Dynamic evaluation of fluid shifts during normothermic and hypothermic cardiopulmonary bypass in piglets

Massive Ascites Causing Presumed Abdominal Compartment Syndrome During Open Heart Surgery With Cardiopulmonary Bypass

Abdominal compartment syndrome (ACS) is a potentially fatal condition and a known cause of morbidity and mortality in critically ill patients. It can be primary, due to abdominal trauma and/or surgical procedures, or secondary, due to excessive abdominal fluid and/or bowel edema. Intra-abdominal hypertension (IAH) is defined as intra-abdominal pressure (IAP) greater than 12 mm Hg. ACS occurs when increased IAP results in organ dysfunction. Although IAPs are known to increase in cardiac surgery, ACS is uncommon, and reports are limited in the literature. We describe a fatal case of presumed ACS during an aortic valve and root replacement with coronary artery bypass grafting (CABG).

Comparison of Early Outcomes for Normothermic and Hypothermic Cardiopulmonary Bypass in Children Undergoing Congenital Heart Surgery

Objective: Comparison of early outcomes of normothermic cardiopulmonary bypass (N-CPB, ≥35°C) with hypothermic cardiopulmonary bypass (H-CPB, 28-34°C) for congenital heart defects. Methods: Data from 99 patients <2 years operated with N-CPB (n = 48) or H-CPB (n = 51) were retrospectively reviewed: aortic X-clamping and CPB duration, vasoactive inotropic score (VIS), arterial lactate, pH and base excess, urine output, extubation, PICU stay, transfusion requirements, chest drain losses, costs of transfusions, and costs of PICU stay. Results: The two groups were homogeneous for diagnosis, risk factors, surgery and demographic variables: N-CPB age 7.7 ± 6.1 months, weight 6.2 ± 2.4 kg, and H-CPB age 6.6 ± 6.5 months, weight 6.1 ± 2.4 kg. There were no hospital deaths in either group. VIS in N-CPB was lower than H-CPB on PICU arrival (9.7 ± 5.9 vs. 13.4 ± 7.9, P < 0.005), after 4 h (7.0 ± 5.2 vs. 11.1 ± 7.3, P < 0.001) and 24 h (2.8 ± 3.6 vs. 5.6 ± 5.6, P < 0.003); arterial pH was better at PICU arrival (7.33 ± 0.09 vs. 7.30 ± 0.09, P = 0.046) after 4 h (7.35 ± 0.07 vs. 7.32 ± 0.07, P = 0.022) and after 24 h (7.37 ± 0.05 vs. 7.35 ± 0.05, P = 0.01). Extubation was earlier in N-CPB than in H-CPB (22 ± 27 vs. 48 ± 57 h, P = 0.003) as PICU discharge (61 ± 46 h vs. 87 ± 69 h, P = 0.021). Transfusion requirements in operating room were lower in N-CPB vs. H-CPB for RBC, FFP, cryoprecipitate, and platelets, while during the first 24 h in PICU were lower only for cryoprecipitate and platelets. Chest drain losses (mL/kg) on PICU arrival, after 4 and 24 h were lower with N-CPB vs. H-CPB (respectively 1.5 ± 1.4 vs. 2.5 ± 2.7, P = 0.013, 7.8 ± 6.0 vs. 10.9 ± 8.7, P = 0.025, and 23.0 ± 12.0 vs. 27.9 ± 15.2, P = 0.043). Tranexamic acid infusion was required in 7/48 (14.6%) patients with N-CPB vs. 18/51(= 35.3%) in H-CPB (P = 0.009). The average total costs/patient of blood and blood products (RBC, FFP, cryoprecipitate, platelets) were lower in N-CPB vs. H-CPB for both the first 24 h after surgery (£204 ± 169 vs. £306 ± 254, P = 0.011) as well as during the total duration of PICU stay (£239 ± 193 vs. £427 ± 337, P = 0.001). The average cost/patient/day of stay in PICU was lower in N-CPB than in H-CPB (£4,067 ± 3,067 vs. £5,800 ± 4,600, P = 0.021). Conclusions: N-CPB may reduce inotropic and respiratory support, shorten PICU stay, and decrease peri-operative transfusion requirements, with subsequent costs reduction, compared to H-CPB. Future studies are needed to validate and support wider use of N-CPB.

