Methylene blue in the hepatopulmonary syndrome

The hepatopulmonary syndrome

The hepatopulmonary syndrome is a disease entity seen in association with liver failure and other disease entities. It is a devastating consequence of liver failure that results in a significant morbidity for affected patients. Currently, there are no identified medications that ameliorate the symptoms of hypoxemia in this disease state. Recent research, however, has begun to unravel the pathobiology of the vascular dilations that arise in the lungs of patients with liver failure. In this article, a compendium of current knowledge is presented, as well as the contemporary methods for identifying and treating patients.

Hepatopulmonary syndrome and liver transplantation: a review of the peroperative management of seven paediatric cases

Until recently, hypoxaemia was considered as a relative contraindication for liver transplantation. The hepatopulmonary syndrome associated with a right to left shunt of blood through the lungs is reversible in adults and children after correction of the cirrhosis by liver transplantation. However, concerns have been raised regarding the risks of anaesthesia in such hypoxaemic patients. Since the peroperative management of children undergoing liver transplantation and suffering from hepatopulmonary syndrome and severe hypoxemia has never been described, we report here our experience in seven children. Despite the fact that severe arterial desaturation was recorded throughout the procedure, no major complications were recorded peroperatively. The postoperative intubation time was 58 +/- 21 h, five children being extubated while still hypoxaemic. All seven patients reversed their hepatopulmonary syndrome after a mean postoperative period of 24 +/- 10 weeks. This shows that liver transplantation can be successfully achieved in severely hypoxaemic children and that postoperative correction of the right to left shunt is then obtained.

Reversal of hypoxemia by inhaled nitric oxide in children with severe hepatopulmonary syndrome, type 1, during and after liver transplantation

BACKGROUND

The hepatopulmonary syndrome with profound hypoxemia is a rare but severe complication for children with liver cirrhosis. It can be reversed by liver transplantation (LT), which is now regarded as a good indication. However, previous reports have described cases of transient or fatal deteriorations of intrapulmonary shunting after pediatric liver transplantation with dramatically worsening hypoxemia.

METHODS AND RESULTS

A similar case during and after LT in a 4-year-old girl with severe hepatopulmonary syndrome is described with prompt reversal of hypoxemia by inhaled nitric oxide, which was discontinued definitely until day 14 after LT.

CONCLUSIONS

During or after LT, worsening hypoxemia may be improved by using inhaled nitric oxide in pediatric patients undergoing liver transplantation for liver cirrhosis and hepatopulmonary syndrome. The mechanisms are unclear, but may involve mismatching lung ventilation-perfusion. However, additional clinical reports are necessary before accepting these results.

Hepatopulmonary syndrome: the paradigm of liver-induced hypoxaemia

The current chapter deals with the concept, clinical manifestations and diagnostic tools of the hepatopulmonary syndrome (HPS) and highlights its most salient pathophysiological, mechanistic and therapeutic aspects. Defined as a clinical triad, including a chronic liver disorder, pulmonary gas exchange abnormalities and generalized pulmonary vascular dilatations, in the absence of intrinsic cardiopulmonary disease, this entity is currently growing in interest with both clinicians and surgeons. The combination of arterial hypoxaemia, high cardiac output with normal or low pulmonary artery pressure, and finger clubbing in a patient with advanced liver disease should strongly suggest the diagnosis of HPS. Its potential high prevalence together with failure of numerous therapeutic approaches depicts a life-threatening unique clinical condition that may dramatically benefit with an elective indication of liver transplantation (LT). A better orchestration of the concepts of the pathophysiology of this lung-liver interplay may foster our knowledge and improve the clinical management and indications of LT.

The hepatopulmonary syndrome

The hepatopulmonary syndrome occurs in subjects with chronic liver disease and/or portal hypertension who develop intrapulmonary vasodilation resulting in arterial deoxygenation. Clinical and basic science studies investigating the pathophysiology of HPS are presented. A diagnostic algorithm is provided using contrast echocardiography, the lung perfusion scan, and pulmonary angiography. Medical therapy and experience with liver transplantation are reviewed.

Scenario number one: hepatopulmonary syndrome

HPS is an increasingly recognized clinical entity resulting from intrapulmonary vasodilatation in patients with liver disease and/or portal hypertension. The pathogenesis of alterations in the pulmonary vascular bed in affected patients is poorly understood and the subject of ongoing investigation. The differential diagnosis of pulmonary symptoms and gas-exchange abnormalities in patients with liver disease being evaluated for transplantation is broad and should be focused on differentiating pulmonary causes that significantly increase the risk for transplantation from HPS where transplantation has emerged as a useful treatment. Specific contraindications to transplantation in patients with HPS have not been identified, though unique postoperative complications have been observed and may be treatable during the frequently prolonged resolution of intrapulmonary vasodilatation. The development of a database of information on patients with HPS undergoing transplantation will provide insight into potential contraindications, prognostic features, and postoperative complications unique to these patients.

