Relative importance of flow versus pressure in splanchnic perfusion during cardiopulmonary bypass in rabbits

BACKGROUND: Decreased gastrointestinal perfusion has been reported during cardiopulmonary bypass (CPB). Conflicting results have been published concerning thresholds of pressure and flow to avoid splanchnic ischemia during CPB. This study compared splanchnic perfusion during independent and randomized variations of CPB pump flow or arterial pressure. METHODS: Ten rabbits were studied during mild hypothermic (36 degrees C) nonpulsatile CPB using neonatal oxygenators. Simultaneous measurements of tissue blood flow in four different splanchnic areas (gastric, jejunum, ileum, and liver) were performed by laser Doppler flowmetry (LDF) before CPB (T0) and during a 4-step factorial experimental block design. Pressure and flow were alternatively high or low in random order. RESULTS: Laser Doppler flowmetry was significantly lower than pre-CPB value but was better preserved (analysis of covariance) in all organs, except liver, when CPB flow was high, whatever the pressure. Splanchnic LDF values in the low- versus high-flow groups expressed as perfusion unit were (mean +/- SD): stomach, 94+/-66 versus 137+/-75; jejunum, 118+/-78 versus 172+/-75; ileum, 95+/-72 versus 146+/-83; and liver, 79+/-72 versus 108+/-118. No significant difference of LDF was observed between the high- and low-pressure groups, whatever the flow, except for liver: stomach, 115+/-64 versus 117+/-83; jejunum, 141+/-80 versus 148+/-83; ileum, 127+/-87 versus 114+/-76; liver, 114+/-88 versus 73+/-70. CONCLUSION: Prevention of splanchnic ischemia during CPB should focus on preservation of high CPB blood flow rather than on high pressure.     

Continuous infusion of prostaglandin E1 facilitates weaning from cardiopulmonary bypass

Vasodilators expedite the rewarming process and facilitate weaning from cardiopulmonary bypass (CPB). We continuously infused prostaglandin E1 (PG-E1) at 0.02-0.05 microgram.kg-1.min-1 (n = 11) or phentolamine (PHENT) at 5-10 micrograms.kg-1.min-1 (n = 13) during rewarming from mild hypothermic CPB. Rectal temperature was 33.3 +/- 1.7 degrees C in PG-E1 group vs. 31.3 +/- 1.3 degrees C in PHENT group at 30 minutes, and 34.0 +/- 1.2 degrees C vs. 32.7 +/- 1.1 degrees C at 40 minutes from the start of rewarming. There were significant differences (P less than 0.01 at 30 min, P less than 0.05 at 40 min) in rectal temperature between the two groups. There were no differences in perfusion index of CPB, arterial perfusion temperature, mean arterial pressure, systemic vascular resistance as well as esophageal, forehead or palm skin temperatures at any point between the two groups. The required time for weaning from CPB was significantly shorter in PG-E1 than in PHENT group (P less than 0.01, 36 +/- 8 min vs. 46 +/- 11 min). Our results also strongly suggest that PG-E1 preferentially improves splanchnic blood flow.     

Relative Importance of Flow versus Pressure in Splanchnic Perfusion during Cardiopulmonary Bypass in Rabbits

Background: Decreased gastrointestinal perfusion has been reported during cardiopulmonary bypass (CPB). Conflicting results have been published concerning thresholds of pressure and flow to avoid splanchnic ischemia during CPB. This study compared splanchnic perfusion during independent and randomized variations of CPB pump flow or arterial pressure.

Methods: Ten rabbits were studied during mild hypothermic (36[degrees]C) nonpulsatile CPB using neonatal oxygenators. Simultaneous measurements of tissue blood flow in four different splanchnic areas (gastric, jejunum, ileum, and liver) were performed by laser Doppler flowmetry (LDF) before CPB (T0) and during a 4-step factorial experimental block design. Pressure and flow were alternatively high or low in random order.

