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Biomedical subjects

C K Mahutte

Publications and source records attributed to C K Mahutte.

At least 19 recordsLinked to original sources
PubMed1999

Effects of sodium bicarbonate administration on the exercise tolerance of normal subjects breathing through dead space.

STUDY OBJECTIVE: The purpose of this study was to determine whether the administration of sodium bicarbonate to normal individuals would increase their PaCO2 and thereby decrease the ventilatory requirements at a given workload. DESIGN: In this double-blind crossover study, six normal men ingested either 3 mEq/kg NaHCO3 or 1 mEq/kg NaCl once a day for 5 days, in addition to 40 mg of furosemide and 40 mEq KCl. After each 5-day treatment, the subjects underwent a symptom-limited maximal bicycle ergometer exercise test while breathing through external dead space (with a volume of approximately 50% of their FEV1), a second exercise test without any external dead space, and an assessment of their respiratory response to hypercapnia. RESULTS: The administration of the NaHCO3 resulted in a significant increase in the arterial HCO3- from 20.8 to 24.0 mEq/L and a significant increase in the PaCO2 from 31.7 to 36.9 mm Hg at rest that persisted during exercise. During exercise periods with the added dead space, the Borg scores were significantly lower at each workload after the subjects received bicarbonate, but the maximal exercise level did not increase. The mean (+/-SD) slope of the mouth occlusion pressure response to hypercapnia was significantly lower after the administration of NaHCO3 than after NaCl, respectively: 0.73+/-0.41 vs 1.27+/-0.97 cm H2O/mm Hg. CONCLUSION: From this study we conclude that the administration of NaHCO3 results in a significant increase in the PaCO2, decreases the ventilation and the Borg score at equivalent workloads, and decreases the hypercapnic response in normal individuals.

Adult↗
PubMed1998

On-line arterial blood gas analysis with optodes: current status.

OBJECTIVES: To summarize the rationale for and the principles of blood gas and pH measurement with photochemical sensors (optodes) placed in the arterial line--either intravascularly (in vivo) or extravascularly (ex vivo). To review the specific problems that occur with in vivo measurement; the clinical data that have been obtained with continuous intravascular and on-demand extravascular systems; and, the role of this technology in the intensive care unit. METHODS AND RESULTS: The principles of absorbance and fluorescent optical sensors are described. The accuracy of intravascular PO2 optodes can be affected by thrombosis, the wall effect (if the sensor touches the arterial wall it may read tissue values) and reduced blood flow past the sensor. Current optical pH, PCO2 and PO2 probe/cannula designs, including hybrid probes with electrochemical PO2 sensors, have not yet fully overcome these problems of the intravascular milieu. On-demand blood gas monitors that locate the optodes extravascularly, within the radial artery line, avoid these intravascular measurement problems. On-demand systems can have accuracy comparable to conventional laboratory blood gas analyzers. With either intravascular or extravascular measurement large patient studies are lacking and the relevant cost benefit ratios are not known. CONCLUSION: Before intravascular monitors can be used routinely for clinical care, reliability, consistency and accuracy will have to be demonstrated in large and widely divergent patient groups. Extravascular on-demand blood gas analysis is accurate, allows trend monitoring of blood gases and decreases the risk of infection, the therapeutic decision time and patient blood loss. As large patient studies are lacking the clinical role of on-line blood gas analysis cannot be clearly delineated.

Biosensing Techniques↗
PubMed1997

O2-induced change in ventilation and ventilatory drive in COPD.

