General description of procedure, equipment, technique
Argon Plasma Coagulation (APC)
Initially defined in 1995 and subsequently described in European Respiratory Society (ERS) and American Thoracic Society (ATS) guidelines, interventional pulmonology is “the art and science of medicine as related to the performance of diagnostic and invasive therapeutic procedures that require additional training and expertise beyond that required in a standard pulmonary medicine training program.” Clinical entities encompassed within the discipline include complex airway management, benign and malignant central airway obstruction, pleural diseases, and pulmonary vascular procedures.
Diagnostic and therapeutic procedures pertaining to these areas include rigid bronchoscopy, transbronchial needle aspiration, autofluorescence bronchoscopy, endobronchial ultrasound, transthoracic needle aspiration and biopsy, laser bronchoscopy, endobronchial electrosurgery, argon-plasma coagulation, cryotherapy, airway stent insertion, balloon bronchoplasty and dilatation techniques, endobronchial radiation (brachytherapy), photodynamic therapy, percutaneous dilatational tracheotomy, trans-tracheal oxygen catheter insertion, medical thoracoscopy, and image-guided thoracic interventions. This presentation focuses on argon plasma coagulation (APC).
Argon plasma coagulation (APC) is an electrosurgical technique similar to laser or electrocautery. APC is used during bronchoscopic procedures to ablate malignant airway tumors, control hemoptysis, remove granulation tissue from stents or anastomoses, and treat a variety of benign disorders.
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Indications and patient selection
The indications for APC are similar to those for laser therapy and electrocautery.
Contraindications
The contraindications for APC are similar to those for laser therapy and electrocautery.
Details of how the procedure is performed
A grounding pad is placed on the patient’s back or thigh. Typical settings include a power of 30 Watts and an argon flow rate of less than 1 L/min. The argon flow rate determines the length of the flame. The probe tip is positioned several centimeters beyond the bronchoscope’s tip to ensure that the bronchoscope will not be burned. The probe tip is placed within 1 cm of the target lesion; the electric current will not be conducted if the probe is farther than 1 cm from the target lesion. Care must be used to ensure that the catheter does not come into direct contact with the target tissue.
As argon gas is expelled, a high-voltage electric current passing along the probe contacts the gas, ionizing it and conducting a monopolar current to the target lesion. The current is applied to the surface in one- to three-second bursts. The tissue effect is similar to that seen with electrocautery.
In the process of debulking an endobronchial lesion, eschar is first formed with the application of APC and then removed using a forceps or a cryotherapy probe. APC is then applied to the underlying fresh tissue. This process is repeated until the tumor is removed. Upon completion of the ablation, APC may be applied to the tumor base to mitigate risk of post-procedure bleeding from the site.
Interpretation of results
Not applicable
Performance characteristics of the procedure (applies only to diagnostic procedures)
Not applicable
Outcomes (applies only to therapeutic procedures)
In a prospective cohort study of 364 patients who underwent APC (482 procedures), a success rate of 67 percent was reported, where success was defined as hemostasis or full or partial airway recanalization. Rigid bronchoscopy was used in 90 percent of the interventions.
In a retrospective cohort study of sixty patients who underwent APC (seventy procedures), treatment was immediately successful in fifty-nine patients; treatment success was defined as resolution of hemoptysis or decreased airway obstruction. (All patients had either hemoptysis or airway obstruction.) Hemoptysis did not recur over a mean follow-up of ninety-seven days, and improvement in dyspnea persisted over a mean follow-up of fifty-three days. A similar study of forty-seven patients reported a success rate of 92 percent, which was maintained over a mean follow-up of 6.7 months. However, an average of more than three sessions per patient was required to achieve this result.
Alternative and/or additional procedures to consider
Alternative treatment modalities to APC include ND:YAG laser therapy, electrocautery, photodynamic therapy, brachytherapy and cryotherapy, and mechanical debridement. External beam radiation effects are often too delayed to be considered for primary management of an acute airway obstruction.
Complications and their management
Complications of APC, while infrequent (less than 1% of procedures), include airway burn and airway perforation, which can cause pneumomediastinum, subcutaneous emphysema, and pneumothorax, equipment damage, and gas embolism.
Gas embolism has been described in a case series, leading to three cases of cardiovascular collapse and one case of death. An animal study indicated that the occurrence of gas embolism to the atria was dose-dependent with the argon gas flow, leading to the recommendation to minimize the gas flow and duration of treatments. Using this modality as a non-contact thereby reducing risk of administering gas under pressure via the vascular bed of the tumor may reduce the risk of this potentially fatal complication.
Airway perforation appears to be less likely when using settings of 40 W and duration of applications of 5 seconds or less. At these settings in a recent animal study, APC appeared to have less chance of causing airway perforation than ND:yag and electrocautery.
Similar to laser and electrocautery, limiting the inspired oxygen concentration, the d power (less than 40 watts), and the application time (less than five seconds) probably minimizes the risk of airway fire, as does keeping the probe tip several centimeters away from any combustible material.
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