Hepatic and splanchnic oxygenation during liver transplantation

Surgical Science and the Evolution of Critical Care Medicine

Surgical science has driven innovation and inquiry across adult and pediatric disciplines that provide critical care regardless of location. Surgically originated but broadly applicable knowledge has been globally shared within the pages Critical Care Medicine over the last 50 years.

A malignant hyperthermialike episode in a liver transplant recipient

We report a case of malignant hyperthermialike syndrome in a living-donor liver transplant recipient with no familial history of malignant hyperthermia or exposure to known triggering drugs. The patient showed many features of a typical malignant hyperthermia episode, and The Clinical Grading Scale defined this case as almost certain to be an episode of malignant hyperthermia (rank 5). However, the diagnosis was questionable. The intraoperative and perioperative periods during liver transplant can involve drastic alterations of physiological parameters, which can make malignant hyperthermia difficult to diagnosis. The data we obtained using a pulmonary artery catheter suggest an intraoperative increase in systemic oxygen consumption.

Targeted Oxygen Delivery within Hepatic Hollow Fiber Bioreactors via Supplementation of Hemoglobin-Based Oxygen Carriers

Hepatic hollow fiber bioreactors are considered a promising class of bioartificial liver assist device (BLAD). Unfortunately, limited oxygen (O(2)) transport to hepatocytes within this device hinders further development. Hepatocytes in vivo (in the liver sinusoid) experience a wide range of oxygen tensions (pO(2) = 25-70 mmHg), which is important for development of proper differentiated function (zonation). Previously, we observed that bovine red blood cell (bRBC) supplementation of the circulating media stream enhanced oxygenation of cultured C3A hepatoma cells compared to a culture with no O(2) carrier (Gordon, J.; Palmer, A. F. Artif. Cells, BloodSubstitutes, Biotechnol. 2006, 33 (3), 297-306). Despite this success, the cells were not exposed to the desired in vivo O(2) spectrum (Sullivan, J.; Gordon, J.; Palmer, A. Biotechnol. Bioeng. 2006, 93 (2) 306-317). We hypothesize that altering the kinetics of O(2) binding/release to/from hemoglobin-based O(2) carriers (HBOCs) could potentially target O(2) delivery to cell cultures. High P(50) (low O(2) affinity) HBOCs preferentially targeted O(2) delivery at high inlet pO(2) values. Conversely, low P(50) (high O(2) affinity) HBOCs targeted O(2) delivery at low inlet pO(2) values. Additionally, inlet pO(2), flow rate, and HBOC concentration were varied to find optimal bioreactor operating conditions. Our results demonstrate that HBOCs can enhance O(2) delivery to cultured hepatocytes, while exposing them to in vivo-like O(2) tensions, which is critical to create a fully functional BLAD.

Enhanced oxygen delivery to primary hepatocytes within a hollow fiber bioreactor facilitated via hemoglobin-based oxygen carriers

The production of a fully functional bioartificial liver assist device (BLAD) would greatly enhance available treatment options for patients suffering from acute liver failure. Currently, inadequate oxygen provision to hepatocytes seeded within hollow fiber bioreactors hampers development of a viable hollow fiber-based BLAD. Experimentally, oxygen provision to primary rat hepatocytes cultured within hollow fiber bioreactors was measured, it was observed that supplementation with an oxygen carrier (bovine red blood cells at approximately 2% human hematocrit) did not significantly improve oxygenation compared to the absence of an oxygen carrier. Therefore, an oxygen transport model of an individual hollow fiber within the bioreactor was developed and simulated (up to approximately 10% human hematocrit) to more fully examine the effect of oxygen carrier supplementation on oxygenation within the bioreactor. The modeling analysis, supported via the experimental results, was utilized to predict optimal bioreactor operating conditions for the delivery of in vivo-like oxygen gradients to cultured hepatocytes in clinically relevant settings.

Reperfusion of the liver allograft with blue blood: is it still the royal perfusate?

