Does hypothermia prevent cerebral ischaemia during cardiopulmonary bypass?

It is believed that moderate hypothermia (25-32 degrees C) during cardiopulmonary bypass provides cerebral protection by reducing the cerebral metabolic rate (CMRO2). Nevertheless episodes of ischaemia do occur and thus it has been suggested that cerebral oxygenation should be monitored by jugular venous oximetry. However, this technique is cumbersome and invasive. Near infrared spectroscopy (NIRS) provides a non-invasive assessment of cerebral oxygenation and this was used together with continuousjugular venous oximetry in 21 patients undergoing hypothermic cardiopulmonary bypass. During the hypothermic period, jugular venous oximetry indicated reduced oxygen extraction consistent with a reduction in CMRO2 (increase from 61 +/- 2.5% to 74 +/- 2.5%). In contrast, near infrared spectroscopy demonstrated increased oxygen extraction (HbO2 - 11.5 +/- 1 microM, HHb + 3.2 +/- 0.3 microM) and a fall in the cerebral concentration of oxidized cytochrome oxidase ( - 1.7 +/- 0.3 microM) indicating ischaemia. These results suggest that cerebral ischaemia occurs during hypothermic cardiopulmonary bypass with a spurious rise in jugular venous oxygen saturation, which represents arterio-venous shunting. Thus if hypothermia does facilitate cerebral protection it does not appear to be a direct result of a reduction in CMRO2 and oxygen requirement.     

Does normoxemic cardiopulmonary bypass prevent myocardial reoxygenation injury in cyanotic children?

OBJECTIVE: To evaluate whether the deleterious effect of cardiopulmonary bypass (CPB) can be prevented by controlling PaO(2) in cyanotic children. DESIGN: Prospective, randomized, clinical study. SETTING: Single university hospital. PARTICIPANTS: Pediatric patients undergoing cardiac surgery for repair of congenital heart disease (n = 24). INTERVENTIONS: Patients were randomly allocated into 3 groups. Patients in the acyanotic group (group I, n = 10) had CPB initiated at a fraction of inspired oxygen (F(I)O(2)) of 1.0 (PO(2), 300 to 350 mmHg). Cyanotic patients were subdivided as follows: Group II (n = 7) had CPB initiated at an F(I)O(2) of 1.0, and group III (n = 7) had CPB initiated at an F(I)O(2) of 0.21 (PO(2), 90 to 110 mmHg). A biopsy specimen of right atrial tissue was removed during venous cannulation, and another sample was removed after CPB before aortic cross-clamping. The tissue was incubated in 4 mmol/L of t-butylhydroperoxide, and the malondialdehyde (MDA) level was measured to determine the antioxidant reserve capacity. Blood samples for cytokine levels, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-6 response to CPB were collected after induction of anesthesia and at the end of CPB before protamine administration. MEASUREMENTS AND MAIN RESULTS: After initiation of CPB, MDA level rose markedly in the cyanotic groups compared with the acyanotic group (210 +/- 118% v 52 +/- 34%, p < 0.05), which indicated the depletion of antioxidants. After initiation of CPB, TNF-alpha and IL-6 levels of the cyanotic groups were higher than for the acyanotic group (168 +/- 77 v 85 +/- 57, p < 0.001; 249 +/- 131 v 52 +/- 40; p < 0.001). When a comparison between the cyanotic groups was performed, group II (initiating CPB at an F(I)O(2) of 1.0) had significantly increased MDA production compared with group III (initiating CPB at an F(I)O(2) of 0.21) (302 +/- 134% v 133 +/- 74%, p < 0.05). Group II had higher TNF-alpha and IL-6 levels than group III (204 +/- 81 v 131 +/- 52, p < 0.001; 308 +/- 147 v 191 +/- 81, p < 0.01). CONCLUSION: Conventional clinical methods of initiating CPB at a hyperoxemic PO(2) may increase the possibility of myocardial reoxygenation injury in cyanotic children. This deleterious effect of reoxygenation can be modified by initiating CPB at a lower level of oxygen concentration. Subsequent long-term studies are needed to determine the best method of decreasing the oxygen concentration of the CPB circuit.     

