Elevations in pulmonary vascular resistance attributable to hypercarbia can be caused by either direct carbon dioxide absorption or hypoventilation.S3.3-19 If clinical urgency precludes transfer, consultation with an anesthesiologist with ACHD expertise would be of benefit to on-site providers who do not have ACHD expertise. Many patients with ACHD have had surgeries in the past, which may have created or identified airway or vascular access concerns. Patients with ACHD can also have underlying restrictive and/or obstructive lung disease that should be Patients with ACHD and pulmonary hypertension Consultation with experts in pulmonary hypertension and ACHD to assist in the interpretation of diagnostic and invasive studies and determine the best course of management. PAH imparts a poor prognosis compared with CHD without PAH. Because of the complexity of PAH in the setting of CHD, patients with ACHD benefit from the expertise of both ACHD providers and pulmonary hypertension Management of PAH in patients with shunts can be difficult. For example, in patients for whom PAH treatment is expected to allow subsequent closure of a shunt, cohort series demonstrate progression of pulmonary vascular resistance or late mortality if defects with associated pulmonary vascular resistance elevation beyond 2.5 Wood units (>4 Wood ) or Qp:Qs >3 were closed.S3.3- The utility of acute administration of pulmonary vasodilator therapy as a marker of reversibility of pulmonary vascular resistance remains uncertain. Treat-to-repair strategies involving use of PAH therapies to bring pulmonary vascular resistance into a range where repair can be considered have been applied, but the utility of such strategies also remains uncertain. *See Tables 3 and 4 for details on the ACHD AP classification system. 