Shahar Bar-Yosef

Continuous cardiac output monitoring with pulse contour analysis: A comparison with lithium indicator dilution cardiac output measurement

Objective:Pulse contour analysis can be used to provide beat-to-beat cardiac output (CO) measurement. The current study sought to evaluate this technique by comparing its results with lithium dilution CO (LiCO) measurements. Design:Prospective, observational study. Setting:Surgical intensive care unit. Patients:Twenty-two patients after cardiac or major noncardiac surgery. Measurements:After initial calibration of the pulse contour CO (PCO) method, CO was measured by PCO and by LiCO methods at 4, 8, 16, and 24 hrs. Recalibration of PCO was performed every 8 hrs. The systemic vascular resistance and dynamic response characteristics of the arterial catheter–transducer system were measured at each time point to determine whether these influenced the agreement between PCO and LiCO methods. Main Results:There was an excellent correlation between methods (r = .94). Bias was small (−0.005 L/min), and clinically acceptable limits of agreement were demonstrated between techniques. Although many catheter-transducer systems had poor dynamic response characteristics, this did not influence the level of agreement between the two techniques. An increase in systemic vascular resistance between two time points did tend to cause overestimation of LiCO by the PCO. Conclusions:PCO measurement compared well with the lithium dilution method and can be considered an accurate technique for measuring beat-to-beat CO with limited risk to the patient.

Prevention of cerebral hyperthermia during cardiac surgery by limiting on-bypass rewarming in combination with post-bypass body surface warming: A feasibility study

Cerebral hyperthermia is common during the rewarming phase of cardiopulmonary bypass (CPB) and is implicated in CPB-associated neurocognitive dysfunction. Limiting rewarming may prevent cerebral hyperthermia but risks postoperative hypothermia. In a prospective, controlled study, we tested whether using a surface-warming device could allow limited rewarming from hypothermic CPB while avoiding prolonged postoperative hypothermia (core body temperature <36°C). Thirteen patients undergoing primary elective coronary artery bypass grafting surgery were randomized to either a surface-rewarming group (using the Arctic Sun® thermoregulatory system;n = 7)or a control standard rewarming group (n = 6). During rewarming from CPB, the control group was warmed to a nasopharyngeal temperature of 37°C, whereas the surface-warming group was warmed to 35°C, and then slowly rewarmed to 36.8°C over the ensuing 4 h. Cerebral temperature was measured using a jugular bulb thermistor. Nasopharyngeal temperatures were lower in the surface-rewarming group at the end of CPB but not 4 h after surgery. Peak jugular bulb temperatures during the rewarming phase were significantly lower in the surface-rewarming group (36.4°C ± 1°C) compared with controls (37.7°C ± 0.5°C; P = 0.024). We conclude that limiting rewarming during CPB, when used in combination with surface warming, can prevent cerebral hypothermia while minimizing the risk of postoperative hypothermia.

Pulse pressure and long-term survival after coronary artery bypass graft surgery.

BACKGROUND: Data from longitudinal studies reveal that widened pulse pressure (PP) is a major predictor of coronary heart disease and mortality, but it is unknown whether PP similarly decreases survival after coronary artery bypass graft (CABG) surgery for coronary heart disease. We therefore assessed long-term survival in patients with increased PP at the time of presentation for CABG surgery. METHODS: In this retrospective observational study of patients undergoing CABG surgery between January 1993 and July 2004, 973 subjects were included for assessment of long-term survival. Baseline arterial blood pressure (BP) measurements were defined as the median of the first 3 measurements recorded by the automated record keeping system before induction of anesthesia. The effect of baseline PP on survival after surgery was evaluated using a Cox proportional hazards regression model and bootstrap resampling with baseline mean arterial BP, systolic BP, diastolic BP, diabetes, Hannan risk index, aprotinin use, and cardiopulmonary bypass time as covariates. RESULTS: There were 220 deaths (22.9%) during the follow-up period (median, 7.3 yr [Q1: 5, Q3: 10 yr]) including 94 deaths from cardiovascular causes. Increased baseline PP was a significant predictor of reduced long-term survival (P < 0.001) along with Hannan risk index (P < 0.001), duration of cardiopulmonary bypass (P < 0.001), and diabetes (P < 0.001). Baseline systolic (P = 0.40), diastolic (P = 0.38), and mean arterial BPs (P = 0.78) were not associated with long-term survival. The hazard ratio for PP (adjusted for other covariates in the model) was 1.11 (1.05–1.18) per 10–mm Hg increase. CONCLUSIONS: An increase in perioperative PP is associated with poor long-term survival after CABG surgery. Together with our previous report linking PP to in-hospital fatal and nonfatal vascular complications, the established models for surgical risk assessment, patient counseling, and treatment should be revised to include PP.

