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Preoperative Anemia and Postoperative Outcomes
RESEARCH NEWS
Preoperative Anemia and Postoperative Outcomes Mary W. Stewart, PhD, RN WHEN IT COMES TO READING research reports, we all hope for something straight forward. We want a clearly stated purpose, easy-to-follow methodology, and uncomplicated statistical analysis. Ultimately, we would like to skip to the Implications section and trust that what is reported is accurate. This is no different than the average person who avoids legal jargon and fine print. We may assume that those details are unimportant. Regardless, we do not have time to weed through the foreign language, so we quickly mark the ‘‘I accept the terms’’ statement and get on our way. Nurses recognize this as a haphazard approach to accepting contracts, adopting research findings, and making evidence-based practice decisions. We are accountable for the obvious data, as well as that which may be perplexing and subtle. Without the whole account—in a surgical consent document, a contract for employment, and research purporting practice guidelines—we may find ourselves in a quandary. In this column, the author attempts to translate relevant information from reputable sources that will empower the perianesthesia nurse with knowledge learned from good research. The challenge includes presenting a fair appraisal of diverse perspectives. Similar to two lawyers debating the meaning of a particular regulation, scientists deliberate the significance of data. In the two studies that follow, researchers investigated the same topic (preoperative anemia and perioperative outcomes) using the same information (the American Mary W. Stewart, PhD, RN, is a Professor and Director of the PhD program, Special Assistant to the Dean, School of Nursing, University of Mississippi Medical Center, Jackson, MS. Conflict of interest: None to report. Address correspondence to Mary W. Stewart, School of Nursing, University of Mississippi Medical Center, 2500 North State, Street, Jackson, MS 39216-4505; e-mail address: [email protected]. Ó 2014 by American Society of PeriAnesthesia Nurses 1089-9472/$36.00 http://dx.doi.org/10.1016/j.jopan.2013.11.005
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College of Surgeons National Surgical Quality Improvement Program database). Nevertheless, their conclusions are not in agreement. The Association between Preoperative Anemia and 30-Day Mortality and Morbidity in Noncardiac Surgical Patients by Saager L, Turan A, Reynolds L, Dalton J, Mascha E, Kurz A. Anesthesia & Analgesia. 2013;117:909-915.
Background and Purpose Patients with anemia present unique considerations when undergoing surgery. This population requires more intraoperative blood transfusions, and those transfusions introduce another set of potential complications. Previous studies on preoperative anemia using established databases have generalized that patients with anemia have poorer postoperative outcomes. The problem is that generalizations do not necessarily fit the whole population. The purpose of this study was to assess the relationship between preoperative anemia and postoperative mortality and morbidity outcomes in noncardiac surgical patients. Special emphasis was placed on the necessity to distinguish variables as confounding or mediating before analysis.
Method and Analysis These authors challenge the conclusions of similar studies and conduct their own analysis, differentiating variables that may influence postoperative issues. These variables are classified as confounding factors and mediating factors. Confounding factors are thought to have a direct line of influence on anemia as well as the perioperative outcomes. Mediating factors are those that do not have influence on anemia; rather they are affected by anemia. Furthermore, mediating factors influence the perioperative outcomes. Think of it like this: alcohol use may affect anemia as well as postoperative infection; alcohol use is a confounding factor. On the other hand, wound contamination may be
Journal of PeriAnesthesia Nursing, Vol 29, No 1 (February), 2014: pp 62-64
RESEARCH NEWS
affected by anemia, but it has no causal effect on anemia. Yet, wound contamination, the mediating variable, does influence postoperative infection. When planning the analysis phase of the study, six factors were identified as potential mediators: intraoperative wound contamination, intraoperative red blood cell transfusion, length of surgery, functional dependence preoperatively, open wound preoperatively, and dyspnea. Potential confounders included the following: primary procedure, gender, race, age, height, body mass index, living situation before admission, smoker status, alcohol use, diabetes, chronic obstructive pulmonary disease, myocardial infarction, previous percutaneous coronary intervention, previous cardiac surgery, angina, hypertension, revascularization or amputation for peripheral vascular disease, transient ischemic attack, stroke with and without neurologic deficit, do not resuscitate status, ventilator dependence, pneumonia, ascites, esophageal varices, acute renal failure, preoperative dialysis, cancer, impaired sensorium, coma, hemiplegia, paraplegia/quadriplegia, steroid use, weight loss, pregnancy, inpatient surgery, general anesthesia, and American Society of Anesthesiologists status. The decision to classify these variables into mediators and confounders was based on clinical considerations as determined by a panel of three independent anesthesiologists. The independent variable, preoperative anemia, was evaluated in relation to 30-day postoperative mortality and morbidity outcomes. Particularly, the nine outcomes were the following: mortality, wound infection, return to surgery, respiratory complications, systemic complications, urinary complications, central nervous system complications, thrombotic complications, and cardiovascular complications. Cases (N 5 971,455) from the National Surgical Quality Improvement Program database were retrospectively evaluated for inclusion in the study. Of the 574,860 eligible cases, 145,218 were anemic (based on the World Health Organization definition) at baseline. Researchers matched non-anemic patients to this cohort and adjusted for differences by using propensity scores. Basically, the researchers balanced the pairs to yield greater precision in the results. These ‘‘fine print’’ details are important in noting the quality of the analysis.
