Energy expenditure in acetaminophen-induced fulminant hepatic failure

OBJECTIVE

To determine energy expenditure in critically ill patients suffering from acetaminophen-induced fulminant hepatic failure and compare it with values obtained in matched, healthy control subjects and in patients studied during the anhepatic period of elective liver transplantation.

DESIGN

Prospective, controlled, observational study.

SETTING

A ten-bed intensive therapy unit and a liver transplant unit at a University teaching hospital.

PATIENTS AND SUBJECTS

Sixteen patients suffering from acetaminophen-induced fulminant hepatic failure who were sedated, paralyzed, and mechanically ventilated; 16 age-, gender-, and weight-matched, awake, healthy control subjects; and 16 patients with chronic liver disease, undergoing elective liver transplantation, who were studied during the anhepatic period of surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The mean energy expenditure was calculated in each case for a 30-min period, using indirect calorimetry. In the patients undergoing liver transplantation, measurements were performed after clamping the hepatic veins and recipient hepatectomy. Energy expenditure was markedly increased in the fulminant hepatic failure group (mean energy expenditure, 4.05 [SD 0.52] kJ x kg(-1) x hr(-1)), in comparison with healthy control subjects (mean, 3.44 [0.27] kJ x kg(-1) x hr(-1); mean difference, 18%; p < .001) and in comparison with patients during the anhepatic period of liver transplantation (mean, 3.15 [0.61] kJ x kg(-1) x hr(-1); mean difference, 29%; p < .001). These differences were even more pronounced when a correction factor for differences in core temperature was included in the calculation. Harris-Benedict predictions of energy expenditure were unreliable in the patients with acute liver failure. No correlations were found among energy expenditure and hemodynamic variables, the requirement for vasoconstrictors, or the presence of renal failure.

CONCLUSIONS

Despite the loss of functioning liver cell mass, the metabolic rate is substantially increased in patients with acetaminophen-induced fulminant hepatic failure. This finding is consistent with the marked systemic inflammatory response, which accompanies acute hepatic failure. The Harris-Benedict equation is unreliable when an estimation of energy expenditure is required in patients with this condition.

Measurement of cerebral blood volume using near-infrared spectroscopy and indocyanine green elimination

Methods for measuring cerebral blood volume (CBV) have traditionally used radioisotopes. More recently, near-infrared spectroscopy (NIRS) has been used to measure CBV by using a technique involving O(2) desaturation of cerebral tissue, where the observed change in the concentration of oxygenated hemoglobin is a marker of the volume of blood contained within the brain. A new integration method employing NIRS is described by using indocyanine green (ICG) as the intravascular marker. After bolus injection, concentration-time integrals of cerebral tissue ICG concentration ([ICG](tissue)) measured by NIRS are compared with corresponding integrals of the cerebral blood ICG concentrations ([ICG](blood)) estimated by high-performance liquid chromatography of peripheral blood samples with allowance for cerebral-to-large-vessel hematocrit ratio. It is shown that CBV = integral [ICG]tissue/[ICG]blood. Measurements in 10 adult volunteers gave a mean value of 1.1 +/- 0.39 (SD) ml/100 g illuminated tissue. This result, although lower than previous NIRS estimations, is consistent with the long extracerebral path of light in the adult head. Scaling of results is required to take into account this component of the optical pathlength.

Hyperlactatemia and pulmonary lactate production in patients with fulminant hepatic failure

STUDY OBJECTIVES

To determine whether the lungs of patients with fulminant hepatic failure release lactate, and if so, whether this release relates to systemic lactate concentration or acid base status. Another objective was to examine the accuracy of lactate flux calculations in critically ill patients.

DESIGN

Prospective observational study.

SETTING

The ICU of a major teaching hospital.

PATIENTS

Twelve patients with fulminant hepatic failure; 30 other critically ill patients in whom a pulmonary artery catheter was in place.

INTERVENTIONS

None.

MEASUREMENT AND RESULTS

The precision of whole-blood lactate measurements was assessed in 30 patients with critical illnesses of variable etiology who had a wide range of arterial lactate concentrations. The reliability of lactate measurements decreased with increasing lactate concentration. In each patient with liver failure, pulmonary lactate flux was calculated on three occasions using the Fick principle. Arterial blood lactate concentration was consistently higher than venous concentrations, indicating lactate release by the lungs (mean difference, 0.15 mmol/L; 95% confidence interval, 0.09 to 0.21; p<0.001). Mean pulmonary lactate production for the 12 patients was 83 mmol/h (range, 22 to 210 mmol/h). No patient had significant acute lung injury. Correlations were found among the arterial lactate concentration and both the arteriovenous (AV) lactate difference (p<0.025) and pulmonary lactate production (p<0.05), but not with acid-base status or cardiac output. The reliability of individual AV lactate difference calculations and pulmonary lactate flux calculations was poor.

