Italo Milocco

Thoracic Epidural Anesthesia During Coronary Artery Bypass Surgery: Effects on Cardiac Sympathetic Activity, Myocardial Blood Flow and Metabolism, and Central Hemodynamics

The effects of high thoracic epidural anesthesia (TEA) on cardiac sympathetic nerve activity, myocardial blood flow and metabolism, and central hemodynamics were studied in 20 patients undergoing coronary artery bypass grafting (CABG). In 10 of the patients, TEA (T1-5 block) was used as an adjunct to a standardized fentanyl-nitrous oxide anesthesia. Hemodynamic measurements and blood sampling were performed after induction of anesthesia but prior to skin incision and after sternotomy. Assessment of total and cardiac sympathetic activity was performed by means of the norepinephrine kinetic approach. Prior to surgery, mean arterial pressure (MAP), great cardiac vein flow (GCVF), and regional myocardial oxygen consumption (Reg-MVO2) were lower in the TEA group compared to the control group. During sternotomy there was a pronounced increase in cardiac norepinephrine spillover, MAP, systemic vascular resistance index (SVRI), pulmonary capillary wedge pressure (PCWP), GCVF, and Reg-MVO2 in the control group. These changes were clearly attenuated in the TEA group. None of the patients in the TEA group had metabolic (lactate) or electrocardiographic signs of myocardial ischemia. Three patients in the control group had indices of myocardial ischemia prior to and/or during surgery. We conclude that TEA attenuates the surgically mediated sympathetic stress response to sternotomy, thereby preventing the increase in myocardial oxygen demand in the pre-bypass period without jeopardizing myocardial perfusion.

The Effects of Nitrous Oxide on Left Ventricular Systolic and Diastolic Performance Before and After Cardiopulmonary Bypass: Evaluation by Computer-assisted Two-dimensional and Doppler Echocardiography in Patients Undergoing Coronary Artery Surgery

We investigated the effects of nitrous oxide (N2 O) on central hemodynamics and left ventricular systolic and diastolic function in 25 patients undergoing coronary artery bypass surgery.All patients were receiving beta-blockers and had good left ventricular function. Global and regional systolic left ventricular performance and diastolic function were determined by computer-assisted analysis of transesophageal echocardiographic (TEE) images, and mitral Doppler flow profiles, respectively. The patients were anesthetized with fentanyl and ventilated with oxygen in air. Hemodynamic and TEE measurements were obtained before and after the introduction of N2 O in oxygen (60%/40%), before and after cardiopulmonary bypass (CPB). N2 O reduced mean arterial pressure, heart rate, stroke volume, and cardiac output both before and after CPB. Left ventricular global area ejection fraction (GAEF) was not changed by the introduction of N2 O, either before or after CPB. N2 O induced a significant change in regional wall motion after, but not before CPB, as assessed by the relationship between segmental area ejection fraction (SAEF) and GAEF. Analysis of the mitral flow profile indicated an increase in early diastolic relaxation in the pre-CPB period after introduction of N2 O, that was absent in the post-CPB period. We conclude that N2 O induces regional wall motion abnormalities and possibly diastolic dysfunction post-CPB. (Anesth Analg 1995;81:243-8)

Insulin and amino acid infusion after cardiac operations: effects on systemic and renal perfusion.

