J. Jalonen

Oxygen Transport to Tissue under Normovolemic Moderate and Extreme Hemodilution during Coronary Bypass Operation

Oxygen transport to tissue was studied in 12 patients undergoing coronary bypass operation under normovolemic moderate and extreme hemodilution. Normovolemic moderate hemodilution (15 ml per kilogram of body weight), carried out immediately after induction of anesthesia, decreased the mean hematocrit from 0.43 to 0.33. Simultaneously, the cardiac index and the left ventricular filling pressure increased slightly but the systemic oxygen transport was reduced by 20%. The subcutaneous tissue oxygen tension (PO2) was approximately 40 mm Hg after induction of anesthesia and underwent a transient increase during moderate hemodilution. During cardiopulmonary bypass and extreme hemodilution, the mean hematocrit declined to 0.16. Concurrently, the mean tissue PO2 fell sharply and reached a minimum of 14 mm Hg at deepest hypothermia. After decannulation and reinfusion of autologous blood, the PO2 rose to 30 mm Hg. In general, total-body oxygen consumption changed along with tissue PO2. Blood lactate concentration underwent a clear increase in the early phase of extracorporeal circulation and remained rather stationary thereafter. No perioperative myocardial infarctions were encountered, and each patient made an uneventful recovery.

Effects of dexmedetomidine on coronary hemodynamics and myocardial oxygen balance

Objective: α2-Adrenergic agonists decrease central sympathetic outflow and maintain normal transmural myocardial blood flow distribution, but intravenous bolus doses of these agents can also induce excessive coronary vasoconstriction and myocardial ischemia. The hypothesis of the present study was that a rapid intravenous bolus of dexmedetomidine, a specific α2-adrenergic agonist, will cause coronary vasoconstriction and accompanying myocardial ischemia in young pigs. Design: Prospective, controlled study on experimental animals. Setting: Animal laboratory of a university cardiorespiratory research center. Participants: Twelve domestic 8-week-old open-chest pigs, anesthetized with high-dose fentanyl. Another six pigs served as controls. Interventions: Sequential intravenous dexmedetomidine boluses of 3, 10, and 30 mg/kg were administered, and responses were measured during peak changes (2 minutes after injection) and during recovery after each dose. Measurements and Main Results: Left anterior descending coronary artery blood flow, calculated regional coronary vascular resistance, myocardial extraction of oxygen and lactate, plasma catecholamine levels, and conventional central hemodynamic parameters were measured. The two higher doses of dexmedetomidine induced 21% and 29% immediate increases in left anterior descending coronary artery blood flow. At the same time mean systemic blood pressure and pulmonary capillary wedge pressure increased, and calculated regional coronary vascular resistance increased. Myocardial extraction of oxygen and lactate remained unchanged. Conclusions: Large intravenous doses of dexmedetomidine caused moderate regional coronary vasoconstriction without metabolic signs of myocardial ischemia in young domestic pigs at the same time as a marked vasoconstrictive response in the systemic circulation.

Use of Activated Clotting Time to Monitor Anticoagulation During Cardiac Surgery

The use of a fixed dosage schedule was compared with the use of activated clotting time (ACT) for monitoring heparin anticoagulation and its neutralization during and after extracorporeal circulation in patients undergoing coronary artery bypass grafting. Use of ACT resulted in a statistically significant decrease in heparin and protamine dosages and statistically significant reductions in postoperative blood loss and blood transfusion needs. Postoperative levels of blood hemoglobin concentration were significantly higher and the activated partial thromboplastin time was significantly shorter with ACT monitoring than with use of a fixed dosage schedule. The results confirmed the superiority of the ACT method for monitoring anticoagulation during cardiac surgery.

Effects of cardiopulmonary bypass on lymphocytes and their subset counts with or without use of autotransfusion devices.

Lymphocytes and their subset counts were determined in 30 cardiac surgery patients during cardiopulmonary bypass (CPB) with or without use of an autotransfusion device. In the autotransfusion group, centrifuged and washed autologous red blood cells (median 400 mL [range 200-770 mL]) and in the control group corresponding amounts of homologous packed red blood cells (median 500 mL [range 250-750 mL]) were transfused after declamping the aorta. The percentages of T lymphocytes (CD3) and T cytotoxic cells (CD8) increased in both groups (CD3 up to 5%, P < 0.05 and CD8 up to 35%, P < 0.01), but the percentage of T helper cells (CD4) did not change. The ratio of CD4/CD8 cells decreased (up to 34%, P < 0.01). The percentage of naive resting T cells (CD45RA) increased slightly (up to 8%, P < 0.05) whereas the percentages of memory T cells (CD45RO), T cells with IL-2 receptor (CD25), and natural killer cells (CD16) remained unaltered. The percentage of HLA-DR positive lymphocytes increased during CPB (up to 18%, P < 0.05), but it was decreased thereafter (up to 16%, P < 0.05). The percentage of monocytes (CD14) decreased first during CPB in both groups (up to 32%, P < 0.01), but it was higher in the autotransfusion device group (decreased 29% from initial value) than in the control group (decreased 65% from initial value) at the end of CPB (P < 0.05). This study shows that extracorporeal circulation has an effect on lymphocytes and their subset counts. The changes were slightly immunosuppressive. By contrast, use of autotransfusion devices had only minor effects.

