Core Medical Equipment Information – Cryosurgical units for the treatment of precancerous cervical lesions
11-067 Cryosurgical Units, General Purpose
18-051 Cryosurgical Units
11067 Cryosurgical units, general purpose
Other common names
Cryotherapy unit/equipment, cryosurgery unit/equipment, cryoprobes
Health problem addressed
Cryosurgical equipment is used to treat many types of skin and other lesions. The equipment described in this document relates specifically to the treatment of precancerous cervical lesions. Extreme cold is applied to the lesion causing it to freeze. The extreme cold and subsequent thawing causes necrosis of the lesion.
Cryosurgical units suitable for the treatment of precancerous cervical lesions consists of a handheld unit with a probe, known as the cryoprobe, and one or more “triggers” or switches to control the temperature of the probe. At the distal end of the probe there is a disc, the “cryotip”, that can be placed in contact with the lesion. The probe is cooled to a temperature of at least -20°C. The hand held unit is attached to a gas cylinder through a suitable hose and connecting unit. The latter is normally fitted with a gauge to monitor the pressure within the cylinder.
Principles of operation
Two main methods are used to cool the cryoprobe, the expansion of a compressed gas through a nozzle, causing cooling by the Joule- Thomson effect, and the use of cryogenic liquids such as liquid nitrogen. Because of the risk of damaging surrounding tissue when using cryogenic liquid based cryotherapy equipment only compressed gas based cryotherapy equipment should be used for the treatment of precancerous cervical lesions. Two gases are commonly used, nitrous oxide and carbon dioxide. In low resource settings carbon dioxide is generally more readily available and less costly.
The patient is prepared for a gynaecological examination, using a speculum. After wiping the cervix with a saline-soaked cotton swab and applying acetic acid to outline the abnormality the cryoprobe tip is applied to the lesion and left in place for three minutes until ice forms on the tip of the cryoprobe and on the cervix, extending over an area 4 mm to 5 mm beyond the edge of the cryoprobe. A thaw cycle is then performed for five minutes during which time the probe is kept in contact with the lesion. The freeze/thaw cycle is then repeated (two freeze/thaw cycles are recommended for the treatment of precancerous cervical lesions).
Blocking of the gas feed within the cryoprobe can occur during freezing, which may prevent the probe cooling to the required temperatures. The use of medical grade or food grade gases minimizes this risk. Different standards and fittings are used on gas cylinders depending upon country and the intended use of the gas and the size of the cylinder. This can make it difficult to match up the connector on the cryotherapy unit with the gas cylinder. Detailed specifications are required for the type of cylinder connectors available depending upon the country and the type and grade of gas used.
Use and maintenance
Users: surgeons and other trained medical staff.
Maintenance: technicians, engineers, medical staff, manufacturer/service staff. Any maintenance of the gas supply equipment including the hose assembly must be done by appropriately qualified personnel trained to work with high pressure gas equipment.
Training: Initial training by manufacturer (if feasible), operator’s manuals, user’s guide. Supervised training by experienced surgeons.
Environment of use
Location; hospitals, gynaecology clinics, outpatient clinics
Requirements: gas supplies, cylinder stands or other cylinder supports, batteries (if equipment is fitted with temperature probes and/or timer), adequate room ventilation to vent exhaust gases, spare parts (hose assembly, cryotips, cryoshafts, O-ring and sealing washers), disinfecting solutions (sodium hypochlorite solution with 0.5% available chlorine if made using non-potable water or 0.1% available chlorine if made using potable), and storage facilities for the gas cylinders.
Hand held compressed gas (nitrous oxide or carbon dioxide) operated cryosurgical unit capable of achieving temperatures at the cryotip below - 20°C with:
- trigger mechanism to control the freeze/thaw cycle (active defrost preferred but not essential)
- removable rounded, closed design cryotips and/or probes of (19 +/- 2) mm diameter with flat surfaces or with a cone extrusion not exceeding 5 mm
- insulated cryoshaft of length between 170 mm and 200 mm
- connecting hose (high pressure) and cylinder connector with pressure gauge and relief valve
- exhaust port to which a hose can be connected to safely vent the exhaust gas
Consumables: compressed gas (nitrous oxide or carbon dioxide)
Price range (USD): 1,000 to 4,000 (excluding cylinders)
Typical product lifetime (years): 10
Type and variations
Handheld unit with or without console. Cryosurgical units can be specified for nitrous oxide or carbon dioxide. Either gas can be used but has to be specified when the equipment is purchased to ensure that the correct cylinder fitting are supplied.