Surgery
A range of specialty gases are used to assist surgical operations. Argon, helium and sulphur hexafluoride all have important roles to play.
Argon cryosurgery
Cryosurgery has been established as a therapeutic option for the treatment of localised prostate cancer and other conditions for many years. Its origins were based on the use of liquid nitrogen, ie at temperatures below −196°C, to create the cryogenic conditions required to freeze the relevant tissue. In recent decades, the expansion of high pressure argon gas from 300 bar has been used as the preferred method to create the extremely cold (−180°C) cryosurgical probe. This allows for more sensitive surgery using narrower and more delicate probes. In the last phase of cryosurgery, helium gas is used to return the tissue to body temperature.
Cryosurgery has been used to treat the following conditions:
- skin tumours and pre-cancerous skin moles
- nodules, skin tags and unsightly freckles
- benign breast lumps, known as fibroadenomas
- retinoblastomas, a childhood cancer of the retina
- prostate, liver, and cervical cancers, especially if surgical resection is not possible
- and, more recently, tumours in other parts of the body, such as the kidneys, bones, spine, lungs and breasts
Argon plasma coagulation (APC)
APC is an endoscopic procedure which controls bleeding from lesions in the gastrointestinal tract. It causes coagulation to a depth of a few millimetres. To form the plasma, argon gas is ionised by a high voltage (6kV) discharge and then a high-frequency electric current is conducted through the gas jet. The plasma is directed through a probe passed down the endoscope. The probe may be placed a small distance from the bleeding lesion and the argon plasma will cause it to coagulate. No physical contact is made with the lesion, so the procedure can be used to treat bleeding in parts of the gastrointestinal tract with thin walls, such as the caecum.
APC is administered during esophagogastroduodenoscopy or colonoscopy and can be used to treat the following conditions:
- angiodysplasias
- gastric antral vascular ectasia (watermelon stomach)
- colonic polyps, after polypectomy
- radiation proctitis
- esophageal cancer
- debulking of tumours, if surgery is not appropriate
SF6 gas for ophthalmology
Retinal eye surgery often involves a vitrectomy. In this procedure the surgeon removes the vitreous humour which lies behind the iris to gain access to the back of the eye so they can repair the damaged retina. On completion of the vitrectomy, the ophthalmologist must fill the space left by the vitreous gel so that the retina will remain in place and heal. This can be achieved by injecting a small amount of high purity SF6 gas into the eye. Due to the high density of the SF6 gas it will take 3 to 4 weeks for the patient's body to absorb the gas. In comparison, the absorption of air would take only 1 to 3 weeks, which is generally insufficient time for the retina and eye to fully heal.
In order to validate the procedure, the ophthalmologist generally analyses the composition of the SF6 gas prior to its use in surgery. In doing so, traceability and quality assurance can be achieved. It would be typical to use a chilled mirror instrument for this application which measures SF6 according to its dew point. Most instruments selected for this application are also capable of moisture composition analysis in the SF6. Chilled mirror dew point sensors are calibrated using certified calibration gas mixtures with known quantities of SF6.
As alternatives to SF6, the gases octafluoropropane and hexafluoroethane are also occasionally used.