Does steroid pretreatment increase endotoxin release during clinical cardiopulmonary bypass?

OBJECTIVE: The mechanism involved in the endotoxemia frequently recognized during cardiopulmonary bypass remains unclear. It has also been suggested that endotoxin levels were higher in steroid-pretreated patients undergoing cardiopulmonary bypass. METHODS: Twenty patients undergoing cardiopulmonary bypass were randomly pretreated with steroids (methylprednisolone, 30 mg/kg) or placebo. Blood samples for endotoxin measurement were drawn simultaneously from the superior and inferior venae cavae before heparin administration, 5 and 50 minutes after the onset of bypass, 5 minutes after aortic declamping, at the end of bypass, and 1, 2, and 20 hours after the end of cardiopulmonary bypass. RESULTS: The perioperative variables in the two groups were similar. Blood endotoxin levels were higher in the inferior vena cava than in the superior vena cava immediately after the onset of bypass. Endotoxin levels in inferior vena cava blood were significantly lower in steroid-pretreated patients than those in patients not receiving steroids. CONCLUSIONS: Endotoxin is released during cardiopulmonary bypass from the region drained by the inferior vena cava. Steroid pretreatment may actually reduce endotoxin release during bypass.     

Does vacuum-assisted venous drainage increase gaseous microemboli during cardiopulmonary bypass?

BACKGROUND: Vacuum-assisted venous drainage enables adequate drainage through small-diameter cannulas but concerns are that it results in more gaseous microemboli delivered to the patient. METHODS: Five identical embolus detectors monitored the propagation of entrained air through a cardiopulmonary bypass (CPB) model. The ability of the CPB circuit to remove gaseous microemboli was studied with vacuum-assisted venous drainage and gravity siphon venous drainage using different pump speeds and rates of gaseous microemboli delivery. RESULTS: Under all conditions entrained venous air resulted in the detection of gaseous microemboli in the perfusate after the arterial filter. In blood-primed circuits, increased flow rates and higher levels of vacuum-assisted venous drainage were independently associated with increased gaseous microemboli counts in the arterial line. Vacuum-assisted venous drainage at -40 mm Hg did not significantly increase gaseous microemboli activity when compared with gravity siphon venous drainage at 4 L/min flow rate. CONCLUSIONS: Vacuum-assisted venous drainage at -40 mm Hg does not statistically reduce the ability of the CPB circuit to remove gaseous microemboli at lower pump rates. High levels of vacuum and increased pump flow rates should be avoided. Air should not be introduced into the venous line.     

Perioperative renal failure: hypoperfusion during cardiopulmonary bypass?

Acute renal failure is one of the most frequent and life-threatening complications after cardiac surgery. There is a recent growing deal of information suggesting that during the time of cardiopulmonary bypass kidneys may suffer from an imbalance between oxygen supply and oxygen needs. A low hematocrit during cardiopulmonary bypass is associated with an increase risk of acute renal failure, mainly due to a low oxygen delivery. An inadequate oxygen delivery during cardiopulmonary bypass is associated with lactate production, and under normothermic conditions, hyperlactatemia appears for an oxygen delivery below 260 mL min(-1) m(-2). The risk of acute renal failure significantly increases for an oxygen delivery approximately at the same value (272 mL min(-1) m(- 2)). During cardiopulmonary bypass, the pump flow should be coupled with the hematocrit to avoid falling below this critical oxygen delivery.     

Can hypocapnia reduce cerebral embolization during cardiopulmonary bypass?