We examined the role of respiratory control during O2-induced hypercarbia in patients with chronic obstructive pulmonary disease (COPD), by comparing the observed change in ventilation (delta VEobs) with the delta VE predicted (delta VEpred) from the patients' ventilatory drive and the O2-induced delta PaCO2 and delta SaO2. Eleven stable hypoxemic COPD patients (mean +/- SD: FEV1 = 1.00 +/- 0.25 L, FVC = 2.33 +/- 0.38 L; room air PaCO2 = 52.7 +/- 7.9 mm Hg, SaO2 87.7 +/- 5.1%) were studied. Using standard rebreathing methods, we measured the ventilatory responses to hypercapnia (delta VE/PCO2 = 0.76 +/- 0.55 L/min/mm Hg) and to hypoxia (delta VE/delta SaO2 = -0.74 +/- 0.31 L/min/%). After breathing 100% O2 for 15 min, the mean delta VEobs was -0.08 +/- 0.62 (SEM) L/min (p = NS), the delta SaO2 was 7.6 +/- 3.6% (p < 0.001), and the delta PaCO2 was 6.6 +/- 3.3 mm Hg (p < 0.001). The delta VEpred was expressed as the sum of a decrease in ventilation due to suppression of hypoxic drive [calculated as the product (delta VE/SaO2) x delta SaO2] and an increase in ventilation due to the O2-induced hypercarbia [calculated as the production (delta VE/delta PCO2) x delta PaCO2]. The mean delta VEpred [-0.96 +/- 0.68 (SEM)] did not differ significantly from mean delta VEobs. We conclude that the O2-induced delta VEobs is equal to that expected from the ventilatory drives and the changes in PaCO2 and SaO2; and that O2-induced hypercarbia does not indicate a failure of respiratory control mechanisms in the maintenance of PaCO2 homeostasis.

Dose-Response Relationship, Drug↗
PubMed1997

Breathing pattern during acute respiratory failure and recovery.

The objective of this study was to compare the breathing pattern of patients who failed to wean from mechanical ventilation to the pattern during acute respiratory failure. We hypothesized that a similar breathing pattern occurs under both conditions. Breathing pattern, mouth occlusion pressure (P[0.1]) and maximum inspiratory pressure (P[I,max]) were measured in 15 patients during acute respiratory failure, within 24 h of the institution of mechanical ventilation, and in 49 patients during recovery, when they were ready for discontinuation from mechanical ventilation. The following indices were calculated: rapid shallow breathing index (respiratory frequency/tidal volume (fR/VT)); rapid shallow breathing-occlusion pressure index (ROP = P[0.1 x fR/VT]); P(0.1)/P(I,max); and effective inspiratory impedance (P[0.1]/VT/(inspiratory time (tI)). Patients who failed to wean (n=11) had a similar ROP,fR/VT and P(0.1)/P(I,max) to those with acute respiratory failure despite a significantly reduced P(0.1)/VT/tI, the value of which was comparable to that of patients who weaned successfully (n=38). The P(I,max) of patients who failed to wean was similar to that of patients who weaned successfully. We conclude that patients who failed to wean had a breathing pattern similar to that during acute respiratory failure, despite a reduced mechanical load on the respiratory muscles and a relatively adequate inspiratory muscle strength. This suggests that strategies that enhance respiratory muscle endurance may facilitate weaning.

Aged↗
PubMed1997

Refractory hypoxemia due to intrapulmonary shunting associated with bronchioloalveolar carcinoma.

Bronchioloalveolar carcinoma caused severe refractory hypoxemia due to intrapulmonary shunting in a patient. Preoperative evaluation by occlusion of the pulmonary lobar artery supplying the tumor showed normalization of the arterial oxygen saturation. Resection of the involved lobe corrected the intrapulmonary shunting, and the patient required no further supplemental oxygen. However, with recurrence of the tumor over the next 6 months the patient became progressively more hypoxemic and died.

Adenocarcinoma, Bronchiolo-Alveolar↗
PubMed1997

The effects of early chest tube placement on empyema resolution.

STUDY OBJECTIVES: The objective of this study was to determine the impact of the timing of chest tube insertion on outcome for the treatment of empyema, using a new animal model of empyema. DESIGN: A prospective, controlled randomized, blinded design was used. SETTING: The study was conducted in an animal research laboratory. PATIENTS OR PARTICIPANTS: Sixty-six 2- to 3-kg rabbits were used in this study. INTERVENTIONS: After induction of empyema, the rabbits were divided into four groups. Fourteen rabbits had chest tubes placed at 24 h after empyema induction. Seventeen rabbits had chest tubes placed at 48 h and 14 rabbits had chest tubes placed at 72 h after empyema induction. Twenty-one rabbits served as control rabbits and had no chest tubes placed. MEASUREMENTS AND RESULTS: Ten days after induction of empyema, the rabbits were killed. The pleural spaces of each rabbit were examined and a gross score, pleural peel score, and a microscopic score were calculated for each rabbit. The median gross score, mean pleural peel score, and median microscopic scores were significantly higher in the rabbits that underwent late chest tube placement (72 h) relative to those that underwent early chest tube placement (24 or 48 h). CONCLUSIONS: This study supports previous expert opinion statements and conclusions from retrospective analyses that early chest tube placement (relative to delayed chest tube placement) is beneficial for the treatment of empyema.