Myocardial oxygen balance during hemodilution in patients undergoing coronary artery bypass grafting.

The myocardial (arterial-coronary sinus) balance of oxygen and lactate was studied before a cardiopulmonary bypass and during the first 5 min of a normothermic bypass in two patient groups undergoing coronary revascularization for multiple coronary artery disease. The hemodilution (HD) group was hemodiluted before the bypass with dextran 70 (15 ml/kg; resulting mean hematocrit 32%) and further at the beginning of the bypass due to nonhemic priming of the oxygenator (mean hematocrit 15%). The control (C) group was not diluted before the bypass, and four units of red blood cells were included in the oxygenator priming (mean hematocrit 27% after the beginning of the bypass). The preoperative dilution produced a decline in the coronary sinus blood oxygen tension and oxygen saturation, but no change in the arterial-coronary sinus lactate balance. After the first 5 min of the bypass, the heart produced lactate in both the HD group and the C group, but the lactate production was more pronounced in the HD group. At the same time, the coronary sinus blood oxygen saturation was lower in the HD group than in the C group. Hypotension frequently accompanied the beginning of the bypass in both groups. It is concluded that the hemodilution to a hematocrit level of 32% in patients undergoing coronary revascularization for multiple stable coronary artery disease produces compensatory changes in myocardial oxygen extraction, but no changes of a generalized ischemia can be demonstrated. The hemodilution to a hematocrit level of 15% produces myocardial ischemia in patients with a normothermic unloaded heart, adding to the effect of hypotension at the beginning of the bypass.

Prostanoids and hemodynamics in man before and during cardiopulmonary bypass

The plasma concentration of 6-keto-PGF1 alpha, the stable degradation product of prostacyclin, was similar in the radial and pulmonary arteries and in the coronary sinus before and after the induction of the anesthesia in patients undergoing coronary artery bypass surgery. After the beginning of the mechanical ventilation and anesthesia the pulmonary vascular resistance decreased although no changes were detected in the plasma levels of 6-keto-PGF1 alpha or TXB2. During the prebypass period after the sternotomy and cannulation of the large vessels the plasma level of 6-keto-PGF1 alpha was increased similarly in the radial and pulmonary arteries and even more in the coronary sinus. During the cardiopulmonary bypass the concentration of 6-keto-PGF1 alpha remained at the increased level as compared to the values before the anesthesia. This indicates that pulmonary circulation is perhaps not the main source of prostacyclin in man. The plasma level of TXB2 was increased during the prebypass period significantly only in the coronary sinus, but during the bypass also in the radial artery. The concentration ratio of 6-keto-PGF1 alpha/TXB2 was increased significantly during the prebypass period in the radial and pulmonary arteries. At the same time the pulmonary vascular resistance was, however, returned to the preanesthesia level and was thus not decreased. The vascular resistance in the systemic circulation was increased during the prebypass period. The plasma level of 6-keto-PGF1 alpha or TXB2 in the radial and pulmonary arteries did not correlate significantly with the total vascular resistance in the systemic and pulmonary circulation, respectively. The vascular resistance in the coronary circulation did not correlate significantly with TXB2 level in the radial artery or coronary sinus. There was, however, a slight positive correlation between the blood flow and the concentration of TXB2 in the coronary sinus (r = 0.76, P less than 0.01). Coronary sinus flow did, however, not correlate with the plasma level of 6-keto-PGF1 alpha in the radial artery or coronary sinus. These results indicate that the detected plasma concentrations of prostacyclin and thromboxane A2 have no significant effects on the total vascular resistance in vivo.