Hepatopulmonary syndrome. A pulmonary vascular complication of liver disease

Hepatopulmonary syndrome is part of the spectrum of pulmonary vascular disorders seen in advanced liver disease. The pathophysiology of these entities likely is dependent on the degree of pulmonary vasoconstriction or vasodilation that occurs. Our understanding of hepatopulmonary syndrome has helped further our knowledge of the interaction of the liver and the lung. Advances in the management of this disorder, especially liver transplantation, finally have allowed us to offer some hope to patients with this disease.

Mediators, cytokines, and growth factors in liver-lung interactions

Multiple mediators have been implicated in the interactions between the liver and the lungs in various disease states. The best characterized mediator of liver-lung interaction is alpha 1-antitrypsin. Several cytokines and mediators may be involved in the pathogenesis of the hepatopulmonary syndrome and in the cytokine cascades that are activated in systemic inflammatory states such as acute respiratory distress syndrome. Hepatocyte growth factor or scatter factor is a recently described peptide with a broad range of biologic effects that may mediate lung-liver interactions.

Mechanisms of gas exchange impairment in patients with liver cirrhosis

This article reviews the basic pathophysiologic mechanisms underlying the abnormal pulmonary gas exchange often seen in patients with cirrhosis. To summarize, the following keypoints seem appropriate: (1) Patients with cirrhosis have a low pulmonary vascular tone characterized by a poor or absent hypoxic pressor response. This results in a marked dilation of the pulmonary vasculature. (2) This abnormal pulmonary vascular tone, independently of airway disease, causes VA/Q mismatch and mild to moderate hypoxemia. Yet, as liver disease progresses and hepatocellular function deteriorates, more severe degrees of intrapulmonary shunt emerge and, probably, O2 diffusion limitation ensues, causing severe respiratory failure (see Table 1). (3) At rest, the high cardiac output and minute ventilation of cirrhosis minimize the degree of arterial hypoxemia that otherwise would be expected from the observed degree of both VA/Q inequality and intrapulmonary shunt. During exercise, the relative "normalization' (with respect to metabolic demands) of the hemodynamic and ventilatory status of the patient explains the fall in PaO2. (4) A clear pathogenic mechanism of these pathophysiologic abnormalities is still lacking, although available evidence suggests that both the liver and the endothelial cells may play a pivotal role in the regulation of the pulmonary vascular tone in these patients. (5) To date, no pharmacologic intervention has been effective in treating hypoxemia in these patients. Yet liver transplantation helps in most of them. This observation reinforces the functional nature of the gas exchange abnormalities of cirrhosis.

Endogenous pulmonary nitric oxide production measured from exhaled air is increased in patients with severe cirrhosis

BACKGROUND/AIMS

Endogenous pulmonary nitric oxide production may be increased in severe cirrhosis and contribute to pulmonary vasodilation. This study assessed pulmonary nitric oxide production by measuring nitric oxide in the exhaled air in patients with severe cirrhosis and examined the relationship between exhaled nitric oxide and pulmonary hemodynamics in these patients.

METHODS

Nitric oxide concentrations and production were measured in the exhaled air in six Child-Pugh class C patients with cirrhosis and 21 non-smoking healthy controls. Systemic and pulmonary hemodynamics were measured in patients only.

RESULTS

Nitric oxide concentration (32.0 +/- 1.7 (mean +/- SEM) vs. 8.9 +/- 1.0 ppb) and production (9.2 +/- 1.3 vs. 3.1 +/- 0.3 nmol/min) in exhaled air were significantly higher in patients than in controls. Patients had high cardiac output (8.5 +/- 0.9 l/min), low pulmonary and systemic vascular resistance (57 +/- 10 and 767 +/- 93 dyn.s.cm-5, respectively) under baseline conditions. A significant negative correlation was found between pulmonary vascular resistance and exhaled nitric oxide production (r=0.943, p=0.05) but not between cardiac output or systemic vascular resistance and nitric oxide measured in exhaled air.

CONCLUSIONS

Endogenous pulmonary nitric oxide production measured from exhaled air is increased in patients with cirrhosis and liver failure. Increased in patients with cirrhosis and liver failure. Increased nitric oxide production may also contribute to cirrhosis-induced pulmonary vasodilatation.