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Department of Cardiothoracic-Vascular Anesthesia and Intensive Care, IRCCS Policlinico S. Donato, Milan, Italy
Accepted for publication July 31, 2008.
* Address correspondence to Dr Ranucci, Department of Anesthesia and Intensive Care, IRCCS Policlinico S. Donato, Via Morandi 30, San Donato Milanese, Milan, 20097, Italy (Email: cardioanestesia{at}virgilio.it).
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Abstract |
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Methods: This was a retrospective study of 232 patients having undergone surgical reexploration owing to postoperative bleeding after cardiac operations, compared with a control, propensity-matched group.
Results: Patients in the surgical reexploration group had greater morbidity (low cardiac output, acute renal failure, sepsis) and longer mechanical ventilation time and intensive care unit stay than did control patients, and a significantly higher mortality rate (14.2% versus 3.4%, p = 0.001). The timing of surgical reexploration was not associated with morbidity or mortality. The amount of packed red cells transfused was significantly associated with increased morbidity (acute renal failure, low cardiac output syndrome, sepsis), with mechanical ventilation time and intensive care unit stay, and with the mortality rate (0.25% increase for each unit transfused).
Conclusions: The main determinant of morbidity and mortality for patients requiring a surgical reexploration after cardiac operations is the amount of packed red cells transfused. Delaying the timing of reexploration may represent a risk factor only when the delay creates the need for an excessive use of allogeneic blood products, or in the presence of clinical signs of cardiac tamponade.
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Introduction |
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Recently, Choong and coworkers [4] demonstrated that delaying surgical reexploration after 12 hours from the end of the operation results in a longer intensive care unit (ICU) stay, a higher need for intra-aortic balloon pump support, and increased mortality in a population of patients having undergone coronary revascularization. Similar information was published in 2004 by Karthik and coworkers [5], who could demonstrate, using a propensity-matched control group, that patients needing a surgical reexploration have a worse outcome in terms of morbidity (low cardiac output, renal failure, prolonged mechanical ventilation, and ICU/hospital stay) but not a significantly higher mortality rate. Moulton and coworkers [6] found a significantly higher mortality rate together with an increased risk of renal failure, sepsis, and need for prolonged ventilation in the group needing reexploration. Owing to the limited number of patients studied, or to patient selection (only coronary patients), the role of reexploration in worsening the postoperative outcome remains unclear. Moreover, the impact of reexploration timing and the relationship among reexploration timing, blood products used, and outcome variables are in need of further study.
The present retrospective, propensity-matched study is aimed to assess first, morbidity and mortality rates in patients needing surgical reexploration after cardiac operations versus control patients, and second, the association between reexploration timing and the use of blood products on the postoperative outcome, in terms of morbidity and mortality rates, in a population of patients having undergone different kinds of cardiac surgical procedures.
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Patients and Methods |
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TopAbstractIntroductionPatients and MethodsResultsCommentReferences |
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Patients
The study group comprised all the patients having undergone surgical reexploration because of bleeding. The exclusion criterion was a primary operation for congenital heart disease in patients less than 18 years of age. The patients had received surgical operations with cardiopulmonary bypass (CPB) for different kinds of cardiac pathologies, excluding cardiac transplantation.
The control group of patients who had not undergone surgical reexploration was created using a propensity-score approach.
Intraoperative Anesthetic Management and Cardiopulmonary Bypass
Anesthesia was induced and maintained with intravenous agents. All the patients received tranexamic acid intravenously at 15 mg/kg before CPB and at 15 mg/kg after protamine administration. Aprotinin was never used (it is not commercially available in Italy).
Cardiopulmonary bypass was conducted using either closed or open circuits, standard or phosphorylcholine-coated hollow-fiber oxygenators, and roller or centrifugal pumps according to availability. Regardless of the circuit used, the priming volume was always minimized to 800 to 1,000 mL. A cell-saving device was used to process blood remaining in the cardiotomy reservoir at the end of the operation, if the amount was more than 300 mL.
Blood and Derivates Management
The transfusion threshold for packed red cells usually settled at a hemoglobin value of 6 g/dL during CPB and 8 g/dL in the ICU. According to our local policy, none of the mediastinal blood collected in the cardiotomy reservoir was used to transfuse the patients.
