The Effect of Hemodialysis on Whole Blood, Plasma and Erythrocyte Viscosity

The effect of hemodialysis (HD) on blood viscosity has not been adequately investigated. We studied blood viscosity during HD employing coneplate viscometry. Ten patients with end-stage renal disease were studied before and immediately after HD. To dissect the possible effects of HD on plasma and red blood cell (RBC) determinants, we measured whole blood, plasma, and reconstituted erythrocyte viscosities. The latter consisted of RBC's suspended in a buffered saline solution (pH = 7.4 units). In addition, serum, electrolytes and hematocrit (HCT) were measured. The results revealed a significant rise in whole blood viscosity after dialysis. Likewise, plasma viscosity rose considerably with dialysis. However, when the RBC's were reconstituted to a constant HCT, no significant difference was noted before and after HD. As expected, body weight, blood urea nitrogen (BUN) and creatinine concentrations fell while HCT and protein concentration rose with HD. A significant correlation was found between the observed rise in HCT, and dialysis-induced rise in whole blood viscosity. Likewise, the observed rises in plasma viscosity after dialysis significantly correlated with the rise in protein concentration. In addition, the change in whole blood and plasma viscosity values correlated with the degree of ultrafiltration (weight loss). In conclusion, whole blood and plasma viscosity rises with hemodialysis. The observed rise in viscosity is primarily due to hemoconcentration.

Encephalopathy with combined lithium-risperidone administration

OBJECTIVE

Lithium-neuroleptics induced encephalopathy is a rare drug interaction. Here I am reporting a patient who developed reversible encepatholopathy with lithium-risperidone combination.

METHOD

A single case report.

RESULT

A patient of bipolar disorder, who presented with manic symptoms with psychotic feature, started with a combination of lithium and risperidone. Within few days, the patient developed encepatholopathy, which reversed upon discontinuation of lithium and risperidone.

CONCLUSION

Combining lithium and neuroleptic is useful in treatment of bipolar disorder. However, encepatholapthy can be anticipated to result when lithium is used with high potency anti-psychotic such as haloperidol and risperidone and there are baseline EEG abnormalities.

Pharmacodynamic modeling of the in vivo interaction between cefotaxime and ofloxacin by using serum ultrafiltrate inhibitory titers

The pharmacokinetics (PK) and pharmacodynamics (PD) of cefotaxime and ofloxacin and of their combination were examined in a three-period randomized crossover study involving 12 healthy adults. The PK of cefotaxime and ofloxacin were modeled. PD was assessed from the predicted concentrations in serum and serum untrafiltrate inhibitory titers for 10 test organisms. An inhibitory sigmoid Emax model based on the probability of bacterial growth was used, where Emax = 1 and EC50 is the concentration resulting in a 50% probability of growth. The total body clearance (CL(T)) and volume of distribution at steady state (V(SS)) for cefotaxime were 0.236 liters/kg/h and 0.207 liters/kg, respectively, for the monotherapy and 0.231 liters/kg/h and 0.208 liters/kg for the combination therapy. Ofloxacin exhibited PK parameters of 0.143 liters/kg/h for CL(T) and 1.20 liters/kg for V(SS) following the monotherapy and of 0.141 liters/kg/h for CL(T) and 1.16 liters/kg for V(SS) following combination therapy. For the combination therapy, an interaction term, theta, defined the type and relative extent of interaction. The range of observed theta values (-0.033 to 0.067) is consistent with an additive PD interaction according to standards similar to those used for the in vitro fractional inhibitory concentration index.

Evaluation of two opioid-acetaminophen combinations and placebo in postoperative oral surgery pain

STUDY OBJECTIVE

To determine the relative analgesic potency and adverse effect liability of hydrocodone bitartrate 7.5 mg with acetaminophen 500 mg, codeine phosphate 30 mg with acetaminophen 300 mg, and placebo in the treatment of pain following oral surgery.

