\t\t \t\t \t\t \t\t\u00a0 \t\t \t\t \t\t \t <\/p>\n
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Phantoms <\/p>\n
It\u0092s pretty easy (and messy).<\/p>\n
First, pre-heat your oven to 350 degrees.<\/p>\n
Just kidding.<\/p>\n
Just heat some water and make a 10% solution of gelatin.<\/p>\n
You don\u0092t want to heat the water too much or you will burn the gelatin when you add it.<\/p>\n
Regular gelatin you make at home is less than 1% gelatin, you just need to concentrate it more.<\/p>\n
10% means 100 mg per cc of liquid.<\/p>\n
For example, if you boil 1 liter of water, you need 100 gm of gelatin.<\/p>\n
Just do the math for whatever amount you need.<\/p>\n
You will need an electric mixer because this stuff is hard to dissolve, remember you are making a super-saturated solution (I bet you haven\u0092t heard that word since the biochemistry days).<\/p>\n
Don\u0092t freeze it after you are done or it will crack, just put it in the refrigerator.<\/p>\n
It will last forever in the fridge, unless it contaminates. <\/p>\n
Just make sure the container is airtight so no evaporation occurs.<\/p>\n
I\u0092ve left the gelatin blocks out of the fridge (I actually put them in the closet), for about 5 days and they didn\u0092t melt and nothing grew on them.<\/p>\n
Gelatin is also used to make glue, so whatever container you use, make sure you clean it off right away or you will be scrubbing for a long time.<\/p>\n
The good news is that once you make the gelatin blocks, if they break you can just re-melt them and use them again, no need to mix or anything.<\/p>\n
Have fun, let me know how it goes.<\/p>\n
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Manny \t<\/p>\n
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\tUltrasound-guided central venous access: a homemade phantom for simulation<\/strong> \t<\/p>\n John L. Kendall, MD, FACEP; Jeffrey P. Faragher, MD<\/p>\n Department of Emergency Medicine, Denver Health Medical Centre, Denver, \tColo.<\/p>\n Can J Emerg Med<\/em> 2007;9(5):371-3<\/p>\n Various medical specialty organizations and the Agency for Healthcare \tResearch and Quality (AHRQ)1 \thave advocated using ultrasonography to guide central venous cannulation. It \tis surprising then, that very few instructional models have been described \tto teach this technique. Consequently, we developed a model to teach \tultrasound-guided central venous access. This paper presents a recipe for an \tultrasonographic model or “phantom” that is easily made, inexpensive and \tsimulates vessel cannulation extremely well.<\/p>\n The phantom is formed using water, unflavored gelatin, sugar-free \tMetamucil, latex tubes and a rectangular Pyrex glass cake pan (17 \u00d7 27 \u00d7 5 \tcm). Preparation of the container includes cleaning the inner surface and \tspraying it with a small amount of a non-stick product.<\/p>\n To make the phantom mixture, first determine the volume of water needed \tto fill the desired container one-third full. Boil the water and then \tgradually whisk in 3 packets of gelatin for every 250 mL of water. Continue \tto whisk or stir the mixture until the gelatin is completely dissolved. \tNext, add the Metamucil in portions of 1 tablespoon for every 250 mL of \twater. Whisk until it is completely dissolved. Any remaining clumps of \tgelatin and Metamucil should be removed at this time. Lastly, pour this \tmixture into the container and put it in the refrigerator for 1-2 hours or \tuntil it is firm. This concoction now forms the base layer of the mould.<\/p>\n While the base layer of the mould is congealing, select the latex tubes \t(Penrose drains) that will be used to simulate the vessels. One-half inch \tdiameter tubes work well to simulate the neck and femoral vessels and \tone-quarter inch diameter tubes appear like brachial vessels. Tie the latex \ttubes at one end and fill them with water, being careful to minimize the \tamount of trapped air. The volume of water in each tube determines whether \tit will be used to simulate an artery or a vein. For example, tubes that \thave less water will compress easily and therefore will appear like veins. \tAfter the desired volume of water is placed in the latex tube, tie off the \topen end.<\/p>\n After the base layer of the mould is firm, place the latex tubes on top \tof it. A second aliquot of the gelatin-Metamucil mixture (enough to fill \tone-third of the container’s volume, as described above) is poured onto the \tbase layer, with enough volume to surround and cover the latex drains. This \twill form the middle layer. Chill the mould again until firm.<\/p>\n Lastly, prepare another gelatin-Metamucil mixture and pour it on top of \tthe middle layer until the container is filled to the point that the latex \tdrains are no longer visible. Chill the mould a third time until it is firm \tand then remove it from the Pyrex container. At this point the phantom is \tready for use.<\/p>\n Unlike other indications for emergency ultrasound, where the primary goal \tof the exam is recognition of normal and abnormal structures, \tultrasound-guided central access involves unique spatial orientation and \thand-eye coordination. These characteristics make this skill difficult to \tacquire without real-time practice. Unfortunately, practical education is \tnot currently available and the standard methods for teaching the Focused \tAssessment with Sonography for Trauma (FAST) exam, such as normal or \tdialysis models, cadavers, swine or simulators, have significant \tlimitations.