Preoperative low molecular weight heparin reduces heparin responsiveness during cardiac surgery

PurposeCardiac surgery with cardiopulmonary bypass requires systemic anticoagulation, defined by an activated clotting time (ACT) of 400–480 sec. Patients with altered heparin responsiveness require disproportionately higher doses of heparin to achieve this target ACT. A common risk factor for heparin resistance is preoperative heparin therapy. Recently, therapy with low molecular weight heparin (LMWH) has become an acceptable substitute for prolonged heparin therapy. The current study examines the effect of preoperative LMWH therapy on subsequent heparin responsiveness during cardiac surgery.MethodsRecords of patients undergoing cardiac surgery with cardiopulmonary bypass over a period of four months were reviewed. We identified patients who, during the week preceding surgery, had received prolonged (> 24 hr) therapy with eithersc LMWH (LMWH group) or continuousiv unfractionated heparin (Heparin group). A Control group consisted of patients who received neither heparin nor LMWH preoperatively. The heparin sensitivity index (calculated as the first change in ACT from baseline divided by the first intraoperative heparin dose, normalized to body weight), was compared among groups using ANOVA.ResultsOne hundred and thirty-nine patients were included in the analysis. The heparin sensitivity index was 33–45% higher in the Control group (1.6 ± 0.7 sec·IU−1·kg−1;P < 0. 0001) compared to the LMWH (1.2 ± 0.4 sec·IU−1·kg−1) and Heparin (1.1 ± 0.5 sec·IU−1·kg−1) groups. In a multivariable model, the use of preoperative LMWH remained a significant predictor of reduced intraoperative heparin responsiveness (P = 0.002).ConclusionProlonged preoperative LMWH therapy, similar to the known effect of prolonged unfractionated heparin infusion, reduces subsequent intraoperative response to heparin.RésuméObjectifLa chirurgie cardiaque sous circulation extra-corporelle nécessite une anti-coagulation systémique, définie par un temps de coagulation activé (TCA) de 400–480 sec. Les patients présentant une réponse modifiée á l’héparine nécessitent des doses nettement plus importantes d’héparine pour atteindre le TCA cible. Un facteur de risque commun de la résistance á l’héparine est la thérapie préopératoire à l’héparine. L’héparine à bas poids moléculaire (HBPM) est récemment devenue un substitut approprié des thérapies prolongées à l’héparine. Cette étude porte sur l’effet de thérapies préopératoires HBPM sur la réaction à l’héparine durant la chirurgie cardiaque.MéthodeLes dossiers de patients subissant une chirurgie cardiaque sous circulation extra-corporelle sur une période de quatre mois ont été étudiés. Les patients ayant suivi une thérapie prolongée (<24 h) d’HBPMsc (groupe HBPM) ou d’héparine non fractionnée iv en continu (groupe Héparine) la semaine précédant la chirurgie ont été identifiés. Le groupe témoin était composé de patients n’ayant reçu ni héparine non fractionnée ni HBPM avant l’opération. L’indice de sensibilité à l’héparine (calculé comme l’augmentation du TCA depuis la ligne de base divisé par la première dose d’héparine intra-opératoire, normalisé à la masse corporelle), a été comparé entre les groupes à l’aide d’une ANOVA.RésultatsCent-trente-neuf patients ont été analysés. L’indice de sensibilité à l’héparine fut de 33–45 % plus élevé dans le groupe témoin (1,6 ± 0,7 sec·IU−1·kg−1; P > 0,0001) que dans les groupes HBPM (1,2 ± 0,4 sec·IU−1·kg−1) et Héparine (1,1 ± 0,5 sec·IU−1·kg−1). Dans un modèle multivarié, l’utilisation de HBPM préopératoire demeure un indice prédicteur significatif de réponse diminuée à l’héparine intra-opératoire (P=0,002).ConclusionUne thérapie préopératoire prolongée à l’HBPM, comme l’effet connu d’une perfusion prolongée d’héparine non-fractionnée, réduit la réponse intra-opératoire à l’héparine.

