Use of long catheters for multipatient anesthetic monitoring at high respiratory frequencies

Anesthetic gases from several patients can be monitored simultaneously with a centrally located mass spectrometer. Such monitoring requires catheters from patient to spectrometer that are several meters long. Scamman (J Clin Monit 1988;4:227–229) found that when the respiratory frequency is high, as with infants, the CO₂ signal from the patient is unacceptably distorted during passage down the catheter. This is due to Taylor dispersion of the input signal. An outline of the theory of Taylor dispersion is given. The equations describe the interaction between the velocity distribution (which, in laminar flow, is parabolic) and the radial diffusion of CO₂. This interaction keeps a tracer signal together in a pulse, as it moves down the tube with themean velocity, spreading somewhat as it proceeds. How much does an initially sharp signal become blurred? The spread of such a signal when it reaches the detector, measured in time, can be expressed in various ways. Measurement is complicated, however, by the fact that the gas pressure may fall by as much as a factor of 10 along the line. The resultant expansion and acceleration of the gas cannot be ignored. A full treatment of this complication is given elsewhere, but the following simple equation is described: {ie237-1} Typically, the spread time is up to a quarter of a second for catheters of 50 m, such as used by Scamman. This is comparable with the period of CO₂ rise and fall for infants and explains the serious distortion in wave form that Scamman found. Some distortion can be eliminated by reducing R to 0.1 or less, but the extent of this improvement is small. Ideally, for fast-breathing patients, the catheter length should be reduced to 20 m or less, if possible.     

Familiar Hyperkalaemic Acidosis

We evaluated a 26-years-old man with hyperkalaemic acidosis,apparently inherited as an autosomal dominant trait. Type IIpseudohypoaldosteronism was suggested by normal aldosteroneproduction and renal sodium conservation. The cause of acidosisin this syndrome is unknown. Both urinary ammonium excretionand bicarbonate threshold were low during hyperkalaemia. Aftercorrecting the hyperkalaemia ammonium excretion was normal,but bicarbonate threshold remained low. Maximum bicarbonatereabsorption, urine to blood pCO₂ gradients, and minimum urinepH were normal. These findings suggest that hyperkalaemia mightcontribute to the acidosis by limiting urinary buffer, but thatthe primary defect is reduced mineralocorticoid effect on hydrogenion and secretion. When the poorly reabsorbed anion, sulphate,was infused, hydrogen ion and potassium secretion were normal.When the relatively reabsorbable anion, chloride, was infused,potassium secretion was decreased. Thesefinding suggest thatthe attenuated mineralocorticoid effect on hydrogen ion secretionis due to increased reabsorptive avidity for chloride in thedistal nephron. To determine if this defect caused resistanceto mineralocorticoid we increased mineralocorticoid by dietarysodium restriction and later administered desoxycorticosteroneand fludrocortisone. Both endogenous and exogenous mineralocorticoidcaused increased net acid excretion and corrected the acidosis,indicating no resistance to mineralocorticoid. Hydrochlorothiazide50 mg daily promptly corrected the acidosis and the hyperkalaemiaby increased urinary potassium excretion. We conclude that theacidosis of type II pseudohypoaldosteronism is due in part toattenuation of the voltage-dependent moiety of mineralocorticoid-drivenacidification caused by enhanced distal chloride reabsorption.Suppression of ammoniagenesis by hyperlkalaemia exaggeratesthe acidosis. The acidosis and hyperkalemia are corrected byhydrochlorothiazide. ¹Present address: Department of Medicine, Naval Medical Center,Okinawa The opinions and assertions contained herein are the privateones of the authors and are not to be construed as officialor reflecting the views of the Naval Medical Command or theUnited States Navy. ³Present address: 28 Deerpath Dr.,New Hartford, NY 13413, USA     

Dietary Changes Favorably Affect Bone Remodeling in Older Adults

OBJECTIVE: To determine whether dietary counseling to increase milk intake could produce useful changes in the calcium economy and what, if any, other nutrition-related changes might be produced. DESIGN: Randomized, open trial. SUBJECTS/SETTING: Two hundred four healthy men and women, aged 55 to 85 years, who habitually consumed fewer than 1.5 servings of dairy foods per day. Six academic health centers in the United States. INTERVENTION: Subjects were instructed to consume 3 servings per day of nonfat milk or 1% milk as a part of their daily diets, or to maintain their usual diets, for a 12-week intervention period, which followed 4 weeks of baseline observations. MAIN OUTCOME MEASURES: Energy and nutrient intake assessed from milk intake logs and 3-day food records; serum calciotrophic hormone levels at baseline and at 8 and 12 weeks; urinary excretion of calcium and N-telopeptide at 12 weeks. STATISTICAL ANALYSES: Repeated-measures analysis of variance. RESULTS: In the milk-supplemented group, calcium intake increased by 729 +/- 45 mg/day (mean +/- standard error), serum parathyroid hormone level decreased by approximately 9%, and urinary excretion of N-telopeptide, a bone resorption marker, decreased by 13%. Urine calcium excretion increased in milk-supplemented subjects by 21 +/- 7.6 mg/day (mean +/- standard error), less than half the amount predicted to be absorbed from the increment in calcium intake. All of these changes were significantly different from baseline values in the milk group and from the corresponding changes in the control group. Bone-specific alkaline phosphatase level (a bone formation marker) fell by approximately 9% in both groups. Serum level of insulin-like growth factor-1 (IGF-1) rose by 10% in the milk group (P < .001), and the level of insulin-like growth factor binding protein-4 (IGFBP-4) fell slightly (1.9%) in the milk group and rose significantly (7.9%) in the control group (P < .05). APPLICATIONS/CONCLUSIONS: The changes observed in the calcium economy through consumption of food sources of calcium are similar in kind and extent to those reported previously for calcium supplement tablets. The increase in IGF-1 level and the decrease in IBFBP-4 level are new observations that are beneficial for bone health. Important improvements in skeletal metabolism can feasibly occur in older adults by consumption of food sources of calcium. Dietitians can be confident that food works, and that desired calcium intakes can be achieved using food sources.     

A Field Test of the Sweat Patch

The sweat patch is a new, noninvasive method designed to estimate the ethanol consumption of drinking subjects. It consists of salt-impregnated absorbent pads protected by a plastic chamber with attached water-tight adhesive. The patch reportedly collects transepidermal fluid at a steady rate for up to 10 days. Recent laboratory research has indicated a linear relationship between the concentration of ethanol in transepidermal fluid and mean concentration of ethanol in blood. Levels of ethanol in the sweat patch allowed identification of persons drinking at least 0.5 g of ethanol/kg/day with 100% sensitivity and specificity. The study reported here was conducted to test the field effectiveness of this sweat patch in normal, active research subjects. First, several pretests were conducted to determine the optimal location of the patch on the body and its fluid uptake at various sites. A laboratory experiment using nonalcoholic subjects was conducted to replicate previous work, and methods of measuring ethanol concentration in the patch were refined. A field test of the patch was then carried out. Healthy active volunteers drank a single "moderate" dose of ethanol (0.5 g of ETOH/kg of body weight) and then remained abstinent for the next 3 days. A week later, a "heavy" dose (1.0/kg of body weight) was consumed. Only a trace of ethanol was detected in any of the patches worn in either experiment. The patch did not measure ethanol in the transepidermal fluid under field conditions. Thus, further design modifications and pilot testing are required before the full benefits of this unobtrusive measure of drinking can be realized.