63
Results Researchers reported total effect odds ratios (controlling for only confounding factors) for postoperative complications as well as direct effect odds ratios (controlling for both confounding and mediating factors). The total effect of anemia was statistically significant for: systemic, cardiovascular, respiratory, urinary, and thrombotic complications; return to surgery; and mortality. The direct effects were all lower. In fact, the total effect odds ratio ranged from 1.20 to 1.30, except for mortality, which was 1.59. However, the direct effect odds ratio was 1.24 for mortality and ranged between 0.95 and 1.13 for the other outcomes. This suggests that anemia may affect these outcomes only through mediating factors—not directly.
Conclusions Because preoperative anemia is a common consideration, it is worthwhile to understand its role on perioperative outcomes. To state that the presence of preoperative anemia alone leads to particular postoperative complications is too generic. A more thorough assessment of the factors at play is necessary to understand the complex relationships that exist in patients with anemia. Preoperative Anemia and Perioperative Outcomes in Patients Who Undergo Elective Spine Surgery by Seicean A, Seicean S, Alan N, et al. Spine. 2013;38:1331-1341.
Background and Purpose Like the first report, this manuscript was reviewed in January 2013. Another commonality is the presence of researchers from Cleveland Clinic in Ohio. Although they were reviewed around the same time, this second article was accepted and published a few months before the first one. Therefore, this study was publicly available first, but it was not available as reference for the study by Saager et al. Also of note is that external funding was available from the Agency for Healthcare Research and Quality. The significance of anemia in the surgical population was noted, along with a void in the literature for the effect of anemia on postoperative complications for patients undergoing elective spine surgery. Some references cited to support this study
MARY W. STEWART
64
were also included in the most recent publication. The purpose of this report was to assess the influence of preoperative anemia on perioperative outcomes in this particular group.
was included in the statistical analysis, study outcomes for the patients with severe anemia did not reach a level of significance.
Conclusions Method and Analysis Researchers analyzed data from the American College of Surgeons National Surgical Quality Improvement Program database. In this study, 24,473 adults who underwent elective spine surgery were categorized into degrees of anemia: severe (0.4%); moderate (1.3%); and mild (22.4%). Postoperative complications within 30 days of surgery were assessed for each group of patients with anemia as well as those who did not have preoperative anemia. In addition to laboratory values, factors included in the analysis were age, gender, race, residence before admission, smoking status, functional dependency, American Society of Anesthesiologists classification, body mass index, pulmonary comorbidities, cardiovascular comorbidities, hypertension, dyspnea, central nervous system comorbidities, renal comorbidities, diabetes, cancer, open wound, recent weight loss, steroid use, chemotherapy/radiotherapy, sepsis, bleeding disorder, and previous surgery.
