Keywords navigation - percutaneous kidney puncture - kidney stone surgery - renal access - PCNL
Introduction
Percutaneous puncture of the renal pelvicalyceal system is a well-established and
widely used urological technique. The technique was first described in 1955 by
Goodwin and colleagues [1 ]. In addition to
ensuring reliable urine drainage in obstructed urinary diversion pathways, it serves
as an access route for percutaneous nephrolitholapaxy (PCNL) in cases of distinctive
nephrolithiasis. Despite widespread and frequent use, it takes a lot of time and
practice to correctly perform this technique to puncture the renal pelvicalyceal
system. Important factors that influence the successful puncture are body mass index
(BMI) [2 ], the hydronephrosis grade, patient
positioning technique, and, in case of a PCNL, the stone location and size and the
selected access route to the renal pelvicalyceal system [3 ]
[4 ]
[5 ]. One of the main factors is the
surgeon's experience, as it has been proven that a novice surgeon requires an
average of 60 punctures before being able to perform them adequately and reliably
[6 ]. The most common puncture techniques
for percutaneous renal access are the “bullseye” and “triangulation” techniques
[7 ]. Both techniques require fluoroscopy.
To simplify the procedure, puncture aids [8 ]
[9 ] as well as new supportive
systems such as CT- [10 ]
[11 ], iPad- [12 ], MRI- [13 ]
[14 ] and robot- assisted [15 ] puncture and electromagnetic guided PCNL
[16 ] were developed. New techniques are
being implemented to further optimize the training process of the puncture technique
itself using virtual reality (VR) simulators [17 ]. A disadvantage of these systems, however, is that additional
instruments, devices, or even access routes [18 ]
[19 ] are needed, creating
additional acquisition and operating costs. In addition, new working techniques and
work steps must be learned and practiced by the user. The future trend of
percutaneous renal access is evolving away from fluoroscopically assisted puncture,
to reduce radiation exposure [20 ]. This could
reduce the harmful long-term effects of radiation exposure and make the use of PCNL
in pediatric urology [21 ] safer. The purpose of
this study is to find out if the novel ultrasound-guided renal puncture method used
in a prevalidated pig kidney animal bench-top model [22 ] is feasible, safe, radiation-free, and easy to learn in comparison to
traditional freehand percutaneous renal puncture. The novel ultrasound-guided needle
tip tracking technology used for renal puncture in the study was first invented for
peripheral nerve block procedures in the field of anesthesiology and was described
previously [23 ].
Materials & Methods
We prospectively performed freehand percutaneous renal access in a previously
described animal bench-top model using the novel ultrasound-guided technique
compared to the conventional ultrasound technique. The freehand punctures were
performed for both techniques by 25 participants utilizing the Xperius ultrasound
system (Philips Medical Systems International BV, Eindhoven, The Netherlands).
For this study we recruited 10 urologists, 7 residents of the urology department, and
8 medical students. The participants were divided into 2 groups – the 10 urologists
formed the experienced group, and the other 15 participants were defined as the
novice group. Despite the wide range of available training options and models, there
is currently no established standardized training curriculum for puncturing the
renal pelvicalyceal system. The typical training of beginners essentially consists
of supervised use in the operating room. It is therefore difficult to clearly define
the term expert. In this study the definition of the “experienced” group was based
on the number of ultrasound-guided organ punctures performed by the surgeon to date
(e. g.: percutaneous nephrostomies, lymphoceles, and abscesses). The minimum number
of punctures per surgeon was>75. As already mentioned, studies have shown that a
safe and adequate puncture procedure can be assumed if the number of punctures is at
least 60 [6 ]. Participants in the “beginner”
group, meanwhile, had never previously performed an ultrasound-guided puncture. It
was randomized by lot which participant should use which puncture technique
(navigated vs. conventional). The kidney model ([Fig. 1 ]) consists of an en bloc specimen (a pair of pig kidneys
connected to the big vessels and the ureter) embedded in ballistic gelatin. The
feasibility of this animal bench-top model was validated with respect to face,
construct, and content validity in a previous study [22 ]. We placed a standard 5F ureteral catheter in the ureter to fill the
calyceal system with a sodium chloride solution combined with indigo carmine amino
dye to mimic an obstructive calyceal system and as a tool for verifying the correct
puncture of the calyceal system ([Fig. 2 ]).
