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Biomedical subjects

L Landow

Publications and source records attributed to L Landow.

At least 37 records · Page 2Linked to original sources
PubMed1993

Association between gastric intramucosal pH and splanchnic endotoxin, antibody to endotoxin, and tumor necrosis factor-alpha concentrations in patients undergoing cardiopulmonary bypass.

OBJECTIVES: To determine the association between gastric intramucosal pH, a minimally invasive marker reflecting the adequacy of oxygen delivery to the gastrointestinal tract, and splanchnic endotoxin, antibody to endotoxin, and tumor necrosis factor (TNF)-alpha concentrations in patients undergoing cardiopulmonary bypass. DESIGN: Single-arm, prospective study. SETTING: University hospital. PATIENTS: Adults (n = 10) free of hepatic, pulmonary, and renal disease undergoing nonemergent coronary artery bypass surgery. INTERVENTIONS: After induction of general anesthesia and endotracheal intubation, a tonometer nasogastric tube was positioned in the stomach, and triple-lumen fiberoptic catheters were inserted into the hepatic vein and pulmonary artery. Hepatic venous and mixed venous blood samples were analyzed for endotoxin, antibody to endotoxin, and TNF-alpha at six times: 30 mins after induction of anesthesia (time 1); during vena caval cannulation (time 2); after 15 mins of hypothermic cardiopulmonary bypass (time 3); during spontaneous left ventricular ejection after release of the aortic cross-clamp, but before termination of cardiopulmonary bypass (time 4); 15 mins after termination of cardiopulmonary bypass (time 5); and 1 hr after termination of cardiopulmonary bypass (time 6). Gastric intramucosal pH, systemic oxygen delivery (DO2), mixed venous oxygen saturation, hepatic venous oxygen saturation, and hepatic venous lactate concentrations were recorded at these same times. Data for each variable were compared with baseline values (time 1) for statistical significance. MEASUREMENTS AND MAIN RESULTS: Cardiopulmonary bypass was associated with an increase (p < .05) in systemic endotoxin concentrations from ventricular ejection until the end of the study. Virtually identical changes in the splanchnic circulation at this time approached, but did not reach, statistical significance, because hepatic venous endotoxin concentrations were higher than the mixed venous endotoxin concentrations at baseline (41.6 +/- 11.2 vs. 16.9 +/- 4.9 pg/mL). Gastric intramucosal pH was abnormal (< 7.35) at 15 mins (p > .05) and at 1 hr after termination of cardiopulmonary bypass (p > .05). The relationship between endotoxin and gastric intramucosal pH was not statistically significant (p = .15). The decrease in endotoxin antibody was small and statistically insignificant. TNF-alpha was not detected in any patient. Systemic DO2 decreased (p < .05) after 15 mins of hypothermic cardiopulmonary bypass, but returned to baseline values thereafter. There were no significant changes in mixed venous and hepatic venous oxygen saturation values. Splanchnic lactate concentrations increased at cannulation (p < .05), after 15 mins of hypothermic cardiopulmonary bypass (p < .05), and 15 mins after termination of cardiopulmonary bypass (p < .05). CONCLUSIONS: These observations are consistent with the hypothesis that impaired gut-barrier function is responsible for endotoxemia occurring during cardiopulmonary bypass. It is unclear whether increased mucosal permeability and mucosal acidosis are causally related phenomena or simply independent markers of damage to gut epithelium.

Adult↗
PubMed1993

Splanchnic lactate production in cardiac surgery patients.