This observational study added to the dialogue surrounding the influence of anemia preoperatively on postoperative outcomes. Patients who had anemia versus those who did not were more likely to experience extended lengths of stay. It is not clear why the odds for complications were lower for those with severe anemia. Perhaps, the small sample size of that group (N 5 88) played a role. Nonetheless, these researchers suggested that the risks for complications justified delaying elective spine surgery for patients with preoperative anemia.
Perianesthesia Nursing Implications If taken as presented—simply and digestible—we might be tempted to route patients with anemia toward non-surgical interventions. Is this based on real data? Does it differ depending on how the data are manipulated or analyzed? What does this tell us as perianesthesia specialists about taking care of patients with anemia?
Propensity scores and matching between anemic patients to non-anemic patients were also used to achieve a less biased measure of the relationships between anemia and the outcomes of interest. Covariates (confounding variables) that remained unbalanced after the matching were included in the analysis. No variables were identified as potentially mediating factors.
As perianesthesia nurses, we consider the whole. We have to read the fine print. Sometimes, we have to get an interpreter for the jargon. Our patients depend on us to do that kind of detailed work. We cannot ignore the complexity that exists in human pathophysiology. Neither can we presume the presence of absolutes. Sometimes, there is not a clear answer.
Outcomes of interest included prolonged length of hospital stay, which was defined as 4 days in this sample. Complications (minor and major), return to surgery, and mortality were also measured.
First of all, we are to focus on real risks. These reports differ in their conclusions about the independent power of a preoperative anemia condition on postoperative outcomes. This example of scientific dialogue tells us a couple of things: (1) there is enough evidence to date that implies preoperative anemia is a serious consideration and (2) researchers and practitioners are continually learning how that condition affects patient outcomes. Our responsibility is to stay informed of the discussion, be alert for perianesthetic and perioperative experiences when patients are diagnosed with anemia, and assure our patients that we are their quality assurance agents throughout the process.
Results Of the total, 7.5% (n 5 1,845) had one or more complication; 3.1% (n 5 749) returned to surgery within 30 days; and 0.1% (n 5 101) died within the same time period. The mean length of stay was 3 days overall and lowest for the non-anemic patients. Those in the moderate anemia group had the most complications, including the longest length of stay. Even when propensity matching
Preoperative Anemia and Postoperative Outcomes Mary W. Stewart, PhD, RN WHEN IT COMES TO READING research reports, we all hope for something straight forward. We want a clearly stated purpose, easy-to-follow methodology, and uncomplicated statistical analysis. Ultimately, we would like to skip to the Implications section and trust that what is reported is accurate. This is no different than the average person who avoids legal jargon and fine print. We may assume that those details are unimportant. Regardless, we do not have time to weed through the foreign language, so we quickly mark the ‘‘I accept the terms’’ statement and get on our way. Nurses recognize this as a haphazard approach to accepting contracts, adopting research findings, and making evidence-based practice decisions. We are accountable for the obvious data, as well as that which may be perplexing and subtle. Without the whole account—in a surgical consent document, a contract for employment, and research purporting practice guidelines—we may find ourselves in a quandary. In this column, the author attempts to translate relevant information from reputable sources that will empower the perianesthesia nurse with knowledge learned from good research. The challenge includes presenting a fair appraisal of diverse perspectives. Similar to two lawyers debating the meaning of a particular regulation, scientists deliberate the significance of data. In the two studies that follow, researchers investigated the same topic (preoperative anemia and perioperative outcomes) using the same information (the American Mary W. Stewart, PhD, RN, is a Professor and Director of the PhD program, Special Assistant to the Dean, School of Nursing, University of Mississippi Medical Center, Jackson, MS. Conflict of interest: None to report. Address correspondence to Mary W. Stewart, School of Nursing, University of Mississippi Medical Center, 2500 North State, Street, Jackson, MS 39216-4505; e-mail address: [email protected]. Ó 2014 by American Society of PeriAnesthesia Nurses 1089-9472/$36.00 http://dx.doi.org/10.1016/j.jopan.2013.11.005
62
College of Surgeons National Surgical Quality Improvement Program database). Nevertheless, their conclusions are not in agreement. The Association between Preoperative Anemia and 30-Day Mortality and Morbidity in Noncardiac Surgical Patients by Saager L, Turan A, Reynolds L, Dalton J, Mascha E, Kurz A. Anesthesia & Analgesia. 2013;117:909-915.
