Intraoperative physiologic variables and outcome in cardiac surgery: Part I. In-hospital mortality

A systematic review of cardiac surgery clinical prediction models that include intra-operative variables

BACKGROUND

Most cardiac surgery clinical prediction models (CPMs) are developed using pre-operative variables to predict post-operative outcomes. Some CPMs are developed with intra-operative variables, but none are widely used. The objective of this systematic review was to identify CPMs with intra-operative variables that predict short-term outcomes following adult cardiac surgery.

METHODS

Ovid MEDLINE and EMBASE databases were searched from inception to December 2022, for studies developing a CPM with at least one intra-operative variable. Data were extracted using a critical appraisal framework and bias assessment tool. Model performance was analysed using discrimination and calibration measures.

RESULTS

A total of 24 models were identified. Frequent predicted outcomes were acute kidney injury (9/24 studies) and peri-operative mortality (6/24 studies). Frequent pre-operative variables were age (18/24 studies) and creatinine/eGFR (18/24 studies). Common intra-operative variables were cardiopulmonary bypass time (16/24 studies) and transfusion (13/24 studies). Model discrimination was acceptable for all internally validated models (AUC 0.69-0.91). Calibration was poor (15/24 studies) or unreported (8/24 studies). Most CPMs were at a high or indeterminate risk of bias (23/24 models). The added value of intra-operative variables was assessed in six studies with statistically significantly improved discrimination demonstrated in two.

CONCLUSION

Weak reporting and methodological limitations may restrict wider applicability and adoption of existing CPMs that include intra-operative variables. There is some evidence that CPM discrimination is improved with the addition of intra-operative variables. Further work is required to understand the role of intra-operative CPMs in the management of cardiac surgery patients.

Sequential regression measurement error models with application

Sequential regression approaches can be used to analyze processes in which covariates are revealed in stages. Such processes occur widely, with examples including medical intervention, sports contests and political campaigns. The naïve sequential approach involves fitting regression models using the covariates revealed by the end of the current stage, but this is only practical if the number of covariates is not too large. An alternative approach is to incorporate the score (linear predictor) from the model developed at the previous stage as a covariate at the current stage. This score takes into account the history of the process prior to the stage under consideration. However, the score is a function of fitted parameter estimates and, therefore, contains measurement error. In this article, we propose a novel technique to account for error in the score. The approach is demonstrated with application to the sprint event in track cycling and is shown to reduce bias in the estimated effect of the score and avoid unrealistically extreme predictions.

Transfusion strategy: impact of haemodynamics and the challenge of haemodilution

Blood transfusion is associated with increased morbidity and mortality and numerous reports have emphasised the need for reduction. Following this there is increased attention to the concept of patient blood management. However, bleeding is relatively common following cardiac surgery and is further enhanced by the continued antiplatelet therapy policy. Another important issue is that cardiopulmonary bypass leads to haemodilution and a potential blood loss. The basic role of blood is oxygen transport to the organs. The determining factors of oxygen delivery are cardiac output, haemoglobin, and saturation. If oxygen delivery/consumption is out of balance, the compensation mechanisms are simple, as a decrease in one factor results in an increase in one or two other factors. Patients with coexisting cardiac diseases may be of particular risk, but studies indicate that patients with coexisting cardiac diseases tolerate moderate anaemia and may even benefit from a restrictive transfusion regimen. Further it has been shown that patients with reduced left ventricular function are able to compensate with increased cardiac output in response to bleeding and haemodilution if normovolaemia is maintained. In conclusion the evidence supports that each institution establishes its own patient blood management strategy to both conserve blood products and maximise outcome.

