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.

Preoperative angiotensin-converting enzyme inhibition can cause severe post CPB vasodilation--current UK opinion.

Preoperative use of angiotensin-converting enzyme inhibitors in cardiac surgery patients is thought to cause extreme vasodilatation in post cardiopulmonary bypass period. Opinions are divided as to whether it is beneficial or not to stop it prior to operation. A national survey in the UK was carried out on this issue. Questionnaires were sent to 167 currently practicing UK cardiac surgeons, out of which 105 (62%) replied back. Their responses were analyzed. Among the surgeons who replied to the questionnaires, the majority (63%) were of the opinion that the use of angiotensin-converting enzyme inhibitors leads to vasodilatation resulting in increased usage of fluids, inotropes and vasoconstrictors. However, there was no agreement on the issue of stopping it prior to surgery. Forty one (39%) felt it was beneficial to stop the angiotensin-converting enzyme inhibitors prior to surgery whereas 40 (38%) of them thought it was harmful to stop it. Twenty one (20%) were of the opinion that it made no difference. 39% of respondents practiced stopping the drug prior to planned operation. This national survey revealed differences in management of patients on angiotensin-converting enzyme inhibitors undergoing cardiac surgery. Recommendations from available literature are equally varied, highlighting the need for multicenter randomized trials to address this clinical problem.

A 15-cm aneurysm of the right coronary artery presenting as a pericardial cyst.

We report an unusual case of a giant right coronary artery aneurysm, measuring 15 cm in diameter, in a 76-year old woman. The aneurysm was initially identified when the patient was investigated for signs of congestive cardiac failure with a computed tomography scan of her thorax; at this stage, the lesion was misdiagnosed as a large pericardial cyst. The aneurysm was successfully excised at surgery and her heavily diseased right coronary artery was secured with a saphenous vein graft.

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.