The technique of liver transplantation has become relatively standardized. Although not commonly practiced, arterial reperfusion has been shown in both animal and human trials to offer hemodynamic and functional benefits to liver allograft recipients. Whether this is the result of shortening the time to re-establishing arterial perfusion or an effect of the sequence which the liver is revascularized remains unknown. Further randomized clinical trials are needed to answer this question and support our practice of arterial reperfusion.

Hemodynamic profile and tissular oxygenation in orthotopic liver transplantation: Influence of hepatic artery or portal vein revascularization of the graft

We performed a prospective, randomized study of adult patients undergoing orthotopic liver transplantation, comparing hemodynamic and tissular oxygenation during reperfusion of the graft. In 30 patients, revascularization was started through the hepatic artery (i.e., initial arterial revascularization) and 10 minutes later the portal vein was unclamped; in 30 others, revascularization was started through the portal vein (i.e., initial portal revascularization) and 10 minutes later the hepatic artery was unclamped. The primary endpoints of the study were mean systemic arterial pressure and the gastric-end-tidal carbon dioxide partial pressure (PCO(2)) difference. The secondary endpoints were other hemodynamic and metabolic data. The pattern of the hemodynamic parameters and tissue oxygenation values during the dissection and anhepatic stages were similar in both groups At the first unclamping, initial portal revascularization produced higher values of mean pulmonary pressure (25 +/- 7 mm of Hg vs. 17 +/- 4 mm of Hg; P < 0.05) and wedge and central venous pressures. At the second unclamping, initial portal revascularization produced higher values of cardiac output and mean arterial pressure (87 +/- 15 mm of Hg vs. 79 +/- 15 mm of Hg; P < 0.05) and pulmonary blood pressure. Postreperfusion syndrome was present in 13 patients (42.5%) in the arterial group and in 11 patients (36%) in the portal group. During revascularization, the values of gastric and arterial pH decreased in both groups and recovered at the end of the procedure, but were more accentuated in the initial arterial revascularization group. In conclusion, we found that initial arterial revascularization of the graft increases pulmonary pressure less markedly, so it may be indicated for those patients with poor pulmonary and cardiac reserve. Nevertheless, for the remaining patients, initial portal revascularization offers more favorable hemodynamic and metabolic behavior, less inotropic drug use, and earlier normalization of lactate and pH values.

Changes in oxyhemoglobin dissociation curve in intrabdominal organs during pig experimental orthotopic liver transplantation

Liver transplantation has become a gold standard treatment for irreversible liver disease. Conventional measures of oxygenation are inadequate to understand the dynamics of regional oxygen metabolism during liver transplantation because they represent global markers of tissue dysoxia. Therefore, the addition of an assessment of the hemoglobin O(2) binding capacity can give a better insight into systemic and regional tissue oxygenation and can reflect a more accurate estimation of oxygen release to the tissues than can the hemoglobin, the PaO(2) and SaO(2) alone. This prospective study was designed to evaluate possible alterations in the oxyhemoglobin dissociation curve of vital end organs (small bowel, liver, and kidney) in an experimental liver transplantation model. Fifteen pigs with body weights ranging from 25 to 30 kg were used for the study. Five healthy pigs underwent a sham operation under general anesthesia (group A-control). Ten pigs underwent orthotopic liver transplantation (OLT). Five of them were healthy (group B), whereas the other five were in acute liver failure, which had been surgically induced (group C). Systemic arterial blood pressure, cardiac index, and pulmonary and systemic vascular resistance indexes were measured. Venous blood gas analysis was also performed from pulmonary artery, superior mesenteric, hepatic, and renal veins at well-defined timepoints during the course of the OLT. A statistically significant (P < 0.05) decrease of P(50) in groups B and C compared with group A was observed 30 minutes after reperfusion in the systemic circulation, hepatic, and renal veins. This coincided with a decrease in animal temperature 30 minutes after reperfusion. Regarding group C, after reperfusion of the newly transplanted liver there was a significant increase of P(50) in the small bowel in comparison to baseline values. In conclusion, these changes in P(50) may suggest the occurrence of abnormal tissue oxygenation after reperfusion.