Results: Laser Doppler flowmetry was significantly lower than pre-CPB value but was better preserved (analysis of covariance) in all organs, except liver, when CPB flow was high, whatever the pressure. Splanchnic LDF values in the low-versus high-flow groups expressed as perfusion unit were (mean +/- SD): stomach, 94 +/- 66 versus 137 +/- 75; jejunum, 118 +/- 78 versus 172 +/- 75; ileum, 95 +/- 72 versus 146 +/- 83; and liver, 79 +/- 72 versus 108 +/- 118. No significant difference of LDF was observed between the high- and low-pressure groups, whatever the flow, except for liver: stomach, 115 +/- 64 versus 117 +/- 83; jejunum, 141 +/- 80 versus 148 +/- 83; ileum, 127 +/- 87 versus 114 +/- 76; liver, 114 +/- 88 versus 73 +/- 70.     

Oxygen free radical regulation of rat splanchnic blood flow.

BACKGROUND. The role of oxygen-derived free radicals on splanchnic prostaglandin (PGI2) synthesis and superior mesenteric artery (SMA) blood flow was examined during acute hemorrhage. METHODS. Sprague-Dawley rats were hemorrhaged to 30 mm Hg for 5, 30, or 45 minutes without (SK5, SK30, and SK45) or with (SK5 + R, SK30 + R, and SK45 + R) blood reperfusion. The SK30 + R and SK45 + R groups were treated with or without superoxide dismutase (10,000 units/kg intravenously). In vivo SMA blood flow was measured continuously for 100 minutes by a transonic flow probe, or in other groups the in vitro-perfused SMA and its end-organ intestine (SV+SI) were assayed for release of PGI2 by radioimmunoassay after 15 and 30 minutes of perfusion. RESULTS. Acute hemorrhage at all time periods increased SV+SI PGI2 release twofold to threefold compared with sham animals (p less than 0.01), which was abolished after blood reperfusion. SMA blood flow was decreased by 79.6% +/- 3.3% and 88.2% +/- 1.4% in the SK30 + R and SK45 + R groups compared with the sham animals (p less than 0.01). Superoxide dismutase treatment restored both SV+SI release of PGI2 after SK and SMA blood flow to control levels. CONCLUSION. Oxygen-derived free radicals locally produced during SK30 + R and SK45 + R inhibited splanchnic PGI2 synthesis, which contributed to decreased splanchnic blood flow.     

Is kidney function altered by the duration of cardiopulmonary bypass?

BACKGROUND: Cardiopulmonary bypass (CPB) is considered responsible for kidney damage. By using sensitive markers of kidney damage we assessed whether the length of CPB influences kidney function. METHODS: In a prospective study, 50 consecutive cardiac operation patients with CPB times of less than 70 minutes were compared with 50 consecutive patients showing CPB times of more than 90 minutes. Aside from creatinine clearance and fractional excretion of sodium, urine concentrations of N-acetyl-beta-D-glucosaminidase, alpha1-microglobulin, glutathione transferase-pi, and glutathione transferase-alpha were measured after induction of anesthesia at the end of the operation, and on the first and second postoperative days in the intensive care unit. RESULTS: CPB times were 58 +/- 12 minutes and 116 +/- 18 minutes, respectively. Hemodynamics, volume replacement, and use of catecholamines during cardiopulmonary bypass (CPB) were without significant differences between groups. Concentrations of all kidney-specific proteins increased significantly after CPB, showing the highest significant increases in the CPB more than 90 minutes group (eg, glutathione transferase-alpha CPB > 90 minutes from 3.0 +/- 1.0 to 12.9 +/- 2.9 microg/L; glutathione transferase-alpha CPB < 70 minutes from 2.4 +/- 0.5 to 5.5 +/- 1.2 microg/L). By the second postoperative day, urine concentrations of kidney-specific proteins had returned to almost baseline in the CPB less than 70 minutes patients, but remained slightly elevated in the other group. CONCLUSIONS: Patients with CPB times more than 90 minutes showed more pronounced kidney damage than patients with CPB times less than 70 minutes as assessed by sensitive kidney-specific proteins. Whether patients with preexisting renal dysfunction undergoing prolonged CPB times would profit from renal protection strategies needs to be elucidated.     

Pharmacokinetics of alfentanil before and after cardiopulmonary bypass in pigs: Part II.