Scientific principles and clinical implications of perioperative glucose regulation and control

Development of hyperglycemia after major operations is very common and is modulated by many factors. These factors include perioperative metabolic state, intraoperative management of the patient, and neuroendocrine stress response to surgery. Acute insulin resistance also develops perioperatively and contributes significantly to hyperglycemia. Hyperglycemia is associated with poor outcomes in critically ill and postsurgical patients. A majority of the investigations use the term "hyperglycemia" very loosely and use varying thresholds for initiating treatment. Initial studies demonstrated improved outcomes in critically ill, postsurgical patients who received intensive glycemic control (IGC) (target serum glucose <110 mg/dL). These results were quickly extrapolated to other clinical areas, and IGC was enthusiastically recommended in the perioperative period. However, there are few studies investigating the value of intraoperative glycemic control. Moreover, recent prospective trials have not been able to show the benefit of IGC; neither an appropriate therapeutic glycemic target nor the true efficacy of perioperative glycemic control has been fully determined. Practitioners should also appreciate technical nuances of various glucose measurement techniques. IGC increases the risk of hypoglycemia significantly, which is not inconsequential in critically ill patients. Until further specific data are accumulated, it is prudent to maintain glucose levels <180 mg/dL in the perioperative period, and glycemic control should always be accompanied by close glucose monitoring.

A comparative analysis of predictive models of morbidity in intensive care unit after cardiac surgery - part I: model planning

Background

Different methods have recently been proposed for predicting morbidity in intensive care units (ICU). The aim of the present study was to critically review a number of approaches for developing models capable of estimating the probability of morbidity in ICU after heart surgery. The study is divided into two parts. In this first part, popular models used to estimate the probability of class membership are grouped into distinct categories according to their underlying mathematical principles. Modelling techniques and intrinsic strengths and weaknesses of each model are analysed and discussed from a theoretical point of view, in consideration of clinical applications.

Methods

Models based on Bayes rule, k-nearest neighbour algorithm, logistic regression, scoring systems and artificial neural networks are investigated. Key issues for model design are described. The mathematical treatment of some aspects of model structure is also included for readers interested in developing models, though a full understanding of mathematical relationships is not necessary if the reader is only interested in perceiving the practical meaning of model assumptions, weaknesses and strengths from a user point of view.

Results

Scoring systems are very attractive due to their simplicity of use, although this may undermine their predictive capacity. Logistic regression models are trustworthy tools, although they suffer from the principal limitations of most regression procedures. Bayesian models seem to be a good compromise between complexity and predictive performance, but model recalibration is generally necessary. k-nearest neighbour may be a valid non parametric technique, though computational cost and the need for large data storage are major weaknesses of this approach. Artificial neural networks have intrinsic advantages with respect to common statistical models, though the training process may be problematical.

Conclusion

Knowledge of model assumptions and the theoretical strengths and weaknesses of different approaches are fundamental for designing models for estimating the probability of morbidity after heart surgery. However, a rational choice also requires evaluation and comparison of actual performances of locally-developed competitive models in the clinical scenario to obtain satisfactory agreement between local needs and model response. In the second part of this study the above predictive models will therefore be tested on real data acquired in a specialized ICU.

Perioperative blood transfusion and blood conservation in cardiac surgery: the Society of Thoracic Surgeons and The Society of Cardiovascular Anesthesiologists clinical practice guideline

BACKGROUND

A minority of patients having cardiac procedures (15% to 20%) consume more than 80% of the blood products transfused at operation. Blood must be viewed as a scarce resource that carries risks and benefits. A careful review of available evidence can provide guidelines to allocate this valuable resource and improve patient outcomes.

METHODS

We reviewed all available published evidence related to blood conservation during cardiac operations, including randomized controlled trials, published observational information, and case reports. Conventional methods identified the level of evidence available for each of the blood conservation interventions. After considering the level of evidence, recommendations were made regarding each intervention using the American Heart Association/American College of Cardiology classification scheme.

RESULTS

Review of published reports identified a high-risk profile associated with increased postoperative blood transfusion. Six variables stand out as important indicators of risk: (1) advanced age, (2) low preoperative red blood cell volume (preoperative anemia or small body size), (3) preoperative antiplatelet or antithrombotic drugs, (4) reoperative or complex procedures, (5) emergency operations, and (6) noncardiac patient comorbidities. Careful review revealed preoperative and perioperative interventions that are likely to reduce bleeding and postoperative blood transfusion. Preoperative interventions that are likely to reduce blood transfusion include identification of high-risk patients who should receive all available preoperative and perioperative blood conservation interventions and limitation of antithrombotic drugs. Perioperative blood conservation interventions include use of antifibrinolytic drugs, selective use of off-pump coronary artery bypass graft surgery, routine use of a cell-saving device, and implementation of appropriate transfusion indications. An important intervention is application of a multimodality blood conservation program that is institution based, accepted by all health care providers, and that involves well thought out transfusion algorithms to guide transfusion decisions.

