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Biomedical subjects

A H Stammers

Publications and source records attributed to A H Stammers.

At least 37 records · Page 2Linked to original sources
PubMed1999

An in vitro evaluation of a self-contained cardioplegia delivery device.

Focus on improved myocardial protection has prompted the development of delivery systems which can accommodate the demands of increasingly refined cardioprotective strategies. The purpose of this study was to evaluate the Sorin Blood Cardioplegia Console (BCC) for accuracy and precision in the delivery of cardioplegia solutions. An in vitro model was designed to evaluate the following performance characteristics of the BCC: delivery volume (blood and crystalloid) at 50, 250, 375, and 500 ml/min flow rates; potassium end-delivery concentration at blood:crystalloid ratios of 4:1, 8:1, and 16:1; intermittent cardioplegia delivery; and heat transfer of the internal heater/cooler. Differences in blood and cardioplegia volumes between measured and calculated values across all flow rates tested were found to be statistically significant and ranged from 1.4 to 21.5 ml; however, the differences were within the accepted variance of the instrument (+/- 5%). Across all tested ratios, the measured end-potassium concentrations were all within 1 mEq of the expected values, except for the 16:1 ratio at 50 ml/min, which had a 2.52 mEq variance. All significant differences were within the accepted variance of the instrument (+/- 5%). In conclusion, the BCC accurately and delivered cardioplegia volumes and potassium concentrations across all tested conditions with reproducible performance.

Cardioplegic Solutions↗
PubMed1999

Perfusion education in the United States at the turn of the century.

The challenges facing institutions charged with the delivery of health care have also affected the delivery of education in the health sciences. In the 30 years since the establishment of a process for formalized perfusion education, significant changes have shaped how the fundamentals of perfusion sciences are learned. The establishment and maintenance of a profession can only be secured through the creation of standards that guide educational facilities in the delivery of formalized instruction in a discipline. Perfusion education programs continue to meet these standards but are doing so at a time where resources continue to dwindle and quantitative assessment of manpower issues are fuzzy, at best. The peak of perfusion education programs occurred in 1994, and 5 years later only 25 programs were still accredited by the Committee on Accreditation of Allied Health Programs (CAAHEP). In the past decade, only one new education program has sought accreditation from CAAHEP. There were 41% fewer graduates in the United States in 1998 than in 1992, which follows a 6-year trend in declining numbers of individuals entering the field of perfusion. Individual programs are challenged by the reordering of university and community hospital structures, which often results in critical reviews of resource allocation to perfusion programs. The health of the perfusion profession remains deeply tied to the success of perfusion education programs. Likewise, the health of these programs can only be assured by means of continued solicitation of support and guidance from practitioners who serve as stewards of perfusion technology.

Costs and Cost Analysis↗
PubMed1999

Quantitative evaluation of heparin-coated versus non-heparin-coated bypass circuits during cardiopulmonary bypass.

The extracorporealization of blood activates various elements of the fibrinolytic, coagulation, and complement systems. It is theorized that advancements in biocompatibility ameliorate many of the changes leading to improved patient management. The purpose of this study was to determine if heparin-coated circuit (HCC) utilization during cardiopulmonary bypass enhances patient outcomes in a cost-effective manner. A search of the English medical literature was completed to identify all clinical, prospective, randomized trials comparing HCC and non-HCC in patients undergoing coronary artery bypass grafting or valvular surgery. Twenty-six papers consisting of a sample size of 1515 patients were identified and included in the study parameters. The study distinguished between Duraflo II and Carmeda coating techniques and matched papers with different heparin loading doses, as well as use of a heparin-coated cardiotomy. Study parameters were matched for all papers and analyzed according to the availability of data. Statistically significant benefits of HCC were found in postoperative blood loss, time in the ICU, end bypass C3a, time to extubation, end bypass lactoferrin, and end platelet count, but not with respect to postoperative chest tube drainage, red blood cell transfusions, and end bypass TAT complex, D-dimers, and BTG. Data comparing the use of coated or uncoated cardiotomy utilization failed to demonstrate a benefit to heparin coating. Several immunological variables were ameliorated when Carmeda HCC was utilized, although data were insufficient to establish a cost-benefit analysis. In conclusion, heparin-coated circuitry provided statistically better results when compared to noncoated circuitry.

