Echocardiography is a powerful diagnostic tool that has become an indispensable part of intensive care medi cine. There is a broad clinical application for the noninva sive real-time structural and functional assessment of the critically ill patient. The echocardiograph provides on-line visual information and software for data manipu lation at the intensive care bedside without significant discomfort or risk. Assessment of ventricular function, hemodynamics, pericardial pathology, valvular status, and the outcomes of cardiac surgical interventions are naturally suited to this modality. Transesophageal echo cardiography is an important adjunct to the standard transthoracic examination, particularly in those pa tients with inadequate precordial images. Anatomic, physiologic, and hemodynamic findings can be corre lated in a variety of clinical conditions to make and confirm diagnoses and to direct management in a manner complementary to routine intensive care. Indi cations for echocardiography in the intensive care unit at this institution included assessment of ventricular function, valvular function, endocarditis, complications of surgery, abnormal hemodynamics, evaluation of intra cardiac source of embolus, and echocardiographic- guided endomyocardial biopsy. In this review, the tech niques, indications, and clinical applications of transthoracic and transesophageal echocardiography in the intensive care setting are explored, with a focus on experience in the cardiac surgical patient.
At the heart of the discussion about blood transfusion is how one strikes a balance between two potentially morbid perioperative exposures: anemia and red blood cell (RBC) transfusion. Which combination of patient demographics, comorbidities, physiologic variables, or laboratory values might favor exposure to one over the other? In an individual patient, in the real-time setting of the fast-paced surgical arena, this decision can be tough. Those of us who practice in this space do not always know if we have made the right decision—uncertainty persists. What we do know is there is a point when hemoglobin (Hb) values reach a threshold below which RBC transfusion is indicated and beneficial—but where is this decision point for an individual patient? At present, lack of specific methods to measure tissue hypoxia directly means reliance on indirect feedback to support decision making regarding anemia and RBC transfusion. With the exception of ongoing hemorrhage, the traditional approach to transfusion has usually involved a specific Hb threshold beneath which one begins to consider a RBC transfusion. This decision point, often referred to as a “transfusion trigger,” varies with practitioner, health care institution, and guideline recommendation. A widely applied Hb transfusion trigger of 7 g/dL seems a simple solution to the question of when to transfuse.1 However, to paraphrase H.L. Mencken, “For every complex problem there is an answer that is clear, simple, and wrong.” There is an underlying complexity to this issue; that is, physiology is geared to adapt to a degree of stress more than it is set to react to a certain trigger. Those who provide care for cardiac surgical patients recognize the complexity of the decision-making process beyond that of a laboratory cutoff value. The individual patient's Hb values and trends, ongoing microvascular bleeding, degree of vasopressor support, and patient comorbidity are among a number of important variables factored into our real-time mental models triggering transfusion decisions. The study by Hogervorst and colleagues2 stands to broadly inform our decision-making capability regarding the choice of RBC transfusion versus tolerating anemia at the point of care for an individual patient. They report that a “relative” reduction in the patient's baseline Hb value of more than 50% is an important factor associated with poor postoperative outcomes, even when specific Hb values may not have reached a traditional “trigger.” The fact that there is an intolerance to a relative reduction in Hb versus an absolute threshold trigger suggests that there is a patient-specific response in terms of ability to adapt to the onset of an acute anemic episode. The ingenuity of the current study goes beyond a new tool for deciding when to give blood; it is the realization that there is a dynamic underlying the decision that reflects the ability of the system to adapt. There is biologic and clinical plausibility to the authors' findings, supported by a number of investigations characterizing risk associated with acute anemia. These investigations suggest that there is an adaptive response to anemia up to a point after which one witnesses organ damage, presumably related to hypoxia.3-7 In the present study setting, cardiac patients are often treated with perioperative beta blockade, have substantial comorbidity, or may experience the potential for post–cardiopulmonary bypass ischemic reperfusion injury and heart block—all of which impair cardiovascular physiologic responses to anemia.3, 5 By their nature, these elements also complicate feedback, which might signal stress or the need for transfusion. Tissue hypoxia related to varying levels of anemia may be manifest by biomarker stress signaling. It has been suggested that biomarkers of tissue hypoxia, signaling subsequent changes in hypoxic cellular response related to anemia, may be specific and dynamic enough to eventually provide optimal patient-specific feedback indicating that the lower Hb threshold has been reached and a RBC transfusion may be indicated.5, 7-10 There is additional evidence suggesting that the magnitude of Hb reduction associated with acute anemia may have organ-specific effects; that is, sensitivity to the negative effects of anemia may vary by Hb threshold for different organs.6, 8 Hence, tolerance of anemia may be relative to reduction in a patient-specific