DESIGN

Randomized, double-blind, single-dose, placebo-controlled, parallel-group study with self-ratings at 30 minutes and then at hourly intervals from hour 1 to hour 6.

SETTING

Private, oral surgery practice sites.

PATIENTS

Three hundred twenty-four outpatients with moderate or severe pain after the surgical removal of impacted third molars were selected. One was lost to follow-up and 32 did not need an analgesic; 232 patients had valid efficacy data.

INTERVENTIONS

Patients were treated with a single oral dose of hydrocodone bitartrate 7.5 mg with acetaminophen 500 mg, codeine phosphate 30 mg with acetaminophen 300 mg, or placebo when they experienced steady, moderate or severe pain that, in their opinion, required an analgesic. Using a self-rating record, subjects rated their pain and its relief for 6 hours after medicating; estimates of peak and total analgesia were derived from these subjective reports.

MEASUREMENTS AND MAIN RESULTS

This study was a valid analgesic assay. Both active treatments were significantly superior to placebo for all measures of analgesic efficacy. The hydrocodone-acetaminophen combination was significantly superior to the codeine-acetaminophen combination for total pain relief and the number of evaluations with 50% relief. Both active treatments manifested an analgesic effect within 30 minutes; the effect persisted for 5 hours for the codeine combination and 6 hours for the hydrocodone combination. Adverse effects were transient, consistent with the pharmacologic profiles of opioids, and none required treatment.

CONCLUSIONS

A slight advantage in analgesic efficacy was demonstrated in this single-dose study for the hydrocodone-acetaminophen combination. Repeat-dose studies, however, should be conducted to determine the clinical significance of the difference in analgesic effect of these opioid combinations.

The effect of sensor malpositioning on pulse oximeter accuracy during hypoxemia

BACKGROUND

Previous studies have shown that pulse oximeters whose sensors are positioned improperly may yield erroneously low saturation (SpO2) values on normoxemic subjects. The behavior of oximeters with malpositioned sensors during hypoxemia has not been studied. The current study is aimed at determining the behavior of several different pulse oximeters over a wide range of arterial oxygen saturation (SaO2).

METHODS

In each of 12 healthy volunteers, a radial artery cannula was inserted, and eight different pulse oximeters, five of which had malpositioned sensors, were applied. Subjects breathed controlled mixtures of nitrogen and oxygen to slowly vary their SaO2 from 100% to 70%. Arterial blood samples were analyzed and pulse oximeter data were recorded at five stable SaO2 values for each subject.

RESULTS

The oximeters with malpositioned sensors vary greatly in their behavior, depending on both the actual SaO2 and the manufacturer and model. One oximeter underestimated saturation at all SaO2 values, while three others underestimated at high SaO2 and overestimated at low SaO2. Linear regression analysis shows a decrease in the slope of SpO2 versus SaO2 in most cases, indicating a loss of sensitivity to SaO2 changes. Between-subject variation in response curves was significant.

CONCLUSIONS

The calibration curves of the pulse oximeters studied were changed greatly by sensor malpositioning. At low SaO2 values, these changes could cause the oximeter to indicate that a patient was only mildly hypoxemic when, in fact, hypoxemia was profound. It is recommended that sensor position be checked frequently and that inaccessible sensor locations be avoided whenever possible.

A comparison of bag mask and mouth mask ventilation in anaesthetised patients

Anaesthetic residents used bag valve mask (BVM) or mouth mask (MM) ventilation, both with an O2 flow of 15 l min-1 to ventilate 30 ASA I or II anaesthetised patients for 4 min prior to endotracheal intubation. Mean nasopharyngeal O2 was higher with BVM (BVM 95% (S.D. 3%) MM 54% (S.D. 12%)). End tidal CO2 (ETCO2) was similar in both groups (ETCO2% at 4 min: BVM 4.65 (S.D. 0.84) MM 4.53 (S.D. 0.54)) but respiratory rate was faster with BVM (BVM 17 min-1 (S.D. 5) MM 12 min-1 (S.D. 4)). Peak (Paw) and mean (Paw) airway pressures were higher with MM and MM produced significant expiratory pressure [cmH2O: BVM Paw 16.7 (S.D. 5.3) Paw 4.2 (S.D. 2.1) MM: Paw 20.9 (S.D. 5.2) Paw 7.8 (S.D. 2.1)) minimum expiratory pressure: MM 2.4 (S.D. 1.1) BVM 0.2 (S.D. 0.4). Gastric insufflation was detected in two MM and two BVM patients. This tended to be more severe with MM ventilation. Although MM ventilation has some important disadvantages it can be used effectively by resuscitators with little or no experience in its use.

