transfusions (moderate certainty of evidence), and the units of blood transfused was consistent with benefits and harms. None of the included studies explicitly reported on serious adverse events.Individual interventions versus placebo or no prophylaxisIn comparison with placebo or no prophylaxis, antacids, H2 receptor antagonists, and sucralfate were effective in preventing upper GI bleeding in ICU patients. Researchers found that with H2 receptor antagonists compared with placebo or no prophylaxis, 11% less developed upper GI bleeding (95% CI -0.16 to -0.06; RR 0.50, 95% CI 0.36 to 0.70; 24 studies; 2149 participants; moderate certainty of evidence). Of ICU patients taking antacids versus placebo or no prophylaxis, 9% less developed upper GI bleeding (95% CI -0.17 to -0.00; RR 0.49, 95% CI 0.25 to 0.99; eight studies; 774 participants; low certainty of evidence). Among ICU patients taking sucralfate versus placebo or no prophylaxis, 5% less had upper GI bleeding (95% CI -0.10 to -0.01; RR 0.53, 95% CI 0.32 to 0.88; seven studies; 598 participants; moderate certainty of evidence). The remaining interventions including proton pump inhibitors did not show a significant effect in preventing upper GI bleeding in ICU patients when compared with placebo or no prophylaxis.Regarding the occurrence of nosocomial pneumonia, the effects of H2 receptor antagonists (RR 1.12, 95% CI 0.85 to 1.48; eight studies; 945 participants; low certainty of evidence) and of sucralfate (RR 1.33, 95% CI 0.86 to 2.04; four studies; 450 participants; low certainty of evidence) were consistent with benefits and harms when compared with placebo or no prophylaxis. None of the studies comparing antacids versus placebo or no prophylaxis provided data regarding nosocomial pneumonia.H2 receptor antagonists versus proton pump inhibitorsH2 receptor antagonists and proton pump inhibitors are most commonly used in practice to prevent upper GI bleeding in ICU patients. Proton pump inhibitors significantly more often prevented upper GI bleeding in ICU patients compared with H2 receptor antagonists (RR 2.90, 95% CI 1.83 to 4.58; 18 studies; 1636 participants; low certainty of evidence). When taking H2 receptor antagonists, 4.8% more patients might experience upper GI bleeding (95% CI 2.1% to 9%). Nosocomial pneumonia occurred in similar proportions of participants taking H2 receptor antagonists and participants taking proton pump inhibitors (RR 1.02, 95% CI 0.77 to 1.35; 10 studies; 1256 participants; low certainty of evidence).

AUTHORS' CONCLUSIONS

This review shows that antacids, sucralfate, and H2 receptor antagonists might be more effective in preventing upper GI bleeding in ICU patients compared with placebo or no prophylaxis. The effect estimates of any treatment versus no prophylaxis on nosocomial pneumonia were consistent with benefits and harms. Evidence of low certainty suggests that proton pump inhibitors might be more effective than H2 receptor antagonists. Therefore, patient-relevant benefits and especially harms of H2 receptor antagonists compared with proton pump inhibitors need to be assessed by larger, high-quality RCTs to confirm the results of previously conducted, smaller, and older studies.

Pharmacological Approach to the Prevention and Treatment of Stress Ulcers

The mortality associated with bleeding stress ulcers in patients in intensive care units exceeds 50%. Iden tification of patients at risk and use of early and effec tive prophylaxis are necessary in the management of patients in intensive care units. The use of antacids is inconvenient, expensive, and associated with electro lyte disturbances and erratic pH control. H2-receptor antagonists are the preferred agents for stress ulcer pro phylaxis because of their proven efficacy, safety, and ease of administration. Adjunct therapy with cyto protective agents may be useful in patients with com promised mucosal defences.

