GEOPHYSICS: Enhanced: A Strained Earth, Past and Present.

Plate tectonics leads to deformation within converging or transforming plates, but the rates at which this happens are difficult to evaluate. In this Perspective, Ramsay highlights a new technique reported by Müller et al. for overcoming this problem in past and present mountain-building regions, which have particularly complex deformation patterns.

Cardiac management in the ICU.

Coronary artery disease (CAD) is common in the surgical population, with up to 50% of postoperative deaths due to cardiac events. Most of these events are ischemic, with some being exacerbations of underlying congestive heart failure (CHF). Recent data indicate that acute perioperative beta-adrenergic blockade can reduce ischemia and ischemic events. Postoperative monitoring should focus on myocardial ischemia, with preparation for rapid treatment using IV therapy. A few studies suggest that elderly patients with known CAD undergoing major procedures might benefit from perioperative treatment guided by information from a pulmonary artery catheter. Postoperative CHF, which is likely to present early after surgery, may need aggressive management with diuretics, vasodilators, and inotropic drugs. Mechanical ventilation should be considered. When the patient develops severe or refractory dysrhythmias, serum magnesium levels should be supplemented and consideration given to IV use of amiodarone. Postoperative hypertension is common and can precipitate ischemia, CHF, and arrhythmias as well as cause bleeding. Newer IV drugs are arterial specific and can lower BP in a smooth and predictable manner. All acute cardiac disorders can be precipitated or exacerbated by inadequate pain control, hypoxemia, and fluid or electrolyte disorders.

Protamine reversal of heparin affects platelet aggregation and activated clotting time after cardiopulmonary bypass.

UNLABELLED: Bleeding after cardiopulmonary bypass (CPB) is related to multiple factors. Excess protamine weakens clot structure and decreases platelet function; therefore, an increased activated clotting time (ACT) after protamine reversal of heparin may be misinterpreted as residual heparin anticoagulation. We evaluated the effects of protamine, recombinant platelet factor 4 (rPF4), and hexadimethrine on ACT in blood obtained after CPB. In addition, we examined the effect of protamine on in vitro platelet aggregation. Incremental doses of protamine, rPF4, and hexadimethrine were added to heparinized blood from CPB, and ACTs were performed. Incremental concentrations of protamine were added to heparinized platelet-rich plasma, and aggregometry was induced by adenosine diphosphate (ADP) and collagen. The mean heparin concentration at the end of CPB was 3.3 U/mL. Protamine to heparin ratios >1.3:1 produced a significant prolongation of the ACT that was not seen with rPF4 and was observed only with 5:1 hexadimethrine to heparin ratios. ADP-induced platelet aggregation was reduced with protamine administration > or =1.3:1. Excessive protamine reversal of heparin prolongs ACT and alters ADP-induced platelet aggregation in a dose-dependent manner in vitro. Additional protamine administered to treat a prolonged ACT may further increase clotting time, reduce platelet aggregation, and potentially contribute to excess bleeding after CPB. IMPLICATIONS: We found that excess protamine prolonged the activated clotting time and altered platelet function after cardiopulmonary bypass, whereas heparin antagonists, such as recombinant platelet factor 4 and hexadimethrine, exhibited a wider therapeutic range without adversely affecting the activated clotting time. Approaches to avoid excess protamine or use of alternative heparin antagonists after cardiopulmonary bypass may be beneficial.

Renal dysfunction after myocardial revascularization: risk factors, adverse outcomes, and hospital resource utilization. The Multicenter Study of Perioperative Ischemia Research Group.