Surgical Reexploration Policy
At our institution, the following conditions usually lead to a surgical reexploration: (1) drainage of more than 500 mL during the first hour, more than 400 mL during each of the first 2 hours, more than 300 mL during each of the first 3 hours, or more than 1,000 mL in total during the first 4 hours; (2) subtle, continuous bleeding throughout the first 12 hours, leading to a total bleeding exceeding 100 mL/hour; (3) sudden massive bleeding; (4) obvious signs of cardiac tamponade; (5) excess bleeding despite correction of coagulopathies; and (6) cardiac arrest of a patient who continues to bleed. This scheme is within a decision-making framework, and individual clinical conditions may lead to different decisions.
Data Collection and Definitions
The preoperative risk profile was assessed according to the EuroSCORE (European System for Cardiac Operative Risk Evaluation) [7]. Operative data included type of operation and CPB duration (minutes). For surgical reexploration, only reexploration for postoperative bleeding has been included; reoperations for other reasons were not considered. Timing of reexploration was defined as number of hours after the arrival of the patients to the ICU. Thirteen time intervals were settled upon: 1-hour intervals within the first 12 hours and 1 single interval for patients undergoing reexploration after more than 12 hours. Allogeneic blood products used were defined as the number of units of packed red cells (PRCs), fresh frozen plasma (FFP), and platelets (PLTs) transfused during the hospital stay.
Outcome variables were postoperative blood loss (mL) during the first 12 hours after the initial arrival to the ICU; peak serum creatinine value (mg/dL); acute renal failure (peak serum creatinine value > 2 mg/dL and twice the baseline value); low cardiac output (need for inotropes for more than 24 hours); need for an intra-aortic balloon pump (IABP); myocardial infarction (new Q waves plus enzymatic criteria); severe lung dysfunction (need for more than 48 hours of mechanical ventilation owing to poor arterial blood gas analyses); stroke; sepsis; mesenteric infarction; composite morbidity index (with one of the following: low cardiac output, myocardial infarction, IABP, stroke, acute renal failure, sepsis, mesenteric infarction); mechanical ventilation time (hours); ICU stay (days); hospital mortality (within 30 days from the operation).
Statistical Analysis
The control group of patients not requiring surgical reexploration was extracted from the general file using a propensity score-based technique, and following these subsequent steps. (1) All the preoperative and intraoperative variables have been explored for univariate association with postoperative surgical reexploration using a relative risk analysis for binary variables and a logistic regression analysis for continuous variables. Factors being associated at a p value less than 0.05 were admitted to the next step. (2) A multivariable logistic regression analysis was applied to create a predictive model for surgical reexploration. The model included only independent predictors of surgical reexploration. (3) Patients in the surgical reexploration group were divided into deciles according to their propensity of being surgically reexplored (from 0% to 100%). (4) Patients not requiring a surgical reexploration were assessed for their propensity of being surgically reexplored, and divided into deciles according to their score. (5) For each decile, we have randomly extracted a number of control patients equal to the correspondent number of surgically reexplored patients. The final control group was therefore created, including patients having a surgical reexploration risk similar to the one of the study group.
Differences between the two groups were explored using a Pearson's 
2 for categorical binary variables and a Student's t test for continuous variables. Differences in outcome variables between the two groups were explored with a Student's t test for continuous variables and a relative risk analysis for categorical binary variables.
Associations between timing of surgical reexploration, number of PRCs transfused, and outcome variables were explored using a logistic regression analysis. Adequate multivariable analyses have been applied for assessing the role of potential confounding factors.
The data in tables are reported as mean and standard deviation of the mean, median, and range, or as a count and percentage. A p value less than 0.05 was considered significant for all the statistical tests. Statistical calculations were performed using a computerized statistical program (SPSS version 11.0; SPSS Inc, Chicago, IL).
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Results |
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The propensity-matched control group was created according to the above risk factors, following the technique explained in the methods section. The two group were homogeneous with respect to preoperative and intraoperative variables (Table 1).
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Comment |
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The first comment addressing our results confirms the findings of Choong and coworkers [4], and Karthik and coworkers [5], who demonstrated that delaying surgical reexploration may represent a morbidity risk factor only after 12 hours from the arrival to the ICU. In our series, only 18 patients were reexplored after more than 12 hours, and therefore we are lacking the power for addressing this subgroup. Our data support the hypothesis that no time-related differences in outcome are detectable within the first 12 hours.
