Invasive Hemodynamic Monitoring of Aortic and Pulmonary Artery Hemodynamics in a Large Animal Model of ARDS

This method can help answer key questions in the field of intensive care medicine about hemodynamic monitoring, right-ventricular dysfunction, and ARDS. The main advantages of this technique are that it is simple and easy to reproduce. The implications of this technique extend toward patient volume status assessment in the critical field of ARDS.

Though this method can provide insight into disease pathogenesis, monitoring and volume status in ARDS, it can also be applied to heart failure, sepsis, or respiratory failure. Generally, individuals new to this method will struggle since the success of this procedure requires skilled anesthesia, cardiac surgery, and intensive care medicine implementation. Visual demonstration of this method is critical.

The bleeding that occurs during open heart surgery can impair your vision as you are learning the steps of the procedure. Using an ultrasound and Seldinger’s technique, place a needle into the left femoral artery of an anesthetized pig. Then, place an eight French introducer sheath, with a combined dilator onto the wire, taking care that the end of the wire is observed at the end of the catheter.

After verifying correct placement of the wire, remove the needle, and place the catheter into the vessel, using gentle pressure. Place five French thermistor-tipped arterial catheter into the right femoral artery, and a central venous catheter, and an eight French introducer sheath into the jugular vein as just demonstrated. Next, insert a seven French pulmonary artery catheter into an eight French introducer sheath, and place the pulmonary artery catheter into the right ventricle.

Then insert the first Millar tip catheter into the eight French introducer sheath in the left femoral artery, and place the sheath into the aorta. Using electrocautery, make a five to 10 centimeter incision from above the symphysis down to the linea alba, and use scissors to open the linea alba. Gently exteriorize the bladder, and use a 3-0 suture to place a purse string suture in the bladder.

Use a number 11 scalpel blade to make an approximately five millimeter incision in the bladder, and insert a urinary catheter into the bladder. Then inflate the catheter balloon with water, and use a purse string suture to secure the balloon, closing the abdomen with a second 3-0 suture. To prepare the heart, increase the inspiratory oxygen rate to one, and administer eight milligrams of pancuronium intravenously.

Using electrocautery, make a medial incision down the sternum, and gently dissect the sternum from the surrounding tissue. Divide the bone with an oscillating saw, and use electrocautery to reduce the bleeding. Seal the sternum with bone wax, and use a sternal rib spreader to open the chest as much as necessary for the surgery.

Using scissors and forceps, gently open the pericardium, and fix the tissue to the skin with a 2-0 suture. Gently dissect down the pulmonary artery and ascending aorta, and carefully place ultrasound flow probes around both arteries. Using a 5-0 suture, place two purse string sutures in the pulmonary artery, and use a number 11 scalpel blade to make an approximately one millimeter stitch incision between the purse strings.

Place the Millar catheter into the pulmonary artery before fixing the catheter with the sutures, and carefully clamp the left atrial appendage. Use a 4-0 suture to place two purse string sutures in the atrium, followed by a small incision. Place a central venous line into the left atrium, before fixing the line with the purse string sutures.

And suture a sterile glove over the pericardial opening. Then perform a sternal closure with wires, and close the skin with a 3-0 suture, according to standard procedures. To measure the hemodynamic parameters, use the data analysis software to obtain two minutes of aortic and pulmonary arterial flow measurements, as well as aortic and pulmonary artery pressure measurements.

To perform transcardiopulminary thermodilution, click TD start in the pulse contour cardiac output system two. Then inject 15 milliliters of 10 degree Celsius saline into a thermistor at the central venous line in the jugular vein three times for thermodilution at each measurement step, and obtain an arterial, central venous, and mixed venous blood gas sample after each transcardiopulminary thermodilution measurement step. After obtaining a baseline measurement for each parameter, connect an infusion pump to the central venous line to deliver five milligrams per kilogram of colloidal infusion.

After five minutes of equilibration, start another measurement step, and continue with the volume loading and equilibration steps until a balanced fluid status is reached. To induce acute respiratory distress syndrome with consecutive right-ventricular dysfunction, first increase the inspiratory oxygen rate to between 5 to 8, as necessary, to maintain a peripheral capillary oxygen saturation of at least 90%Next, infuse oleic acid into the superior vena cava using a profuser to deliver continuous adrenaline to keep the hemodynamics stable, and delivering calcium, magnesium, and antiarrythmics as necessary to maintain a stable sinus rhythm. When mild to moderate acute respiratory distress has been achieved, measure all of the same hemodynamic parameters as just demonstrated.

Oleic acid infusion, as just demonstrated, induces mild to moderate acute respiratory distress, as evidenced by a robust oxygenation index decrease that is accompanied by a statistically significant increase in carboxylated blood. To measure the pulmonary vascular resistance to monitor pulmonary hypertension, a catheter can be placed in the left atrial, as a pulmonary artery catheter placed in the pulmonary artery through the pulmonary flow probe can result in incorrect flow measurements. Once mastered, this technique can be completed in five hours, if it’s performed properly.

While attempting this procedure, it’s important to take up to two hours of time to administer the oleic acid, as a too quick delivery has severe negative effects on hemodynamics. After its development, this technique paved the way for researchers in the field of ARDS and consecutive right-ventricular dysfunction to explore the appropriate volume-load, and find a better treatment in these high morbidity and mortality diseases. Don’t forget that working with living animals, such as pigs, requires ethical approval, and should only be done if absolutely necessary for the understanding of the treatment of a disease.