Animals↗
PubMed1997

Acute hemorrhagic leukoencephalitis during treatment for disseminated tuberculosis in a patient with AIDS.

A 45-year-old man with the acquired immune deficiency syndrome (AIDS) developed disseminated Mycobacterium tuberculosis infection and was started on isoniazid, rifampin, pyrazinamide and ethambutol. The treatment was interrupted because of side effects. On resumption of treatment be developed a rapidly progressive neurological illness characterized by left hemiparesis, right gaze preference, convulsions, coma, evidence of cerebral edema on computed tomography scan and death 9 days later. Autopsy showed the presence of miliary tuberculosis affecting the lungs, liver, spleen, lymph nodes and bone marrow. The brain showed evidence of acute hemorrhagic leukoencephalitis (AHL)-the first such case in a patient with AIDS. We speculate that treatment-induced lysis of mycobacteria with concomitant release of mycobacterial lipoproteins may have activated T-lymphocytes to cause AHL in this patient.

AIDS-Related Opportunistic Infections↗
PubMed1996

Resolution of recurrent atelectasis in spinal cord injury patients with administration of recombinant human DNase.

Atelectasis occurs frequently in patients with spinal cord injury (SCI). Impaired cough leads to ineffective clearance of secretions. If the secretions cannot be cleared and become thick and purulent, atelectasis may occur. Recombinant human DNase (rhDNase) has been shown to decrease purulent sputum viscosity in vitro. We report two SCI patients with respiratory failure due to recurrent atelectasis from purulent secretions in whom conventional treatment methods had failed. Administration of rhDNase resulted in successful resolution of atelectasis. These results suggest the need for a controlled clinical trial.

Deoxyribonucleases↗
PubMed1996

Relationship of changes in cardiac output to changes in heart rate in medical ICU patients.

OBJECTIVE: To determine whether changes in cardiac output are correlated with changes in other commonly measured covariables (heart rate, respiratory rate, mean arterial pressure, mean pulmonary artery pressure, pulmonary artery occlusion pressure, and temperature). DESIGN: Case series. SETTING: Medical intensive care unit (ICU) in a Veterans Administration Medical Center. PATIENTS: Twenty-three patients with Swan-Ganz catheters placed by the primary care team were studied on 25 occasions. Patients were managed by the primary team as clinically indicated. INTERVENTIONS: Thermodilution cardiac output and covariables were determined at baseline and at hourly intervals for the next 5 h. Each cardiac output measurement was calculated by averaging the last four of five individual measurements at each time point. RESULTS: The mean cardiac output (9.21/min), heart rate (107/min), and pulmonary artery occlusion pressure (19 mmHg) were elevated. The hourly mean change in cardiac output was 10.2%. Using least-squares linear regression analysis, we found clinically significant changes in cardiac output (> 6.4%) to be most closely correlated with changes in heart rate (R2 = 0.29, p < 0.001). Stepwise linear regression analysis showed that none of the other covariables added significantly to this relationship. No significant relationship was found between changes in cardiac output and changes in pulmonary artery occlusion pressure. Despite these correlations clinically significant changes in cardiac output were accompanied by changes in heart rate in the same direction only 62% of the time. CONCLUSION: Changes in cardiac output were best correlated with changes in heart rate. Changes in pulmonary artery occlusion pressure were not correlated with changes in cardiac output in this population of medical ICU patients. A change in any of the covariables (alone or in combination) cannot be reliably used to indicate a simultaneous change in cardiac output.

Adult↗
PubMed1996

Arterial blood gas changes during breath-holding from functional residual capacity.