Anesthesia for thoracoscopic laser ablation of bullous emphysema

BACKGROUND

We describe the anesthetic management for a new surgical procedure: laser ablation of emphysematous bullae via thoracoscope. Although thoracoscopy is not new, this is the first description of a series of patients with bilateral, chronic lung disease who underwent long periods of one-lung ventilation (OLV) during thoracoscopic therapy.

METHODS

Twenty-six laser ablation procedures were performed in 22 patients. The patients were elderly (mean age 63 yr) with a large incidence of coexisting cardiovascular disease. Most required chronic home oxygen therapy. Patients were monitored invasively, and hemodynamic data were recorded every 5 min. Arterial blood gas analyses were performed every 15 min. Comparisons were made between three intraoperative periods: two-lung ventilation (TLV) before thoracoscopy, OLV during thoracoscopy, and TLV after thoracoscopy.

RESULTS

All patients survived the operation despite a mean OLV duration of 170 min, but several experienced serious intraoperative problems, such as hypoxemia or hypotension. Hypoxemia was treated with nondependent lung continuous positive airway pressure and dependent lung positive end-expiratory pressure. In all patients the lungs were adequately ventilated, but bronchopleural fistulae occurred upon return to TLV in every case. The resulting air leaks, often 50% of inspired tidal volume, required the use of a pressure-cycled ventilator to maintain oxygenation. Postoperative air leaks greater than 50% of inspired tidal volume usually required subsequent surgical correction, while smaller leaks resolved spontaneously. Mechanical ventilation was required for an average of 5 days. Eighty-four percent have survived at least 6 months, and nearly all survivors report symptomatic improvement.

CONCLUSIONS

Ablation of bullae appears to provide symptomatic improvement, and thoracoscopy might be better tolerated than thoracotomy, especially in patients with severe bullous emphysema.

The Laerdal pocket mask: effects of increasing supplementary oxygen flow

To determine the effect of increasing supplementary oxygen flow during ventilation with the Laerdal pocket mask 24 subjects ventilated a modified recording mannikin for four 90 s periods using the mask with oxygen flows of 5 l, 10 l, 15 l and 20 l.min-1. Oxygen concentration increased and carbon dioxide concentration decreased with increasing oxygen flow. Tidal volume also increased with oxygen flow. The delivered oxygen concentrations were lower than previously reported at all four rates; however, mask function improved with increasing flow up to 20 l.

A new technique for two-hand bag valve mask ventilation

A method of bag valve mask ventilation (BVM) in which the resuscitator compresses the self-inflating bag between the open palm and body was compared with both standard single resuscitator and two-resuscitator BVM ventilation. Eighteen subjects ventilated a modified recording manikin using each method in random order. The tidal volume (VT) was greater with the open palm (mean 684 (SD 182) ml) than standard single resuscitator ventilation (mean 520 (152) ml). The difference was greater in the nine subjects with small hands (mean 196 (103) ml). VT was less than with two-resuscitator ventilation (mean VT 953 (236) ml).

