Fundamentals of Arterial Blood Gas Interpretation.

Acid-base disturbances in patients with cardiopulmonary or other disorders are common and are often misinterpreted or interpreted incompletely. Treating acid-base disorders in greater detail facilitates pathophysiologic understanding and improved therapeutic planning. Understanding the ratiometric relationship between the lungs, which excrete volatile acid as carbon dioxide, and the kidneys, which contribute to maintenance of plasma bicarbonate, allows precise identification of the dominant acid-base disturbance when more than a simple disorder is present and aids in executing a measured treatment response. Concordantly, mapping paired values of the partial pressure of carbon dioxide (PCO2) and the bicarbonate concentration ([HCO3 -]) on a Cartesian coordinate system visually defines an acid-base disorder and validates the ratiometric methodology. We review and demonstrate the algebraic and logarithmic methods of arterial blood gas analysis through the example of a complex acid-base disorder, emphasizing examination of the PCO2-to-[HCO3 -] ratio.

Sodium-based osmotherapy for hyponatremia in acute decompensated heart failure.

Acute decompensated heart failure (ADHF) accounts for more than 1 million hospital admissions annually and is associated with high morbidity and mortality. Decongestion with removal of increased total body sodium and total body water are goals of treatment. Acute kidney injury (AKI) or chronic kidney disease (CKD) is present in two-thirds of patients with ADHF. The pathophysiology of ADHF and AKI is bidirectional and synergistic. AKI and CKD complicate the management of ADHF by decreasing diuretic efficiency and excretion of sodium and water. Among patients hospitalized with ADHF, hyponatremia is the most common electrolyte abnormality and is classically encountered with volume overload. ADHF represents an additional therapeutic challenge particularly when oligoanuria is present. Predilution continuous venovenous hemofiltration with sodium-based osmotherapy can safely increase plasma sodium concentration without deleteriously increasing total body sodium. We present a detailed methodology that addresses the issue of hypervolemic hyponatremia in patients with ADHF and AKI.

Sodium-Based Osmotherapy in Continuous Renal Replacement Therapy: a Mathematical Approach.

Cerebral edema, in a variety of circumstances, may be accompanied by states of hyponatremia. The threat of brain injury from hypotonic stress-induced astrocyte demyelination is more common when vulnerable patients with hyponatremia who have end stage liver disease, traumatic brain injury, heart failure, or other conditions undergo overly rapid correction of hyponatremia. These scenarios, in the context of declining urinary output from CKD and/or AKI, may require controlled elevations of plasma tonicity vis-à-vis increases of the plasma sodium concentration. We offer a strategic solution to this problem via sodium-based osmotherapy applied through a conventional continuous RRT modality: predilution continuous venovenous hemofiltration.

The prevalence of primary aldosteronism in diabetic patients.

Increased plasma aldosterone concentrations (PACs) are associated with higher cardiovascular risk and target organ damage (TOD). Hyperglycemia can potentiate the cellular effects of aldosterone, and the prevalence of diabetes in primary aldosteronism (PA) is 7%-59%. The prevalence of PA in hypertensive individuals is estimated to be 10%-14%. This study of 61 hypertensive diabetic patients not taking spironolactone and with serum creatinine values <2.5 mg/dL sought to establish the prevalence of PA in hypertensive diabetics and compare the prevalence of PA in patients with TOD with those patients without TOD. PA was suspected if PACs were >15 ng/dL and plasma renin activity was <1 ng/dL/h (ratio >30). Although 14 patients had suppressed renin with PACs >8 ng/dL (including two with PACs >11 ng/dL), none met our criteria for PA. There was no correlation between PAC and TOD. This study indicates that routine screening for PA in hypertensive diabetic patients is not justified and that PAC does not correlate with TOD. Further study is needed.