Breath-holding serves as a model for studying gas exchange during clinical situations in which cessation of ventilation occurs. We chose to examine the arterial blood gas changes that occurred during breath-holding, when breath-holding was initiated from functional residual capacity (FRC) while breathing room air. Eight normal subjects who had a radial artery catheter placed for another study were taught to breath-hold on command from FRC. FRC was determined using respiratory inductance plethysmography. Arterial blood gas specimens were obtained at 5-s intervals until the termination of breath-holding. The average breath-holding time (+/-SD) was 35 (+/-10 s). The PaO2, PaCO2, and pH values were plotted against time and individually fit to logistic equations for each subject. The arterial PaO2 fell by a mean of 50 mm Hg during the first 35 s of breath-holding under these conditions, while the arterial PCO2 rose by a mean of 10.2 mm Hg during the first 35 s and the pH fell by a mean of 0.07 in the first 35 s. The rapid decline in PaO2 is greater than that previously reported using different methods and should be considered in clinical situations in which there is an interruption of oxygenation and ventilation at FRC while breathing room air. The changes in PaCO2 and pH are similar to those previously reported in paralyzed apneic patients.

Adolescent↗
PubMed1995

Effect of measurement errors on cardiac output calculated with O2 and modified CO2 Fick methods.

We have investigated the effect of measurement errors on cardiac output, calculated via three different Fick methods. In method 1, the classic O2 Fick equation is expressed in terms of oxygen uptake (VO2), arterial pulse (SaO2) and venous oximetry (SVO2) saturations. The second method, a modified CO2 Fick method, is obtained by replacing VO2 in method 1 with carbon dioxide production (VCO2) divided by the respiratory quotient. In method 3, cardiac output is expressed as VCO2 divided by the product of the SaO2-SVO2 difference and a constant. This constant is determined from initial measurements of VCO2, SaO2, SVO2, and thermodilution cardiac output (Qth). This determination of the constant results in equality of the initial cardiac output of method 3 with the simultaneously determined Qth and, therefore, is similar to performing an autocalibration. For each of the three preceding Fick methods, we derive general expressions that explicitly show how measurement errors (random and systematic) in the Fick variables (VO2, VCO2, SaO2, and SVO2) propagate into errors in calculated cardiac output. The errors in theoretically calculated cardiac output decrease as the SaO2-SVO2 difference increases, except for the systematic error in method 3. The systematic error of method 3 is constant and depends only upon the accuracy of the initial Qth. Analytic expressions for the sensitivity of calculated cardiac output to errors in individual Fick variables are also obtained. Using estimates from the literature for typical systematic and random measurement errors in the Fick variables, the resultant errors in cardiac output are numerically calculated. The effect of random measurement errors on errors in calculated cardiac output was comparable among the three methods. However, the systematic error was least with method 3. Total errors (random and systematic) were comparable among the three methods. Using these numerical measurement errors, we conclude that continuous cardiac output may be calculated with comparable accuracy with each of these methods.

Bias↗
PubMed1995

Arterial oxygenation time after an FIO2 increase in mechanically ventilated patients.

The time for arterial PO2 to reach equilibrium after a 0.2 increase in the fraction of inspired oxygen (FIO2) was studied, using arterial blood gases measured at 1, 2, 3, 4, 5, 7, 9, and 11 min in 30 stable, mechanically ventilated medical intensive care unit (ICU) patients. Eight patients also underwent a 0.4 increase in FIO2. Each patient's rise in PO2 over time [PO2(t)] was fit to the following exponential equation: PO2(t) = PO2i + (PO2f-PO2i) (1-e-kt), where t refers to time, PO2i and PO2f refer to the initial and final equilibrated PO2. The time constant k and PO2f were determined by a nonlinear curve fitting technique. The 90% oxygenation times (t90%), defined as the time required to reach 90% of the final equilibrated PO2, were calculated. The mean t90% (+/- SD) was 6.0 (+/- 3.4) min for all patients (range 1.7 to 14.3 min); 7.1 +/- 2.1 min for 18 patients with chronic obstructive pulmonary disease (COPD) and 4.4 +/- 2.0 min for 12 patients without COPD (p < 0.05). In the subgroup of patients undergoing both an FIO2 increase of 0.2 and 0.4, there was no significant difference in the mean t90%'s for the two FIO2 changes (7.7 versus 7.7 min). We conclude that after a 0.2 or 0.4 increase of FIO3, a 15-min equilibration time period is adequate for 90% of the increase in PO2 to occur, in stable, mechanically ventilated medical ICU patients.

