Hypotension induced by prostacyclin treatment during cardiopulmonary bypass does not increase the risk of cerebral complications

Effects of Iloprost on Oxygenation during One-Lung Ventilation in Patients with Low Diffusing Capacity for Carbon Monoxide: A Randomized Controlled Study

The protective mechanism of hypoxic pulmonary vasoconstriction during one-lung ventilation (OLV) is impaired in patients with a low diffusing capacity for carbon monoxide (DLCO). We hypothesized that iloprost inhalation would improve oxygenation and lung mechanics in patients with low DLCO who underwent pulmonary resection. Forty patients with a DLCO < 75% were enrolled. Patients were allocated into either an iloprost group (ILO group) or a control group (n = 20 each), in which iloprost and saline were inhaled, respectively. The partial pressure of arterial oxygen/fraction of inspired oxygen (PaO2/FiO2) ratio, pulmonary shunt fraction, alveolar dead space, dynamic compliance, and hemodynamic parameters were assessed 20 min after the initiation of OLV and 20 min after drug administration. Repeated variables were analyzed using a linear mixed model between the groups. Data from 39 patients were analyzed. After iloprost inhalation, the ILO group exhibited a significant increase in the PaO2/FiO2 ratio and a decrease in alveolar dead space compared with the control group (p = 0.025 and p = 0.042, respectively). Pulmonary shunt, dynamic compliance, hemodynamic parameters, and short-term prognosis were comparable between the two groups. Selective iloprost administration during OLV reduced alveolar dead space and improved oxygenation while minimally affecting hemodynamics and short-term prognosis.

Effects of Alprostadil Infusion During Extracorporeal Circulation on Blood Rheology and Postoperative Blood Loss

The authors have investigated the effects a low dose of alprostadil (synthetic prostaglandin E1: S-PGI1) infusion during cardiac surgery on blood rheology and postoperative blood loss. S-PGE1 (20 ng/kg/minute) was given to 13 patients undergoing aortocoronary bypass. Another 13 patients who received no S-PGE1 during bypass surgery served as controls. To assess blood rheology, blood samples for red and white cell filterability (RFR and WFR) and for platelet count were collected preoperatively, immediately after the end of extracorporeal circulation (ECC), and twenty-four hours later. Records of blood loss were taken twelve and twenty-four hours postoperatively. RFR, WFR, and platelet counts at twenty-four hours were significantly reduced in the control group as compared with the S-PGE1 group, p = 0.002, p = 0.004, and p = 0.0026, respectively. Concomitantly, the means of the postoperative blood loss at twelve and twenty-four hours were lower in the S-PGE1 group, p= 0.0001 and p=0.0004, respectively. Furthermore, the use of blood transfusion products was significantly less in the S-PGE, group, p < 0.02. These results showed that the use of S-PGE, during ECC preserves blood rheology in association with significant reductions in blood loss and in the need for blood transfusion postoperatively.

Markers of cerebral ischemia after cardiac surgery

The objective of this review is to provide an overview of the use of biochemical markers for the detection of Central Nervous System (CNS) complications after cardiac surgery and extracorporeal circulation (ECC). A computerized literature search in MEDLINE from 1966 onward was the basis for the references. The literature covering the following biochemical markers is reviewed: adenylkinase, creatine phosphokinase isoenzyme BB (CK-BB), lactate, neuron-specific enolase (NSE), S-100 protein, myelin basic protein, lactate dehydrogenase, aspartate aminotransferase, glutathione, vasointestinal neuropeptide, and 7B2-specific neuropeptide. For clinical purposes, it is necessary to have a biochemical marker that can be measured in blood. Lactate, although a primary marker of anaerobic metabolism, and CK-BB values, calculated from the arterio-internal jugular venous difference, appear to correlate with periods of ischemia during ECC. S-100 protein levels have been shown to correlate with duration of ECC, and when combined with NSE values, could be used to identify patients with CNS dysfunction after cardiac surgery. The use of NSE may be limited by its presence in erythrocytes and platelets because the high levels that can result from hemolysis can render it less specific. Although recently introduced, S-100 protein may have the potential to be a valuable marker for CNS dysfunction after ECC.