Hyperventilation reduces transcutaneous oxygen tension and skin blood flow

Transcutaneous oxygen tension (PtcO2) is often used to monitor neonates and infants in special care units and the operating room. The transcutaneous index (TCI = PtcO2/arterial oxygen tension [PaO2]) is known to depend both on age and on cardiac index but is assumed to be independent of other physiologic variables. In this study we have shown that TCI also depends upon arterial carbon dioxide tension (PaCO2). Five young pigs were anesthetized and paralyzed and their lungs mechanically ventilated while they were monitored with PtcO2 electrodes and serial arterial blood gas analyses. For a 45 degrees C PtcO2 sensor, the mean TCI during normocapnia was 0.78, whereas during hyperventilation (PaCO2 = 20 mmHg) the mean TCI was reduced 65%, to 0.27. The corresponding TCI values for a 43 degrees C sensor were 0.33 and 0.065, representing an 80% decrease in TCI during hyperventilation. Hypoventilation had little effect upon TCI as long as hypoxemia was avoided. Twelve awake adult volunteers with radial artery cannulas were monitored with PtcO2 sensors at several body sites and two sensor temperatures. For a 44 degrees C sensor on the chest, the mean TCI decreased from 0.77 at normocapnia to 0.60 at a PaCO2 of 17 mmHg, a 22% change. For the same sensor on the foot, TCI decreased from 0.63 to 0.32, a 49% change. For a 42 degrees C sensor under the same conditions, the corresponding TCI decreases were 51 and 64%. Six of the volunteers were also monitored with laser-Doppler skin blood flow probes located on the chest, hand, and foot.(ABSTRACT TRUNCATED AT 250 WORDS)

Continuous measurement of intraarterial pHa, PaCO2, and PaO2 in the operating room

Miniaturized sensors based upon the principles of optical fluorescence can measure the pH, PCO2, and PO2 of liquid or gas media. A prototype of a three-component fiberoptic sensor has been developed for intraarterial application by CDI, 3M Health Care, Irvine, California. We report the first study of this continuous intraarterial monitor in patients undergoing surgical procedures under general anesthesia. Fourteen patients participated in the study. The fiberoptic sensor was calibrated before insertion and then passed through an existing 18-gauge radial artery cannula. Blood samples were drawn at frequent intervals through the same cannula for in vitro blood gas analysis. For each of the 87 arterial blood gas samples obtained, the in vitro values of pHa, PaCO2, and PaO2 were compared with simultaneous readings from the fiberoptic sensor. For pHa, the mean error (error = fiberoptic value minus in vitro value) or "bias" of the fiberoptic data was -0.032 and the standard deviation of error or "precision" was 0.042. For PaCO2, the bias was -3.8 mm Hg and the precision was 4.7 mm Hg. For PaO2, the bias was -9.0 mm Hg and the precision was 23.3 mm Hg. For PaO2 values less than 175 mm Hg, the bias was -8.5 mm Hg and the precision was 8.3 mm Hg. Expressed in terms of percentage errors, the bias +/- precision values were -11.5% +/- 13.3% for PaCO2, and -6.2% +/- 10.0% for PaO2. The duration of the surgical procedures ranged from 1.6 to 8 h with an average of 4.2 h.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo tumor oxygen tension measurements for the evaluation of the efficiency of photodynamic therapy

Among the sequence of events which occur during photodynamic therapy (PDT) are depletion of oxygen and disruption of tumor blood flow. In order to more clearly understand these phenomena we have utilized transcutaneous oxygen electrodes to monitor tissue oxygen disappearance. These results provide, for the first time, non-invasive real-time information regarding the influence of light dose on tissue oxygenation during irradiation. Measurements were conducted on transplanted VX-2 skin carcinomas grown in the ears of New Zealand white rabbits. Rabbits were treated with Photofrin II and tumors were irradiated with up to 200 kJ/m2 (500 W/m2) of 630-nm light. Substantial reductions in tumor oxygen tension were observed upon administration of as little as 20 kJ/m2. For a series of brief irradiations, oxygen tension was modulated by the appearance of laser light. Tissue oxygen reversibility appeared to be dependent upon PDT dose. Long-term, irreversible tissue hypoxia was recorded in tumors for large (200 kJ/m2) fluences. These results suggest that transcutaneous oxygen tension may be useful as a general indicator of the effectiveness of PDT and as an in situ predictor of the energy required to elicit tumor damage.

