Severe acute extrinsic airway compression by mediastinal tumor successfully managed with extracorporeal membrane oxygenation.

The successful use of femoral venoarterial extracorporeal membrane oxygenation to support an adult patient with extrinsic airway compression secondary to a large mediastinal tumor is presented. Extracorporeal membrane oxygenation was continued until a combination of chemotherapy and radiation therapy allowed sufficient tumor shrinkage to permit decannulation. This method should be considered and available before manipulation of the airway in similar patients.

Echocardiographic and hemodynamic indexes of left ventricular preload in patients with normal and abnormal ventricular function.

BACKGROUND: Transesophageal echocardiography (TEE) is used to diagnose hypovolemia despite the lack of validation studies. The objective was to determine the effects of acute graded hypovolemia on TEE and conventional hemodynamic determinants of left ventricular (LV) preload in anesthetized patients with normal and abnormal LV function. METHODS: Determinants of LV preload derived from TEE and hemodynamic monitoring were measured serially in 35 anesthetized cardiac surgical patients without valvular heart disease. Patients were stratified into two groups: those with normal LV function (group 1, n = 17) and those with LV wall motion abnormalities (group 2, n = 13). Patients in groups 1 and 2 were subjected to graded hypovolemia produced by collecting 6 aliquots of blood, each equal to 2.5% of their estimated blood volume (EBV). A third group of patients (group 3, n = 5), not subjected to graded hypovolemia, were studied to test for time-dependent changes. RESULTS: Group 2 had a significantly greater baseline (mean +/- SD) pulmonary artery occlusion pressure (17 +/- 6 vs. 11 +/- 6 mmHg), LV end-diastolic area (23 +/- 5 vs. 18 +/- 4 cm2), LV end-diastolic wall stress (23 +/- 10 vs. 14 +/- 6 x 10(3) dyne.cm-2), and smaller fractional area change (35 +/- 13 vs. 59 +/- 7%). In groups 1 and 2, the LV end-diastolic area, pulmonary artery occlusion pressure, and LV end-diastolic wall stress decreased linearly in response to blood loss in the range of 0-15% of the EBV. No significant changes in the measured parameters occurred in group 3. A significant decrease in the central venous pressure, pulmonary artery occlusion pressure, and LV end-diastolic area was detected in response to a 2.5% EBV deficit (approximately 1.75 ml.kg-1) in groups 1 and 2. The mean change in LV end-diastolic area (0.3 cm2/1.0% EBV deficit) in response to equivalent EBV deficits was the same in groups 1 and 2. In contrast, the mean change in cardiac output and LV end-diastolic wall stress was less in group 2 despite a greater decrease in pulmonary artery occlusion pressure. Compared to group 1, a greater EBV deficit (7.5% to 12.5% vs. 2.5% to 5%) was required in group 2 to cause a significant decrease in the cardiac output, stroke volume, mixed venous oxygen saturation, and LV end-diastolic wall stress. CONCLUSIONS: TEE and hemodynamic determinants of LV preload detected changes in LV function caused by acute blood loss. Acute blood loss caused directional changes in LV end-diastolic area, pulmonary artery occlusion pressure, and LV end-diastolic wall stress even in patients with LV wall motion abnormalities. Changes in LV end-diastolic wall stress, derived from both TEE and hemodynamic measurements corresponded to changes in cardiac output, stroke volume, and mixed venous oxygen saturation that occurred during acute blood loss.

Cardiovascular stability with rapid intravenous infusion of ondansetron.

The acute cardiovascular effects of rapid iv administration of the antiemetic ondansetron, a selective serotonin (5-HT3) receptor antagonist were determined in a randomized, blinded, placebo-controlled study. Measurements of heart rate, blood pressure, oxygen saturation and respiratory rate were made preoperatively over a five-minute period which followed a two-minute infusion of the medication. Intraoperative and postoperative data were not collected. None of the variables recorded changed significantly during the infusion or in the observation period which followed. Within the limitations of this study, we detected no cardiovascular change in the five minutes between the end of the drug infusion and the induction of anaesthesia.

Modelling steady state pulmonary elimination of He, SF6 and CO2: effect of morphometry.