Stress Ulcer Syndrome

Stress ulcer syndrome refers to gastroduodenal erosions or ulcers that develop acutely in relation to major physi ological stress, usually manifested clinically as upper gastrointestinal (UGI) bleeding. These lesions occur most often in the gastric fundus. Endoscopy has shown gastroduodenal mucosal lesions in 75 to 100% of inten sive care unit (ICU) patients within 72 hours of admis sion. Patients at high risk for stress ulcer include those with large body surface area burns, intracranial lesions associated with coma, fulminant hepatic failure, sepsis, and trauma and abdominal, cardiovascular, and thoracic surgery patients. Also considered high risk are ICU pa tients with superimposed complications such as shock, mechanical ventilation for more than 3 days, coagulopa thy, jaundice, and sepsis. Approximately 15% of ICU pa tients will experience UGI bleeding from stress ulcer. Patients bleeding from stress ulcer have an overall mor tality rate approaching 65% compared with 9 to 22% mortality in patients without stress ulcer. When strati fied according to occult blood loss versus clinically significant bleeding, mortality can be as high as 90% in patients overtly bleeding; 30% of deaths are directly related to bleeding. Both antacids and H2 receptor an tagonists are effective in prophylaxis for stress ulcer bleeding.

Antacids revisited: a review of their clinical pharmacology and recommended therapeutic use

Antacids are commonly used self-prescribed medications. They consist of calcium carbonate and magnesium and aluminum salts in various compounds or combinations. The effect of antacids on the stomach is due to partial neutralisation of gastric hydrochloric acid and inhibition of the proteolytic enzyme, pepsin. Each cation salt has its own pharmacological characteristics that are important for determination of which product can be used for certain indications. Antacids have been used for duodenal and gastric ulcers, stress gastritis, gastro-oesophageal reflux disease, pancreatic insufficiency, non-ulcer dyspepsia, bile acid mediated diarrhoea, biliary reflux, constipation, osteoporosis, urinary alkalinisation and chronic renal failure as a dietary phosphate binder. The development of histamine H2-receptor antagonists and proton pump inhibitors has significantly reduced usage for duodenal and gastric ulcers and gastro-oesophageal reflux disease. However, antacids can still be useful for stress gastritis and non-ulcer dyspepsia. The recent release of proprietary H2 antagonists has likely further reduced antacid use for non-ulcer dyspepsia. Other indications are still valid but represent minor uses. Antacid drug interactions are well noted, but can be avoided by rescheduling medication administration times. This can be inconvenient and discourage compliance with other medications. All antacids can produce drug interactions by changing gastric pH, thus altering drug dissolution of dosage forms, reduction of gastric acid hydrolysis of drugs, or alter drug elimination by changing urinary pH. Most antacids, except sodium bicarbonate, may decrease drug absorption by adsorption or chelation of other drugs. Most adverse effects from antacids are minor with periodic use of small amounts. However, when large doses are taken for long periods of time, significant adverse effects may occur especially patients with underlying diseases such as chronic renal failure. These adverse effects can be reduced by monitoring of electrolyte status and avoiding aluminum-containing antacids to bind dietary phosphate in chronic renal failure. Antacids, although effective for discussed indications of duodenal and gastric ulcer and gastro-oesophageal reflux disease, have been replaced by newer, more effective agents that are more palatable to patients. Antacids are likely to continue to be used for non-ulcer dyspepsia, minor episodes of heartburn (gastro-oesophageal reflux disease) and other clear indications. Although their wide-spread use may decline, these drugs will still be used, and clinicians should be aware of their potential drug interactions and adverse effects.

[Concept of stress ulcer prevention. Is re-thinking necessary?]

BACKGROUND

The efficiency of stress ulcer prophylaxis in the prevention of gastrointestinal bleeding in critically ill patients has led to its widespread use. The lower incidence of stress ulcer bleeding, the side-effects and the cost of the prophylaxis have made it necessary targeting this preventive therapy to those patients most likely to benefit. Metaanalysis of studies on patients who received no stress ulcer prophylaxis showed few critically ill patients with important gastrointestinal bleeding.

INDICATIONS

Patients who benefit most from receiving stress ulcer prophylaxis are critically ill patients with coagulopathy, or those requiring mechanical ventilation for more than two days. In patients with headinjuries, widespread burns or severe hypotension, the effects of stress ulcer prophylaxis have not been fully researched, but we would recommend administering stress ulcer prophylaxis in these cases.

TREATMENT

Following a recent metaanalysis, stress ulcer prophylaxis is performed either with H2-blockers (ranitidine, famotidine) or sucralfate.