Cardiac pheochromocytoma originating in the interatrial septum

A 36-year-old woman with classic clinical and biochemical features of pheochromocytoma was found to have a cardiac pheochromocytoma originating in the interatrial septum and a significant obstructive lesion in the left anterior descending coronary artery. Complete resection of the pheochromocytoma and an aortosaphenous vein graft were performed. This is the first reported case of successful resection of an interatrial pheochromocytoma.

Effects of midazolam on fentanyl antinociception and respiration in a rabbit model

Clinical antinociception is difficult to assess because of difficulties with controls and the incorporation of bias. The rabbit antinociceptive model is highly sensitive and predictive of analgesia in humans. We found that the combination of midazolam with fentanyl enhanced antinociception compared with fentanyl alone. In addition, with this model there were relatively unimportant increases in respiratory depression.

Effect of erythropoietin administration on blood and plasma viscosity in hemodialysis patients

The effect of recombinant human erythropoietin (EPO) on whole blood and plasma viscosity was studied in six anemic hemodialysis (HD) patients, and five equally anemic placebo treated HD patients. Viscosity was determined pre- and postdialysis using cone-plate viscometry. Predialysis values for hematocrit and whole blood viscosity increased significantly over a 12 week period in the EPO but not the placebo treated group; plasma viscosity did not change in either group. Whole blood viscosity measured before and after a single HD session during week 12 revealed a significant rise. This change, expressed as a percent of the predialysis values, was similar in the two groups. Thus, the rise in whole blood viscosity seen in EPO treated patients is a result of the increase in erythrocyte concentration and not a result of an effect of EPO on plasma. In addition, EPO does not seem to alter the acute effect of HD on blood viscosity.

Effects of methemoglobinemia on pulse oximetry and mixed venous oximetry

The performance of three commercially available pulse oximeters was assessed in five anesthetized dogs in which increasing levels of methemoglobin were induced. Hemoglobin oxygen saturation in each dog was monitored with three pulse oximeters (Nellcor N-100, Ohmeda 3700, and Novametrix 500) and a mixed venous saturation pulmonary artery catheter (Oximetrix Opticath). Arterial and mixed venous blood specimens were analyzed for PaO2, PaCO2, and pHa using standard electrodes. An IL-282 Co-oximeter was used on the same specimens to determine oxyhemoglobin and methemoglobin as percentages of total hemoglobin. Methemoglobin levels of up to 60% were induced by intratracheal benzocaine. As MetHb gradually increased while the dogs were breathing 100% inspired oxygen, the pulse oximeter saturation (SpO2) overestimated the fractional oxygen saturation (SaO2) by an amount proportional to the concentration of methemoglobin until the latter reached approximately 35%. At this level the SpO2 values reached a plateau of 84-86% and did not decrease further. When, at fixed methemoglobin levels, additional hemoglobin desaturation was induced by reducing inspired oxygen fraction, SpO2 changed by much less than did SaO2 (regression slopes from 0.16 to 0.32). Thus, at high methemoglobin levels SpO2 tends to overestimate SaO2 by larger amounts at low hemoglobin saturations. Plots of SpO2 versus functional saturation (oxyhemoglobin/reduced hemoglobin plus oxyhemoglobin) show an improved but still poor relationship (regression slopes from 0.32 to 0.46). The Oximetrix Opticath pulmonary artery catheter behaves similarly but provides somewhat better agreement with functional saturation than do the pulse oximeters in the presence of methemoglobinemia. Pulse oximetry data (SpO2) should be used with caution in patients with methemoglobinemia.