Neonatal Aortic Arch Reconstruction With Direct Splanchnic Perfusion Avoids Deep Hypothermia

BACKGROUND

Neonatal aortic arch reconstruction, typically performed with deep hypothermia and selective cerebral perfusion, leaves splanchnic organ protection dependent on hypothermia alone. A simplified method of direct in-field descending aortic perfusion during neonatal arch reconstruction permits the avoidance of deep hypothermia. We hypothesize that direct splanchnic perfusion at mild hypothermia provides improved or equivalent safety compared with deep hypothermia and may contribute to postoperative extracardiac organ recovery.

METHODS

Included were 138 biventricular patients aged younger than 90 days undergoing aortic arch reconstruction with cardiopulmonary bypass. Patients were grouped according to perfusion method A (selective cerebral perfusion with deep hyperthermia at 18° to 20°C) or method B (selective cerebral perfusion and splanchnic perfusion at 30° to 32°C). Patient characteristics and perioperative clinical and serologic data were analyzed. Significance was assigned for p of less than 0.05.

RESULTS

Of the 138 survivors, 63 underwent method A and 75 underwent method B. The median age at operation was 8.5 days (range, 6 to 15 days), and median weight was 3.2 kg (range, 2.8 to 3.73 kg), with no significant differences between groups. Cardiopulmonary bypass times were comparable between the two perfusion methods (p = 0.255) as were the ascending aortic cross-clamp times (p = 0.737). The postoperative glomerular filtration rate was significantly different between our groups (p = 0.028 to 0.044), with method B achieving a higher glomerular filtration rate. No significant differences were seen in ventilator time, postoperative length of stay, fractional increase of postoperative serum creatinine over preoperative serum creatinine, and postoperative lactate.

CONCLUSIONS

A simplified method of direct splanchnic perfusion during neonatal aortic arch reconstruction avoids the use of deep hypothermia and provides renal protection at least as effective as deep hypothermia.

Effects of Constant Flow vs. Constant Pressure Perfusion on Fluid Filtration in Severe Hypothermic Isolated Blood-Perfused Rat Lungs

Background

Victims of severe accidental hypothermia are prone to fluid extravasation but rarely develop lung edema. We hypothesize that combined hypothermia-induced increase in pulmonary vascular resistance (PVR) and a concomitant fall in cardiac output protect the lungs against edema development. Our aim was to explore in hypothermic-isolated blood-perfused rat lungs whether perfusion at constant pressure influences fluid filtration differently from perfusion at constant flow.

Methods

Isolated blood-perfused rat lungs were hanging freely in a weight transducer for measuring weight changes (ΔW). Fluid filtration coefficient (Kfc), was determined by transiently elevating left atrial pressure (Pla) by 5.8 mmHg two times each during normothermia (37°C) and during hypothermia (15°C). The lung preparations were randomized to two groups. One group was perfused with constant flow (Constant flow group) and the other group with constant pulmonary artery pressure (Constant PPA group). Microvascular pressure (Pmv) was determined before and during elevation of Pla (ΔPmv) by means of the double occlusion technique. Kfc was calculated with the formula Kfc = ΔW/ΔPmv/min. All Kfc values were normalized to predicted lung weight (P_LW), which was based on body weight (BW) according to the formula: P_LW = 0.0053 BW − 0.48 and presented as Kfc_PLW in mg/min/mmHg/g. At cessation, bronchoalveolar lavage (BAL) fluid/perfusate protein concentration (B/P) ratio was determined photometrically. Data were analyzed with parametric or non-parametric tests as appropriate. p < 0.05 considered as significant.

Results

Perfusate flow remained constant in the Constant flow group, but was more than halved during hypothermia in the Constant PPA group concomitant with a more fold increase in PVR. In the Constant flow group, Kfc_PLW and B/P ratio increased significantly by more than 10-fold during hypothermia concerted by visible signs of edema in the trachea. Hemoglobin and hematocrit increased within the Constant flow group and between the groups at cessation of the experiments.

Conclusion

In hypothermic rat lungs perfused at constant flow, fluid filtration coefficient per gram P_LW and B/P ratio increased more than 10-fold concerted by increased hemoconcentration, but the changes were less in hypothermic lungs perfused at constant PPA.

