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© 1999 International Anesthesia Research Society
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Abstract |
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We conducted a retrospective review of 10 patients with sickle cell trait (SCT) and 30 patients (cohort control) without SCT undergoing first-time coronary artery bypass graft surgery with cardiopulmonary bypass. Demographic, perioperative management, and outcome data were collected. Both groups were matched according to age, weight, duration of surgery, and preoperative hemoglobin (Hb) concentration. Distribution of gender, medical conditions, pharmacological treatment, and preoperative left ventricular function were similar between the groups. The comparisons were analyzed in respect to postoperative blood loss and transfusion rates, as well as duration of intubation, intensive care unit, and hospital length of stay (LOS). All patients underwent fast-track cardiac anesthesia. A combination of cold crystalloid and blood cardioplegia was used. The lowest nasopharyngeal temperature was 33°C. There were no episodes of significant hypoxemia, hypercarbia, or acidosis. None of the patients had sickling crisis during the perioperative period. The postoperative blood loss was 687 ± 135 vs 585 ± 220 mL in the SCT and control groups, respectively. The trigger for blood transfusion during cardiopulmonary bypass was hematocrit <20% and Hb <75 g/L postoperatively. Three SCT patients (30%) and 10 control patients (33%) received a blood transfusion. Median extubation time was 4.0 vs 3.9 h; intensive care unit LOS was 27 vs 28 h; and hospital LOS was 6.0 vs 5.5 days in the SCT and control groups, respectively. There were no intraoperative deaths. One patient in the SCT group died from multiorgan failure 2 mo after surgery.
Implications: Fast-track cardiac anesthesia can be used safely in patients with sickle cell trait undergoing first-time coronary artery bypass graft surgery. Extubation time and intensive care unit and hospital length of stay are comparable to those of matched controls, and blood loss and transfusion requirements are not increased. A hematocrit of 20% seems to be a safe transfusion trigger during cardiopulmonary bypass in these patients.
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Introduction |
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Sickle cell hemoglobinopathies represent an inherited disorder that ranges from the usually benign sickle cell trait (SCT) to the potentially fatal sickle cell anemia. The degree of abnormality and the quantity of sickle cell hemoglobin (HbS) dictate the clinical severity of the disease. Sickle cell disease (SCD) is represented by a homozygous genotype (HbSS), in which the fractional concentration of HbS varies from 70% to 98%. The SCT is a heterozygote (HbAS) manifestation of SCD with the concentration of HbS <50%. Confirmation of the presence of HbS is dependent on hemoglobin electrophoretic studies.
Patients with sickle cell abnormalities who undergo surgery are generally considered to be at greater risk of perioperative complications (1,2). The classical precipitants that induce sickling are hypoxia, dehydration, acidosis, exposure to cold, stress, and intercurrent infections. Under these circumstances, the globin chains form an insoluble polymer, therefore increasing blood viscosity and causing vasoocclusive phenomena. The use of cardiopulmonary bypass (CPB), low-flow states, aortic cross-clamping, topical hypothermia, and cold crystalloid cardioplegia may all predispose patients to sickling crisis during cardiac surgery.
Fast-track cardiac anesthesia is becoming a standard of cardiac surgical care. This practice has been established as safe and cost-effective (3,4). The prevalence of SCD among African Americans is approximately 0.2%, but that of SCT is much higher, reaching 10%. It seems that individuals with SCT require cardiac surgery at the same rate as people without this condition. In this article, we report the perioperative management of 10 patients with SCT who underwent fast-track cardiac anesthesia.
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Methods |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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With institutional ethics committee approval, we conducted a retrospective review of 10 patients with SCT and 30 patients without SCT undergoing first-time coronary artery bypass graft (CABG) surgery with CPB over a 2-yr period. Relevant demographic and perioperative management data, duration of surgery, length of stay (LOS) in the intensive care unit (ICU), duration of hospitalization, and outcomes were recorded. To reflect the overall indices of perfusion and oxygenation in the study, the perioperative changes in hemodynamic, respiratory, and metabolic variables were documented. The lowest pre- and postoperative hemoglobin (Hb) concentrations, intraoperative hematocrit (Hct), postoperative blood loss, and blood transfusion rates were recorded.