We studied the influence of acinar morphometry on the shape of simulated expirograms computed from a single path convection-diffusion model that includes a source term for gas evolution from the blood (Scherer et al., J. Appl. Physiol. 64: 1022-1029, 1988). Acinar structure was obtained from published data of 3 different lung morphometries. The simulations were performed over a range of tidal volumes (VT) and breathing frequencies (f) comparable to those observed in a previously reported human study. Airways dead space (VDaw) increased with VT in all the morphometric models tested and in the experimental data. The increase in VDaw with VT was inversely related to the diffusivity of the evolving gas and to the rate of increase in airway cross-section of the most mouthward (proximal) alveolated generations of the models. Normalized phase III slope for all the gases decreased with increasing VT in all the models as was previously reported for healthy human subjects. In the model simulations, the greatest sensitivity of phase III slope to VT was seen with the least diffusible gas using the airway morphometry with the smallest cross-sectional areas in the proximal alveolated generations. We conclude that both VDaw and phase III slope of an evolving gas are sensitive to the geometry of the proximal acinar airways and that this is manifest by their dependence on tidal volume, breathing frequency, molecular diffusivity and alveolar/blood source emission rate. The model simulations indicate that heterogeneity of gas washout is not required to explain the magnitude of the phase III slope in healthy human subjects.

Measurement of pulmonary blood flow with transesophageal two-dimensional and Doppler echocardiography.

Transesophageal echocardiography permits measurement of the pulmonary artery diameter (two-dimensional echocardiography) and pulmonary artery blood flow velocity (pulsed-wave Doppler). These measurements considered with the heart rate allow for the determination of pulmonary artery blood flow, which is equivalent to cardiac output. This study compared the precision of transesophageal Doppler-derived cardiac output (DdCO) with the precision of thermodilution cardiac output (TdCO) and examined the agreement between DdCO and TdCO in 33 cardiac surgical patients. The proximal pulmonary artery diameter was measured in triplicate during systole and end expiration, and the local blood flow velocity was recorded on video tape. The instantaneous pulmonary artery blood flow velocity (centimeters per second) for three random cardiac beats was integrated with respect to time. DdCO was calculated as the product of the flow velocity integral (centimeters per beat), heart rate (beats per min), and the mean cross-sectional area (centimeters squared) of the main pulmonary artery. At the same time that the velocity recordings were made, three serial determinations of TdCO were made by an independent observer. Pulmonary blood flow could be measured in 25 of the 33 patients. The anatomical relationship among the esophagus, the left main stem bronchus, and the pulmonary artery did not allow adequate imaging of the pulmonary artery in 8 (24%) of the patients. A total of 45 sets of triplicate measurements were made. The range of cardiac outputs encountered was 1.7-6.6 l.min-1 by TdCO and 1.5-6.9 l.min-1 by DdCO. The 95% confidence limits for the difference between the two methods (agreement) was 0.030 +/- 0.987 l.min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Diffusivity, respiratory rate and tidal volume influence inert gas expirograms.

We modified, and developed software for, a computer-controlled quadrupole mass spectrometer to measure complete breath-by-breath expirograms of helium (He) and sulfur hexafluoride (SF6) exhaled during the infusion of saline saturated with the inert gases. He and SF6 have similar blood solubilities but very different gas phase diffusivities allowing examination of the influence of gas phase diffusivity on steady state inert gas expirograms. We studied six normal human volunteers in nine separate studies and examined the influence of tidal volume (VT) and breathing frequency (f) on the airways dead space (VDaw) and alveolar plateau slope (phase III) for the inert gases and CO2. The experimental data showed a reduction in VDaw with rapid shallow breathing, while phase III slope increased by a factor of two to three. We critically evaluated the data and methodology of these and previously reported studies of continuous and single breath washout of He and SF6. In general the 15 to 20 ml differences in VDaw between He and SF6 were in keeping with previous studies by others. The ratio of phase III slopes of SF6 to He reported by us previously (Scherer et al., J. Appl. Physiol. 64: 1022-1029, 1988) was 3.13. In the current study, which includes the analysis of more than 400 He and SF6 breaths, the ratio of SF6 to He slope was 1.85. The difference between the two studies was largely related to the improved methodology of the current study, particularly for the measurement of He. The results support the conclusion that diffusivity is an important component of both phase II and phase III of the expirogram. However, the difference in phase III between He and SF6 is somewhat less than previously reported.