The pharmacokinetics of alfentanil before and after cardiopulmonary bypass (CPB) were investigated in six pigs undergoing mitral valve replacement. Before bypass, alfentanil, 100 micrograms/kg, was infused in 10 minutes and after bypass, alfentanil, 40 micrograms/kg, was infused in 10 minutes. Low inspiratory concentrations of halothane were given concomitantly. Arterial blood was obtained before and after CPB for determination of plasma alfentanil concentrations by gas chromatography. Bi-exponential functions were fitted to the plasma concentration-time data using weighted least-squares nonlinear regression analysis. The steady-state volume of distribution (Vss; 258 +/- 70 mL/kg), elimination clearance (Cle; 10.7 +/- 3.0 mL/kg/min), and distribution clearance (Cld; 6.8 +/- 3.3 mL/kg/min) before CPB were smaller than the Vss (1,107 +/- 373 mL/kg; P less than 0.01), Cle (20.0 +/- 3.0 mL/kg/min; P less than 0.002), and Cld (23.0 +/- 6.7 mL/kg/min; P less than 0.02) after CPB. The distribution half-life (t1/2 lambda 1; 2.8 +/- 0.8 minutes) was longer and the elimination half-life (t1/2 lambda 2; 36 +/- 8 minutes) was shorter before CPB than the t1/2 lambda 1 (1.7 +/- 0.2 minutes; P less than 0.05) and t1/2 lambda 2 (68 +/- 20 minutes; P less than 0.02) after CPB.     

Disadvantages of prostacyclin infusion during cardiopulmonary bypass: a double-blind study of 50 patients having coronary revascularization

Prostacyclin (PGI2) has been suggested for use in cardiopulmonary bypass (CPB) because of its positive effects on platelet number and function. Fifty patients who underwent coronary artery bypass grafting using a bubble oxygenator received heparin, 3 mg per kilogram of body weight, and then were randomly assigned to receive PGI2, 25 ng/kg/min, beginning 5 minutes before and until the end of CPB (26 patients) or a placebo (24 patients). Both groups were similar in sex, age, heparin dose, protamine dose, and CPB time. During CPB, mean arterial pressure fell significantly with PGI2 (76 +/- 2 mm Hg to 53 +/- 2 mm Hg; p less than 0.05) and necessitated pressor substances. Platelet counts fell significantly in both groups with the start of CPB, but after 60 minutes were similar in both groups (118 +/- 9 X 10(3) versus 130 +/- 8 X 10(3); not significant [NS]) and were unchanged 3 hours after CPB. Total chest tube output was 647 +/- 51 ml (placebo group) versus 576 +/- 34 ml (PGI2 group) (NS); 18 of the patients given PGI2 required 26 transfusions compared with 16 transfusions in 8 of the patients given a placebo (p less than 0.05). In PGI2 patients, arterial oxygen tension on 100% oxygen fell from 281 +/- 18 mm Hg before CPB to 223 +/- 17 mm Hg immediately after CPB (p less than 0.05). The placebo patients did not show a change in this variable.(ABSTRACT TRUNCATED AT 250 WORDS)     

Femoral artery pressures are more reliable than radial artery pressures on initiation of cardiopulmonary bypass

OBJECTIVE: To compare radial and femoral artery perfusion pressure during initiation and various stages of cardiopulmonary bypass (CPB). DESIGN: Prospective study. SETTING: The cardiac center of a tertiary referral teaching institute. PARTICIPANTS: Sixty consecutive patients of all ages undergoing a variety of cardiac operations. INTERVENTIONS: Radial and femoral arterial pressures were measured in all patients on the same transducer, from the beginning to end of CPB. MEASUREMENTS AND MAIN RESULTS: Mean perfusion pressures on CPB measured at the femoral artery at 1, 5, 10, and 15 minutes of CPB were 38.4+/-3.6, 46.2+/-3.1, 49.7+/-3.9, and 52.8+/-4.1 mmHg and were significantly greater than the corresponding radial artery pressures (29.9+/-4.1, 35.3+/-6.1, 40.9+/-4.8, and 41.8+/-5.3 mmHg) (p < 0.001). At 30 minutes and 60 minutes of CPB, femoral artery pressures are higher (60.3+/-8.8 mmHg and 66.4+/-8.2 mmHg) compared with radial artery pressures (54.7+/-6.9 mmHg and 59.6+/-6.1 mmHg), but the difference is less significant (p < 0.05). On conclusion of CPB, mean femoral artery pressures (70.9+/-6.7 mmHg) are greater than mean radial artery pressures (67.6+/-8.1 mmHg) (NS). CONCLUSIONS: Although radial artery pressures are more commonly monitored during cardiac surgery, femoral artery perfusion pressures are more reliable during the initial part of CPB, and routine monitoring of femoral artery pressures may prevent vasoconstrictor use on initiation of CPB.     

