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Background: Previous studies in patients undergoing cardiopulmonary bypass (CPB) have documented gastric mucosal hypoperfusion and hypoxia. This study examines the influence of the CPB protocol on the adequacy of gut blood flow and oxygenation., Methods: Twenty-four patients were prospectively randomized into one of four CPB groups: nonpulsatile hypothermic (NP 28); pulsatile hypothermic (P 28); non-pulsatile normothermic (NP 37); and pulsatile normothermic (P 37). Gastric wall blood flow was assessed using laser Doppler flow measurement and gastric mucosal oxygenation (intramucosal pH), using tonometry., Results: After 10 minutes of CPB, the NP 28 group had the greatest reduction in gastric wall blood flow (-60.6% +/- 3.8%) compared with baseline (p < 0.05). Thirty minutes into CPB, the P 37 group had less gastric mucosal hypoperfusion (-9.7% +/- 10.3%) than the NP 28 patients (-53.0% +/- 8.6%; p < 0.05). All groups showed a hyperemic response immediately after CPB. No significant differences between the four groups were found for gastric mucosal oxygenation during or after CPB. A progressive decline occurred in this variable during the period 3 to 4 hours after CPB. At this time, total-body oxygen consumption and extraction were at their maximum., Conclusions: This study found that perfusion protocol can influence mucosal blood flow, but other overriding factors that operate during and after CPB act to cause mucosal hypoxia. These findings, particularly the timing of mucosal hypoxia, may have implications for centers contemplating early extubation or "fast tracking" of patients after CPB.

Objective: To compare the effects of dopexamine and dopamine on the mucosal permeability of the gastrointestinal tract (GIT)., Design: Prospective, randomised clinical trial., Setting: Intensive care unit of a postgraduate teaching hospital, London, England., Patients: Thirty patients undergoing elective surgery involving cardiopulmonary bypass, performed by a single surgeon., Interventions: Patients were randomly assigned to receive either dopexamine 2.0 micrograms/kg per min or dopamine 2.5 micrograms/kg per min for the duration of the study period., Measurements and Main Results: Hemodynamic parameters and gastric intramucosal pH (pHi) were measured at intervals throughout the study. GIT permeability was measured once, post-operatively, using the ratio of absorbed lactulose to L-rhamnose. The groups were similar with respect to demographics, pre- and post-operative risk factors. The lactulose/rhamnose ratio was (mean +/- SEM) 0.44 +/- 0.10 in the dopexamine group vs 0.65 +/- 0.08 in that receiving dopamine (p < 0.05). The dopexamine group had a significantly higher oxygen delivery preoperatively (479.5 +/- 32.0 ml/min per m2 vs 344.4 +/- 23.9 ml/min per m2 for dopamine, p < 0.01), but no other significant differences emerged between the groups., Conclusions: Compared to dopamine, dopexamine reduces GIT permeability following surgery involving cardiopulmonary bypass. The mechanism of this effect remains unclear.

Cardiopulmonary bypass (CPB) is associated with blood heparin level fluctuations and a reduction in haematocrit due to crystalloid haemodilution. The effect of these changes on the reliability of the Limulus amoebocyte lysate (LAL) chromogenic microassay for the measurement of plasma endotoxin was assessed in vitro. It was shown that the assay could be significantly compromised by twofold haemodilution which can occur during CPB. The interference effect on the assay caused by CPB-associated heparin was not significant if a comparatively large amount of heparin (25 IU/ml) was added to the blood at the time of sampling. The effect of haemodilution was counteracted by prediluting plasma samples with crystalloid by a factor dependent on the sample haematocrit (to ensure that the proportion of plasma was similar in all samples). A correction was then required to determine the endotoxin level in the original sample. The modified assay was used to determine sequential plasma endotoxin levels in 14 patients undergoing hypothermic nonpulsatile CPB. Endotoxaemia occurred at the time of aortic cross-clamp release and reached a peak of 48.9 +/- 12.9 ng/l shortly before the end of CPB, which was significantly higher than baseline values pre-CPB (p < 0.05). Thereafter, there was a decline in endotoxin levels to 28.9 +/- 13.6 ng/l 24 hours later which was still significantly higher than baseline levels (p < 0.05). Peak endotoxaemia was a predictor of protracted hospital stay when compared with haemodynamic and tissue perfusion parameters.

