Cerebral perfusion during human liver transplantation

Relation between partial arterial carbon dioxide pressure and pH value and optic nerve sheath diameter: a prospective self-controlled non-randomized trial study

OBJECTIVE

This study aims to determine if there is a correlation between differences in optic nerve sheath diameter (ONSD) and changes in PaCO2 and pH values that were measured in the arterial blood gas (ABG) before and after treatment in COPD patients with acute hypercarbic respiratory failure (AHRF).

MATERIALS AND METHODS

This study serves as a prospective self-controlled non-randomized trial study conducted in the emergency clinic of a tertiary hospital. Forty-four patients with COPD, who were found to have acidosis and hypercarbia in ABG and had an indication for non-invasive mechanic ventilation (NIMV), were analyzed prospectively. Demographic information, vital findings, initial ABG values, the ONSD measurement (before the NIMV treatment), consciousness state, and the ABG results obtained in the second hour of the monitoring and the ONSD measurement (after the NIMV treatment) were recorded.

RESULTS

In this study, 13 (29.5%) of the patients were female and 31 (70.5%) were male. The age distribution was evaluated as 68.3 ± 9.2 years; the minimum age was 54 and the maximum was 91. A high level of positively significant correlation was found between the mean ONSD and PaCO2 (p < 0.0001). There is a high fit (0.72) between the mean ONSD and PaCO2. A moderate level of negatively significant correlation was found between the mean ONSD and the pH (p < 0.0001). However, there is an insignificant low fit (0.32) between the mean ONSD and the pH.

CONCLUSION

The ONSD changed significantly and in a highly correlated manner to acute changes in PaCO2 levels.

Akut solunum yetmezliğinde optik sinir kılıf çapının prognostik önemi

Purpose: The primary aim of this study was to determine the role of the optic nerve sheath diameter (ONSD) measured using ultrasonography in the differentiation of hypoxemic respiratory failure and hypercarbic respiratory failure. The secondary aim was to determine the value of ONSD in predicting the clinical outcome in hypercarbic patients. Materials and Methods: Non-traumatic adult patients presenting with dyspnea were included in this study. Arterial blood gas and concurrent ONSD measurements were obtained from all patients included in the study during presentation and at the second hour of treatment. The patients were divided into two groups - hypoxic and hypercarbic respiratory failure. An equivalent number of healthy volunteers were enrolled as the control group. Result: Mean ONSD values were 3.8±0.2 mm in the 24 patients with type 1 respiratory failure, 5.2 ± 0.5 mm in the 25 patients with type 2 respiratory failure, and 3.9±0.3 mm in the healthy controls. The ONSD of the hypercarbic patients was statistically significantly greater than that of the hypoxic patients and healthy volunteers. The ONSD of the hypercarbic patients was 5.2±0.5mm at baseline and 4.4±0.6 mm after treatment, the difference being statistically significant. However, the difference in ONSD was not statistically significant in predicting hospitalization and mortality. Conclusion: Sonographically measured ONSD may be an effective parameter in the differential diagnosis of type 1 and 2 respiratory failure. ONSD values changed significantly with treatment in patients with type 2 respiratory failure.

Neurocritical care monitoring of encephalopathic children with acute liver failure: A systematic review

Research on non-invasive neuromonitoring specific to PALF is limited. This systematic review identifies and synthesis the existing literature on non-invasive approaches to monitoring for neurological sequelae in patients with PALF. A series of literature searches were performed to identify all publications pertaining to five different non-invasive neuromonitoring modalities, in line with PRISMA guidelines. Each modality was selected on the basis of its potential for direct or indirect measurement of cerebral perfusion; studies on electroencephalographic monitoring were therefore not sought. Data were recorded on study design, patient population, comparator groups, and outcomes. A preponderance of observational studies was observed, most with a small sample size. Few incorporated direct comparisons of different modalities; in particular, comparison to invasive intracranial pressure monitoring was largely lacking. The integration of current evidence is considered in the context of the clinically significant distinctions between pediatric and adult ALF, as well as the implications for planning of future investigations to best support the evidence-based clinical care of these patients.