CONCLUSIONS

Based on available evidence, institution-specific protocols should screen for high-risk patients, as blood conservation interventions are likely to be most productive for this high-risk subset. Available evidence-based blood conservation techniques include (1) drugs that increase preoperative blood volume (eg, erythropoietin) or decrease postoperative bleeding (eg, antifibrinolytics), (2) devices that conserve blood (eg, intraoperative blood salvage and blood sparing interventions), (3) interventions that protect the patient's own blood from the stress of operation (eg, autologous predonation and normovolemic hemodilution), (4) consensus, institution-specific blood transfusion algorithms supplemented with point-of-care testing, and most importantly, (5) a multimodality approach to blood conservation combining all of the above.

Indications for Blood Transfusion in Cardiac Surgery

In addition to its life-saving effect in hemorrhagic shock, transfusion of allogenic packed red blood cells can be beneficial in situations where a critically low hematocrit is contributing to a state of oxygen-supply dependency. These benefits are countered by the risks of transfusion-associated lung injury, transfusion-associated immunomodulation, and cellular hypoxia after RBC transfusion. The critical hematocrit is patient and organ specific, and varies intraoperatively according to the duration and temperature of bypass, as well as for a variable postoperative period. Future randomized studies must prospectively evaluate regional indicators of tissue oxygenation in transfusion algorithms.

Prevention of Ischemic Neurologic Injury With Intraoperative Monitoring of Selected Cardiovascular and Cerebrovascular Procedures: Roles of Electroencephalography, Somatosensory Evoked Potentials, Transcranial Doppler, and Near-Infrared Spectroscopy

All neuromonitoring techniques, although imperfect, provide useful information for monitoring cardiothoracic and carotid vascular operations. They may be viewed as providing complementary information, which may help surgical technique and, as a result, possibly improve clinical outcomes. As of this writing, the efficacy of TCD and NIRS monitoring during cardiothoracic and vascular surgery cannot be considered established. Well designed, prospective, adequately powered, double-blind, and randomized outcome studies are needed to determine the optimal neurologic monitoring modality (or modalities), in specific surgical settings.

Cardiopulmonary bypass management and neurologic outcomes: an evidence-based appraisal of current practices

Neurologic complications after cardiac surgery are of growing importance for an aging surgical population. In this review, we provide a critical appraisal of the impact of current cardiopulmonary bypass (CPB) management strategies on neurologic complications. Other than the use of 20-40 microm arterial line filters and membrane oxygenators, newer modifications of the basic CPB apparatus or the use of specialized equipment or procedures (including hypothermia and "tight" glucose control) have unproven benefit on neurologic outcomes. Epiaortic ultrasound can be considered for ascending aorta manipulations to avoid atheroma, although available clinical trials assessing this maneuver are limited. Current approaches for managing flow, arterial blood pressure, and pH during CPB are supported by data from clinical investigations, but these studies included few elderly or high-risk patients and predated many other contemporary practices. Although there are promising data on the benefits of some drugs blocking excitatory amino acid signaling pathways and inflammation, there are currently no drugs that can be recommended for neuroprotection during CPB. Together, the reviewed data highlight the deficiencies of the current knowledge base that physicians are dependent on to guide patient care during CPB. Multicenter clinical trials assessing measures to reduce the frequency of neurologic complications are needed to develop evidence-based strategies to avoid increasing patient morbidity and mortality.

A multivariate Bayesian model for assessing morbidity after coronary artery surgery

Introduction

Although most risk-stratification scores are derived from preoperative patient variables, there are several intraoperative and postoperative variables that can influence prognosis. Higgins and colleagues previously evaluated the contribution of preoperative, intraoperative and postoperative predictors to the outcome. We developed a Bayes linear model to discriminate morbidity risk after coronary artery bypass grafting and compared it with three different score models: the Higgins' original scoring system, derived from the patient's status on admission to the intensive care unit (ICU), and two models designed and customized to our patient population.