BACKGROUND: Acute changes in renal function after elective coronary bypass surgery are incompletely characterized and represent a challenging clinical problem. OBJECTIVE: To determine the incidence and characteristics of postoperative renal dysfunction and failure, perioperative predictors of dysfunction, and the effect of renal dysfunction and failure on in-hospital resource utilization and patient disposition after discharge. DESIGN: Prospective, observational, multicenter study. SETTING: 24 university hospitals. PATIENTS: 2222 patients having myocardial revascularization with or without concurrent valvular surgery. MEASUREMENTS: Prospective histories, physical examinations, and electrocardiographic and laboratory studies. The main outcome measure was renal dysfunction (defined as a postoperative serum creatinine level > or = 177 mumol/L with a preoperative-to-postoperative increase > or = 62 mumol/L). RESULTS: 171 patients (7.7%) had postoperative renal dysfunction; 30 of these (1.4% overall) had oliguric renal failure that required dialysis. In-hospital mortality, length of stay in the intensive care unit, and hospitalization were significantly increased in patients who had renal failure and those who had renal dysfunction compared with those who had neither (mortality: 63%, 19%, and 0.9%; intensive care unit stay: 14.9 days, 6.5 days, and 3.1 days; hospitalization: 28.8 days, 18.2 days, and 10.6 days, respectively). Patients with renal dysfunction were three times as likely to be discharged to an extended-care facility. Multivariable analysis identified five independent preoperative predictors of renal dysfunction: age 70 to 79 years (relative risk [RR], 1.6 [95% CI, 1.1 to 2.3]) or age 80 to 95 years (RR, 3.5 [CI, 1.9 to 6.3]); congestive heart failure (RR, 1.8 [CI, 1.3 to 2.6]); previous myocardial revascularization (RR, 1.8 [CI, 1.2 to 2.7]); type 1 diabetes mellitus (RR, 1.8 [CI, 1.1 to 3.0]) or preoperative serum glucose levels exceeding 16.6 mmol/L (RR, 3.7 [CI, 1.7 to 7.8]); and preoperative serum creatinine levels of 124 to 177 mumol/L (RR, 2.3 [CI, 1.6 to 3.4]). Independent perioperative factors that exacerbated risk were cardiopulmonary bypass lasting 3 or mor hours and three measures of ventricular dysfunction. CONCLUSIONS: Many patients having elective myocardial revascularization develop postoperative renal dysfunction and failure, which are associated with prolonged intensive care unit and hospital stays, significant increases in mortality, and greater need for specialized long-term care. Resources should be redirected to mitigate renal injury in high-risk patients.

Electrocardiographic and hemodynamic changes and their association with myocardial infarction during coronary artery bypass surgery. A multicenter study. Multicenter Study of Perioperative Ischemia (McSPI) Research Group.

BACKGROUND: Electrocardiographic (ECG) changes during coronary artery bypass graft surgery have not been described in detail in a large multicenter population. The authors describe these ECG changes and evaluate them, along with demographic and clinical characteristics and intraoperative hemodynamic alterations, as predictors of myocardial infarction (MI) as defined by two sets of criteria. METHODS: Data from 566 patients at 20 clinical sites, collected as part of a clinical trial to evaluate the efficacy of acadesine for reducing MI, were analyzed at core laboratories. Perioperative ECG changes were identified using continuous three-lead Holter ECG. Systolic blood pressure, diastolic blood pressure, and heart rate were recorded each minute during operation. The occurrence of MI by Q wave or myocardial fraction of creatine kinase (CK-MB) or autopsy criteria, and by (Q wave and CK-MB) or autopsy criteria was determined. RESULTS: During perioperative Holter monitoring, episodes of ST segment deviation, major cardiac conduction changes > or = 30 min, or use of ventricular pacing > or = 30 min occurred in 58% patients, primarily in the first 8 h after release of aortic occlusion. Of the 25% patients who met the Q wave or CK-MB or autopsy criteria for MI, 19% had increased CK-MB as well as ECG changes. (Q wave and CK-MB) or autopsy criteria for MI were met by 4% of patients. The CK-MB concentration generally peaked by 16 h after release of aortic occlusion. In patients with (n = 187) and without a perioperative episode of ST segment deviation, the incidence of MI was 36% and 19%, respectively (P < 0.01), by Q wave or CK-MB or autopsy criteria, and 6% and 3%, respectively (P = 0.055), by (Q wave and CK-MB) or autopsy criteria. Multiple logistic regression analysis showed that intraoperative ST segment deviation, intraventricular conduction defect, left bundle branch block, duration of hypotension (systolic blood pressure < 90 mmHg) after cardiopulmonary bypass, and duration of cardiopulmonary bypass are independent predictors of Q wave or CK-MB or autopsy MI. The independent predictors of (Q wave and CK-MB) or autopsy MI are intraoperative ST segment deviation and duration of aortic occlusion. CONCLUSIONS: Major ECG changes occurred in 58% of patients during coronary artery bypass graft surgery, primarily within 8 h after release of aortic occlusion. Multicenter data collection revealed a substantial variation in the incidence of MI and an overall incidence of up to 25%, with most MI occurring within 16 h after release of aortic occlusion. Intraoperative monitoring of ECG and hemodynamics has incremental value for predicting MI.

Advances in anesthesia for cardiac surgery: an overview for the 1990s.

Anesthetic care for patients undergoing cardiac surgery has changed dramatically in the past 10 years. Examples of such change include same-day admissions, "fast-track" protocols, selective use of pulmonary artery catheters, transesophageal echocardiography, and the introduction of new drugs such as phosphodiesterase inhibitors and antifibrinolytic agents. Under pressure from our peers and those funding health care, we are making major efforts to reduce costs and the length of hospitalization while maintaining high quality of care.