Cardiopulmonary Bypass↗
PubMed1999

Removal of hepatocarcinoma cells from blood via cell washing and filtration techniques.

Utilization of autotransfusion during tumor resection remains controversial due to viability of carcinoma cells remaining in collected blood. The purpose of this study was to evaluate autotransfusion techniques combined with leukocyte depleting filters (LDF) for removal of hepatocarcinoma cells from autotransfusate. An in vitro model was created by contaminating expired human erythrocytes with cultured hepatocarcinoma (HEP G2) cells. Autotransfusion devices evaluated were Cobe BRAT2, Sorin STAT-P, and Fresenius CATS. Autotransfusate collected from varying processing conditions were filtered using the Pall Leukoguard RS or Pall Purecell RCQ LDF. Carcinoma concentrations were quantified via Coulter Counter technology. The CATS exhibited higher concentrations of cancer cells in the autotransfusate prior to washing, a 449% increase. This was significantly higher than either the BRAT2 or STAT-P, 350% and 315% respectively. Post washing HEP G2 concentrations in the BRAT2 were significantly higher than the STAT-P and CATS. Doubled wash volumes removed more HEP G2 cells in all trials, reaching statistical significance only in the CATS. LDF resulted in a significant 75% reduction of HEP G2 cells, with no difference between filters. While combination use of autotransfusion devices and leukocyte depleting filters did result in a product with concentrated hematocrit, no technique removed all hepatocarcinoma cells.

Blood Transfusion, Autologous↗
PubMed1998

Aprotinin enhances the endogenous release of interleukin-10 after cardiac operations.

BACKGROUND: Cardiopulmonary bypass (CPB) is characterized by the systemic release of proinflammatory cytokines, such as tumor necrosis factor-alpha and the interleukins 1 and 6, as well as endogenous antiinflammatory cytokines, including interleukin-10 (IL-10). Glucocorticoids reduce tumor necrosis factor-alpha plasma concentrations while enhancing IL-10 plasma concentrations after CPB. Aprotinin, a serine protease inhibitor used primarily to reduce blood loss after CPB, reduces CPB-induced proinflammatory cytokine tumor necrosis factor-alpha release similarly to glucocorticoids. This study evaluates the effect of full-dose aprotinin on the plasma concentrations of IL-10 after CPB. METHODS: Twenty adults were randomized into a control (group C, n = 10) and a full-dose aprotinin-treated group (group A, n = 10). Plasma levels of IL-10 were measured by enzyme-linked immunosorbent assay technique at baseline (before anesthetic induction), and at 1 and 24 hours after CPB termination. RESULTS: A significant (p < 0.05) increase of IL-10 occurred in both groups at 1 and 24 hours after termination of CPB when compared with the same group at baseline. In group A, the increase in IL-10 was significantly greater than in group C (p < 0.05) at 24 hours after CPB. CONCLUSIONS: These results demonstrate an endogenous antiinflammatory response generated after CPB, characterized by IL-10 release, that is enhanced by aprotinin therapy. This study demonstrates a unique antiinflammatory activity of aprotinin that may be of clinical significance.

Aprotinin↗
PubMed1998

Clinical evaluation of a new generation membrane oxygenator: a prospective randomized study.

