- Email: [email protected]
Systemic vascular resistance: an unreliable index of left ventricular afterload
264
oxygen free radicals peroxidizing the lipids of the cell membrane are quantitated by the thiobarbituric acid reaction. Reperfusion after a period of cardiac asystole resulted in a central venous-toqeft atrial gradient for neutrophils and an increase in thiobarbituric acid reactivity. There was a correlation between lipid peroxidation and neutrophil sequestration after cardiopulmonary bypass. Thus, it appears that the tissue oxidants are released by neutrophils sequestered in the lung. Associated with these findings was an increase in lung protein flux (measured by transvascular flux of labeled transferrin), which may result from changes in pulmonary vascular permeability induced by the oxidants.
Tuman KJ, Ivankovich AD: Bronchospasm during cardiopuimonary bypass. Etiology and management. Chest 90:635-637, 1986 Some of the findings noted in the previous abstract may be applicable to the case report of severe bronchospasm noted at the resumption of ventilation during the later stages of cardiopulmonary bypass. Three case reports of patients without a history of bronchospasm who developed severe wheezing during cardiopulmonary bypass arc presented. None of the patients demonstrated cutaneous signs of allergic reactions. All responded to aggressive therapy with steroids, bronchodilators, anticholinergics, atropine, or halothane. Possible etiologies included cold urticaria, complementmediated reactions, or other unidentified factors.
Huddleston CB, Stoney WS, Alford WC, et al: Internal mammary artery grafts: Technical factors influencing patency. Ann Thorac Surg 42:543-549, 1986 Life table analysis was used to evaluate the patcncy of the internal mammary artery as a conduit for coronary bypass grafting in a long-term study of 814 patients. Although three different methods, mobilization of the internal mammary artery as a wide pedicle with 1 to 2 cm of cndothoracic fascia, skeletenization of the artery, or mobilization of the artery with surrounding fat and veins, were used to harvest the internal mammary artery, no differences in patency were attributable to method of harvest. The highest patency rates occurred when the internal mammary artery was anastomosed to the left anterior descending (LAD) coronary artery, with similar patency rates at 1 year, but markedly divergent rates at 5 years (89.2% patency of LAD v 84.2% patency of the diagonal). Left internal mammary grafts also had higher patency rates than saphenous vein grafts (51% v 20% at 10 years), although right internal mammary grafts had similar patency rates to saphcnous veins. As demonstrated by previous studies, higher initial flow rates through the mammary artery were associated with improved patency. Reasons suggested for the lower patency rates of the right internal mammary artery were its anastomosis to the diagonal coronary artery, and anastomosis of a more distal segment of the mammary artery because of the distance necessary to reach the diagonal.
Lang RM, Borow KM, Neumann A, et al: Systemic vascular resistance: An unreliable index
LITERATURE REVIEW
of left ventricular afterload. Circulation 74:11141123, 1986 Systemic vascular resistance is frequently used clinically to estimate ventricular afterload. True ventricular afterload is the force opposing ventricular fiber shortening during left ventricular ejection. Afterload is essentially left ventricular wall stress, which includes peak systolic wall stress and the integral of left ventricular systolic wall stress over time. Geometric factors such as increasing wall thickness and decreasing ventricular size determine instantaneous wall stress. Left ventricular afterload peaks during the first one third of ventricular ejection and decreases throughout the rest of systole, even while ventricular pressure is increasing. An experimental canine preparation was used to evaluate the use of end-systolic wall stress to reflect the effects of left ventricular wall thickness, dimension, and chamber pressure as well as peripheral loading conditions rather than systemic vascular resistance to determine changes in afterload during pharmacological interventions. End-systolic pressure was measured with a catheter-tipped transducer, and end-systolic and diastolic dimensions and wall thicknesses were measured echocardiographically. Minimal changes in afterload associated with augmented contractility (norepinephrine administration) were inaccurately predicted by systemic vascular resistance. Similarly, when afterload alone was decreased with nitroprusside, systemic vascular resistance underestimated the decrease by 22%. It also underestimated an increased afterload produced by methoxamine by 54%. The combination of increased contractility and decreased afterload produced by dobutamine was also underestimated. Thus, measurements of left ventricular afterload must take into account both myocardial and peripheral factors. Systemic vascular resistance reflects only peripheral arteriolar tone and neglects the ventricular component of afterload.
Demas K, Wyner J, Mihm FG, et ai: Anaesthesia for heart transplantation. Br J Anaesth 58:1357-1364, 1986 Although cardiac transplantation is now being widely performed, the anaesthetic management of patients undergoing transplantation has not been extensively reviewed. The authors of this paper described a large series (261 patients) of cardiac transplantations at Stanford University. Although the majority were anesthetized with high-dose narcotic techniques, narcotic anesthesia was associated with a high incidence of dysrhythmias requiring either pharmacological or electrical conversion. In the 17% of patients receiving volatile anesthetics, hypotension to less than 90/50 mmHg (mean of 60) for longer than five minutes was the major problem. However, no morbidity was associated with this type of anesthesia. The authors also detail the general management of patients undergoing transplantation. Fentanyl or sufentanil with diazepam is the recommended anesthetic regimen. In addition, the need to use sterile airway equipment, bacterial filters on both sides of the anesthetic circuit, and aseptic placement of intraarterial and central venous catheters is emphasized. Pulmonary artery catheters are not placed since
oxygen free radicals peroxidizing the lipids of the cell membrane are quantitated by the thiobarbituric acid reaction. Reperfusion after a period of cardiac asystole resulted in a central venous-toqeft atrial gradient for neutrophils and an increase in thiobarbituric acid reactivity. There was a correlation between lipid peroxidation and neutrophil sequestration after cardiopulmonary bypass. Thus, it appears that the tissue oxidants are released by neutrophils sequestered in the lung. Associated with these findings was an increase in lung protein flux (measured by transvascular flux of labeled transferrin), which may result from changes in pulmonary vascular permeability induced by the oxidants.
