Oddbjørn Haugen

Mean arterial pressure about 40 mmHg during CPB is associated with cerebral ischemia in piglets

Objective. To investigate if a mean arterial pressure below 50 mmHg during CPB may lead to cerebral ischemia. Material and methods. Piglets with low mean arterial pressure by nitroprusside (LP-group) (n = 6) were compared with piglets given norepinephrine to obtain high pressure (HP-group) (n = 6) during normothermic and hypothermic CPB. Intracranial pressure, flow and markers of cerebral energy metabolism (microdialysis) were recorded. Results. Mean arterial pressure differed significantly between the groups and stabilized about 40–45 mmHg in the LP-group. Cerebral perfusion pressure decreased to 21.3 (7.7) mmHg in the LP-group and increased to 51.8 (11.2) mmHg in the HP-group at 150 min of CPB (P < 0.001, between groups). During bypass the intracerebral glucose concentration decreased significantly in the LP-group. In this group the lactate/pyruvate ratio increased from 15.5 (5.3) to 64.5 (87.6) at 90 min and 45.0 (36.5) at 150 min (P < 0.05) with no such changes in the HP-group. Similarly the cerebral glycerol concentration increased significantly in the LP-group, whereas glycerol remained stable in the HP-group. Conclusion. Mean arterial pressure about 40 mmHg during CPB is associated with cerebral ischemia.

Fluid shift is moderate and short‐lived during acute crystalloid hemodilution and normothermic cardiopulmonary bypass in piglets

Background:  Crystalloids are commonly used as priming solutions during cardiopulmonary bypass (CPB). Consequently, hemodilution is a regular occurrence at the start of a CPB. This study describes the time‐course variations of hemodynamic parameters, plasma volume (PV) and fluid exchange following crystalloid hemodilution at start of normothermic CPB.

Reduced fluid gain during cardiopulmonary bypass in piglets using a continuous infusion of a hyperosmolar/hyperoncotic solution

Background:  The aim of this study was to evaluate how a continuous infusion of a hyperosmolar/hyperoncotic solution influences fluid shifts and intracranial pressure during cardiopulmonary bypass in piglets.

Isoflurane in contrast to propofol promotes fluid extravasation during cardiopulmonary bypass in pigs.

Background:A highly positive intraoperative fluid balance should be prevented as it negatively impacts patient outcome. Analysis of volume-kinetics has identified an increase in interstitial fluid volume after crystalloid fluid loading during isoflurane anesthesia. Isoflurane has also been associated with postoperative hypoxemia and may be associated with an increase in alveolar epithelial permeability, edema formation, and hindered oxygen exchange. In this article, the authors compare fluid extravasation rates before and during cardiopulmonary bypass (CPB) with isoflurane- versus propofol-based anesthesia. Methods:Fourteen pigs underwent 2 h of tepid CPB with propofol (P-group; n = 7) or isoflurane anesthesia (I-group; n = 7). Fluid requirements, plasma volume, colloid osmotic pressures in plasma and interstitial fluid, hematocrit levels, and total tissue water content were recorded, and fluid extravasation rates calculated. Results:Fluid extravasation rates increased in the I-group from the pre-CPB level of 0.27 (0.13) to 0.92 (0.36) ml·kg−1·min−1, but remained essentially unchanged in the P-group with significant between-group differences during CPB (pb = 0.002). The results are supported by corresponding changes in interstitial colloid osmotic pressure and total tissue water content. Conclusions:During CPB, isoflurane, in contrast to propofol, significantly contributes to a general increase in fluid shifts from the intravascular to the interstitial space with edema formation and a possible negative impact on postoperative organ function.

