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Critical Care Research Program,
*Departments of Anesthesia and Intensive Care, and
Surgery, Kuopio University Hospital, Kuopio, Finland
Address correspondence and reprint requests to Pekka Pölönen, Department of Anesthesia and Intensive Care, Kuopio University Hospital, FIN-70211 Kuopio, Finland. Address e-mail: to pekka.polonen{at}kuh.fi
| Abstract |
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2.0 mmol/L from admission to the ICU and up to 8 h thereafter. Hemodynamics, oxygen transport data, and organ dysfunctions were recorded. The median hos-pital stay was shorter in the protocol group (6 vs 7 days, P < 0.05), and patients were discharged faster from the hospital than those in the control group (P < 0.05). Discharge from the ICU was similar between groups (P = 0.8). Morbidity was less frequent at the time of hospital discharge in the protocol group (1.1% vs 6.1%, P < 0.01). Increasing oxygen delivery to achieve normal SvO2 values and lactate concentration during the immediate postoperative period after cardiac surgery can shorten the length of hospital stay. Implications: Health care economics has challenged clinicians to reduce costs and improve resource use in cardiac surgery and anesthesia in a patient population increasing in age and in severity of disease. Optimizing cardiovascular function to maintain adequate oxygen delivery during the immediate postoperative period after cardiac surgery can decrease morbidity and reduce length of hospital stay.
| Introduction |
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2 mmol/L immediately after cardiac surgery, would shorten the length of hospital stay and length of ICU stay, compared with the control group treated according to standard clinical care. | Methods |
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2.0 mmol/L from admission to the ICU and up to 8 h (Figure 1). During the operation, standard treatment was given to both groups. Patients were randomized the day before surgery by sealed envelope technique, and after randomization, the caregivers were aware of the randomization group. Nine patients were dropped from the study after the randomization but before the operation. Of these nine, eight patients were already enrolled in another study, including a Jehovahs witness because the protocol algorithm required red blood cell infusion. One patient died during the operation and, therefore, was excluded from the study population. Altogether, 393 patients fulfilled the study protocol.
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The standard clinical postoperative care after weaning from CPB included the following: 1) If cardiac index was <2.5 L · min-1 · m-2 despite volume expansion [pulmonary capillary wedge pressure 1218 mm Hg], dobutamine infusion was started. 2) Mean arterial pressure was kept between 60 and 90 mm Hg by using either vasopressor (dopamine or norepinephrine) or vasodilator (sodium nitroprusside) infusion when appropriate. 3) Hemoglobin concentration was kept
100 g/L with packed red blood cells. 4) Patients were weaned from mechanical ventilation when rewarmed and hemodynamically stable.
Radial arterial and thermodilution pulmonary arterial catheters were routinely used. Cardiac output was measured in triplicate and the mean value was used for calculations. Oxygen delivery was calculated according to standard formula, multiplying the thermodilution cardiac output with arterial oxygen content (CaO2) and indexed to body surface area. Oxygen consumption was calculated by multiplying cardiac output with the arteriovenous oxygen content difference. Oxygen contents were derived as [1.39 x hemoglobin concentration x SaO2 or mixed venous oxygen saturation + dissolved oxygen]. Oxygen extraction rate was calculated dividing
O2 by DO2. Hemoglobin oxygen saturation was measured by using co-oximetry (IL 282; Instrumentation Laboratories, Lexington, MA) and oxygen tension was measured by clinical blood gas analyzer (Stat profile 4®; NOVA Biomedical, Waltham, MA). Arterial blood lactate levels were measured by an enzymatic reaction (YSI 2300; Yellow Springs Instrument Laboratory, Yellow Springs, OH).
Hemodynamics and oxygen transport data were recorded 15 min after weaning from CPB, at admission to the ICU, and 2, 6, and 8 h after ICU admission. The data for organ functions were recorded on the first postoperative morning and on the day the patient was discharged from the hospital. Dysfunction of organ systems was defined as follows: (a) central nervous system: hemiplegia, stroke, or Glasgow coma scale score <10 in the absence of sedation; (b) circulatory: need for vasoactive medication to treat hypotension (dopamine or norepinephrine) or decreased cardiac output (dopamine, dobutamine or epinephrine), or intraaortic balloon counterpulsation, (c) respiratory: need for mechanical or assisted ventilation, (d) renal: urine output <750 mL/24 h or increase of serum creatinine concentration >150 µmol/L from preoperatively normal levels, (e) hepatic: serum alanine aminotransferase activity >40 IU/L and serum bilirubin concentration >40 µmol/L, (f) gastrointestinal: macroscopic bleeding or paralytic ileus, (g) hematological: leukocyte count <3.5 x 109/L and platelet count <80 x 109/L.