Assessment of peripheral blood perfusion during open heart surgery with sublingual PCO2 measured by ISFET-PCO2 sensor

Sublingual tissue PCO2 (PSLCO2) was continuously monitored with an ISFET-based PCO2 sensor during and after the open-heart surgery under cardiopulmonary bypass (CPB) in order to study the effect of CPB on the peripheral blood perfusion. In addition, PSLCO2 monitoring was carried out in several cases of off-pump CABG. In the cases of open-heart surgery with CPB, PSLCO2 increased from 35.0 +/- 5.6 mmHg at the induction of anesthesia to the maximum value of 55.7 +/- 6.0 mmHg during CPB. After declamping of the aorta, PSLCO2 decreased gradually to 49.0 +/- 4.0 mm Hg 6 hr after the admission to ICU. The value of arterial lactate as another index of peripheral blood perfusion also increased gradually after the start of CPB, reaching to the maximum value of 8.8 +/- 1.1 mmol.l-1 just after being admitted into ICU. In the case of off-pump CABG, PSLCO2 and arterial lactate showed a slight increase during the later part of the surgery, but the change was not so significant as in the case of open-heart surgery under CPB. Through this study, typical changing pattern of PSLCO2 during the open-heart surgery was recognized. The change of PSLCO2 always preceded that of arterial lactate. We also experienced one case in which early stage of hypoperfusion was detected through the monitoring of PSLCO2. These results suggest clinical advantages of PSLCO2 monitoring.     

Differences in pH management and pulsatile/nonpulsatile perfusion during cardiopulmonary bypass do not influence renal function.

The renal effects of pulsatile (pulse pressure 18.0 +/- 1.5 mm Hg [mean +/- SEM]) or nonpulsatile perfusion (mean pulse pressure 1.9 +/- 0.4 mm Hg) during either alpha-stat (mean PaCO2 41.2 +/- 0.9 mm Hg measured at 37 degrees C) or pH-stat (mean PaCO2 60.6 +/- 1.7 mm Hg measured at 37 degrees C) pH management of hypothermic cardiopulmonary bypass (CPB) were studied in 100 patients undergoing elective coronary artery bypass surgery. Mean urine output, fractional excretion of sodium and potassium, and renal failure index all increased during the study period; however, there was no difference among the four different CPB management groups. Mean postoperative creatinine and blood urea nitrogen values decreased compared with preoperative values, again without differences among treatment groups. Three patients developed acute renal insufficiency; of these, two had received nonpulsatile perfusion and pH-stat management, and the other had been managed with pulsatile perfusion and pH-stat management. These three patients all had undergone prolonged CPB and required at least two vasoactive drugs and the use of an intraaortic balloon pump to be weaned from CPB. In patients with normal preoperative renal function undergoing hypothermic CPB, neither the mode of perfusion, pulsatile or nonpulsatile, nor the method of pH management, pH-stat or alpha-stat, influences perioperative renal function.     

Markers of splanchnic perfusion and intestinal translocation of endotoxins during cardiopulmonary bypass: effects of dopamine and milrinone.