OBJECTIVE The purpose of this study was to answer two questions: (1) Does a mixed amino acid infusion enhance systemic and renal perfusion in the early postoperative period after heart operations? (2) Does the addition of insulin (glucose-insulin-potassium solution) provide additional effects to those of an amino acid infusion? METHODS Thirty-three male patients undergoing coronary artery bypass grafting (mean age 65.9 +/- 1.2 years) were included in a prospective, controlled, randomized study. Eleven patients (AA group) received infusion of mixed amino acids (11.4 gm), 11 patients (AA + GIK group) received infusion of mixed amino acids (11.4 gm) and insulin solution (225 IU insulin, glucose with glucose clamp technique, and potassium), and 11 patients served as control subjects. RESULTS Amino acid infusion alone had no effect on systemic vascular resistance or cardiac index but increased renal blood flow 51% +/- 11% (from 114 +/- 13 to 172 +/- 24 ml.min-1.m-2 in one kidney, p < 0.05 vs the control group). Insulin solution in addition to amino acid infusion reduced systemic vascular resistance 24% +/- 3% (from 1280 +/- 85 to 960 +/- 57 dyn.sec.cm-5, p < 0.05 vs the control and AA groups) and increased cardiac index 13% +/- 3% (from 2.3 +/- 0.2 to 2.6 +/- 0.2 L.min-1.m-2, p < 0.05 vs the control and AA groups). Insulin had no significant additive effect on renal blood flow. CONCLUSIONS Our data imply that (1) infusion of mixed amino acids enhances renal blood flow after cardiac operations but has no effect on systemic perfusion and (2) the addition of insulin solution improves systemic perfusion. The combined treatment may potentially reduce the risk of renal hypoperfusion injury in the postoperative period after coronary artery bypass grafting.

Glucose and lactate balances in heart and leg after coronary surgery: Influence of insulin infusion

Glucose and lactate balances in leg (representing mainly skeletal muscle) and heart were studied 1 hour after aortocoronary bypass surgery and insulin treatment. Seventeen men were randomized to receive 25 U fast-acting insulin as a bolus injection, followed by continuous infusion of 1 U/kg b.w. for 1 hour, or to serve as controls. In the leg a small glucose uptake was found while the lactate balance was negative. During the study period the lactate release increased further in the control group. In the myocardium no significant extraction of glucose or lactate could be demonstrated. Insulin treatment resulted in a fivefold increment of leg glucose uptake and in significant myocardial glucose uptake. Myocardial lactate balance was also improved by insulin treatment, with fractional extraction increased from 6 to 21%. It is concluded that myocardial carbohydrate metabolism is restricted in the early period after cardiac surgery, and that this seems to result from insulin resistance induced by the surgical trauma.

Effects of Adenosine Infusion on Systolic and Diastolic Left Ventricular Function After Coronary Artery Bypass Surgery: Evaluation by Computer-Assisted Quantitative 2-D and Doppler Echocardiography

The effects of adenosine on central hemodynamics, ST-segment changes, and left ventricular (LV) systolic and diastolic function, determined by transesophageal 2-D and Doppler echocardiography, were investigated in 20 patients shortly after coronary surgery. After control measurements, adenosine was infused at incremental infusion rates (30, 60, and 120 micro gram centered dot kg-1 centered dot min (-1)). Adenosine caused dose-dependent increases in heart rate (68.0 +/- 11.2-74.0 +/- 15.7 bpm), cardiac output (3.23 +/- 0.76-4.17 +/- 0.67 L/min), and stroke volume (48.8 +/- 12.5-56.7 mL), decreases in arterial pressure (84.8 +/- 16.6-63.3 +/- 15.2 mm Hg), and systemic and pulmonary vascular resistances (1994 +/- 510-1106 +/- 309 and 209 +/- 54-116 +/- 58 dyne centered dot s centered dot cm-5, respectively), but no changes in cardiac filling pressures. The mean ST segment was slightly but significantly depressed by adenosine (from 0.003 to 0.019 mV). Analysis of LV wall motion showed that adenosine caused no changes in the global area ejection fraction (GAEF), the segmental area ejection fraction (SAEF), or in the SAEF/GAEF ratio, indicating that no regional wall motion abnormalities appeared. Maximum early and late diastolic flow rates (Emax, Amax), determined by mitral Doppler analysis, increased (from 30.1 +/- 14.8 to 40.1 +/- 24.1 and from 37.8 +/- 15.7 to 46.4 +/- 31.3 cm/s, respectively), as did the deceleration slope of the early diastolic filling (from -151 +/- 67 to -210 +/- 107 cm/s-2), whereas no changes were found in the ratio between Emax and Amax, the deceleration time of early diastolic filling, or the velocity time integrals of early or late diastolic filling. These changes in the Doppler flow profile during adenosine infusion can be attributed to the increased heart rate and stroke volume. We conclude that adenosine may cause ischemia in some patients after coronary artery bypass surgery without causing obvious changes in regional LV wall motion or diastolic function. (Anesth Analg 1995;80:47-53)

