Kane M. High

Clinical trials of an intravenous oxygenator in patients with adult respiratory distress syndrome

In patients with severe adult respiratory distress syndrome, mechanical ventilation may not be able to ensure gas exchange sufficient to sustain life. We report the use of an intravenous oxygenator (IVOX) in five patients who were suffering from severe adult respiratory distress syndrome as a result of aspiration, fat embolism, or pneumonia. IVOX was used in an attempt to provide supplemental transfer of CO2 and O2 and thereby reduce O2 toxicity and barotrauma. All patients were tracheally intubated, sedated, and chemically paralyzed and had a PaO2 < 60 mmHg when the lungs were ventilated with an FIO2 = 1.0 and a positive end expiratory pressure of > or = 5 cmH2O. The right common femoral vein was located surgically, and the patient was systemically anticoagulated with heparin. A hollow introducer tube was inserted into the right common femoral vein, and the furled IVOX was passed into the inferior vena cava and advanced until the tip was in the lower portion of the superior vena cava. IVOX use ranged from 2 h to 4 days. In this group of patients, IVOX gas exchange ranged from 21 to 87 ml x min-1 of CO2 and from 28 to 85 ml x min-1 of O2. One of the five patients survived and was discharged from the hospital. The IVOX transferred up to 28% of metabolic gas-exchange requirements. One patient with a small vena cava showed signs of caval obstruction. Three other patients demonstrated signs of a septic syndrome after the device was inserted.(ABSTRACT TRUNCATED AT 250 WORDS)

Perioperative Management of Patients With Left Ventricular Assist Devices Undergoing Noncardiac Procedures: A Survey of Current Practices

OBJECTIVES To describe perioperative management of patients with left ventricular assist devices (LVAD) in noncardiac procedures. DESIGN Survey of (1) respondent demographic characteristics, (2) anesthetic practices for LVAD patients having endoscopies, and (3) low-risk surgeries requiring general anesthesia. SETTING Internet-based. PARTICIPANTS Society of Cardiovascular Anesthesiologists membership. INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS Inpatient endoscopic procedures were done mainly in the endoscopy suite (71.7%) by a solo practitioner or 1:1 staffing ratio 59% of the time. LVAD-specific support personnel were present in more than 80% of all procedures. Both endoscopy and surgical patients used post-anesthesia recovery units and intensive care units for recovery; however, compared with endoscopy patients, surgical patients recovered in the ICU more frequently (45.5% v 29.1%, p<0.001). In addition, 18% of endoscopy patients recovered on site. Regarding patient monitoring, more than 90% of responders used electrocardiogram, pulse oximetry, end-tidal CO2, and blood pressure monitors on LVAD patients. Responders reported using arterial catheters to monitor blood pressure in 49% of endoscopy cases and 71% of surgical patients. The reported use of invasive monitors by individual clinicians was related inversely to institutional LVAD volume (p = 0.04 and p = 0.01 in endoscopy and surgical procedures, respectively). CONCLUSIONS This survey found heterogeneity in hospital resource utilization for noncardiac LVAD procedures. There was a decrease in the use of invasive monitors with increased institutional LVAD volume in both endoscopy and surgical procedures.

Small intrapulmonary artery lung prototypes: design, construction, and in vitro water testing.

Blind-ended, hollow fibers mounted on a pulmonary artery catheter may allow O2 and CO2 transfer in the vena cava, right ventricle, and pulmonary artery. The effects of fiber length, manifold number, and gas oscillation on mass and momentum transfer with water perfusate using mass spectrometry and mass flow controllers were studied. Manifolds with 112-196 microporous polypropylene fibers were mounted on 8 Fr multiple lumen, commercially available pulmonary artery catheters. Fiber lengths varied from 0.5 to 16 cm and surface areas from 7 to 220 cm2. Prototypes with 2 cm long fibers were constructed with 1-15 manifolds. A two manifold prototype with 8 cm long fibers and a surface area of 378 cm2 was also studied. The transfer failed to scale with manifold number because the steady gas flow was maldistributed to the manifolds. Oscillating gas pressures from 780 to 76 mmHg absolute at a rate of 40 cycles/min increased CO2 transfer up to 15-fold and O2 transfer up to 2.5-fold. Oscillation also corrected the maldistribution. Optimal fiber lengths of 3 and 1 cm for O2 and CO2, respectively, were seen with steady gas flow, and 8 cm for both with oscillatory gas flow.