Methods

We analyzed 88 operative risk factors; 1,090 consecutive adult patients who underwent coronary artery bypass grafting were studied. Training and testing data sets of 740 patients and 350 patients, respectively, were used. A stepwise approach enabled selection of an optimal subset of predictor variables. Model discrimination was assessed by receiver operating characteristic (ROC) curves, whereas calibration was measured using the Hosmer-Lemeshow goodness-of-fit test.

Results

A set of 12 preoperative, intraoperative and postoperative predictor variables was identified for the Bayes linear model. Bayes and locally customized score models fitted according to the Hosmer-Lemeshow test. However, the comparison between the areas under the ROC curve proved that the Bayes linear classifier had a significantly higher discrimination capacity than the score models. Calibration and discrimination were both much worse with Higgins' original scoring system.

Conclusion

Most prediction rules use sequential numerical risk scoring to quantify prognosis and are an advanced form of audit. Score models are very attractive tools because their application in routine clinical practice is simple. If locally customized, they also predict patient morbidity in an acceptable manner. The Bayesian model seems to be a feasible alternative. It has better discrimination and can be tailored more easily to individual institutions.

Advanced neurologic monitoring for cardiac surgery

Cardiac surgery (CS) with cardiopulmonary bypass (CPB) is currently the most common surgery in the United States. Understanding, avoiding, and preventing postoperative complications, including neurologic deficits following CS, represents a great public and economic benefit for society, especially considering our aging population. There is a critical need to identify new strategies that will prevent harmful events during and after CS. At present, experience with neurophysiologic techniques includes the ability to measure cerebral blood flow velocity/emboli and regional cerebral venous oxygen saturation by transcranial Doppler ultrasound, and by near-infrared spectroscopy, respectively. Continuous monitoring of these variables along with systemic hemodynamics will provide a better understanding of mechanisms of brain and other organ injury during CPB. Neuroprotective interventions based on multimodality neurologic monitoring would ideally eliminate postoperative complications and improve patient outcomes.

Anesthesia and Neurocerebral Monitoring for Aortic Dissection

Patients presenting to the operating room for repair of aortic dissection are challenging in all aspects of their care. Without exception, they require a multidisciplinary team approach. This article will review some of the specific challenges faced by anesthesiologists and neurologists when confronted with such a diagnosis. Specifically, we will discuss the myriad anesthetic issues that present in the preoperative stage and continue into the postoperative period. Neurologic complications during dissection repair result in increased morbidity and mortality. A variety of neurophysiologic monitoring techniques exist that may reduce this risk and will be discussed in detail. Finally, we will present some "controversies in care," emphasizing that our respective fields continue to grow, learn, and improve what information we have on the morbidity and mortality of aortic dissection.

Intraoperative hyperglycemia and perioperative outcomes in cardiac surgery patients

OBJECTIVE

To estimate the magnitude of association between intraoperative hyperglycemia and perioperative outcomes in patients who underwent cardiac surgery.

PATIENTS AND METHODS

We conducted a retrospective observational study of consecutive adult patients who underwent cardiac surgery between June 10, 2002, and August 30, 2002, at the Mayo Clinic, a tertiary care center in Rochester, Minn. The primary independent variable was the mean intraoperative glucose concentration. The primary end point was a composite of death and infectious (sternal wound, urinary tract, sepsis), neurologic (stroke, coma, delirium), renal (acute renal failure), cardiac (new-onset atrial fibrillation, heart block, cardiac arrest), and pulmonary (prolonged pulmonary ventilation, pneumonia) complications developing within 30 days after cardiac surgery.

RESULTS

Among 409 patients who underwent cardiac surgery, those experiencing a primary end point were more likely to be male and older, have diabetes mellitus, undergo coronary artery bypass grafting, and receive insulin during surgery (P< or =.05 for all comparisons). Atrial fibrillation (n=105), prolonged pulmonary ventilation (n=53), delirium (n=22), and urinary tract infection (n=16) were the most common complications. The initial, mean, and maximal intraoperative glucose concentrations were significantly higher in patients experiencing the primary end point (P<.01 for all comparisons). In multivariable analyses, mean and maximal glucose levels remained significantly associated with outcomes after adjusting for potentially confounding variables, including postoperative glucose concentration. Logistic regression analyses indicated that a 20-mg/dL increase in the mean intraoperative glucose level was associated with an increase of more than 30% in outcomes (adjusted odds ratio, 1.34; 95% confidence Interval, 1.10-1.62).