Intercompartmental fluid volume shifts during cardiopulmonary bypass measured by A-mode ultrasonography

To investigate the time course of fluid extravasation during cardiopulmonary bypass (CPB), we measured the peripheral tissue thickness (TT) by A-mode ultra-sound in 34 patients undergoing elective cardiac surgery. TT of the forehead was determined by a handheld A-mode ultrasound device and 10 MHz Transducer at nine defined intervals, from the night before surgery until the first postoperative day.

Mean calculated loss of 1700±40 mL (SEM) water during the fasting period resulted in a significant reduction of TT by 0.28±0.03 mm. From induction to start of CPB, rehydration with 1000 mL of fluid was performed and TT increased to baseline. After 60 min of extracorporal circulation, forehead TT increased significantly by 0.75±0.08 mm and remained unchanged until the end of surgery when the measured fluid gain was 1580±138 mL. At discharge from ICU, negative fluid regimen resulted in a balance of -127±146 mL whereas TT declined significantly to + 0.16±0.09 mm compared to baseline.

Dehydration due to fasting and the marked interstitial fluid extravasation during CPB could be detected by the changes of the peripheral TT. We conclude that parts of the fluid load during CPB are shifted from the intravascular compartment to the interstitial space in a time-dependent manner.

Normothermia for pediatric and congenital heart surgery: an expanded horizon

Cardiopulmonary bypass (CPB) in pediatric cardiac surgery is generally performed with hypothermia, flow reduction and hemodilution. From October 2013 to December 2014, 55 patients, median age 6 years (range 2 months to 52 years), median weight 18.5 kg (range 3.2-57 kg), underwent surgery with normothermic high flow CPB in a new unit. There were no early or late deaths. Fifty patients (90.9%) were extubated within 3 h, 3 (5.5%) within 24 h, and 2 (3.6%) within 48 h. Twenty-four patients (43.6%) did not require inotropic support, 31 (56.4%) received dopamine or dobutamine: 21 ≤5 mcg/kg/min, 8 5-10 mcg/kg/min, and 2 >10 mcg/kg/min. Two patients (6.5%) required noradrenaline 0.05-0.1 mcg/kg/min. On arrival to ICU and after 3 and 6 h and 8:00 a.m. the next morning, mean lactate levels were 1.9 ± 09, 2.0 ± 1.2, 1.6 ± 0.8, and 1.4 ± 0.7 mmol/L (0.6-5.2 mmol/L), respectively. From arrival to ICU to 8:00 a.m. the next morning mean urine output was 3.8 ± 1.5 mL/kg/h (0.7-7.6 mL/kg/h), and mean chest drainage was 0.6 ± 0.5 mL/kg/h (0.1-2.3 mL/kg/h). Mean ICU and hospital stay were 2.7 ± 1.4 days (2-8 days) and 7.2 ± 2.2 days (4-15 days), respectively. In conclusion, normothermic high flow CPB allows pediatric and congenital heart surgery with favorable outcomes even in a new unit. The immediate post-operative period is characterized by low requirement for inotropic and respiratory support, low lactate production, adequate urine output, minimal drainage from the chest drains, short ICU, and hospital stay.

Fluid distribution kinetics during cardiopulmonary bypass

OBJECTIVE

The purpose of this study was to examine the isovolumetric distribution kinetics of crystalloid fluid during cardiopulmonary bypass.

METHODS

Ten patients undergoing coronary artery bypass grafting participated in this prospective observational study. The blood hemoglobin and the serum albumin and sodium concentrations were measured repeatedly during the distribution of priming solution (Ringer's acetate 1470 ml and mannitol 15% 200 ml) and initial cardioplegia. The rate of crystalloid fluid distribution was calculated based on 3-min Hb changes. The preoperative blood volume was extrapolated from the marked hemodilution occurring during the onset of cardiopulmonary bypass. Clinicaltrials.gov: NCT01115166.

RESULTS

The distribution half-time of Ringer's acetate averaged 8 minutes, corresponding to a transcapillary escape rate of 0.38 ml/kg/min. The intravascular albumin mass increased by 5.4% according to mass balance calculations. The preoperative blood volume, as extrapolated from the drop in hemoglobin concentration by 32% (mean) at the beginning of cardiopulmonary bypass, was 0.6-1.2 L less than that estimated by anthropometric methods (p<0.02). The mass balance of sodium indicated a translocation from the intracellular to the extracellular fluid space in 8 of the 10 patients, with a median volume of 236 ml.