Background and Purpose Patients with anemia present unique considerations when undergoing surgery. This population requires more intraoperative blood transfusions, and those transfusions introduce another set of potential complications. Previous studies on preoperative anemia using established databases have generalized that patients with anemia have poorer postoperative outcomes. The problem is that generalizations do not necessarily fit the whole population. The purpose of this study was to assess the relationship between preoperative anemia and postoperative mortality and morbidity outcomes in noncardiac surgical patients. Special emphasis was placed on the necessity to distinguish variables as confounding or mediating before analysis.
Method and Analysis These authors challenge the conclusions of similar studies and conduct their own analysis, differentiating variables that may influence postoperative issues. These variables are classified as confounding factors and mediating factors. Confounding factors are thought to have a direct line of influence on anemia as well as the perioperative outcomes. Mediating factors are those that do not have influence on anemia; rather they are affected by anemia. Furthermore, mediating factors influence the perioperative outcomes. Think of it like this: alcohol use may affect anemia as well as postoperative infection; alcohol use is a confounding factor. On the other hand, wound contamination may be
Journal of PeriAnesthesia Nursing, Vol 29, No 1 (February), 2014: pp 62-64
RESEARCH NEWS
affected by anemia, but it has no causal effect on anemia. Yet, wound contamination, the mediating variable, does influence postoperative infection. When planning the analysis phase of the study, six factors were identified as potential mediators: intraoperative wound contamination, intraoperative red blood cell transfusion, length of surgery, functional dependence preoperatively, open wound preoperatively, and dyspnea. Potential confounders included the following: primary procedure, gender, race, age, height, body mass index, living situation before admission, smoker status, alcohol use, diabetes, chronic obstructive pulmonary disease, myocardial infarction, previous percutaneous coronary intervention, previous cardiac surgery, angina, hypertension, revascularization or amputation for peripheral vascular disease, transient ischemic attack, stroke with and without neurologic deficit, do not resuscitate status, ventilator dependence, pneumonia, ascites, esophageal varices, acute renal failure, preoperative dialysis, cancer, impaired sensorium, coma, hemiplegia, paraplegia/quadriplegia, steroid use, weight loss, pregnancy, inpatient surgery, general anesthesia, and American Society of Anesthesiologists status. The decision to classify these variables into mediators and confounders was based on clinical considerations as determined by a panel of three independent anesthesiologists. The independent variable, preoperative anemia, was evaluated in relation to 30-day postoperative mortality and morbidity outcomes. Particularly, the nine outcomes were the following: mortality, wound infection, return to surgery, respiratory complications, systemic complications, urinary complications, central nervous system complications, thrombotic complications, and cardiovascular complications. Cases (N 5 971,455) from the National Surgical Quality Improvement Program database were retrospectively evaluated for inclusion in the study. Of the 574,860 eligible cases, 145,218 were anemic (based on the World Health Organization definition) at baseline. Researchers matched non-anemic patients to this cohort and adjusted for differences by using propensity scores. Basically, the researchers balanced the pairs to yield greater precision in the results. These ‘‘fine print’’ details are important in noting the quality of the analysis.
63
Results Researchers reported total effect odds ratios (controlling for only confounding factors) for postoperative complications as well as direct effect odds ratios (controlling for both confounding and mediating factors). The total effect of anemia was statistically significant for: systemic, cardiovascular, respiratory, urinary, and thrombotic complications; return to surgery; and mortality. The direct effects were all lower. In fact, the total effect odds ratio ranged from 1.20 to 1.30, except for mortality, which was 1.59. However, the direct effect odds ratio was 1.24 for mortality and ranged between 0.95 and 1.13 for the other outcomes. This suggests that anemia may affect these outcomes only through mediating factors—not directly.
Conclusions Because preoperative anemia is a common consideration, it is worthwhile to understand its role on perioperative outcomes. To state that the presence of preoperative anemia alone leads to particular postoperative complications is too generic. A more thorough assessment of the factors at play is necessary to understand the complex relationships that exist in patients with anemia. Preoperative Anemia and Perioperative Outcomes in Patients Who Undergo Elective Spine Surgery by Seicean A, Seicean S, Alan N, et al. Spine. 2013;38:1331-1341.
