EIT Evaluation of Different Antihypertensive Agents on the Ventilation-Perfusion Ratio in Patients With Acute Respiratory Failure

Effect of Nicardipine and Nitroglycerin on the Ventilation-Perfusion Ratio in Patients With Acute Respiratory Failure Using Electrical Impedance Tomography: A Prospective Pilot Study

This prospective, single-center interventional study aims to evaluate the effect of two commonly used intravenous antihypertensive agents - nicardipine and nitroglycerin - on lung ventilation-perfusion (V/Q) distribution in patients with acute respiratory failure complicated by hypertension. Electrical Impedance Tomography (EIT) will be used for noninvasive monitoring of pulmonary ventilation and perfusion distribution before and after drug administration.

The study will compare the changes in V/Q ratio, oxygenation index, and hemodynamic variables after administration of the two drugs. The findings are expected to provide evidence for the optimal antihypertensive strategy in critically ill patients with respiratory failure and to clarify whether specific vasodilators exacerbate or improve ventilation-perfusion mismatch.

Eligible adult patients diagnosed with acute respiratory failure (PaO₂/FiO₂ ≤ 300 mmHg) and concomitant hypertension (including post-surgical or aortic dissection cases) admitted to the ICU will be enrolled after stabilization.

After baseline EIT and blood gas measurements, participants will sequentially receive nitroglycerin and nicardipine under controlled conditions, with each medication infused over a standardized time period while continuously monitoring vital signs.

EIT-derived ventilation and perfusion images will be acquired at baseline, 30 minutes after nitroglycerin, and 30 minutes after nicardipine.

The primary endpoint is the change in the regional ventilation-perfusion matching index (V/Q-MI). Secondary endpoints include changes in oxygenation, arterial blood gases, and hemodynamic parameters.

All data will be statistically analyzed using paired comparisons and multivariate regression to assess drug-specific effects on pulmonary gas exchange.

Inclusion Criteria Diagnosis of acute respiratory failure with PaO₂/FiO₂ ≤ 300 mmHg, requiring invasive mechanical ventilation.

Requires intravenous antihypertensive infusion (such as nicardipine or nitroglycerin) to maintain controlled and stable blood pressure during ICU treatment.

Written informed consent obtained from the patient or the legally authorized representative.

Exclusion Criteria:

Body mass index (BMI) ≥ 50 kg/m² or presence of massive subcutaneous edema interfering with EIT signal acquisition.

Implanted cardiac pacemaker, defibrillator, or any metallic thoracic device that may distort impedance measurements.

Hemodynamic instability or severe hypotension occurring during drug titration. Pregnancy or lactation. Known hypersensitivity or contraindication to nicardipine or nitroglycerin. Use of phosphodiesterase-5 inhibitors, such as sildenafil, tadalafil, or vardenafil, within the clinically relevant washout period.

Severe anemia, markedly increased intracranial pressure, or other clinical conditions in which nitroglycerin administration is considered inappropriate by the treating physician.

Incomplete clinical documentation preventing accurate evaluation of primary endpoints.