Introduction
Much debate still exists on the minimum level of normovolemic hemodilutional anemia that is safe to maintain oxygen delivery within the physiological range [1]. Normothermia during cardiopulmonary bypass (CPB) raises the question of adequate regional and whole body oxygen delivery under conditions of hemodilutional anemia [2]. We performed a prospective, controlled and randomized study to investigate oxygen delivery, oxygen consumption and clinical outcome of patients who were randomly allocated to a hematocrit of 20% or 25%, respectively, during normothermic cardiopulmonary bypass for isolated CABG surgery.
Patients and methods
After approval of the local ethical committee and informed written consent 50 patients were randomized to a hematocrit of 20 ± 1% versus 25 ± 1% during normothermic CPB. Inclusion criteria were: informed consent, isolated CABG surgery, age >18 and < 75 years, Hct > 36% and bodyweight > 70 kg. Prior to CPB patients were subjected to isovolemic hemodilution using HES130/0.4 (Voluven, Fresenius, Germany). Outcome measures of this study were: blood lactate, postoperative drainage loss and transfusion requirements, incidence of organ dysfunction (neurological, cardiac, respiratory and renal), stay in ICU (hours) and hospital stay (days). Postoperative intensive care therapy followed a standardized protocol. Statistical analysis was performed using the chi-squared test and Fisher's exact test for categorical and dichotomous variables, respectively. The Mann–Whitney U test was applied for intergroup comparison of continuous variables.
Results
One patient had to be excluded from statistical analysis due to clot formation in the autologous blood that had to be discarded. Basic patient characteristics are presented in Table 1, showing no significant differences between groups. Patients were discharged from the ICU after a median 23 hours in both groups (P = 0.87). Outcome variables were not significantly different between groups (Table 2) and within the normal range. Duration of hospital stay was not different between groups. One patient in the 20% group died of septic multiorgan failure due to pneumonia occurring on day 3 after surgery.
Table 1.
Basic patient characteristics
| Hematocrit 25% | Hematocrit 20% | ||||
|---|---|---|---|---|---|
| Median | IQR | Median | IQR | P | |
| Age (years) | 60 | 56–67 | 64 | 58–71 | 0.28 |
| Gender (male/female) | 25/2 | 22/0 | 0.50 | ||
| Body mass index (kg/m2) | 28.1 | 26.1–32.6 | 28.6 | 25.2–29.4 | 0.36 |
| Preoperative hematocrit (%) | 41.8 | 40.2–43.0 | 41.9 | 39.4–43.4 | 0.92 |
| Duration of anesthesia (min) | 300 | 285–320 | 305 | 290–325 | 0.28 |
| Duration of surgery (min) | 195 | 160–220 | 205 | 175–250 | 0.15 |
| CPB time (min) | 70 | 52–82 | 73 | 65–81 | 0.40 |
| Cross-clamp time (min) | 45 | 32–57 | 45 | 38–49 | 0.72 |
| APACHE II score | 14 | 11–19 | 17 | 12–20 | 0.18 |
Table 2.
Outcome variables
| Hematocrit 25% | Hematocrit 20% | ||||
|---|---|---|---|---|---|
| Median | IQR | Median | IQR | P | |
| Hematocrit on admission to ICU (%) | 25.8 | 24.0–26.9 | 23.5 | 20.8–25.3 | 0.04 |
| DO2 on admission to ICU (ml/m2/min) | 819 | 675–1089 | 787 | 665–948 | 0.43 |
| VO2 on admission to ICU (ml/m2/min) | 227 | 190–289 | 211 | 185–263 | 0.78 |
| DO2 18 hours after admission to ICU (ml/m2/min) | 991 | 743–1299 | 910 | 807–1032 | 0.66 |
| VO2 18 hours after admission to ICU (ml/m2/min) | 327 | 269–399 | 285 | 265–347 | 0.16 |
| Blood lactate on admission to ICU (mmol/l) | 1.4 | 1.1–2.1 | 1.4 | 1.1–2.0 | 0.95 |
| Blood lactate 18 hours after admission to ICU (mmol/l) | 1.4 | 1.1–2.1 | 1.8 | 1.2–2.2 | 0.69 |
| Drainage loss (ml) | 390 | 280–470 | 400 | 270–580 | 0.88 |
| Transfused patients (n) | 0 | 0% | 2 | 9% | 0.51 |
| Agitated arousal reaction (n) | 3 | 13% | 3 | 14% | 0.59 |
| Myocardial infarction (n) | 0 | 0% | 0 | 0% | 0.99 |
| CK/CK-MB | 0.05 | 0.04–0.07 | 0.05 | 0.04–0.08 | 0.99 |
| Ventilator support (hours) | 10 | 7–13 | 10 | 9–12 | 0.74 |
| Creatinine 18 hours after admission to ICU (mg/dl) | 0.86 | 0.80–1.08 | 1.02 | 0.82–1.13 | 0.65 |
| Patients with acute renal failure (n) | 1 | 4% | 1 | 5% | 0.73 |
| ICU stay (hours) | 23 | 22–25 | 23 | 21–35 | 0.87 |
| Mortality (n) | 0 | 0% | 1 | 5% | 0.47 |
Conclusion
The results of our study showed that whole body oxygen delivery was sufficiently maintained as blood lactate levels were not different between groups. Clinical outcome after elective CABG surgery was not impaired by an hematocrit of 20% during normothermic CPB. Furthermore, lowering the safe degree of hemodilutional anemia during CPB may prevent patients being exposed to blood products.