OBJECTIVES: To investigate markers of splanchnic perfusion and the extent of endotoxemia during cardiopulmonary bypass (CPB) and to compare the effects of dopamine and milrinone on both splanchnic perfusion and endotoxemia. DESIGN: Prospective, randomized, blinded study. SETTING: University teaching hospital. PARTICIPANTS: Twenty-four patients scheduled for elective coronary artery bypass graft surgery (CABG). INTERVENTIONS: Patients were allocated to receive placebo (eight patients), dopamine (eight patients), or milrinone (eight patients) during CPB, and at seven times intraoperatively assays were performed of arterial and hepatic venous endotoxin levels, as well as measurements and/or calculations of intramucosal gastric pH (pHi), arterial and hepatic venous lactate-pyruvate ratio (lac/pyr), and hepatic venous oxygen saturation (S(HV)O2). MEASUREMENTS AND MAIN RESULTS: Both splanchnic and systemic endotoxin levels increased significantly, and this was unaffected by either dopamine or milrinone. Gastric pHi did not change, and there were only modest increases in lac/pyr, which remained within the normal range of less than 10 in both splanchnic and systemic blood. In the placebo group, S(HV)O2 decreased at the onset of CPB and also significantly decreased during rewarming and at the end of CPB and surgery. In the dopamine-treated patients, S(HV)O2 was greater compared with placebo and milrinone during both hypothermic and rewarming phases. CONCLUSION: Endotoxemia occurs during routine CPB. Neither pHi nor lac/pyr values showed adverse change, but hepatic venous oximetry may be a more sensitive indicator of splanchnic dysoxia in that S(HV)O2 was reduced during rewarming. Whether dopamine or milrinone confer protection against splanchnic ischemia remains uncertain.     

Epidural analgesia with bupivacaine does not improve splanchnic tissue perfusion after aortic reconstruction surgery

Inadequate splanchnic tissue perfusion is relatively common during and after aortic surgery. We hypothesized that vasodilation caused by thoracic epidural analgesia improves splanchnic blood flow and tissue perfusion after aortic surgery. In this prospective, randomized, controlled study, we studied 20 patients undergoing elective aortic- femoral or aortic-iliac reconstruction surgery. Gastric and sigmoid colon mucosal PCO2 and pH were measured during surgery. An epidural bolus of bupivacaine 40 mg followed by infusion of 15 mg h-1 was started after operation in 10 patients. After operation, splanchnic blood flow and gastric and sigmoid colon mucosal PCO2 and pH were measured before and 2 h after the start of epidural analgesia. During surgery, the gastric mucosal-arterial PCO2 difference remained stable, whereas the sigmoid mucosal-arterial PCO2 difference increased during aortic clamping but returned to pre-clamping values after declamping. After operation, epidural analgesia had no effect on gastric or sigmoid mucosal-arterial PCO2 differences or on splanchnic blood flow.      

The influence of heparin-coated and uncoated extracorporeal circuits on blood rheology during cardiac surgery

The effect of heparin-coated perfusion circuits on blood trauma during clinical cardiopulmonary bypass (CPB) was studied in order to find out if traumatic changes in the blood could be minimized. Twenty-four patients undergoing coronary artery bypass surgery were randomized prospectively to CPB with heparin-coated circuits (HCC) or non-coated circuits (NCC). The trauma to blood was assessed by measuring damage to blood cells by estimating red and white cell rheology changes. These were measured as red cell filtration rate (RFR) and white cell filtration rate (WFR) using standard microfiltration methods. Furthermore, changes in plasma hemoglobin (P-Hb), whole blood and plasma viscosity were simultaneously assessed. The RFR was significantly reduced in both groups during CPB by 10% in the HCC and 32% in the NCC groups (p less than 0.01). When comparing the HCC and NCC groups, a significant difference was first seen after 30 minutes of bypass (p less than 0.05) and increased at the end of CPB (p less than 0.01). Similar results were seen regarding WFR (15% and 36%, p less than 0.01). After 30 minutes of bypass, a significant difference was seen between HCC and NCC groups (p less than 0.05). Furthermore, a significant increase in P-Hb levels were seen during CPB in both patient groups. At the end of CPB, there was a significant difference in P-Hb levels (HCC 305+/-90 mg/L; NCC 455+/-78 mg/L, p less than 0.01) when comparing the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increasing cardiac output by epinephrine after cardiac surgery: effects on indocyanine green plasma disappearance rate and splanchnic microcirculation