CONCLUSIONS

The distribution half-time of Ringer's solution during isovolumetric cardiopulmonary bypass was 8 minutes, which is the same as for crystalloid fluid infusions in healthy subjects. The intravascular albumin mass increased. Most patients were hypovolemic prior to the start of anesthesia. Intracellular edema did not occur.

Intra-abdominal hypertension in cardiac surgery

OBJECTIVES

The occurrence of intra-abdominal hypertension (IAH), as well as its promoting factors in cardiac surgery, has been poorly explored. The aim of the present study was to characterize intra-abdominal pressure (IAP) variations in patients undergoing cardiac surgical procedures, and to identify the risk factors for IAH in this setting.

METHODS

All consecutive adult patients requiring postoperative intensive care unit admission for >24 h were enrolled. Demographic data, pre-existing comorbidities, type and duration of surgery, cardiopulmonary bypass (CPB) use and duration, perioperative IAP, organ function and fluid balance were recorded. IAH was defined as a sustained increase in IAP >12 mmHg. Multivariate logistic regression and stepwise analyses identified the baseline and perioperative variables associated with IAH.

RESULTS

Of 69 patients, 22 (31.8%) developed IAH. In the logistic model, baseline IAP, high central venous pressure, vasoactive drugs administration, positive fluid balance, AKI, CPB, total sequential organ failure assessment score and age were all promoting factors for IAH (Hosmer-Lemeshow χ(2) = 7.23; P = 0.843). Baseline IAP, high central venous pressure and positive fluid balance were independent risk factors for IAH in the stepwise analysis. The ROC curve analysis, obtained by plotting the occurrence of IAH vs the IAP baseline value, showed an AUC of 0.75 (SE 0.064; 99% CI 0.62-0.87; P < 0.0001). The best IAP cut-off value was at 8 mmHg (sensitivity 63% and specificity 76%). Considering on- and off-pump surgery groups, fluid balance and vasoactive drugs use were significantly higher in the on-pump group. Linear regression analysis showed a positive correlation (P = 0.0001) between IAP changes and fluid balance only in the on-pump group.

CONCLUSIONS

IAH develops in one-third of cardiac surgery patients and is strongly associated with higher baseline IAP values, higher central venous pressure, positive fluid balance, extracorporeal circulation, use of vasoactive drugs and AKI. Determinants of IAH should be accurately assessed before and after surgery, and patients presenting risk factors must be monitored properly during the perioperative period. In this context, the baseline value of IAP may be a valuable and early warning parameter for IAH occurrence.

Warm pediatric cardiac surgery: European experience

Cold pediatric cardiac surgery has been a dogma for 50 years. However, the beneficial effects of cold perfusion are counterbalanced by the drawbacks of hypothermia. Thus, we propose a major paradigm shift from hypothermic surgery to warm perfusion and intermittent warm blood cardioplegia. This approach gives satisfactory results even with prolonged aortic crossclamp times. The major advantages are reduced time to extubation and shorter intensive care unit stay. Warm pediatric surgery is an anecdotal phenomenon no more; over 10,000 procedures have been carried out in Europe. All types of cardiopathy have been treated, including arterial switch, total pulmonary anomalous venous return, interruption of the aortic arch, and hypoplastic left heart syndrome. Once surgeons decide to shift from hypothermia to normothermia, they never decide to shift back to hypothermia. This fact is evidence of the satisfactory clinical outcome obtained with this technique. The technique and the composition of microplegia is identical in all European centers, the only variable factor being the interval between microplegia injections, which varies from 10 to 25 min. We hope that the increasing interest in pediatric warm surgery will hearten new candidates.

Intra-abdominal and abdominal perfusion pressure in patients undergoing coronary artery bypass graft surgery

BACKGROUND

In 2006, the International Conference of Experts on Intra-abdominal Hypertension defined abdominal perfusion pressure (APP) as the difference between mean arterial pressure (MAP) and intra-abdominal pressure (IAP).The aim of the study was to analyse changes in IAP and APP in patients undergoing elective coronary artery bypass grafting (CABG).

PATIENTS AND METHODS

Fifty patients undergoing CABG with extracorporeal circulation (ECC) and normovolemic haemodilution (NH) under general anaesthesia were studied. IAP and APP were measured during CABG and in the early postoperative period. Changes in IAP and APP were analysed according to degree of normovolemic haemodilution, age, body weight, body mass index (BMI), duration of anaesthesia, surgery, ECC, aorta clamping and other haemodynamic parameters.