The value of early enteral nutrition in the prophylaxis of stress ulceration in the severely burned patient

A retrospective analysis of prospectively collected data was performed to compare the frequency of upper gastrointestinal bleeding (GIB) in seriously burned patients treated with either cimetidine and antacids or enteral nutrition for ulcer prophylaxis. Five hundred and twenty-six seriously burned patients admitted to the burn intensive care unit of the BG Trauma Centre Ludwigshafen during a 4-year period were included into the study. All patients admitted to the burn unit from 1989 to 1991 received i.v. cimetidine (400 mg q4) for ulcer prophylaxis. If the intragastric pH dropped below 3.5, gastric pH was titrated with antacids up to > or = 4 via nasogastric tube. During the second 2-year period (1992-1993) early enteral nutrition alone was regarded to be ulcer protective and no further interventions for ulcer prophylaxis were routinely performed. Signs of overt upper GIB were monitored and documented through the entire study period. The overall occurrence rate of upper GIB in the cimetidine/antacids (C/A) group (n = 253) was 8.3 per cent with six cases of serious bleeding in five patients (1.98 per cent). In the enteral nutrition (EN) group (n = 273) the overall incidence of GIB was 3.3 per cent with two cases of serious bleeding (0.73 per cent). There were no deaths directly related to ulcer haemorrhage. The difference in the overall frequency of overt GIB between the groups studied was statistically significant (< 0.05). In our experience, early enteral nutrition is effective in the prevention of stress haemorrhage in the upper gastrointestinal tract. Additional medicinal prophylaxis is not required in burn patients.

Prospective double-blind placebo-controlled randomized trial on the use of ranitidine in preventing postoperative gastroduodenal complications in high-risk neurosurgical patients

To determine the efficacy of ranitidine in preventing clinically acute overt gastroduodenal (GD) complications (bleeding and/or perforation) after neurosurgery, 101 patients with nontraumatic cerebral disease considered at high risk of developing postoperative GD complications were randomized in a standard double-blind manner to receive either ranitidine (50 mg every 6 hours) or placebo medication preoperatively. Postoperative serial GD endoscopy was used to document the occurrence of complications: an overt symptomatic complication was defined as bleeding requiring blood transfusion and/or surgery. Fifty-two patients received ranitidine and 49 received a placebo preoperatively; 30 developed overt GD bleeding; nine of these received ranitidine and 21 received a placebo. Ranitidine significantly reduced the incidence of bleeding (p < 0.05). Multivariate logistic regression analysis revealed three factors of independent significance in predicting overt GD bleeding: use of a placebo drug, a gastric pH of less than 4, and a high daily volume of gastric output. The authors conclude that ranitidine is useful in preventing postoperative GD complications in high-risk neurosurgical patients.

Stress ulcer prophylaxis: gastrointestinal bleeding and nosocomial pneumonia. Best evidence synthesis

PURPOSE

To examine the effect of stress ulcer prophylaxis on gastrointestinal bleeding, pneumonia, and mortality.

METHODS

Computerized search of published and unpublished research, bibliographies, pharmaceutical and personal files and abstract reports. Independent review of 257 articles identified 71 relevant randomized trials for inclusion. We made independent, duplicate assessment of the methodologic quality, population, intervention and outcomes of each trial.

RESULTS

This overview demonstrates that prophylaxis with histamine-2-receptor antagonists decreases the incidence of overt gastrointestinal bleeding (odds ratio 0.29 [95% CI 0.17-0.45]) and clinically important bleeding (odds ratio 0.35 [95% CI 0.15-0.76]). There is a trend to decreased overt bleeding when antacids are compared with no therapy (odds ratio 0.35 [95% CI 0.08-1.33]). Although sucralfate, antacids, and histamine-2-receptor antagonists are equivalent in reducing clinically important bleeding, sucralfate decreases the incidence of nosocomial pneumonia compared with antacids and/or histamine-2-receptor antagonists (odds ratio 0.50 [95% CI 0.21-0.79]). Sucralfate is associated with lower mortality relative to antacids (odds ratio 0.70 [95% CI 0.52-0.94]), and relative to histamine-2-receptor antagonists (odds ratio 0.71 [95% CI 0.49-1.04]).

CONCLUSIONS

All stress ulcer prophylactic agents appear to be effective in decreasing bleeding. Prophylaxis with sucralfate is associated with a lower rate of nosocomial pneumonia and mortality, providing strong evidence for use of this agent in clinical practice.