The puncture was rated successful if the blue fluid could be aspirated via the
puncture needle ([Fig. 3 ]). Fluoroscopy was
not needed to verify the correct placement of the needle. The ultrasound machine
(Xperius ultrasound system, Philips Medical Systems International BV, Eindhoven, The
Netherlands) consists of a 100mm Stimuplex Onvision hollow needle (“Luer version”,
30°, 20G, 100mm, B. Braun Melsungen AG, Melsungen, Germany) with a piezoelectric
sensor integrated at the tip of the needle ([Fig.
2 ]) and an integrated electronic console that processes computerized
signals [23 ]. The Xperius ultrasound system
used in this study, including the Stimuplex hollow needle, is a fully commercially
available system.
Fig. 1 Overview of the gel model. (a ) Stimuplex Onvision hollow
needle (“Luer version”, 30°, 20G, 100mm) with needle sensor in the needle
tip and connecting cable (b ) to the ultrasound device. (c )
10ml syringe, Braun company, connected by tube to the Stimuplex Onvision
needle to inject or aspirate fluids. (d ) Gel model, containing a real
pair of porcine kidneys with one ureter per each kidney that are intubated
by 5 french ureteral catheters (e ).
Fig. 2 Experimental setup with successful puncture of the gel model
(a ), the renal pelvis is filled with blue fluid via the inserted
ureteral catheter (b ). The blue fluid as a control of successful
puncture, was aspirated with a 10ml syringe (c ), via a tube of the
hollow needle. (d ) Xperius ultrasound system with the guided needle
tip (green circle) of the Stimuplex Onvision hollow needle (“Luer version”,
30°, 20G, 100mm; B. Braun Melsungen AG, Melsungen, Germany) with a
piezoelectric sensor which is integrated in the needle tip, on the
ultrasound image of the pig kidney. Needle navigation is switched on. The
correct position of the needle tip within the ultrasound beam is indicated
by a green circle projected around the needle tip on the ultrasound screen
(D).
Fig. 3 Close-up view of the successful puncture. (a ) Stimuplex
hollow needle. (b ) Gel model. (c ) Inserted ureteral catheter
with blue dyed water, to fill the renal pelvic calyceal system. The blue
fluid as a control of successful puncture was aspirated with a 10ml syringe
(d ), via a tube of the hollow needle (a ). (e )
Connecting cable of the sensor (which is wrapped around the needle tip) with
the ultrasound device.
The correct position of the needle tip within the ultrasound beam is indicated by a
green circle projected around the needle tip on the ultrasound screen ([Fig. 4 ]). Once the needle tip is positioned
slightly outside the ultrasound beam, but is still visible for the surgeon, the
green circle turns into a red circle and an additional blue circle appears around
the red circle ([Fig. 5 ]). As the needle tip
moves further away from the ultrasound beam, the diameter of the blue circle
increases ([Fig. 6 ]). The maximum size of the
blue circle can become twice the size of the red circle. Afterwards, it
disappears.
Fig. 4 Ultrasound image of the kidney model. Needle navigation is
switched on. The correct position of the needle tip within the ultrasound
beam is indicated by a green circle projected around the needle tip on the
ultrasound screen
Fig. 5 Ultrasound image of the kidney model. Needle navigation is
switched on. The needle tip is positioned slightly outside the ultrasound
beam but is still visible. An inner red circle and an outer blue circle
appear at the tip of the needle. This indicates that the needle tip is not
on track. The direction must be corrected.
Fig. 6 Ultrasound image of the kidney model. Needle navigation is
switched on. The blue circle becomes larger the further the needle tip
deviates from the sound plane. The direction must be corrected.
To standardize the procedure, all participants went through a defined 15-minute
introduction. First, the participants were shown a video clip that demonstrated the
technique and technology of visualizing the needle tip. To adapt to the anatomy of
the puncture model and to get used to the handling of the ultrasound transducer, a
short exercise sequence was performed on the model under qualified supervision.
Thereafter, the attendees were randomized per lot into two puncture groups, one with
a visually guided needle tip and one without (conventional). Each participant had to
puncture successively first the lower, then the middle, and lastly the upper pole of
the calyceal system of the model. The primary endpoint was successful access to the
calyceal system. Needle correction during the puncture was allowed, but if the
participant removed the needle completely, he had to restart with a new puncture
attempt. The puncture time in seconds and the number of puncture attempts were
measured.
Due to the prospective nature of the feasibility study with a sample size of 25
subjects (N=25), the focus of this study was on providing a detailed description of
the collected data. For descriptive statistics, medians, minimum and maximum values,
ranges and the 25%, 50%, and 75% percentiles were determined separately for each of
the two puncture methods. The descriptive evaluation was carried out once for the
entire group of test subjects and separately according to the two degrees of
experience of the surgeons: “experienced” and “novice”.
