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CHAPTER 38: Acute Right Heart Syndromes 317

data supporting meaningful improvements in outcomes, measurable hypoxemia. PFO has been estimated to present in as many as 20%
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potential for adverse effects and a very high acquisition cost from a of patients with severe ARDS and is associated with RV dilation and
single supplier in North America, we rarely administer iNO for patients higher Pa pressures. Application of supraphysiological levels of PEEP
46
with acute or acute-chronic RHS. significantly increases R-L shunting without enhancing oxygenation as
a consequence of cardiopulmonary interaction. This effect can signifi-
Endothelin Receptor Modulators: Endothelin-1 is a potent regulator of cantly confound mechanical ventilatory efforts resulting in intractable
pulmonary vascular tone and is associated with progression of angiopro- and profound hypoxemia. While iNO may occasionally ameliorate this,
liferative lesions and vascular remodeling in primary pulmonary arterial PPV does not appear to beneficially affect R-L shunting despite its
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hypertension. Both prostacyclin and the newer nonselective endothelin other salutary effects on RV function. 59
receptor antagonists (ETRA) have been demonstrated to have antiprolif- The dominant effect of mechanical ventilation is related to its
erative activity on the pulmonary vasculature. This mechanism has been effect on preload. Sustained airway pressure increases in euvolemic
suggested to account for the modest functional improvement in patients patients with normal RV function result in a mild increase in right
with chronic pulmonary hypertension. 147 atrial pressure that is offset by increases in abdominal pressures that
The parenterally administered ETRA, tezosentan has been dem- sustain venous return. However, it remains to be determined if this is
onstrated in a porcine model of hypoxia induced acute pulmonary true for patients with acute RHS and elevated right heart pressures.
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hypertension and RV pressure overload to be as effective as the PDE Large-tidal-volume breathing impairs RV systolic function, presum-
inhibitor vardenafil in reducing pulmonary vascular resistance but ably by increasing pulmonary vascular resistance in alveolar vessels.
increased cardiac index more effectively than vardenafil, mainly In a canine model with normal lungs, raising the tidal volume above
through systemic vasodilatory effects. The VERITAS trials of 10 mL/kg caused a detectable rightward and downward shift of the
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tezosentan for acutely decompensated left heart failure, while not RV function curve. 157
meeting predefined endpoints for symptomatic improvement or clini- These effects of mechanical ventilation on right ventricular function
cal outcomes, were notable for the significant physiological improve- suggest the following strategy in patients with critical compromise
ment in elevated MPAP and PVR, disproportionate to the reduction in of the RV: (1) give sufficient oxygen to reverse any hypoxic vasocon-
RAP, PCWP, or CI increase in those patients monitored with a PAC for striction; (2) avoid hypercapnia; (3) keep PEEP at or below a level at
severe LV systolic failure. These data suggest that tezosentan is likely which continued alveolar recruitment can be demonstrated and seek
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to be an acutely active and relatively potent pulmonary vasodilator in to minimize self-controlled PEEP (auto-PEEP); and (4) use the low-
those patients. ETRAs, however have not been subjected to rigorous est tidal volume necessary to effect adequate elimination of carbon
evaluation in patients with acute right heart syndromes, and they may dioxide while maintaining Pplat <27 to 28 cm H O. Of course, the
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2
have limited potential in critically ill patients because of significant acute effects of each intervention should be measured to confirm that
associated hepatic toxicity and systemic vasodilatory properties. Those cardiac output increases. These principles are consonant with the goals
extrapulmonary effects, are likely to limit the utility of these agents in of ventilation in most patients with ARDS, except that when there is an
acute RHS. https://kat.cr/user/tahir99/
RHS, hypercapnia should be avoided if it leads to further hemodynamic
■ ANCILLARY THERAPIES FOR ACUTE RIGHT HEART SYNDROMES deterioration.
Surgical and Mechanical Therapies: Balloon atrioseptostomy (BAS),
Mechanical Ventilator Management: Ventilator manipulation has the while potentially beneficial in patients with stable severe pulmonary
potential to dramatically affect the circulation in patients with shock, hypertension is contraindicated in patients with RV failure and RA
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including those with acute RHS. For example, in animal models of pressure >20 mm Hg and/or rest O saturation <80% on room air.
2
shock, institution of mechanical ventilation significantly prolongs Extracorporeal life support systems (ECLS). In contrast to the now
survival, an effect much greater than that seen with fluid therapy well-defined role for mechanical assist devices in decompensated left
or vasoactive drugs. Of particular interest in patients with RHS is heart failure, 160,161 (Chap. 37) there is limited published experience
the maintenance of oxygenation, the role of hypercapnia (including with mechanical therapy for the acutely failing right heart. Notably,
permissive hypercapnia), and the effects of tidal volume and positive progressive right ventricular dysfunction complicates left ventricular
end-expiratory pressure (PEEP). assist device implantation or orthotopic heart transplantation for
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Hypercapnia increases pulmonary artery pressure. In patients with decompensated left heart failure 163-165 and is associated with progressive
ARDS, reducing minute ventilation as part of the strategy of permissive end-organ dysfunction. Additionally, several reports of selective right
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hypercapnia leads to small but real increases in mean pulmonary artery ventricular mechanical assist device insertion in patients with acute
pressure. 150-152 In most patients with ARDS who do not exhibit right inferior and RV myocardial infarctions in the perireperfusion period
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heart limitation, this effect of hypercapnia is probably unimportant. and in patients undergoing pulmonary thrombectomy for acute or
However, in the subset of patients with severe pulmonary hypertension, chronic PE, raise important questions regarding efficacy, safety and
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permissive hypercapnia and the attendant respiratory acidosis may lead outcome that have to date not been systematically addressed. The pres-
to unacceptable hemodynamic deterioration. 152 ently available approaches include extracorporeal and paracorporeal
The effects of large tidal volumes and PEEP on right ventricular pulsatile and centrifugal pump ventricular assist systems. An alterna-
162
function is complex, controversial, highly variable from patient to tive approach uses a right atrial catheter to draw blood into a centrifu-
patient 85,153,154 and is significantly modified by the effectiveness of cir- gal pump and a percutaneously placed pulmonary artery catheter as
culatory filling. Many studies are limited by the failure to correlate the outflow cannula. Small implantable centrifugal pumps inserted
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169
hemodynamic pressures to juxtacardiac pressure. The effect of PEEP via a transjugular approach are more recently available and appear to
can be expected to differ depending on whether atelectatic or flooded be effective and tolerated. 170,171 Lastly, the use of a extracorporeal mem-
lung is recruited, or whether relatively normal lung is overdistended. In brane oxygenation (ECMO) systems have been described with particu-
a studies of patients with ARDS, PEEP has little effect on RV function larly encouraging outcomes for a pumpless oxygenator (Novalung) in 4
when given in amounts up to that associated with improving respiratory PH patients with severe acute or chronic RV failure as a bridge to organ
system compliance. At higher levels of PEEP, the dominant effect is to transplantation. 172
153
impair RV systolic function. 152 Before wider adoption, the efficacy and safety of mechanical support in
A particularly challenging aspect to the management of patients conjunction with pulmonary vasodilator therapies or atrial septostomy as
with ARDS and acute RHS is the presence of a patent foramen ovale a bridge to definitive surgical treatment including transplantation, must
(PFO) with consequential right-to-left (R-L) shunting and worsened be established.

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