BACKGROUND: Cerebral embolization is a major cause of central nervous dysfunction after cardiopulmonary bypass. Experimental studies demonstrate that reductions in arterial carbon dioxide tension (PaCO2) can reduce cerebral embolization during cardiopulmonary bypass. This study examined the effects of brief PaCO2 manipulations on cerebral embolization in patients undergoing cardiac valve procedures. METHODS: Patients were prospectively randomized to either hypocapnia (PaCO2 = 30 to 32 mm Hg, n = 30) or normocapnia (PaCO2 = 40 to 42 mm Hg, n = 31) before aortic cross-clamp removal. With removal of the aortic cross-clamp embolic signals were recorded by transcranial Doppler ultrasonography for the next 15 minutes. RESULTS: Despite significant differences in PaCO2, groups did not differ statistically in total cerebral emboli counts. The mean number of embolic events was 107 +/- 100 (median, 80) in the hypocapnic group and 135 +/- 115 (median, 96) in the normocapnic group, respectively (p = 0.315). CONCLUSIONS: Due to the high between-patient variability in embolization, reductions in PaCO2 did not result in a statistically significant decrease in cerebral emboli. In contrast to experimental studies, the beneficial effect of hypocapnia on cerebral embolization could not be demonstrated in humans.     

Is prophylactic haemofiltration during cardiopulmonary bypass of benefit during cardiac surgery?

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether prophylactic haemofiltration during cardiopulmonary bypass is of benefit during cardiac surgery? Altogether 273 papers were found using the reported search, of which nine presented the best evidence to answer the clinical question. The author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results, and study weaknesses of these papers are tabulated. We conclude that haemofiltration will increase the haematocrit, reduce some inflammatory markers and may increase the variability of heparin levels. It may also reduce post-operative blood transfusion and possibly increase BP and cardiac index immediately after haemofiltration, although no differences in morbidity or mortality has ever been shown.     

What is a normal lactate level during cardiopulmonary bypass?

Blood lactate levels during cardiopulmonary bypass are often used to verify adequacy of perfusion. The present investigation aimed to propose a threshold for hyperlactatemia. Blood lactate levels in 5 121 cardiac surgical patients were retrospectively analysed by a review of database records. Hyperlactatemia was defined as a value equal to the 90th percentile of the identified lactate distribution at weaning from cardiopulmonary bypass. Patient demographics, background and outcome statistics were performed stratified on presence of hyperlactatemia. The threshold for hyperlactatemia was found to equal 2 mmol/l. Significant predictors of hyperlactatemia based on logistic regression modelling were age, complex surgery, duration of cardiopulmonary bypass, blood transfusion, acid base level, emergency operations, diabetes, vasoactive intervention, venous-blood-return to the heart-lung machine and renal function. Patients with hyperlactatemia required longer intensive care and postoperative ventilatory support. Complications were more frequent, especially: renal dysfunction, infections, respiratory and circulatory disorders. Hospital mortality was 13.3% compared to an overall level at 2.2%. The threshold for hyperlactatemia during cardiopulmonary bypass attained 2 mmol/l and predicted increased morbidity and mortality.     

Does ischemia-induced prostate damage during cardiac surgery involving cardiopulmonary bypass cause bladder outlet obstruction?

