Page 1489 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

1028 PART 9: Gastrointestinal Disorders

avoid unnecessarily raising central venous pressures and exacerbating ■ PORTOPULMONARY HYPERTENSION
portal hypertension. Increased ascites can lead to abdominal compart- The pathophysiology of portopulmonary hypertension (PPH) is not
ment syndrome, compress the vena cava, reduce preload, and cause completely understood. Some theorize that increased intrapulmonary
hypovolemic hypotension.
vascular flow causes shear stress that may trigger remodeling of the
vascular endothelium. Other theories support the notion that porto-
PULMONARY DERANGEMENTS systemic shunting and decreased phagocytic capacity of the cirrhotic
■ MECHANICAL VENTILATION liver allows circulating bacteria and toxins to enter the pulmonary
circulation causing cytokine release and triggering vascular inflam-
16
In the event that a cirrhotic patient requires mechanical ventilatory support matory changes. Histopathology reveals intimal fibrosis, smooth
for respiratory failure, there are no current guidelines or evidence-based muscle hypertrophy, and characteristic plexiform lesions seen in small
17
data on the optimal ventilator modes or settings. There are data suggest- arteries and arterioles. While dyspnea on exertion is the most com-
ing the predilection of cirrhotic patients for developing ALI/ARDS. mon presenting symptom, patients may also present with chest pain,
11
In addition, the sequelae of chronic liver disease including ascites, pleu- fatigue, hemoptysis, or orthopnea. In late stages of the disease, they may
ral effusions, and chest wall edema all alter respiratory mechanics. Given demonstrate lower extremity edema, elevated jugular venous pressure,
these factors, it is important to consider that mechanical ventilation with and signs of volume overload, all of which are difficult to interpret in the
traditional tidal volumes can increase pulmonary pressures resulting setting of chronic liver disease. Physical examination may reveal a loud
in ventilator induced lung injury. Mechanical damage of lung tissue P2 with murmurs of tricuspid and pulmonic regurgitation and a right
10
may further activate cytokines resulting in biotrauma, that may trigger ventricular heave. Cirrhotic patients who have an estimated pulmonary
or further worsen a systemic inflammatory response or septic shock. artery systolic pressure >50 mm Hg on echocardiogram should undergo
12
Extrapolation from the acute respiratory distress syndrome network right heart catheterization to evaluate for PPH. 1
study in 2000 would support the use of low tidal volumes at 6 mL/kg Diagnostic criteria for PPH include a mean pulmonary artery pressure
ideal body weight to minimize barotrauma as well as biotrauma in >25 mm Hg, normal pulmonary wedge pressure, and an elevated pulmo-
5 1
patients with cirrhosis, especially in the setting of ALI or ARDS. nary vascular resistance >125 dynes . sec/cm . PPH can further be divided
13
into mild (mPAP 25-34 mm Hg), moderate (mPAP 35-44 mm Hg), and
■ HEPATOPULMONARY SYNDROME severe (mPAP >45 mm Hg). The importance of subcategorization rests
16
in the increased mortality in patients who undergo liver transplantation
While there are multiple etiologies for hypoxemia in the cirrhotic patient with moderate to severe portopulmonary hypertension. 18
including atelectasis, pneumonia, and effusions, hepatopulmonary syn- Currently, data suggest that patients with mild PPH, defined as a
drome (HPS) is a distinct pathophysiologic process specifically related mean PA pressure <35 mm Hg, can proceed with liver transplantation.
to portal hypertension that causes hypoxemia due to a diffusion-limited Given the data indicating increased mortality with liver transplantation
transfer of oxygen across the alveolar-capillary interface. HPS is charac- in patients with moderate or severe PPH with significant right ventricu-
terized by the triad of an increased arterial to alveolar oxygen gradient, lar dysfunction, this subset of patients is not eligible for liver transplant
pulmonary vascular vasodilation, and underlying liver disease. 14 listing. However, studies conducted by Kuo et al and Krowka et al have
1
The pathogenesis of hepatopulmonary syndrome lies in increased cir- shown a preoperative reduction in mean PAP and pulmonary vascular
