Clearance and distribution of intratracheally instilled vanadium compounds in the rat.

Intratracheally instilled 48V2O5 was rapidly cleared from the lung into blood, liver and bone. Approx. 40% of the recovered 48V was excreted, primarily in urine by day 3, while the skeleton accounted for 30% by day 7. The behavior of instilled 48VO2Cl was similar to that of 48V2O5. Uptake of gavaged 48V2O5 was 2.6% of administered dose. Skeleton, lung, kidney and liver are primary targets for intratracheally instilled 48V with uptake being much greater via the intratracheal route than by the oral route.

Carbon dioxide elimination measures resolution of experimental pulmonary embolus in dogs.

Patients with severe pulmonary embolism can suffer progressive hypercapnia refractory to supramaximal mechanical ventilation, and may require open-thoracic or transvenous emergency embolectomy in addition to anticoagulation and/or thrombolysis. The functional recovery of gas exchange would be signaled by an increase in pulmonary CO2 elimination and decrease in CO2 retention; such data could guide the course of operative embolectomy. Accordingly, we studied five chloralose-urethane anesthetized, mechanically ventilated dogs with open thoraces in which the right pulmonary arteries (RPAs) were reversibly occluded with cloth snares. After waiting for steady state, we abruptly released the snare to restore RPA perfusion and experimentally simulate resolution of pulmonary embolism. For 70 min we serially measure the CO2 volume exhaled per breath (VCO2,br), arterial, mixed venous, and end-tidal PCO2 (PACO2, PVCO2, PETCO2), cardiac output (QT), and the alveolar dead space fraction (VDalv/VTalv = [PaCO2 - PETCO2/PaCO2). RPA reperfusion caused VCO2,br to significantly and abruptly increase from 8.9 +/- 2.7 to 11.6 +/- 3.6 mL; 70 min later VCO2,br had returned to baseline. PaCO2 and PVCO2 steadily decreased during 70 min of RPA reperfusion. PETCO2 increased from 25 +/- 5 to 33 +/- 5 mm Hg immediately after RPA reperfusion, as VDalv/VTalv decreased from 54% +/- 10% to 32% +/- 12%, but PETCO2 was still significantly greater than baseline at 70 min of RPA reperfusion. QT did not significantly change. We conclude that intraoperative measurement of VCO2,br should immediately detect and follow the resolution of CO2 retention in the lung and peripheral tissues after RPA reperfusion. PETCO2 could not detect the decrease of VCO2,br back to baseline because PETCO2 does not measure exhaled volume or the PCO2 waveform.

Capnometer transport delay: measurement and clinical implications.

The sidestream capnogram is delayed behind real time by transport delay (TD; time to aspirate gas through the sampling tubing) and by the dynamic response (DR) of the measurement cuvette. In six capnometers, we measured TD and DR by plunging the end of the sample tubing into a flask containing CO2 and then digitally analyzing the capnogram. TD ranged from 0.6 to 5.0 s and accounted for 89% or more of the total response time (TD + DR) of the capnometer. TD was generally not reported in the manufacturers' specifications. TD was further prolonged by low aspiration rates or by sampling tube extensions. During a series of quick breaths after endotracheal intubation, long TD can delay the appearance of CO2 and result in a false diagnosis of esophageal intubation. Also, long TD can prolong DR, which can result in underestimation of end-tidal PCO2 during rapid ventilation in pediatric anesthesia.

How does experimental pulmonary embolism decrease CO2 elimination?