Risk factors for gastrointestinal bleeding in critically ill patients. Canadian Critical Care Trials Group

BACKGROUND

The efficacy of prophylaxis against stress ulcers in preventing gastrointestinal bleeding in critically ill patients has led to its widespread use. The side effects and cost of prophylaxis, however, necessitate targeting preventive therapy to those patients most likely to benefit.

METHODS

We conducted a prospective multicenter cohort study in which we evaluated potential risk factors for stress ulceration in patients admitted to intensive care units and documented the occurrence of clinically important gastrointestinal bleeding (defined as overt bleeding in association with hemodynamic compromise or the need for blood transfusion).

RESULTS

Of 2252 patients, 33 (1.5 percent; 95 percent confidence interval, 1.0 to 2.1 percent) had clinically important bleeding. Two strong independent risk factors for bleeding were identified: respiratory failure (odds ratio, 15.6) and coagulopathy (odds ratio, 4.3). Of 847 patients who had one or both of these risk factors, 31 (3.7 percent; 95 percent confidence interval, 2.5 to 5.2 percent) had clinically important bleeding. Of 1405 patients without these risk factors, 2 (0.1 percent; 95 percent confidence interval, 0.02 to 0.5 percent) had clinically important bleeding. The mortality rate was 48.5 percent in the group with bleeding and 9.1 percent in the group without bleeding (P < 0.001).

CONCLUSIONS

Few critically ill patients have clinically important gastrointestinal bleeding, and therefore prophylaxis against stress ulcers can be safely withheld from critically ill patients unless they have coagulopathy or require mechanical ventilation.

Stress ulcer prophylaxis in the critically ill: a meta-analysis

PURPOSE

To examine the differential effect of stress ulcer prophylaxis on overt bleeding, clinically important bleeding, and mortality in critically ill patients.

DATA IDENTIFICATION

Computerized bibliographic search of published and unpublished research.

STUDY SELECTION

Independent review of 168 articles identified 42 relevant randomized trials for inclusion.

DATA ABSTRACTION

The validity, population, intervention, and outcomes of each trial were evaluated.

RESULTS

Stress ulcer prophylaxis with antacids (odds ratio 0.40 [95% confidence interval (CI) 0.20 to 0.79]) or histamine-2-receptor antagonists (odds ratio 0.29 [95% CI 0.17 to 0.45]) decreases the incidence of overt gastrointestinal bleeding. Histamine-2-receptor antagonists are more effective than antacids at reducing overt hemorrhage (odds ratio 0.56 [95% CI 0.33 to 0.97]). A significant reduction in clinically important gastrointestinal hemorrhage is evident only with histamine-2-receptor antagonist therapy. There is a trend favoring antacids over sucralfate in the outcome of clinically important bleeding (odds ratio 0.65 [95% CI 0.16 to 2.49]); however, there are insufficient data to evaluate histamine-2-receptor antagonists versus sucralfate. No difference in mortality between treated and untreated patients was found.

CONCLUSIONS

Overt gastrointestinal bleeding in critically ill patients is reduced by prophylaxis with antacids or histamine-2-receptor antagonists. Histamine-2-receptor antagonists are more effective than antacids at decreasing overt bleeding and are more effective than no treatment at reducing the incidence of clinically important bleeding. Mortality rates in the intensive care unit are not decreased by stress ulcer prophylaxis.

Management of Stress Gastritis

Management of stress gastritis is primarily directed toward prevention of gastrointestinal bleeding. Antacids and H2 blockers have been the standard agents used for prophylactic therapy in critically ill patients. However, growing evidence that gastric alkalization leads to an increased incidence of nosocomial pneumonias has led to the development of other prophylactic agents that do not decrease gastric acidity. These cytoprotective agents presumably enhance gastric mucosal defenses and stimulate mucosal repair. Approximately 3% of patients bleed despite prophylactic therapy. Bleeding is usually controlled with intensive medical management, and the need for surgical intervention is rare.