Aged↗
PubMed1994

Oxygen Fick and modified carbon dioxide Fick cardiac outputs.

OBJECTIVE: To compare cardiac outputs estimated from the classical oxygen Fick and modified CO2 Fick methods with thermodilution cardiac output. The modified CO2 Fick cardiac output was obtained by replacing the oxygen uptake (VO2) in the Fick equation with the CO2 production (VCO2) divided by either an assumed or measured value of the respiratory exchange ratio or with an independently determined constant (Crit Care Med 1991; 19:1270-1277). DESIGN: Criterion standard study. SETTING: The medical and surgical intensive care unit (ICU) in a Veterans Affairs Medical Center. PATIENTS: A total of 17 patients (26 studies) and 11 surgical patients (13 studies), predominantly mechanically ventilated using the intermittent mandatory ventilation mode, were studied over a period of 4.3 hrs. MEASUREMENTS: A respiratory gas exchange monitor was used to measure VO2, VCO2, and respiratory exchange ratio at 3-min intervals. Calculations were performed with arterial and venous oxygen saturations measured with both a laboratory cooximeter and bedside pulse and venous reflectance oximeters. In the oxygen Fick method, cardiac output was calculated from VO2 together with arterial and venous oxygen saturations. In the modified CO2 Fick methods, cardiac output values were calculated from arterial and venous oxygen saturations with VCO2, divided by either: a) an assumed value of the respiratory exchange ratio equal to 0.8 for all patients (method 1); b) the patient's measured value of the respiratory exchange ratio (method 2); or c) a constant, determined from an initial, simultaneous measurement of thermodilution cardiac output, VCO2, and oximetry saturations. Data were examined by linear regression analysis and bias and precision calculations. MAIN RESULTS: Thermodilution cardiac output was more related to cardiac outputs calculated with the 3 modified CO2 Fick methods than to the oxygen Fick cardiac output. Thermodilution cardiac output was closely related to the modified CO2 Fick cardiac output calculated via method 3. For this method, with pulse and venous reflectance oximetry saturations, linear regression yielded an r2 = .85, a standard error of the estimate of 0.88 L/min (n = 111) and a bias and precision of 0.11 and 0.97 L/min, respectively. Thermodilution cardiac output was less closely related to oxygen Fick cardiac output, which, when calculated with pulse and venous reflectance oximetry saturations, yielded an r2 = .50, a standard error of the estimate of 1.47 L/min (n = 128), and a bias and precision of 0.01 and 1.85 L/min, respectively. CONCLUSIONS: We conclude from this study that thermodilution cardiac output is more closely related to cardiac output calculated from modified CO2 Fick methods than to oxygen Fick cardiac output. Since cardiac output calculated with the modified CO2 Fick method 3 obviates the difficulties associated with measuring VO2 accurately and requires neither an assumption of nor measurement of the respiratory exchange ratio, method 3 may prove to be clinically useful for continuous cardiac output monitoring via oximetry in ICU patients.

Adult↗
PubMed1994

Variability of cardiac output over time in medical intensive care unit patients.