Comparison of three oxygen monitors in detecting endobronchial intubation

Rapid and reliable detection of inadvertent endobronchial intubation is an essential function of oxygen monitoring. We have studied the detection of this event by using three oxygen monitoring techniques: pulse oximetry, transcutaneous measurement of oxygen tension, and intraarterial fiberoptic measurement of oxygen tension. Four dogs were anesthetized, intubated, and monitored with these three techniques and with arterial and central venous cannulas. Endotracheal tubes were moved from the trachea into the right mainstem bronchi at several inspired oxygen fraction (FIO2) values for each dog, and the responses of the oxygen monitors were recorded for 20 minutes thereafter. The pulse oximeter showed little change in oxygen saturation (SpO2) during endobronchial intubation at FIO2 values above 0.3. SpO2 decreased by an average of 1.3 +/- 2.1% at an FIO2 of 1.0 and by 4.0 +/- 4.1% at an FIO2 of 0.5. Simultaneously measured transcutaneous oxygen tensions decreased by 42 to 64% and the optode reading decreased by 64 to 79%. At lower FIO2 values, the changes in SpO2 were more significant: a decrease of 6.0 +/- 6.3% at an FIO2 of 0.3 and of 9.8 +/- 6.1% at an FIO2 of 0.2. The transcutaneous oxygen and optode readings decreased by 31 to 45% under these conditions. Endobronchial intubations at FIO2 values greater than 0.3 may not yield immediate decreases in arterial saturation and hence may go undetected by pulse oximetry. Transcutaneous oxygen tension decreases significantly with endobronchial intubation at any FIO2. The experimental, intraarterial optode consistently yielded the greatest changes with the fastest time response.

The effect of hemodialysis on whole blood, plasma and erythrocyte viscosity

The effect of hemodialysis (HD) on blood viscosity has not been adequately investigated. We studied blood viscosity during HD employing coneplate viscometry. Ten patients with end-stage renal disease were studied before and immediately after HD. To dissect the possible effects of HD on plasma and red blood cell (RBC) determinants, we measured whole blood, plasma, and reconstituted erythrocyte viscosities. The latter consisted of RBC's suspended in a buffered saline solution (pH = 7.4 units). In addition, serum, electrolytes and hematocrit (HCT) were measured. The results revealed a significant rise in whole blood viscosity after dialysis. Likewise, plasma viscosity rose considerably with dialysis. However, when the RBC's were reconstituted to a constant HCT, no significant difference was noted before and after HD. As expected, body weight, blood urea nitrogen (BUN) and creatinine concentrations fell while HCT and protein concentration rose with HD. A significant correlation was found between the observed rise in HCT, and dialysis-induced rise in whole blood viscosity. Likewise, the observed rises in plasma viscosity after dialysis significantly correlated with the rise in protein concentration. In addition, the change in whole blood and plasma viscosity values correlated with the degree of ultrafiltration (weight loss). In conclusion, whole blood and plasma viscosity rises with hemodialysis. The observed rise in viscosity is primarily due to hemoconcentration.

Laser Doppler velocimetry in critically ill patients

Cutaneous blood flow may be an indirect measure of circulatory function estimated by continuous, noninvasive laser Doppler velocimetry (LDV). It has been postulated that LDV may be a useful monitor of cardiac output changes. To test this hypothesis, LDV was evaluated in 67 critically ill adult patients with simultaneous measurements of cardiac index (CI) and other physiologic variables. Heated and unheated laser probes were utilized. The results indicate that LDV reflects acute directional changes of CI. Further, with the heated laser probe, the magnitude of acute CI change is reflected. However, there are gradual changes over time of LDV which may occur independently of CI or other monitored variables. Hence, absolute LDV values are not predictive of absolute CI values.

Effect of an air-fluidized bed on insensible water loss

Air-fluidized beds are increasingly used for patients with burns, decubitus ulcers, trauma, and generalized debility. Fluidized beds provide a medium that is more dense than water for patients to float on by pumping air through silicone-coated microspheres separated from the patient by a monofilament polyester sheet. A continuous stream of warm air flowing across the patient increases insensible evaporative water loss and may lead to dehydration. The air-fluidized bed has a wide range of operating temperatures (82 degrees to 102 degrees F), but surprisingly few data are available on the amount of water loss at different bed temperatures. This lack of information is probably secondary to difficulties in obtaining accurate fluid balance measurements in patients. Our objective was to construct a nomogram of insensible water loss for the fluidized bed using healthy volunteers under controlled conditions. We then prospectively compared this nomogram to data obtained from hospitalized patients.