The association of anti‐platelet factor 4/heparin antibodies with early and delayed thromboembolism after cardiac surgery

Essentials We evaluated antibody status, thromboembolism and survival after cardiac surgery. Positive antibody tests are common – over 50% are seropositive at 30 days. Seropositivity did not increase thromboembolism or impair survival after cardiac surgery. Results show heparin induced thrombocytopenia antibody screening after surgery is not warranted.

Unusual cause of superior vena cava syndrome diagnosed with transesophageal echocardiography

Purpose: An unusual case of superior vena cava (SVC) syndrome caused by an infected right atrial-SVC junction thrombus may be diagnosed using transesophageal echocardiography.Clinical features: A 59-yr-old male with end-stage renal disease requiring hemodialysis presented with fungemia and later developed facial and bilateral upper extremity edema. Transesophageal echocardiography revealed subtotal occlusion of the SVC at its junction with the right atrium. The mass was surgically removed with cardiopulmonary bypass support. Pathological examination of the mass confirmed the presence of a large fungal colony ofCandida species mixed in the thrombus. The patient’s signs and symptoms of SVC obstruction resolved, and he was discharged from the hospital four weeks later in stable condition.Conclusion: Although usually caused by extrinsic tumour compression, SVC syndrome can result from intravascular caval obstruction. This etiology should also be considered in the differential diagnosis, particularly in patients with intravascular devices. Transesophageal echocardiography is a valuable diagnostic tool in these cases.RésuméObjectif: Un cas inhabituel de syndrome de la veine cave supérieure provoqué par un thrombus infecté à la jonction de l’oreillette droite et de la veine cave supérieure peut être dépisté grâce à l’échocardiographie transoesophagienne.Éléments cliniques: Un homme de 59 ans souffrant d’insuffisance rénale terminale et nécessitant une hémodialyse a manifesté une septicémie à champignons, puis un oedème facial et bilatéral des membres supérieurs. L’échocardiographie transoesophagienne a révélé une occlusion sous-totale de la veine cave supérieure à sa jonction avec l’oreillette droite. Une excision chirurgicale de la masse sous circulation extracorporelle a pu être réalisée. L’examen pathologique de la masse a confirmé la présence d’une importante colonie fongique de l’espèce Candida dans le thrombus. Les signes et symptômes d’obstruction de la veine cave supérieure ont disparu, et le patient a reçu son congé de l’hôpital quatre semaines plus tard, dans un état stable.Conclusion: Bien que généralement causé par une compression tumorale extrinsèque, le syndrome de la veine cave supérieure peut être provoqué par une obstruction intravasculaire de la veine cave. Cette étiologie devrait faire partie du diagnostic différentiel, tout particulièrement chez les patients dotés d’appareils intravasculaires. L’échocardiographie transoesophagienne constitue un outil diagnostic précieux dans de tels cas.

