Effects of ramipril and enalapril on cerebral blood flow in elderly patients with asymptomatic carotid artery occlusive disease

We wished to determine in asymptomatic hypertensive patients with > or = 70% stenosis of an internal carotid artery the change in regional cerebral blood flow (rCBF) produced by ramipril and enalapril and to evaluate the influence of age on drug-induced changes in rCBF. In a prospective, randomized, single-blind, placebo-controlled investigation, using the 133Xenon inhalation technique, we assessed baseline rCBF in 15 patients (9 men and 6 women aged 60-79 years) after a 24-h antihypertensive drug-free period. All patients then received a single 5-mg oral dose of ramipril, enalapril, or placebo. rCBF was reassessed 2 h postdose. There was no significant change in the median rCBF in any of the three treatment groups. Neither did we observe any lateralization of BF to any specific cerebral region in any of the three groups. There were no observed or patient-reported adverse events (AE). Single 5-mg oral doses of either ramipril or enalapril did not decrease CBF significantly in asymptomatic hypertensive patients with > or = 70% stenosis of an internal carotid artery and are probably safe starting doses in such patients. In addition, this effect was not modified by age.

Prophylaxis for stress-related gastrointestinal hemorrhage: a cost effectiveness analysis

OBJECTIVE

To assess the cost-effectiveness of prophylaxis for stress-related gastrointestinal hemorrhage in patients admitted to the intensive care unit.

DESIGN

Decision model of the cost and efficacy of sucralfate and cimetidine, two commonly used drugs for prophylaxis of stress-related hemorrhage. Outcome estimates were based on data from published studies. Cost data were based on cost of medications and costs of treatment protocols at our institutions.

MEASUREMENTS AND MAIN RESULTS

The marginal cost-effectiveness of prophylaxis, as compare with no prophylaxis, was calculated separately for sucralfate and cimetidine and expressed as cost per bleeding episode averted. An incremental cost-effectiveness analysis was subsequently employed to compare the two agents. Sensitivity analyses of the effects of the major clinical outcomes on the cost per bleeding episode averted were performed. At the base-case assumptions of 6% risk of developing stress-related hemorrhage and 50% risk-reduction due to prophylaxis, the cost of sucralfate was $1,144 per bleeding episode averted. The cost per bleeding episode averted was highly dependent on the risk of hemorrhage and, to a lesser degree, on the efficacy of sucralfate prophylaxis, ranging from a cost per bleeding episode averted of $103,725 for low-risk patients to cost savings for very high-risk patients. The cost per bleeding episode averted increased significantly if the risk of nosocomial pneumonia was included in the analysis. The effect of pneumonia was greater for populations at low risk of hemorrhage. Assuming equal efficacy, the cost per bleeding episode averted of cimetidine was 6.5-fold greater than the cost per bleeding episode averted of sucralfate.

CONCLUSIONS

The cost of prophylaxis in patients at low risk of stress-related hemorrhage is substantial, and may be prohibitive. Further research is needed to identify patient populations that are at high risk of developing stress-related hemorrhage, and to determine whether prophylaxis increases the risk of nosocomial pneumonia.

Vancomycin removal by high-flux polysulfone hemodialysis membranes in critically ill patients with end-stage renal disease

To define the pharmacokinetics of vancomycin in patients undergoing maintenance hemodialysis in an acute care setting and to characterize the rebound phenomenon occurring after hemodialysis, vancomycin t1/2 during the interdialytic and intradialytic phases and intradialytic clearance were measured in eight critically ill patients undergoing high-flux hemodialysis using F-80 or F-60 polysulfone dialyzers. Intradialytic clearance was determined using the recovery method. In patients dialyzed with F-80 dialyzers, interdialytic and intradialytic t1/2 for vancomycin were 162 +/- 69.8 hours and 4.7 +/- 1.3 hours, respectively. Intradialytic clearance was 108.5 +/- 16.3 mL/min, and 238 +/- 55 mg of vancomycin was recovered in the dialysate. In patients dialyzed with F-60 dialyzers, interdialytic and intradialytic t1/2 were 211.0 +/- 166.8 and 4.6 +/- 0.4 hours, respectively. Intradialytic clearance was 100.6 +/- 18.3 mL/min and the amount of vancomycin recovered was 252 +/- 79 mg. Vancomycin concentrations rebounded by 16% to 37% between 3 and 6 hours in patients dialyzed with the F-80 dialyzer and 15% to 38% between 2 and 3 hours in patient dialyzed with F-60 dialyzers. Hemodialysis with high-flux polysulfone dialyzers removes significant amounts of vancomycin in patients dialyzed in an acute care setting. A suggested scheme for vancomycin dosage adjustments in these patients is presented.