OBJECTIVES: To determine the amount of spontaneous variability of cardiac output over time in critically ill patients, and to determine the effect of mechanical ventilation on cardiac output variability over time. DESIGN: Case series. SETTING: Medical intensive care unit in a Veterans Affairs Medical Center. PATIENTS: Twenty-two patients with indwelling pulmonary artery flotation catheters were studied. Two patients were studied twice. INTERVENTIONS: During a 1-hr time period in which no interventions were required or made, thermodilution cardiac output was determined at baseline and then every 15 mins for 1 hr. At each time point, five individual cardiac output measurements were made and a mean was computed. The covariables of heart rate, respiration rate, mean arterial pressure, mean pulmonary arterial pressure, pulmonary artery occlusion pressure, and temperature were also recorded at each time point. MEASUREMENTS AND MAIN RESULTS: The variability of the five cardiac output measurements made at each time point was expressed by calculating for each patient a coefficient of variation of the measurements. The overall mean coefficient of variation of the measurements was 5.8%. The variability of the cardiac output measurements over time was expressed by calculating for each patient a coefficient of variation over time. The overall mean coefficient of variation over time was 7.7%. A subgroup of 15 "covariable stable" patients (defined as those patients with covariables within +/- 5% of the mean covariable values during the hour) had a mean coefficient of variation over time of 6.4%, whereas "covariable unstable" patients (with > +/- 5% changes in any covariable) had a mean coefficient of variation over time of 9.9% (p < .05). Patients breathing spontaneously had a mean coefficient of variation over time of 10.1%, whereas mechanically ventilated patients had a mean coefficient of variation over time of 6.3% (p < .05). CONCLUSIONS: The spontaneous variability of cardiac output should be considered when interpreting two cardiac output determinations made at separate times. Due to spontaneous variability alone, a patient with a baseline cardiac output of 10.0 L/min would be expected (95% confidence interval) to have a cardiac output range of 9.2 to 10.8 L/min if covariables were stable, and a range of at least 8.8 to 11.2 L/min if covariables were unstable. Patients who were mechanically ventilated displayed less variability than patients who were breathing spontaneously.

Adult↗
PubMed1994

Development of a patient-dedicated, on-demand, blood gas monitor.

A new monitor (CDI 2000) that brings blood gas measurements to the patient's bedside has been developed. To measure blood gases, blood is drawn into the patient's arterial pressure-monitoring line past in-line fluorescent-based sensors. After measurement, the blood is returned to the patient, avoiding blood loss and delays in sample turnaround and reducing the risk of infection to both patient and operator. We assessed this system's performance in vitro with tonometered bovine blood. Bias (mean difference between monitor and tonometered gas or measured pH values) +/- the standard deviation (SD) were 0.01 +/- 0.02 at pH = 7.39; 0.0 +/- 0.7 mm Hg at Pco2 = 39 mm Hg; and 2.4 +/- 3.2 mm Hg at a Po2 = 100 mm Hg (n = 54). Changes in hematocrit, blood temperature, or serum sodium concentration did not have clinically significant effects on system performance. Studies in normal volunteers, in whom large changes in blood gases were induced, showed a bias (mean difference between monitor and IL 1306 values) +/- SD of 0.00 +/- 0.02 for pH, -0.4 +/- 2.0 mm Hg for Pco2, and -3.6 +/- 7.7 mm Hg for Po2 (n = 69). We conclude from the present study that the performance of this system is comparable to that of conventional blood gas analyzers.

Animals↗
PubMed1994

Performance of a patient-dedicated, on-demand blood gas monitor in medical ICU patients.

We examined the performance characteristics of a new bedside blood gas monitor. This monitor's fluorescent pH, PCO2, and PO2 sensors are embedded in a cassette, which is calibrated in vitro and then inserted into the patient's radial artery tubing set. In 50 medical ICU patients, 683 paired monitor and conventional blood gas analyzer values were obtained. Performance was assessed via calculations of bias (mean monitor and analyzer difference) and its standard deviation (SD), plots of monitor and analyzer differences against the means (of monitor and analyzer), and linear regression analysis of the sequential changes in monitor values versus the corresponding sequential changes in analyzer values. The ex vivo calibration, assessed using the initial paired blood samples, showed a bias +/- SD of 0.02 +/- 0.02 for pH, -0.1 +/- 1.9 mm Hg for PCO2, and 4.3 +/- 6.0 mm Hg for PO2. For all paired samples (n = 683), the biases +/- SD were 0.004 +/- 0.023 for pH, 0.6 +/- 2.4 mm Hg for PCO2, and 2.7 +2- 6.4 mm HG for PO2. The PO2 bias increased as PO2 increased. The standard deviations (imprecision) of both PCO2 and PO2 also increased as the magnitudes of these variables increased. Sequential changes in monitor values versus the corresponding sequential changes in analyzer values revealed regression lines close to the line of identity. Serum sodium had no effect on pH bias. Daily drift of the sensors was inconsequential, with values of -0.01/d for pH, 1.7 mm Hg/d for PCO2, and 1.1 mm Hg/d for PO2. We conclude that the performance of this monitor is comparable to that of conventional blood gas analyzers.

Blood Gas Analysis↗