Tuman KJ, Ivankovich AD: Bronchospasm during cardiopuimonary bypass. Etiology and management. Chest 90:635-637, 1986 Some of the findings noted in the previous abstract may be applicable to the case report of severe bronchospasm noted at the resumption of ventilation during the later stages of cardiopulmonary bypass. Three case reports of patients without a history of bronchospasm who developed severe wheezing during cardiopulmonary bypass arc presented. None of the patients demonstrated cutaneous signs of allergic reactions. All responded to aggressive therapy with steroids, bronchodilators, anticholinergics, atropine, or halothane. Possible etiologies included cold urticaria, complementmediated reactions, or other unidentified factors.
Huddleston CB, Stoney WS, Alford WC, et al: Internal mammary artery grafts: Technical factors influencing patency. Ann Thorac Surg 42:543-549, 1986 Life table analysis was used to evaluate the patcncy of the internal mammary artery as a conduit for coronary bypass grafting in a long-term study of 814 patients. Although three different methods, mobilization of the internal mammary artery as a wide pedicle with 1 to 2 cm of cndothoracic fascia, skeletenization of the artery, or mobilization of the artery with surrounding fat and veins, were used to harvest the internal mammary artery, no differences in patency were attributable to method of harvest. The highest patency rates occurred when the internal mammary artery was anastomosed to the left anterior descending (LAD) coronary artery, with similar patency rates at 1 year, but markedly divergent rates at 5 years (89.2% patency of LAD v 84.2% patency of the diagonal). Left internal mammary grafts also had higher patency rates than saphenous vein grafts (51% v 20% at 10 years), although right internal mammary grafts had similar patency rates to saphcnous veins. As demonstrated by previous studies, higher initial flow rates through the mammary artery were associated with improved patency. Reasons suggested for the lower patency rates of the right internal mammary artery were its anastomosis to the diagonal coronary artery, and anastomosis of a more distal segment of the mammary artery because of the distance necessary to reach the diagonal.
Lang RM, Borow KM, Neumann A, et al: Systemic vascular resistance: An unreliable index
LITERATURE REVIEW
of left ventricular afterload. Circulation 74:11141123, 1986 Systemic vascular resistance is frequently used clinically to estimate ventricular afterload. True ventricular afterload is the force opposing ventricular fiber shortening during left ventricular ejection. Afterload is essentially left ventricular wall stress, which includes peak systolic wall stress and the integral of left ventricular systolic wall stress over time. Geometric factors such as increasing wall thickness and decreasing ventricular size determine instantaneous wall stress. Left ventricular afterload peaks during the first one third of ventricular ejection and decreases throughout the rest of systole, even while ventricular pressure is increasing. An experimental canine preparation was used to evaluate the use of end-systolic wall stress to reflect the effects of left ventricular wall thickness, dimension, and chamber pressure as well as peripheral loading conditions rather than systemic vascular resistance to determine changes in afterload during pharmacological interventions. End-systolic pressure was measured with a catheter-tipped transducer, and end-systolic and diastolic dimensions and wall thicknesses were measured echocardiographically. Minimal changes in afterload associated with augmented contractility (norepinephrine administration) were inaccurately predicted by systemic vascular resistance. Similarly, when afterload alone was decreased with nitroprusside, systemic vascular resistance underestimated the decrease by 22%. It also underestimated an increased afterload produced by methoxamine by 54%. The combination of increased contractility and decreased afterload produced by dobutamine was also underestimated. Thus, measurements of left ventricular afterload must take into account both myocardial and peripheral factors. Systemic vascular resistance reflects only peripheral arteriolar tone and neglects the ventricular component of afterload.
Demas K, Wyner J, Mihm FG, et ai: Anaesthesia for heart transplantation. Br J Anaesth 58:1357-1364, 1986 Although cardiac transplantation is now being widely performed, the anaesthetic management of patients undergoing transplantation has not been extensively reviewed. The authors of this paper described a large series (261 patients) of cardiac transplantations at Stanford University. Although the majority were anesthetized with high-dose narcotic techniques, narcotic anesthesia was associated with a high incidence of dysrhythmias requiring either pharmacological or electrical conversion. In the 17% of patients receiving volatile anesthetics, hypotension to less than 90/50 mmHg (mean of 60) for longer than five minutes was the major problem. However, no morbidity was associated with this type of anesthesia. The authors also detail the general management of patients undergoing transplantation. Fentanyl or sufentanil with diazepam is the recommended anesthetic regimen. In addition, the need to use sterile airway equipment, bacterial filters on both sides of the anesthetic circuit, and aseptic placement of intraarterial and central venous catheters is emphasized. Pulmonary artery catheters are not placed since