In the protocol group, additional targets of hemodynamic management were to maintain SvO2 >70% and arterial blood lactate concentration
2 mmol/L from admission to the ICU to 8 h thereafter (Figure 1). If the goals could not be achieved at a certain time point despite volume substitution, dobutamine infusion up to 15 µg · kg-1 · min-1 was started to increase cardiac index. The effect of the treatment on SvO2 and lactate was assessed 2 h later. In patients who achieved the goals, therapy was maintained and adjusted on the following data recording time points, when necessary: 1) In those who had not achieved the goals, therapy was continued with incremental volume expansion and increasing doses of dobutamine. 2) The same protocol algorithm was used at the following time points, except at 8 h after admission to the ICU, the end point of the protocol treatment, in which patients who had SvO2 >70% and arterial blood lactate
2.0 mmol/L were deemed as responders. 3) All others were deemed as nonresponders, even if they had achieved the targets at earlier time points and had no inotropes. 4) After the end of data recording, protocol treatment was gradually withdrawn.
Because of the small, expected mortality rate in cardiac surgical patients, the length of hospital and ICU stay were chosen as primary outcome variables. Postoperative morbidity was estimated by the number of organ dysfunctions and by the use of ICU and hospital resources. Secondary end points of the study were hospital, 6-mo, and 12-mo mortality.
Sample size was estimated from our previous observational study (20). A sample size of 400 patients was estimated to have at least 90% power at
= 0.05 to detect 3 days difference in the length of hospital stay, given an SD of 8 days, and to allow for a 10% dropout rate. The primary analysis was performed on an intention-to-treat basis. The
2 test or Fishers exact test was applied to categorical variables, and Students t-tests or Mann-Whitney U-test was used for independent continuous variables when appropriate. Analysis of variance for repeated measures was used for repeated continuous variables to determine differences between the two groups over the study period. One-way analysis of variance with Bonferroni correction was used to locate the differences between the groups during the study protocol. Kaplan-Meier analysis with log-rank statistics was used to test the differences in the use of hospital and ICU resources between the groups. Statistical significance was assumed at P < 0.05. Data are presented as median (range) or mean ± SD when appropriate.
| Results |
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O2I, O2ER, and SvO2 were different between the groups (Table 3). Accordingly, each oxygen transport (Table 3) and hemodynamic (Table 4) variable included in the analysis changed during the first 8 h in the ICU. During the study protocol, cardiac index and stroke volume index were higher, whereas central venous pressure was lower in the protocol group compared with the control group (Table 4).
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2 mmol/L) were achieved in 70 (35.1%) patients in the protocol group and in 66 (33.5%) patients in the control group by means of volume substitution only and in 42 (21.4%) patients in the protocol group and in 17 (8.6%) patients in the control group with inotropes in addition to volume substitution (Figure 3). In the protocol group, there were 84 (42.9%) patients and in the control group there were 114 (57.9%) patients who did not achieve the targets at 8 h after arrival at the ICU. Of the nonresponders 38% (32 of 84) in the protocol group and 55.3% (63 of 114) in the control group had volume substitution only and 62% (52 of 84) in the protocol group and 44.7% (51 of 114) in the control group in addition had inotropes.
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Oxygen Delivery and Outcome in the Whole Study Population
To clarify the role of oxygen delivery on outcome a posteriori, we compared patients who achieved the targets (n = 195) to those who did not achieve the targets (n = 198) in the whole study population (353 ± 83 and 329 ± 81 mL · min-1 · m-2 after weaning from bypass, 418 ± 87 and 377 ± 76 mL · min-1 · m-2 after arrival at the ICU, 488 ± 110 and 419 ± 95 76 mL · min-1 · m-2 at 2 h in the ICU, 508 ± 105 and 434 ± 96 76 mL · min-1 · m-2 at 6 h in the ICU, 533 ± 96 and 441 ± 88 mL · min-1 · m-2 after 8 h in the ICU, respectively). Patients who achieved the targets had faster discharge from the hospital and from the ICU (Kaplan-Meier, P < 0.001 for both). The median hospital stay was 5 days (range 236) in patients who achieved the targets and 7 days (range 393) in patients who did not achieve the targets (P < 0.001). The median ICU stay was 1 day (range 125) in patients who achieved the targets and 1 day (range 152) in patients who did not achieve the targets (P < 0.001). Prolonged ICU stay was less (P = 0.05) in patients who achieved the targets. Mortality rate was similar at 28 days and at 6 mo but less at 1 yr after randomization (P = 0.05) in patients who achieved the targets. Patients who achieved the targets had better preoperative ejection fraction (P < 0.01) and less diabetes (P < 0.05) than patients who did not achieve the targets. Patients who achieved the targets had fewer valvular or combined valvular and coronary artery bypass procedures (P < 0.01), shorter aortic occlusion time (P < 0.05), perfusion time (P < 0.01), and operation time (P < 0.05). Reoperations for bleeding or tamponade (P < 0.01), myocardial infarctions (P < 0.05), and arrhythmias (P = 0.05) were less common in patients who achieved the targets.