Sensitivity of CO2 washout to changes in acinar structure in a single-path model of lung airways.

A numerical solution of the convection-diffusion equation with an alveolar source term in a single-path model (SPM) of the lung airways simulates steady state CO2 washout. The SPM is used to examine the effects of independent changes in physiologic and acinar structure parameters on the slope and height of Phase III of the single-breath CO2 washout curve. The parameters investigated include tidal volume, breathing frequency, total cardiac output, pulmonary arterial CO2 tension, functional residual capacity, pulmonary bloodflow distribution, alveolar volume, total acinar airway cross sectional area, and gas-phase molecular diffusivity. Reduced tidal volume causes significant steepening of Phase III, which agrees well with experimental data. Simulations with a fixed frequency and tidal volume show that changes in blood-flow distribution, model airway cross section, and gas diffusivity strongly affect the slope of Phase III while changes in cardiac output and in pulmonary arterial CO2 tension strongly affect the height of Phase III. The paper also discusses differing explanations for the slope of Phase III, including sequential emptying, stratified inhomogeneity, and the issue of asymmetry, in the context of the SPM.

Numerical and experimental study of steady-state CO2 and inert gas washout.

The predictions of a single-path trumpet-bell numerical model of steady-state CO2 and infused He and sulfur hexafluoride (SF6) washout were compared with experimental measurements on healthy human volunteers. The mathematical model used was a numerical solution of the classic airway convention-diffusion equation with the addition of a distributed source term at the alveolar end. In the human studies, a static sampling technique was used to measure the exhaled concentrations and phase III slopes of CO2, He, and SF6 during the intravenous infusion of saline saturated with a mixture of the two inert gases. We found good agreement between the experimentally determined normalized slopes (phase III slope divided by mixed expired concentration) and the numerically determined normalized slopes in the model with no free parameters other than the physiological ones of upper airway dead space, tidal volume, breathing frequency, and breathing pattern (sinusoidal). We conclude 1) that the single-path (Weibel) trumpet-bell anatomic model used in conjunction with the airway convection-diffusion equation with a distributed source term is adequate to describe the steady-state lung washout of CO2 and infused He and SF6 in normal lungs and 2) that the interfacial area separating the tidal volume fron from the functional residual capacity gas, through which gas diffusion into the moving tidal volume occurs, exerts a major effect on the normalized slopes of phase III.

A departmental policy addressing chemical substance abuse.

Substance abuse is a major socioeconomic problem. However, the ready availability of potent narcotic and sedative drugs probably constitutes a unique risk for anesthesiologists. Until recently, few anesthesia departments were prepared to recognize or safely manage afflicted colleagues. Because we felt it important to educate our staff and residents and to have a response mechanism established prior to the advent of a substance abuse problem, a departmental committee was formed to develop a Substance Abuse Policy. The policy has served to increase our general awareness and to direct our actions effectively when dealing with physician impairment. It is presented here in the belief that other departments might find it useful in tailoring their approach to this problem.

Errors in measurement of oxygen uptake due to anesthetic gases.

Errors in measurement of exhaled gas volume, mixed expired oxygen and carbon dioxide concentrations, and inspired oxygen concentration and the presence of exhaled anesthetic agents cause errors in on-line calculated oxygen uptake that increase geometrically with increasing inspired oxygen concentration. No one has quantified the decrease in the magnitude of the error that might be realized if directly measured nitrogen concentration were included in the calculation. We used a computer model to evaluate this improvement, assuming an oxygen uptake of 200 ml/min and normal ventilatory parameters. Using a Monte Carlo technique, we generated 100 sets of data points, with random errors averaging 0.5% around the expected gas concentrations, and compared the accuracy of oxygen uptake calculated with and without inclusion of directly measured inspired and expired nitrogen concentrations. When the inspired oxygen fractions were 0.2, 0.5, and 0.8, the calculated oxygen uptakes +/- % standard deviation were 200 +/- 4.3, 200 +/- 12, and 196 +/- 21 when directly measured nitrogen was included versus 200 +/- 3.5, 196 +/- 16, and 205 +/- 71 when it was not. The procedure was repeated, assuming 50 ml/min of anesthetic excretion and the calculated oxygen uptakes were 200 +/- 4.6, 202 +/- 12, and 195 +/- 17 versus 212 +/- 3.8, 251 +/- 17, and 398 +/- 64. Including direct measurement of inhaled and exhaled concentrations of nitrogen or another insoluble inert tracer gas allows accurate measurement of oxygen uptake, even in the presence of exhaled anesthetic gases. It also decreases the error in oxygen uptake determination by a factor of nearly six when the inhaled oxygen fraction is 0.8.