OBJECTIVE: The effects of increasing cardiac output by epinephrine on indocyanine green plasma disappearance rate (ICG-PDR) and gastric mucosal PCO(2) (P(R)CO(2)) were studied as indicators of splanchnic microcirculation. DESIGN: A prospective clinical study. SETTING: Intensive care unit of a university hospital. PARTICIPANTS: With ethics approval and written consent, 12 elective cardiac surgical patients (5 female, 7 male, 71 +/- 8 years) were studied. INTERVENTIONS: Patients underwent pulmonary artery and left atrial catheterization for clinical indications. Measurements were made at intensive care unit admission and 1 hour after (increased) epinephrine treatment. Mean epinephrine dose was changed from 0.02 to 0.08 microg/kg/min. RESULTS: Heart rate significantly increased from 97 +/- 11 to 106 +/- 12 beat/min. Central venous (10 +/- 3 v 10 +/- 4 mmHg) and left atrial (10 +/- 5 v 11 +/- 5 mmHg) pressures were unchanged. Cardiac index and stroke volume index significantly increased from 2.7 +/- 0.5 to 3.2 +/- 0.5 L/min/m(2) and from 28 +/- 6 to 31 +/- 5 mL/m(2), respectively. Although systemic O(2) delivery and O(2) consumption significantly increased, ICG-PDR did not change significantly (ie, from 18.0% +/- 5.6% to 19.5% +/- 6.4% per minute). P(R)CO(2) and PCO(2) gap (difference between regional and end-tidal PCO(2)) significantly increased from 5.4 +/- 1.0 to 5.9 +/- 1.1 kPa and 1.2 +/- 0.8 to 1.5 +/- 0.7 kPa, respectively. CONCLUSION: Increasing cardiac output by epinephrine in patients after cardiac surgery was not associated with a change in flow-dependent liver function but a deterioration in gastric mucosal perfusion.     

Systemic and regional effects of supraceliac aortic occlusion during experimental hepatic vascular exclusion

BACKGROUND: Supraceliac aortic occlusion (AO) has been recommended to avoid hypotension during hepatic vascular exclusion (HVE). We hypothesized that AO may negatively affect splanchnic perfusion during HVE. METHODS: Twenty-six dogs (16 +/- 0.3 kg) were randomly assigned to HVE (n = 13) or HVE+AO (n = 13), during 30 minutes followed by a 60-minute reperfusion period. Cardiac output (CO), mean arterial pressure (MAP), superior mesenteric artery blood flow (SMABF, ultrasonic flowprobe), gastric mucosal PCO(2) (gas tonometry) and PCO(2)-gap were evaluated. RESULTS: HVE alone induced decreases in MAP from 115 +/- 5.1 to 26 +/- 1 mm Hg, in CO from 2.0 +/- 0.1 to 0.4 +/- 0.1 L/min and SMABF from 398 +/- 42 to 16 +/- 7.6 mL/min, while PCO(2) gap increased from 4 +/- 3.7 to 52 +/- 5.4 mm Hg. Supraceliac aortic occlusion only avoided severe hypotension. During reperfusion MAP, CO, and SMABF were partially restored, while PCO(2) gap showed no improvements in either group. CONCLUSIONS: HVE promotes major systemic and splanchnic perfusional derangement. Concomitant AO may avoid HVE-induced hypotension without producing further deleterious effects.     

Cardiopulmonary bypass in humans--jejunal mucosal perfusion increases in parallel with well-maintained microvascular hematocrit

BACKGROUND: An imbalance between splanchnic oxygen supply and demand occurs during cardiopulmonary bypass (CPB) in man, which might disrupt the intestinal mucosal barrier function. The aim of the present study was to evaluate the effects of mild hypothermic CPB on intestinal mucosal perfusion in man undergoing cardiac surgery. Additionally we aimed to identify variables, which independently could predict changes of intestinal mucosal microcirculatory variables during CPB. METHODS: Jejunal mucosal perfusion (JMP), jejunal mucosal hematocrit (JMHt), red blood cell (RBC) velocity and arteriolar vasomotion using endoluminal jejunal laser Doppler flow metry were studied in eight cardiac surgical patients before and during CPB at a temperature of 34 degrees C. RESULTS: Cardiopulmonary bypass and the accompanied hemodilution (25-30%) induced a 44% increase in JMP (P < 0.05) and a 42% increase in RBC velocity (P < 0.01), with no change in JMHt. The oscillation amplitude of JMP, at a fundamental frequency of 2.8 cycles min(-1), increased with 175% (P < 0.05) during CPB. Splanchnic oxygen extraction increased by 64% during CPB (P < 0.05). Stepwise multiple regression analysis identified systemic hematocrit, arterial O2 and CO2 tension and splanchnic oxygen extraction as independent predictors of RBC velocity during CPB (R2=0.63, P < 0.001). The oscillation amplitude of JMP was predicted by RBC velocity and splanchnic oxygen extraction (R2= 0.68, P <0.0001). CONCLUSIONS: The increase in RBC velocity and enhanced arteriolar vasomotion, as well as maintained jejunal mucosal hematocrit, are microcirculatory, compensatory mechanisms for the splanchic oxygen supply/demand mismatch seen during cardiopulmonary bypass in humans.     

