A human cadaveric model for venous air embolism detection tool development

Abstract

Purpose: A human cadaveric model combining standard lung protective mechanical ventilation and modified cardiac bypass techniques was developed to allow investigation into automated modes of detection of venous air emboli (VAE) prior to in vivo human or animal investigations.

Methods: In this study, in order to create an artificial cardiopulmonary circuit in a cadaver that could mimic VAE physiology, the direction of flow was reversed from conventional cardiac bypass. Normal saline was circulated in isolation through the heart and lungs as opposed to the peripheral organs by placing the venous cannula into the aorta and the arterial cannula into the inferior vena cava with selective ligation of other vessels.

Results: Mechanical ventilation and this reversed cardiac bypass scheme allowed preliminary detection of VAE independently but not in concert in our current simulation scheme due to pulmonary edema in the cadaver. A limited dissection approach was used initially followed by a radical exposure of the great vessels, and both proved feasible in terms of air signal detection. We used electrical impendence as a preliminary tool to validate detection in this cadaveric model however we theorize that it would work for echocardiographic, intravenous ultrasound or other novel modalities as well.

Conclusion: A cadaveric model allows monitoring technology development with reduced use of animal and conventional human testing.

Fig 1. Schematic diagram of reversed cardiac bypass cadaveric cardiopulmonary perfusion technique.

An arterial cannula is inserted into the vena cava to allow blood flow to the heart and lungs preferentially, followed by drainage into a venous cannula in the distal ascending aorta.

Fig 2. First approach with distal reverse cannulation.

Initial exposure with reverse (heart-excluding) bypass cannulation of the abdominal aorta and IVC, using a double purse string technique with 3-0 Prolene at the level of the iliac bifurcation. The inferior mesenteric artery and vein were noted at this point and ligated. The arterial cannulae was placed in the aorta, and venous cannulae was placed in the IVC to simulate cardiac and pulmonary flows at the exclusion of the systemic circulation, which is reversed from what is normally done in bypass.

Fig 3. Second approach with evisceration of the abdomen.

A right and left medial visceral rotation were performed and the entire colon was mobilized. The venous cannula was advanced into the thoracic aorta and numerous branches and tributaries of the aorta and IVC were ligated to reduce systemic flow.

Fig 4

A-D Third approach with midline sternotomy. The receiving catheter was moved into distal ascending aorta and impedance measurements were performed using multiple thoracic positions including the right atrium, diaphragm and esophagus.

Fig 5. Bipolar impedance recordings measured between right ventricular to esophagus measured at a frequency of 50 kHz with samples recorded 100 times per second.

The steps at approximately 7 and 13 seconds correlated with injection of 30 mL of air (red triangles) into a central venous line during reversed cardiac bypass circulation with central catheter placement via thoracotomy. Recordings were performed using the Analog Discovery 2 digital oscilloscope (Diligent Corp., Pullman, Washington, USA) and proprietary scripting software.