To test how large pulmonary embolism changes non-steady state CO2 kinetics, the right pulmonary artery (RPA) was occluded in 5 anesthetized, ventilated, thoracotomized dogs. By 1 min after RPA occlusion, CO2 volume exhaled per breath (VCO2,br) decreased from 9.3 +/- 2.8 to 7.0 +/- 2.6 ml and end-tidal PCO2 (PETCO2) decreased from 28.7 +/- 4.2 to 21.8 +/- 3.3 Torr. During the ensuing 70 min, VCO2,br increased back to baseline but PETCO2 was still 13% less than baseline. Both PaCO2 (41.5 +/- 1.7 to 55.1 +/- 8.1 Torr) and PvCO2 (48.2 +/- 1.9 to 62.8 +/- 6.5 Torr) steadily increased and approached equilibrium by 45 min of RPA occlusion. Cardiac output did not significantly change. In summary, RPA occlusion immediately decreased VCO2,br by 25%, due mostly to increased alveolar VD (VDalv). Then, VCO2,br recovered back to baseline as CO2 accumulated in tissues and lung. In contrast, elevated VDalv caused persistent decreased PETCO2, which did not detect recovery of VCO2,br nor increase in PaCO2 during RPA occlusion.

Comparison of end-tidal PCO2 and average alveolar expired PCO2 during positive end-expiratory pressure.

The measurement of average alveolar expired PCO2 (PAECO2) weights each PCO2 value on the alveolar plateau of the CO2 expirogram by the simultaneous change in exhaled volume. PAECO2 can be determined from a modified analysis of the Fowler anatomic dead space (VDANAT). In contrast, end-tidal PCO2 (PETCO2) only measures PCO2 in the last small volume of exhalate. In conditions such as mechanical ventilation with positive end-expiratory pressure (PEEP), where the alveolar plateau can have a significant positive slope, we questioned how much PETCO2 could overestimate PAECO2. Accordingly, in six anesthetized ventilated dogs, we digitally measured and processed tidal PCO2 and flow to determine VDANAT. We determined PETCO2 and PAECO before and after the application of 7.6 cm H2O PEEP. Alveolar dead space to tidal volume fraction (VD/VT) was determined by [arterial PCO2- alveolar PCO2]/arterial PCO2, where alveolar PCO2 was determined by either PETCO2 or PAECO2. During baseline ventilation, PETCO2 was 3.4 mm Hg (approximately 11%) greater than PAECO2. Because PEEP significantly increased the slope of the alveolar plateau from 28 to 74 mm Hg/L, the difference between PETCO2 and PAECO2 significantly increased to 6.6 mm Hg (approximately 20% difference). The concurrent increase in VDANAT during PEEP decreased alveolar tidal volume and tended to limit the overestimation of PETCO2 compared to PAECO2. When alveolar PCO2 was estimated by PETCO2, alveolar VD/VT was 18%, compared to an alveolar VD/VT of 26% when alveolar PCO2 was estimated by PAECO2. This difference was significantly magnified during PEEP ventilation. The overestimation of PAECO2 by PETCO2 can result in a falsely high assessment of overall alveolar PCO2. Moreover, the use of PETCO2 to estimate alveolar PCO2 in the determination of the alveolar dead space fraction can result in falsely low and even negative values of alveolar dead space.

Diarrhea and abnormalities of gastrointestinal function in a cohort of men and women with HIV infection.

OBJECTIVE: The aim of this study was to determine the prevalence of gastrointestinal dysfunction in the era of improved treatment of HIV infection. METHODS: Gastrointestinal function was studied cross-sectionally in 671 persons with HIV. Absorptive function was measured by a 25-g D-xylose test, a Sudan-III stain for fecal fat on a 100-g fat diet, and serum levels of micronutrients. RESULTS: Eighty-eight percent had at least one abnormality of gastrointestinal function: 47.7% had low D-xylose absorption; 40.3% had a history of liver disease; 38.9% had diarrhea; 28.3% had chronic diarrhea; 22.5% had borderline or low serum vitamin B12 levels; 12.2% had stool pathogens; and 7.2% were hypoalbuminemic. Men were more likely to have low D-xylose absorption, diarrhea, and stool pathogens than women. Intravenous drug users (IVDUs) were more likely to have a history of liver disease and hypoalbuminemia. However, borderline or low vitamin B12 levels were less frequent in IVDUs; they tended to have less diarrhea and a lower prevalence of stool pathogens. Despite less history of liver disease, 14.1% of women were hypoalbuminemic. Differences in patterns of gastrointestinal dysfunction are unlikely to be due to severity of immunosuppression as abnormalities were seen in all risk groups with CD4 >200 cells/mm3. D-xylose absorption below 30 mg/dl, current diarrhea, and borderline levels of vitamin B12 were associated with advanced immunosuppression. CONCLUSIONS: Abnormalities of gastrointestinal function are common in the current era of HIV treatment, appear early in the course of HIV infection, and in the absence of diarrhea. Gender and IVDU are important determinants of the type and frequency of gastrointestinal abnormalities.

