Development of Competency in Needle-Guided Procedures Through the Use of Soft-Embalmed Cadavers

Abstract

This study evaluated soft-embalmed human cadavers for ultrasound needle-guidance training. Second-year medical students used peripherally inserted central catheter (PICC) line and central line models and a Thiel-embalmed cadaver for training and provided feedback. Most (85%) agreed the cadaver was useful. There were positive correlations between performing the PICC line (r=0.44, P=.11) and central line (r=0.63, P=.03) procedures on a cadaver and in a clinical setting. Thiel-embalmed cadavers may provide important hands-on training.

Introduction

Ultrasound needle-guided procedures are commonly used across a variety of medical specialties,^1–3 so medical students and residents are taught to master these procedures throughout their medical training.^{4, 5} However, since it is unacceptable for students to practice clinical skills on patients,⁶ medical educators are constantly searching for new methods to teach procedural skills.^{7, 8}

Since training for technical procedures is often disorganized and unstructured, there is an ongoing effort to find the best methods to learn invasive procedures with ultrasonography using simulators.^{5, 9, 10} Simulators for learning needle-guided procedures include engineered models (phantoms), cadavers, animal models, computer-based methods, and virtual reality models.¹¹ However, there is a lack of evidence regarding the applicability, rationality, and reliability of most of these tools for learning needle-guided procedures. Phantoms have low background echogenicity, which enhances the needle visibility but can lead to false confidence with regard to clinical ability.¹¹ On the other hand, meat phantoms have excellent feasibility, are cheap, can be constructed with minimal preparation, and can be disposed of easily.^{12, 13} Animal models can also be useful simulators, but they lack the physical reality of an actual human patient and have a limited lifespan (1–2 days).¹³ Computer-based training imparts knowledge, but it is insufficient to improve procedural skills.¹⁴ The quality of modern synthetic models is very high and they provide a realistic experience with needle penetration, but these models are expensive and require additional training by the faculty.⁴

Cadavers can be used for learning ultrasound anatomy and practicing skills, such as hand-eye coordination, probe handling on an irregular surface (e.g., the supraclavicular region), and needle-probe alignment.¹⁵ For medical education purposes, cadavers are traditionally embalmed with formalin for long-term preservation.¹⁶ However, formalin causes the cadaver’s tissues to have a rigid feel¹⁷ and can negatively affect the color. Moreover, the formaldehyde in formalin is linked to several health hazards,¹⁸ such as headache, skin irritation, and mucous membrane irritation.¹⁹ Formaldehyde is also classified as a carcinogenic substance and can cause long-term health consequences for students and faculty.²⁰ Reducing the hazards associated with formalin-embalmed cadavers involves improving laboratory air flow, decreasing formaldehyde content, or using alternative embalming solutions.²¹ Embalming solutions with low formaldehyde content are low cost and preserve the lifelike quality of tissue. However, this type of embalming only lasts for several weeks.²² Because of the time constraint, this type of embalming is not suitable for most medical schools where anatomy courses run for several months. Neutralizing formaldehyde is another cost-effective way to reduce formaldehyde content while providing long-term preservation of cadavers.²¹ Adding monoethanolamine after the embalming process is one way to reduce formaldehyde, but it extends the required time for embalmment²³ and leaves a white film on the cadaver’s tissues.

Soft-embalmed human cadavers are increasingly being used as a model to train surgeons and anesthesiologists because they look and feel like real patients. A recent soft-embalming solution was developed by Walter Thiel in 1992.²⁴ This method uses a mixture of 4-chloro-3-methylphenol and various salts for fixation, boric acid for disinfection, and ethylene glycol for preservation of tissue pliability.²⁵ Thiel embalming solutions are less carcinogenic (8.9% formaldehyde) than formalin embalming (37%–40% formaldehyde), but Thiel cadavers are much more expensive.²⁶ A Thiel cadaver can cost 10–20 times more than a formalin cadaver.²⁷ Despite the high cost, Thiel-embalmed cadavers are described as exceptionally lifelike with representation of structures almost corresponding to a real patient.²⁸ They also produce more realistic ultrasonography images and fascial “pop” sensations than fresh (recently deceased) cadavers.^{28, 29} A Thiel-embalmed cadaver has well-preserved organs and tissues with natural color, consistency, and flexibility.²⁵ Moreover, vessel diameters are well preserved.³⁰ The retained structure and consistency of tissues leads to clearer ultrasound images than those obtained from formalin cadavers.³¹ Because they are exceptionally lifelike, Thiel-embalmed cadavers have been reported to have a positive impact on dissection and skills training.³² Because Thiel embalming is a relatively new method, research investigating learning and skills training with these cadavers is limited.²⁷

Although many medical schools and residency programs include ultrasound in their curricula,^33–36 there is limited evidence on the comparative efficiency of different training modalities for teaching and learning invasive procedures with ultrasonography in medical education. Therefore, the purpose of the current study was to evaluate student perception and potential benefits of using soft-embalmed human cadavers for ultrasound needle-guidance training.

