Fractal or biologically variable delivery of cardioplegic solution prevents diastolic dysfunction after cardiopulmonary bypass.

OBJECTIVE: To determine whether myocardial protection is improved by restoring physiologic variability to the cardioplegia pressure signal during cardiopulmonary bypass, we compared cardiac function in pigs in the first hour after either conventional cold-blood cardioplegia (group CC) or computer-controlled biologically variable pulsatile cardioplegia (group BVC). METHODS: Invasive monitors and sonomicrometry crystals were placed, and cardiopulmonary bypass was initiated. The aorta was crossclamped, and cold blood cardioplegic solution was infused intermittently through the aortic root with either conventional cardioplegia (n = 8) or biologically variable pulsatile cardioplegia (n = 8; mean pressure, 75 mm Hg for 85 minutes). The crossclamp was released, cardiac function was restored, and separation from cardiopulmonary bypass was completed. With stable temperature and arterial blood gases, hemodynamics and systolic and diastolic indices were compared at 15, 30, and 60 minutes after cardiopulmonary bypass. RESULTS: Diastolic stiffness doubled from 0.027 +/- 0.016 mm Hg/mm (mean +/- SD) at baseline to 0.055 +/- 0.036 mm Hg/mm (P =.003) at 1 hour after bypass in group CC, associated with increased left ventricular end-diastolic pressure from 9 +/- 2 to 11 +/- 2 mm Hg (P =.001), mean pulmonary artery pressure from 14 +/- 2 to 20 +/- 3 mm Hg (P =.003), and serum lactate levels from 2.0 +/- 0.5 to 5.6 +/- 2.3 mmol/L (P =.008). Systolic function was not affected. In group BVC diastolic stiffness, left ventricular end-diastolic pressure, and pulmonary artery pressure values were not different from control values at any time after bypass, and serum lactate levels were significantly less than with conventional cold blood cardioplegia. Peak pressure variability with biologically variable pulsatile cardioplegia fit a power-law equation (exponent = -3.0; R(2) = 0.97), indicating fractal behavior. CONCLUSION: Diastolic cardiac function is better preserved after cardiopulmonary bypass with biologically variable pulsatile cardioplegia and fractal perfusion. This may be attributed to enhanced microcirculatory perfusion with improved myocardial protection. A model supporting these results is presented.

Biologically variable pulsation improves jugular venous oxygen saturation during rewarming.

BACKGROUND: Conventional pulsatile (CP) roller pump cardiopulmonary bypass (CPB) was compared to computer controlled biologically variable pulsatile (BVP) bypass designed to return beat-to-beat variability in rate and pressure with superimposed respiratory rhythms. Jugular venous O2 saturation (SjvO2) below 50% during rewarming from hypothermia was compared for the two bypass techniques. A SjvO2 less than 50% during rewarming is correlated with cognitive dysfunction in humans. METHODS: Pigs were placed on CPB for 3 hours using a membrane oxygenator with alpha-stat acid base management and arterial filtration. After apulsatile normothermic CPB was initiated, animals were randomized to CP (n = 8) or BVP (roller pump speed adjusted by an average of 2.9 voltage output modulations/second; n = 8), then cooled to a nasopharyngeal temperature of 28 degrees C. During rewarming to stable normothermia, SjvO2 was measured at 5 minute intervals. The mean and cumulative area for SjvO2 less than 50% was determined. RESULTS: No between group difference in temperature existed during hypothermic CPB or during rewarming. Mean arterial pressure, arterial partial pressure O2, and arterial partial pressure CO2 did not differ between groups. The hemoglobin concentration was within 0.4 g/dL between groups at all time periods. The range of systolic pressure was greater with BVP (41 +/- 18 mm Hg) than with CP (12 +/- 4 mm Hg). A greater mean and cumulative area under the curve for SjvO2 less than 50% was seen with CP (82 +/- 96 versus 3.6% +/- 7.3% x min, p = 0.004; and 983 +/- 1158 versus 42% +/- 87% x min; p = 0.004, Wilcoxon 2-sample test). CONCLUSIONS: Computer-controlled BVP resulted in significantly greater SjvO2 during rewarming from hypothermic CPB. Both mean and cumulative area under the curve for SjvO2 less than 50% exceeded a ratio of 20 to 1 for CP versus BVP. Cerebral oxygenation is better preserved during rewarming from moderate hypothermia with bypass that returns biological variability to the flow pattern.

Computer-controlled cardiopulmonary bypass increases jugular venous oxygen saturation during rewarming.