Polysulfone coating for hollow fiber artificial lungs operated at hypobaric and hyperbaric pressures

Carbon dioxide transfer is increased when the gas phase of a hollow fiber membrane lung is operated at hypobaric pressures. Oxygen transfer is augmented by hyperbaric pressures. However, uncoated hollow fibers transmit gas bubbles into the blood when operated at a pressure greater than 800 mmHg and may have increased plasma leakage when operated at hypobaric pressures. Ultrathin polymer coatings may avoid this problem while reducing thrombogenicity. The authors coated microporous polypropylene hollow fibers with 380 microns outer diameter and 50 microns walls using 1, 2, 3, and 4% solutions of polysulfone in tetrahydrofuran by dipping or continuous pull through. These fibers were mounted in small membrane lung prototypes having surface areas of 70 and 187 cm2. In gas-to-gas testing, the longer the exposure time to the solution and the greater the polymer concentration, the less the permeation rate. The 3% solutions blocked bulk gas flow. The coating was 1 micron thick by mass balance calculations. During water-to-gas tests, hypobaric gas pressures of 40 mmHg absolute were tolerated, but CO2 transfer was reduced to 40% of the bare fibers. Hyperbaric gas pressures of 2,100 mmHg absolute tripled O2 transfer without bubble formation.

CARBON DIOXIDE ELIMINATION DURING TOTAL CARDIOPULMONARY BYPASS IN INFANTS AND CHILDREN

The authors measured the rate of carbon dioxide elimination (VCO2) in 25 pediatric patients (age 2 days to 9 yr) during total cardiopulmonary bypass at average venous blood temperatures ranging from 19.5 to 35.9°C. A multiplexed mass spectrometer was connected to the gas inlet and exhaust ports of the bubble oxygenator, and the gas-phase Fick principle was used to determine VCO2. A curvilinear relationship was found between log VCO2 and venous blood temperature, and a quadratic regression equation (r2 = 0.74) was fit to the data. Q10 (the ratio of VCO2 before and after a 10°C temperature change) was estimated to be 2.7 or 3.0, depending on the analytic method used. Venous blood temperature as a predictor variable explained a greater proportion of the variability of log VCO2 than did nasopharyngeal or rectal temperatures. Analysis of covariance revealed that total circulatory arrest during bypass (utilized in 10 patients for 34 ± 4 min, mean ± SEM) affected the relationship of venous blood temperature with log VCO2, by increasing the y-intercept (P = .008) but not the slope. These data, with associated 95% prediction intervals, define the expected CO2 elimination rates at various temperatures during standard bypass conditions in our patients. Real-time measurement of VCO2 using mass spectrometry can be a useful routine monitor during CPB that may help to assess patient metabolic function, adequacy of perfusion, and oxygenator performance.

Effects of blood phase oscillation on gas transfer in a microporous intravascular lung

It may be possible to design an intravascular membrane lung with gas transfer properties augmented by the natural flow oscillations in the venous and pulmonary circulation caused by the beating heart and ventilatory movements. The authors used a simple dye visualization technique, the Pierce-Donachy assist pump, and mass spectrometry to investigate these effects on membrane lungs made with tethered, blind-ended, microporous, polypropylene fibers using in vitro tests in water saturated with O2, CO2, and He. Prototypes were constructed on a 7.5 Fr pulmonary artery catheter. The fibers had an outer diameter (OD) of 380 microns and a wall thickness of 50 microns and were mounted on 4.8 mm OD sleeves. Control measurements were taken over a range of steady water flows from 0.4 l/min to 3 l/min. While pumping the same water flow rates with a roller pump, the Pierce-Donachy pump generated pulsatile flow at a rate of 45 beats/min and a systolic duration of 300 msec. This produced a phasic flow with an instantaneous average flow velocity varying from 0 to as high as 46 cm/sec. O2 and CO2 transfer increased by as much as 91% and 59%, respectively. The largest effects were seen at the lower water flow rates.