Comparison of pH-state and Alpha-stat Cardiopulmonary Bypass on Cerebral Oxygenation and Blood Flow in Relation to Hypothermic Circulatory Arrest in Piglets

Background: Deep hypothermic circulatory arrest is used in neonatal cardiac surgery. Recent work has suggested improved neurologic recovery after deep hypothermic arrest with pH-stat cardiopulmonary bypass (CPB) compared with alpha-stat CPB. This study examined cortical oxygen saturation (ScO(2)), cortical blood flow (CBF), and cortical physiologic recovery in relation to deep hypothermic arrest with alpha-stat or pH-stat CPB.

Methods: Sixteen piglets were cooled with pH-stat or alpha-stat CPB to 19 [degree sign]C (cortex) and subjected to 60 min of circulatory arrest, followed by CPB reperfusion and rewarming and separation from CPB. Near infrared spectroscopy and laser Doppler flowmetry were used to monitor ScO(2) and CBF. Cortical physiologic recovery was assessed 2 h after the piglets were separated from CPB by cortical adenosine triphosphate concentrations, cortical water content, CBF, and ScO(2).

Results: During CPB cooling, ScO(2) increased more with pH-stat than with alpha-stat bypass (123 +/- 33% vs. 80 +/- 25%); superficial and deep CBF were also greater with pH-stat than with alpha-stat bypass (22 +/- 25% vs. -56 +/- 22%, 3 +/- 19% vs. -29 +/- 28%). During arrest, ScO(2) half-life was greater with pH-stat than with alpha-stat bypass (10 +/- 2 min vs. 7 +/- 2 min), and cortical oxygen consumption lasted longer with pH-stat than with alpha-stat bypass (36 +/- 8 min vs. 25 +/- 8 min). During CPB reperfusion, superficial and deep CBF were less with alpha-stat than with pH-stat bypass (-40 +/- 22% vs. 10 +/- 39%, -38 +/- 28% vs. 5 +/- 28%). After CPB, deep cortical adenosine triphosphate and CBF were less with alpha-stat than with pH-stat bypass (11 +/- 6 pmole/mg vs. 17 +/- 8 pmole/mg, -24 +/- 16% vs. 16 +/- 32%); cortical water content was greater with alpha-stat than with pH-stat bypass (superficial: 82.4 +/- 0.3% vs. 81.8 +/- 1%, deep: 79.1 +/- 2% vs. 78 +/- 1.6%).     

Splanchnic oxygen transport, hepatic function and gastrointestinal barrier after normothermic cardiopulmonary bypass

