Clinical Briefs
Hyponatremia: Evaluating the Correction Factor for Hyperglycemia
In 1949, seldin and tarail reported that elevated glucose resulted in a lower serum sodium concentration, which they attributed to a shift of water to the extracellular space due to the osmotic effect of glucose. At that time, the correction factor of 2.8 was suggested (i.e., it was stated that for every 100 mg/dL increase in blood glucose over the normal level of 100, a drop of 2.8 in sodium would be seen). This factor evolved based upon the assumption that 100 mg/dL of glucose (= 5.6 mmol) would have a similar osmotic behavior as 2.8 meq of sodium (= 5.6 mosm NaCl). Evolution of different theoretic concerns has prompted suggested revision of this correction factor so that reported conversion numbers range from 1.2-2.0.
To evaluate the effect of hyperglycemia on serum sodium concentration, Hillier and colleagues studied six healthy patients by suppressing insulin through somatostatin infusion, coupled with high-dose glucose infusion to achieve a plasma glucose of at least 600 mg/dL in less than one hour’s time. Restoration of glucose to normal with insulin infusion followed. Serum sodium and plasma glucose were measured simultaneously every 10 minutes.
The response of serum sodium depression to acute hyperglycemia was essentially immediate; restoration of the serum sodium in response to serum glucose normalization was equally acute. Overall, a 2.4 meq/L sodium change was seen per 100 mg/dL glucose elevation. However, this change was not uniform (e.g., in blood sugars < 400 mg/dL, the conversion factor was 1.6, whereas for sugars > 440, the conversion factor was 4.0). Hillier et al note that the conversion factor of 2.4 is perhaps the more useful tool, since at severe levels of hyperglycemia, in which correction of sodium level is most important, this number is more accurate than the 1.6 conversion factor currently in use.
Hillier TA, et al. Am J Med 1999;106: 399-403.
Transcutaneous Nitroglycerine in the Treatment of Erectile Dysfunction
The role of nitric oxide (no) as an important neurotransmitter responsible for dilation of penile arteries and relaxation of sinusoidal chambers of the corpora cavernosa and corpus spongiosum to allow erection is well defined. Nitroglycerin is known to enhance NO availability and leads directly to NO formation. Case reports of beneficial effects of topical nitroglycerin on erectile function have encouraged further evaluation of this modality.
This study evaluated 18 men with erectile dysfunction of a variety of etiologies. This double-blind placebo-controlled trial evaluated the erectile response to trandsdermal application of nitroglycerin by means of a Rigiscan monitor in the laboratory; a home study portion of the trial assessed patient- reported success in achieving a good, moderate, or no effect in response to topical nitroglycerin.
In this study, transdermal nitroglycerin did not demonstrate activity greater than placebo in either the laboratory or the home setting. Additionally, headache, the most frequently reported side effect of nitrates seen in cardiovascular use, was the most commonly reported adverse event in this group, including a female sex partner who also suffered post-coital headache attributed to nitroglycerin.
Gramkow and associates conclude that nitroglycerin transdermally is not superior to placebo for treatment of erectile dysfunction.
Gramkow J, et al. Int J Impotence Research 1999;11:35-39.
Occult Vitamin D Deficiency
European studies have shown that up to one-third of women with hip fractures have signs of osteomalacia, which is often caused by vitamin D deficiency. U.S. studies to date have demonstrated less substantial (up to 25%), but still impressive, frequency of osteomalacia with hip fracture. The current study compared the prevalence of low vitamin D levels and high PTH among subjects with acute osteoporotic fractures, compared with patients scheduled for joint replacement surgery without hip fractures (the latter group chosen to represent normal, or even below normal bone mineral density).
Among the 805 women studied, 543 were in the elective joint replacement group and 262 in the acute hip fracture group. Fifty percent of the study group with postmenopausal acute hip fractures had subnormal vitamin D levels, and 36.7% had elevated PTH. The median PTH level of women with osteoporotic fractures was 1.5 times higher than in the control group.
Leboff and associates demonstrate that postmenopausal women with acute hip fracture have a noteworthy incidence of otherwise subclinical vitamin D deficiency, with accompanying PTH elevation. Such deficits are generally remediable with supplementation.
Leboff MS, et al. JAMA 1999; 281:1505-1511.
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