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* From the Departments of Internal Medicine (Drs. Ferguson and McLennan), Urology (Drs. Rippentrop and Fallon), and Anesthesia (Dr. Ross), University of Iowa, Iowa City, IA.
Correspondence to: J. Scott Ferguson, MD, FCCP, Department of Internal Medicine, Division of Pulmonary, Critical Care, and Occupational Medicine, 200 Hawkins Dr, C-33 GH, Iowa City, IA 52242-1089; e-mail: john-s-ferguson{at}uiowa.edu
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Abstract |
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Key Words: airway obstruction • bronchoscopy • lasers • lithiasis • lithotripsy • lymph nodes
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Introduction |
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The Nd-YAG and holmium-yttrium aluminum garnet (Ho-YAG) lasers are possible alternatives to surgery and mechanical crushing.34 However, these modalities are associated with rare but important complications,5 some of which may be lessened by the use of advanced imaging techniques used to improve the operator’s knowledge of the anatomy, which aids in preprocedural planning.
Preprocedural planning with three-dimensional (3D) multidetector CT (MDCT) imaging enhances the bronchoscopist’s knowledge of the relationships of the target lesions with critical structures, and improves the efficiency of the application of specific endobronchial therapies. We report two cases of obstructive broncholiths managed via bronchoscopic Ho-YAG laser lithotripsy after planning with 3D reconstruction of the airway utilizing MDCT.
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Case Reports |
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Patient 2
A 78-year-old man with a 6-month history of shortness of breath, cough, and recurrent left-sided pneumonia despite long-term administration of antibiotics was evaluated using chest CT, which demonstrated a broncholith in the left mainstem bronchus. A planning MDCT scan with virtual endoscopy was performed, demonstrating an abnormal course of the left main bronchus that contained a large broncholith in close proximity to the pulmonary artery (Fig 2
). The patient underwent flexible bronchoscopy under general anesthesia demonstrating near-total occlusion of the left main bronchus by a large broncholith. The Ho-YAG laser (200-µm, 365-µm, 1,000-µm fibers; 0.6 to 1.2 J; 8 to 15 pulses per second) was applied via the flexible bronchoscope. Much of the stone was vaporized during lithotripsy, and a plane within the stone was treated causing the stone to split into two large fragments. The two fragments of stone were removed with N-circle and Dormia baskets, leaving one piece of stone embedded in the bronchial wall intact, thus avoiding potential bleeding from the immediately adjacent pulmonary artery. Copious amounts of purulent material were aspirated from the bronchial tree distal to the former site of obstruction. The patient was extubated at the conclusion of the procedure. The patient was discharged home on postoperative day 4 after resolution of pneumonia. A follow-up MDCT scan showed patency of the left main bronchus (Fig 2).
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Discussion |
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Ho-YAG lasers are commonly used in urology to fragment urologic stones, resect or vaporize prostatic tissue, and treat urethral strictures. Unlike other lasers, eg, pulsed-dye lasers, which fragment calculi through a photoacoustic effect, the Ho-YAG laser acts through a photothermal effect. With a wavelength of 2,010 nm, well into the infrared spectra, the laser energy is in part absorbed by water contained within the stones, causing expansion and fragmentation in a process termed microexplosion.7 The temperature rise in the proximity to the laser tip appears to cause a chemical breakdown of the stone, resulting in weakening of the stone allowing fragmentation without appreciable collateral mechanical or thermal damage.8
The energy imparted by the Ho-YAG laser is weaker than with other modalities used for stone removal, such as electrohydraulic lithotripsy. This results in slower lithotripsy and smaller fragments but less forceful propulsion of the stone and stone fragments. For optimal efficiency, the end-firing fibers should be oriented at a right angle to the stone surface. Side-firing fibers are available if there is difficulty with this owing to location of stones in awkward, hard-to-reach areas.