Background and Purpose Like the first report, this manuscript was reviewed in January 2013. Another commonality is the presence of researchers from Cleveland Clinic in Ohio. Although they were reviewed around the same time, this second article was accepted and published a few months before the first one. Therefore, this study was publicly available first, but it was not available as reference for the study by Saager et al. Also of note is that external funding was available from the Agency for Healthcare Research and Quality. The significance of anemia in the surgical population was noted, along with a void in the literature for the effect of anemia on postoperative complications for patients undergoing elective spine surgery. Some references cited to support this study
MARY W. STEWART
64
were also included in the most recent publication. The purpose of this report was to assess the influence of preoperative anemia on perioperative outcomes in this particular group.
was included in the statistical analysis, study outcomes for the patients with severe anemia did not reach a level of significance.
Conclusions Method and Analysis Researchers analyzed data from the American College of Surgeons National Surgical Quality Improvement Program database. In this study, 24,473 adults who underwent elective spine surgery were categorized into degrees of anemia: severe (0.4%); moderate (1.3%); and mild (22.4%). Postoperative complications within 30 days of surgery were assessed for each group of patients with anemia as well as those who did not have preoperative anemia. In addition to laboratory values, factors included in the analysis were age, gender, race, residence before admission, smoking status, functional dependency, American Society of Anesthesiologists classification, body mass index, pulmonary comorbidities, cardiovascular comorbidities, hypertension, dyspnea, central nervous system comorbidities, renal comorbidities, diabetes, cancer, open wound, recent weight loss, steroid use, chemotherapy/radiotherapy, sepsis, bleeding disorder, and previous surgery.
This observational study added to the dialogue surrounding the influence of anemia preoperatively on postoperative outcomes. Patients who had anemia versus those who did not were more likely to experience extended lengths of stay. It is not clear why the odds for complications were lower for those with severe anemia. Perhaps, the small sample size of that group (N 5 88) played a role. Nonetheless, these researchers suggested that the risks for complications justified delaying elective spine surgery for patients with preoperative anemia.
Perianesthesia Nursing Implications If taken as presented—simply and digestible—we might be tempted to route patients with anemia toward non-surgical interventions. Is this based on real data? Does it differ depending on how the data are manipulated or analyzed? What does this tell us as perianesthesia specialists about taking care of patients with anemia?
Propensity scores and matching between anemic patients to non-anemic patients were also used to achieve a less biased measure of the relationships between anemia and the outcomes of interest. Covariates (confounding variables) that remained unbalanced after the matching were included in the analysis. No variables were identified as potentially mediating factors.
As perianesthesia nurses, we consider the whole. We have to read the fine print. Sometimes, we have to get an interpreter for the jargon. Our patients depend on us to do that kind of detailed work. We cannot ignore the complexity that exists in human pathophysiology. Neither can we presume the presence of absolutes. Sometimes, there is not a clear answer.
Outcomes of interest included prolonged length of hospital stay, which was defined as 4 days in this sample. Complications (minor and major), return to surgery, and mortality were also measured.
First of all, we are to focus on real risks. These reports differ in their conclusions about the independent power of a preoperative anemia condition on postoperative outcomes. This example of scientific dialogue tells us a couple of things: (1) there is enough evidence to date that implies preoperative anemia is a serious consideration and (2) researchers and practitioners are continually learning how that condition affects patient outcomes. Our responsibility is to stay informed of the discussion, be alert for perianesthetic and perioperative experiences when patients are diagnosed with anemia, and assure our patients that we are their quality assurance agents throughout the process.
Results Of the total, 7.5% (n 5 1,845) had one or more complication; 3.1% (n 5 749) returned to surgery within 30 days; and 0.1% (n 5 101) died within the same time period. The mean length of stay was 3 days overall and lowest for the non-anemic patients. Those in the moderate anemia group had the most complications, including the longest length of stay. Even when propensity matching