OBJECTIVE: This study sought to investigate whether ischemia-induced prostate damage during cardiac surgery involving cardiopulmonary bypass causes bladder outlet obstruction. MATERIALS AND METHODS: The study involved 37 men who underwent elective cardiac surgery involving cardiopulmonary bypass. Prostate-specific antigen (PSA) levels were determined preoperatively (baseline) and on postoperative days 1, 5, and 30. In 4 cases, the PSA level after the operation was unchanged from the preoperative level, so these 4 men were excluded from the study. In the remaining 33 patients, symptoms of bladder outlet obstruction were assessed using the International Prostate Symptom Score. Each subject completed this test preoperatively and 3, 6 and 9 months postoperatively, and the means scores at these time points were compared. The effects of patient age, operative time, CPB time, and aortic clamping time on postoperative increases in PSA levels were investigated. RESULTS: Thirty-three (89.2%) of the 37 men exhibited increased postoperative PSA levels compared to baseline. The mean PSA level for the 33 cases on day 5 was significantly higher than the baseline mean, but the mean levels on postoperative days 1 and 30 were comparable to baseline. Nine (24.3%) of the 33 men had postoperative PSA levels greater than 4.0 ng/dl (the upper normal limit). There was no significant difference between preoperative and postoperative International Prostate Symptom Scores. CONCLUSION: The study indicates that men's PSA levels are, indeed, increased after cardiac surgery with cardiopulmonary bypass. However, in 9 months of follow-up, there was no association between this PSA rise and development of BOO, according to International Prostate Symptom Scores.     

Can cardioplegia management influence cytokine responses during clinical cardiopulmonary bypass?

BACKGROUND: Cytokines play an important role in the inflammatory response associated with cardiopulmonary bypass (CPB) and may contribute to postoperative complications. Although it has been shown that the production of tumor necrosis factor a (TNF-a) and interleukin (IL)-6 were higher following normothermic CPB than hypothermic CPB, whether different cardioplegic management could influence the release of cytokines remains unknown. METHODS: We compared the blood concentrations of four cytokines (TNF-a, IL-6, IL-8, and IL-10) in two groups of patients undergoing complete revascularization with CPB in the same study period. Seventeen patients received cold crystalloid cardioplegia at a Belgian center (group-CC), while 21 patients received warm blood cardioplegia at a center in Hong Kong (group-WB). Blood samples were collected before and after surgery in each patient. RESULTS: There were no differences between the 2 groups in terms of age, sex ratio, number of grafts, duration of CPB and aortic crossclamping. All patients survived their hospital stay. The levels of TNF-a, IL-6 and IL-8 after surgery were higher in group-CC than in group-WB. However, IL-10 levels were significantly lower at the end of surgery in group-CC than in group-WB. CONCLUSIONS: Our data suggest that the use of warm blood cardioplegia, rather than cold crystalloid cardioplegia, may reduce the inflammatory response to CPB. This observation warrants future randomized investigation to determine its clinical relevance.     

Does the technique of cardiopulmonary bypass affect lung water content?

Several efforts have been made to improve the technique of cardiopulmonary bypass (CPB), including the use of pulsatile flow and the modification of cannulation technique. The present study focused upon extravascular lung water (EVLW) in 60 aortocoronary bypass patients subjected to four different perfusion techniques during CPB: group 1 (n = 15): non-pulsatile flow and standard cannulation; group 2 (n = 15); pulsatile flow and standard cannulation; group 3 (n = 15): nonpulsatile flow and monoatrial cannulation (i.e., always "partial" bypass during CPB); group 4 (n = 15): pulsatile flow and monoatrial cannulation. EVLW content was measured using the double-indicator dilution technique with indocyanine green; in addition, various hemodynamic and laboratory variables were measured. Lung water content rose above normal values (mean: 5.79 +/- 0.33 ml/kg) only in the groups submitted to the standard cannulation technique, irrespective of whether the perfusion flow was pulsatile or not (group 1: + 27.4%; group 2: + 25.5%). Pulmonary gas exchange, too, was compromised only in these patients (PaO2 in group 1 -19% and in group 2 -17%; Qs/Qt in group 1 + 36 rel. % and in group 2 + 29 rel. %), whereas all patients with monoatrial cannulation and partial bypass throughout the CPB period showed no rise in EVLW content or Qs/Qt and no drop in PaO2. From the results of this study we conclude that pulsatile perfusion during open heart surgical procedure has no advantages in regard to lung water content. Monoatrial cannulation with partial bypass at all times during CPB, however, seems to be beneficial, probably owing to the maintenance of pulmonary circulation during the bypass period.