Ventilatory strategy during liver transplantation: implications for near-infrared spectroscopy-determined frontal lobe oxygenation

BACKGROUND

As measured by near infrared spectroscopy (NIRS), cerebral oxygenation (ScO2) may be reduced by hyperventilation in the anhepatic phase of liver transplantation surgery (LTx). Conversely, the brain may be subjected to hyperperfusion during reperfusion of the grafted liver. We investigated the relationship between ScO2 and end-tidal CO2 tension (EtCO2) during the various phases of LTx.

METHODS

In this retrospective study, 49 patients undergoing LTx were studied. Forehead ScO2, EtCO2, minute ventilation (VE), and hemodynamic variables were recorded from the beginning of surgery through to the anhepatic and reperfusion phases during LTx.

RESULTS

In the anhepatic phase, ScO2 was reduced by 4.3% (95% confidence interval: 2.5-6.0%; P < 0.0001), EtCO2 by 0.3 kPa (0.2-0.4 kPa; P < 0.0001), and VE by 0.4 L/min (0.1-0.7 L/min; P = 0.0018). Conversely, during reperfusion of the donated liver, ScO2 increased by 5.5% (3.8-7.3%), EtCO2 by 0.7 kPa (0.5-0.8 kPa), and VE by 0.6 L/min (0.3-0.9 L/min; all P < 0.0001). Changes in ScO2 were correlated to those in EtCO2 (Pearson r = 0.74; P < 0.0001).

CONCLUSION

During LTx, changes in ScO2 are closely correlated to those of EtCO2. Thus, this retrospective analysis suggests that attention to maintain a targeted EtCO2 would result in a more stable ScO2 during the operation.

Noninvasive estimation of raised intracranial pressure using ocular ultrasonography in liver transplant recipients with acute liver failure -A report of two cases-

Intracranial pressure (ICP) monitoring is an important issue for liver transplant recipients, since increased ICP is associated with advanced hepatic encephalopathy or graft reperfusion during liver transplantation. Invasive monitoring of ICP is known as a gold standard method, but it can provoke bleeding and infection; thus, its use is a controversial issue. Studies have shown that optic nerve sheath diameter > 5 mm by ocular ultrasonography is useful for evaluating ICP > 20 mmHg noninvasively in many clinical settings. In this case report, we present experiences of using ocular ultrasound as a diagnostic tool that could detect changes in ICP noninvasively during liver transplantation.

Moderate hypothermia prevents cerebral hyperemia and increase in intracranial pressure in patients undergoing liver transplantation for acute liver failure

BACKGROUND

During orthotopic liver transplantation (OLT) for acute liver failure (ALF), some patients develop acute increases in intracranial pressure (ICP). The authors tested the hypothesis that increases in ICP during OLT for ALF can be prevented by moderate hypothermia.

METHODS

Sixteen patients with ALF undergoing OLT were studied. Depending on the measured ICP before OLT, the patients were divided into three groups as follows: group I (n=6), did not require treatment for increased ICP (ICP <15 mm Hg); group II (n=5), had episodes of increased ICP that were controlled by conventional treatment (group I and group II patients were maintained normothermic during OLT); and group III (n=5), had uncontrolled increased ICP before OLT for which they had been cooled and underwent OLT with the median core temperature of 33.4 degrees C (92.1 degrees F) (range, 31.9 degrees -33.8 degrees C [89.4 degrees -92.8 degrees F])

RESULTS

There was a significant increase in ICP during the dissection and reperfusion phases in the patients in groups I and II (P=0.004 and P=0.006, respectively). Patients in group III had no significant increase in ICP during the OLT. The increase in ICP in groups I and II was associated with an increase in cerebral blood flow, which was not observed in group III. The increase in ICP was corrected during the anhepatic phase of the operation. There was no difference in the requirement of transfusions or incidence of postoperative infection between the groups.

CONCLUSIONS

Moderate hypothermia is safe and successfully prevents increases in ICP during OLT for ALF.

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.