Vasopressor agents without volume expansion as a safe alternative to venovenous bypass during cavaplasty liver transplantation

BACKGROUND

Cavaplasty orthotopic liver transplantation (OLT) offers advantages for hepatectomy and implantation and eliminates the risk of outflow obstruction. However, it does require clamping of the cava. This study describes the use of a vasopressor without fluid expansion or venovenous bypass (VB) for hemodynamic control during the anhepatic phase.

METHODS

The cavaplasty OLT technique was used routinely. A vasopressor was administered if the mean arterial blood pressure (MAP) was less than 60 mm Hg after clamping of the cava. If the MAP did not reach 60 mm Hg after adjusting the dosage of the vasopressor, femoro-axillary VB would be used. VB was also indicated for preexisting cardiac disease or for massive hemorrhage from severe portal hypertension and extensive adhesions.

RESULTS

Among all the 121 adult cavaplasty OLTs, 33 were supported with VB and 50 received a vasopressor. The remaining 38 were excluded. However, baseline variables were well matched, except that preexisting cardiac disease was more frequent in the VB group. The median dosage of epinephrine was 0.07 microg/kg/min (range 0.01-0.6). The VB and vasopressor groups were similar in the reduction in mean MAP and the accumulation in arterial lactate upon clamping as well as in the central venous pressure upon unclamping. Postreperfusion hypotension was more frequent in the VB than in the vasopressor group (27.3% vs. 4.0%, P=0.006). There was no primary graft nonfunction or intraoperative right heart failure. One patient in the vasopressor group required postoperative temporary dialysis. Ninety-day patient and graft survival for the VB and vasopressor groups were 97.0% vs. 98.0% and 97.0% vs. 94.0%, respectively.

CONCLUSION

Modest doses of vasopressor without volume expansion or VB can maintain hemodynamic stability during the anhepatic phase of cavaplasty OLT.

Portal vein pressure and graft oxygen consumption monitoring during liver transplantation

Abnormal splanchnic circulation (ASC) is often detected too late, when hepatic circulation is already irreversibly compromised. If we could detect surgical or metabolic problems early after graft reperfusion, we might be able to correct them immediately before the damage becomes irreversible. The aim of this study was to determine if ASC can be predicted early after liver transplantation (LT) using portal vein pressure measurements and graft oxygen consumption monitoring.

PATIENTS AND METHODS

Twenty-patients (13 men, 7 women of mean age 46 years) undergoing LT with the piggyback technique for hepatitis C virus (HCV)/hepatitis B virus (HBV)-related cirrhosis were retrospectively divided in two groups. Group A (16 patients), in which LT was successful, and group B (4 patients) in which LT was unsuccessful because of primary nonfunction (2 patients), infrahepatic portal vein thrombosis (1 patient), or hepatic vein kinking (1 patient). We then compared the portal blood pressure values and the prehepatic and posthepatic oxygen content difference (p-pDO(2)) before portal clamping; at the end of anhepatic phase; 5, 15, and 25 minutes after portal vein (PV) reperfusion; and 5, 20, 40, and 100 minutes after hepatic artery anastomosis.

RESULTS

Early after graft reperfusion; portal pressure decreased to levels lower than that at baseline in group A, but remained high until the end of surgery in group B. At the end of surgery, p-pDO(2) increased more among group B than group A.

CONCLUSION

ASC, specifically an increased PV resistance, can be predicted early after LT by portal vein pressure measurements and graft oxygen consumption monitoring.