Vasodilation with adenosine or sodium nitroprusside after coronary artery bypass surgery : a comparative study on myocardial blood flow and metabolism

The effects of adenosine and sodium nitroprusside (SNP) on central hemodynamics and myocardial blood flow and metabolism were investigated postoperatively after elective coronary artery bypass (CABG) surgery in ten sedated and mechanically ventilated patients in the intensive care unit. During three consecutive 15-min periods, SNP (0.8 +/- 0.1 micrograms.kg-1 x min-1), adenosine (88.9 +/- 13.3 micrograms.kg-1 x min-1), and then again SNP (0.7 +/- 0.1 micrograms.kg-1 x min-1) were infused to control postoperative hypertension at a mean arterial pressure of approximately 80 mm Hg. Systemic and pulmonary hemodynamics and global (coronary sinus flow, CSF) as well as regional (great cardiac vein flow, GCVF) myocardial blood flow and metabolic variables were measured. During adenosine infusion, in comparison to SNP, heart rate was unchanged, stroke volume index and cardiac index increased (24% and 32%, respectively), and the systemic vascular resistance index decreased (-26%). Mean pulmonary arterial pressure (24%) as well as pulmonary capillary wedge pressure (27%) and central venous pressure (18%) were higher with adenosine compared to SNP. Adenosine also increased CSF and GCVF (108% and 103%, respectively) without altering the CSF/GCVF flow ratio compared to SNP. Furthermore, adenosine increased the coronary oxygen content (51%) and decreased the arterio-great cardiac vein oxygen content difference (-48%) without changing regional myocardial oxygen consumption, indicating a more pronounced hyperkinetic myocardial circulation compared to SNP. In addition, adenosine infusion decreased arterial PO2 (-11%) and increased the intrapulmonary shunt fraction (57%). The PR interval time of the electrocardiogram was prolonged (12%) and the ST segment was more depressed during adenosine infusion compared to SNP.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of adenosine on renal function and central hemodynamics after coronary artery bypass surgery.

In the early postoperative period after coronary artery bypass surgery, arterial hypertension commonly occurs which requires intravenous vasodilator therapy. Purine adenosine is a potent vasodilator and when exogenously administered it decreases systemic arterial blood pressure effectively. We evaluated the effects of adenosine on central hemodynamics and renal function when used to control postoperative hypertension after coronary artery bypass grafting (CABG). Two separate series of experiments were performed postoperatively in the Intensive Care Unit (ICU). In the first study (n = 10), postoperative hypertension was controlled in the rewarming phase, with sodium nitroprusside (SNP, 1.7 +/- 0.4 micrograms.kg-1 x min-1) or adenosine (147.2 +/- 38.9 micrograms.kg-1 x min-1) to keep mean arterial systolic pressure at approximately 80 mm Hg. In the second study on a separate group of patients (n = 9), low doses of adenosine (0, 30, 60, 90, and 0 micrograms.kg-1 x min-1) were infused when the patients were normotensive and rewarmed. Central hemodynamics, urine flow (UF), renal blood flow (RBF), glomerular filtration rate (GFR), and ECG were evaluated during periods of 30 min for each drug in the first study and during each dose of adenosine in the second study. RBF and GFR were determined using standard urinary clearance methods for 51Cr-ethylenediaminetetraacetic acid and p-aminohippuric acid. In the first study, adenosine infusion, compared to SNP, decreased (A - V)O2, increased central filling pressures and heart rate, and caused a more pronounced ST segment depression. During adenosine administration RBF (-44%), GFR (-52%), and UF (-76%) decreased, while renal vascular resistance and filtration fraction (FF) were unaltered compared to data obtained during SNP infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Control of intraoperative hypertension with isoflurane in patients with coronary artery disease: effects on regional myocardial blood flow and metabolism

