Oxygen delivery and hemoglobin concentration in cardiac surgery: when do we have enough?

For many years it has been assumed that patients undergoing cardiac surgery utilizing cardiopulmonary bypass accumulate an "oxygen debt" that requires a higher postoperative hemoglobin concentration for its reversal. Much of this evidence has now been discredited due to mathematical error with recent research suggesting critical levels of oxygen delivery are lower than previously thought. This article aims to explore the relationship between observed and critical oxygen delivery with an estimation of the minimal hemoglobin required. This was a single-center observational study. Nineteen adult elective cardiac surgery patients were recruited to participate with four subsequently excluded. Observed measurements of oxygen delivery were recorded and compared with calculated "critical" values adjusted for temperature. The hemoglobin value that represented critical oxygen delivery was compared with the observed value to identify any "hemoglobin reserve." At no perioperative time point did observed oxygen delivery or critical hemoglobin concentration significantly approach its corresponding critical value. Current transfusion practice in noncritically ill cardiac surgery patients may be considered excessive if systemic oxygen requirement is the sole parameter considered.

A comparison of activated coagulation time-based techniques for anticoagulation during cardiac surgery with cardiopulmonary bypass.

OBJECTIVE: The inadequacy of heparinization during cardiopulmonary bypass (CPB) can lead to hemostatic activation with increases in postoperative blood loss and blood product requirements after cardiac surgery. Because activated coagulation time (ACT) measurements may not be accurate during CPB, the use of a heparin management system (HMS) has been advocated. This study compared the efficacy of a modified ACT-based system versus an HMS (Hepcon; Medtronic Inc, Minneapolis, MN) for CPB anticoagulation. DESIGN: Randomized controlled trial. SETTING: Regional cardiac surgery center. PARTICIPANTS: Adult elective cardiac surgical patients. INTERVENTIONS: Patients allocated to the HMS group (HC) received individualized heparin doses as indicated by the Hepcon system. Patients in the modified ACT group (C) received a standard weight-based heparin bolus with further doses as dictated by the ACT (Max-ACT, Helena Labs, Sunderland, UK). In addition, group C received supplemental heparin, independent of the ACT, as dictated by the volume of crystalloid added to the extracorporeal circuit. Outcome measures examined were hemostatic activation, postoperative chest tube loss, and blood product requirements. RESULTS: This study showed no significant difference in efficacy between the modified ACT and HMS heparinization strategies. Although the HC group received significantly greater amounts of heparin, this did not reduce hemostatic activation, postoperative blood loss, or transfusion requirements. CONCLUSION: ACT-based heparinization was found to be as efficacious as the Hepcon HMS system.

Troponin-I release after cardiac surgery with different surgical techniques and post-operative neurological outcomes.

Cerebral hypoperfusion during cardiopulmonary bypass surgery has been thought to be a factor in the aetiology of brain damage with evidence of post-operative neurological deficits. Cardiac-specific biomarkers such as troponin-I, troponin-T and CK-MB have been used extensively to predict myocardial injury and ischaemia. This prospective study investigated the level of troponin-I release in both off-pump and CPB-technique CABG surgery, as well as postulated a relationship of troponin release and post-operative neurological outcome. A total of 44 adult patients undergoing coronary artery bypass graft (CABG) were enrolled into either an off-pump or on-pump groups, with 22 patients participating in each. Group A (on-pump) underwent myocardial revascularisation with CPB and cardioplegic arrest, while Group B (off pump) underwent beating heart surgery. The measurement of troponin-I is a 1-step enzyme immunoassay method, with specificity and sensitivity set at 0.4 ug/mL. Neurological assessment was done using the NIH Stroke Scale, and neuropsychologic assessment was assessed on cognitive function using modified Weschler Memory Scale, for which scores were standardized to achieve a composite measure of concentration. A set of statistical analysis was done to correlate troponin-I release with different surgical techniques of CPB and OPCAB. Although each independent technique showed a marked rise of troponin-I from baseline to 6 hours post-operatively, the difference in troponin release was not significant between the 2 groups at specified time intervals (p=0.124). There was however a significant correlation of troponin-I release with the number of grafts used in the surgery, irrespective of the type of grafts or surgical technique. None of the patients in either group showed any neurological or cognitive deficits presenting at day 3 and day 7 post-operatively. The findings of this study demonstrate that there is no significant short-term cognitive or neurological dysfunctions post-operatively, as indicated by troponin-I release in assessing the severity of myocardial injury.

Predictors of mortality in early surgical intervention for active native valve endocarditis and significance of antimicrobial therapy: a single-center experience.

BACKGROUND AND AIM OF THE STUDY: Cardiac surgery for active infective endocarditis remains a challenging and high-risk procedure. The outcome from early surgical intervention for active native valve endocarditis (ANVE) was studied, the aim being to identify significant predictors of mortality and the relationship between duration of preoperative antibiotics and outcome. METHODS: Between January 1996 and February 2002, 61 patients with ANVE underwent surgery within four weeks of diagnosis. Preoperatively, 29 patients received antibiotics for <2 weeks (group A), and 32 received antibiotics for 2-4 weeks (group B). The median follow up period was 37.4 months (range: 21-55 months). Data were collected retrospectively and analyzed. To determine factors related to mortality, Kaplan-Meier survival analysis was employed, utilizing log-rank statistics to identify evidence of significant differences between the groups. The relationship between the duration of preoperative antibiotics and morbidity was determined using chi-square and Fisher's Exact tests, as appropriate. RESULTS: Overall operative mortality was 14.8% (group A, 13.8%; group B, 15.6%). Rates of early and late prosthetic valve endocarditis were 1.8% and 1.9% (only in group B) respectively. The overall survival rate for the follow up period was 81.9%. Predictors of mortality were extensive infection (p = 0.01), poor left ventricular function (p <0.0001), progressive cardiac failure as an indication for surgery (p <0.0001), postoperative sepsis (p <0.0001), renal failure after surgery (p = 0.0002) and use of a bioprosthetic valve (p = 0.045). There were no significant inter-group differences for extensive infection (p = 1.00), postoperative sepsis (p = 1.00), reoperation (p = 1.00) and mortality (p = 1.00). CONCLUSION: In patients with ANVE, early aggressive surgical intervention before the onset of cardiac failure and spread of infection is warranted. The present data suggest that, in these patient groups, the duration of preoperative antibiotics had no significant influence on postoperative morbidity and mortality.

