The effect of PaCO2 on cerebral perfusion: an experimental swine model.

Adequate cerebral perfusion is of particular concern to the clinician and is a major factor in postoperative morbidity. Cerebral circulation has the ability to autoregulate blood flow in order to maintain nutrient delivery and prevent high intravascular pressures. The focus of this study was to characterize the impact of gradually changing arterial CO2 levels on cerebral perfusion. A total of eight porcine subjects were placed into either a normothermic group (NG, N = 4, rectal temperature = 35.4+/-1.2 degrees C) or a hypothermic group (HG, N = 4, 30.6+/-0.6 degrees C). After initiation of cardiopulmonary bypass, the PaCO2 values sequentially varied between 24 and 56 mmHg. Arterial, venous, and internal jugular blood gas data were collected at 4 mmHg increments, and relative cerebral blood flow was calculated as CBF = 1 (CarterialO2-CjugularO2)(-1) Physiological parameters were similar in both groups across all test conditions: mean arterial pressure-NG 81.6+/-11.9 mmHg versus HG 73.4+/-7.0 mmHg, p = NS, and systemic oxygen consumption-HG 110.6+/-30.0 mL min versus NG 136.4+/-37.9 mL min(-1), p = NS. No significant differences were found in CBF in the NG (21.8+/-4.4 mL min(-1) 100 gL at PaCO2 = 56 mmHg versus 20.5+/-5.0 mL min(-1) 100 g(-1) at PaCO2 = 24 mmHg) or the HG (24.3+/-9.5 mL min(-1) 100 g(-1) at PaCO2 = 56 mmHg versus 25.6+/-12.0 mL min(-1) 100 g(-1) at PaCO2 = 24 mmHg). In conclusion, the alteration of PaCO2 under both hypothermic and normothermic conditions resulted in no significant differences in 1 (CarterialO2 - CjugularO2)(-1) in this model.

An in vitro study of the effects of isoflurane on oxygen transfer.

A common anesthetic technique utilized during cardiopulmonary bypass (CPB) includes the use of various inhalation agents, such as isoflurane. The purpose of this study was to evaluate the effects of this agent on oxygen transfer during CPB. An in vitro model was designed using bovine blood. Blood flow was held constant at 2 l/min, while gas flow was manipulated at 1 and 3 l/min. The percentage of inspired oxygen (FiO2) was set at 50 and 100%, and isoflurane was manipulated to 1.0, 3.0 and 5.0%. Blood gas analysis, oxygen transfer, and inlet and outlet isoflurane concentrations were measured at each of the given conditions. A total of 12 trials with four oxygenators were conducted. In the four oxygenators used in our study, no significant differences in oxygenator performance were found. At conditions of 1 I/min gas flow, 50% FiO2 and 1% isoflurane, there were no significant changes in O2 transfer between baseline and measurements taken during isoflurane administration (100.18 +/- 12.49 vs 102.35 +/- 10.99 ml O2/min, p=0.8031). At 3 I/min gas flow, 100% FiO2 and 5% isoflurane, no significant differences were found (142.35 +/- 10.76 vs 154.04 +/- 8.95 ml O2/min, p=0.1459). The only significant differences found for oxygen transfer were between 50 and 100% FiO2, all other conditions being set equal (102.35 +/- 10.99 vs 137.68 +/- 8.62 ml O2/min, p=0.0023). In conclusion, increasing concentrations of isoflurane up to 5% does not affect the efficiency of oxygen transfer in an in vitro circuit. Further studies are necessary to evaluate the effects in an in vivo setting.

Effect of partial-filling autotransfusion bowls on the quality of reinfused product.

Intraoperative autotransfusion is used in a variety of surgical procedures with the quantity of blood loss dependent upon numerous factors. These procedures may or may not produce a full autotransfusion bowl. The inadequate removal of contaminants has been correlated to the incomplete filling of bowls, resulting in a condition called "Salvaged Blood Syndrome." The purpose of this study was to assess the quality of aspirated whole blood after processing with an autotransfusion system using various fill volumes and two wash volumes. An in vitro circuit was designed to mimic the mechanical effects of extracorporeal flow on blood. Twenty-four Baylor-style bowls were filled at 400 mL min(-1) and washed at 300 mL min(-1). Two wash volumes, 1000 and 2000 mL, and three bowl volumes: low, mid, and full, were used in this study. The bowl volumes were determined by using red cell quantities of 60, 100, and 135 mL for the low-fill, mid-fill, and full bowls, respectively. Samples were drawn pre-autotransfusion and post-autotransfusion and analyzed for plasma-free hemoglobin, IL-8, white blood cell count, platelet count, albumin, and total protein. All data were analyzed using one-way analysis of variance (ANOVA) with significance accepted at p > or = .05. Plasma-free hemoglobin levels and hematocrit were concentrated significantly (p < .05) as bowl volume increased. A significant difference in IL-8 levels was found in the wash volumes in the low-fill bowls (p < .02). Platelet count was significantly decreased between the full bowl with 1000 mL wash and the full bowl with 2000 mL wash (p < .0004). Total protein reduction was significantly less in the low-fill bowl with 1000 mL wash as compared to the other bowl treatments (p < .05). In conclusion, the quality of the washed product did not vary significantly between fill or wash volumes, with the exception of the low-fill bowl with 1000 mL wash.