RESULTS

The induction of anaesthesia decreased IAP. Extracorporeal circulation resulted in IAP elevation, which was dependent on the degree of blood dilution. At any time point of the postoperative period IAP higher than 12 mmHg was noted in 22 patients (44%). Abdominal perfusion pressure decreased during ECC and on the morning of the first postoperative day. Intra-abdominal pressure strongly correlated with BMI and central venous pressure. The correlation between IAP and APP and other haemodynamic parameters was poor.

CONCLUSIONS

1) The induction of anaesthesia decreased IAP. 2) ECC resulted in an increase in IAP. 3) IAP increased in 44% of patients. 4) IAP strongly correlated with BMI and central venous pressure. 5) CABG with ECC resulted in a decrease in APP. 6) Changes in APP strongly correlated with MAP and poorly correlated with other haemodynamic parameters. 7) The changes in APP demonstrated a double-phase character.

Pediatric warm open heart surgery and prolonged cross-clamp time

BACKGROUND

The safety of normothermic pediatric cardiac surgery remains controversial. This study evaluated the performance of normothermic cardiopulmonary bypass (CPB) associated with intermittent warm blood cardioplegia during prolonged aortic cross-clamp time (CCT).

METHODS

This retrospective study included 234 consecutive patients weighing less than 10 kg operated under CPB from August 2006 to November 2007. Patients were divided into two groups: group 1 contained 38 patients with CCT exceeding 90 minutes, and group 2 had 196 patients with shorter CCT. Classic factors were used to analyze outcomes, and outcomes were compared with those from the Society of Thoracic Surgeons-European Association for Cardio-Thoracic Surgery database.

RESULTS

Results, expressed as values for group 1 vs those for group 2, were mortality rate, 5.3% vs 2%; length of hospital stay exceeding 21 days, 5% vs 0.5%; delayed chest closure, 21% vs 2.6%; epinephrine infusion, 45% vs 11%; organ failure, 13% vs 2%; reoperation due to bleeding, 3% vs 0.5%; heart block, 3% vs 1%; time to extubation, in hours, 64 +/- 94 vs 19 +/- 48; plasma lactate concentrations after bypass, 2.6 vs 1.9 mmol/L; length of stay in intensive care, in hours, 100 +/- 105 vs 52 +/- 48.

CONCLUSIONS

Despite expected differences between the two groups, our results were within the range of values described in the literature. This led us to conclude that warm pediatric cardiac surgery with a long CCT is safe. A large, multicenter, randomized prospective study comparing normothermic and hypothermic pediatric cardiac surgery is underway.

A transthoracic Doppler echocardiography study of C-reactive protein and coronary microcirculation in children after open heart surgery

BACKGROUND

Systemic inflammation has been suggested to underlie in part the elevated risk of arrhythmias and myocardial dysfunction during the first weeks after cardiac surgery. Recent transthoracic Doppler studies from our centre indicated increased basal coronary arterial flow in children 5 days after cardiopulmonary bypass surgery. In these children, we investigated whether the inflammatory mediator, C-reactive protein, could influence this association.

METHODS

The peak flow velocity, velocity time-integral in diastole and systole, and basal blood flow in the proximal part of the left anterior descending artery, were assessed by transthoracic Doppler echocardiography 1 day before, and 5 days after, cardiac surgery in 17 children with ventricular and atrioventricular septal defects whose mean age at surgery was 6 months. Levels of C-reactive protein in the plasma were measured at both time-points.

RESULTS

Prior to surgery, all children had levels of C-reactive protein under the limit for detection, that is less than 0.8 milligrams per litre. The levels of the protein had increased significantly by the second day, when the median value was 25, and the range from 20 to 142 milligrams per litre. They remained elevated on the fifth day after surgery, when the median was 11, and the range from 3 to 20 milligrams per litre. On the fifth day, the percentage increase in velocity time integral corrected for left ventricular mass was significantly lower in those patients with C-reactive protein greater than or equal to 10 milligrams per litre than in the remaining patients. Also, both the velocity time integral and the velocity of diastolic peak flow correlated inversely with log C-reactive protein, r being equal to -0.54 and p less than 0.02 and r equal to -0.74 and p less than 0.01, respectively, particularly among those patients in whom clamping of the aorta lasted for more than 1 hour, r for this statistic being equal to -0.8.

