Hepatopulmonary syndrome (HPS) is a lung complication of liver disease in which tiny blood vessels inside the lungs widen abnormally, making it harder for oxygen to pass from inhaled air into the bloodstream. It is formally defined as the triad of liver disease, intrapulmonary vascular dilatations, and impaired gas exchange that leads to low blood oxygen levels.1PubMed Central. Current concepts in the management of hepatopulmonary syndrome The condition carries a poor prognosis when untreated, and liver transplantation remains the only therapy shown to reliably reverse it.2PubMed. Defining and characterizing severe hypoxemia after liver transplantation in hepatopulmonary syndrome
What Goes Wrong in the Lungs
In a healthy person, lung capillaries are narrow enough that red blood cells pass through in single file, giving each one close contact with the oxygen-rich air in the tiny air sacs. In HPS, those capillaries dilate well beyond their normal diameter. Blood rushes through too quickly and too far from the air sacs for oxygen to diffuse into it properly. The result is a mismatch between ventilation (air getting in) and perfusion (blood flowing past), along with outright shunting of blood that never picks up oxygen at all. Thickening of capillary walls compounds the problem by creating an additional barrier to gas exchange.3PubMed Central. Hepatopulmonary Syndrome: A Comprehensive Review
The driving force behind this vascular widening traces back to the diseased liver. Endothelin-1, a signaling molecule released during liver injury, stimulates the production of nitric oxide in lung blood vessels. Nitric oxide is a potent vasodilator, and its overproduction in the pulmonary circulation causes the capillaries to relax and expand.4PubMed. Endothelin-1 stimulation of endothelial nitric oxide synthase in the pathogenesis of hepatopulmonary syndrome On top of that, bacterial fragments from the gut can leak into the bloodstream when the liver is too sick to filter them out. This bacterial translocation triggers inflammation and draws immune cells called macrophages into the lung vasculature. In rat studies, cirrhotic animals with bacterial translocation had a dramatically higher incidence of HPS compared to those without it.5PubMed. Cirrhotic rats with bacterial translocation have higher incidence and severity of hepatopulmonary syndrome These accumulated macrophages release growth factors that spur the formation of new, abnormal blood vessels in the lungs, a process that worsens the shunting over time.6PubMed Central. Pulmonary Angiogenesis in a Rat Model of Hepatopulmonary Syndrome
The Hallmark Symptoms
The most common complaint is progressive shortness of breath. What makes HPS distinctive, though, is how body position affects it. Many people with HPS experience platypnoea, meaning their breathlessness gets worse when they sit or stand upright and improves when they lie down. The corresponding drop in blood oxygen upon standing is called orthodeoxia, typically defined as a fall in oxygen saturation of more than 5 percent. Up to about 88 percent of HPS patients have orthodeoxia, compared with fewer than 5 percent of people who have cirrhosis alone.7PubMed Central. Platypnoea and orthodeoxia in the hepatopulmonary syndrome This positional worsening happens because gravity pulls more blood into the dilated vessels at the lung bases when the person is upright, increasing the amount of blood that bypasses oxygen exchange.