Fluid overload during cardiopulmonary bypass is effectively reduced by a continuous infusion of hypertonic saline/dextran (HSD)

Objective. Cardiopulmonary bypass (CPB) is associated with fluid overload. We examined how a continuous infusion of hypertonic saline/dextran (HSD) influenced fluid shifts during CPB. Materials and methods. Fourteen animals were randomized to a control-group (CT-group) or a hypertonic saline/dextran-group (HSD-group). Ringers solution was used as CPB-prime and as maintenance fluid at a rate of 5 ml/kg/h. In the HSD group, 1 ml/kg/h of the maintenance fluid was substituted with HSD. After 60 min of normothermic CPB, hypothermic CPB was initiated and continued for 90 min. Fluid was added to the CPB-circuit as needed to maintain a constant level in the venous reservoir. Fluid balance, plasma volume, total tissue water (TTW), intracranial pressure (ICP) and fluid extravasation rates (FER) were measured/calculated. Results. In the HSD-group the fluid need was reduced with 60% during CPB compared with the CT-group. FER was 0.38(0.06) ml/kg/min in the HSD-group and 0.74 (0.16) ml/kg/min in the CT-group. TTW was significantly lower in the heart and some of the visceral organs in the HSD-group. In this group ICP remained stable during CPB, whereas an increase was observed in the CT-group (p <0.01). Conclusions. A continuous infusion of HSD reduced the fluid extravasation rate and total fluid gain during CPB. TTW was reduced in the heart and some visceral organs. During CPB ICP remained normal in the HSD-group, whereas an increase was present in the CT-group. No adverse effects were observed.

Surface cooling versus core cooling: Comparative studies of microvascular fluid- and protein-shifts in a porcine model

OBJECTIVE To describe how surface cooling compared with core cooling influences fluid and protein distribution, vascular capacity and hemodynamic variables. METHODS 14 anesthetized piglets were, following 60 min normothermic stabilization, randomly cooled by surface cooling (ice-sludge) (n=7) or core cooling (endovascular cooling) (n=7) to about 28 degrees C. Fluid balance, hemodynamic variables, colloid osmotic pressures (plasma/interstitial fluid), hematocrit, serum-albumin and -protein concentrations, intracranial pressure (ICP) and cerebral metabolic markers of ischemia were measured. Fluid shifts and changes in albumin and protein masses were calculated. At the end total tissue water content was assessed and compared with a normothermic control group. RESULTS Both cooling modes induced an increase in fluid extravasation rate from 33.9 (31.9) and 27.8 (28.0) to 109.0 (16.5) (P=0.006) and 95.6 (29.1) ml/kg/min x 10(-3) (P=0.024) in the surface-cooled and core-cooled groups, respectively. Albumin extravasation was reflected by a significant drop in the albumin mass from 148.8 (11.7) to 111.4 (10.3) (P=0.000) and from 163.4 (27.8) to 136.8 (19.0) g/kg x 10(-2) (P=0.001) in the surface-cooled and core-cooled animals, respectively. Similar findings were obtained concerning serum-protein masses. The total tissue water content increased in most organs including brain in both study groups compared with a control. ICP and cerebral metabolic markers remained normal in both groups. CONCLUSION Rapid lowering of body core temperature results in extravasation of water and proteins. The amount of extravated fluid and proteins is similar either cooling is a result of surface cooling or core cooling. Cold-induced fluid extravasation is associated with edema in most tissues including brain.

A hyperosmolar-colloidal additive to the CPB-priming solution reduces fluid load and fluid extravasation during tepid CPB:

Cardiopulmonary bypass(CPB) is associated with fluid overload. We hypothesized that fluid gain during CPB could be reduced by substituting parts of a crystalloid prime with 7.2% hypertonic saline and 6% poly(O-2-hydroxyethyl) starch solution (HyperHaes®). 14 animals were randomized to a control group (Group C) or to Group H. CPB-prime in Group C was Ringer’s solution. In group H, 4 ml/kg of Ringer’s solution was replaced by the hypertonic saline / hydroxyethyl starch solution. After 60 min stabilization, CPB was initiated and continued for 120 min. All animals were allowed drifting of normal temperature (39.0°C) to about 35.0°C. Fluid was added to the CPB circuit as needed to maintain a 300-ml level in the venous reservoir. Blood chemistry, hemodynamic parameters, fluid balance, plasma volume, fluid extravasation rate (FER), tissue water content and acid-base parameters were measured/calculated. Total fluid need during 120 min CPB was reduced by 60% when hypertonic saline/hydroxyethyl starch solution was added to the CPB prime (p<0.01). The reduction was related to a lowered FER. The effect was most pronounced during the first 30 min on CPB, with 0.6 (0.43) (Group H) compared with 1.5 (0.40) ml/kg/min (Group C) (p<0.01). Hemodynamics and laboratory parameters were similar in both groups. Serum concentrations of sodium and chloride increased to maximum levels of 148 (1.5) and 112 (1.6) mmol/l in Group H. To conclude: addition of 7.2% hypertonic saline and 6% poly(O-2-hydroxyethyl) starch solution to crystalloid CPB prime reduces fluid needs and FER during tepid CPB.