The SCT and control groups were matched according to demographic data (age, weight, duration of surgery) and preoperative Hb concentration. Blood loss from chest drains (24 h after surgery), transfusion rates, duration of intubation, and ICU and hospital LOS were assessed in all patients.
All patients presented with unstable angina and receiving maximal medical treatment, including ß-adrenergic blocking drugs, calcium channel antagonists, nitrates and angiotensin-converting enzyme inhibitors. Seven patients had a history of hypertension and myocardial infarction, five had coexisting diabetes mellitus, and three had had previous strokes with no focal neurological deficit. Two patients had renal dysfunction preoperatively, and one had mild asthma. The preoperative left ventricular (LV) function was grade 1–3 (based on preoperative angiography findings: 1 = >60%, 2 = 40%–59%, 3 = 21%–39%, and 4 = <20% ejection fraction).
All patients were cared for under our current fast-track cardiac anesthesia protocol. Usual cardiac medications were continued up to the morning of surgery. Patients received premedication with sublingual lorazepam 2 mg 1–2 h before surgery. After preoxygenation, anesthesia was induced with midazolam 0.05–0.1 mg/kg, fentanyl 10–15 µg/kg, and either propofol 0.5–1 mg/kg or thiopental 1–2 mg/kg. Muscle relaxation was achieved with pancuronium 0.1 mg/kg. After tracheal intubation, controlled ventilation with 100% oxygen was commenced, and anesthesia maintained with isoflurane. A propofol infusion 2–6 mg · kg-1 · h-1 was commenced on initiation of CPB and was continued into the postoperative period in the ICU. Propofol sedation was stopped when the patient fulfilled the criteria for extubation (3,4). Postoperative pain relief was achieved with intermittent morphine injections, indomethacin suppositories, and acetaminophen. Tranexamic acid 50 mg/kg was used routinely in all cases.
Routine monitoring included continuous direct arterial blood pressure, central venous pressure, pulmonary artery catheter, electrocardiography (leads II and V) with continuous ST-segment analysis and trending, pulse oximetry, capnography, and nasopharyngeal temperature measurements.
Data are expressed as mean ± SD or median (range). Statistical comparisons were made with t-tests and Fisher's exact test where appropriate. A P value <0.05 was considered significant.
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Results |
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None of the patients had a sickling crisis perioperatively. Distribution of gender, medical conditions, pharmacological treatment, and preoperative LV function were similar between the groups. A comparison of demographic data between patients with and without SCT is listed in Table 1. Left internal thoracic artery conduit was used in all patients.
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The CPB circuit was primed with a mixture of crystalloid and colloid solutions (2236 ± 48 mL), 100 mL of mannitol 25%, and 50 mL of sodium bicarbonate 8.4%. A combination of intermittent cold (4°C) crystalloid and blood cardioplegia (range 32–34°C) was applied. The mean flow rate was 4.8 ± 0.8 L/min, and perfusion pressure ranged from 65 to 75 mm Hg. None of the patients underwent active systemic cooling or experienced circulatory arrest. Urine output during CPB was 365 ± 124 vs 395 ± 142 mL in the SCT and control groups, respectively. No topical cooling was used. Intraoperative nasopharyngeal temperature range was 33–35°C. All patients were actively rewarmed to 37–38°C before separation from CPB. No pharmacologically induced diuresis was used. Warming blankets were applied postoperatively to maintain an adequate body temperature.
There was a reduction in mean arterial blood pressure (MAP) and cardiac output (CO) during the intraoperative period in both groups. The MAP decreased from baseline by 30% in the SCT group and by 27% in the control group. The reduction in CO was not as dramatic: 18% vs 15% in SCT and control groups, respectively. Both the CO and MAP returned toward baseline in the 24-h period after surgery. There were no significant episodes of hypoxemia, hypercarbia, or acidosis in either group.