Blood anesthesia for cardiopulmonary bypass

Cardiopulmonary bypass (CPB) causes bleeding and thrombotic complications, fluid retention and temporary dysfunction of every organ system. This morbidity of CPB is primarily do to activation of blood proteins and cells by contact with nonendothelial cell surfaces of the wound and biomaterials of the extracorporeal perfusion circuit. CPB is not possible without heparin, yet heparin is not an ideal anticoagulant and does not prevent activation of at least five plasma protein systems and five blood cells. Stimulation of these blood elements produces over 25 vasoactive substances that alter vascular tone, capillary permeability, and cardiac myocyte contractility. In addition, CPB produces showers of microemboli that pass filters to obstruct arterioles and precapillaries to produce necrosis of widely dispersed, small groups of cells. Attempts to develop nonthrombogenic synthetic materials have failed; only the endothelial cell is nonthrombogenic and achieves this property by active metabolic processes. Although some biomaterials are less thrombogenic than others, all activate blood elements to initiate clotting and the body's defense reaction. The concept of "blood anesthesia" envisions the use of reversible inhibitors of key blood reactions to temporarily prevent activation of blood elements during CPB. If the initial reactions of blood with nonendothelial surfaces are blocked, production of many vasoactive substances and microemboli by CPB is suppressed. This conserves blood elements that are normally consumed during CPB and makes them available after the inhibitor is reversed. Effective, reversible inhibitors of platelets are entering clinical trials; reversible inhibitors of other key blood relations are being developed and tested at a rapid rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of alprostadil on pulmonary dysfunction after a cardiac operation

To test the effects of alprostadil on pulmonary dysfunction after cardiac operations, we studied 24 male patients undergoing aortocoronary bypass. Twelve were given an intravenous infusion of alprostadil (synthetic prostaglandin E1), 20 ng.kg-1.min-1, in a double-blind manner during operation; the other 12 were controls. Duration of artificial respirator use and frequent blood gas analyses were used to assess postoperative pulmonary function. Use of the artificial respirator postoperatively was significantly lower in the prostaglandin group (mean time. 5.25 +/- 1.81 hours) compared with the controls (mean time, 8.34 +/- 4.35 hours) (p = 0.047). The proportion of patients with hypercapnia and with hypoxia determined every 4 hours for the first 24 hours after extubation was significantly lower in the prostaglandin group compared with the controls (p less than 0.0001). These results indicate that synthetic prostaglandin E1 may play a role in protecting lung tissue during extracorporeal circulation.

Neuropsychological dysfunction after cardiopulmonary bypass: a comparison of two institutions

The authors compared perioperative neuropsychologic dysfunction in patients participating in two studies conducted in institutions using different strategies to manage cardiopulmonary bypass. These differences included hypothermia versus normothermia, presence versus absence of arterial microfilters, and the presence versus absence of glucose-containing solution in the pump prime. Other differences between the two institutions included the type of surgery (intracardiac v extracardiac), the mean duration of cardiopulmonary bypass, and degree of low perfusion pressure during bypass. Despite these major differences, perioperative neuropsychologic dysfunction measured by the two-part Trail-Making psychometric test was similar in the two institutions. Several factors were analyzed for their possible contribution to development of dysfunction, including institution, anesthetic management, age, sex, degree of low perfusion pressure during bypass, and duration of bypass; only age was significant. These results suggest that differences in surgical procedure and management of cardiopulmonary bypass previously thought to contribute to the development of subtle cognitive deficits after cardiac surgery may have been overemphasized.

Brain protection: physiological and pharmacological considerations. Part II: The pharmacology of brain protection

Neuroprotective agents may exert their effect by reducing cerebral oxygen demand (CMRO2), increasing cerebral oxygen delivery, or by altering ongoing pathological processes. Barbiturates provide neuroprotection by reducing the CMRO2 necessary for synaptic transmission while leaving the component necessary for cellular metabolism intact. Isoflurane may exert a neuroprotective effect by a similar mechanism but its efficacy is likely less than that of barbiturates due to adverse effects on cerebral blood flow. Lidocaine reduces CMRO2 by affecting both cellular metabolic processes and synaptic transmission and thus resembles hypothermia in its mechanism of action. Benzodiazepines reduce CMRO2 by reducing synaptic transmission and their use as neuroprotectants produces less haemodynamic compromise than barbiturates. The mechanism of protection by calcium entry blocking agents appears to be due to improved blood flow as opposed to altering abnormal Ca++ fluxes. In contrast, agents such as ketamine and MK-801 may prevent abnormal Ca++ fluxes through their competitive interaction with N-methyl-D-aspartate receptors. Phenytoin prevents K(+)-mediated ischaemic events from progressing. Agents worthy of further investigation include corticosteroids, free radical scavengers, prostaglandin inhibitors and iron chelators.