Materials and Methods

In the current study, we recruited second-year medical students (N=13) to voluntarily participate in ultrasound needle-guidance training sessions that used a peripherally inserted central catheter (PICC) model (Figure 1A), a central line model (Figure 1B), and a Thiel-embalmed cadaver (Figure 1C). Student participants used PICC line and central line models for mastering procedures with ultrasound needle-guidance before they practiced the same procedure on the Thiel-embalmed cadaver. The local institutional review board granted exempt status for the current study.

Figure 1.

Ultrasound Training Models Used for the Needle-Guided Training Procedures of the Current Study

A: PICCLineMan Training Model (Simulab Corporation). B: Gen II Ultrasound Central Line Training Model (CAE Healthcare). C: Thiel-embalmed cadaver. D: Ultrasound image showing a needle in the basilic vein using the PICCLineMan Training Model. E: Ultrasound image showing a needle in the internal jugular vein using the Gen II Ultrasound Central Line Training Model. F: Ultrasound image showing a needle in the internal jugular vein using the Thiel-embalmed cadaver.

The PICC line training used the PICCLineMan Model (Simulab Corporation), which contains the basilic, brachial, and cephalic veins; median nerve; brachial artery; and the humerus (Figure 1A and 1D). Palpable landmarks included the antecubital fossa, clavicle, sternum, 1st–4th intercostal spaces, acromion, ribs 1–7, and the humeral head.

The Gen II Ultrasound Central Line Training Model (CAE Healthcare), which contains the internal jugular vein and common carotid artery, was used for the central line training (Figure 1B and 1E). Pulsatility of the artery can be simulated with a manual hand pump or an automated pump and can be demonstrated using color Doppler ultrasound. The model allows for full thread guide wires, dilators, and catheters without resistance.

The Thiel-embalmed cadaver was used for both PICC line and central line training. The target vessels included the basilic and internal jugular veins (Figure 1F). Because these vessels were empty and collapsed, they were filled with ultrasound gel at the procedure sites for better visualization.

For the PICC line procedure with the cadaver, a longitudinal, superficial 3-cm cut was made along the medial aspect of the biceps brachii about 5–7 cm superior to the antecubital fossa to expose the basilic vein. Right angle forceps were used to pass a string deep to the vein. The basilic vein was then tied off at its most inferior point of exposure. A PICC line catheter was cut to 3 cm in length and inserted into the exposed basilic vein. The catheter was then sutured to the skin. Ultrasound gel was heated for 10 seconds in a microwave to decrease its viscosity. The gel was loaded into a syringe that was connected to the catheter and was inserted into the basilic vein. As the ultrasound gel was injected into the vein through the catheter, ultrasound was used to monitor the filling of the basilic vein 7–10 cm superior to the exposed vein. Once the vein was inflated, the injection was stopped. On average, it took 15–20 mL of gel to inflate the vessel.

For the central line procedure with the cadaver, a 3-cm longitudinal cut was made directly anterior to the mastoid process. The tissues were dissected and retracted to visualize the internal jugular vein and carotid arteries. At the most superior point of exposure, right angle forceps were used to pass a string deep to the internal jugular vein. The string was then used to tie off the vein so that the ultrasound gel could not pass superiorly. A central line catheter was cut to 3 cm in length and inserted into the exposed internal jugular vein. The catheter was then sutured in place to the skin. Ultrasound gel was again heated in a microwave for 10 seconds to decrease its viscosity. The gel was then loaded into a syringe and connected to the catheter so the gel could be injected into the internal jugular vein. Once the vein was inflated, the injection was stopped. On average, it took 20–30 mL of gel to inflate the vessel.

Before participating in the needle-guided procedures laboratory, medical students had mastered basic ultrasonography techniques and applications during their clinical ultrasound coursework.³⁴ Before each training session of the current study, a review of the basic indications, contraindications, and techniques to perform the ultrasound-guided procedures was provided. The learning objectives, management of procedures, possible complications, and clinical relevance of the exercise were also outlined. The introduction was followed by a quick demonstration that allowed students to gain familiarity with the models, Thiel-embalmed cadaver, and equipment used during the training session. Students performed the PICC line and central line procedures with the phantoms and cadaver using sterile techniques and equipment. Students used real-time ultrasonography to scan the models and cadaver, identify target structures, and perform the procedure.