CONCLUSION

The postsurgical increase in the velocity of coronary arterial flow in children is inversely associated with rising levels of C-reactive protein. The duration of the aortic cross-clamping during surgery strengthens the association between levels of C-reactive protein and the microcirculatory changes.

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.

METHODS

Seven piglets were given nitroprusside to a mean arterial pressure of 35-40 mmHg during 60 min of normothermic and 90 min of hypothermic CPB (LP group). They were compared with a control group (C group, n = 7) without blood pressure interventions. Blood chemistry, net fluid balance, plasma volume, colloid osmotic pressure in plasma and interstitial fluid, intravascular protein masses, fluid extravasation rate and total tissue water content were measured or calculated.

RESULTS

Mean arterial pressure was significantly lower in the LP group than in the C group during CPB. Plasma volume tended to increase in the LP group (P > 0.05), but remained essentially unchanged in the C group. Net fluid balance in the LP group was more positive than in the C group 30 min after CPB start [1.02 (0.15) vs. 0.56 (0.13) ml/kg/min (Mean (SEM) P < 0.05)]. Fluid extravasation rate tended to be higher in the LP group and total tissue water content of the gastrointestinal tract, left myocardium and skin was significantly elevated compared with the C group.

CONCLUSION

During CPB, lowering of the mean arterial pressure using nitroprusside did not reduce fluid extravasation. On the contrary, the data may implicate an increase in edema formation during low pressure CPB.

Cold-induced fluid extravasation during cardiopulmonary bypass in piglets can be counteracted by use of iso-oncotic prime

OBJECTIVE

Hypothermic cardiopulmonary bypass is associated with increased fluid extravasation. This study aimed to compare whether iso-oncotic priming solutions, in contrast to crystalloids, could reduce the cold-induced fluid extravasation during cardiopulmonary bypass in piglets.

METHODS

Three groups were studied: the control group (CT group; n = 10), the albumin group (Alb group; n = 7), and the hydroxyethyl starch group (HES group; n = 7). Prime (1000 mL) and supplemental fluid were acetated Ringer solution, 4% albumin, and 6% hydroxyethyl starch, respectively. After 1 hour of normothermic cardiopulmonary bypass, hypothermic cardiopulmonary bypass (cooling to 28 degrees C within 15 minutes) was initiated and continued to 90 minutes. Fluid needs, plasma volume, changes in colloid osmotic pressure in plasma and interstitial fluid, hematocrit levels, and tissue water content were recorded, and protein masses and fluid extravasation rates were calculated.

RESULTS

Colloid osmotic pressure in plasma decreased immediately after the start of cardiopulmonary bypass in the CT group but remained stable in the Alb and HES groups. Colloid osmotic pressure in interstitial fluid tended to decrease in the CT group and remained unchanged in the Alb group, whereas a slight increase was observed in the HES group. Immediately after the start of cooling, fluid extravasation rates increased from 0.15 +/- 0.10 to 0.64 +/- 0.12 mL . kg -1 . min -1 in the CT group, whereas no such increase was observed in the Alb and HES groups. The changes in fluid extravasation rates were reflected by corresponding changes in tissue water content.

CONCLUSION

The use of albumin or hydroxyethyl starch as prime to preserve the colloid osmotic pressure during cardiopulmonary bypass causes a reduction in the cold-induced fluid extravasation compared with that seen with crystalloids. Albumin seems more effective than hydroxyethyl starch to limit cold-induced fluid shifts during cardiopulmonary bypass.

Time course variations of haemodynamics, plasma volume and microvascular fluid exchange following surface cooling: an experimental approach to accidental hypothermia

OBJECTIVE

To describe how surface cooling influences fluid distribution, vascular capacity and haemodynamic variables.

METHODS

Seven anaesthetised pigs, following normothermic stabilization for 60 min, were cooled to 27.8+/-1.6 degrees C. Fluid balance, haemodynamics, colloid osmotic pressures (plasma/interstitial fluid), haematocrit [s-albumin/protein] were recorded and plasma volume measured together with tissue perfusion during normothermia, cooling and stable hypothermia (coloured microspheres). Fluid shifts and changes in albumin and protein masses were calculated. At the end tissue water content was assessed.