The clinical indicator for surgical reexploration in the presence of bleeding is, of course, the magnitude of the blood loss. However, this blood loss is usually assessed in terms of milliliters per hour. That means that patients having very early reexploration surgery are usually suffering from acute blood loss within the first 2 to 3 hours, usually exceeding 500 mL. Postoperative blood loss is not associated with the timing of reexploration. Therefore, the amount of blood products used to maintain an adequate hemoglobin level during the bleeding period is not different depending on the timing of reexploration, at least until the 12th hour. Patients receive, more or less, the same amount of blood products within the first 12 hours, because patients receive more blood products per hour in a limited period of time (early reexploration) or less blood products per hour in a longer period of time (late reexploration). Conversely, patients undergoing reexploration after more than 12 hours received significantly higher volumes of PRCs and FFP.
The amount of allogeneic blood products transfused is a major determinant of morbidity and mortality in our patient population. The deleterious effects of blood products are well known in the setting of cardiac surgery [8–10], and the present study confirms that the amount of blood products used is associated with many adverse effects. This information is confirmed in our control, propensity-matched group, even with some interesting differences. Mortality risk is always higher in the surgical reexploration group when the number of PRCs transfused is limited to less than 6 units, than the two functions become closer. Patients in need for massive PRCs transfusions have a higher mortality risk if not surgically reexplored. Our interpretation is that patients not needing a surgical reexploration are receiving PRCs for two reasons: correction of hemodilution or limited bleeding, or both; and the need for maintaining adequate hemoglobin levels within the context of a prolonged, complicated postoperative ICU stay. In the first case, the number of PRCs units is limited, and the mortality risk is moderately increased if the patient receives 6 units or less; in the second case, PRCs transfusions are both an epiphenomenon of the chronic conditions of the patient, and a cause of increased mortality at the same time. In the surgical reexploration group, PRCs are always transfused to maintain an acceptable hemoglobin level in the context of a bleeding patient and within a limited amont of time; under these conditions, they represent a risk factor for mortality, with an almost linear increase of about 0.25% per each unit of PRCs transfused.
In their articles, Choong and coworkers [4] did not observe any difference in outcome when allogeneic blood and derivates were used for transfusions, and Karthik and associates [5] did not address this point.
Considering that the major determinant of morbidity and mortality in patients undergoing reexploration is the amount of PRCs transfused, our study suggests that reexploration may be delayed even after 12 hours without an increase in morbidity or mortality, provided that the patient is not in need of a large amount of PRCs, and of course unless the patient has clinical signs of cardiac tamponade.
Considering that PRC transfusions are generally triggered by the hemoglobin value, this means that other factors should be considered when deciding the timing for a surgical reexploration. Among these, the most important is probably the hemoglobin value at the arrival to the ICU, and its subsequent changes. Of course, a patient reaching the ICU with a low hemoglobin value will require markedly more PRCs transfused to maintain an acceptable hemoglobin value throughout the postoperative bleeding period. Conversely, patients with a high hemoglobin value may be treated with less PRCs during transfusions. Another factor to be considered in the decision process is the hemodynamic profile of the patient. Delaying surgical reexploration in the presence of hemodynamic instability and difficult maintenance of an adequate filling volume may result in a prolonged period of impaired oxygen delivery to the peripheral organs.
Therefore, the surgical reexploration should be conducted earlier in the presence of low hemoglobin levels and unstable hemodynamics. Conversely, surgical reexploration can be safely delayed in the presence of an acceptable level of hemoglobin, with the evidence that this level can be maintained without excessive PRC transfusions, and a stable hemodynamic profile. This "conservative" strategy, aimed to avoid surgical reexploration, has a clinical rationale. As a matter of fact, reexploration itself induces a mortality rate that is higher than 3% even in the absence of PRC transfusions (Fig 3).
There are two main limitations of our study. The first one is that we could not evaluate the role of different strategies in maintaining the hemoglobin level at an acceptable value during the bleeding period, namely, the reinfusion of mediastinal blood from the cardiotomy reservoir. This strategy may limit the need for allogeneic PRC transfusions and surgical reexploration [11], but previous studies have highlighted the possible deleterious effects of this technique [12, 13]. The second limitation is that our finding of the increased mortality in undergoing reexploration patients (double than predicted with the EuroSCORE) is mainly dependent on the amount of PRCs transfused does not explain why patients receiving very few PRCs still experience a high mortality rate. Other factors directly linked to the reexploration itself should be considered in further studies.
In conclusion, this study confirms that patients needing a surgical reexploration for postoperative bleeding experience a severe increase in morbidity and mortality, and demonstrates that the amount of allogeneic blood products used during the bleeding period is a risk factor for patient outcome, and excludes postoperative complications as being simply related to the timing of surgical reexploration.
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References |
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