Oxygen availability during orthotopic liver transplantation

Studies have stressed the role of adequate tissue oxygenation in the light of an optimal patient outcome and allograft viability in liver transplantation. The practice of monitoring conventional hemodynamic parameters during liver transplantation could be complemented by parameters assessing real oxygen availability. In the present prospective study, real arterial available oxygen content (CavlO(2)) and its extraction ratio (O(2)ERavl) were calculated. These parameters include the effect of changes in oxyhemoglobin dissociation curve (ODC; expressed by P(50)) on oxygen availability, under the different circumstances occurring during liver transplantation. Sixteen adult cirrhotic patients were studied during orthotopic liver transplantation with the use of venovenous bypass. Classic hemodynamic measurements using a Swan-Ganz thermodilution catheter and arterial and mixed venous blood gas analysis were performed, and P(50), oxygen delivery index (DO(2 ind)), oxygen consumption index (VO(2 ind)), oxygen extraction ratio (O(2)ER), CavlO(2), and O(2)ERavl were calculated. Statistical analysis was performed using ANOVA for repeated measures and Spearman correlation coefficient matrix among the six variables (DO(2 ind), VO(2 ind), O(2)ER, P(50), CavlO(2), and O(2)ERavl) taken two at a time at every phase. Parameter P(50) changed from 25.98 +/- 1.10 to 23.15 +/- 2.24 (at the end of operation). A leftward shift of the ODC was observed. The results showed positive association between P(50) and CavlO(2) after the removal of the native liver, and a weak and inconsistent relation of DO(2 ind) with any of the other study variables. The intraoperative changes in P(50) values, which represent a shift of the ODC to the left, may reflect a more accurate estimation of O(2) release to the tissues, than the hemoglobin, Pao(2) and Sao(2) alone. Besides conventional hemodynamic parameters, P(50), which includes the effect of alterations in ODC on oxygen availability, could be of value in monitoring the systemic oxygenation during liver transplantation.

Measurement of liver tissue oxygenation after orthotopic liver transplantation using a multiparameter sensor. A pilot study

The currently used methods of monitoring liver perfusion and oxygenation after liver transplantation have major limitations in clinical use. We describe the use of a multiparameter sensor to enable continuous monitoring of liver tissue oxygen tension, carbon dioxide tension and hydrogen ion concentration in the early postoperative period in 12 patients after liver transplantation. The sensor was inserted under direct vision via the falciform ligament into the liver before skin closure. Tissue oxygen tension values decreased in the first 24 h and subsequently increased to a mean (SD) = 7.3 (2.8) kPa at 48 h after surgery. This was associated with a decrease in the degree of acidosis. There were no complications attributable to the sensor. This study demonstrates that continuous measurement of liver oxygen tension, carbon dioxide tension and pH is possible. This technique may be useful as a continuous monitor to help identify grafts at risk of ischaemia.

Cerebral blood flow and oxygenation in liver transplantation for acute or chronic hepatic disease without venovenous bypass

The autoregulation of cerebral blood flow (CBF) is impaired in patients with end-stage liver disease and encephalopathy. These patients are vulnerable to sudden deterioration of cerebral perfusion and oxygenation during liver transplantation. We compared CBF and metabolism during liver transplantation without venovenous bypass and 24 hours postoperatively in 9 patients with acute liver failure (ALF) and 16 patients with chronic liver disease. A fiberoptic catheter was inserted cranially through the left internal jugular vein for determination of jugular venous oxygen saturation, cerebral oxygen extraction ratio (COER), lactate level, and neuron-specific enolase (NSE) level. Arterial concentrations of lactate were also measured. Flow velocity in the middle cerebral arteries was monitored bilaterally using transcranial Doppler sonography. Mean flow velocity and pulsatility index (PI) were regarded as indicators of intracranial pressure. Core body temperatures were recorded. Mild hyperventilation, perioperative hemofiltration, and N-acetylcysteine infusion were used according to our clinical practice. NSE level was greater in acute patients at the end of surgery (P <.05), but not 24 hours later. Lactate concentrations were greater in patients with ALF (P <.001) preoperatively and intraoperatively but were similar in both groups 24 hours postoperatively. There was no difference between arterial and jugular venous concentrations of lactate. Changes in blood flow velocity, PI, and COER were parallel and without statistical significance between the groups. The patients' core temperature did not correlate with CBF, NSE level, or clinical outcome. Caval clamping was well tolerated in both patient groups.