1 Department of Anaesthesia, University Medical Centre Utrecht and 2 Julius Centre for Health Sciences and Primary Care, University Medical Centre Utrecht, Utrecht, The Netherlands. 3 Department of Cardiac Anesthesia, Isala Clinics, Zwolle, The Netherlands
* Corresponding author: Department of Anesthesiology, University Medical Center Utrecht Heidelberglaan 100, 3584 CX Utrecht, The Netherlands. E-mail: C.J.Kalkman{at}azu.nl
Accepted for publication October 22, 2004.
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Abstract |
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Methods. One hundred and eighty-seven patients were assigned randomly to off-pump or on-pump coronary artery surgery. Oxygen saturation in the jugular bulb () was measured during revascularization of the three main coronary vessels in the off-pump group, and at the start of CPB, before rewarming, and after rewarming in the on-pump group. We compared samples with jugular bulb with desaturation (
50%) between treatment groups.
Results. One hundred and seventy-five patients (81 in the off-pump group [93%] and 94 in the on-pump group [94%]) had complete jugular oxygen saturation data. Thirty-nine patients in the off-pump group (48%) and 25 patients in the on-pump group (27%) had one or more samples with desaturation during revascularization or CPB (odds ratio after adjustment for other factors, 0.39; 95% confidence interval, 0.210.73, P<0.01).
Conclusion. Jugular bulb desaturation occurs more frequently during off-pump coronary artery surgery than during conventional coronary artery surgery.
Keywords: surgery, coronary artery, off-pump and on-pump ; veins, jugular, bulb saturation
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Introduction |
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Off-pump procedures, in particular when the posterior wall of the heart is exposed, require movement of the heart from its natural position. This movement reduces cardiac output and arterial pressure and increases central venous pressure, because of mild right heart dysfunction. Central venous pressure is also increased by the Trendelenburg manoeuvre, which is applied to overcome the decrease in left ventricular preload.2023 As a result, mean arterial pressure, cerebral perfusion pressure and cerebral blood flow might be diminished. Since off-pump coronary artery surgery is performed at normothermia, cerebral oxygen demand may be greater than with conventional procedures at mild hypothermia. As a consequence of both reduced flow and increased demand, global cerebral oxygenation could be compromised during off-pump coronary artery surgery.
We speculated that the lack of difference in cognitive outcome between patients undergoing on-pump and off-pump surgery might be explained by greater impairment of cerebral oxygenation in the off-pump group. We set out to compare episodes of poor global cerebral oxygenation, defined as a jugular bulb oxygen saturation less than 50%, in patients randomized to off-pump or (conventional) on-pump coronary artery surgery, with special emphasis on the period of graft placement during off-pump procedures.
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Methods |
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Procedures
Off-pump coronary artery surgery
Anaesthetic technique was dictated by the trial protocol. Briefly, if there were no contraindications for placement of an epidural catheter, thoracic epidural anaesthesia with local anaesthetics was used, combined with light general (propofol) anaesthesia. The lungs of the patients were ventilated with a mixture of 40% oxygen in air. Ventilation was adjusted to achieve an arterial partial pressure of carbon dioxide () of 3540 mm Hg. If thoracic epidural anaesthesia was not feasible, a total i.v. technique was used as described below for the on-pump cases. The use of vasodilators, vasopressors and inotropes was left to the discretion of the attending anaesthetist. Surgical access was through a median sternotomy in all cases in which revascularization was targeted on two or more vessels. When only the left anterior descending coronary artery was to be treated, a small anterolateral approach was used. In these cases a double-lumen tracheal tube was inserted to allow deflation of the left lung during harvesting of the left internal mammary artery and to facilitate revascularization. Regional immobilization of the cardiac wall during revascularization was achieved with the Octopus Stabilizer®. All measurements during revascularization were made when conditions were judged to be sufficiently stable to complete the coronary anastomosis.
Conventional (on-pump) coronary artery surgery
A standardized anesthetic technique was used. Anaesthesia was induced with sufentanil and maintained with a continuous infusion of sufentanil and midazolam. The lungs of the patients were ventilated with a mixture of oxygen 40% in air. Ventilation was adjusted to achieve a of 3540 mm Hg. After systemic heparinization (activated clotting time >480 s) the ascending aorta and right atrium were cannulated in all cases. The extra corporeal circuit consisted of a hollow-fibre membrane oxygenator, arterial line filter (40 µm) and a roller pump (Sarns 9000). The CPB was primed with a crystalloidcolloid mixture and the minimal nasopharyngeal temperature was maintained at 32°C. A pump flow rate of 2.4 litre m2 min1 and
-stat management were used throughout the procedure. During aortic cross-clamping, cold crystalloid cardioplegia (St Thomas solution) was used for myocardial protection. To reduce blood loss, blood was recollected using a suction cardiotomy reservoir in the CPB group, whereas a cell-saver was used in the off-pump group. Rewarming to achieve a nasopharyngeal temperature of 37°C was started when the last distal anastomosis was performed.
Outcome: jugular bulb desaturation
The primary outcome of this analysis was the incidence of episodes of jugular desaturation, defined as one or more measurements of oxygen saturation in the jugular bulb () less than or equal to 50% during revascularization or CPB. For this purpose a blood sampling catheter (Hydrocath® 16 G) was inserted after induction of anaesthesia via the internal jugular vein and advanced in a retrograde direction to the jugular bulb. A lateral X-ray of the cervical spine confirmed the correct position. The position was judged to be correct if the tip of the catheter was superior to the first cervical vertebra.