Reduced Lactate Washout from the Myocardium after Combining St. Thomas I Type Cardioplegia with Topical Cooling of the Heart: Myocardial Oxygenation and Performance after Cardioplegia in Coronary Artery Bypass Grafting Patients

The myocardial oxygen extraction was diminished with a resulting coronary sinus blood oxygen saturation of 48 +/- 5 (SEM) %, as compared to the pre-bypass control level of 30 +/- 1%, two minutes after the ischaemic period in St. Thomas I type cardioplegia (CPL) with topical cooling of the heart during a coronary bypass operation. The myocardial oxygen extraction returned to prebypass levels after ten minutes of reperfusion following ischaemia and remained so after the bypass. The postischaemic myocardial lactate washout of the CPL-patients was compared to that of another group of coronary surgical patients, in whom intermittent ischaemia and topical cooling (IITC) were used for myocardial protection. It was found that the lactate washout two minutes after the single ischaemic period in the CPL-patients was far less than the lactate washout two minutes after each ischaemic period in the IITC-group. The greatest arterial-coronary sinus lactate difference in the IITC-group was -1.7 +/- 0.2 mmol/l and in the CPL-group -0.7 +/- 0.2 mmol/l. Cardiac performance (assessed by the CI-PCWP relationship) which was moderately depressed by the anaesthesia and surgery before bypass, returned gradually to the control level within 20 hours after operation. The present study shows that no apparent postischaemic abnormality in myocardial oxygen utilization develops when single dose cardioplegia, together with topical cooling of the heart, is used for myocardial protection, and that the accumulation of myocardial lactate during ischaemia is less during cardioplegia with topical cooling of the heart than during intermittent ischaemic with topical cooling for coronary artery bypass grafting operations.

Myocardial Reperfusion after Coronary Bypass Surgery: Suture of Only Distal or All Anastomoses with the Aorta Cross-clamped?

Sixty patients undergoing elective coronary artery bypass grafting were randomly allocated into two groups, each of 30 patients and similar as regards age, sex, number of coronary artery bypasses and left ventricular ejection fraction. In group A the proximal anastomoses of vein grafts were sutured after aortic declamping during partial occlusion of the aorta, and in group B these anastomoses were done during aortic cross-clamping. The aortic cross-clamp time was significantly longer in group B than in group A (72 vs 57 min, p < 0.0001). Myocardial cooling and rewarming and the number of sustained or possible perioperative myocardial infarctions were equal in both groups. Central haemodynamics showed no intergroup difference, before or after induction of anaesthesia or at the end of surgery. Conduction disturbances were more common in group A than in group B (12 vs 3, p = 0.0246), and transient external pacing was more often required in group A (9 vs 2, p = 0.0534). Myocardial reperfusion via native coronary arteries and bypass grafts gives better protection against conduction disturbances than does reperfusion via only native arteries, despite longer aortic cross-clamping time.

Myocardial Oxygenation and Recovery after Topical Cooling of the Ischaemic Heart and after Hypothermic Coronary Perfusion: A Clinical Study of Aortic Valve Replacement Patients

Myocardial oxygenation and recovery during aortic valve replacement were studied at different stages of operations, in which either topical cooling of the ischaemic heart (TCI) or hypothermic coronary perfusion (HCP) was used for myocardial protection. During HCP the utilization of available oxygen by the myocardium decreased by 65%. During rewarming significant lactate washout and production by the myocardium was found in the TCI-group with no significant signs of defective oxygen utilization. Already 10 min after initiation of reperfusion a greater oxygen extraction by the heart was seen in the TCI-group than in the HCP-group. This tendency persisted until the end of operation. There was some lactate production in the HCP-group during rewarming. The CI relative to PCWP showed a marked increase over prebypass values after bypass during lonotropic load in both patient groups, but the increase was more marked in the HCP-group, probably indicating a greater reserve of mechanical performance capacity. The in...

Is there any Benefit from Adding Single-Dose Cardioplegia to Topical Cooling of the Ischaemic Myocardium in Aortic Valve Replacement Operations?

The myocardial oxygen extraction, lactate metabolism and cardiac performance were studied after topical cold myocardial ischaemia (TCI) with or without associated cold potassium cardioplegia (CPL) in aortic valve replacement (AVR) patients. There were no such differences between the CPL + TCI-group and the TCI-group in the postischaemic coronary sinus blood oxygen tension, coronary sinus blood haemoglobin oxygen saturation, arterial-coronary sinus blood oxygen content difference, arterial-coronary sinus blood lactate difference, CI-PCWP or LVSWI-PCWP relationship that could be attributed to the cardioplegia. The coronary sinus blood oxygen values did not indicate any gradually developing postischaemic disturbances in the myocardial oxygen utilization. There was, however, a marked myocardial lactate washout and production in both groups five and ten minutes after initiation of reperfusion after ischaemia. There was a marked increase in the CI after bypass in the CPL + TCI-group, and the cardiodepression at late post-operative stages was minimal in both groups according to the CI-PCWP and LVSWI-PCWP relationship. These results suggest that the topical cooling technique used provides a degree of protection of the myocardial energy metabolism and function that cannot be further improved by adding single-dose cardioplegia by means of the direct coronary cannulation method used here.