Cardiovascular responses during sedation after coronary revascularization. Incidence of myocardial ischemia and hemodynamic episodes with propofol versus midazolam. Institutions of the McSPI Research Group.

BACKGROUND: Propofol sedation offers advantages for titration and rapid emergence in the critically ill patient, but concern for adverse hemodynamic effects potentially limits its use in these patients. The current study compares the cardiovascular effects of sedation with propofol versus midazolam during the first 12 h after coronary revascularization. METHODS: Three hundred fifty-one patients undergoing coronary revascularization were anesthetized using a standardized sufentanil/midazolam regimen, and assigned randomly to 12 h of sedation with either propofol or midazolam while tracheally intubated. The incidence and characteristics of hemodynamic episodes, defined as heart rate less than 60 or greater than 100 beats/min or systolic blood pressure greater than 140 or less than 90 mmHg, were determined using data electronically recorded at 1-min intervals. The presence of myocardial ischemia was determined using continuous three-channel Holter electrocardiography (ECG) and of myocardial infarctions (MI) using 12-lead ECG (Q wave MI, Minnesota Code) or creatine kinase isoenzymes (CK-MB) analysis (non-Q wave MI, peak CK-MB > 70 ng/ml, or CK-MB > 70 IU/I). RESULTS: Ninety-three percent of patients in both treatment groups had at least one hemodynamic episode during the period of postoperative sedation. Propofol sedation resulted in a 17% lower incidence of tachycardia (58% vs. 70%, propofol vs. midazolam; P = 0.04), a 28% lower incidence of hypertension (39% vs. 54%; P = 0.02), and a greater incidence of hypotension (68% vs. 51%; P = 0.01). Despite these hemodynamic effects, the incidence of myocardial ischemia did not differ between treatment groups (12% propofol vs. 13% midazolam; P = 0.66), nor did its severity, as measured by ischemic minutes per hour monitored (8.7 +/- 5.8 vs. 6.2 +/- 4.6 min/h, propofol vs. midazolam; P = 0.19) or ischemic area under the curve (6.8 +/- 4.0 vs. 5.3 +/- 4.2; P = 0.37). The incidence of cardiac death (one per group), Q wave MI (propofol, n = 7; midazolam, n = 3; P = 0.27), or non Q wave MI (propofol, n = 16; midazolam, n = 18; P = 0.81) did not differ between treatment groups. CONCLUSIONS: Hemodynamic episodes occur frequently in the first 12 h after coronary revascularization. Compared with a standard sedation regimen (midazolam), propofol sedation appears to modulate postoperative hemodynamic responses by reducing the incidence and severity of tachycardia and hypertension and increasing the incidence of hypotension. Both sedation regimens appear similarly safe with respect to myocardial ischemia. These findings indicate that propofol infusion provides effective sedation without deleterious hemodynamic effects in patients recovering from cardiac surgery.

Pure opioid versus opioid-volatile anesthesia for coronary artery bypass graft surgery: a prospective, randomized, double-blind study.

This study was designed to assess, in a prospective, randomized, blinded fashion, the hemodynamic effects of different anesthetics used in the prebypass period during coronary artery bypass grafting (CABG) and the effect on incidence of ischemia. Seventy-five patients were randomly assigned to receive sufentanil increments, isoflurane, or enflurane after a standard premedication and anesthetic induction with sufentanil 5 micrograms/kg. Myocardial ischemia was monitored intraoperatively by the anesthesiologist with electrocardiogram (ECG) leads V5(CB5) and II, and by a Holter monitor of the same leads from which recordings were analyzed postoperatively by a cardiologist. A continuous recording of the blood pressure was analyzed to determine the duration of hypertensive responses. Arterial blood pressure control was best in the patients supplemented with anesthetic vapors; patients receiving beta-adrenergic blockers or those receiving isoflurane were less likely to require treatment for tachycardia. All episodes of myocardial ischemia occurred within 5 min of induction-intubation and were diagnosed more frequently by the anesthesiologist than on the Holter monitor (29% vs 9%), with no difference between groups. There were five perioperative myocardial infarctions with no difference between groups. After anesthetic induction with sufentanil 5 micrograms/kg, isoflurane or enflurane given during CABG provides better hemodynamic control than increments of sufentanil and is associated with a similar incidence of prebypass ischemia and perioperative infarction.

Amrinone before termination of cardiopulmonary bypass: haemodynamic variables and oxygen utilization in the postbypass period.