Prophylaxis of gastrointestinal tract bleeding with magaldrate in patients admitted to a general hospital ward

A randomized, placebo-controlled trial was performed to assess the effect of magaldrate (800 mg every 4 h) in reducing the rate of upper gastrointestinal tract bleeding among 100 consecutive patients with severe diseases admitted to a general hospital ward. Upper gastrointestinal tract bleeding occurred in 11 of 48 placebo-treated patients and in only 1 of 52 magaldrate-treated patients (p less than 0.01). Endoscopic examination of these patients showed gastric ulcer (two cases), multiple gastric mucosa ulcerations (nine), and no lesions (one). In three patients who received placebo the hemorrhage was clinically relevant and required transfusion of two or more blood units. Patients with two or more risk factors showed a higher rate of gastrointestinal hemorrhage (p less than 0.05). Respiratory failure and treatment with a high dose of corticosteroids were associated with the highest incidence of bleeding (p less than 0.05 for both). The only adverse reaction associated with magaldrate was a mild and self-limiting diarrhea in two cases. We conclude that patients seriously ill admitted to a general hospital ward should be treated with a prophylactic agent against stress-induced ulcer bleeding. Magaldrate is an effective and safe antacid to prevent gastrointestinal tract bleeding in such patients.

Stress gastritis revisited

In current ICU populations, overt bleeding from stress gastritis occurs in 10% to 20% of patients. Bleeding rates may be reduced to about 3% in patients receiving prophylactic therapy. Although patients with bleeding have higher mortality rates than other critically ill patients, it is not clear that the mortality rate is improved with prophylactic therapy, as most patients die from their underlying disease. As new complications of prophylactic therapy are identified, better definitions of the population at risk to develop complications of stress gastritis will be necessary to select those patients who will benefit most from prophylactic therapy.

Incidence of Clinically Important Bleeding in Mechanically Ventilated Patients

The purpose of this study was to determine the incidence of clinically important gastrointestinal hemorrhage in mechanically ventilated patients, and to determine the risk factors for overt bleeding in this population. One hundred consecutive critically ill medical and surgical patients requiring mechanical ventilation for more than 48 hours were prospectively evaluated in a university-based tertiary care, medical/surgical intensive care unit. Seventyfour patients received stress ulcer prophylaxis. Overt bleeding occurred in nine paticnts (9.0%; 95% confidence interval [CI], 3.4-14.6%); eight of the nine patients had a coagulopathy. Clinically important bleeding occurred in two additional patients (2.0%; 95% CI, 0-6.2%). Multiple logistical regression analysis revcaled that only the presence of a coagulopathy (odds ratio 12.5; 95% CI, 3.4-46.5) and the presence of occult bleeding for six or more days (odds ratio 5.5; 95% CI, 1.2-25.4) were independently predictive of overt gastrointestinal hemorrhage. Sixteen patients died, two of whom had overt bleeding and one of whom had clinically important gastrointestinal bleeding. Clinically important gastrointestinal bleeding is uncommon in ventilated patients receiving stress ulcer prophylaxis. In the two patients who bled, both had peptic ulcer disease; one of these had stress ulceration. The presence of a coagulopathy is a powerful independent risk factor for overt bleeding in this population. The risk of overt bleeding also increases with the number of days of positive occult bleeding.

The effect of duodenojejunal alimentation on gastric pH and hormones in intensive care unit patients

We evaluated effects of duodenojejunal (DJ) feeding on gastric pH and selected gastrointestinal hormones in 13 randomly selected patients in an intensive care unit (ICU). To obtain baseline values for gastric pH, a nasogastric (NG) tube was placed in each patient and gastric pH was measured every 30 minutes for 2 hours. To obtain control values, a Dobbhoff tube was placed fluoroscopically and 0.45 percent saline solution (NaCl), 75 ml, was infused for 1 hour and gastric pH was measured again; the previously placed NG tube was left in position. Then, by randomization, either 0.45 percent NaCl (pH = 5) was continued (n = 6) or a high-nitrogen, isotonic, enteral feeding solution (Osmolite HN, pH = 6.4) (n = 7) was infused, both at 75 ml/h. Gastric pH was noted hourly for 96 hours; antacid (Maalox TC, 15-ml aliquots) was given by NG tube when the pH was 4 or less. After 96 hours, the infusion was stopped and gastric pH was noted for 4 additional hours. Before and during initial saline solution infusion; after 24, 48, 72, and 96 hours of continuous infusion; and 4 hours after stopping the infusion, peripheral venous blood was obtained for measurement of plasma gastric inhibitory polypeptide (GIP) and serum gastrin. Data were analyzed by ANOVA (RMD), Fishers' exact test, and the unpaired t-test. Groups did not differ demographically. Throughout the infusion, gastric pH tended to be higher with the enteral feeding solution than with saline solution, but this was significant only at 24 hours. Less antacid was required with the enteral feeding solution at 24 and 48 hours than with saline solution. Plasma GIP levels were significantly higher with the enteral feeding solution than with saline solution during most of the infusion. Serum gastrin levels did not differ between the groups. In this cohort, infusion of the enteral feeding solution tended to maintain a gastric pH of more than 4 and was associated with increased plasma GIP levels, which may inhibit gastric acid secretion. Early enteral feeding may benefit certain ICU patients.

