Limited repair with tear-oriented approach for type A aortic dissection.

Acute type A aortic dissection (ATAAD) remains an eminent, life-threatening disease. Although centers of excellence report mortality rate after ATAAD repair as low as 5% to 8%, data from the International Registry of Acute Aortic Dissection continue to demonstrate a high mortality rate of around 17% to 18%. Tear-oriented approach to determine the extent of repair has been widely accepted to treat ATAAD. In recent years, aggressive approach with total arch replacement - especially using hybrid procedure with the antegrade stent grafting in the proximal descending aorta - have been advocated to decrease the future downstream reoperations in younger patients or to treat malperfusion syndrome. In this article, we review outcomes comparing limited/tear-oriented approach vs. extended repair based on updated outcomes after ATAAD repair to evaluate for the indications and validity of each approach. We found that extended repair remains a high-risk operation in most hands and distal reoperation rate in contemporary series are as low as 10%. In addition, we did not find data to support concomitant antegrade stenting to improve outcomes in patients with distal malperfusion. In conclusion, we do not recommend beyond the tear-oriented approach, as any future benefit with extended repair seems outweighed by the incremental risk with the short-term risk in most hands.

Defining the role of albumin infusion in cirrhosis-associated hyponatremia.

The presence of negatively charged, impermeant proteins in the plasma space alters the distribution of diffusible ions in the plasma and interstitial fluid (ISF) compartments to preserve electroneutrality and is known as Gibbs-Donnan equilibrium. In patients with hypoalbuminemia due to underlying cirrhosis, the decrease in the plasma water albumin concentration ([Alb-]pw) would be expected to result in a decrease in the plasma water sodium concentration ([Na+]pw) due to an alteration in the distribution of Na+ between the plasma and ISF. In addition, cirrhosis-associated hyponatremia may be due to the renal diluting defect resulting from the intravascular volume depletion due to gastrointestinal losses and overdiuresis and/or decreased effective circulatory volume secondary to splanchnic vasodilatation. Therefore, albumin infusion may result in correction of the hyponatremia in cirrhotic patients either by modulating the Gibbs-Donnan effect due to hypoalbuminemia or by restoring intravascular volume in patients with intravascular volume depletion due to gastrointestinal losses and overdiuresis. However, the differential role of albumin infusion in modulating the [Na+]pw in these patients has not previously been analyzed quantitatively. In the present study, we developed an in vitro assay system to examine for the first time the quantitative effect of changes in albumin concentration on the distribution of Na+ between two compartments separated by a membrane that allows the free diffusion of Na+. Our findings demonstrated that changes in [Alb-]pw are linearly related to changes in [Na+]pw as predicted by Gibbs-Donnan equilibrium. However, based on our findings, we predict that the improvement in cirrhosis-associated hyponatremia due to intravascular volume depletion results predominantly from the restoration of intravascular volume rather than alterations in Gibbs-Donnan equilibrium.

Acid-base analysis: a critique of the Stewart and bicarbonate-centered approaches.

When approaching the analysis of disorders of acid-base balance, physical chemists, physiologists, and clinicians, tend to focus on different aspects of the relevant phenomenology. The physical chemist focuses on a quantitative understanding of proton hydration and aqueous proton transfer reactions that alter the acidity of a given solution. The physiologist focuses on molecular, cellular, and whole organ transport processes that modulate the acidity of a given body fluid compartment. The clinician emphasizes the diagnosis, clinical causes, and most appropriate treatment of acid-base disturbances. Historically, two different conceptual frameworks have evolved among clinicians and physiologists for interpreting acid-base phenomena. The traditional or bicarbonate-centered framework relies quantitatively on the Henderson-Hasselbalch equation, whereas the Stewart or strong ion approach utilizes either the original Stewart equation or its simplified version derived by Constable. In this review, the concepts underlying the bicarbonate-centered and Stewart formulations are analyzed in detail, emphasizing the differences in how each approach characterizes acid-base phenomenology at the molecular level, tissue level, and in the clinical realm. A quantitative comparison of the equations that are currently used in the literature to calculate H(+) concentration ([H(+)]) is included to clear up some of the misconceptions that currently exist in this area. Our analysis demonstrates that while the principle of electroneutrality plays a central role in the strong ion formulation, electroneutrality mechanistically does not dictate a specific [H(+)], and the strong ion and bicarbonate-centered approaches are quantitatively identical even in the presence of nonbicarbonate buffers. Finally, our analysis indicates that the bicarbonate-centered approach utilizing the Henderson-Hasselbalch equation is a mechanistic formulation that reflects the underlying acid-base phenomenology.

A new method for determining plasma water content: application in pseudohyponatremia.

Pseudohyponatremia is a clinical condition characterized by an increased fraction of protein or lipid in plasma, thereby resulting in an artificially low plasma sodium concentration ([Na(+)](p)). Since the automated method of measuring [Na(+)](p) in most laboratories involves the use of an indirect ion-selective electrode (I-ISE), this method does not correct for elevated protein or lipid concentrations. In I-ISE, the plasma sample is diluted before the actual measurement is obtained, and the [Na(+)](p) is determined based on the assumption that plasma is normally composed of 93% plasma water. Therefore, the [Na(+)](p) as determined by I-ISE will be artificially low in clinical conditions when the plasma water content (PWC) is <93%. In contrast, the plasma is not diluted when the [Na(+)](p) is measured using direct ISE (D-ISE). This method directly measures Na(+) activity in plasma water and is therefore unaffected by the proportion of plasma occupied by water. In this study, we report a novel quantitative method for determining the PWC utilizing I-ISE and D-ISE. To validate this new method experimentally, we altered the PWC in vitro by dissolving varying amount of salt-free albumin in human plasma. We then measured PWC gravimetrically in each sample and compared the gravimetrically determined PWC with the ISE-determined PWC. Our findings indicate that the PWC can be accurately determined based on differences in the [Na(+)](p) as measured by I-ISE and D-ISE and that this new quantitative method can be a useful adjunct in the analysis of the dysnatremias.