CONCLUSION

Intraoperative hyperglycemia is an independent risk factor for complications, including death, after cardiac surgery.

Strategies for transfusion therapy

Transfusion of allogeneic red blood cells (RBCs), fresh frozen plasma (FFP) and platelets is associated with risks, and outcome studies comparing liberal and restrictive transfusion regimens are lacking in surgical patients. Therefore, guidelines have been established. They recommend first maintaining normovolaemia by the use of crystalloids and colloids. RBC transfusions are recommended for haemoglobin levels < 6 g/dl and for physiological signs of inadequate oxygenation such as haemodynamic instability, oxygen extraction > 50% and myocardial ischaemia (new ST-segment depressions > 0.1 mV, new ST-segment elevations > 0.2 mV or new wall motion abnormalities in transoesophageal echocardiography). FFP transfusions are recommended for urgent reversal of anticoagulation, known coagulation factor deficiencies, microvascular bleeding in the presence of elevated (> 1.5 times normal) prothrombin time (PT) or partial thromboplastin time (PTT) and microvascular bleeding after the replacement of more than one blood volume when PT or PTT cannot be obtained. Platelet transfusions are recommended prior to major operations in patients with platelet counts < 50,000/microl, intraoperatively with microvascular bleeding at platelet counts < 50,000/microl and in the range of 50,000-100,0000/microl following cardiopulmonary bypass and in patients undergoing surgery where already minimal bleeding may cause major damage such as in neurosurgery.

Transfusion in the cardiac patient

Transfusion guidelines in patients with coexisting cardiac diseases are similar to the ones in patients without such comorbidity, in that allogeneic blood transfusions most often are indicated at hemoglobin levels of less than 6.0 g/dL and hardly ever at hemoglobin levels greater than 10 g/dL. In the hemoglobin range of 6 to 10 g/dL, signs of impaired oxygenation should serve as transfusion indications, and such signs may be reached at higher hemoglobin values than in healthy patients. An inadequate oxygenation may become manifest globally in the form of a general hemodynamic instability with a tendency to hypotension and tachycardia despite normovolemia or an oxygen extraction of greater than 50%. An inadequate oxygenation in the form of myocardial ischemia may be manifested by new ST-segment depressions of greater than 0.1 mV, new ST-segment elevations greater than 0.2 mV, or new wall motion abnormalities in transesophageal echocardiography. Institutional guidelines also should consider local logistic characteristics such as the level of knowledge of physician and nurse staff caring for patients and the level of surveillance possible justifying eventually higher hemoglobin transfusion triggers, particularly in the postoperative period.

The association of lowest hematocrit during cardiopulmonary bypass with acute renal injury after coronary artery bypass surgery

BACKGROUND

Acute renal injury is a common serious complication of cardiac surgery. Moderate hemodilution is thought to reduce the risk of kidney injury but the current practice of extreme hemodilution (target hematocrit 22% to 24%) during cardiopulmonary bypass (CPB) has been linked to adverse outcomes after cardiac surgery. Therefore we tested the hypothesis that lowest hematocrit during CPB is independently associated with acute renal injury after cardiac surgery.

METHODS

Demographic, perioperative, and laboratory data were gathered for 1,404 primary elective coronary bypass surgery patients. Preoperative and daily postoperative creatinine values were measured until hospital discharge per institutional protocol. Stepwise multivariable linear regression analysis was performed to determine whether lowest hematocrit during CPB was independently associated with peak fractional change in creatinine (defined as the difference between the preoperative and peak postoperative creatinine represented as a percentage of the preoperative value). A p value of less than 0.05 was considered significant.

RESULTS

Multivariable analyses including preoperative hematocrit and other perioperative variables revealed that lowest hematocrit during CPB demonstrated a significant interaction with body weight and was highly associated with peak fractional change in serum creatinine (parameter estimate [PE] = 4.5; p = 0.008) and also with highest postoperative creatinine value (PE = 0.06; p = 0.004). Although other renal risk factors were significant covariates in both models, TM50 (an index of hypotension during CPB) was notably absent.