A new generation hollow-fibre membrane oxygenator (Spiral Gold) has been introduced by Baxter Healthcare (Irvine, CA, USA). The purpose of this study was to evaluate the operational performance of this device under clinical conditions and to compare it to the Univox Gold membrane oxygenator. Following institutional review board approval, and the obtainment of informed consent, 26 patients undergoing coronary artery bypass grafting were randomly assigned to either a Spiral Gold (Spiral) (n = 13) or Univox Gold (Univox) (n = 13) group. Study parameters were grouped into the following categories: haematological, haemodynamic, oxygenator performance and perioperative outcomes. All patients received identical surgical, anaesthesia and postoperative care. There were no statistically significant differences in either preoperative or operative parameters between groups. During cardiopulmonary bypass, the Spiral group had a significantly lower pressure drop (26.9 +/- 8.2 vs 46.7 +/- 16.2 mmHg, p < 0.001). The Spiral group had significantly lower plasma free haemoglobin levels during all time periods of CPB compared to the Univox group. Heat exchange coefficients were higher during the rewarming period in the Spiral patients (0.59 +/- 0.28) compared to the Univox group (0.36 +/- 0.19), p = 0.06. There were no differences in oxygen transfer between groups, but ventilation gas sweep rates and FiO2 levels were statistically lower in the Spiral group at two of the three sampling time periods. The ratio of ventilating gas sweep rate to blood flow rate was lower in the Spiral group (0.56 +/- 0.12) compared to the Univox group (0.74 +/- 0.23), p < 0.03. The Spiral Gold oxygenator had superior oxygen transfer efficiency and lower haemolysis rates than the Univox Gold oxygenator.

Adult↗
PubMed1998

Hematological abnormalities in neonatal patients treated with extracorporeal membrane oxygenation (ECMO).

The physical process of extracorporeal membrane oxygenation (ECMO) results in derangement of the hemostatic mechanism, which may lead to increased morbidity, secondary to the disease process. The purpose of this study was to evaluate the hematological status of neonates undergoing ECMO therapy, and to evaluate coagulation tests in predicting hemorrhagic risk. Following Institutional Review Board approval, 30 patients undergoing ECMO treatment were retrospectively entered into this study. Medical records were reviewed and indicators of hemostasis, transfusion, morbidity, and outcomes recorded. Assessment of coagulation was determined through serial analysis of platelet count, fibrinogen concentration, prothrombin time (PT), activated partial thromboplastin time (aPTT), antithrombin III, fibrin split products, D-dimers, plasma free hemoglobin, activated clotting time, ionized calcium, and thrombelastography (TEG). Median total transfusion requirements for all patients were 1.79 ml/kg/ECMO hr. Fifty-seven percent of the 30 patients were diagnosed as coagulopathic according to Extracorporeal Life Support Organization standards. Patients were separated into either a hemorrhagic group (HEM, > 2.0 ml/kg/ECMO hr, n = 13) or a nonhemorrhagic group (N-HEM, n = 17), with HEM patients requiring twice the transfusion volume of N-HEM (p < 0.0001). Hemorrhagic complications were reported in 53.8% of the HEM patients vs. 35.3% in the N-HEM group. HEM patients were transfused with significantly greater quantities of platelets on days 1, 3, 5, and 8 and packed red blood cells on day 7 when compared to N-HEM (p < 0.05). TEG determination showed significant differences between groups on days 3 and 6 (p < 0.005), and 8 (p < 0.05). Derangements in hemostasis resulting from ECMO are profound, with methods of assessing coagulation complicated by both the variability in patient condition and lack of specificity of laboratory tests. Interpretation of TEG data has shown to be a valuable supplement for managing this challenging patient population.

Antifibrinolytic Agents↗
PubMed1998

Clinical evaluation of a new in-line continuous blood gas monitor.