After the needle-guided procedures training laboratory, students were asked to complete a 14-question paper survey about their perceptions of the importance of the models and Thiel-embalmed cadaver for education and future practice. The survey was created specifically for the current study; it was voluntary and anonymous and did not collect demographic information. Twelve items were Likert-scale questions (strongly disagree, disagree, neither agree nor disagree, agree, and strongly agree) and evaluated student agreement or disagreement with statements about understanding of the procedures, their comfort level with performing the ultrasound needle-guided procedures after using the models and cadaver, and their capability of performing the procedures in a clinical setting (Table). The survey also asked about challenges in interpreting the ultrasound images on the different training models and the benefits of using models and cadavers for development of their clinical skills. The last two survey items were open-ended questions that asked the following: What is one thing that you found useful about the cadaver training model? and Is there another procedure that you would like to practice using the cadaver model?

Table 1.

Likert-Scale Survey Question Responses of Second-Year Medical Students (N=13) Participating in a Voluntary Ultrasound Needle-Guided Training

Survey Item	Likert Responses, No. (%)			Mean (SD)
	Disagree*	Neither Agree Nor Disagree	Agree**
Practicing vascular access on a cadaver has improved my understanding of the PICC line procedure	0	0	13 (100)	4.9 (0.3)
Practicing vascular access on a cadaver has improved my understanding of the central line procedure	0	0	13 (100)	5.0 (0)
I feel capable of performing the PICC line procedure on a cadaver	0	1 (8)	12 (92)	4.5 (0.7)
I feel capable of performing the PICC line procedure in a clinical setting	0	(31)	9 (69)	4.0 (0.8)
I feel capable of performing the central line procedure on a cadaver	0	1 (8)	12 (92)	4.6 (0.7)
I feel capable of performing the central line procedure in a clinical setting	1 (8)	1 (8)	11 (85)	3.9 (0.8)
I find it challenging to interpret an ultrasound image on the PICC line model	13 (100)	0	0	1.0 (0)
I find it challenging to interpret an ultrasound image on the central line model	13 (100)	0	0	1.0 (0)
I find it challenging to interpret an ultrasound image of upper limb veins on a cadaver	7 (54)	1 (8)	5 (38)	2.0 (1.2)
I find it challenging to interpret an ultrasound image of upper limb veins on a real person	10 (77)	0	3 (23)	2.5 (1.5)
The use of a cadaver for guided injections was beneficial for the development of my clinical skills	0	1 (8)	12 (92)	4.7 (0.6)
A cadaver is a useful tool to learn and practice skills associated with vein cannulation	0	2 (15)	11 (85)	4.7 (0.8)

^*Includes disagree and strongly disagree responses.

^**Includes agree and strongly agree responses.

Abbreviation: PICC, peripherally inserted central catheter.

Frequency and percentage were reported for survey responses; agree and strongly agree responses and disagree and strongly disagree responses were grouped under a single agree or disagree category. Wilcoxon signed rank tests were used to test whether the level of agreement differed from “neither agree nor disagree” for each question. Pearson correlation coefficients were used to assess the linear relationships between feeling capable of performing on a cadaver and in a clinical setting for both the PICC line and central line procedures. Wilcoxon signed rank tests were used to test for differences in the perception of difficulty of image interpretation among models, a cadaver, and a real person. SAS version 9.4 software (SAS Institute, Inc) was used to conduct the analyses. A P<.05 was considered statistically significant.

Results

All students (100%, 13/13) agreed that practicing vascular access on a cadaver improved their understanding of both the PICC line and central line procedures (Table and Figure 2). The majority of students (92%, 12/13) felt capable of performing the PICC line and central line procedures on a cadaver after completing the training, but only 69% (9/13) felt capable of performing the PICC line procedure in a clinical setting and 85% (11/13) of performing the central line procedure in a clinical setting. All students (100%, 13/13) disagreed that it was challenging to interpret ultrasound images on either of the commercial models, but only 54% (7/13) disagreed that it was challenging to identify structures on the cadaver using ultrasonography. The majority of participants (85%, 11/13) agreed that the Thiel-embalmed cadaver was a useful tool to learn and practice vein cannulation.

Figure 2.

Survey Responses of Second-Year Medical Students Participating in a Voluntary Ultrasound Needle-Guided Training Session

Abbreviation: PICC, peripherally inserted central catheter.

There was high positive, but not significant, correlation between feeling capable of performing the PICC line on a cadaver and performing the procedure in a clinical setting (r=0.44, P=.11). There was a strong positive correlation between feeling capable of performing the central line procedure on a cadaver and in a clinical setting (r=0.63, P=.03). Students felt it was easier to perform the procedure and interpret the image on PICC and central line models than on the cadaver and a real person (all P<.001). Students felt it was equally challenging to identify veins on a cadaver and a real person (P =.27). There was no variation in how each student perceived the difficulty of the PICC line and the central line procedures; all indicated strongly disagree.