What factors should we consider in deciding when to transfuse patients undergoing elective cardiac surgery?

Blood transfusion remains one of the commonest interventions carried out upon individuals undergoing cardiac surgery. Despite this, the scientific rationale on which to base this decision is limited. Currently, hemoglobin concentration is often used as the sole guide as to when a transfusion may be required. A fall in hemoglobin concentration is often assumed to be associated with a similar drop in red cell volume. A review was undertaken of all the relevant peer-reviewed literature to determine what factors we should consider when deciding to transfuse elective cardiac surgery patients. The large fluid load associated with cardiac surgery, primarily from the cardiopulmonary bypass circuit, may have a significant dilutional effect. In such a scenario, several interlinked protective mechanisms may ensure that tissue oxygenation is maintained, including a reduction in blood viscosity, a decrease in systemic afterload, and an increase in cardiac output. Furthermore, oxygen requirements during the initial perioperative phase are reduced because of the effect of general anesthesia and hypothermia during cardiopulmonary bypass. When deciding to transfuse, consideration should be given to red cell volume, circulatory status, and oxygen requirement. It is possible that such an all-encompassing approach would reduce the incidence of unnecessary, and potentially counterproductive, red cell transfusion in cardiac surgery.

Perioperative red cell, plasma, and blood volume change in patients undergoing cardiac surgery.

BACKGROUND: Current blood prescription in cardiac surgery is based largely on hemoglobin (Hb) concentration. Hb may not provide a reliable guide to the patient's red cell (RBC) volume (RCV) during cardiac surgery as a consequence of the high fluid loads infused. This study provides estimates of the perioperative changes in RCV, plasma volume (PV), and blood volume (BV) with a view to developing a more accurate way of assessing a patient's need for transfusion. STUDY DESIGN AND METHODS: Thirty adult elective cardiac surgery patients were recruited to the study. The preoperative RCV was calculated by use of a standard nomogram. Losses and gains in RCV at several time points were added or subtracted from the baseline value. Estimates of PV and BV were derived from patient hematocrit level and RCV for each time point. RESULTS: The greatest perioperative loss of RCV occurred during cardiopulmonary bypass (CPB); however, half of this loss was returned to the patient at the end of CPB. A net gain of RCV occurred during the period of intensive care management. PV and BV showed two distinct peaks, immediately after CPB and at 16 hours after intensive therapy unit return. CONCLUSIONS: PV and BV expansion are significant factors that may lead to a Hb value that is misleadingly low in that it overestimates the decrease in RCV. This effect could lead to unnecessary transfusion if the RBC transfusion threshold is based only on Hb concentration.

The effect of gain in total body water on haemoglobin concentration and body weight following cardiac surgery.

BACKGROUND: Haemodilution contributes to a low post-operative haemoglobin concentration in cardiac surgery patients. An assessment of the degree of haemodilution could contribute to the avoidance of red cell transfusion when such an act is based simply on a haemoglobin "transfusion trigger". We have recorded post-operative change in total body water along with body weight to assess the impact of haemodilution on haemoglobin concentration. METHODS: Total body water, measured by bio-electrical impedance analysis, haemoglobin and body weight were measured pre-operatively and on the 1st, 3rd, 5th and 10th post-operative days. The percentage peri-operative change in all three variables was used to examine the paired associations. RESULTS: Total body water and body weight underwent a fall from day 1, with both variables significantly associated up until day 10. Haemoglobin rose steadily from day 1 to 10. This rise was associated with falling total body water and body weight until day 5, but not from day 5 to 10. CONCLUSION: Following cardiac surgery, an individual's fluid state should be considered in determining a patient's need for red cell transfusion. Monitoring body weight provides a simple estimate. Such an approach may reduce the incidence of unnecessary, and potentially counterproductive, transfusion in cardiac surgery patients.

Cor-triatriatum sinister presenting in the adult as mitral stenosis: an analysis of factors which may be relevant in late presentation.

BACKGROUND: Cor-triatriatum sinister is a rare congenital heart defect resulting from the division of the left atrium by a fibro-muscular membrane. It is usual for patients to present in infancy and early childhood, although some cases remain undetected until adult life. As a consequence of trans-membrane flow obstruction, the clinical features often mimic mitral stenosis. At present, the reasons for late presentation are poorly understood. METHODS: A complete review of all cases of cor-triatriatum sinister published in the English literature from 1966 to date as mitral stenosis was performed. Statistical analysis was carried out to determine associations between measurements reflecting the communicating membrane fenestration area, the presence of several clinical variables and patient age at initial presentation. RESULTS: Both pulmonary capillary wedge pressure and mean pressure gradient were significantly higher in younger adults. In addition, the incidence of atrial fibrillation and mitral regurgitation was found to rise with advancing age. CONCLUSIONS: Cor-triatriatum sinister remains an uncommon form of congenital heart disease although it is being diagnosed with increasing frequency in adults due to improvements in diagnostic imaging. This diagnosis should be considered in all patients presenting with signs or symptoms of mitral stenosis.