This study will evaluate the use of N-acetyl cysteine in post-reperfusion pulmonary injury in patients with chronic thromboembolic pulmonary hypertension undergoing pulmonary balloon angioplasty and pulmonary endarterectomy. Half of the patients will receive N-acetyl cysteine and the other placebo.

For chronic pulmonary embolism thrombus hypertension, the potentially curative treatment is endarterectomy, however in 12 to 60% it does not present surgical susceptibility, so pulmonary balloon angioplasty is the secondary option. In these procedures the complication that occurs most frequently is pulmonary oedema after reperfusion is a frequent complication (17.8-65%), appears between 24-72 hours after the intervention and the diagnosis is made in the presence of infiltrate interstitial in chest radiography or computed tomography of the chest. Initially it was believed that it was difficult due to the increase in perfusion of secondary flow in the territory due to pulmonary vascular dilation, it is now believed that microtraumatism is involved by the guides and balloon used, vascular dysfunction and cytokines and innate immunity and adaptive, complement activation, coagulation cascade activation, apoptosis pathway activation, endothelial dysfunction caused by reperfusion contribute to cell dysfunction.

The use of N-acetyl cysteine for its antioxidant properties, inflammatory response attenuator, reduction of reactive oxygen species (ROS) and that in addition to having already had to reduce the condition of decrease in post-reperfusion ischemia15,16 in other situations is a viable option in the treatment of acute post-reperfusion edema in patients sometimes a pulmonary endarterectomy and balloon pulmonary angioplasty.

Inclusion Criteria:

- Patients who are diagnosed with group 4 pulmonary hypertension and are susceptible to pulmonary endarterectomy or balloon angioplasty in patients over 18 years.

Exclusion Criteria:

• Patients who do not accept admission to the trial.
• Presence of arterial hypotension or sepsis.

De-identified individual participant data for all primary and secondary outcome measures will be made available.

Data will be available within 8 months of study completion.

Data access request will be reviewed by an internal review panel. Requestors will be required to sign a Data Access Agreement.

It will be through sealed, opaque and numbered envelopes sequentially. The assignment sequence will be done by the pharmacist, the principal investigator will recruit the patients. Researchers and site staff (with the exception of the investigating pharmacologist) will be blinded to the assigned treatment. There will be no circumstances to unmask and reveal the intervention.