Interference of cerebral near-infrared oximetry in patients with icterus

Near-infrared spectrophotometry assesses cerebral oxygen saturation (ScO(2)) based on the absorption spectra of oxygenated and deoxygenated hemoglobin and the translucency of biological tissue in the near-infrared band. In patients with icterus, however, bilirubin can potentially hinder cerebral oximetry. In 48 patients undergoing orthotopic liver transplantation, we related total plasma bilirubin to ScO(2) as determined from spectrophotometry with wavelengths of 733 and 809 nm. Before surgery, ScO(2) was 59% (15%-78%) (median with range) and bilirubin was 71 (6-619) micromol/L with a negative correlation (r = -0.72; P < 0.05). The 95% prediction interval included the lowest measurable ScO(2) of 15% at a bilirubin level of 370 micromol/L. During reperfusion of the grafted liver, the ScO(2) increased by 7% (-8% to 17%) (P < 0.05), and bilirubin did not influence this increase. In one patient, the ScO(2) remained below 15% despite a decrease in bilirubin from 619 to 125 micromol/L, suggesting that tissue pigmentation deposits also absorb light. In conclusion, bilirubin dampens the spectrophotometry-determined cerebral oxygen saturation at 733 and 809 nm. A bilirubin level of 370 micromol/L, tissue pigment deposits, or both, may render determination of cerebral oxygen saturation impossible. Even at high bilirubin values, changes in cerebral perfusion may be visible.

IMPLICATIONS

In 48 patients undergoing liver transplantation, the interference of icterus on cerebral oximetry by near-infrared light was investigated. Bilirubin absorbed the near-infrared light and lowered the measured cerebral oxygen saturation. Even at high bilirubin values, changes in cerebral oxygenation, as seen during reperfusion of the grafted liver, may be visible.

Cerebrovascular metabolic autoregulation is impaired during liver transplantation

BACKGROUND

We determined whether the coupling between cerebral blood flow (CBF) and oxygen metabolism (CMRO2) is preserved during liver transplantation. Because of cerebrovascular dilatation, we hypothesized that cerebral metabolic autoregulation is impaired, because CBF becomes uncoupled from CMRO2 during the reperfusion phase of the operation.

MATERIALS AND METHODS

In a prospective study, 13 patients (8 women, median age 46, range 21-6) with liver failure (10 with end-stage chronic liver disease and 3 with acute liver failure) were enrolled. Catheters were placed in a femoral artery and in the internal jugular vein for calculation of the cerebral arteriovenous oxygen content difference (AVDO2). CBF was recorded by the 133Xenon injection technique, and by transcranial Doppler sonography determined mean flow velocity (Vmean) in the middle cerebral artery. The CMRO2 was calculated as the AVDO2 times CBF and the cerebrovascular resistance (CVR) as the mean arterial pressure to CBF ratio. An index of large cerebral artery diameter was expressed by the CBF to Vmean ratio.

RESULTS

From induction of anesthesia to the anhepatic period, CBF decreased from a median of 47 (interquartiles 31-55) to 41 (37-48) ml 100 g(-1) min(-1), whereas the CMRO2 remained unchanged (1.3 [0.9-2.5] vs. 1.7 [0.9-2.3] ml 100 g(-1) min(-1)). In the reperfusion phase, the CBF increased to 51 (45-54) ml 100 g(-1) min(-1), whereas the CMRO2 remained unchanged at 1.1 (1.0-2.5) ml 100 g(-1) min(-1). The CVR decreased from 2.0 mm Hg (1.4-2.1) to 1.4 (1.1-1.8) mm Hg(-1) min 100 g ml. In the anhepatic phase, mean arterial pressure decreased from 92 mm Hg (84-98) to 85 (80-92) mm Hg and at reperfusion it was 80 (71-105) mm Hg. From the anhepatic to the reperfusion phase, the CBF increased 7% (0 to 26) for each mm Hg concomitant increase in PaCO2. The CBF to Vmean ratio remained stable (1.0 [0.8-1.2] vs. 0.9 [0.7-1.1] ml 100 g(-1) min(-1) cm(-1) sec).

CONCLUSION

During the reperfusion phase of liver transplantations, cerebrovascular dilatation uncouples cerebral oxidative metabolism from blood flow. The increase in CBF is beyond what can be explained by changes in arterial carbon dioxide tension and arterial pressure.

