Cardiac output affects the response to pulsed inhaled nitric oxide in mechanically ventilated anesthetized ponies determined by CT angiography of the lung.

This study investigates how the delivery of pulsed inhaled nitric oxide (PiNO) during hypotension and normotension affects lung perfusion in anesthetized ponies, by using computed tomography (CT) angiography. The researchers found that administering PiNO to ponies under these conditions promoted beneficial redistribution of blood flow in the lungs, improving the exchange of gases.

Equipment and Procedure

• In this experimental study, CT angiography was used to assess changes in regional lung perfusion. This is the flow of blood to the lung tissues.
• The subjects of the study were mechanically ventilated, anesthetized ponies. These ponies were placed under anesthesia on two different occasions and then given PiNO for a duration of 60 minutes.
• Pulmonary arterial, right atrial, and facial arterial catheters were also inserted in these ponies to aid in their monitoring.

Anesthesia Conditions and Imaging

• The first anesthesia condition (Anesthetic 1) involved a state of hypotension, where the mean arterial pressure was less than 70 mmHg. Dobutamine, a medication that improves heart contractility, was used to treat this hypotension after 30 minutes of PiNO administration. Subsequently, the lungs were imaged at intervals of 30, 60 and 105 minutes.
• In the second anesthesia condition (Anesthetic 2), the state of hypotension was maintained throughout the procedure. The lung imaging in this condition was performed at 30, 60, and 90 minutes respectively.
• At all time points, arterial and mixed venous blood samples were collected for analysis, and cardiac output was measured.

Results

• The study found that the perfusion to well-ventilated lung areas increased when the ponies were in a normotensive state during the PiNO administration. This led to improved arterial oxygen levels, reduced alveolar dead space (regions of the lungs where gas exchange is inefficient), and a decrease in the difference between alveolar and arterial oxygen tensions.
• However, when the administration of PiNO was stopped and dobutamine continued, there was an increase in alveolar dead space and in venous admixture (mixture of oxygenated and deoxygenated blood). This contrasted with the condition where both PiNO and dobutamine were stopped together.

Conclusions

• The study concluded that administering PiNO, when combined with low cardiac output and concurrent hypotension, needs to be adequately supported in mechanically ventilated, anesthetized ponies. This is essential to attain favorable redistribution of pulmonary perfusion for improved lung gas exchange.