One hundred patients were randomly allocated to receive saline or amrinone, 0.75 mg.kg-1, ten minutes before separation from cardiopulmonary bypass (CPB) after elective coronary artery bypass grafting, in order to determine the effects of this agent on haemodynamic variables and O2 utilization. Anaesthesia and CPB were managed in a standard fashion. Before induction of anaesthesia, at pericardiotomy, then at 1, 10, 20 and 30 min after CPB, haemodynamic profiles, haematocrit, and O2 saturation of arterial and mixed venous blood were measured. Incremental doses of ephedrine or phenylephrine, or an infusion of norepinephrine with phentolamine were administered when required. The groups were demographically similar and surgical variables were also similar. Haemodynamic measurements were similar between groups at all times; however, a higher dose of phenylephrine was given immediately before weaning from CPB in the amrinone group, and more patients in this group received phenylephrine in the first 30 min after CPB. Mixed venous saturation (SvO2) was higher in the amrinone patients at all times after CPB, leading to lower calculated oxygen consumption (VO2) (P less than 0.05). Insufficient dosage may explain the lack of haemodynamic effect, while possible reasons for the higher SvO2 and lower VO2 are either reduced whole body VO2 or peripheral shunting.

Methods of reducing blood loss and non-blood substitutes.

A variety of techniques can aid the anaesthetist in reducing requirements for perioperative blood products. These include careful preoperative assessment of the patient, and employing techniques during surgery which reduce the blood pressure and help preserve the normal haemostatic mechanism. If the level to which haematocrit will be permitted to decrease is decided, then physiological crystalloid and/or colloid solutions may be used to maintain circulating volume. Where large volumes of fluids are required cardiac filling pressures should be monitored because of the complex nature of the fluid shifts which occur. There is no evidence that any one fluid (physiological crystalloids, colloids) is better than any other in terms of the incidence of perioperative morbidity.

Dose-related effects of isoflurane associated with low plasma concentrations of verapamil on global and regional function in normal and compromised canine myocardium.

Global and regional myocardial functions were studied in seven open-chest dogs with constant low plasma concentrations of verapamil as increasing concentrations of isoflurane (0.75, 1, 1.5 MAC) were administered in the presence of normal myocardial perfusion and after application of critical constriction of the left anterior descending coronary artery. In the presence of verapamil, increases in isoflurane concentrations caused dose-dependent myocardial depression both before and after critical coronary constriction. The systemic and coronary vasodilatation associated with high concentrations of isoflurane did not occur in the presence of verapamil. The association of verapamil with isoflurane caused regional myocardial dysfunction that worsened at high isoflurane concentrations. This regional dysfunction could not be antagonized in two dogs. The effects of isoflurane on regional function were not modified by application of a critical coronary constriction.

Verapamil and nitrous oxide exert only minor effects on the normal myocardium in the presence of fentanyl.

While the association of inhalational anaesthetics and verapamil has been shown to cause myocardial dysfunction, the interactions between fentanyl, verapamil and nitrous oxide on regional function in normal hearts have not been investigated. Seven mongrel dogs were instrumented to measure aortic and left-ventricular pressure, aortic blood flow and apical and basal regional left-ventricular function (sonomicrometry). Haemodynamic values were recorded during anaesthesia with 1% halothane, fentanyl 100 micrograms kg-1 (followed by 1.5 micrograms kg-1 min-1) and then after the addition of verapamil 250 micrograms kg-1 over 30 min (followed by 60 micrograms kg-1 min-1). At each stage 67% nitrous oxide was added and recordings obtained before and during its administration. The addition of verapamil during fentanyl anaesthesia caused a moderate depression of global haemodynamics. Only little dysfunction of the apical region (9.5 +/- 2.4% post-systolic shortening) was noted. The addition of nitrous oxide caused a small amount of additional depression without significant regional dysfunction.

Weaning from ventilation after cardiopulmonary bypass: evaluation of a non-invasive technique.

Weaning of patients from IPPV after cardiopulmonary bypass (CPB) is usually monitored by frequent arterial blood gas analysis. Non-invasive monitoring has the advantage of providing continuous and instantaneous information and could reduce the frequency of arterial blood gas sampling. Twenty patients were studied to determine the reliability of capnometry and pulse oximetry in this situation. The effects of hypothermia and moderate haemodynamic instability were examined. A further 40 patients were then weaned using non-invasive monitoring. Correlation between PaCO2 and PETCO2 was 0.64-0.79 for the mass spectrometer and 0.67-0.81 for the infra-red analyser. No clinical problems arose. The detection rate for mild hypercarbia was 78.6 per cent and 50 per cent for hypoxia. Possible reasons for this are discussed. Once CO2 and O2 gradients are established, pulse oximetry and capnometry provide sufficiently reliable monitoring to enable weaning from IPPV, with the advantage of continuous display, and allow a reduction in the use of arterial blood gas analyses.