culating vasodilators such as nitric oxide that lead to vasodilation in the resistance in patients treated with continuous IV epoprostenol. While
19
capillary and precapillary beds of the lung, as well as arteriovenous mal- limited data exist regarding the long-term benefit of epoprostenol, it
15
formations. Although these can coexist, when capillary vasodilatations may be a therapeutic option to downgrade the severity of PPH and right
predominate, the syndrome is referred to as type I hepatopulmonary syn- ventricular dysfunction so that patients may be listed for liver transplan-
drome. When arteriovenous malformations predominate, it is referred to tation after improved cardiopulmonary hemodynamics. Currently, no
1
as type II hepatopulmonary syndrome. The distinction between type I guidelines exist regarding the efficacy of phosphodiesterase inhibitors
and type II hepatopulmonary syndromes is useful, since therapeutic such as sildenafil in improving PPH. It has, however, shown benefit
interventions may differ. The hypoxemia that develops in HPS is a result in other etiologies of pulmonary hypertension and has been used with
of pulmonary vasodilation causing intrapulmonary shunts that result in promising results in case reports of patients with PPH. 20
excess lung perfusion. Rapid blood flow through a dilated pulmonary
being adequately oxygenated due to diffusion-limited oxygen transfer ■ HEPATIC HYDROTHORAX
arterial circulation prohibits deoxygenated red blood cells (RBC) from
from the alveolus to the RBC that resides in a dilated capillary. 16 Hepatic hydrothorax occurs in up to 12% of patients with cirrhosis
Classic clinical manifestations of hepatopulmonary syndrome include and has been identified as a distinct pulmonary complication of portal
platypnea, orthodeoxia, cyanosis, digital clubbing, shortness of breath, hypertension. It is defined as the accumulation of fluid in the pleural
<70 mm Hg on room space in a patient with portal hypertension and no underlying cardio-
and hypoxemia. Diagnostic criteria include a Pa O 2
21
16
air with an increased A-a gradient without CO retention. Further pulmonary disease. The fluid is thought to originate in the abdominal
2
work-up includes an arterial blood gas on 100% O and a double bubble cavity and flows into the pleural space through defects in the diaphragm.
2
echo or 99 mTC macro-aggregated albumin lung perfusion scan to On a microscopic level, these defects are breaks in the collagen bundle
establish the presence of intrapulmonary vascular vasodilatation. A that constitutes the tendonous portion of the diaphragm. Increased
delayed appearance of bubbles in the left heart 3 to 6 beats after visual- intra-abdominal pressure causes the peritoneum to herniate through
ization in the right heart and a shunt fraction greater than 6% indicates these breaks resulting in pleuroperitoneal blebs. These blebs tend to
the presence of intrapulmonary vascular dilation and confirms the diag- occur more frequently on the right given the heightened muscularity of
nosis of hepatopulmonary syndrome. 1 the left diaphragm. Eventually, these blebs rupture and allow free pas-
While the pharmacologic treatment for hepatopulmonary syndrome sage of intraperitoneal fluid preferentially into the pleural space given
remains disappointing, supplemental oxygen does temporarily improve the negative intrathoracic pressure. Hepatic hydrothorax occurs when
hypoxemia in type I hepatopulmonary syndrome. Given that type II the rate of fluid accumulation exceeds rate of reabsorption. 22
hepatopulmonary syndrome involves shunting of blood supplemental Patients present clinically with symptoms of dyspnea, cough, and
oxygenation will not improve hypoxemia in this subset; embolization pleuritic chest pain. Typically, patients also present with abdominal
therapy may improve oxygenation in these patients. Ultimately, a more ascites, although there have been case reports of hepatic hydrothorax
16
promising option for patients with hepatopulmonary syndrome is ortho- occurring in the absence of ascites. Due to the physiology described
topic liver transplantation. above, hepatic hydrothorax often occurs in the right thorax, but may

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