OBJECTIVE: To review the pathophysiology of lactic acidosis in patients undergoing open-heart surgery, with special reference to the splanchnic circulation. DATA SOURCE: MEDLINE search of pertinent experimental and clinical research studies. RESULTS: Lactate is an end-product of anaerobic metabolism and is in dynamic equilibrium with its precursor, pyruvate. The ratio of serum lactate to pyruvate concentrations in arterial blood is normally < or = 10:1. In patients with lactic acidemia, measurement of serum pyruvate concentrations may yield valuable clinical information. Lactate/pyruvate ratios > 10:1 suggest that oxygen delivery (DO2) is inadequate to meet metabolic demand, whereas increases in both lactate and pyruvate values with preservation of normal lactate/pyruvate ratios suggest a defect in oxidative utilization (e.g., a fractional increase in the inactive form of the pyruvate dehydrogenase enzyme complex) despite adequate DO2. Meaningful changes in regional oxygen kinetics occur during extracorporeal circulation. Increased production of endogenous vasoconstrictors in response to nonpulsatile flow, together with a decrease in arterial oxygen content resulting from the addition of 2 L of pump prime to the patient's circulation at the beginning of cardiopulmonary bypass, decrease DO2 to the gastrointestinal tract. The effect of this reduction is mitigated, in part, by lowering core temperature and reducing tissue oxygen demand. CONCLUSIONS: The abdominal organs tolerate reductions in DO2 when they are cold (25 degrees C), since gastric intramucosal pH (a marker of inadequate DO2), and hepatic venous lactate/pyruvate ratios and oxygen saturation during the first half of cardiopulmonary bypass are normal. As surgery nears completion and core temperature is increased, tissue oxygen demands escalate. The presence of gastric mucosal acidosis, coupled with lactic acidemia and oxygen desaturation of hepatic venous blood, suggest that delivery of oxygen to the abdominal organs at the conclusion of cardiopulmonary bypass is insufficient to meet demand. A growing proportion of cardiac surgery patients are older and many have concomitant medical problems that can impair their recovery. Useful strategies are needed to reduce the occurrence of splanchnic ischemia in these and other high-risk populations if surgical outcome is to improve in the future.

Coronary Artery Bypass↗
PubMed1993

Use of ultrahigh frequency ventilation in patients with ARDS. A preliminary report.

STUDY OBJECTIVE: Our objective was to compare the efficacy of ultrahigh frequency ventilation (UHFV) (frequencies > 3 Hz) with respect to oxygenation, airway pressures, and hemodynamic parameters in patients with adult respiratory distress syndrome (ARDS) who were not responding to conventional ventilation. DESIGN: We used a prospective, multicenter, nonrandomized study design in which each patient served as his own control. SETTING: Three university-affiliated, tertiary-care medical centers participated. PATIENTS: Persons aged 16 to 79 years old with ARDS and unresponsive to conventional ventilation, as defined by a Food and Drug Administration (FDA) approved protocol, were included. INTERVENTIONS: Ninety patients who were not responding to conventional ventilation were changed to UHFV using a microcomputer-controlled device. MEASUREMENTS AND RESULTS: The patient's blood gas, hemodynamic, and airway pressure variables were measured just before, and at 1 and 24 h after the switch to UHFV. We demonstrated clinically significant improvements in arterial oxygen tension (PaO2) and reductions in peak and mean inspiratory pressures. CONCLUSIONS: In a multicenter study, UHFV improved respiratory gas exchange and reduced airway pressure variables at both 1 h and 24 h after the onset of UHFV when compared with conventional ventilation just prior to the change and without hemodynamic deterioration, in patients with severe ARDS.

Adolescent↗
PubMed1991

An improved lidocaine infusion protocol for cardiac surgical patients.

