Acute Respiratory Failure (ARF), Aortic Dissection (Subset), Hypertension, Pulmonary Perfusion Imbalance
Conditions
Keywords
Electrical Impedance Tomography, Ventilation-Perfusion Ratio, Nicardipine, Acute Respiratory Failure, Intensive Care Unit, Nitroglycerin
Brief summary
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.
Detailed description
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.
Interventions
DRUGNitroglycerin
Continuous intravenous infusion of nitroglycerin for blood pressure reduction in acute respiratory failure. The drug is administered at an initial rate of 5 µg/min, titrated up to 100 µg/min as needed to maintain target mean arterial pressure (MAP 65-85 mmHg). Each infusion period lasts 30 minutes under stable mechanical ventilation. Hemodynamic parameters, arterial blood gases, and electrical impedance tomography (EIT) data are recorded at Baseline, 30 min, and 60 min. A washout phase is observed before crossover to the second intervention.
DRUGNicardipine
Continuous intravenous infusion of nicardipine for blood pressure control during mechanical ventilation. The infusion begins at 1 mg/h and is titrated up to 5 mg/h according to real-time blood pressure monitoring to maintain target MAP 65-85 mmHg. Each infusion period lasts 30 minutes. Electrical impedance tomography (EIT) is used to record ventilation-perfusion matching, dead-space, and shunt fraction at Baseline, 30 min, and 60 min. After completion, a 30-minute washout period or until baseline hemodynamics are restored precedes the next crossover phase.
Sponsors
First Affiliated Hospital of Wannan Medical College
Study design
Allocation
NA
Intervention model
SINGLE_GROUP
Primary purpose
BASIC_SCIENCE
Masking
NONE
Intervention model description
This study uses a prospective single-center crossover design. Each participant serves as his or her own control and receives two sequential antihypertensive interventions, nitroglycerin and nicardipine, in different study phases under stable mechanical ventilation settings. The order of drug administration is alternated between participants according to a computer-generated assignment list to minimize sequence effect. A 30-minute washout period or until hemodynamic parameters return to baseline is maintained between the two infusion periods. Continuous monitoring with electrical impedance tomography (EIT) allows within-subject comparison of ventilation-perfusion matching, dead space, and shunt fraction at defined time points (Baseline, 30 min, 60 min). This crossover model permits reduction of inter-individual variability and optimizes statistical power with a limited sample size.
Eligibility
Sex/Gender
ALL
Age
18 Years to No maximum
Healthy volunteers
No
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.
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Change in Ventilation-Perfusion Matching Index | Baseline (prior to infusion), 30 minutes after infusion initiation, 60 minutes after infusion initiation. | The ventilation-perfusion matching index quantifies the correlation between regional ventilation and perfusion signals derived from EIT imaging. The index ranges from 0 to 1; higher values indicate better matching. |
| Change in Physiological Dead Space Fraction (Vd/Vt) | Baseline, 30 minutes, and 60 minutes. | Physiological dead space is calculated as (PaCO₂ - PeCO₂)/PaCO₂, supplemented by EIT-based regional ventilation analysis. The expected range is 0 to 0.8; higher values indicate greater alveolar wastage and poorer gas exchange. |
| Change in Intrapulmonary Shunt Fraction (%) | Baseline, 30 minutes, and 60 minutes. | The shunt fraction represents the percentage of non-oxygenated blood flowing through the lungs without gas exchange. It is computed as Qs/Qt = (CCO₂ - CaO₂) / (CCO₂ - CvO₂), approximated by EIT regional perfusion measurement. Typical range 0-40 %; higher values indicate worse oxygenation efficiency. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Change in Pulmonary Perfusion Distribution | Baseline, 30 minutes, and 60 minutes. | Regional perfusion ratio analyzed via EIT contrast impedance variation after saline bolus indicator; expressed as percentage of dependent to non-dependent lung regions. Higher ratios reflect more homogeneous perfusion. |
| Change in Pulmonary Ventilation Distribution | Baseline, 30 minutes, and 60 minutes. | Regional ventilation heterogeneity index calculated from EIT ventilation waves; value ranges 0-1, where higher values represent less homogeneous ventilation. |
| Change in Oxygenation Index (PaO₂/FiO₂ Ratio) | Baseline, 30 minutes, and 60 minutes. | Ratio of arterial oxygen partial pressure to fraction of inspired oxygen, unit mmHg; range ≤ 300 mmHg inclusion criterion; higher values indicate better oxygen exchange. |
Countries
China
Contacts
CONTACTqiancheng xu, PhD
Outcome results
None listed