Studies documenting rises in endotoxin after cardiopulmonary bypass (CPB) have postulated gut mucosal hypoperfusion. We have investigated alterations in jejunal blood flow by laser Doppler flow measurement, intramucosal pH (pHi) by tonometry, and oxygen utilization in a canine model of hypothermic CPB (n = 11 dogs). After 10 minutes of hypothermic CPB, despite no major reduction in superior mesenteric artery flow, mucosal laser Doppler flow decreased to -38.2% +/- 9.3% of levels obtained before bypass (p = 0.008) and serosal laser Doppler flow, to -47.3% +/- 11.4% (p = 0.006). During the hypothermic phase, mesenteric oxygen consumption fell from 0.18 +/- 0.01 to 0.098 +/- 0.01 mL.min-1.kg-1 (p = 0.005), and mesenteric oxygen delivery fell from 1.97 +/- 0.39 to 1.14 +/- 0.12 mL.min-1.kg-1 (p = 0.05). There was no change in jejunal pHi. During the rewarming phase, there was a substantial increase in mucosal laser Doppler flow, peaking at +69.8% +/- 15.2% (p = 0.03), whereas serosal laser Doppler flow returned to values seen prior to CPB (-16.4% +/- 21.5%; p = 0.25). These changes coincided with a surge in oxygen consumption (0.33 +/- 0.042 mL.min-1.kg-1; p = 0.009), while mesenteric oxygen delivery remained depressed at 1.09 +/- 0.12 mL.min-1.kg-1 (p = 0.04). Jejunal pHi fell from a value of 7.36 +/- 0.04 before CPB to 7.12 +/- 0.07 (p = 0.02), thus indicating mucosal hypoxia. During the rewarming phase of hypothermic CPB, there is a disparity between mesenteric oxygen consumption and oxygen delivery with villus tip ischemia; these findings may explain the pathophysiology of endotoxemia during CPB.

In a study to assess the potential effect of nonpulsatile hypothermic cardiopulmonary bypass (CPB), intramucosal pH (pHi) of the gastric and colonic mucosae was determined by tonometry (n = 8). During the hypothermic phase of CPB, gastric and colonic pHi did not change significantly. Forty minutes after the start of rewarming, despite increases in the cardiac index and mean arterial blood pressure, gastric pHi fell from 7.53 +/- 0.02 to 7.31 +/- 0.03 (p = 0.017) and colonic pHi fell from 7.50 +/- 0.02 to 7.32 +/- 0.03 (p = 0.028). Forty minutes after the end of CPB both the colonic (p = 0.017) and gastric (p = 0.046) pHi remained depressed below pre-CPB values. The difference in the arterial (pHa) and the gastric mucosal pH changed from -0.097 before CPB to 0.016, 40 minutes after the end of CPB (p = 0.027). This alteration in the pHa-pHi underlines the importance of measuring intramucosal pH by tonometry, since the pHa and pHi may move in opposite directions during episodes of haemodynamic stress. Both the gastric and colonic pHi were found to have a linear correlation with the pHa, although changes in the gastric pHi (r = 0.41, p = 0.018) were more strongly correlated with the pHa than the colonic pHi (r = 0.23, p = 0.19) in the rewarming phase of CPB and the immediate post-CPB period when there was a tendency towards intramucosal acidosis. The development of intramucosal acidosis in the rewarming and immediate post-CPB phases following hypothermic nonpulsatile CPB may impair the gut barrier and predispose patients to the absorption of luminal toxins.

Background/aims: Mean arterial pressure is reduced during hypothermic cardiopulmonary bypass. The aim of this study was to assess whether this was associated with intestinal hypoperfusion and whether it affected intestinal absorption and permeability., Methods: Twenty-six patients undergoing coronary artery bypass grafting underwent an intestinal absorption-permeability test involving ingestion of 3-O-methyl-D-glucose, D-xylose, L-rhamnose, and lactulose. Ingestion took place 2 days before, within 3 hours, and 5 days after hypothermic cardiopulmonary bypass. Hemodynamic parameters and gastric mucosal laser Doppler blood flow were measured perioperatively in eight patients., Results: Hypothermic (28 degrees C), nonpulsatile cardiopulmonary bypass resulted in a 25% reduction in mean blood pressure, 10% reduction in cardiac index, and a 46% reduction in gastric mucosal laser Doppler blood flow. There was 85.4%, 85.5%, and 73.6% reduction (P < 0.01) in active (3-O-methyl-D-glucose) and passive (D-xylose) carrier-mediated transport and passive, nonmediated transcellular (L-rhamnose) transport in the immediate postoperative period, respectively. The differential urine excretion of lactulose/L-rhamnose increased sixfold. All parameters returned to control levels by the fifth postoperative day., Conclusions: Cardiopulmonary bypass, while maintaining generally acceptable levels of hemodynamic performance, is associated with significant intestinal hypoperfusion and malabsorption of monosaccharides, which may have implications for enteral drug treatment in the immediate postoperative period.

