Seminars in Cardiothoracic and Vascular Anesthesia

Despite efforts to reduce blood transfusion rates in cardiac surgery over the past 40 years, cardiac surgery still consumes 10% to 20% of the blood transfused in the United States. This large demand has not only placed a significant pressure on the national blood supply, resulting in frequent shortages, but also has lead to many technical and pharmacological advances in blood conservation strategies in recent years. Recently, studies have shown that an organized approach to blood conservation in cardiac surgery is effective in significantly reducing the perioperative use of allogeneic blood and blood products. However, blood conservation techniques are multiple, varied, and in many situations costly and thus cannot be uniformly applied to all patients. Early preoperative planning and a coordinated perioperative plan allow the appropriate use of blood conservation modalities to ensure that their benefits span the entire perioperative period. This article describes some of the modalities currently used in patients undergoing cardiac surgery.

Cardiopulmonary bypass has unpredictably deleterious effects on platelet function. Patients with cardiovascular disease have treatments aimed at reducing platelet aggregation and are at risk of excessive bleeding during surgery. Transfusion of blood products, particularly platelets, probably causes increased morbidity and mortality. Conversely, patients with excessive platelet aggregation are at risk of thrombotic complications—undesirable outcomes in the context of myocardial revascularization and prevention of stroke. Platelet function is difficult to monitor. Laboratory tests take time, and the results are not immediately available. Point-of-care (POC) testing of platelet function should facilitate the clinical management of bleeding patients by rationalizing platelet transfusion and avoiding unnecessary transfusion. Furthermore, POC platelet function could alert the clinician to risks of excessive platelet activation and measure the efficacy of antiplatelet therapy. This article outlines some of the POC platelet function monitors available as well as their potential applications.

There are several perfusion techniques that can contribute to blood conservation. Minimizing existing circuit components, using mini-circuits and the maneuver of retrograde autologous priming can be considered steps in prime reduction. Microplegia systems may also reduce systemic as well as cardiac hemodilutional effects. Cell savers can scavenge shed blood, wash the red cells, and may return the red cells to the patient in a concentrated form. When a patient is already hemodiluted, ultrafiltation can be used to hemoconcentrate the patient and to drive their existing hemoglobin levels up. Ultimately, the optimal form of blood conservation comes from team-work, communication, and a combination of efforts.

Unfractionated heparin and protamine have been integral to cardiopulmonary bypass since cardiac surgery was first undertaken. These drugs are inexpensive and well understood but are contraindicated in some individuals, and resistance to heparin can be problematic in others. The interplay between the endothelium, anticoagulants, the coagulation cascade, and the inflammatory response that characterizes cardiac surgery may contribute to some of the complications associated with cardiopulmonary bypass. Various alternative drugs and strategies have been used to manage patients unsuitable for heparin or protamine, but each has its own disadvantages. At present, direct thrombin inhibitors may offer the best available alternative to heparin in cardiac surgery, particularly the short-acting bivalirudin, but this class of anticoagulants is relatively expensive and has no reversal agent. Balanced anticoagulation using combinations of drugs that act at different stages in the coagulation system may improve the management of coagulation in cardiac surgery, but careful investigation of this concept is needed.

Postoperative hemorrhage following cardiac surgery increases morbidity, mortality, and costs. Several case reports have described the successful use of recombinant factor VIIa to decrease or stop bleeding in patients undergoing cardiac surgery. The mechanism of action of recombinant factor VIIa is thought to be increased site-specific thrombin generation by tissue factor—mediated activation of coagulation or from activated platelets. However, there have also been many reports of thrombotic complications after recombinant factor VIIa administration. Randomized clinical trials and further laboratory studies should help better clarify the efficacy, safety, cost-effectiveness, and optimal dosing of recombinant factor VIIa in the cardiac surgical setting.