Intraoperative Hemodynamic Monitoring

The combination of V5 with another lead (II, III, V4, or V6) increases the sensitivity of ischemia detection to 90%. In high-risk patients, most intraoperative ST segment changes occur in the absence of major hemodynamic lability, and maintenance of hemodynamic variables (blood pressure and heart rate) to within 20% of baseline values does not appear to reduce intraoperative ischemic events. Electrocardiograph (ECG) monitoring for myocardial ischemia augmented by continuous, computerized ECG monitors should be continued into the early postoperative period for high-risk patients. Invasive blood pressure monitoring is indicated when (1) large or abrupt hemodynamic changes are anticipated intraoperatively, (2) coexisting disease necessitates close hemodynamic management, (3) pharmacologic or mechanical intervention is anticipated or planned, or (4) noninvasive methods are impractical or impossible. Excessive variation of the systolic blood pressure (>15 mm Hg) is a strong predictor of occult hypovolemia. Overall, the risk of an ischemic complication from peripheral arterial catheterization is less than 0.1%. Central venous pressure (CVP) reflects the balance among intravascular volume, venous tone, and right ventricular function. In general, a single isolated CVP value provides little information unless it is very high or very low. Recent development of small, portable ultrasound machines has made it possible to image the great veins of the neck prior to or during placement of central venous catheters. This has been shown in multiple clinical studies as well as in a recent meta-analysis to decrease the incidence of failed catheter placement as well as the complication rate, especially in high-risk patients. Pulmonary artery catheter (PAC)-derived filling pressures are a poor index of right and left ventricular preload as they are influenced by heart rate, valvular disease, myocardial compliance, myocardial ischemia, and positive pressure ventilation. Perioperative goal-directed therapy, that is, the “optimization” of oxygen delivery and cardiac index, has been shown to reduce mortality, complications, and hospital length of stay in high-risk surgical patients. According to current American Society of Anesthesiologists (ASA) recommendations, the use of PAC is considered necessary only in high-risk patients undergoing high-risk surgery, and under the condition that the practice environment is favorable (i.e., knowledgeable and experienced physicians and intensive care unit nurses). Mixed venous oxygen saturation depends on the balance between oxygen delivery and consumption, and might be one of the more telling indices for judging the adequacy of the patient’s hemodynamic status. Thermodilution is the standard method for measuring cardiac output; it is subject, however, to intrinsic variability, effect of intracardiac shunts and right-sided valvular regurgitation, and influence of other factors affecting instantaneous blood temperature. Two newer cardiac output measurement methods that obviate the need for a PAC include the transpulmonary arterial thermodilution and the lithium dilution. Both seem to offer accuracy similar to the traditional thermodilution method. Several methods exist for continuous measurement of cardiac output. The first method employs a modified PAC with a blood-warming filament. It does not produce true real-time continuous measurements, but rather a trend of recent measurements over a couple of minutes. Esophageal Doppler cardiac output (CO) measurement employs a probe inserted into the lower esophagus to measure descending aorta blood flow. It tends to underestimate CO measured by other methods, although accurately tracking changes occurring over time. Pulse contour methods derive continuous beat-to-beat CO from the arterial pressure waveform. In ventilated patients, they also allow measurement of stroke volume variation, an index of the adequacy of cardiac preload. Despite its classification as category II for use in routine coronary artery bypass graft (CABG) surgery, transesophageal echocardiography (TEE) in high-risk patients seems to be associated with better outcome. Transesophageal echocardiography has become invaluable in planning for mitral valve repair and reconstruction with excellent agreement between mechanism and location between TEE and surgical findings. Following valve repair or replacement, TEE is especially useful in immediate evaluation of paravalvular leaks, leafl et motion, and other forms of valvular dysfunction. Although TEE has been reported to be more predictive than ECG in identifying patients who suffer perioperative myocardial infarction, concordance between TEE and ECG-detected ischemia is poor. Direct complications of TEE are the result of mechanical trauma to the upper gastrointestinal tract and oropharynx, and include abrasion, laceration, and perforation.