Two methodologies for obtaining accurate blood gas and electrolyte values during cardiopulmonary bypass (CPB) are traditional laboratory analyzers, which use an electrochemical technology, and continuous in-line monitoring systems, which use a fluorometric and/or spectrophotometric technology. The purpose of the present study was to evaluate the accuracy of a new continuous in-line monitor, the 3M CDI Blood Parameter Monitoring System 500, which provides continuous in-line measurements of pH, PCO2, PO2, potassium (K+), oxygen saturation, hematocrit, hemoglobin, and temperature, during partial or complete CPB. Study parameters included arterial pH, PCO2, PO2, and K+ values. Overall performance was analyzed by calculating the mean difference (expressed as the bias) between the CDI system 500 and the laboratory analyzer for each parameter. The accuracy of the arterial pH, PCO2, and K+ values provided by the CDI system 500 was then evaluated using target values established in the acceptable performance standards for laboratory analyzers from the Clinical Laboratory Improvement Act of 1988 (CLIA '88). The accuracy of the PO2 value provided by the CDI system 500 was evaluated using a target value of +/- 10% of the reference, or laboratory analyzer, value. A prospective multi-center trial was conducted following Institutional Review Board approval. A total of 75 cases was included in the analyses, with over 200 data points from 4 clinical locations. Results for pH, PCO2, and K+ were within the target values established by CLIA '88. pH bias was 0.00 +/- 0.02 pH units. PCO2 bias was -0.3 +/- 3.3 mm Hg. K+ bias was approximately +0.12 +/- 0.31 mmole/l. Results for PO2 were within 10% of the reference value. PO2 bias was 7.5 +/- 13.8 mm Hg. The results of this clinical trial show that the CDI System 500 continuous in-line monitoring system provides values that meet the accuracy standards for laboratory analyzers for arterial pH, PCO2, PO2, and K+.

Bias↗
PubMed1997

Historical aspects of cardiopulmonary bypass: from antiquity to acceptance.

Cardiopulmonary bypass has evolved from an extremely risky procedure into a safe systematic process, and is practiced daily in thousands of centers throughout the world. Numerous individuals, from diverse specialities, have contributed to the knowledge of the processes of extracorporeal flow. The developmental sequence of advances in cardiopulmonary bypass has been divided into three nonexclusive periods based on the major changes observed during the time: (1) a conceptual and developmental period, consisting of events that occurred before 1950; (2) an applied technological period, 1950 to 1970; and (3) a refinement period, 1970 to present. Within each time frame, the major findings regarding biological and technical challenges, extracorporeal device development, and applied clinical practice will be explored. Technological advances in cardiopulmonary bypass have permitted surgeons to treat patients with both congenital and acquired heart disease, and anesthesiologists to identify appropriate mixtures of treatment regimens, whereby the risks associated with managing this challenging patient population could be minimized.

Anesthesiology↗
PubMed1997

Coagulopathic-induced membrane dysfunction during extracorporeal membrane oxygenation: a case report.

This paper describes an unusual complication of membrane dysfunction during extracorporeal membrane oxygenation (ECMO) for treatment of neonatal respiratory distress. A 2.8-kg term infant presented to our facility in severe respiratory distress and was diagnosed with primary pulmonary hypertension. After routine priming of the extracorporeal circuit, the patient was placed on veno-arterial ECMO with 8 F arterial and 12 F venous cannulae. Transfusion criteria were established which included trigger values of the following: platelet count 100,000/microliters, fibrinogen 150 mg/dl, haematocrit 40%. The ECMO course was uneventful until approximately the 132nd hour on support when the patient developed a consumptive coagulopathy, as evidenced by 55-60% reductions in both platelet count and fibrinogen concentrations, despite transfusion therapy. Total autogeneic blood product transfusion during the first 120 h of ECMO averaged 4.4 +/- 2.2 ml/h, while the transfusion rate for the final 35 h was 7.8 +/- 3.5 ml/h. Coinciding with this rise in transfusion requirements was an increase in transmembrane pressure from 0.29 to 1.52 mmHg/ml blood flow. The patient was separated from ECMO after 175 h due to a continuing coagulopathy and haemothorax. The patient was then treated with nitric oxide therapy before succumbing on the twelfth postoperative day due to refractory respiratory failure. The circuit was dissected and significant clots found in both the venous bladder and oxygenator. In addition, approximately one-third of the membrane compartment had a 'fused' circumferential pattern of dessicated clot which interrupted blood path continuity. In conclusion, this report describes an unusual complication of the ECMO oxygenator that occurred during long-term extracorporeal life support which most likely resulted from a coagulopathy.