baseline, relative to the ability of the patient to adaptively respond.3 Cardiac surgery is a unique setting considering significant patient comorbidity, extent of surgical incisions, degree of blood loss and arrest of the heart. Is there evidence to suggest the authors' study findings could be extrapolated to less complicated operative or even nonoperative settings or is there a unique interaction between this particular surgical milieu and exposure to acute anemia? Data suggest that development of acute anemia during the course of hospitalization for both medical and surgical patients places a patient at a heightened risk for bad outcomes. In a recent investigation of more than 180,000 mixed medical and surgical hospitalizations, patients who were admitted with normal Hb values and who developed acute anemia during the course of hospitalization had higher risk-adjusted in-hospital mortality and greater resource utilization. This relationship was dose dependent with greater degrees of anemia associated with higher risk. Although relative Hb reduction was not a measured variable, if one calculated relative reductions from set normal Hb values, the overall relative reduction in Hb in the range of 25% was associated with increased risk, less than the more than 50% cutoff in this study.11 Recognizing that the relative reduction of Hb by more than 50% is a more dynamic indicator than an absolute threshold, it is nonetheless dichotomous in nature. If the study by Hogervorst and colleagues treated data on a continuum, would we find a more graded response to acute relative reduction in Hb and poor outcomes? Although clinicians tend to dichotomize variables for decision making, statistical methodologic literature discourages such practice, except for rare circumstances.12-15 Embracing data measured on a continuum rather than categorizing such data is recommended to avoid loss of information and power.12-16 Examining a continuous spectrum of anemia exposure and a patient's ability to adaptively respond may get us closer to making better patient-specific decisions to address declining Hb values. Use of a composite outcome does not allow insight into organ-specific sensitivity to reduction in Hb values or perhaps the benefit of more timely intervention. A smaller percent reduction in Hb from baseline may be more detrimental to renal function than other organ function, or the ability of the kidney to adapt may depend on baseline renal function in a specific relationship to the magnitude of reduction. Findings in laboratory5, 6, 8 and clinical studies17 suggest that specific organs have varying sensitivity to varying levels of anemia. The strength of the current study's composite endpoint lies partly in its straightforward relationship to increasing risk with decreasing levels of Hb and partially to the fact that all components of the studies' composite outcome behaved similarly in relationship of anemia.18-20 Still, it suggests that there is an abundance of understanding to be gained by evaluating more organ-specific or patient-specific outcomes. How can we integrate the study findings into patient care? This investigation excluded patients with preoperative anemia; hence development of anemia was an acute event occurring as a result of either blood loss or hemodilution. Blood loss can be due to events such as surgical misadventure or coagulopathy with microvascular bleeding. The contribution of the hemodilutional effects of intravenous fluids, cardiopulmonary bypass prime, and cardioplegia can be substantial and is potentially modifiable. Using Kirklin's algorithm21 for calculating patient-machine hematocrit (Hct) modified for pre–cardiopulmonary crystalloid volume, estimates for cardiopulmonary bypass prime and cardioplegia volume could be simulated preoperatively for an average cardiac surgical patient. Kirklin suggested using this algorithm of calculating patient-machine Hct in an automated manner preoperatively. Is such a formula useful for predicting what relative reductions in Hb might be reached or specifically when relative reductions of more than 50% in baseline Hb would occur? Estimates of contributions to relative reductions in Hb might change processes of care to reduce the role of hemodilution in development of acute anemia. The current study by Hogervorst and colleagues complements findings from other investigations that may suggest that current guideline recommendations for Hb triggers may be set too low.5, 9, 10 Relative reductions in Hb might provide additional perspective from a clinical viewpoint. Certainly these observations at least represent a call to better understand the role of biomarkers of anemic stress in the clinical assessment of inadequate tissue oxygen delivery.5 The study by Hogervorst and colleagues provides an immediately useful, practical tool for evaluating anemia in the operative setting. Beyond this contribution, it echoes the call to develop a better understanding, more advanced technology, and practical applicability in the complex process of blood management in cardiac surgery. From the data, we can only comment on association rather than causation. In this type of study design there is a likelihood of unmeasured confounding giving rise to unanswered questions, but also sowing the seeds of new directions in research and treatment. However, across disciplines, and in different settings, anemia appears to place patients at risk, as does the treatment to a point. This dilemma magnifies the mission to make research patient centric with aggressive application of advances in technology versus any practice that seems to be “one size fits all.” The elegance of this study is not only the management tool it provides, but the question it raises about the complexity of adaptation to anemia. The author has disclosed no conflicts of interest.
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