Statistical analysis was performed with SPSS Statistics 26 (IBM Corporation, Armonk,
New York, USA) using the unpaired t test. Results with p≤0.05 were considered
significant.
Results
The results are summarized in [Table 1 ] and
shown graphically in [Fig. 7 ]. Navigated
access for experienced participants reduced the number of punctures by 0.2 attempts
(8%) and the time to calyceal access by 15 seconds (26%). These results were not
significant (puncture attempts (PA) p=0.42; time to access (TTA) p=0.19; see [Table 1 ]). The novice group using navigated
puncture required 1.2 fewer attempts (36%) and 70 seconds less (61%) in comparison
to the conventional puncture technique. These results were significant (PA p=0.037;
TTA p=0.042; see [Table 1 ]).
Fig. 7 Graphical illustration of the number of puncture attempts and
time to successful puncture of the two groups studied. The green graph
represents the experienced participants and the blue graph represents the
novices. (a ) Average number of puncture attempts according to the
puncture method and level of experience. *Shown is the median of the
averaged number of punctures (mean values from puncture 1, 2, and 3) needed
for calyceal access, grouped according to the puncture method and level of
experience. (b ) Average puncture time according to the puncture
method and level of experience *Shown is the median of the mean puncture
time (mean values from puncture 1, 2, and 3 in seconds), grouped according
to the puncture method and the level of experience. Navigated access for
experienced participants reduced the number of punctures by 0.2 attempts
(8%) and time to calyceal access by 15 seconds (26%). These results were not
significant (puncture attempts (PA) p=0.42; time to access (TTA) p=0.19; see
[Table 1 ]). The novice group using
navigated puncture required 1.2 fewer attempts (36%) and 70 seconds less
(61%) in comparison to the conventional puncture technique. These results
were significant (PA p=0.037; TTA p=0.042; see [Table 1 ]).
Table 1 Puncture attempts and puncture times of the different
puncture groups.
Group (N=25)
Average number of puncture attempts (PA) (median* (range))
Average puncture time in seconds time to access (TTA) (median**
(range))
1 (n=5) Experienced/conventional
2.5 (±1.5)
57 (±36)
2 (n=5) Experienced/navigated
2.3 (±0.5)
42 (±8)
3 (n=9) Novice/conventional
3.3 (±1.5 )
114 (±87)
4 (n=6) Novice/navigated
2.1 (±0.6 )
44 (±28)
*Median of the mean values of puncture attempts needed for calyceal
access.**Median of the mean values of puncture time needed to calyceal
access in seconds.
Discussion
Our data show that use of the navigational system did not make a significant
difference in the number of puncture attempts, or the time required for successful
access to the renal pelvicalyceal system for well-trained urologists. In contrast,
for participants in the novice group, use of the navigational system significantly
reduced both the number of puncture attempts and the time needed for successful
access. Furthermore, the results of the beginner group using the navigation system
are comparable to the results of experienced users with or without navigation. These
findings suggest that use of navigation, particularly for trainees, provides safer
and easier handling of the percutaneous puncture technique and would theoretically
be associated with increased patient safety. Fewer puncture attempts would reduce
the risk of intra- and postoperative complications. While severe and
life-threatening complications like intestinal perforation, sepsis, uncontrolled
hemorrhage requiring an explorative laparotomy and potential nephrectomy, cardiac
arrest, or death are rare, occurring with a frequency of 0–4% [24 ]
[25 ]
[26 ]
[27 ]. The most frequent complications described
in the literature, including pain, postoperative fever, transient hematuria, urinary
tract infections, and tube dislodgment or occlusion, occur with an average rate of
4–38% [24 ]
[25 ]
[27 ]
[28 ] and cause significant stress and additional
expense.
Of course, the results must be viewed critically, since they are limited by the small
cohort number and the model construction. As this is a bench-top model, the
punctures were performed under near-optimal and highly repeatable experimental
conditions. The use of real pig kidneys, which are very similar in morphology to
those of humans, offers an excellent training model with a low cost-benefit factor
[29 ], and could be enhanced by the use of
dyed liquid for confirmation of successful puncture. Natural disruptive factors
present in real-life percutaneous puncture, such as resistance of the abdominal wall
layers, excess patient weight, respiratory movement, poor positioning of the
patient, higher degrees of congestion, such as II-III° hydronephrosis of the
calyceal system, all would be expected to increase the complexity in real
procedures.