Near-infrared oximetry of the brain

Near-infrared (IR) light easily penetrates biological tissue, and the information offered by in vivo spectroscopy of cerebral oxygenation is detailed and comes with a high temporal resolution. Near-IR light spectroscopy (NIRS) reflects cerebral oxygenation during arterial hypotension, hypoxic hypoxaemia and hypo- and hypercapnia. As determined by dual-wavelength NIRS, the cerebral O2 saturation integrates the arterial O2 content and the cerebral perfusion, and as established for skeletal muscle, NIRS obtains information on tissue oxygenation and metabolism beyond that obtained by venous blood sampling. Caveats of cerebral NIRS include insufficient light shielding, optode displacement and a sample volume including muscle or the frontal sinus mucous membrane. The relative influence from the extracranial tissue is minimized by optode separation and correction for an extracranial sample volume, or both. The natural pigment melatonin and also water are of little influence to spectroscopic analysis of cerebral oxygenation, whereas bilirubin systematically lowers ScO2 and attenuates the detection of changes in cerebral oxygenation. By NIRS, reduction of cytochrome oxidase is demonstrated during hypoxic hypoxaemia and head-up tilt-induced arterial hypotension, but the changes are small. In the clinical setting, NIRS offers useful information in patients with both systemic and local cerebral circulatory impairment, for example, during cranial trauma, surgery on the cerebral arteries, orthostasis and acute heart failure. Whereas mapping of the brain circulation is needed for jugular venous sampling to reflect either global or local oxygenation, the determination of cerebral oxygenation by NIRS has the advantage of localized monitoring of the cerebral cortex.

Middle cerebral artery flow velocity and cerebral oxygenation during abdominal aortic surgery

Cerebral perfusion was evaluated in twelve patients undergoing elective infra-renal abdominal aortic aneurysmectomy by transcranial Doppler ultrasonography-determined middle cerebral artery mean flow velocity, near-infrared spectroscopy-assessed cerebral oxygen saturation and systemic haemodynamic variables. The middle cerebral artery mean flow velocity and cerebral oxygen saturation decreased during cross-clamping of the aorta, and both increased upon declamping of the aorta with the oxygen saturation change lagging behind the change in the flow velocity. The changes in cerebral flow velocity and oxygen saturation paralleled the deviations in cardiac output and end-tidal carbon dioxide tension.

Intracranial pressure during liver transplantation for fulminant hepatic failure

During orthotopic liver transplantation (OLT) for fulminant hepatic failure (FHF), some patients develop cerebral injury secondary to intracranial hypertension. We monitored intracranial pressure (ICP) and cerebral perfusion pressure (CPP) before and during OLT in 12 FHF patients undergoing transplantation. All four patients who had normal ICP preoperatively maintained normal ICP/CPP throughout OLT. During OLT, four of the eight patients with pretransplant intracranial hypertension had six episodes of ICP increase. These episodes of intracranial hypertension occurred during failing liver dissection (n=3) and graft reperfusion (n=3). At the end of the anhepatic phase, the ICP was lower than the preoperative ICP in all patients, and was below 15 mmHg in all but one patient. These data suggest that in FHF patients who develop intracranial hypertension before OLT, dissection of the native liver and graft reperfusion are associated with a risk of brain injury resulting from intracranial hypertension and cerebral hypoperfusion.

Cerebral blood flow and metabolism in patients with chronic liver disease undergoing orthotopic liver transplantation

Changes in cerebral hemodynamics and metabolism associated with anesthesia and liver transplantation may present particular hazards for patients with cirrhosis. Fifteen patients undergoing liver transplantation were studied, 7 of whom had encephalopathy. Cerebral blood flow (CBF) was measured at the start of surgery, during veno-venous bypass and post reperfusion, using a method based on the Kety-Schmidt method. Cerebral metabolism was assessed by measuring the cerebral metabolic rate for oxygen (CMRO2) and the lactate oxygen index (LOI). The cerebral vascular reactivity to carbon dioxide (CO2) was studied during the preanhepatic and post reperfusion phases. During the preanhepatic period, the median CBF was 44 mL/100 g/min at an arterial carbon dioxide tension (PaCO2) of 3.8 kPa. After reperfusion the CBF increased (P < .02) to 102 mL/100 g/min, the arterial hydrogen ion concentration increased from 39 nmol/L to 53 nmol/L (P < .02) and the jugular venous oxygen saturation from 74% to 89% (P < .02). CBF was similar in patients with and without encephalopathy. The cerebral vascular reactivity to CO2 remained intact, although after reperfusion, the CBF for a given PaCO2 was greater, and the slope of the CBF/CO2 response curve diminished. The CMRO2 was normal in patients without encephalopathy. In the encephalopathic patients, the CMRO2 was low during all stages of transplantation (0.54, 0.86, 1.24 mL/100 g/min, respectively). Patients with encephalopathy may be at increased risk of hypoxemic brain injury during transplantation. To minimize this possibility, more detailed neurological monitoring may be useful.