[Digestive stress hemorrhage. Physiopathology and prevention]

Lesions of the gastroduodenal mucosa are seen very early on in virtually 100% of patients suffering from organ failure. Bleeding, even if it is only occult, defines acute stress-induced gastrointestinal tract bleeding (SGIB). The rates of SGIB vary according to the inclusion criteria: 13 to 100% microscopic SGIB, 2.3 to 9.5% haemorrhage with blood transfusion and/or shock. Gastrointestinal bleeding does not really influence the death rate of patients with SGIB (0 to 5% increase). Damage to the gastric mucosa may be due to an intraluminal aggression, and/or decreased mucosal and mural defence mechanisms. H+ ions and bile salts are mostly responsible for the former. Physiological quantities of H+ ions may be sufficient, as their abnormal diffusion into the gastric mucosa will reduce the mucosal pH (pHm), which is itself sensitive to microcirculatory modifications and systemic acidosis. There is a good correlation between bleeding and pHm. Bile salts are involved because of the usual increase in frequency and volume of gastric biliary reflux due to stress. Surfactant, mucosal alkaline layer and the microcirculation are all involved in gastric protection. The PGE2 synthetized by the gastric mucosa have a favourable influence on these 3 mechanisms. Changes in microcirculation and hypoxia are the predominant factors involved in stress-induced mucosal damage. The prevention of SGIB relies on the treatment of risk factors, a reduction of intraluminal aggression, and the support and/or stimulation of gastric defence mechanisms. Antacids and anti-H2 drugs aim to neutralize most of the H+ ions, being more efficient than placebo in increasing gastric pH greater than 4, although anti-H2 agents are responsible of a greater number of failures. The non-homogenous character of the patient groups studied and the diagnostic methods, as well as the increasing lack of placebo groups in the published studies make the interpretation of the results rather risky. Antacids and anti-H2 drugs are more efficient than placebo, and equally efficient, in preventing overt SGIB. Efficiency is increased by giving anti-H2 drugs continuously, and antacids hourly. Other agents are thought to protect mucosal cells, probably increasing mucosal defences. Amongst them are the prostaglandins, the most interesting of which are still being investigated, and sucralfate. The latter molecule is as efficient as antacids and anti-H2 drugs, and does not alter gastric pH, so reducing the number of nosocomial pneumonias. Its reduced cost and easy administration make it, at the present time, the treatment of choice of SGIB. The few rare contraindications of sucralfate will justify the infusion of anti-H2 drugs in those patients at risk.

Common complications in critically ill patients

Patients in intensive care units (ICUs) are subject to many complications connected with the advanced therapy required for their serious illnesses. Complications of ventilatory support include problems associated with short-term and long-term intubation, barotrauma, gastrointestinal tract bleeding, and weaning errors. Cardiac tachyarrhythmias can arise from a patient's intrinsic cardiac disease, as well as from drug therapy itself. Hemodynamic monitoring is crucial to careful patient management, but it is associated with technical complications during insertion such as pneumothorax, as well as interpretive errors such as those caused by positive end-inspiratory pressure. Acute renal failure can develop as a result both of therapy with drugs such as aminoglycosides and hypotension of many etiologies, as well as the use of contrast media. Nosocomial infection, which is a dreaded complication in ICU patients, usually arises from sources in the urinary tract, bloodstream, or lung. Complications frequently can arise if the interactions of drugs commonly used in the ICU are not recognized. Further, the ICU patient is subject to nutritional complications, acid base problems, and psychological disturbances. This monograph deals with the frequency, etiology, and prevention of these common ICU complications.