CONCLUSION

The lungs release lactate in patients with fulminant hepatic failure at a rate proportional to the degree of systemic hyperlactatemia. However, the measurement errors associated with pulmonary lactate flux calculations using the Fick principle are large, so individual measurements should be interpreted with caution.

Effect of graft reperfusion on haemodynamics and gas exchange during liver transplantation

We have documented the changes in gas exchange, haemodynamic state and associated physiological variables which occurred after graft reperfusion in 20 patients undergoing uncomplicated orthotopic liver transplantation. Gas exchange was measured during constant ventilation using a metabolic monitor. After reperfusion, there were increases in VO2 (mean increase 57 (SD 25) ml min-1) (P < 0.001), VCO2 (mean increase 38 (17) ml min-1) (P < 0.001) and PaCO2 (mean increase 0.88 (0.56) kPa) (P < 0.001). These were associated with increases in cardiac output (1.2 (1.0) litre min-1 m-2) (P < 0.001) and mean pulmonary artery pressure (9 (6) mm Hg) (P < 0.001). There was a decrease in standard bicarbonate concentration (0.96 (1.6) mmol litre-1) (P < 0.02) and increase in hydrogen ion concentration (8.15 (5.9) mmol litre-1) (P < 0.001) consistent with the release of an acid load from the graft and previously ischaemic tissues. The increases in PaCO2 and hydrogen ion concentration were significantly larger in patients in whom venovenous bypass was used during the anhepatic period compared with the "piggyback" surgical technique. We found correlations between the changes in PaCO2 and VCO2 (r2 = 0.25, P < 0.02), cardiac output and VCO2 (r2 = 0.34, P < 0.01), and cardiac output and VO2 (r2 = 0.34, P < 0.01). We conclude that major alterations in gas exchange occur after reperfusion which result from alterations in metabolic rate and haemodynamic changes. These may be clinically relevant, particularly in patients at risk of cerebral oedema.

Influence of dose of domperidone on the acute ventilatory response to hypoxia in humans

We have studied the ventilatory responses to acute isocapnic hypoxia (SpO2 78.8 (SD 1.4)% for 10 min) in 10 male volunteers given three different doses of oral domperidone: placebo, domperidone tablets 10 mg, 20 mg or 30 mg every 8 h for 48 h on separate days. Neither baseline ventilation nor the acute hypoxic ventilatory response was significantly different from placebo for any of the domperidone doses. However, hypoxic responses were either increased with increments of domperidone or subjects were not sensitive. We arbitrarily divided subjects into two groups according to their hypoxic response-plasma domperidone concentration relationship. Analysis of subjects (n = 5) who demonstrated at least a 2-litre min-1 increase in ventilation per 10 ng ml-1 increase in plasma domperidone concentration showed the greatest augmentation of hypoxic responses with the 20-mg dose (median 19.45 (range 13.37, 22.30) litre min-1) compared with placebo (median 8.21 (3.74, 9.47)) (P = 0.003). We were unable to predict which subjects would be sensitive to the effects of domperidone.

A comparison between the Fick method and indirect calorimetry for determining oxygen consumption in patients with fulminant hepatic failure

OBJECTIVE

To compare the Fick method of determining oxygen consumption (VO2) with a gas exchange method in a group of patients in whom the cardiac output and mixed venous oxygen saturation values were consistently high.

DESIGN

A prospective, observational study.

SETTING

A ten-bed intensive therapy unit at a university teaching hospital.

PATIENTS

Seventeen patients suffering from fulminant hepatic failure who required ventilatory support and invasive hemodynamic monitoring. All patients were sedated and paralyzed throughout the study period.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

VO2 was determined simultaneously by indirect calorimetry and by the Fick method five or six times in each patient over a 5-hr period after resuscitation with fluids and, if clinically indicated, norepinephrine infusion. The agreement between the methods was poor (limits of agreement +19 to -101 mL/min/m2) and the Fick method consistently underestimated gas exchange measurements (mean bias 41 mL/min/m2). The bias varied widely, both between and within individual patients. The reproducibility of the Fick-derived VO2 was worse than the indirect calorimetry measurements, indicating that the dispersion of data attributable to measurement error was greater with the Fick method.