Due to the designed approach of a feasibility study based on a gel model and under
near optimal puncture conditions, possible complications occurring under real
conditions could not be detected. The only thing that stood out, which can be
transferred to the real world, is that with frequent punctures (>7) per kidney,
there was leakage of fluid from the kidney. This would be an indication of urinoma
formation or possibly postoperative hemorrhage. This occurred in a total of 3
subjects only from the beginner group, who performed a conventional puncture without
a needle tracking system.
An important advantage of sonographically guided puncture is the complete lack of
X-rays, which significantly increases the safety for the patient and the surgeon in
terms of radiation exposure.
A limitation of the commercially available system used here is mainly the size of the
available Onvision Stimuplex hollow needle. The needle is 100mm in length and 20G in
width. In the gel model used here, the length was adequate to achieve sufficient
organ puncture. Under real circumstances, it would be too short, especially in
patients with obesity. Needles up to 150mm in length are available but were not able
to be obtained at the time of the study. These, too, might be too short under
real-world conditions. In addition, a slightly thicker needle, e. g., 18G, would be
advantageous for placing common wires.
To simplify the puncture procedure, increase patient safety, and reduce surgical
complications, new techniques have already been developed. Various puncture aids and
additional imaging techniques such as CT- [10 ],
MRI- [13 ], or iPad- supported [12 ] percutaneous puncture have been successfully
tested (see supplementary table 1 ). For example, in 2015, Ritter et al. [10 ] demonstrated a new and safe puncture
technique for complex punctures in PCNL, biopsy, or drainage tube insertion, using
the Uro-Dyna CT scan and 3D reconstruction of organ structures. However, this also
required special training with regard to using the technique. In 2008, Kariniemi et
al. [13 ] also demonstrated MRI-assisted
complication-free and radiation-free nephrostomy in 8 patients in a feasibility
study. In this case, however, puncture was performed by radiologists and an average
puncture time of 26 minutes was demonstrated. In addition, a special MRI-capable
puncture set was required. Puncture robots such as the AcuBot system were also
developed, but are not yet well established [15 ]. The advantages of puncture combined with sectional imaging are the
ability to determine the exact location of the puncture needle as well as targeted
puncture in the desired organ area. This also allows puncture of smaller or
sonographically difficult-to-access target structures such as small masses and
abscesses or complex punctures with a pronounced stone load in the kidney and
reduces the risk of complications such as injury to surrounding structures and
multiple puncture attempts. One disadvantage is the additional time needed for
imaging. In Germany, the puncture procedure and a CT or MRI examination must be
performed in a radiology department and require additional personnel to operate the
equipment. In addition, the use of CT entails radiation exposure. For iPad-navigated
puncture, a CT examination is required in advance. Furthermore, real-time imaging
during iPad-navigated puncture is not possible, so that fluoroscopy is also
required. In summary, the visually combined procedures result in an increase in
time, are cost-intensive, require spatial and personnel expenditure, and, depending
on the procedure, require additional radiological radiation exposure.
Sonographically guided renal puncture is firmly established as an alternative.
Freehand puncture without the use of puncture aids also provides the surgeon with
more degrees of freedom and puncture angles. However, sonographically assisted
puncture is technically more demanding of the surgeon because the puncture needle is
very difficult to track on ultrasound. Thus, a certain discrepancy between the
needle seen on ultrasound and the actual needle position in the desired target area
can be assumed. In addition, the needle has to be corrected as soon as it is lost
from the ultrasound field. This leads to trauma in the target tissue, which can lead
to complications such as severe secondary bleeding and hematoma. Studies show that
at least 60 punctures are necessary to master sonographically supported puncture
[6 ]. There have been various approaches to
simplify sonographically supported percutaneous renal puncture, while avoiding
radiation exposure. Already in 2011, Huber et al. published an experimental study on
electromagnetically supported, ultrasound-guided percutaneous renal puncture [30 ]. More recently, in a single-center study by
Chau et al. in 2016, percutaneous nephrolithotomy was successfully performed on 18
patients without X-ray radiation. In this study, sonographic puncture was supported
by a magnetic field for better visualization of the needle position [20 ].
Conclusion
Navigated freehand puncture of the calyceal system utilizing the Xperius ultrasound
system, in combination with needle tracking using the Stimuplex Onvision hollow
needle in an ex vivo pig-kidney model embedded in gel is feasible and allows novice
users to perform like experienced users in terms of puncture time and number of
attempts. The major technical drawback is the limited length and diameter of the
available needle. The small cohort of participants is a limitation of our study.
Because of the constraints of the bench-top model that was used, the transferability
of the results to real-world scenarios must be verified using an in vivo
clinical study.
Parts of this work were previously published as a dissertation by M. Hohmann [31 ].
Bibliographical Record