| Discussion |
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The main finding of our study was that protocolized care aiming to normal oxygen transport and normal SvO2 and lactate during immediate postoperative period (up to eight hours) after cardiac surgery, can improve outcome. In the protocol group, this was reflected in a one-day shorter length of hospital stay and reduced number of organ dysfunctions at hospital discharge. Although the difference in length of hospital stay was small, the impact on resource use may be substantial. Assuming the volume of 1000 cardiac operations per year, the care according to the protocol would lead to a reduction of 1000 care days in the cardiothoracic surgical ward. Organ dysfunctions detected in the control group are those typically related to peri- and postoperative hypoperfusion and causing increased use of hospital resources. These findings are in agreement with other studies of surgical patients in which decreased morbidity and shorter length of ICU and hospital stay have been reported in the protocol groups (7,8,17). The fact that there were no differences in mortality rate between the study groups may be because of overall low mortality rate in cardiac surgical patients and because we did not design our study to find differences in mortality rates. Faster hospital discharge and decreased morbidity in the protocol group suggests that optimizing cardiovascular function, either with volume loading or with the use of inotropes, in addition to volume substitution, has significantly contributed to improved outcome.
An additional important finding was that the achievement of the hemodynamic targets in the protocol group was difficult, even with the addition of inotropes. Approximately one half of the patients (57%) in the protocol group achieved the targets of SvO2 and lactate. Difficulty achieving the targets has been common also in other randomized studies (8,9,1012). In the study by Gattinoni et al. (12), 66.7% of the patients in the SvO2 group and 44.9% of the patients in the cardiac index group achieved the targets. Similarly, 73% of the patients in the study by Tuchschmidt et al. (9) and 66% of the patients in the study by Yu et al. (10) were able to reach the targets. In the study by Hayes et al. (11), only 30% of the patients achieved the targets, whereas in the study by Ziegler et al. (16), all patients in the treatment group achieved the targets. Thus, the proportion of patients who achieve the targets varies according to the targets used. When
O2I is used as the target in addition to DO2I, CI, or SvO2 the achievement of the targets has been least frequent. In our study, the low achievement of the targets in the protocol group may partly be attributable to the protocol. For example, some patients who achieved the targets with volume substitution only at six hours were nonresponders at eight hours after arrival at the ICU (end point of the protocol). As in the study by Gattinoni et al. (12), patients who achieved the targets in the protocol group were younger and had better cardiovascular function reflected as a better preoperative ejection fraction. Shorter operative times may reflect more favorable operative conditions caused by a better underlying disease state in patients who achieved the targets. Also, reoperations for excessive bleeding or tamponade in the postoperative period may have jeopardized adequate oxygen delivery when cardiac function was already compromised. Improved outcome in patients who achieved the targets in the protocol group suggests better cardiovascular reserves and thus, capability to adequately respond to increasing surgical stress and hemodynamic crisis, either spontaneously with volume substitution or with the help of inotropes.
In the whole study population, achievement of hemodynamic targets was also associated with improved outcome. Patients who did not achieve the targets had more co-morbidity and limited cardiovascular reserves. These patients were operated on more often for valvular or combined procedures and thus, had longer operative times, indicating more complex surgery or advanced disease state. Arrhythmias, myocardial infarction, and resternotomies also complicated the postoperative course more frequently in patients who did not achieve the targets.
One limitation in our study design was that had we had enrolled patients for only coronary revascularization, the patient population would have been more homogeneous. Therefore, a posteriori, we ran the statistics for patients who had only a revascularization procedure and found that the results were similar with our protocol (Kaplan-Meier for the hospital stay, P < 0.05). Although the study was randomized, it was not blinded, and the data of the oxygen transport measurements of both groups were open to those taking care of patients during the study period. This may have caused some bias in the intensity of treatment in the control group despite the fact that targeted criteria for the groups were different. In addition, the study protocol periodeight hours after admission to the ICUmay have been too short to allow hemodynamic and metabolic stabilization to occur in all of patients because of excessive bleeding or immediate reoperations, although the rate of reoperations was equal in the study groups. The high proportion of nonresponders with volume substitution only in the protocol group may also be a source of bias.
In conclusion, the results show that therapy, targeting SvO2 >70% and lactate concentration
2 mmol/L immediately after cardiac surgery, improves outcome as shown in decreased use of hospital resources. Difference in hospital stay between groups was small, but assuming 1000 cardiac surgical operations per year, this could reduce the need for beds in the cardiothoracic surgical ward. The use of hospital resources is an adequate end point to reflect outcome both from the economical and quality of care point of view. We used the hospital and ICU length of stay as outcome measures, because prolonged stay in the ICU after cardiac surgery, although rare, has a major impact on postoperative use of intensive care and hospital facilities (5). In addition, achievement of the therapeutic targets in cardiac surgical patients was difficult, despite vigorous fluid resuscitation and use of inotropes.
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