Low arterial pressure during cardiopulmonary bypass in piglets does not decrease fluid leakage

Background:  Cardiopulmonary bypass (CPB) is associated with increased fluid filtration occasionally leading to post‐operative organ dysfunction. One of the factors determining fluid filtration is the capillary hydrostatic pressure which depends on arterial pressure, venous pressure and pre‐ to post‐capillary resistance ratio. The purpose of this study was to assess whether lowering of the mean arterial pressure and/or the central venous pressure could reduce fluid extravasation during normothermic and hypothermic CPB.

Intraoperative fluid balance during cardiopulmonary bypass: effects of different mean arterial pressures

Financial support . This study was financially supported by The Western Norway Regional Health Authority, The Norwegian Council on Cardiovascular Diseases, Faculty of Medicine, University of Bergen and The Frank Mohn Foundation, Norway. Introduction. This study investigated whether two levels of mean arterial pressure (MAP) during cardiopulmonary bypass did influence per-operative fluid shifts. Methods. Sixteen pigs underwent 60 minutes of normothermic cardiopulmonary bypass (CPB) followed by 90 minutes of hypothermic CPB. Eight animals had a MAP of 60—80 mmHg by norepinephrine (HP group). Another 8 animals had a MAP of 40—45 mmHg by phentolamine (LP group). Blood chemistry, plasma/interstitial colloid osmotic pressures, plasma volume, fluid balance, fluid extravasation rate and tissue water content were measured or calculated. Results. The plasma volume was significantly lower in the HP group compared with the LP group after 60 minutes of CPB. Net fluid balance was 0.18 (0.05) ml·kg - 1·min - 1 in the HP group and 0.21 ml·kg - 1·min - 1 in the LP group (P > 0.05) while fluid extravasation rate was 1.18 (0.5) and 1.13 (0.4) ml·kg - 1·min - 1 in the HP group and the LP group during CPB (P > 0.05). Conclusion. Net fluid balance and fluid extravasation rate were similar in the animals with elevated and with lowered MAP during CPB. Perfusion (2007) 22, 273—278.

Low perfusion pressure during CPB may induce cerebral metabolic and ultrastructural changes

Background. Recently we reported on cerebral metabolic changes suggesting ischemia in piglets during nitroprusside-induced low-pressure CPB. We here investigated whether a mean arterial pressure (MAP) of 40–45 mmHg could provoke similar changes by a NO-independent intervention. Methods. Piglets underwent 60 minutes normothermic followed by 90 minutes hypothermic CPB. The LP-group (n=8) had MAP of 40–45 mmHg by phentolamine while the HP-group (n=8) had MAP of 60–80 mmHg by norepinephrine. Cerebral glucose, lactate, pyruvate and glycerol were determined. In the last two animals of each group, cerebral tissue was examined by electron microscopy. Results. Cerebral lactate was higher in the LP-group than the HP-group during normothermic CPB. Compared with baseline, cerebral glucose of the LP-group decreased whereas lactate/pyruvate-ratio, lactate and glycerol-concentrations increased during normothermic CPB. In the HP-group these parameters remained unchanged. Electron microscopy showed 31.2% and 8.3% altered mitochondria in the cortical micrographs taken from the LP- and the HP-group, respectively (p<0.001). Conclusion. MAP below 45 mmHg during CPB was associated with cerebral biochemical and morphological changes consistent with anaerobic metabolism and subcellular injury.