Proarrhythmic effects of intravenous vasopressors

OBJECTIVE

To review the electrophysiologic properties and the in vitro, ex vivo, animal, and human data regarding proarrhythmic effects of intravenous vasopressors.

DATA SOURCES

A comprehensive (MEDLINE) search (1960-1994) was conducted for dopamine, epinephrine, norepinephrine, phenylephrine, and methoxamine.

STUDY SELECTION

In vitro and ex vivo studies and investigations performed in animals or humans reporting electrophysiologic and/or proarrhythmic effects of the above intravenous vasopressors were selected. A comprehensive search of all human studies involving these agents was conducted to reveal any proarrhythmic effects that may have been reported. In addition, case reports of proarrhythmic effects associated with these agents were reviewed.

DATA EXTRACTION

Data regarding electrophysiologic and proarrhythmic effects of these agents were extracted from in vitro, ex vivo, animal, and human studies. Because few studies with the specific purpose of investigating proarrhythmic effects of vasopressors have been performed in humans, all studies involving these drugs for evaluation of hemodynamic effects, clinical efficacy, or other endpoints in humans were reviewed. In addition, data were extracted from case reports of proarrhythmic effects associated with these agents.

DATA SYNTHESIS

Dopamine increases automaticity in Purkinje fibers and has a biphasic effect on action-potential duration. Dopamine has caused both atrial and ventricular tachyarrhythmias in animals. Human data have revealed dose-related sinus tachycardia, with few reports of clinically significant ventricular arrhythmias. Epinephrine shortens sinus cycle length, increases atrial and ventricular automaticity, promotes atrioventricular nodal conduction, and decreases ventricular effective refractory period (ERP). It is well known to induce ventricular fibrillation and decrease the ventricular fibrillation threshold (VFT) in ex vivo models as well as intact animals. In humans, epinephrine may cause dose-related sinus tachycardia, supraventricular arrhythmias, or, more commonly, ventricular arrhythmias. Norepinephrine increases automaticity of the sinoatrial node, atria, and ventricles; promotes atrioventricular nodal conduction; and decreases ventricular ERP. In vitro/ex vivo and animal data have shown that norepinephrine significantly decreases VFT. Although electrophysiologic studies suggest that norepinephrine may be proarrhythmic, few supporting data exist in humans. Phenylephrine demonstrates differential electrophysiologic effects in atrial and ventricular tissue. Most data suggest that phenylephrine causes prolongation of the ventricular ERP. Rather than being proarrhythmic, phenylephrine may be protective against arrhythmias. The drug elevates VFT in dogs. In humans, phenylephrine effectively terminates supraventricular tachycardias and may be protective against ventricular arrhythmias. Like phenylephrine, methoxamine elevates the repetitive extrasystolic, atrial, and ventricular fibrillatory thresholds. Methoxamine also may have antiarrhythmic effects because of alpha-receptor stimulation and reflex vagal activity. Despite the relatively low risk of arrhythmogenicity associated with intravenous vasopressors, patients should be monitored for potential proarrhythmic effects and appropriate action taken as necessary. Critically ill patients often have concurrent conditions, electrolyte disturbances, and underlying arrhythmias that predispose them to a higher risk of vasopressor proarrhythmic effects.

CONCLUSIONS

Controlled data supporting the proarrhythmic potential of intravenous vasopressors in humans are lacking. Sinus tachycardia, asymptomatic ventricular ectopic activity, and other ventricular or supraventricular arrhythmias have been reported in association with dopamine and epinephrine. Phenylephrine and methoxamine have been associated with sinus bradycardia, but otherwise may be antiarrhythmic. Intravenous vasopressors appear relatively safe w

Prophylaxis for stress-related gastric hemorrhage in the medical intensive care unit. A randomized, controlled, single-blind study

OBJECTIVE

To determine the efficacy and safety of cimetidine and sucralfate prophylaxis for stress-related gastrointestinal hemorrhage in patients admitted to a medical intensive care unit.

SETTING

Medical intensive care unit of a nonprofit, university-affiliated teaching hospital.

PATIENTS

300 patients admitted to the medical intensive care unit during a 10-month period.

DESIGN

Randomized, controlled, single-blind clinical trial.