Therapeutic goals and treatment options for prevention of stress ulcer syndrome

Stress ulcer syndrome, the occurrence of acute upper gastrointestinal bleeding or perforation from stress-related mucosal damage, is a significant cause of morbidity and mortality in critically ill patients. The mortality rate in critically ill patients who have bled from stress ulcers ranges from 50 to 77 percent, whereas the mortality rate for similar patients without stress ulcer bleeding ranges from 9 to 22 percent. The mortality rate may be as high as 90 percent in patients with clinically overt bleeding; as many as one-third of these deaths can be directly related to bleeding. Prophylactic therapy for prevention of stress ulcer bleeding is based on three premises: (1) morbidity and mortality related to stress ulcer syndrome are significant; (2) the population at risk can be identified prior to bleeding; and (3) therapy that decreases gastric acidity or improves gastric mucosal defense mechanisms will prevent ulcer formation or progression to bleeding. A review of prospective clinical studies utilizing prophylactic therapy in critically ill patients and patients undergoing surgery revealed a 17 percent overall bleeding rate for placebo groups compared with lower bleeding rates for antacid- and histamine (H2)-receptor-antagonist-treated groups (4 and 7 percent, respectively). Studies varied greatly in definition of bleeding, dosage regimens, and gastric pH goals. The need to measure gastric pH during treatment is controversial, and the optimal pH goal and the length of time for which it must be maintained remain unknown. Controversy exists as to the best therapeutic option for prophylaxis of stress ulcer syndrome, but when prevention of clinically significant bleeding is the therapeutic goal, antacids and H2-receptor antagonists appear to be equally efficacious.

Recognizing, setting therapeutic goals, and selecting therapy for the prevention and treatment of stress-related mucosal damage

Advances in the care of critically ill patients and in diagnostic techniques, such as fiberoptic endoscopy, have enabled greater recognition of stress-related mucosal damage (SRMD). This condition is distinguished from chronic peptic ulcer disease by its greater number of lesions, proximal location in the acid-producing portion of the stomach, and superficial bleeding. Endoscopy is considered the best method for detecting and monitoring mucosal damage. The onset of SRMD occurs early, within hours of the traumatic insult. Pharmacologic treatment has been oriented toward suppressing intraluminal acid and enhancing mucosal defense mechanisms. Antacid therapy is considered the best method for treatment of SRMD, although extensive experience has been gained with the H2-receptor antagonists. The vast majority of experience with the H2-receptor antagonists has been with cimetidine, which is as effective as antacids, as shown by endoscopy. Investigations of alternative forms of therapy (e.g., prostaglandins) are in progress.

Intragastric pH profile during acute respiratory failure in patients with chronic obstructive pulmonary disease. Effect of ranitidine and enteral feeding

The ability of H2 receptor antagonists and continuous enteral alimentation to maintain high intragastric pH in patients with chronic obstructive pulmonary disease (COPD) requiring mechanical ventilation was evaluated by continuously monitoring intragastric pH prior to and following sequential addition of ranitidine or continuous enteral alimentation (or both) to their therapeutic regimen. Prior to therapy, intragastric pH was less than 4.0 for 75 +/- 10 percent of the time, but never less than 1.0. Nevertheless, this moderate gastric acidity was associated with evidence of mucosal injury. Ranitidine failed to continuously maintain a high intragastric pH (pH less than 4.0 for 35 +/- 11 percent of the time; p greater than 0.2 compared to patients treated with placebo). Following administration of continuous enteral alimentation, intragastric pH fell, and ranitidine therapy only partially blocked this increase in gastric acidity induced by continuous enteral alimentation. We conclude that without treatment, patients with COPD who have acute respiratory failure may develop gastric mucosal injury despite the presence of only moderate intragastric acidity; however, ranitidine and continuous enteral alimentation are not effective in maintaining a high intragastric pH.

The comparative efficacy of cimetidine and ranitidine in controlling gastric pH in critically ill patients

The comparative efficacy of intravenous cimetidine and ranitidine in controlling gastric pH in 100 intensive care unit patients was assessed in a double blind, prospective, randomized study. The total number of gastric pH determinations and the number of pH determinations with pH less than five were recorded. Patients received either cimetidine or ranitidine via continuous infusion, with dosage adjustments for patients with renal insufficiency. Antacids were administered each time the gastric pH was less than five. There was no difference overall in the number of patients who had at least one gastric pH determination less than pH 5. There was however, a larger proportion of patients with greater than or equal to 10, greater than or equal to 15, greater than or equal to 20 and greater than or equal to 25 per cent of gastric pH determination less than pH 5 in the cimetidine group than in the ranitidine group. This difference was statistically significant for greater than or equal to 25 per cent. The drugs were well tolerated. Ranitidine was as effective as cimetidine and possibly more so in controlling gastric pH.

