The interaction of carbon dioxide and hypoxia in the control of cerebral blood flow.

Both hypoxia and carbon dioxide increase cerebral blood flow (CBF), and their effective interaction is currently thought to be additive. Our objective was to test this hypothesis. Eight healthy subjects breathed a series of progressively hypoxic gases at three levels of carbon dioxide. Middle cerebral artery velocity, as an index of CBF; partial pressures of carbon dioxide and oxygen and concentration of oxygen in arterial blood; and mean arterial blood pressure were monitored. The product of middle cerebral artery velocity and arterial concentration of oxygen was used as an index of cerebral oxygen delivery. Two-way repeated measures analyses of variance (rmANOVA) found a significant interaction of carbon dioxide and hypoxia factors for both CBF and cerebral oxygen delivery. Regression models using sigmoidal dependence on carbon dioxide and a rectangular hyperbolic dependence on hypoxia were fitted to the data to illustrate this interaction. We concluded that carbon dioxide and hypoxia act synergistically in their control of CBF so that the delivery of oxygen to the brain is enhanced during hypoxic hypercapnia and, although reduced during normoxic hypocapnia, can be restored to normal levels with progressive hypoxia.

Adjusting eptifibatide doses for renal impairment: a model of dosing agreement among various methods of estimating creatinine clearance.

BACKGROUND: Because of the renal elimination and increased risk for bleeding events at supratherapeutic doses of eptifibatide, the manufacturer recommends dosing adjustment in patients with renal dysfunction. Methods commonly used to estimate renal dysfunction in hospital settings may be inconsistent with those studied and recommended by the manufacturer. OBJECTIVE: To compare hypothetical renal dosing adjustments of eptifibatide using both the recommended method and several other commonly used formulas for estimating kidney function. METHODS: Sex, age, weight, height, serum creatinine, and estimated glomerular filtration rate (eGFR) were obtained retrospectively from the records of patients who received eptifibatide during a 12-month period. Renal dosing decisions were determined for each patient based on creatinine clearance (CrCl) estimates via the Cockcroft-Gault formula (CG) with actual body weight (ABW), ideal body weight (IBW) or adjusted weight (ADJW), and eGFR from the Modification of Diet in Renal Disease formula. Percent agreement and Cohen κ were calculated comparing dosing decisions for each formula to the standard CG-ABW. RESULTS: In this analysis of 179 patients, percent agreement as compared to CG-ABW varied (CG-IBW: 90.50%, CG-ADJW: 95.53%, and eGFR: 93.30%). All κ coefficients were categorized as good. In the 20% of patients receiving an adjusted dose by any of the methods, 68.6% could have received a dose different from that determined using the CG-ABW formula. CONCLUSIONS: In the patients with renal impairment (CrCl <50 mL/min) in this study, two thirds would have received an unnecessary 50% dose adjustment discordant from the manufacturer's recommendation. Because failure to adjust eptifibatide doses in patients with renal impairment has led to increased bleeding events, practitioners may be inclined to err on the side of caution. However, studies have shown that suboptimal doses of eptifibatide lead to suboptimal outcomes. Therefore, correct dosing of eptifibatide is important to both patient safety and efficacy.

Initial results of the chordal-cutting operation for ischemic mitral regurgitation.

OBJECTIVE: Division of secondary chords (chordal cutting) has been proposed as a method for decreasing mitral valve leaflet tethering and mitral regurgitation in patients with ischemic mitral regurgitation. However, very little clinical data exist to date for this procedure. METHODS: We compared echocardiographic and clinical data in patients who underwent chordal-cutting mitral valve repair (n = 43) and those undergoing conventional mitral valve repair (control, n = 49) for ischemic mitral regurgitation. RESULTS: Patients who underwent chordal cutting had a higher prevalence of recent myocardial infarction, left main disease, diabetes, and peripheral vascular disease (all P < .05). Left ventricular ejection fraction was lower in the chordal-cutting group (33 +/- 2% vs 44 +/- 2%) (mean +/- SE) and preoperative tent height was greater (11.7 +/- 0.5 vs 9.7 +/- 0.6 mm; both P < .01). In-hospital mortality was 10% in control patients and 9% in the chordal-cutting group (P = .9). Other complication rates were similar for the two groups. The reduction in tent height before-to-after repair was similar in the two groups of patients, but those undergoing chordal cutting had a greater reductions in tent area (53 +/- 3% vs 41 +/- 3%; P = .01). The chordal-cutting group also had greater mobility of the anterior leaflet, as measured by a reduction in the distance between the free edge of the anterior mitral valve leaflet and the posterior left ventricular wall (24 +/- 3% vs 11 +/- 4%; P = .01). Control patients had more recurrent mitral regurgitation during 2 years of follow-up by univariate (37% vs 15%; P = .03) and multivariate analysis (P = .03). Chordal cutting did not adversely affect postoperative left ventricular ejection fraction (10% +/- 5% relative increase in left ventricular ejection fraction vs 11% +/- 6% in the control group; P = .9). CONCLUSION: Chordal cutting improves mitral valve leaflet mobility and reduces mitral regurgitation recurrence in patients with ischemic mitral regurgitation, without any obvious deleterious effects on left ventricular function.

Hypoxemia complicating LVAD insertion: novel application of the Amplatzer PFO occlusion device.

We report a case of profound systemic hypoxemia complicating left ventricular assist device (LVAD) insertion due to right to left shunting through a patent foramen ovale (PFO) in association with a Chiari network. The patient was successfully managed with percutaneous closure of the interatrial defect using an Amplatzer PFO occlusion device and judicious reduction in LVAD flows.

Chronic ischemic mitral regurgitation: repair, replace or rethink?

Ischemic mitral regurgitation (IMR) is a common complication of coronary artery disease and is the focus of a rapidly increasing amount of research. Mechanistic studies have determined that IMR is caused by apical displacement and tethering of the mitral valve leaflets after myocardial infarction, resulting in incomplete coaptation. Despite the relatively high prevalence of IMR, most centers have only a small surgical experience with this disorder. The result is that a number of different procedures have been recently developed without clear improvement in patient outcomes. The current review will examine the myriad surgical options for IMR with a focus on clinical outcomes.

Transfusion of ABO-nonidentical platelets is not associated with adverse clinical outcomes in cardiovascular surgery patients.

BACKGROUND: Current blood transfusion standards in Canada and the United States permit transfusion of ABO-nonidentical platelets when ABO-identical platelets are not available. This practice increases the availability of platelets, a component in chronic shortage in Ontario, Canada because of the 5-day shelf-life. The impact of transfusing ABO-nonidentical platelets on patient outcomes is unknown. STUDY DESIGN AND METHODS. A retrospective review of 1721 patients who had cardiovascular surgery between November 1989 and December 1999 and who had also received a platelet transfusion perioperatively was conducted. The impact of platelet and plasma incompatibility on clinical outcomes was analyzed. RESULTS: The analysis included 1691 patients who were divided into two groups according to the compatibility of the first platelet transfusion received: ABO-identical platelet transfusion (n = 1008) and ABO-nonidentical platelet transfusion (n = 683). The only difference in baseline characteristics between the two groups was that there were more urgent cases in the ABO-identical platelet transfusion group (p = 0.04). There were no significant differences in mortality at 30 days (10% for both groups, p = NS) or in postoperative length of stay (median, 7.0 days for both groups, p = NS). No significant differences were found with respect to the use of blood components, indices of bleeding, incidence of infection, or platelet CCIs. CONCLUSION: Transfusion of ABO-nonidentical platelets in patients undergoing cardiovascular surgery is not associated with an adverse impact on patient outcome.