BACKGROUND: Conventional roller pump apulsatile cardiopulmonary bypass (CPB) was compared with computer-controlled pulsatile bypass, which was designed to recreate biological variability (return of beat-to-beat variability in rate and pressure with superimposed respiratory rhythms). The degree of jugular venous oxygen saturation (SjvO2) less than 50% during rewarming from hypothermic CPB was compared for the two bypass techniques. An SjvO2 less than 50% during rewarming from hypothermic CPB is correlated with cognitive dysfunction in humans. METHODS: Pigs were placed on CPB for 3 hours using a membrane oxygenator with alpha-stat acid-base management and arterial filtration. After baseline measurements and normothermic CPB, the animals were randomized to apulsatile CPB (n = 12) or computer-controlled pulsatile CPB (roller pump speed adjusted by an average of 2.9 voltage output modulations/s; n = 12). The animals were then cooled to a nasopharyngeal temperature of 28 degrees C. During rewarming to stable normothermic temperatures, SjvO2 was measured at 5-minute intervals. The mean and cumulative areas for an SjvO2 less than 50% were determined for all animals. RESULTS: No between-group differences in temperature were noted during hypothermic CPB or during rewarming. The rate of rewarming was not different between groups. Mean arterial pressure, partial pressure of oxygen in arterial blood, and partial pressure of carbon dioxide in arterial blood also did not differ between groups. The hemoglobin concentration was within 0.4 g/dL between groups at all time periods. Mean pulse pressure was 10.0 +/- 4.8 mm Hg in the apulsatile CPB group and 20.7 +/- 5.2 mm Hg in the pulsatile CPB group (p = 0.0002; unpaired t test). Markedly greater mean and cumulative areas under the curve for SjvO2 less than 50% were seen with apulsatile CPB (164 +/- 209 versus 1.9 +/- 3.6% x min, p = 0.021; and 1,796 +/- 2,263 versus 23 +/- 45% x min, p = 0.020, respectively). CONCLUSIONS: Computer-controlled pulsatile CPB was associated with significantly greater SjvO2 during rewarming from hypothermic CPB. Both the mean and cumulative areas under the curve for SjvO2 less than 50% exceeded a ratio of 75:1 for apulsatile versus computer-controlled pulsatile CPB. These experiments suggest that cerebral oxygenation was better preserved during rewarming from moderate hypothermia with computer-controlled pulsatile CPB, which returned biologic variability to the flow pattern.

Cerebral hypoxia during cardiopulmonary bypass: a magnetic resonance imaging study.

BACKGROUND: Neurocognitive deficits after open heart operations have been correlated to jugular venous oxygen desaturation on rewarming from hypothermic cardiopulmonary bypass (CPB). Using a porcine model, we looked for evidence of cerebral hypoxia by magnetic resonance imaging during CPB. Brain oxygenation was assessed by T2*-weighted imaging, based on the blood oxygenation level-dependent effect (decreased T2*-weighted signal intensity with increased tissue concentrations of deoxyhemoglobin). METHODS: Pigs were placed on normothermic CPB, then cooled to 28 degrees C for 2 hours of hypothermic CPB, then rewarmed to baseline temperature. T2*-weighted, imaging was undertaken before CPB, during normothermic CPB, at 30-minute intervals during hypothermic CPB, after rewarming, and then 15 minutes after death. Imaging was with a Bruker 7.0 Tesla, 40-cm bore magnetic resonance scanner with actively shielded gradient coils. Regions of interest from the magnetic resonance images were analyzed to identify parenchymal hypoxia and correlated with jugular venous oxygen saturation. Post-hoc fuzzy clustering analysis was used to examine spatially distributed regions of interest whose pixels followed similar time courses. Attention was paid to pixels showing decreased T2* signal intensity over time. RESULTS: T2* signal intensity decreased with rewarming and in five of seven experiments correlated with the decrease in jugular venous oxygen saturation. T2* imaging with fuzzy clustering analysis revealed two diffusely distributed pixel groups during CPB. One large group of pixels (50% +/- 13% of total pixel count) showed increased T2* signal intensity (well-oxygenated tissue) during hypothermia, with decreased intensity on rewarming. Changes in a second group of pixels (34% +/- 8% of total pixel count) showed a progressive decrease in T2* signal intensity, independent of temperature, suggestive of increased brain hypoxia during CPB. CONCLUSIONS: Decreased T2* signal intensity in a diffuse spatial distribution indicates that a large proportion of cerebral parenchyma is hypoxic (evidenced by an increased proportion of tissue deoxyhemoglobin) during CPB in this porcine model. Neuronal damage secondary to parenchymal hypoxia may explain the postoperative neuropsychological dysfunction after cardiac operations.

Seatbelt injury to the abdominal aorta.

Seatbelt injury to the abdominal aorta is a rare finding with an unresolved mechanism. We present a case in which a rear-seat passenger wearing a lap belt was involved in a motor vehicle accident. Injuries sustained included a contused abdominal aorta. At the time of aortic repair, the involved segment was found to be atheromatous, had an intimal tear, and a flap that caused complete occlusion. Graft replacement was carried out employing a 12-mm DeBakey woven dacron prosthesis, which restored satisfactory circulation to both lower limbs. The patient developed myoglobinemia and subsequently died due to multiple organ failure 19 days following the accident. Tearing against the vertebral column, and bowel loop entrapment, in high-speed deceleration have been implicated as injury mechanisms as well as impingement by the belt or metal buckle, in such injuries. Also, our patient had existing atheromatous plaque, which was ruptured.

Surgical experience in descending thoracic aneurysmectomy with and without adjuncts to avoid ischemia.

Over the past twelve years, surgical treatment of descending thoracic aneurysms has been performed in 360 patients. Three different operative strategies were employed during resection to provide distal aortic perfusion by temporary bypass (Group 1, 75 patients) or shunt (Group 2, 22 patients) or to simplify the operative procedure with aortic cross-clamping alone (Group 3, 263 patients). The surgical results were determined primarily by patient-related and disease-related variables. Advanced age (older than 70 years), atherosclerotic cause, and emergency operation significantly increased the risks of early mortality and morbidity. The incidence of death (11.7%), paraplegia (6.5%), or renal failure (6%) was not reduced by the use of adjunctive perfusion, and bleeding complications increased significantly in Groups 1 and 2. Spinal cord injury was increased significantly by emergency operations, cross-clamp times exceeding 30 minutes, and extensive aneurysms (p less than 0.05). The risk of renal failure was increased by advanced age and atherosclerotic cause (p less than 0.05). With an experienced surgical team, the primary risks of descending thoracic aneurysmectomy are not influenced by the method of adjunctive perfusion, but are determined by patient factors such as the nature and extent of the aneurysm.