Gastrointestinal damage occurs in 0.6% to 2% of patients after cardiopulmonary bypass (CPB), and carries a mortality of 12% to 67%. The incidence of subclinical gastrointestinal damage may be much greater. We examined the effects of nonpulsatile, hypothermic CPB on intestinal absorption and permeability in 41 patients. Bowel mucosal saccharide transport and permeation were evaluated using 100 mL of an oral solution containing 3-O-methyl-D-glucose (0.2 g), D-xylose (0.5 g), L-rhamnose (1.0 g), and lactulose (5.0 g) to assess active carrier-mediated, passive carrier-mediated, transcellular, and paracellular transport, respectively, with a 5-hour urine analysis. Patients were studied before, immediately after, and 5 days after CPB. Immediately after CPB there was a decrease in urinary excretion of 3-O-methyl-D-glucose (from 34% +/- 2.2% to 5.2% +/- 0.7%; p < 0.0001), D-xylose (from 25.4% +/- 1.4% to 4.1% +/- 0.8%; p < 0.0001), and L-rhamnose (from 8.3% +/- 0.6% to 2.6% +/- 0.4%; p < 0.0001). The permeation of 3-O-methyl-D-glucose and D-xylose returned to normal levels 5 days after CPB, but that of L-rhamnose remained significantly below pre-CPB values at 6.6% +/- 0.5% (p = 0.004). However, the permeation of lactulose increased after CPB (from 0.35% +/- 0.04% to 0.59% +/- 0.1%; p = 0.018), and the lactulose/L-rhamnose gut permeability ratio increased markedly (from 0.045 +/- 0.04 to 0.36 +/- 0.08; normal = 0.06 to 0.08; p = 0.004). Patients who had a CPB time of 100 minutes or more had a greater increase in gut permeability (p = 0.049).(ABSTRACT TRUNCATED AT 250 WORDS)

Objective: To study the impact of continuous veno-venous haemofiltration on survival in patients with acute renal failure (ARF) following cardio-pulmonary bypass (CPB) surgery., Design: A retrospective study of all patients requiring haemofiltration after CPB over a 2 year period., Setting: A 20 bedded, adult cardothoracic intensive care unit in a postgraduate teaching hospital., Patients: 35 patients (26 male, age range 24-74 years) required haemofiltration (2.7% of the total number of patients undergoing CPB)., Main Results: Cardiovascular failure post CPB was the commonest causes of ARF (n = 16). Indications for haemofiltration were uremia (21), oligo-anuria (11), volume overload (2) and hyperkalaemia (1). Mean time from CPB to the initiation of haemofiltration was 8 days (range 0-15 days). Mean urea was 30 mmol/l and creatinine 362 mumol/l immediately prior to treatment. Urea was well-controlled in all patients, although 2 needed haemodiafiltration. Twenty-six patients died during their admission to the ICU (74% mortality). A further 3 patients died during their hospital admission, following discharge from ICU. Outcome was particularly poor in patients with cardiovascular failure following CPB (16 cases, 0 survivors). Survivors tended to commence filtration earlier (mean of 4 vs 7 days for non-survivors) and required treatment for a mean period of 8 days (range 1-26 days). Survival was determined by the number of failed organ systems at the start of haemofiltration. Thus, 100% of patients with single system failure survived, compared to only 10% with 3 or more system failure., Conclusions: Despite the theoretical advantages of haemofiltration and the effective control of uraemia the mortality associated with ARF following CPB remains high and is probably determined by the number of failed organs systems.

The outcome of adult respiratory distress syndrome complicating cardiopulmonary bypass has changed little in recent years. A retrospective, case-controlled study was designed to assess the incidence of the adult respiratory distress syndrome in these circumstances and the extent to which it could be linked with pre and peri-operative predictive factors. Eleven patients who developed the syndrome out of 840 who underwent cardiopulmonary bypass over a 9 month period were compared with 53 controls matched for sex, operation and surgeon. The incidence of adult respiratory distress syndrome and its mortality were 1.3% and 53% respectively. Significant predictors were a high intra and postoperative intervention score, the total volume of blood pumped during bypass (greater than 300 l) and age (greater than 60 years). These risk factors should alert the clinician to the possibility of severe postoperative pulmonary complications.

In the light of several incidences at Brompton Hospital in which enoximone brought about a striking improvement in cardiac index in patients with refractory left ventricular failure, a study was initiated to compare the effects of enoximone and dobutamine following cardiopulmonary bypass in patients with impaired left ventricular function (preoperative ejection fraction less than 0.5). In two groups of 10 patients, similar responses of haemodynamic variables were obtained with enoximone or dobutamine administration. In particular, mean cardiac index increased by 25% in the first 15 min and by 60% over the 24-hour study period after bypass. Mean systemic vascular resistance fell by approximately 10%. Mixed venous oxygen saturation increased marginally from a preoperative value of approximately 76% within 15 min of drug administration and then fell and stabilized at about 65% in the next 12 h during re-warming. Patients were weaned from enoximone, after 24 h, without event. Both drugs were shown to produce favourable haemodynamic profiles and to be well tolerated in this relatively high-risk cohort of patients.