Models to teach lung sonopathology and ultrasound-guided thoracentesis.

Lung sonography allows rapid diagnosis of lung emergencies such as pulmonary edema, hemothorax or pneumothorax. The ability to timely diagnose an intraoperative pneumothorax is an important skill for the anesthesiologist. However, lung ultrasound exams require an interpretation of not only real images but also complex acoustic artifacts such as A-lines and B-lines. Therefore, appropriate training to gain proficiency is important. Simulated environment using ultrasound phantom models allows controlled, supervised learning. We have developed hybrid models that combine dry or wet polyurethane foams, porcine rib cages and human hand simulating a rib cage. These models simulate fairly accurately pulmonary sonopathology and allow supervised teaching of lung sonography with the immediate feedback. In-vitro models can also facilitate learning of procedural skills, improving transducer and needle positioning and movement, rapid recognition of thoracic anatomy and hand - eye coordination skills. We described a new model to teach an ultrasound guided thoracentesis. This model consists of the experimenter's hand placed on top of the water-filled container with a wet foam. Metacarpal bones of the human hand simulate a rib cage and a wet foam simulates a diseased lung immersed in the pleural fluid. Positive fluid flow offers users feedback when a simulated pleural effusion is accurately assessed.

Introduction

Lung sonography is an essential component of LCI (lung, cardiac, inferior vena cava) ultrasound exam(. Lung emergencies in the operating room such as pulmonary edema or pneumothorax are low-incidence events. Therefore, appropriate training in a simulated environment is important. We have developed models that simulate pulmonary sonopathology and allow supervised teaching of lung sonography. We also describe a new model to teach an ultrasound guided thoracentesis.

Methods

Lung is a bi-compartmental (air and tissue) organ and can be modeled by a polyurethane foam(. Pig rib cages (fig. 1) or hands of the investigators (fig. 2) were placed on polyurethane foams. Transverse sonograms of the metacarpal bones of the hand and images of intermetacarpal tissue resemble sonographic images of ribs and intercostal spaces.

Fig. 1

The hybrid simulation model of the lung (foams with the attached pig rib cages wrapped in the Ioban™ dressing). A. An intercostal sonogram of the foam. R – rib, P – pleura, a – A-line. B. The rib cage elevated above the foam (= pneumothorax)

Fig. 2

Scanning of the palmar aspect of the hand (M – metacarpal bones). A. The hand elevated above the foam (pneumothorax). The hand on the surface of wet (B and D) and almost dry foams (C and E)

Results

Fig. 1 A shows an intercostal sonogram of the foam with a single horizontal reverberation artifact (a). To simulate pneumothorax the rib cage was elevated few centimeters above the polyurethane foam. An intercostal sonogram (fig. 1B) shows multiple horizontal reverberation artifacts (a). Similar images of multiple horizontal artifacts (A-lines) were obtained during scanning of the hand elevated above the foam (fig. 2A). When the dorsum of hand was placed on the wet foam A-lines disappeared (fig. 2B ) but began to reappear during drying of the foam (figs. 2C and E). Faint vertical lines (B-lines) appeared. They were well visualized when a high resolution (15 MHz) transducer was used (fig. 2E). Sonography can rule out pneumothorax by visualizing sliding visceral and parietal pleurae. We could demonstrate this sign by sliding the dorsum of hand back and forth on the surface of a PU foam or a metal plate.

In this study we also describe a new model to teach ultrasound guided thoracentesis. This model consists of the experimenter's hand placed on top of the water-filled container with a wet foam. Metacarpal bones of the human hand simulate a rib cage and a wet foam simulates a diseased lung immersed in the pleural fluid (fig. 3).

Fig. 3

Thoracentesis model. The experimenter's hand is placed on top of the fluid-filled container with a wet foam (left panel). A sonogram (right panel) of metacarpal bones (M) of the human hand which simulate a rib cage and a wet foam underneath simulates a diseased lung (L) that is immersed in the pleural fluid (F); N – needle

Discussion

Sonographic exam of the pathological lung requires interpretation of real images and artifacts such as A-lines (beam reflections from the pleura) and B-lines (beam reflections between fluid-filled or air-filled alveoli). A-lines can be visualized in the normal lung but their number increases dramatically during pneumothorax. This quantitative difference can be confusing to the novice lung sonographer but can be easily taught in our model. The use of human hand to simulate a sonogram of a rib cage has been described before(. The authors used sliding fingers across the dorsum of hand to simulate lung sliding. In this study we have combined the use of human hand with the use of dry or wet PU foams simulating normal or fluid overloaded lungs and lung sliding sign. Both our models produced images that accurately depict sonopathology of the lung.

Several ultrasound guided procedures require, for safety reasons, initial training in animal models or phantoms. In-vitro models can facilitate learning of scanning techniques and hand-eye coordination skills. The elastomeric phantoms that are usually used for training lack tissue feedback, are expensive, rapidly deteriorate and become unusable due to needle tracks. The thoracentesis model presented in this study is simple, inexpensive and easy to assemble. Metacarpal bones of the human hand convincingly simulate a rib cage, but at a minimal extra cost can be replaced by animal ribs with intercostal muscles placed on top of the water-filled container with a wet foam simulating a diseased lung. The thoracentesis needle can then be inserted through the muscles above the rib.