RESULTS

Haemodynamic variables changed with the start of cooling in parallel with a decreasing cardiac output. During hypothermia the haematocrit increased from 0.31+/-0.01 to 0.35+/-0.01 (P < 0.01). Plasma volume decreased from 1139.0+/-65.4 ml at start of cooling to 882.0+/-67.5 ml 3 h later (P < 0.05). In parallel the plasma albumin and protein masses decreased from 37.8+/-2.5 g and 54.6+/-4.0 g to 28.0+/-2.7 g (P < 0.05) and 41.2+/-4.1 g (P > 0.05), respectively. The main changes occurred 120-180 min after start of each experiment. In this period the fluid extravasation rate was elevated (P < 0.05) without influencing the colloid osmotic pressure of plasma/interstitial fluid. The increased fluid filtration was reflected by an increase in tissue water content.

CONCLUSION

Our results are in favour of a shift of plasma from circulation to the interstitial space during surface cooling. This conclusion is based on the parallel losses of fluid and proteins from circulation with unchanged colloid osmotic pressures (plasma/interstitial fluid). Inflammation may be involved.

Hemodilution During Cardiopulmonary Bypass Increases Cerebral Infarct Volume After Middle Cerebral Artery Occlusion in Rats

Although the optimal hematocrit during cardiopulmonary bypass (CPB) is not defined, excessive hemodilution may lead to organ ischemia via a reduction in oxygen-carrying capacity uncompensated by autoregulatory and/or rheologic increases in organ blood flow. As a result, the consequences of hemodilution in patients at risk for cerebral ischemia are not clearly understood. We designed this study to evaluate the effects of hemodilution in the setting of focal cerebral ischemia during CPB. Wistar rats surgically prepared for CPB were randomized to either hemodilution (hemoglobin (Hb), 6 g/dL; n = 9) or control (Hb, 11 g/dL; n = 8) groups and subsequently exposed to focal cerebral ischemia induced by middle cerebral artery occlusion (MCAO). Immediately after the onset of MCAO (maintained for 90 min), 65 min of hypothermic (28 degrees C) CPB was initiated. Twenty-four hours later, functional neurological outcome and cerebral infarct volume were determined. Compared with controls, the hemodilution group had worse neurological performance (new score = 8 [2], hemodilution; versus 10 [2], control; P = 0.030) and larger total cerebral infarct volumes (182 +/- 84 mm(3), hemodilution; versus 103 +/- 58 mm(3), control; P = 0.043). In this experimental model of CPB with reversible MCAO-induced focal cerebral ischemia, hemodilution worsened neurological function and increased cerebral infarct volume.

Fluid extravasation during cardiopulmonary bypass in piglets--effects of hypothermia and different cooling protocols

BACKGROUND

Hypothermic cardiopulmonary bypass (CPB) is associated with capillary fluid leak and edema generation which may be secondary to hemodilution, inflammation and hypothermia. We evaluated how hypothermia and different cooling strategies influenced the fluid extravasation rate during CPB.

METHODS

Fourteen piglets were given 60 min normothermic CPB, followed by randomization to two groups: 1: rapid cooling (RC-group) ( approximately 15 min to 28 degrees C); 2: slow cooling (SC-group) ( approximately 60 min to 28 degrees C). Ringer's solution was used as CPB prime and for fluid supplementation. Fluid input/losses, plasma volume, colloid osmotic pressures (plasma, interstitial fluid), hematocrit, serum-proteins and total tissue water (TTW) were measured and fluid extravasation rates calculated.

RESULTS

Start of normothermic CPB resulted in a 25% hemodilution. During the first 5-10 min the fluid level of the reservoir fell markedly due to an intravascular volume loss necessitating fluid supplementation. Thereafter a steady state was reached with a constant fluid need of 0.14 +/- 0.04 ml kg-1 min-1. After start of cooling the fluid needs increased in the following 30 min to 0.91 +/- 0.11 ml kg-1 min-1 in the RC group (P < 0.001) and 0.63 +/- 0.10 ml kg-1 min-1 in the SC-group (P < 0.001) with no statistical between-group differences. Fluid extravasation rates after start of hypothermic CPB increased from 0.20 +/- 0.08 ml kg-1 min-1 to 0.71 +/- 0.13 (P < 0.01) and 0.62 +/- 0.13 ml kg-1 min-1 (P < 0.05) in the RC- and SC-groups, respectively, without any changes in degree of hemodilution. TTW increased in most tissues, whereas the intravascular albumin and protein masses remained constant with no between group differences.