The mean preoperative Hb concentration was 126 ± 11 and 126 ± 16 g/L in the SCT and control groups, respectively. The mean preoperative fractional concentration of HbS in the SCT group was 34% ± 2%. It decreased to 25% ± 11.5% in the postoperative period secondary to blood transfusion (Table 2). An overall reduction of Hb concentration after surgery was significant in both groups (P < 0.0002). Three SCT and 10 control patients received blood transfusions in the perioperative period. The pump blood and postoperative autotransfusion of mediastinal blood were not used to limit mechanically induced red cell damage in the SCT group. There was no significant difference between SCT and control patients with respect to mean postoperative blood loss and transfusion rates (Table 3).
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There were no intraoperative deaths. One patient in the SCT group died 58 days after surgery. There were no deaths in the control group. Details of the patient who died are summarized below.
A 66-yr-old man with a history of diabetes, hypertension, mild stroke, and renal impairment developed unstable angina and underwent urgent quintuple CABG. He required considerable inotropic support and insertion of an intraaortic balloon pump to enable separation from CPB. Echocardiography revealed grade 3 LV function. The next day, he developed acute renal failure and pulmonary edema. Dialysis was commenced with some improvement. The patient was extubated on the sixth postoperative day with stable hemodynamics. Unfortunately, 2 days later, he developed respiratory insufficiency secondary to pneumonia and required reintubation. This was followed by tracheostomy to facilitate weaning. He responded well and was eventually weaned from the ventilator and transferred to the surgical floor. Two weeks later, the patient developed respiratory failure and sustained cardiac arrest. He was transferred back to the ICU, but despite initial improvement, he continued to deteriorate and eventually died from multiple organ failure. A postmortem examination was not performed.
Nine SCT and 30 control patients were alive at 6–36 mo during the postoperative follow-up period. Postoperative extubation time and length of ICU and hospital stays did not differ significantly between the SCT and control groups. Comparison of outcome data is shown in Table 4.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Most studies regarding the coexistence of sickle cell hemoglobinopathies and cardiac surgery are confined to either single (5–11) or serial (12–14) case report studies, and most are limited to children undergoing correction of congenital heart defects.
Fast-track cardiac anesthesia is becoming a common practice in North America. Optimization in anesthetic management, advances in myocardial protection, and improvement in surgical techniques allow cardiac patients to be safely extubated and mobilized early. The effects of fast-tracking on sickle cell patients have not yet been defined.
The presence of increased creatinine level and diabetes preoperatively in combination with low CO syndrome after separation from CPB predisposed Patient 7 to postoperative renal failure. Although there were no direct signs of sickling, the presence of SCT might have increased the risk of renal insufficiency and infection, leading to multiorgan failure, prolonged ICU stay, and death. The one death in the SCT group comprised a mortality of 10%. This mortality rate is higher than that previously reported for fast-track cardiac surgery patients, which ranged from 1.5% to 4% (3,4,15–17); however, to validate this finding, a much larger study would be necessary.
The actual mortality due to SCD-related multiorgan failure in a review of 3765 patients undergoing 1079 surgical procedures was rather low (0.8%); however, only 7 procedures were related to cardiovascular surgery (2). A retrospective analysis of 31 patients (30 HbAS and 1 HbSS) with a mean age of 17 years scheduled for cardiac surgery was undertaken in the West Indies (14). The four-week postoperative mortality was 26%. After review of autopsy data, the authors concluded that intravascular sickling was not responsible for the deaths after surgery. In their mixed series of adult and pediatric cardiac cases with sickle cell hemoglobinopathies (13 HbAS, 1 HbSC, 1 ß-thalassaemia) Metras et al. (12) reported that 2 of 15 patients died due to low CO state in the early postoperative period. Balasundaram et al. (13) reviewed successful management of five pediatric cases with SCD undergoing correction of congenital heart defects. The authors reported no mortality and highlighted the importance of preoperative exchange transfusion for patients with SCD.