CONCLUSIONS

Under clinical conditions, the agreement between Fick calculations and indirect calorimetry measurements of VO2 in hyperdynamic patients with fulminant hepatic failure was extremely poor. The reproducibility of Fick calculations was less than the reproducibility derived by gas exchange measurements because of the large measurement errors that may occur with the Fick method when the cardiac output is large and the arterial-venous oxygen content difference is small. Fick calculations systematically underestimate gas exchange measurements. The Fick method is inaccurate and unreliable when an estimation of VO2 is required in patients with this hemodynamic pattern.

The effect of N-acetylcysteine on oxygen transport and uptake in patients with fulminant hepatic failure

We have investigated the effect of N-acetylcysteine on hemodynamic variables, oxygen delivery (DO2), oxygen consumption (VO2), and oxygen extraction in patients with fulminant hepatic failure using independent methods of determining DO2 and VO2, thereby eliminating the effect of mathematical coupling, which may have biased previous studies. In 11 patients with severe fulminant hepatic failure, we documented the hemodynamic effects of N-acetylcysteine during the first 5 hours of a standard infusion regime and simultaneously measured VO2 using a method based on respiratory gas analysis. We related physiological changes to plasma N-acetylcysteine concentrations, and compared this group with 7 patients who received placebo infusions. A variable hemodynamic response to N-acetylcysteine was observed that did not differ significantly in comparison with the placebo group, and did not correlate with plasma drug concentrations. The most significant relationship observed between DO2 and VO2 in any patient predicted a 13-mL x min(-1) x m(-2) increase in VO2 when DO2 increased by 100 mL x min(-1) x m(-2); in 8 patients, VO2 was independent of DO2 over the range observed. In the group that received N-acetylcysteine, a small (mean 6 [SD 6] mL x min(-1) x m[-2]) increase in VO2 occurred in comparison with baseline after 1 hour of infusion (P < .01), but changes were not significantly different from the placebo group and were not sustained. N-Acetylcysteine infusion did not increase oxygen extraction or result in an improvement in whole-blood lactate levels or base excess during the study period. We conclude that N-acetylcysteine infusion does not result in clinically relevant improvements in global VO2, or in clinical markers of tissue hypoxia in patients with severe fulminant hepatic failure.

Pro-inflammatory cytokine release and mediation of the acute phase protein response in fulminant hepatic failure

OBJECTIVE

To study the relationship between interleukin-6 (IL-6), tumour necrosis factor (TNF) and the acute phase protein C-reactive protein (CRP) in patients with fulminant hepatic failure (FHF) and to investigate the potential of peripheral blood mononuclear cells (PBMC) isolated from these patients to stimulate CRP production by isolated human hepatocytes in vitro.

SETTING

Patients with FHF were studied at the time of their admission to the intensive care unit.

STUDY DESIGN

Serum TNF and IL-6 were measured in 12 patients with FHF, PBMC from 6 of these patients were then cultured in the presence and absence of lipopolysaccharides (LPS). TNF and IL-6 in serum and supernatants were measured by ELISA. PBMC supernatants were added to isolated human hepatocytes and CRP production was measured.

RESULTS

Serum IL-6 (348 +/- 172 pg/ml) and TNF (118.5 +/- 15.5 pg/ml) were elevated compared with healthy controls (not detected) and these observations were matched by elevated serum CRP in patients with FHF (38.9 +/- 7 mg/l). Both the production of IL-6 and TNF by PBMC isolated from patients with FHF and the potential of supernatants from these cells to stimulate CRP production by hepatocytes in vitro was significantly reduced compared with controls.

CONCLUSION

Despite the observation that patients with FHF have an elevated hepatic acute phase response, PBMC from patients with FHF have reduced potential to produce IL-6 and TNF and elicit an acute phase response in vitro by the time of patient admission to the intensive care unit. One explanation for this observation is early activation and exhaustion of PBMC in vivo.

Anaesthesia and cystic fibrosis

Cystic fibrosis occurs in 1 in 2000 children and the majority now reach adulthood. The disease is a complex multisystem disorder which is likely to challenge anaesthetists with increasing frequency. In this review the presentation and genetics of the disease are briefly described, followed by a detailed account of the pathophysiology relevant to anaesthesia. The pre-operative assessment and conduct of anaesthesia are discussed and some suggestions made regarding management.