For the open-ended question regarding what was most useful about the cadaver training model, 11 of the 13 written responses mentioned the difference between real anatomy and the models, which were considered “too ideal.” For the question about what other procedures students would like to practice using the cadaver model, students mentioned chest tubes (n=3), arterial access (n=2), lumbar puncture (n=2), thoracentesis (n=1), and joint injections (n=1).

Discussion

Using modern tools to incorporate procedural skills training and ultrasound simulation into preclinical medical education may improve clinical practice and decision-making by increasing confidence and competence with ultrasound needle-guided procedures.^{37, 38} The goal of the procedural training in the current study was to evaluate student perception and potential benefits of using soft-embalmed human cadavers for ultrasound needle-guided training. We hypothesized that a Thiel-embalmed cadaver could be used as a clinical training tool and that it would yield effective learning and adequate clinical performance of needle-guided procedures for future physicians. Our results suggested that the majority of participating second-year medical students felt the Thiel-embalmed cadaver contributed to better understanding of clinical procedures and increased their capability of performing those procedures in a real clinical setting. Students commented that the Thiel-embalmed cadaver “gives more of a real feel compared to models,” “gives feel for human tissue,” and provides a “real life experience.”

Even though there was no difference in how students perceived the difficulty of the PICC line and central line procedures, results indicated a difference in their perceived capability of performing these procedures in a clinical setting. We did not expect students to feel more capable of performing the central line procedure in a clinical setting since it is a more challenging and invasive procedure than the PICC line procedure.³⁹ This result was likely caused by differences in the procedures: the PICC line procedure involves smaller vessels and requires more practice for ultrasound guidance using models, while the central line is associated with more complications in real clinical encounters.

Our results also suggested that students became competent in ultrasound imaging interpretation and procedural skills after completing the training session. The majority of students could interpret ultrasound images identifying vascular structures without difficulty after the training. The ability to interpret ultrasound images while performing the PICC line and central line procedures is an important aspect of medical training, and it can have an impact on physician competence and patient safety. In a review of the role of medical simulation, physicians trained with simulation-based techniques outperformed and were more competent than traditionally trained physicians for a specific procedure.⁴⁰ Further, using simulation-based education increased patient safety.⁴⁰ Thus, models are important for early medical training because they build student confidence with invasive procedures and increase comfort level when performing needle guidance before practicing on a cadaver. Students in the current study felt it was easier to perform the procedures and interpret the images on the models than the cadaver, which suggests cadavers are more realistic and better prepare the students for future clinical practice. Our results also showed a strong positive correlation between students feeling capable of performing the PICC line and central line procedures on the cadaver and in a clinical setting, which suggested the training that included the Thiel-embalmed cadaver increased their confidence in performing these procedures in real life.

The training exercise of the current study allowed medical students to use actual PICC line and central line equipment on the models and Thiel-embalmed cadaver, which added a realistic feel to the procedural exercise and contributed to the positive student perceptions. In an open-ended response, one student wrote the cadaver training model was useful for “looking at the vasculature on an actual body and being able to thread instruments through,” which supports the uniqueness of this training experience. The training format also included ultrasonography of a real person’s vasculature to better understand the anatomy for ultrasound needle guidance. As a result, students felt it was equally challenging to identify veins on a cadaver and a real person, which supports our hypothesis that a Thiel-embalmed cadaver can be used as a clinical training tool to yield effective learning and adequate clinical performance of needle-guided procedures.

Procedural training, such as that provided to students in the current study, is one of the key requirements for producing competent physicians. To assess the acquisition of a procedural clinical skill, ultrasound milestones can be used. These milestones are competency-based developmental outcomes that mark a progression toward independent practice,³⁷ and medical students should complete them before graduation.⁴¹ Generally, a milestone outcome, such as a procedural skill, can only be developed with repeated practice.⁴¹ Therefore, increasing student comfort with needle-guided procedures is an important milestone since ultrasound-guided techniques for central venous cannulation may reduce the risk of misplacement and complications.⁴²

The main limitation of the current study was its small size; only 13 students from one institution participated. We deliberately kept the number of students small because we were unsure of how many needle sticks were possible in the Thiel-embalmed cadaver before the puncture site would degrade. Future studies should include multiple cadavers and recruit a larger group of students or residents. Another limitation was that training involved only two procedures, the PICC line and central line. In future studies, we are planning on using soft-embalmed cadavers for thoracentesis, paracentesis, and lumbar puncture procedures.

Conclusion

In the current study, the ultrasound models and Thiel-embalmed cadaver provided students with a unique training opportunity, and the majority agreed the training helped them improve their practical skills associated with vein cannulation using ultrasound imaging. These results suggest a Thiel-embalmed cadaver can be used as a clinical training tool for learning needle-guided procedures. Therefore, new cadaver-based ultrasound training exercises during preclinical medical education should be developed and used to enhance student understanding and learning of invasive procedures and to facilitate higher confidence in the clinical setting.