A new protocol for lidocaine administration was tested to determine whether it would provide higher free and total serum lidocaine concentrations during and after weaning from cardiopulmonary bypass (CPB), without leading to accumulation toxicity, than those resulting from a conventional protocol (1.5 mg/kg loading dose bolus + 2 mg/min infusion rate). Ten elective adult cardiac surgical patients were studied. Ten seconds prior to aortic cross-clamp release (0 min), each patient received a lidocaine bolus (1.5 mg/kg) and simultaneous lidocaine infusion (5 mg/min for 1 hour, followed by 2 mg/min for 23 hours). Weaning occurred 20 to 30 minutes after cross-clamp release. Lidocaine levels were determined from arterial blood samples at 0, 10, 20, 30, and 60 minutes, and at 2, 4, and 24 hours postcross-clamp release. Compared with the conventional protocol, the new protocol showed a significant increase in mean total lidocaine concentration (P less than or equal to 0.02) at 30 and 60 minutes, and a significant increase in mean free lidocaine concentration (P less than or equal to 0.005) at 20, 30, and 60 minutes. No patient had toxic levels at 24 hours. Results of this study suggest that in patients undergoing cardiac surgery, a "5 + 2" mg/min infusion protocol is safe and superior to a conventional protocol in achieving therapeutic serum levels of free and total lidocaine.

Adult↗
PubMed1991

Gastric tonometry and venous oximetry in cardiac surgery patients.

OBJECTIVE: To determine the relationship between gastric intramucosal pH and several other indices of splanchnic perfusion in patients undergoing cardiopulmonary bypass. DESIGN: Prospective, single-arm study. SETTING: University Hospital. METHODS: Elective cardiac surgery patients (n = 8), free of hepatic disease, were studied. Before anesthetic induction, a triple-lumen, heparin-bonded fiberoptic catheter was inserted into the hepatic vein under fluoroscopic guidance. An identical catheter was inserted into the pulmonary artery. After endotracheal intubation, a nasogastric tube modified to permit measurement of gastric intramucosal pH was inserted into the stomach. Systemic oxygen delivery (DO2), and arterial, mixed venous, hepatic venous, and femoral venous blood gases and lactate concentrations were recorded at the following times: immediately before induction of anesthesia (time 1); during atrial cannulation (time 2); after 30 mins of hypothermic cardiopulmonary bypass (time 3); 15 mins after termination of cardiopulmonary bypass (time 4); and 1 hr after arrival in the ICU (time 5). Hepatic venous hemoglobin saturation (SO2) and mixed venous hemoglobin saturation (SvO2) were monitored continuously from times 1 to 5. Gastric intramucosal pH was recorded at times 2, 3, 4, and 5. The hepatic catheter was removed as soon as the last samples were collected in the ICU. RESULTS: The square of the weighted mean correlation coefficients (rw)2 for gastric intramucosal pH vs. hepatic venous lactate concentrations, gastric intramucosal pH vs. hepatic venous PO2, and gastric intramucosal pH vs. hepatic venous pH were (rw)2 = .50, (rw)2 = .58, and (rw)2 = .32, respectively. Systemic DO2, hepatic venous lactate concentrations, hepatic venous PO2, and hepatic venous pH were significant determinants in the multiple regression model for gastric intramucosal pH (r2 = .89). There were significant differences between SvO2 and hepatic venous SO2 at times 4 and 5. CONCLUSION: Gastric intramucosal pH may provide a minimally invasive way to monitor the adequacy of splanchnic DO2 in patients undergoing cardiopulmonary bypass. Additional data are necessary to determine whether low gastric intramucosal pH is truly a marker of supply-dependent oxygen uptake across the hepatosplanchnic vascular bed under these conditions.

Aged↗
PubMed1990

Free and total lidocaine levels in cardiac surgical patients.

A lidocaine bolus of 2 mg/kg has been shown to decrease the incidence of ventricular fibrillation in cardiac surgical patients during reperfusion following aortic cross-clamp release (CCR). In an effort to extend this effect into the immediate postoperative period, many centers routinely administer a prophylactic lidocaine infusion for the first 12 to 24 hours after surgery. Sequential total serum lidocaine levels were measured over 6 hours in 28 adult cardiac surgical patients without liver, kidney, or respiratory disease, and free serum lidocaine levels were measured in 15 of these patients. In addition, pharmacokinetic data were collected and analyzed in 8 of these patients. Each patient received a lidocaine bolus of 1.5 mg/kg and an infusion at 2 mg/min immediately before CCR. Serum levels were determined just before CCR, and at 10, 20, 30, 60, 120, 240, and 480 minutes after CCR. More than 50% of patients had subtherapeutic total serum lidocaine levels from 20 to 120 minutes after CCR, but free lidocaine levels remained within the therapeutic range. No patient showed malignant ventricular dysrhythmias during the study. The results suggest that (1) it may be misleading to estimate free lidocaine concentration based on total lidocaine levels; and (2) free drug is the moiety responsible for lidocaine's antiarrhythmic effect.