BACKGROUND: The effect of non-pulsatile, normothermic cardiopulmonary-bypass (CPB) on the splanchnic blood-flow and oxygen-transport, the hepatic function and the gastrointestinal barrier were observed in a prospective observational study in 31 adults undergoing cardiac valve replacement surgery. METHODS: The splanchnic (i.e. hepatic) blood-flow (HBF) was measured by the constant infusion of indocyanine-green (ICG) using a hepatic-venous catheter. Liver function was examined by calculation of lactate uptake, ICG extraction and the monoethylglycinexylidide (MEGX) test. A day before and after surgery the gastrioduodenal and intestinal permeability was measured by determination of sucrose and lactulose/mannitol excretion. RESULTS: Splanchnic blood flow and oxygen delivery did not decrease during and after surgery while splanchnic oxygen consumption (P < 0.0125) and arterial lactate concentrations increased. The splanchnic lactate uptake paralleled the lactate concentration. After but not during CPB an increase of systemic oxygen consumption was observed. The MEGX test values decreased on the first day after surgery. The ICG extraction was attenuated during the operation. The gastroduodenal and the intestinal permeability increased significantly postoperatively (P < 0.002, respectively, P < 0.001). There was no correlation between these findings and the duration of CPB. There was a significant correlation of the intestinal permeability but not of the gastroduodenal permeability between the prior and after surgery values (P < 0.001). CONCLUSION: Increased oxygen consumption during CPB may indicate an inflammatory reaction due to the pump beginning in the splanchnic area or a redistribution of the splanchinc blood flow during the CPB. Normothermic CPB does not lead to a significant or prolonged reduction of liver function. Normothermic CPB causes an increase of gastrointestinal permeability. The intestinal barrier function prior to surgery was accountable for the degree of loss of intestinal barrier function following surgery.     

Jejunal mucosal perfusion is well maintained during mild hypothermic cardiopulmonary bypass in humans

In the present study, the effects of mild hypothermic (34 degrees C) cardiopulmonary bypass (CPB) on jejunal mucosal perfusion (JMP), gastric tonometry, splanchnic lactate, and oxygen extraction were studied in low-risk cardiac surgical patients (n = 10), anesthetized and managed according to clinical routine. JMP was assessed by endoluminal laser Doppler flowmetry. Patients were studied during seven 10-min measurement periods before, during, and 1 h after the end of CPB. Splanchnic oxygen extraction increased during hypothermia and particularly during rewarming and warm CPB. JMP increased during hypothermia (26%), rewarming (31%), and warm CPB (38%) and was higher 1 h after CPB (42%), compared with pre-CPB control. The gastric-arterial PCO(2) difference was slightly increased (range 0.04-2.26 kPa) during rewarming and warm CPB as well as 1 h after CPB, indicating a mismatch between gastric mucosal oxygen delivery and demand. None of the patients produced lactate during CPB. We conclude that jejunal mucosal perfusion appears well preserved during CPB and moderate (34 degrees C) hypothermia; this finding is in contrast to previous studies showing gastric mucosal hypoperfusion during CPB. Implications: Jejunal mucosal perfusion increases during mild hypothermic cardiopulmonary bypass (CPB). Intestinal laser Doppler flowmetry, gastric tonometry, and measurements of splanchnic lactate extraction could not reveal a local or global splanchnic ischemia during or after CPB. A mismatch between splanchnic oxygen delivery and demand was seen, particularly during rewarming and warm CPB.     

Autoregulation of human jejunal mucosal perfusion during cardiopulmonary bypass

Animal studies have suggested that autoregulation of intestinal blood flow is severely impaired during cardiopulmonary bypass (CPB). We investigated the jejunal mucosal capacity to autoregulate perfusion during nonpulsatile CPB (34 degrees C) in 10 patients undergoing elective cardiac surgery. Changes in mean arterial blood pressure (MAP) were induced by altering the CPB flow rate randomly for periods of 3 min from 2.4 L/min/m2 to either 1.8 or 3.0 L/min/m2. Jejunal mucosal perfusion (JMP) was continuously recorded by laser Doppler flowmetry. A typical pattern of flow motion (vasomotion) was recorded in all patients during CPB. Variations in CPB flow rates caused no significant changes in mean JMP, jejunal mucosal hematocrit, or red blood cell velocity within a range of MAP from 50 +/- 15 to 74 +/- 16 mm Hg. The vasomotion frequency and amplitude was positively correlated with CPB flow rate. IV injections of prostacyclin (10 microg, Flolan) blunted vasomotion and increased JMP from 192 +/- 53 to 277 +/- 70 (P < 0.05) perfusion units despite a reduction in MAP from 59 +/- 12 to 45 +/- 10 mm Hg (P < 0.05). Prostacyclin-induced vasodilation resulted in loss of mucosal autoregulation (pressure-dependent perfusion). We conclude that autoregulation of intestinal mucosal perfusion is maintained during CPB in humans.