&NA; The effect of isoflurane on regional myocardial metabolism and blood flow, when used as an adjunct to fentanyl‐nitrous oxide anesthesia, to control intraoperative hypertension was investigated. Twenty‐two patients with two‐ or three‐vessel coronary artery disease with an ejection fraction >0.5 and on beta‐blockers up to the morning of surgery were studied during elective coronary artery by‐pass grafting. Systemic and pulmonary hemodynamics, and regional (great cardiac vein, GCVF) myocardial blood flow and myocardial metabolic parameters were measured. In 10 patients, both GCVF and global (coronary sinus, CSF) myocardial blood flows were recorded. Measurements were made 1) after induction of anesthesia but prior to skin incision, 2) during sternotomy, and 3) during isoflurane administration after its use to reduce arterial pressure to the presternotomy level. The increase in systemic arterial pressure during sternotomy was due to an increase in systemic vascular resistance accompanied by increases in heart rate, pulmonary capillary wedge pressure, (PCWP) regional myocardial oxygen consumption and extraction, GCVF and total coronary vascular resistance. Isoflurane reduced systemic arterial pressure but not PCWP, to presternotomy levels within 6.9 ± 0.7 minutes at an end‐tidal concentration of 1.5 ± 0.2%. Isoflurane induced a pronounced systemic and coronary vasodilatation and increases in cardiac index, heart rate and regional myocardial oxygen extraction while the GCVF/CSF ratio remained unchanged. While mean regional—MLE% values were not effected by sternotomy, in two patients myocardial lactate production was seen during sternotomy but not during isoflurane. In another two patients, isoflurane induced lactate production. The two latter patients differed from the group as a whole mainly because of their higher heart rates during isoflurane. We conclude that isoflurane may induce myocardial ischemia even in the abscence of hypotension. This in turn may be caused by an isoflurane‐induced reflex tachycardia and not necessarily redistribution of coronary flow. On the other hand, isoflurane may also have beneficial effects on stress‐induced myocardial ischemia.

Effects of surgical stress and volatile anesthetics on left ventricular global and regional function in patients with coronary artery disease : evaluation by computer-assisted two-dimensional quantitative transesophageal echocardiography

We investigated the effects of halothane, enflurane, and isoflurane on central hemodynamics and left ventricular global and regional function when used to control intraoperative hypertension in 39 patients with coronary artery disease. Left ventricular short-axis, midpapillary images were obtained by transesophageal echocardiography. Using a centerline algorithm, we analyzed left ventricular images for global area ejection fraction (GAEF) and segmental area ejection fraction (SAEF). The SAEF/GAEF ratio was calculated for each of eight segments. Measurements were performed after induction of anesthesia but before skin incision; 1 min after sternotomy; and during administration of the inhaled anesthetic. The increase in arterial blood pressure during sternotomy was due to an increase in vascular resistance accompanied by increases in heart rate and filling pressures while GAEF decreased. No changes in the SAEF/GAEF ratio appeared during sternotomy. The inhaled anesthetics restored arterial blood pressure by a similar decrease in vascular resistance. Isoflurane caused an increase in cardiac index that was not seen with halothane or enflurane (halothane vs isoflurane, P < 0.05). The GAEF was decreased by halothane but unaffected by isoflurane and enflurane (halothane vs enflurane; P < 0.05). Isoflurane induced a decrease in the SAEF/GAEF ratios of two segments corresponding to the inferolateral wall of the left ventricle that was, in one of these segments, significantly more pronounced compared with both halothane and enflurane. Halothane or enflurane did not cause any change in regional wall motion. We conclude that isoflurane is more likely to cause regional wall motion changes than halothane or enflurane in patients with coronary artery disease.

Insulin Sensitivity and Glucose Uptake in the Course of Surgical Treatment for Valvular Aortic Stenosis

The dose-response relationship between plasma insulin and systemic glucose uptake was studied before, one hour after and 6 months after valvular surgery in 11 patients with valvular aortic stenosis. The immediate effect of valvular surgery was a dramatic rightward shift of the dose-response curve and a decrease in glucose uptake at peak insulin activity. From a comparison between the preoperative and the 6-month postoperative dose-response curves it is concluded that the patients had adapted metabolically to the preoperative haemodynamic situation with increased insulin sensitivity.