Other signs can include spider angiomas on the skin, finger clubbing, and a bluish tint to the lips or fingertips. Because these overlap with findings in advanced liver disease generally, HPS can go unrecognized for months unless a clinician specifically looks for it. Quality of life suffers as the oxygen deficit deepens: patients report worse functional capacity compared with liver-disease patients who do not have HPS.8PubMed Central. Impact of hepatopulmonary syndrome on quality of life and survival in liver transplant candidates
How HPS Is Diagnosed
The diagnostic workup rests on three pillars: confirming liver disease or portal hypertension, detecting the dilated lung vessels, and documenting abnormal gas exchange. The gold-standard test for finding intrapulmonary vascular dilatations is a contrast-enhanced echocardiogram, commonly called a “bubble study.” A technician injects agitated saline containing tiny microbubbles into a vein. Normally, these bubbles are too large to pass through the lung capillaries and never appear on the left side of the heart. If the lung capillaries are abnormally widened, the bubbles slip through and show up in the left heart chambers after a delay of three or more heartbeats.9JHEP Reports. Hepatopulmonary syndrome That delay is what distinguishes HPS from a hole between the heart chambers, where bubbles appear almost immediately.10PubMed Central. A case of hepatopulmonary syndrome
An arterial blood gas test measures the oxygen level in the blood directly. HPS is diagnosed when the alveolar-arterial oxygen gradient is at least 15 mmHg, or at least 20 mmHg in people over 65.11JHEP Reports. Hepatopulmonary syndrome A complementary imaging option is a lung perfusion scan using technetium-99m-labeled macroaggregated albumin (Tc-MAA). In this test, radioactive particles slightly larger than normal capillaries are injected. If they bypass the lungs and show up in organs like the brain, the degree of shunting can be quantified. A shunt fraction above about 6 percent is considered abnormal.12PubMed Central. Hepatopulmonary Syndrome with Right-to-left Shunt in Cirrhotic Patients Using Macro-Aggregated Albumin Lung Perfusion Scan The bubble study is more sensitive for detecting dilated vessels, while the Tc-MAA scan adds the ability to measure how much blood is actually shunting past the lungs.13PubMed Central. Technetium-99m-labeled macroaggregated albumin lung perfusion scan for diagnosis of hepatopulmonary syndrome
Severity Grading
Once HPS is confirmed, severity is classified by how low the blood oxygen level has dropped on room air at sea level. The most widely used system divides HPS into four tiers based on the partial pressure of oxygen (PaO2):
- Mild: PaO2 of 80 mmHg or above
- Moderate: PaO2 between 60 and 79 mmHg
- Severe: PaO2 between 50 and 59 mmHg
- Very severe: PaO2 below 50 mmHg
This classification matters because it shapes transplant urgency and predicts post-operative recovery. Patients in the very severe category face higher surgical risk and often need prolonged oxygen support after a transplant.14PubMed Central. Hepatopulmonary syndrome: pathophysiological mechanisms and clinical implications
How HPS Differs from Portopulmonary Hypertension
Both HPS and portopulmonary hypertension (PoPH) are lung problems caused by liver disease, and they are often discussed together. But they are essentially opposite vascular disorders. HPS involves blood vessels that are too wide and floppy, causing oxygen levels to drop. PoPH involves blood vessels that constrict and stiffen, raising the pressure in the pulmonary arteries and eventually straining the right side of the heart. Patients with PoPH rarely develop significant hypoxemia in the way HPS patients do; instead, their main threat is progressive right heart failure.15PubMed Central. Hepatopulmonary Syndrome and Portopulmonary Hypertension: Current Status and Implications for Liver Transplantation The treatment strategies diverge accordingly. HPS resolves with liver transplantation in most cases, whereas PoPH may actually worsen after transplant if pulmonary pressures are not controlled first. Getting the right diagnosis is essential because the management paths point in different directions.
Liver Transplantation as the Definitive Treatment
No medication has been proven to reliably cure HPS. Liver transplantation remains the only treatment that consistently resolves the underlying vascular abnormalities. Once the liver disease is corrected, the dilated pulmonary capillaries gradually return to normal size, the shunting diminishes, and oxygen levels improve. In one large review, about 80 percent of HPS patients showed complete resolution of their hypoxemia after transplant, and the five-year survival rate was roughly 76 percent, which is comparable to transplant recipients who never had HPS.16PubMed Central. Hepatopulmonary Syndrome and Liver Transplantation: A Recent Review of the Literature