Ho-YAG laser fibers are available in 200-micron, 365-micron, and 1,000-micron sizes. The 365-micron size is the most efficient, but the 200-micron size is most commonly used through a 7F flexible ureteroscope, as it interferes less with flexion. For most lithotripsy, low energy (0.6 J) and low frequency (6 to 12 Hz) are sufficient. All stone types can be broken with these settings. If faster lithotripsy is desired, energy can be increased to 1 J. Higher than this level, fiber degradation tends to occur.8
Application of Ho-YAG laser directly to tissue will cause injury with a penetration depth of 0.4 mm. This allows for tissue vaporization and ablation and extends the uses of the laser to soft-tissue applications, such as prostate vaporization or resection, incision of strictures, ablation of transitional cell tumors in the bladder or kidney, and coagulation of tissue that assists in controlling bleeding. Repeated applications of laser energy to mucosa or underlying tissue that is not intended for laser can lead to perforation of the organ, and possibly excessive bleeding if a vessel is breached. Stricture of the ureter is reported as a late complication of Ho-YAG if there has been prolonged contact of the laser fiber and energy with the ureteral mucosa.
The attributes of the Ho-YAG laser as used in urology lend information that is of value to the pulmonary system. The relatively low-energy photothermal effect of the Ho-YAG laser is well suited to destruction of stones in the bronchial tree. The small fragments can be irrigated and suctioned from the airway, while larger fragments can be removed with baskets or forceps. Additionally, while the photoacoustic wave energy of pulsed-dye lasers could possibly propel the stone further into the airway and potentially cause mechanical collateral damage, the photothermal effect of the Ho-YAG slowly causes disintegration of the stone from within, resulting in smaller fragments and more controlled breakage. In addition, the shallower depth of penetration (0.4 mm) of the Ho-YAG laser might provide some safety margin over the more familiar Nd-YAG laser with a depth of penetration up to 6 mm. Although not observed in our two patients, we would expect that bronchial strictures could also develop as a complication if the Ho-YAG laser is applied to a significant amount of the bronchial mucosa or in a circumferential pattern.
The use of laser energy in the bronchial tree is an advanced bronchoscopy technique that requires specific training to be used effectively and safely. Several "rules" have been proposed to reduce the likelihood that a major complication will occur during laser bronchoscopy.9 Although uncommon, one of the most serious complications that can occur during the use of lasers in the bronchial tree includes perforation of the bronchial wall into an adjacent vascular structure and resultant hemorrhage. Preprocedural knowledge of the anatomic relationship of vascular structures to the target lesion is likely to improve the safety of the application of laser energy in the airway.
MDCT has improved to the extent that the entire thorax can be imaged in < 10 s with isotropic voxels, allowing 3D display, measurement, and analysis of the image data set. At the University of Iowa, we have built software for this particular use and have successfully translated the software applications to the bronchoscopic clinical environment.6 It is important that this type of value-added software provides accurate 3D reconstructions with accurate measurements.
We used 3D reconstruction of the MDCT images of the airway to plan our procedures.6 3D imaging permitted preoperative visualization of the anatomic relationships of critical structures in and near the airway, relationships that are sometimes difficult to appreciate from standard two-dimensional (2D) CT images.101112 Specifically, 3D imaging allowed us to determine preoperatively the attachment (embedment) location of the broncholith, the proximity to the adjacent pulmonary artery, and the angle and caliber of the airway distal to the lesion. This information was invaluable in planning the bronchoscopy, allowing us to approach the lesion from the luminal surface, avoid collateral laser impact with the distal bronchial wall, and avoid the embedded portion of the stone that was near the pulmonary artery.
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Conclusion |
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We are currently using 3D imaging for planning complex airway procedures, as we believe that 3D imaging modalities provide a better understanding of the anatomic relationships within this complex space of the bronchial tree, and thus allow us to anticipate the sequence of steps during an intervention. This in turn improves the safety of the procedure.
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Footnotes |
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Drs. Ferguson and Rippentrop participated equally in the preparation of this article.
This work was performed at the University of Iowa.
Drs. Ferguson, Rippentrop, Fallon, and Ross have no conflicts of interest to declare. Dr. McLennan is part owner of VIDA Diagnostics (Iowa City, IA), which is a company that develops three-dimensional software imaging solutions.
Received for publication October 11, 2005. Accepted for publication February 21, 2006.
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This article has been cited by other articles:
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  A. J. Reddy, J. A. Govert, T. A. Sporn, and M. M. Wahidi Broncholith Removal Using Cryotherapy During Flexible Bronchoscopy: A Case Report Chest, November 1, 2007; 132(5): 1661 - 1663. [Abstract] [Full Text] [PDF]
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