<\/p>\n Ultrasound phantoms were first described in the 1970s. They are generally \tof 2 types: those for simulating tissue and those for practising biopsy \tprocedures. The tissue-like phantoms are meant to produce a B-scan \tappearance similar to the parenchyma of an organ, such as the liver (a \tfinely textured echo pattern). They are used for routine testing and \tcalibration of grey-scale ultrasound scanning equipment so great effort is \ttaken to control factors like the speed of sound through the phantom and the \tcoefficients related to scattering and attenuation.2-4 \tAs such, they can be time-consuming and expensive to produce, which \ttypically precludes them from being used to simulate procedural ultrasound.4<\/p>\n In contrast to the tissue-like phantoms that mimic the acoustic \tproperties of tissue, biopsy phantoms are developed to represent the \tsonographic appearance of tissue. They are made with inexpensive materials \tthat are easy to obtain, so many homemade models have been developed. The \ttypical ingredients have 3 components: one to provide bulk, another to \tsimulate ultrasound scatter and a third to represent targets.<\/p>\n The components of the phantom described in this paper were chosen for \ttheir unique properties. Unflavored powdered gelatin was chosen as the \tbulking agent because it is commercially available, inexpensive ($3.00-$5.00 \tper phantom) and easy to suspend in water. When mixed in a concentration of \t20 g (3 packages) in 250 mL of water, it gels quickly and provides both \tfirmness and elasticity to the phantom. When refrigerated, the mould can \tlast several weeks before significant microbial degeneration occurs. One \tdownside of using gelatin is that the phantom can tear relatively easily. \tThis damage can occur when a finger, transducer, or large-bore needle \tlacerates the mould. To minimize this problem, a thin layer of gauze can be \tcoated onto the scanning surface with a small amount of gelatin, prolonging \tthe life of the phantom.5 \tAgar can also be used as a bulking agent. Although it typically has a longer \tlife span, it is more difficult to obtain and much more complicated and \ttime-consuming to create.5<\/p>\n Sugar-free Metamucil was used because it contains psyllium hydrophilic \tmucilloid fibre, which is an excellent scattering agent. When mixed with \tgelatin, it has an echo texture that simulates testicular, thyroid or \tsubcutaneous tissue, and it is opaque. Thus the needle and targets are only \tvisible sonographically, not with the naked eye. As well, after the mixture \tis initially prepared, no further mixing is required to maintain an even \tsuspension of the scattering medium. It is also easy to obtain (most \tsupermarkets carry bulk quantities) and relatively inexpensive. The \tsugar-containing variety can also be used, but 3 times the volume will be \trequired to obtain the same amount of psyllium fibre. Other materials, such \tas flour, cornstarch or calcium carbide,*can be used as scattering agents, \tbut they require intermittent stirring during cooling until the mixture \tcongeals, which can take more than an hour.4<\/p>\n Finally, one-half inch latex drains were used in this phantom to simulate \tvessels in the neck (internal jugular vein and carotid) or groin (Fig. 1). \tIf both arteries and veins are being simulated, 2 tubes can be placed \tside-by-side in the mould, with one filled more tensely than the other. \tOther sizes of latex drains can also be used. For example, one-quarter inch \tmost closely simulates the diameter of brachial vessels. While latex drains \tsimulate the sonographic appearance of vessels extremely well, the downside \tof their use is that they have a limited life span. Most can be punctured \tmultiple times with little deformity of their structure (Fig. 2), but if \tfluid is removed, they will collapse quickly. From experience, each \tsimulated vessel can be cannulated 5-10 times with little change in its \tappearance except for the delineation of each needle track as air enters it \tduring the procedure.<\/p>\n<\/p>\n Fig. 1. Comparison of the sonographic appearance of the internal jugular \tand carotid artery vessels in the neck (left) with those simulated by the \tphantom (right).<\/p>\n<\/p>\n Fig. 2. Sonographic view of the phantom vessel being cannulated in the \tlong axis plane.<\/p>\n Ultrasound-guided central venous access is a skill that emergency \tphysicians will need to add to their armamentarium. Prior educational tools \tare limited, and this paper describes a phantom that is easily made, \tinexpensive and simulates ultrasound guidance of vessel cannulation \textremely well. Further study will need to address whether it improves skill \tacquisition and subsequently, procedural success.<\/p>\n<\/span>TIPS FROM THE TRENCHES<\/span><\/h2>\n
<\/span>Introduction<\/span><\/h3>\n
<\/span>Methods<\/span><\/h3>\n
<\/span>Discussion<\/span><\/h3>\n
<\/span>Conclusion<\/span><\/h3>\n
<\/span>References<\/span><\/h3>\n
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