INTERVENTION

Patients were assigned to receive no prophylaxis (control), 1 g sucralfate given orally every 6 hours, or continuous intravenous cimetidine titrated to maintain gastric pH at 4.0, intervention was maintained until the occurrence of clinically severe hemorrhage, onset of drug-related complications, death, or discharge from the medical intensive care unit.

OUTCOME MEASURES

The primary outcome measure was the incidence of clinically severe hemorrhage from endoscopically verified stress-related gastritis. Other outcome measures were transfusion requirements, duration of medical intensive care unit stay, incidence of nosocomial pneumonia, adverse drug reactions, and death.

RESULTS

100 patients were randomly assigned to each treatment. The three groups were similar with regard to demographic characteristics, intensive care unit admission diagnoses, and APACHE II scores. Stress-related hemorrhage was seen in 6% of control participants and in 5% of those receiving sucralfate or cimetidine (relative risk compared with control, 0.83 for each group; 95% CI, 0.26 to 2.64; P = 0.75). No statistically significant differences were found for transfusion requirements, duration of medical intensive care unit stay, and mortality rates among the three groups. Nosocomial pneumonia was diagnosed in 6%, 12%, and 13% of controls, sucralfate recipients, and cimetidine recipients, respectively (sucralfate: relative risk, 2.0 [CI, 0.79 to 5.01], P = 0.14; cimetidine: relative risk, 2.2 [CI, 0.88 to 5.33], P = 0.09). Prophylaxis caused no definite adverse drug reactions.

CONCLUSIONS

The observed effects of cimetidine and sucralfate on the incidence and severity of hemorrhage from stress-related gastritis were not significant when compared with no treatment. Routine prophylaxis with these agents for patients entering the medical intensive care unit does not seem warranted.

Estimation of total body and extracellular water using single- and multiple-frequency bioimpedance

OBJECTIVE

To determine the precision and bias of single- and multiple-frequency bioimpedance estimates of total body water (TBW) and extracellular water (ECW) volumes in comparison with the true values for these volumes established by gold standard dilution techniques.

DESIGN

Controlled, prospective, open-label investigation.

SETTING

Private, not-for-profit university-affiliated, acute care hospital.

PARTICIPANTS

Normal, healthy men (n = 8) and women (n = 6) volunteers, 25-46 years of age.

INTERVENTIONS

A single oral dose of a mixture of deuterium oxide 10 g and bromine 30 mmol; bioimpedance analysis pre- and three hours postmixture administration.

MAIN OUTCOME PARAMETERS

TBW and ECW volumes established by deuterium oxide and bromine dilutional spaces (gold standards), respectively, and single- and multiple-frequency bioimpedance estimates of those same volumes.

RESULTS

The mean multiple-frequency bioimpedance (MFB) and single frequency bioimpedance (SFB) estimates of TBW, 41.2 and 42.1 L, respectively, were not statistically different (NS) from the 41.2 L deuterium oxide value. Although the two methods had similar precision (NS), MFB was less biased. For ECW, the mean MFB and SFB values of 19.5 and 24.8 L, respectively, were significantly different from the bromine value of 18.8 L (p = 0.013 and p = 0.001, respectively). MFB was the more precise and less biased predictor of ECW.

CONCLUSIONS

Compared with SFB, the MFB approach is a more precise and less biased predictor of TBW and ECW volumes in young, healthy adults, and may offer more accurate assessment in subjects with aberrant physiology.

Labetalol: response and safety in critically ill hemorrhagic stroke patients

OBJECTIVE

To observe and characterize the blood pressure (BP)-lowering and adverse hemodynamic and/or central nervous system effects of intravenous bolus doses of labetalol in hemorrhagic stroke patients.

DESIGN

Observational, prospective, pilot survey conducted over an eight-week period.

SETTING

Surgical intensive care unit.

PARTICIPANTS

Patients admitted with an intracerebral or subarachnoid hemorrhage.

MAIN OUTCOME PARAMETERS

Absolute decline in systolic BP (SBP) and diastolic BP (DBP), time to peak reduction in SBP and DBP, and adverse hemodynamic and mental status changes.

RESULTS

Labetalol at doses between 5 and 25 mg lowered SBP by 6-19 percent (baseline 152-184 mm Hg) and DBP by 3-26 percent (baseline 50-99 mm Hg). Adverse hemodynamic or mental status changes were not detected following labetalol administration.

CONCLUSIONS

Small (< or = 25 mg) intravenous bolus doses of labetalol produce mild decreases in BP in hemorrhagic stroke patients.