Acute renal failure is one of the most frequent and life-threatening complications after cardiac surgery. There is a recent growing deal of information suggesting that during the time of cardiopulmonary bypass kidneys may suffer from an imbalance between oxygen supply and oxygen needs. A low hematocrit during cardiopulmonary bypass is associated with an increase risk of acute renal failure, mainly due to a low oxygen delivery. An inadequate oxygen delivery during cardiopulmonary bypass is associated with lactate production, and under normothermic conditions, hyperlactatemia appears for an oxygen delivery below 260 mL min^{− 1} m⁻². The risk of acute renal failure significantly increases for an oxygen delivery approximately at the same value (272 mL min⁻¹ m^{− 2}). During cardiopulmonary bypass, the pump flow should be coupled with the hematocrit to avoid falling below this critical oxygen delivery.

In this review the role of PaCO2 in regulating cerebral blood flow and flow/metabolism coupling, as well as its impact on intracellular metabolic processes are discussed. Starting with a discussion of alpha-stat versus pH-stat ventilatory management, the apparently contradictory finding of exacerbation of ischemic injury by extracellular acidosis in some experimental models versus others in which neuroprotection is evidenced is discussed and contrasted with the conclusion that the relatively small degree of change in pH associated with clinical changes in PaCO2 is unlikely to directly impact ischemia/reperfusion processes. However, examples of susceptible patients in whom relatively small changes in PaCO2 can produce adverse effects on cerebral perfusion are also illustrated re-emphasizing the necessity for individualization rather than generalization of care.

Near-infrared spectroscopy (NIRS) is a technique that can be used as a noninvasive and continuous monitor of the balance between cerebral oxygen delivery and consumption. The authors develop and propose an algorithm for the use of NIRS based on optimizing factors that can affect cerebral oxygen supply/demand. These factors are the position of the vascular cannula, perfusion pressure, arterial oxygen content, partial pressure of carbon dioxide, haemoglobin, cardiac output, and the cerebral metabolic rate of oxygen. Dissemination of a useful treatment algorithm is the primary purpose of this article. Further multicenter studies are necessary to confirm the benefits and cost-effectiveness of this promising monitoring modality.

As we enter the fifth decade in cardiac surgery, traditionally cardiac surgery has been performed using a median sternotomy with cardiopulmonary bypass providing great access to the heart and all the surrounding structures. During the last decade, there has been a paradigm shift in the methods by which surgery has been performed. The invasiveness of many procedures has been dramatically reduced, with significantly superior outcomes, as evidenced by improved survival, fewer complications, and quicker return to functional health and productive life. This resulted in significant interest and excitement in adopting less invasive techniques in cardiac surgery. Unfortunately, this was an unrealistic expectation due to the limitations that existed in cardiac surgical techniques and conventional endoscopic instruments, cardiac anesthesia, and cardiopulmonary bypass techniques. In this article, the advances in minimally invasive surgical, cardiac anesthesia, and cardiopulmonary bypass techniques in the evolution of minimal access cardiac surgery are summarized.

Intraoperative transesophageal echocardiography (TEE) is currently being used routinely during aortic valve replacement (AVR). TEE provides information that can lead to modifications of anesthetic and surgical care that leads to improved outcome. Numerous studies have shown that modifications in therapy occur from 10% to more than 40% of cases. The impact of TEE can be divided among modifications of therapy before, during, and after cardiopulmonary bypass. Before cardiopulmonary bypass, TEE can provide prognostic information, optimize hemodynamics, and diagnose conditions that were not appreciated before surgery, including patient—prosthesis mismatch. TEE can guide and modify the placement of various bypass cannulae. After bypass, TEE verifies the surgical result, rules out left and right ventricular outflow tract obstruction, and assures stable hemodynamics. Although current guidelines state that aortic valve surgery is a class IIa indication for TEE use, the authors' experience suggests that TEE should be routinely used in AVR.

Intraoperative assessment of the mitral valve (MV) in patients undergoing repair for MV regurgitation is a valuable support for the cardiac surgical team; results can be favored by adequate assessment tailored to the main condition affecting the MV. This article will review current available data for assessment of the MV in degenerative and ischemic mitral regurgitation.