Complications of acute respiratory failure

Many complications can occur during the management of acute respiratory failure and may involve multiple organs. Some of these complications can be avoided by preventive measures. We find evaluation of serial chest roentgenograms extremely useful for the early detection of several complications (figure 4). In addition, prophylactic use of heparin to prevent pulmonary emboli, prophylactic antacid or cimetidine therapy to prevent gastric bleeding, careful monitoring of renal function, appropriate measures to reduce the incidence of colonization and nosocomial infection, and early recognition of nosocomial infections are some of the measures essential to increased survival of patients with acute respiratory failure.

Prophylaxis of stress ulcers: antacid titration vs. histamine2-receptor blockade

The near universal occurrence of stress ulcers in critically ill patients emphasizes the need for early and effective prophylaxis. Intraluminal gastric acidity, ischemic insult to the bowel, and the presence of stress factors are the major precipitants of stress ulcers. The use of H2-receptor antagonists vs. antacid titration for stress ulcer prophylaxis is reviewed. The goals of preventive therapy are to eliminate the stress factors and to maintain intragastric pH greater than 5. Hourly gastric pH monitoring and antacid titration are the mainstay of stress ulcer prophylaxis, with high potency antacids being the preferred agents. H2-receptor antagonists may serve as adjuncts in patients requiring large doses of antacids or having acid-base abnormalities from high gastric output states.

Acute stress ulceration

Stress ulceration is usually considered a mucosal abnormality of the oesophagus, stomach or duodenum in the critically ill. It is found to a varying degree in all such patients. Only about one-quarter of lesions are associated with blood loss and less than 5% need resuscitation and treatment. However, because treatment of established bleeding is unsatisfactory, and associated with a high mortality, prophylactic measures are usually employed. These include optimising gastric mucosal blood flow and oxygen delivery, correcting coagulation abnormalities and treating underlying infection. Enteral feeding should also be employed whenever possible. Other prophylactic measures currently used involve raising gastric pH above 4, with either antacids or H2 receptor antagonists. This is best achieved by measuring the gastric pH hourly and titrating it against an appropriate dose of either type of drug or a combination of both. Newer drugs, such as omeprazole, sucralfate and prostaglandins, are proving very successful in the treatment and prevention of gastric and duodenal ulcers and may prove even more effective than currently available agents.

Prospective evaluation of the risk of upper gastrointestinal bleeding after admission to a medical intensive care unit

One hundred seventy-four patients (179 admissions) were prospectively evaluated for the subsequent occurrence of upper gastrointestinal ("stress") bleeding after admission to a medical/respiratory intensive care unit. Evidence for either overt or occult gastrointestinal bleeding developed in 25 (14 percent). The group of bleeders had a higher mortality (64 percent versus 9 percent), duration of intensive care unit stay (median 14.2 versus 4.2 days), number of patients requiring mechanical ventilatory support (84 percent versus 26 percent), and duration of such support for those who required it (median 9.5 versus 4.2 days) than the group who did not bleed. In three patients, death was related to bleeding. Upon patients' admission to the intensive care unit, diagnoses of an acute respiratory illness (but not specifically chronic obstructive pulmonary disease), a malignancy, or sepsis were more common among those who subsequently bled. Of factors tested, a coagulopathy and the need for mechanical ventilation were most strongly associated with the risk of bleeding. Other factors did not add to the risk once these two were taken into account. Among patients receiving mechanical ventilation, the risk of overt bleeding was particularly low for those who required such support for less than five days (only 3 percent). It is concluded that (1) significant upper gastrointestinal bleeding occurring after medical intensive care unit admission is an uncommon event, and (2) prolonged mechanical ventilation and/or the presence of a coagulopathy are the most potent risk factors. Medical patients with either of the latter conditions are most likely to benefit from prophylaxis regimens against "stress"-induced upper gastrointestinal bleeding.