Cerebral oxygen saturation and blood flow during liver transplantation

After reperfusion of a liver graft, transcranial Doppler determined middle cerebral artery flow velocity, increases more than expected from the arterial carbon dioxide tension (PaCO2). We evaluated if this indication of cerebral hyperperfusion is reflected in the jugular oxygen saturation (SjO2) (n = 31) and oxygen saturation (ScO2) (near-infrared spectrophotometry, n = 22). From the dissection phase to the anhepatic phase SjO2 71.0% (range 62.3%-78.5%), ScO2 70% (range 65%-77%), and PaCO2 34.9 mm Hg (range 30.8-38.3) remained statistically unchanged. In contrast, during the early reperfusion phase, SjO2 increased to 77.0% (71.4%-83.0%) (P < 0.01) and the ScO2 to 75% (68%-80%) (P < 0.05) as PaCO2 increased to 37.5 mm Hg (34.8-41.9) (P < 0.001). Notably, SjO2 also increased at reperfusion from 71.6% (66.5%-78.0% mm Hg) to 80.0% (76.8%-84.8%) in the four patients in whom PaCO2 decreased at reperfusion from 37.6 mm Hg (36.8-39.5) to 34.0 mm Hg (32.3-36.8). If the changes in SjO2 after reperfusion of the grafted liver should be explained as a reflection of changes in cerebral blood flow, in response to PaCO2, it would indicate a highly accentuated CO2 reactivity of 13%/mm Hg. The results support that cerebral blood flow and, in turn, oxygenation increase after reperfusion because the grafted liver liberates a vasodilating substance(s).

Dissociated cerebral vasoparalysis in acute liver failure. A hypothesis of gradual cerebral hyperaemia

BACKGROUND/AIMS

Normally, cerebral blood flow responds to changes in the arterial carbon dioxide tension (PaCO2) but not to changes in mean arterial pressure, commonly referred to as the cerebral CO2-reactivity and autoregulation. In patients with fulminant hepatic failure and in the rat with thioacetamide-induced liver failure, autoregulation is absent, presumably due to cerebral vasoparalysis. Since also CO2-reactivity may then be compromised, it was studied in patients with fulminant hepatic failure and rats with thioacetamide-induced liver failure.

METHODS

In ten patients (median age 32 (range 20-48) years)) and in ten age-matched volunteers, cerebral perfusion was elevated by transcranial Doppler assessed mean flow velocity (V(mean)) in the middle cerebral artery during hypo- and hyper-capnia. In six rats with liver failure and in six control rats, cerebral blood flow was measured repeatedly by the intracarotid 133 Xenon injection technique.

RESULTS

In the patients and volunteers, PaCO2 was lowered from 33 (23-44) to 28 (23-39) mmHg by hypocapnia and raised to 40 (34-48) mmHg by hypercapnia or 5% CO2 inhalation. During hypocapnia, the CO2-reactivity did not differ significantly between patients and volunteers, 4.0 (1.1-7.4) vs. 3.0 (1.7-5.0)% mmHg(-1), while it was reduced during hypercapnia in the patients, 2.2 (1.8-5.2) vs. 4.6 (3.0-8.0)% mmHg(-1) (p < 0.05). In the rats, PaCO2 was reduced from 39 (37-40) to 30 (29-31) mmHg and then raised to 51 (41-55) mmHg. During hypocapnia, CO2-reactivity was similar in rats with liver failure and in control rats, 2.3 vs 2.7% mmhg(21), respectively. In all rats with liver failure CO2-reactivity was abolished during hypercapnia, while it was 1.5% mmHg(-1) in the control rats (p < 0.01).

CONCLUSIONS

The finding that cerebral CO2 reactivity is reduced in hypercapnia, while it is preserved in hypocapnia, suggests that gradual dilation of the cerebral resistance vessels develops in fulminant hepatic failure and connects previous morphological studies with changes in the regulation of cerebral blood flow, i.e. impaired cerebral autoregulation and blunted CO2-reactivity.