Continuous fiberoptic arterial oxygen tension measurements in dogs

An experimental study using a new fiberoptic sensor for the continuous intraarterial measurement of oxygen tension is described. This "optode" sensor uses the phenomenon of fluorescence quenching to determine the oxygen tension of the surrounding medium. To assess the accuracy of this device, we anesthetized 4 dogs and monitored them continuously with arterial catheters and an intraarterial optode probe, and intermittently with arterial blood gas analysis. The inspired oxygen fraction was varied from 1.0 to 0.1, and arterial blood gases were measured for comparison with the optode reading. Two hundred ninety data sets yielded a correlation coefficient of 0.96, with a linear regression slope of 0.98 and intercept of 5.1 mm Hg. In the 72 data sets from the last dog, the bias and precision of the optode arterial oxygen tension values were -10.3 mm Hg and 20.0 mm Hg, respectively. The optode probe was easily inserted through a 20-gauge catheter and did not interfere with continuous arterial pressure measurement or blood sampling. This study suggests that the optode has great potential as a continuous, real-time monitor of arterial oxygen tension.

Comparison of clinical effects and pharmacokinetics of once-daily Uniphyl and twice-daily Theo-Dur in asthmatic patients

A pharmacokinetic study using theophylline syrup in adult asthmatic patients demonstrated a mean apparent volume of distribution of 0.38 liters/kg, mean elimination rate constant of 0.10 hours-1, and variable rates of clearance of theophylline (total body clearance of 0.38 to 0.96 ml/kg per minute). Subsequently, the asthmatic patients were compared using a cross-over design after maintenance Uniphyl (once daily at 8 a.m. or at 8 p.m.) and Theo-Dur (twice daily at 8 a.m. and 8 p.m.). Total daily maintenance theophylline dosage, calculated from the pharmacokinetic data, was identical in all three cross-over phases. At the end of each phase, plasma theophylline levels were measured every two hours and spirometric determinations were made every four hours (excluding 4 a.m.) for 24 hours. The following results were observed: highest peak and mean plasma theophylline concentration and area under the concentration-time curves with evening Uniphyl (p less than 0.05); prolonged time-to-peak theophylline concentration after nocturnal compared with daytime dosing; diurnal variation in pulmonary function and plasma theophylline concentrations; no significant differences between the three maintenance treatments in asthmatic symptoms or spirometric results.

Dialysis hypoxemia. Role of dialyzer membrane and dialysate delivery system

Arterial blood gas values, carbon monoxide diffusion capacity, oxygen consumption, carbon dioxide production, respiratory quotient, minute ventilation, and pulmonary capillary blood flow were determined before and during hemodialysis. In addition, the effect of single passage through the dialyzer on blood carbon dioxide tension, pH, and bicarbonate concentration was evaluated. Acetate-based dialysate was used in all experiments. Cellulosic dialyzer with single-pass dialysate delivery system was used in one group, and polyacrylonitrile dialyzers with recirculating delivery system in another. Although hypoxemia occurred in both groups, it was more severe in the former group. Dialyzer carbon dioxide loss was significantly greater with single-pass dialysate delivery system and cellulosic dialyzers than with recirculating delivery system and polyacrylonitrile dialyzer. To differentiate the role of dialysate delivery system from that of the membrane, the experiments were repeated using recirculating delivery system and cellulosic dialyzer. This resulted in marked attenuation of hypoxemia and dialyzer carbon dioxide tension losses. Since other experimental conditions were the same, the observed differences were thought to be due to the difference in the mode of dialysate delivery. It thus appears that the mode of dialysate delivery per se can modify the changes in arterial oxygen tension during hemodialysis and should be added to the list of factors implicated in the genesis of dialysis hypoxemia.