The effect of priming techniques of ultrafiltrators on blood rheology: an in vitro evaluation.

The increased interest of using ultrafiltration during cardiopulmonary bypass ICPB) has mandated a re-evaluation of the hematological effects of this blood conservation process. 'Rinse-free' ultrafiltrators can be primed using either crystalloid or blood prior to use. It is unknown whether one priming technique results in superior results in ultrafiltration quality. An in vitro circuit was designed to evaluate the Sorin/COBE HC1400 (n=6), the Lifestream HC70 (n=6), and the Terumo/Sarns HC11 (n=6). All test conditions were conducted at a blood flow rate of 250 ml/min and a transmembrane pressure of 250 mmHg. Samples were drawn and analyzed at four distinct time points for hematocrit, total protein, plasma free hemoglobin, interleukin-6 (IL-6), interleukin-8 (IL-8), and tumor necrosis factor-alpha (TNFalpha). The HC11 had significantly greater percent increases in hematocrit under the blood priming protocol (29.2+/-7.9) than either the HC1400 (11.0+/-7.8, p<0.03) or the HC70 (11.9+/-7.8, p<0.04). When crystalloid priming was compared to blood priming, the HC1400 and HC70 produced significant percent increases in hematocrit and total protein levels. The HC1400 devices produced significantly less plasma free hemoglobin when primed with crystalloid rather than blood (43.6+/-38.3 vs 21.3+/-5.6, p<0.01). There were no significant differences between devices or priming techniques for IL-6, IL-8 or TNFalpha levels. In conclusion, the efficiency of the ultrafiltrators was elevated when primed with crystalloid before use. Cytokine levels were relatively unchanged with priming techniques, while plasma free hemoglobin levels were reduced with those devices previously primed with crystalloid.

An experimental evaluation of continuous cardiotomy reservoir ultrafiltration.

Ultrafiltration has been suggested as a means to reduce the morbidity associated with blood activation. However, the application of ultrafiltration to the highly activated blood of the cardiotomy suction subcircuit has not been investigated. The purpose of this study was to determine whether cardiotomy reservoir ultrafiltration (CRUF) would be effective in altering cytokine levels. Six swine, undergoing 90 min of cardiopulmonary bypass (CPB), were divided into two groups; one group was assigned to receive CRUF (N = 3), the other was to serve as controls and did not receive ultrafiltration (N = 3). Blood samples were analyzed for hematocrit, plasma-free hemoglobin, total protein, interleukin-8 (IL-8), and tumor necrosis factor alpha (TNF-alpha). Samples were taken pre-bypass, postheparinization, every 30 min during CPB, post-CPB and postprotamine. All data were analyzed using a one-way analysis of variance (ANOVA), with significance accepted at p < .05. There were no significant differences found between treatment and control groups for plasma-free hemoglobin levels (22.4 +/- 22.2 vs. 14.6 +/- 14.4; 40.1 +/- 26.1 vs. 40.0 +/- 19.3). After 90 min of ultrafiltration, there was a significant decrease in TNF-alpha (261.6 +/- 119.6 vs. 71.8 +/- 11.4; p = .02). Although IL-8 levels decreased from throughout the experiment, concentrations did not reach statistical significance. In conclusion, CRUF can be used without increasing cellular destruction, and can decrease certain cytokine levels. Our results suggest that further clinical studies should be undertaken utilizing this technique with a larger sample size.

In vitro evaluation of the Medtronic cardioplegia safety system.

Myocardial preservation demands the precise and accurate delivery of cardioplegic solutions to provide nutritive delivery and metabolic waste removal. The purpose of this study was to evaluate the performance characteristics of the Medtronic CSS Cardioplegia Safety System in an in vitro setting. The CSS was evaluated under the following conditions: blood to crystalloid ratios of 1:0, 1:1, 4:1, 8:1, 0:1; potassium concentrations of 10, 20, and 40 mEq L-1; volumetric delivery collection at 100, 250, 500, 750, and 990 mL/min; pressure accuracy at 100 and 300 mmHg; and system safety mechanisms. Measured and predicted values from the CSS were compared using one way ANOVA, with statistical significance accepted at p < or = 0.05. The measured values for the tested ratios and volume collections were all within the manufacturer's technical parameters. Potassium concentration results were all within expected values except at 100 mL/min, where the measured value of 17.1 +/- 2.1 mmol was lower than the expected 20.0 +/- 0.2 mmol (p < .034). As flow rates changed, the CSS line pressure error was constant (0.5 to 3.7%), and the only significant difference was observed at 100 mmHg, 500 mL/min (102.3 +/- 1.7 vs. 100.0 +/- 0.0 mmHg, P < .003). The device performed accurately and reliably under all simulated safety conditions, including bubble detection, over pressurization and battery backup. In conclusion, the performance of the CSS was within the manufacturer's specifications for the majority of the tested conditions and operated safely when challenged under varying conditions.