Cardiopulmonary bypass interference with dantrolene prophylaxis of malignant hyperthermia

M ALIGNANT hyperthermia (MH) crisis in susceptible patients carries a high mortality rate, and can often be prevented by pretreatment with dantrolene sodium, l Cardiac surgery with cardiopulmonary bypass (CPB) for correction of congenital heart defects 2 or acquired heart disease 3 may present a particular risk to the MH-susceptible patient. First, dantrolene blood concentrations might decrease below effective prophylactic levels during CPB; and second, active rewarming causing regional hyperthermia during the latter phases of bypass could trigger an MH crisis. 4 While MH is rare, data relating to the management of CPB for susceptible patients are important, because immediate therapy with adequate doses of dantrolene can be lifesaving. 5 This paper reports serial blood dantrolene levels in an MH-susceptible child who underwent cardiac surgery with CPB. There appear to be no previous published reports of the effects of CPB on dantrolene pharmacokinetics. In addition, a study of whole-blood dantrolene levels during in vitro perfusion of a simulated patient was performed to further elucidate the changes in dantrolene pharmacokinetics that are caused by cardiopulmonary bypass.

Small intrapulmonary artery lung prototypes. Mathematical modeling of gas transfer.

Two diffusion models have been developed to analyze gas transfer data previously measured in an intravascular artificial lung consisting of a central gas supply catheter from which are tethered a large number of blind-ended microporous fibers of equal length. A convective-diffusion model (CD) describes the countercurrent transfer of a binary gas pair when gas is supplied at constant pressure conditions, and a well mixed (WM) cycled pressure model predicts transfer when the gas supply pressure is time cycled between compression and vacuum conditions. Regression of gas to gas and liquid to gas excretion data with the CD model resulted in estimates of the liquid phase mass transfer coefficient kAI. Because these values were intermediate between the kAI expected for flow parallel to a cylinder and for flow normal to a cylinder, gas transfer was influenced by both the tethered region of the fiber that was nearly perpendicular to the axis of the test section and the free end of the fiber that rested along the wall of the test section. With a time cycled gas supply pressure, the enhanced carbon dioxide and oxygen excretion predicted by the WM model was similar to the data, but a loss in transfer efficiency with fiber length was not accounted for by the theory.

Hemodynamic effects of muscle relaxant drugs during anesthetic induction in patients with mitral or aortic valvular heart disease

The hemodynamic effects of three nondepolarizing skeletal muscle relaxant drug regimens were compared during the induction of general anesthesia in 64 patients with valvular heart disease using a double-blind protocol. Patients were first stratified according to primary valvular defect (aortic stenosis, aortic regurgitation, mitral stenosis, or mitral regurgitation). Next, patients were randomly allocated to a drug group, either group A (atracurium), group V (vecuronium), or group MP (metocurine plus pancuronium). Data were collected during three periods: awake, postanesthetic induction, and posttracheal intubation. Four cardiovascular variables were designated a priori as primary variables of interest. These were heart rate (HR), mean arterial pressure (MAP), cardiac index (CI), and systemic vascular resistance index (SVRI). Patients with mitral stenosis showed two significant hemodynamic differences among muscle relaxant drug groups: (1) CI increased in group A but decreased in group MP between the awake and postinduction measurements (P = 0.032); and (2) SVRI decreased in group A but increased in group MP between the awake and postintubation periods (P = 0.034). In contrast, patients with aortic stenosis, aortic regurgitation, or mitral regurgitation demonstrated no statistically significant difference in cardiovascular responses among drug groups. Further analysis was performed using the following data: (1) other hemodynamic variables; (2) incidence of deviations from cardiovascular stability; and (3) the frequency of cardiovascular drug use. This examination showed no important differences among the muscle relaxant drug groups. The small but significant hemodynamic changes observed in mitral stenosis patients in drug groups A and MP were not noted with vecuronium.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of a standardized premedication on oxygen saturation in the cardiac patient before transfer to the operating room

The effect of premedication with morphine and scopolamine on arterial hemoglobin oxygen saturation (SaO2) was measured continuously in 26 undisturbed patients in their hospital rooms before coronary artery bypass surgery. Two hours preoperatively each patient received morphine, 0.1 mg/kg, and scopolamine, 0.2 or 0.4 mg. SaO2 was continuously recorded using pulse oximetry from one-half hour before premedication until 1 1/2 hours after premedication. The lowest SaO2 measured both the evening before surgery and one-half hour before premedication was 95% +/- 0.5% (mean +/- SEM). After administration of premedication, the lowest SaO2 for the patient population decreased to 93% +/- 0.4% (P less than 0.001 compared with that before premedication), and occurred 52 +/- 2 minutes after premedication was given. Two patients (8%) had an SaO2 less than 90% (lowest SaO2 for both was 88%). It is concluded that the dose of morphine/scopolamine premedication used was associated with a low risk of clinically important hypoxemia in the patient population studied.