Measurement of blood CO2 concentration with a conventional PCO2 analyzer.

OBJECTIVES: CO2 content can be determined from the Pco2 in an acidified (forces all CO2 into solution) and diluted blood sample. However, Pco2 concentrations measured in conventional blood gas analyzers are only correct for samples with a significant buffer capacity (such as whole blood), so that mixing with the Pco2 in the rinse solution and tubing walls does not significantly change the sample Pco2. This study describes a calibration method and validation data for the Radiometer Medical ABL2 CO2 electrode system to accurately measure unbuffered blood samples used in the determination of blood CO2 content (or other aqueous fluids). DESIGN: Prospective, criterion standard. SETTING: Laboratory. MEASUREMENTS AND MAIN RESULTS: Blood samples (0.4 mL) were acidified and diluted with 0.2 M lactic acid. After measuring Pco2, CO2 content was calculated using the CO2 solubility coefficient and the dilution factor of 20. CO2 content was determined in a series of sodium carbonate (Na2CO3) solutions spanning the physiologic range of CO2 content. Regression of the measured vs. the actual CO2 content data generated a straight line with a slope of 0.796 and y-intercept of 12.5 (r2 = .99; n = 48). These coefficients were successfully used to correct CO2 content determined in blood samples into which graduated amounts of sodium carbonate were added. CONCLUSIONS: This calibration procedure allows accurate measurement of Pco2 in aqueous samples using the Radiometer ABL2 electrode system, and should be applicable to other blood gas analyzers. Necessary syringes and chemicals are readily available, the method is fast and simple, and the sample volume is small. In the practice of critical care medicine, accurate Pco2 measurement in aqueous acidified and diluted blood provides direct determination of blood CO2 content (useful in calculations of modified Fick cardiac output or tissue CO2 production). Determinations of absolute CO2 content in blood requiring complex methodology are not necessary. In addition, accurate measurement of aqueous gastric Pco2 can help determine gastric pH, which is an important marker of tissue perfusion.

Body composition and dietary intake in relation to drug abuse in a cohort of HIV-positive persons.

We examined the relationships between drug abuse, weight, body composition, and dietary intake in persons infected with HIV in a cross-sectional analysis of baseline data from a longitudinal study of nutritional status and HIV. Body composition was measured by bioelectrical impedance analysis. Dietary data were collected by 3-day food records or 24-hour recalls. We analyzed data from 39 current intravenous drug users (IVDU), 103 past intravenous drug users (past-IVDU), 239 users of nonintravenous drugs (users-NIVD), and 61 nonusers (reference category). In the men, there were no differences in weight, body mass index (BMI), or body composition among the drug-use groups. In the women, there was a trend to lower weight and BMI across the drug use categories: IVDU women had lower average weight (-13.7 kg; p = .006), BMI (-5.6 units; p = .003) and less fat mass than non-users (-9.8 kg; p = .0001). In women, drug users had higher weight-adjusted energy intakes than nonusers, whereas in the men both drug using groups, NIVD and IVDU, had higher energy intakes than nonusers. These data suggest that intravenous drug-abuse is associated with lower weight and fat mass in women with HIV infection despite adequate self-reported energy intake.