CONCLUSIONS

These results add to concerns that current CPB management guidelines accepting extreme hemodilution may contribute to postoperative acute renal and other organ injury after cardiac surgery.

Validation of four different risk stratification systems in patients undergoing off-pump coronary artery bypass surgery: a UK multicentre analysis of 2223 patients

BACKGROUND

Various risk stratification systems have been developed in coronary artery bypass graft surgery (CABG), based mainly on patients undergoing procedures with cardiopulmonary bypass.

OBJECTIVE

To assess the validity and applicability of the Parsonnet score, the EuroSCORE, the American College of Cardiology/American Heart Association (ACC/AHA) system, and the UK CABG Bayes model in patients undergoing off-pump coronary artery bypass surgery (OPCAB) in the UK.

METHODS

Data on 2223 patients who underwent OPCAB in eight cardiac surgical centres were collected. Predicted mortality risk scores were calculated using the four systems and compared with observed mortality. Calibration was assessed by the Hosmer-Lemeshow (HL) test. Discrimination was assessed using the receiver operating characteristic (ROC) curve area.

RESULTS

30 of 2223 patients (1.3%) died in hospital. For the Parsonnet score the HL test was significant (p < 0.001) and the receiver operating characteristic curve (ROC) area was 0.74. For the EuroSCORE the HL test was also significant (p = 0.008) and the ROC area was 0.75. For the ACC/AHA system the HL test was non-significant (p = 0.7) and the ROC area was 0.75. For the UK CABG Bayes model the HL test was also non-significant (p = 0.3) and the ROC area was 0.81.

CONCLUSIONS

The UK CABG Bayes model is reasonably well calibrated and provides good discrimination when applied to OPCAB patients in the UK. Among the other three systems, the ACC/AHA system is well calibrated but its discrimination power was less than for the UK CABG Bayes model. These data suggest that the UK CABG Bayes model could be an appropriate risk stratification system to use for patients undergoing OPCAB in the UK.

Risk factors for long intensive care unit stay after cardiopulmonary bypass in children

OBJECTIVES

To determine whether children who experience longer intensive care unit (ICU) stays after open heart surgery may be identified at admission by clinical criteria. To identify factors associated with longer ICU stays that are potential targets for quality improvement.

SETTING

Tertiary pediatric cardiac surgical center.

DESIGN

A retrospective review was performed of pre-, intra-, and postoperative factors for children undergoing open heart surgery. All factors were evaluated for strength of association with length of ICU stay (LOS) using a negative binomial model. After multiple analysis, factors were deemed significant if associated with a LOS with p < .02.

PATIENTS

A total of 355 pediatric patients who had cardiac surgery with cardiopulmonary bypass in a 1-yr period from April 1999 until March 2000.

MEASUREMENTS AND MAIN RESULTS

Children who fell above the 95th percentile for LOS in our institution occupied 30% of bed days and had a three-fold greater mortality. Of all clinical factors considered, those significantly associated with LOS were as follows: preoperative--mechanical ventilation, neonatal status, medical problems, and transfer from abroad; intraoperative--higher operative complexity, increased cardiopulmonary bypass time or ischemic time, and circulatory arrest; and postoperative--delayed sternal closure, sepsis, renal failure, pulmonary hypertension, chylothorax, diaphragm paresis, and arrhythmia. A model combining all factors identified preoperative mechanical ventilation, neonatal status, major medical problems, operative complexity, cardiopulmonary bypass time, and a postoperative complication score as independently associated with LOS (p < .01).

CONCLUSIONS

At the time of ICU admission after open heart surgery, clinical criteria are evident that highlight a child's risk of longer ICU stay. These pre- and intraoperative factors relate to LOS independent of subsequent postoperative events. Those postoperative complications that are most strongly associated with increased LOS are identified and, therefore, made accessible to quality control.