Recovery is not always immediate, however. Patients with severe HPS often need supplemental oxygen for weeks or months after surgery while the lung vessels remodel. In a small series of adults with very severe disease, all patients eventually achieved oxygen saturations above 98 percent on room air, but those who also had elevated pulmonary pressures took roughly ten months to get off oxygen, compared with about two months for the rest.17Liver Transplantation. Retrospective analysis of the results of liver transplantation for adults with severe hepatopulmonary syndrome For the sickest patients who struggle with dangerously low oxygen in the early post-transplant period, an array of rescue strategies can be used, including lying the patient head-down (Trendelenburg positioning), inhaled vasodilators, and in extreme cases, temporary extracorporeal life support to keep the blood oxygenated while the lungs heal.18American Journal of Transplantation. Management of Severe Posttransplant Hypoxemia in Hepatopulmonary Syndrome: A Systematic Approach and Algorithm
Getting on the Transplant List
In the United States, transplant organs are allocated largely based on the MELD score, which estimates the urgency of liver failure by looking at lab values like bilirubin and creatinine. HPS creates an awkward situation: a patient can be severely hypoxemic and functionally incapacitated yet have a MELD score too low to receive an organ in time. To address this, a MELD exception policy grants additional priority points to patients with confirmed HPS whose PaO2 is below 60 mmHg. An analysis of the national transplant database found that HPS exception patients actually had lower overall waitlist mortality than other liver transplant candidates, prompting calls to reassess whether the exception is too generous.19PubMed Central. Impact of the Hepatopulmonary Syndrome MELD Exception Policy on Outcomes of Patients After Liver Transplantation
Despite the overall good outcomes, severity at the extreme end still matters. A pre-transplant PaO2 at or below 44 mmHg has been linked to increased post-transplant mortality.20PubMed Central. Impact of the Hepatopulmonary Syndrome MELD Exception Policy on Outcomes of Patients After Liver Transplantation A more recent study confirmed excellent outcomes across a broad range of pre-transplant oxygen levels but found that patients with PaO2 below 45 mmHg were actually more likely to receive a transplant, presumably because their clinical deterioration prompted faster action.21JHEP Reports. Excellent outcomes with liver transplantation in hepatopulmonary syndrome across pre-transplant PaO2 spectrum The bottom line for patients and families is that transplant evaluation should begin as soon as HPS is diagnosed, because waiting for the oxygen level to fall further adds risk without improving outcomes.
Bridging Therapies While Waiting
Because transplant wait times can stretch for months, clinicians look for ways to stabilize or improve oxygenation in the interim. None of these approaches cure HPS, but some buy time.
Supplemental oxygen is the simplest intervention. Guidelines recommend long-term oxygen therapy for patients with severe HPS whose PaO2 drops below 60 mmHg.22Journal of Hepatology. Hepatopulmonary syndrome It does not fix the underlying shunt but helps keep tissues from suffering the consequences of chronic oxygen deprivation.
A procedure called TIPS (transjugular intrahepatic portosystemic shunt) has been studied as a potential bridge. TIPS creates an artificial channel inside the liver to relieve portal hypertension, theoretically reducing the signal that drives pulmonary vessel dilation. Results have been mixed. One prospective study found that the oxygen gap improved at one month after TIPS placement but lost statistical significance by three months.23PubMed. Effect of Transjugular Intrahepatic Portosystemic Shunt Creation on Pulmonary Gas Exchange in Patients with Hepatopulmonary Syndrome A separate study reported that patients with moderate HPS had sustained improvement after TIPS, while those with mild or severe forms did not fare as well long-term.24PubMed Central. Clinical efficacy of transjugular intrahepatic portosystemic shunt in the treatment of hepatopulmonary syndrome A systematic review of the available evidence confirmed that TIPS produced short-term oxygenation benefits, but these effects generally were not sustained beyond three months.25Journal of Vascular and Interventional Radiology. Effectiveness of Transjugular Intrahepatic Portosystemic Shunt Creation for the Treatment of Hepatopulmonary Syndrome TIPS may have a role as a short bridge to transplant for selected patients, but it is not a standalone solution.
One of the more surprising findings in HPS research comes from a randomized controlled trial of garlic supplements. Patients who took garlic capsules for nine months saw their average arterial oxygen level rise by about 25 percent, and roughly two-thirds experienced reversal of their HPS, compared with just one out of twenty patients on placebo. Fewer patients in the garlic group died during the study period as well.26PubMed Central. The role of garlic in hepatopulmonary syndrome: A randomized controlled trial The proposed mechanism involves compounds in garlic that may inhibit nitric oxide overproduction in pulmonary vessels. These results are intriguing but come from a single trial, and garlic supplementation has not become a standard recommendation. Larger confirmatory studies are still needed before it could be considered a reliable therapy.