Blood Transfusion↗
PubMed1997

Evaluation of a new generation cardioplegia administration system.

The delivery of cardioplegia has traditionally been constrained by the physical limitations of the mechanical devices in use, yet myocardial protective strategies may vary both according to patient condition and operative requirements. The need for a cardioplegia administration device that allows flexibility and safety is evident. The purpose of this study was to evaluate the performance of the Quest Myocardial Protection System (MPS) during clinically simulated conditions. The MPS was evaluated in an in vitro setting under the following conditions: blood to crystalloid ratios (1:1, 4:1, 8:1, all blood), potassium concentrations ([K+]) of 10 and 25 mmol/L, calcium concentrations ([Ca++]) of 1.4 and 2.8 mmol/L, and at flow rates of 100 and 300 ml/min. Predicted values from the MPS were compared with measured values, with statistically significance accepted at p < .05 level. Significant differences were seen between measured and MPS cardioplegia delivery volumes at the 4:1, 8:1 and all blood ratios with a flow rate of 300 ml/min. There were no significant differences seen between measured and expected [K+] and [Ca++] delivery values across all combination of flow rates and ratios. Differences between delivery pressures of the MPS and measured values for flow rates of 100, 250 and 500 ml/min were 0.4, 1.2 and 7.6 mmHg respectively. The mean cardioplegia cooling time from 37 degrees C to 9 degrees C was 37 +/- 4.5 seconds, while rewarming from 7 degrees C to 37 degrees C, took 53 +/- 10.4 seconds. In conclusion, the Myocardial Protection System performance characteristics were precise in ratio delivery, concentrations of potassium agents, additive agent concentration, temperature, and pressure across all experimental conditions, with the exception of delivery volume.

Blood Flow Velocity↗
PubMed1997

Clinical comparison of pulsatile and nonpulsatile perfusion during cardiopulmonary bypass.

Controversy exists concerning the utilization of pulsatile flow during cardiopulmonary bypass (CPB) with regard to improved patient outcomes. The purpose of the present study was to evaluate pulsatile perfusion in patients undergoing CPB in a clinical setting. Seventy patients undergoing open heart surgery for repair of valvular or congenital heart disease were prospectively entered into the study and were randomly assigned to either pulsatile perfusion (PP, n = 35) or nonpulsatile perfusion (NP, n = 35) groups. All patients received identical surgical, perfusion, and postoperative care. Study parameters included: rate of spontaneous cardiac conversion, inotropic drug use, urine output, skin temperature, platelet count, fibrinogen concentration, and plasma free hemoglobin level. There were no statistically significant differences seen in either preoperative or operative parameters between groups. The PP group had a significantly higher rate of spontaneous cardiac conversion, less inotropic drug use, earlier recovery of skin temperature, and higher urine output during CPB (908.8 +/- 87.2 ml/hr vs. 606.1 +/- 57.5 ml/hr, p < .01). There were no significant differences in either platelet count or fibrinogen concentration between groups. There was a steady increase in plasma free hemoglobin during PP, which was not seen in the NP group (p < .01). We conclude that the use of pulsatile flow resulted in improved patient outcomes in maintaining better renal function and preserving cardiac function in the early post-bypass period.

Adult↗
PubMed1996

Methods for monitoring hemostasis during and following cardiac surgery.

The challenges in cardiac surgical hemostasis continue to plague the clinician. Rapid analysis and interpretation of coagulation tests are crucial in identifying coagulopathies that include both hemorrhagic and thrombophilic conditions. An understanding of the hemostatic mechanism, combined with a knowledge of pharmaceutical and transfusion interventions, is necessary to develop effective therapeutic plans. The coagulation tests that provide the most useful information include both end-point determinants and kinetic tests of clot formation. Future evaluation of the efficacy of coagulation tests in meeting these challenges will move beyond quantification of changes within various intermediates of hemostasis and rest with the correlation of these measured values with specific, outcome-directed indicators for optimizing patient care.