CONCLUSION

Hypothermia increased fluid extravasation during CPB independent of cooling strategy. Intravascular albumin and protein masses remained constant. Since inflammatory fluid leakage usually results in protein rich exudates, our data with no net protein leakage may indicate that mechanisms other than inflammation could contribute to fluid extravasation during hypothermic CPB.

Temperature-related fluid extravasation during cardiopulmonary bypass: an analysis of filtration coefficients and transcapillary pressures

BACKGROUND

Cardiopulmonary bypass (CPB) as used for cardiac surgery and for rewarming individuals suffering deep accidental hypothermia is held responsible for changes in microvascular fluid exchange often leading to edema and organ dysfunction. The purpose of this work is to improve our understanding of fluid pathophysiology and to explore the implications of the changes in determinants of transcapillary fluid exchange during CPB with and without hypothermia. This investigation might give indications on where to focus attention to reduce fluid extravasation during CPB.

METHODS

Published data on "Starling variables" as well as reported changes in fluid extravasation, tissue fluid contents and lymph flow were analyzed together with assumed/estimated values for variables not measured. The analysis was based on the Starling hypothesis where the transcapillary fluid filtration rate is given by: JV=Kf [Pc-Pi-sigma(COPp-COPi)]. Here Kf is the capillary filtration coefficient, sigma the reflection coefficient, P and COP are hydrostatic and colloid osmotic pressures, and subscript 'c' refers to capillary, 'i' to the interstitium and 'p' to plasma.

RESULTS AND CONCLUSION

The analysis indicates that attempts to limit fluid extravasation during normothermic CPB should address primarily changes in Kf, while changes in both Kf and Pc must be considered during hypothermic CPB.

Studies on fluid extravasation related to induced hypothermia during cardiopulmonary bypass in piglets

BACKGROUND

Hypothermia, commonly used for organ protection during cardiopulmonary bypass (CPB), has been associated with changes in plasma volume, hemoconcentration and microvascular fluid shifts. Fluid pathophysiology secondary to hypothermia and the mechanisms behind these changes are still largely unknown. In a recent study we found increased fluid needs during hypothermic compared to normothermic CPB. The aim of the present study was to characterize the distribution of the fluid given to maintain normovolemia. In addition, we wanted to investigate the quantity and quality of the fluid extravasated during hypothermic compared to normothermic CPB.

METHODS

Two groups of anesthetized piglets were studied during 2 h of hypothermic (28 degrees C) (n=7) or normothermic (38 degrees C) (n=7) CPB. Net fluid balance (input-output) was recorded. Changes in colloid osmotic pressures of plasma (COPp) and interstitial fluid (COPi), plasma volume (PV), hemoglobin (Hb), hematocrit (HCT), mean corpuscular volume (MCV), s-osmolality, s-albumin and s-total protein was followed throughout the experiments. Fluid extravasation rate was calculated. In addition, total tissue water content was measured and compared with a control group (n=6) (no CPB).

RESULTS

During hypothermic compared with normothermic CPB, the average net positive fluid balance from 10-120 min of extracorporeal circulation was 1.35+/-0.06 ml x kg(-1) x min(-1) and 0.33+/-0.03 ml x kg(-1) x min(-1) respectively (P<0.0001). We found a marked increase in fluid extravasation during hypothermic CPB. The extravasation rate during hypothermia was 1.8+/-0.2 ml x kg(-1) x min(-1), (1st hour) and 1.1+/-0.2 ml x kg(-1) x min(-1) (2nd hour) compared with 0.8+/-0.2 ml x kg(-1) x min(-1), and 0.1+/-(0.1) ml x kg(-1) x min(-1) during normothermia, respectively (P<0.01). The total intravascular protein and albumin masses remained constant in both groups. Following hypothermic CPB, the water content increased significantly in all tissues and organs.

CONCLUSION

During hypothermic CPB an increased extravasation of fluid from the intravascular to the interstitial space was found. As no leakage of proteins could be demonstrated, based on stable values for albumin and protein masses throughout the experiments, the extravasated fluid contained mainly water and small solutes.