Adrenergic beta-Antagonists↗
PubMed1990

Efficacy of large-bore intravenous fluid administration sets designed for rapid volume resuscitation.

We tested the hypothesis that large-bore iv tubing sets provide greater in vitro flow rates than conventional sets currently utilized for the administration of normal saline. The study was conducted in two parts. First, flow rates were measured using a conventional iv tubing set under gravity and 300 mm Hg of pressure, and four large-bore iv tubing sets under gravity. Additional measurements were made after attaching various catheters and sheaths ranging in size from 14 ga to 9 Fr. Five trials were conducted for each combination. Second, we measured the amount of time taken in a mock drill by 28 randomly chosen anesthesiology residents and staff to load a unit of packed RBC into a pressure infusor bag, inflate to 300 mm Hg, and deflate to ambient pressure. Data were analyzed for individual tubing sets as a whole and individual catheter-tubing set combinations, using the Mann-Whitney U test with Bonferroni adjustment. Statistically significant (p less than .03) differences in flow rates were noted between the conventional set under gravity compared with both the pressurized conventional set and the large-bore tubing sets under gravity. There was no statistical difference in flow rates between pressurized conventional iv sets and large-bore iv sets. Mean time necessary for the 28 anesthesiology staff and residents to pressurize and deflate a conventional tubing set was 65 sec/bag of packed RBC. We conclude that a considerable amount of time can be saved by utilizing large-bore iv tubing sets instead of conventional pressurized sets during massive volume resuscitation. Clinical trials are indicated to corroborate these results.

Analysis of Variance↗
PubMed1989

Current trends in neurosurgical critical care medicine.

We conducted a survey of neurosurgeons to discover how they manage specific problems commonly seen in critically ill neurosurgery patients and compared the responses with relevant investigations published in the neurosurgical literature over the past 10 years. The 101 Chiefs of Neurosurgery of every North American academic training program were sent copies of two consecutive surveys for distribution to their attending staff. Among the topics covered were indications for steroid administration, prophylaxis of gastrointestinal bleeding, indications for insertion of ICP monitoring devices and use of prophylactic antibiotics while they are in place, and fluid restriction in patients with cerebral edema. Replies were strictly anonymous. A Medline Computer search for the period 1976-1989 was carried out for each topic. We received 136 and 67 replies each to our two surveys. Over 90 clinical and laboratory studies published in major medical journals, many randomized and prospective, were reviewed. Two trends were evident: (a) a noticeable lack of uniformity among neurosurgeons with respect to management of the same problem; (b) little or no basis of support in the literature for many management practices. Based on these studies and the responses to our survey, we suggest an examination of current clinical practices.

Journal Article↗
PubMed1987

Perioperative hemodilution.

Perioperative hemodilution is one way of minimizing the morbidity and mortality associated with blood transfusion. A review of the literature indicates that, for many patients, substitution of crystalloid solutions for surgical blood loss is safe and physiologically advantageous as long as euvolemia is maintained. Increased stroke volume is the principal mechanism responsible for augmented tissue oxygen delivery. Based on this review the surgical population can be divided into three groups: most patients under 60 years of age (group 1); those with important cardiac disease (group 2); and the elderly (group 3). Patients in group 1 can safely undergo hemodilution to a hematocrit of 0.25; patients in the other groups should probably not be subjected to hemodilution. Implementation of this proposal could diminish the risk and expense of many surgical procedures.

Hemodilution↗