The association of complication type with mortality and prolonged stay after cardiac surgery with cardiopulmonary bypass

Outcome after cardiac surgery varies depending on complication type. We therefore sought to determine the association between complication type, mortality, and length of stay in a large series of patients undergoing cardiac surgery with cardiopulmonary bypass (CPB). Multivariate logistic regression was used to test for differences between complication types in mortality and prolonged length of stay (>10 days) while controlling for preoperative and intraoperative risk factors. In 2609 consecutive cardiac surgical patients requiring CPB, the mortality rate was 3.6%; 36.5% had one or more complications, and 15.7% experienced an adverse outcome (death or prolonged length of stay). Multivariate logistic regression demonstrated that complication type was significantly associated with adverse outcome (P < 0.001) independent of Parsonnet score and CPB time (c-index = 0.80). The development of noncardiac complications only (Group NC) and cardiac complications with other organ involvement (Group B) significantly increased mortality and hospital and intensive care unit length of stay (P < 0.001) when compared with cardiac complications only (Group C). The incidences of adverse outcome in Groups C, NC, and B were 15%, 43%, and 67%, respectively; the mortality rates were 3%, 7%, and 20%, respectively. All these intergroup comparisons were significantly different (adjusted P < 0.05). Complications involving organs other than the heart appear to be more deleterious than cardiac complications alone, underscoring the need for strategies to reduce noncardiac complications.

IMPLICATIONS

Complications, particularly when they involve organs other than just the heart, increase mortality and prolong the length of hospital stay after heart surgery, independent of a patient's preoperative risk factors and the duration of cardiopulmonary bypass. Strategies aimed at preventing damage to other organs during cardiac surgery need to be improved.

Importance of blood pressure regulation in maintaining adequate tissue perfusion during cardiopulmonary bypass

Patients undergoing surgery with the aid of cardiopulmonary bypass (CPB) have an incidence of end-organ dysfunction, caused by embolization, regional hypoperfusion, or some combination of the two. In this article, we attempt to define the effect of mean arterial pressure (MAP) during CPB on postoperative end-organ function. Although early studies reported that cerebral perfusion during hypothermic CPB is independent of MAP, recent laboratory and clinical reports have shown a positive slope in the MAP versus cerebral blood flow relationship. In clinical studies, patients who had higher MAPs during CPB had a lower incidence of cardiac and neurologic complications, as well as late neurocognitive abnormalities compared with patients with lower MAPs. Improving collateral flow in the setting of cerebral embolization has been postulated as the main mechanism for the improved neurologic outcomes in the high MAP groups. Higher perfusion pressure during CPB affects regional blood flow to the kidneys and visceral organs. However, the lower autoregulatory limits of perfusion to abdominal organs differ from the limits to the brain. Enhanced visceral perfusion during CPB is best achieved by increasing perfusion pressure via increases in perfusion flow rates rather than by using peripheral vasoconstriction alone. In conclusion, it is clear that maintenance of a high MAP during CPB may have a significant impact in protecting the brain and abdominal organs, particularly in the subset of patients at high risk for embolization and end-organ dysfunction.

Intraoperative physiologic variables and outcome in cardiac surgery: Part II. Neurologic outcome

BACKGROUND

The impact of alterable physiologic variables on neurologic outcome after coronary artery bypass grafting procedures is unknown. The purpose of this study was to determine whether minimum intraoperative hematocrit, maximum glucose concentration, or mean arterial pressure during cardiopulmonary bypass influences risk-adjusted neurologic outcome after coronary artery bypass grafting.

METHODS

Outcome data from 2,862 patients undergoing coronary artery bypass grafting were merged with intraoperative physiologic data. A preoperative stroke risk index was calculated for each patient. Variables found significant by univariate logistic regression were tested in a multivariable model to determine association with outcome.

RESULTS

The incidence of stroke or coma in the study population was 1.3%. After controlling for stroke risk and bypass time, only an index of low mean arterial pressure during bypass retained a significant inverse association with outcome (p = 0.0304).

CONCLUSIONS

This study found no evidence that glucose concentration or minimum hematocrit are associated with major adverse neurologic outcome. The association between lower pressure during bypass and decreased incidence of stroke or coma persisted in all risk groups. This points to mechanisms other than hypoperfusion as the primary cause of neurologic injury associated with cardiac surgery.