Low-dose fentanyl blunts circulatory responses to tracheal intubation.

The effect of fentanyl, 8 micrograms/kg, used as an adjunct to thiopental for induction of anesthesia, on the circulatory response to tracheal intubation was investigated in 36 patients undergoing major vascular surgery. Patients were randomly assigned to receive either thiopental, 6 mg/kg, alone (N = 18), or thiopental, 3 mg/kg, along with fentanyl, 8 micrograms/kg (N = 18), for induction of anesthesia. The electrocardiogram, arterial pressure, pulmonary capillary wedge pressure, cardiac output, and central venous pressure were measured during induction of anesthesia, laryngoscopy, and intubation. Mean arterial blood pressure increased more following intubation in patients given thiopental than in patients given fentanyl-thiopental, reaching a peak value of 144 +/- 4 torr in patients receiving thiopental only, compared with 108 +/- 6 torr in those receiving fentanyl and thiopental (p less than 0.0001). Increases in systolic blood pressure, diastolic blood pressure, and pulmonary capillary wedge pressure with intubation were also significantly greater following administration of thiopental than following fentanyl-thiopental. Doses of fentanyl that are low enough to cause little postoperative respiratory depression significantly blunt postintubation hypertension when used as an adjunct to thiopental.

The influence of elevated fibronectin levels during sepsis on the distribution of blood-borne particles.

We assessed serum fibronectin levels during septic shock and modification of the levels by intravenous fibronectin infusion. Male rats subjected to cecal ligation and puncture received intravenously, either fibronectin in saline or saline only, 18-20 hours after the cecal ligation. The cecum was then excised. Fibronectin was assessed by electroimmunoassay and RES function by organ localization of gelatinized labeled colloid. Serum fibronectin concentration increased after the cecal ligation. It then fell one hour after the second operation (cecectomy) in saline-treated rats, but increased in fibronectin-treated rats. Fibronectin treatment did not enhance survival. Two other groups of rats received gelatinized labeled colloid one hour after the cecectomy. The fibronectin-treated group did not have increased hepatic uptake, but had increased pulmonary localization of gelatinized labeled colloid. The enhanced pulmonary localization may be due to fibronectin-induced opsonization and aggregation of particles which then embolize in the lungs. Though reversal of fibronectin deficiency has been documented to improve organ function, indiscriminate fibronectin supplementation without documentation of fibronectin deficiency should not be undertaken, since our present study demonstrates that excessive fibronectin levels may lead to particle aggregation.

Evaluation of the Swank IL-201 transfusion filter.

The effects of a new transfusion filter (Swank IL-20U) on stored, whole blood have been examined. Six filters were preloaded by passage of two units of outdated, type-specific bank blood, and the effects of filtration on a third unit of 21-day-old blood flowing under 150 mm Hg pressure were measured. Filtration did not significantly alter erythrocyte or leukocyte count, total or plasma hemoglobin, red-cell fragility, and plasma sodium, potassium, albumin, or globulin. Platelet counts were reduced by 33%. Removal of microaggregates, assessed by Coulter counting, screen filtration pressure, total screen protein, wet and dry weight of material retained, and scanning electron microscopy, was shown to be effective over the entire range of particle size. In comparison with other transfusion filters previously examined in this laboratory, the Swank IL-201 filter combines the features of efficient microaggregate removal with moderate blood-flow rate. Compared to its predecessor, the Swank IL-200, this new filter design has improved flow characteristics without loss of microaggregate removal efficiency. In view of the similarity of performance demonstrated for several of the available filters, it seems likely that relative cost will constitute an important determinant of filter selection.