We decided to use intermittent sampling of blood from the jugular bulb to measure because fibre-optic measurements are cumbersome, especially during on-pump procedures when negative venous pressures often cause unreliable readings by wall artifacts. In the off-pump group measurements were performed at baseline (after induction of anaesthesia) and during revascularization of the coronary artery (right coronary artery [RCA], the left anterior descending artery [LAD] or its diagonal branch or the obtuse marginals from the circumflex artery [RCX]). In the on-pump group measurements were performed at baseline, after starting CPB, just before rewarming and after rewarming. We considered that these sampling times best reflect the true course of
in both groups and were most likely to detect jugular venous samples with desaturation in both study groups.
At the same time as the jugular venous sample, we recorded mean arterial pressure and measured haemoglobin concentration, arterial oxygen saturation (), nasopharyngeal temperature and
. Jugular blood samples were drawn slowly (60 s) from the catheter to avoid contamination with venous blood from other veins. Because
is highly influenced by arterial
, correction of
for the actual
could be applied to allow assessment of the association between type of surgery and jugular bulb desaturation, if consistent differences in
were present between the study groups.25 26 The arterialcerebrovenous oxygen content difference [
(av)O2], expressed in ml dl1, was calculated according to the formula
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Statistical analysis
We compared the incidence of desaturation in blood samples from the jugular bulb between the two treatment groups using odds ratios (OR) with 95% confidence interval (CI) and Fisher's exact test. Adjustments for baseline differences in risk factors were made using multivariate logistic regression modelling. In the off-pump group we also compared the effect of surgical exposure between the three territories (RCA, LAD and RCX) on jugular bulb saturation.
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Results |
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Movement of the heart to expose the three different territories in the off-pump patients was associated with small, non-significant changes in cerebral oxygenation. Revascularization of the right coronary artery was associated with the lowest and in 45% of the patients
was
50% at that time. The number of
measurements
50%, the
values and the (av)O2 difference were not significantly different between the three territories. Other variables were not significantly different between the three territories (Table 3).
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Discussion |
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The incidence of jugular desaturation in the on-pump group in the present study (27%) supports the results of others,27 28 even when only the 14 patients with jugular desaturation after rewarming are considered. Croughwell and colleagues27 found an association between jugular desaturation and lower cerebral blood flow, higher cerebral metabolic oxygen consumption and low mean arterial pressure. They suggested that poor cerebral blood flow (autoregulation impairment) or increased metabolic demand caused jugular desaturation. They found a strong association between low after rewarming from mild hypothermic CPB and postoperative cognitive decline. In contrast, others have associated a high
during CPB with postoperative cognitive decline.29
Investigation of a causal association between jugular bulb desaturation and cognitive outcome would have been interesting, but the design of the Octopus trial did not allow this to be addressed directly. Anesthetic techniques differed for each treatment group. Thoracic epidural anaesthesia, combined with propofol and lower opioid doses in the off-pump group, were chosen in the design of the Octopus trial, because patients randomized to off-pump procedures need less heparin. We expected that this approach would allow more rapid discharge from the intensive care unit for off-pump patients. Thus the causal relationship between differences in cognitive outcome and the occurrence of desaturation, comparing off-pump and on-pump surgery, could not be considered because of differences in anaesthetic technique.
In the off-pump group, shed mediastinal blood was washed in a cell-saver before it was returned to the patient. Activated leucocytes and fat from unwashed mediastinal blood could impair lung function and reduce , but this effect would only be evident after stopping CPB. If activation of the blood increased the formation of microemboli, affecting cerebral vessels, this could cause lower
values in the on-pump group. Fat globules reaching the brain could also reduce oxygen saturation in the jugular vein.
Stabilizing the posterior wall for revascularization of the obtuse marginals reduces stroke volume more than stabilizing the anterior or inferior wall for revascularization of the left anterior descending or the right coronary artery.2023 However, our data suggest that shifting the heart to expose the inferior wall compromised the cerebral circulation more than surgical exposure of the other territories (although this finding was not statistically significant). This may be explained by obstruction of the venous inflow to the right ventricle when the stabilizer is placed to immobilize the territory of the right coronary artery.
There were no differences in intraoperative between study groups, so we did not adjust
values for
. The different incidence of jugular bulb samples with desaturation, comparing off- and on-pump surgery, was unlikely to be caused by differences in
. The slightly greater incidence of jugular desaturation at baseline (after induction of anaesthesia) in the off-pump group suggests an effect of propofol on jugular oxygen saturation. However, as propofol has no influence on metabolic coupling,3032 and pressure autoregulation and carbon dioxide reactivity are preserved during low- and high-dose propofol,3339 the differences in jugular desaturation during surgery cannot be explained solely by the use of propofol in off-pump patients. Moreover, this difference in incidence of jugular desaturation remained after correction for baseline differences in desaturation. Also, relative luxury perfusion after propofol has been reported.40 41 Only when compared with inhalation anaesthesia are jugular samples with desaturation more likely to occur during propofol anaesthesia.42 43 It seems unlikely that the more frequent incidence of jugular desaturation in the off-pump group is attributable to the use of propofol.
In conclusion, jugular bulb desaturation is more frequent during off-pump coronary artery surgery than during coronary artery surgery with cardiopulmonary bypass, after adjustment for other risk factors for jugular bulb desaturation. Since off-pump surgery has shown modest improvements in cognitive outcome, the clinical relevance of this surrogate marker for cerebral ischaemia remains to be determined.
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Acknowledgments |
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Footnotes |
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This article is accompanied by the Editorial.
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References |
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