Thiopental sodium by single bolus dose compared to infusion for cerebral protection during cardiopulmonary bypass

The authors previously demonstrated that thiopental sodium infused throughout cardiopulmonary bypass (CPB) considerably reduced persistent but not transient neuropsychiatric complications after open-chamber cardiac operations. Based on the probability that emboli released at the time of aortic declamping cause most postoperative central nervous system (CNS) dysfunction, this study was designed to test whether administration of a single bolus dose of thiopental before aortic declamping provided cerebral protection equal to that of infusion throughout bypass as well as a decrease in unwanted side effects. One hundred adult patients undergoing open-chamber cardiac operations with CPB received either thiopental sodium by infusion throughout CPB (n = 52) or thiopental sodium 15 mg/kg by bolus before aortic declamping (n = 48). In 90% of the patients, thiopental sodium 15 mg/kg produced electroencephalographic (EEG) burst suppression, with more than 60 seconds between bursts. Postoperative CNS dysfunction occurred in 3 (6%) of the infusion group patients (thiopental sodium 36 +/- 10 mg/kg) and 2 (4%) of the bolus group patients (thiopental sodium 16 +/- 2 mg/kg). CNS dysfunction persisting to the tenth postoperative day occurred in only one patient, who was in the infusion group. Requirements for inotropic support on separation from CPB did not differ between groups, but average time to extubation was 2.7 hours shorter in the bolus group. The authors conclude that thiopental sodium 15 mg/kg given as a single bolus immediately before aortic declamping without the need for EEG monitoring provided the same brain protection as larger doses given by infusion titrated to burst suppression, but it did not reduce the need for inotropic support during separation from CPB.

Placebo-controlled study of Iloprost (ZK 36374) in cardiopulmonary bypass surgery

The effects of infusion of Iloprost (ZK 36374), a prostacyclin analogue, on platelet function, postoperative blood loss and microaggregate deposition on filters and oxygenators were studied in patients undergoing routine coronary operations. In this double-blind randomized study of 50 male patients, 25 received Iloprost and 25 a placebo. Platelet deposition was assessed using Indium-labelled platelets. Comparison of Iloprost and placebo groups showed the mean number of platelets to be significantly higher in the Iloprost group at the end of cardiopulmonary bypass and in early postoperative recovery. Similarly, spontaneous aggregation of platelets was higher in the placebo group. The mean percentages of platelets sequestrated in the extracorporeal circuit were significantly higher in the placebo group. There was no difference in either the amount or pattern of postbypass bleeding between Iloprost and the control patients. Infusion of the tested drug was responsible for significant hypotension, which was correctable with fluid administration alone. Thus, Iloprost diminishes the fall in circulatory platelet count during cardiopulmonary bypass, preserves platelet function, diminishes platelet deposition on filters and oxygenators, but also causes arterial hypotension.

Nitrous oxide and cerebrospinal fluid markers of ischaemia following cardiopulmonary bypass

Twenty patients with good ventricular function undergoing coronary artery bypass surgery were studied to determine whether the pre-bypass use of nitrous oxide resulted in any differences in cerebrospinal fluid markers indicative of cerebral ischaemia. All patients were anaesthetised with diazepam, fentanyl and pancuronium, after which ten patients received 50-60% nitrous oxide in oxygen until commencement of bypass, and the remaining patients 100% oxygen. Because of the known effect of nitrous oxide in expanding gaseous bubbles, any neurological dysfunction of gaseous microembolic origin may be worsened in the presence of nitrous oxide. Patients were lumbar punctured 24 hours after cardiopulmonary bypass and cerebrospinal fluid analysed for the following markers of central nervous system ischaemia: creatine kinase, lactate, total protein, noradrenaline, adrenaline and adenylate kinase. There was a statistically significant difference in cerebrospinal fluid lactate between the two groups. There were no statistically significant differences in the other cerebrospinal fluid markers of ischaemia.

Brain luxury perfusion during cardiopulmonary bypass in humans. A study of the cerebral blood flow response to changes in CO2, O2, and blood pressure