Blood Coagulation↗
PubMed1996

Ultrafiltration of the waste plasma effluent from cardiopulmonary bypass circuit contents processed with a cell-washing device.

Blood conservation methods are commonly practiced throughout most hospitals that conduct cardiothoracic surgery. In an effort to reduce patients' exposure to homologous blood products and due to cost effectiveness of blood conservation techniques, this present study combines autotransfusion of the remaining blood in the extracorporeal circuit and ultrafiltration of the plasma effluent, and describes the resulting product. Seven patients, greater than 19 years of age, requiring cardiopulmonary bypass (CPB) were incorporated into this study. Exclusion criteria included age limitation. At termination of CPB, the remaining blood in the circuit was transferred to an autotransfusion machine and processed. Plasma (1054 +/- 206 ml) effluent was collected directly from the centrifugal bowl and processed through a ultrafiltrator, with a constant flow rate and negative pressure, until the plasma effluent concentrated down to an end processed volume of approximately 150 ml. The following variables were either measured or calculated: plasma-concentrate volumes per three minute interval, inlet/outlet pressures of an ultrafiltrator, transmembrane pressure (TMP), plasma free hemoglobin, fibrinogen, total protein, and colloid osmotic pressure. The average ultrafiltrate volume taken off from the plasma effluent was 828 +/- 237 ml, with an average ultrafiltrate volume of 115 ml in every three minute interval. The TMP did not change over the first 15 minutes of processing but became significantly elevated at the 18th minute interval and continued to increase and reach a maximum TMP of 286.5 +/- 2.1 mmHg at the end of concentration. Fibrinogen levels increased from pre-concentration values of 118.2 +/- 64 to 317 +/- 177 mg/dl (p = .03) along with increases in plasma free hemoglobin from 97.7 +/- 46 to 402.1 +/- 180 mg/dl (p = .0002). The total protein concentration increased by over 330% from baseline values. Ultrafiltrating plasma effluent from autotransfused cell salvaged CPB circuit contents could prove beneficial, but further study is required to discover ways to separate unfavorable products, such as activated platelet-leukocyte products and reduced plasma free hemoglobin, and to lower heparin concentrations of the plasma-concentrate.

Blood Transfusion, Autologous↗
PubMed1996

Evaluation of a variable ratio cardioplegia system.

Gish Biomedical has designed a blood cardioplegia delivery system (MyoManager) which is purported to provide rapid control of blood and crystalloid solution ratios for myocardial preservation. The present study was designed to evaluate the ability of this device to provide cardioplegia solutions of specific hematocrit and potassium ion concentrations ([K+]). An in vitro circuit was designed whereby a blood perfusate with a [K+] of 5 mEq/L was mixed with a base crystalloid solution containing 210 mEq/L of K+. Data was collected at several blood to crystalloid ratios (1:1, 4:1, 8:1, 16:1, 25:1), and at four delivery rates (100, 150, 200, 250 ml/min). Predicted and observed values of total cardioplegia volume, hematocrit, crystalloid volume, and [K+] were statistically (ANOVA) analyzed, and statistical significance accepted at p 0.05. There were no statistically significant differences observed at any flows or ratios in hematocrit. However, at 100 ml/min flow rates, the crystalloid delivery volume difference of 2.4 +/- 2.0 ml was significantly higher than that observed at 250 ml/min, 1.5 +/- 1.5 ml (p < 0.02) and at 200 ml/min flow rates, 1.5 +/- 1.6 ml (p < 0.02). There was no statistical significance in [K+] difference between flows across all ratios. However, within ratios, a significant difference in [K+] at 100 ml/min, 1:1 blood to crystalloid ratio, was observed (p < 0.0001) versus all other ratios and flows. The only statistically significant difference that was shown in total cardioplegia delivery volume was observed between 100 and 200 ml/min (p < 0.04) when analyzed across all ratios. The data suggests that the MyoManager effectively provides precise control of [K+] and hematocrit at cardioplegia flows greater than 100 ml/min.

Analysis of Variance↗