HPS in Children
HPS is not limited to adults. In children, the most common underlying cause is biliary atresia, a condition where the bile ducts fail to form properly. A 20-year review of pediatric HPS identified 20 patients, with biliary atresia accounting for nearly half of them. Shortness of breath was the presenting symptom in the vast majority. The good news is that transplantation was highly effective: 15 out of 16 transplanted children had complete resolution of their HPS, and the five-, ten-, and twenty-year survival rates held steady at about 88 percent.27PubMed. Hepatopulmonary Syndrome in Children: A 20-Year Review of Presenting Symptoms, Clinical Progression, and Transplant Outcome A separate long-term series confirmed similar patterns, with 13 of 14 transplanted children seeing HPS resolve.28PubMed. Long-term outcome and management of hepatopulmonary syndrome in children
The picture is more complicated for children who have both biliary atresia and HPS at the time of transplant. One study of 120 biliary atresia children undergoing liver transplantation found that the 5 percent who had concurrent HPS experienced significantly worse overall survival compared with those without it. HPS was an independent predictor of poor outcomes, alongside vascular complications.29PubMed. Hepatopulmonary syndrome in biliary atresia children increased postoperative complications after liver transplantation This discrepancy likely reflects the challenges of managing post-transplant hypoxemia in very young, very small patients. It underscores why screening for HPS before transplant matters in pediatric liver disease, so that surgical teams can plan for the additional respiratory support these children may need.
Why HPS Can Be Missed
One of the frustrating features of HPS is how easily it flies under the radar. Shortness of breath in a person with cirrhosis tends to be attributed to fluid in the abdomen pressing on the diaphragm, anemia, or muscle wasting. A patient who becomes breathless while walking to the bathroom might not think to mention that lying down makes it better, and a busy clinician might not ask. The positional clue that so strongly suggests HPS can be lost in the noise of a complicated medical picture.
Pulse oximetry, the simple finger-clip device that measures oxygen saturation, can help with screening but has limitations. It may not flag mild HPS because the oxygen deficit at that stage is subtle. The definitive diagnostic steps, the bubble study and arterial blood gas, are not routinely ordered unless HPS is already suspected. Because the condition tends to worsen gradually rather than announce itself with a crisis, the window between early detection and significant oxygen impairment can be wide. Some centers now advocate screening all liver transplant candidates with a bubble study regardless of symptoms, precisely because catching HPS early allows for more timely transplant listing.
Living with HPS Before a Transplant
For patients who are waiting for a transplant or who are not candidates for one, day-to-day management focuses on maintaining function and monitoring for deterioration. Supplemental oxygen keeps tissues from starving, and many patients use portable oxygen concentrators to stay mobile. Altitude matters more than usual: flying in a commercial aircraft exposes passengers to cabin pressures equivalent to roughly 6,000 to 8,000 feet of elevation, which further reduces the available oxygen. People with moderate or severe HPS need to plan air travel carefully and may require in-flight supplemental oxygen.
Exercise tolerance generally declines as the disease progresses. Simple activities like climbing stairs, carrying groceries, or playing with children can become exhausting. The psychological burden is real as well. A study comparing liver transplant candidates with and without HPS found that the HPS group reported significantly worse functional status and lower quality of life.30PubMed Central. Impact of hepatopulmonary syndrome on quality of life and survival in liver transplant candidates Support from hepatology social workers, pulmonary rehabilitation where feasible, and honest conversations with the transplant team about expected timelines all help patients cope with the uncertainty of waiting.
When HPS Occurs Without Cirrhosis
Most descriptions of HPS center on cirrhosis, but the condition can develop whenever portal hypertension or significant liver disease is present. Non-cirrhotic portal hypertension, chronic hepatitis without full-blown cirrhosis, and even some congenital liver disorders can set off the cascade of pulmonary vascular dilation. The diagnostic criteria do not require cirrhosis specifically; they require evidence of liver disease or portal hypertension alongside the vascular and gas-exchange abnormalities.31JHEP Reports. Hepatopulmonary syndrome This matters because a physician who thinks of HPS only in the setting of advanced cirrhosis may overlook it in a patient with an earlier or rarer form of liver disease. Any patient with known liver pathology who develops unexplained breathlessness or low oxygen saturation deserves at least a screening conversation about whether HPS could be part of the picture.