CBF and related parameters were studied in 68 patients before, during, and following cardiopulmonary bypass. CBF was measured using the intraarterial 133Xe injection method. The extracorporeal circuit was nonpulsatile with a bubble oxygenator administering 3-5% CO2 in the main group of hypercapnic patients (n = 59) and no CO2 in a second group of hypocapnic patients. In the hypercapnic patients, marked changes in CBF occurred during bypass. Evidence was found of a brain luxury perfusion that could not be related to the effect of CO2 per se. Mean CBF was 29 ml/100 g/min just before bypass, 49 ml/100 g/min at steady-state hypothermia (27 degrees C), reached a maximum of 73 ml/100 g/min during the rewarming phase (32 degrees C), fell to 56 ml/100 g/min at steady-state normothermic bypass (37 degrees C), and was 48 ml/100 g/min shortly after bypass was stopped. Addition of CO2 evoked systemic vasodilation with low blood pressure and a rebound hyperemia. The hypocapnic group responded more physiologically to the induced changes in hematocrit (Htc) and temperature, CBF being 25, 23, 25, 34, and 35 ml/100 g/min, respectively, during the five corresponding periods. Carbon dioxide was an important regulator of CBF during all phases of cardiac surgery, the responsiveness of CBF being approximately 4% for each 1-mm Hg change of PaCO2. The level of MABP was important for the CO2 response. At low blood pressure states, the CBF responsiveness to changes in PaCO2 was almost abolished. An optimal level of PaCO2 during hypothermic bypass of approximately 25 mm Hg (at actual temperature) is recommended. A normal autoregulatory response of CBF to changes in blood pressure was found during and following bypass. The lower limit of autoregulation was at pressure levels of approximately 50-60 mm Hg. CBF autoregulation was almost abolished at PaCO2 levels of greater than 50 mm Hg. The degree of hemodilution neither affected the CO2 response nor impaired CBF autoregulation, although, as would be expected, it influenced CBF: In 33 women CBF was 55 ml/100 g/min at an Htc of 24%, as compared with 42 ml/100 g/min in 35 men (Htc = 28%). High PaO2 was a vasoconstrictor, the autoregulatory plateau being narrowed. The lower limit of autoregulation was shifted to a higher pressure when PaO2 was low.

Cerebral blood flow and metabolism during cardiopulmonary bypass with special reference to effects of hypotension induced by prostacyclin

Cerebral blood flow and metabolism of oxygen, glucose, and lactate were studied in 43 patients undergoing aortocoronary bypass. Twenty-five patients received prostacyclin infusion, 50 ng per kilogram of body weight per minute, during cardiopulmonary bypass (CPB), and 18 patients served as a control group. Regional cerebral blood flow (CBF) was studied by intraarterially injected xenon 133 and a single scintillation detector. Oxygen tension, carbon dioxide tension, oxygen saturation, glucose, and lactate were measured in arterial and cerebral venous blood. Mean arterial blood pressure decreased during hypothermia and prostacyclin infusion to less than 30 mm Hg. The regional CBF was, on average, 22 (standard deviation [SD] 4) ml/100 gm/min before CPB. It increased in the control group during hypothermia to 34 (SD 12) ml/100 gm/min, but decreased in the prostacyclin group to 15 (SD 5) ml/100 gm/min. It increased during rewarming in the prostacyclin group. After CPB, regional CBF was about 40 ml/100 gm/min in both groups. The cerebral arteriovenous oxygen pressure difference decreased more in the control group than in the prostacyclin group during hypothermia. The cerebral metabolic rate of oxygen decreased in both groups from approximately 2 ml/100 gm/min to about 1 ml/100 gm/min during hypothermia, increased again during rewarming, and after CPB was at the levels measured before bypass in both groups. There was no difference between the groups in regard to glucose and lactate metabolism.

Effects of prostacyclin infusion on renal function during cardiopulmonary bypass

Infusion of prostacyclin inhibits platelet activation during cardiopulmonary bypass (CPB) but also results in systemic arterial hypotension. Therefore, the effects of CPB and prostacyclin on renal function were studied in 36 male patients undergoing aortocoronary bypass. Nineteen patients (Group 1) received prostacyclin, 50 ng per kilogram of body weight per minute, during CPB, and 17 patients (Group 2) served as controls. There was pronounced hypotension in Group 1 only. Urine production during CPB averaged 88 +/- 140 ml and 2,306 +/- 1,112 ml in Groups 1 and 2, respectively. No patient had renal failure. Glomerular filtration rate (GFR), as measured by clearance of chromium 51-labeled ethylenediaminetetraacetic acid, was increased in Group 1 from 86 +/- 14 to 99 +/- 22 ml/1.73 m2/min (p less than 0.05) the day after operation, but remained unchanged in Group 2 (81 +/- 15 to 82 +/- 21 ml/1.73 m2/min). The increased GFR in Group 1 can be regarded as an expected adaptation to the change in body fluids after CPB. Therefore, the unchanged GFR in Group 2 must be regarded as caused by insufficient adaptation or impaired renal function. Proximal tubular function was evaluated by determination of beta 2-microglobulin in urine. In both groups, urinary beta 2-microglobulin and the ratio of urinary beta 2-microglobulin to urinary creatinine were increased the day after operation. The hypotension in Group 1 did not exacerbate the damage to tubular function.