It is generally accepted that patients with SCD undergoing major surgery require a reduction of HbS to <30% to avoid a potential sickling crisis (18). This is usually achieved by exchange transfusion, either preoperatively or intraoperatively (19,20). Howells et al. (21) suggested that blood transfusion in patients with SCD should be considered if the Hb concentration is <70 g/L; however, Koshy et al. (2) found no correlation between the rate of postoperative complications and the HbA level (which is directly proportional to the extent of red cell transfusion). A prospective multicenter study randomized 551 patients with SCD to receive either an aggressive transfusion regimen designed to decrease the HbS level to <30% or a conservative regimen to increase the Hb level to 100 g/L. The authors concluded that a conservative transfusion regimen was as effective as an aggressive regimen in preventing perioperative complications in patients with SCD. The conservative approach resulted in only half as many transfusion-associated complications (22).
It is less clear whether sickle cell carriers should be treated the same way. Exchange transfusions have been used in patients with SCT (23,24); however, there are reports of successful perioperative management of these patients with avoidance of exchange transfusions (5,25). None of the patients in our study received a blood transfusion preoperatively. There was a positive correlation between preoperative Hb concentration and requirements for transfusion. Only patients with preoperative Hb <120 g/L required blood during the perioperative period. This is in agreement with previous reports that identified preoperative Hb as a strong predictor for perioperative blood transfusion in patients undergoing cardiac surgery (26,27).
At our institution, blood transfusion during CPB is generally considered when the Hct approaches 18%; however, a recent article has questioned the wisdom of tolerating severe anemia during CPB for CABG surgery (28). A transfusion trigger for Hct as high as 25% for patients with SCT has been suggested (29). In the current series, a Hct value <20% triggered blood transfusion in the SCT group. We believe that this provides a fair safety margin for this subgroup of patients.
Blood transfusion therapy will continue to be part of the perioperative management of patients with sickle cell disorders. According to our institutional guidelines, perioperative blood transfusion for patients undergoing cardiac surgery is considered when the Hb concentration is <75 g/L in patients aged <70 years and <85 g/L for patients 
70 years old. It seems that the same guidelines can be applied for patients with SCT, as the overall postoperative blood loss and transfusion rates in our series were comparable in both groups of patients.
At no time perioperatively did blood oxygen tension approach critical levels, and blood pH was maintained within physiological limits. The reduction in MAP and CO during the intraoperative period was not sufficient to precipitate any clinically detectable sickling process. The fractional HbS concentration was not measured during CPB, but the postoperative results showed no increase in HbS. There seems to be no need to repeat Hb electrophoretic studies during or after uneventful surgery.
There are case reports of the successful management of patients with SCD applying topical and systemic hypothermia (6,10,13); however, it seems logical to avoid active cooling and reduce the potential risks of hypothermia. Temperature homeostasis management should be extended into the postoperative period to prevent vasoconstriction and stasis of blood flow, which—particularly in presence of low CO and shivering from residual body temperature gradients—may induce hypoperfusion of tissues, a factor well known to incite sickling. Oxygen extraction may increase dramatically during this stage, and if tissue hypoperfusion is not corrected, capillary venous PO2 may decrease to dangerous levels despite adequate arterial oxygenation. Using warming blankets during early postoperative recovery is highly recommended. Early use of incentive spirometry may be helpful in preventing pulmonary complications after cardiac surgery in patients with SCD (30).
In the era of managed healthcare and limited resources, it is important to address the issue of healthcare expenditure and cost containment. Operating room time and length of ICU stay comprise the most expensive parts of in-hospital cardiac surgical care. The presence of SCT did not seem to compromise early tracheal extubation or to prolong ICU or hospital length of stay. Proposed guidelines for perioperative management of patients with sickle cell disorders undergoing CABG surgery are listed in Table 5.
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In conclusion, our study suggests that fast-track cardiac anesthesia can be used safely in patients with SCT undergoing first-time CABG surgery. Further prospective studies are required to confirm that there is no increase of long-term morbidity and mortality in this subgroup of patients.
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References |
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