A gas cylinder is a containment apparatus that will store a gaseous compound under pressure for use in medical settings. The physical form of the stored compound can be gas or liquid, with the ultimate output from the apparatus being gaseous. Gas cylinders allow for the portable and safe storage of compounds needed in a medical setting. The sizing of gas cylinders has been attributed to a nationally recognized letter, with the more commonly used medical sizes listed below. Gas cylinders are labeled from A to M, with increasing volume as the letters of the alphabet proceeds. The E-sized cylinders are the most commonly used size in medical settings. An E cylinder has a service pressure of 1900 psi but may be filled up to 10% more to 2200 psi. Higher filling pressure allows for expansion at temperatures greater than 70 degrees Fahrenheit.
The following are standard cylinder sizes and the volume of oxygen contained at 2200 psig (maximum).
- B: 200 L
- D: 425 L
- E: 660 L
- F: 1360 L
- G: 3400 L
- M: 3450 L
Color System for Compounds
A standardized color system identifies the compound in the cylinder. The United States' color system for oxygen and air differs from those used internationally.
- Oxygen - Green (*White)
- Carbon dioxide - Gray
- Nitrous oxide - Blue
- Nitrogen - Black
- Helium - Brown
- Air - Yellow (*White & Black)
A safety system is in place to prevent connecting the wrong gas cylinders. This system, called the Pin Index Safety System, provides a standardized, unique pin configuration system that acts as a lock and key system to prevent the mismatching of gas cylinders with their corresponding connections in medical settings.
Issues of Concern
Pressure Release Device
The release of pressurized gas can be hazardous, and extreme caution should be exercised. Gas pressure levels should be reduced from stored high pressure to a workable, usable level. A pressure regulator should be used in this situation, and any time contents are being removed or used from the cylinder. Do not tamper with pressure-release devices. Do not use any cylinders with visibly defective pressure-release devices. Pressure-release devices and gas outlets should never be pointed in any direction that could cause harm.
While attached to an anesthesia machine, the cylinder valves should be in the off position while not in use. This is to prevent leakage and to allow for notification via an alarm of failure of the pipeline supply of gas. If the cylinder were to be left open and a pipeline gas supply failure occurred, the anesthesia machine would consume the oxygen in the cylinder, and the provider would not be notified until the cylinder was depleted.
A cylinder should be inspected for malfunctions and defects before use. Full cylinders are usually placed with a tamper-evident seal. This is generally a tear-off seal on the valve outlet and is removed before use. Proper cylinder inspection includes the outlet, pin index safety system, and pressure relief device. The valve outlet should be cleaned before use. Only use cylinders marked with DOT (Department of Transportation) or ICC (Interstate Commerce Commission). In Canada, cylinders may be marked with BTC (Board of Transportation Commissioners) or CTC (Canadian Transport Commission). A cylinder should be connected to a regulator to reduce the compressed, stored pressure to a working, usable pressure. Inspect the regulator for signs of damage or foreign materials.
Safe Storage and Transportation
Cylinders must be stored upright and secured using a rack, strap, or chain to minimize the chance of falling over. Cylinders should be transported using a cart or carrier. Never drop or hit cylinders, and never drag, roll, or slide cylinders, even for a short distance. Only qualified personnel should refill cylinders. While using cylinders, avoid flammable substances, smoking, open flame, or any other incendiary sources. Cylinders should be stored in a dry, cool, well-ventilated area away from exposure to weather. Cylinders should be stored at temperatures less than 125^oF (52^oC).
Oxygen cylinders have more specific storage requirements than other medical gases. While oxygen cylinders can be stored in the same space as other non-flammable medical gases as long as they are properly segregated, full oxygen cylinders and empty oxygen cylinders cannot be stored together. The separation of full and empty cylinders prevents the accidental usage of an empty cylinder during an emergency. Partially full oxygen cylinders may be stored in the same location as full cylinders, provided that they are adequately labeled.
Use Boyle's law to calculate how much oxygen time remains in an E-sized cylinder. Boyle's law states that at a fixed temperature (room temperature) of an ideal gas, the pressure is inversely proportional to volume. Boyle's law can be further rearranged to state that pressure times volume equals a constant. The following is the formula:
One could compare a cylinder of gas at a filled volume (V1 = 660 L) and pressure (P1 = 2200 psi) to the current pressure (P2) read on the cylinder. This would provide the information needed to solve for the current volume (V2) remaining in the tank in liters. The following is the formula:
(Measured pressure remaining using the integrated pressure gauge in psi/2200 psi) * 660 L = Liters of oxygen remaining in the tank.)
This Volume (V2) can be used to determine the amount of unit time remaining on the cylinder, given the current flow rate of the gas.
- V2/Flow rate = unit time remaining, or
- Liters of oxygen remaining in the tank/oxygen setting in liters/minute = Minutes of oxygen remaining
The same formulas can be used in cylinders containing a pure gaseous form. However, calculations for nitrous oxide are only applicable once the pressure drops below 745 psi due to the presence of liquid and gaseous forms within the tank. The pressure will remain constant until 75% of the 1590 L gas is consumed, which is approximately equal to 400 L remaining within the cylinder. From this point until empty, the above formulas apply. Prior to this point, the cylinder must be weighed to determine the amount of gas remaining within the cylinder.
The transportation of gas cylinders is highly regulated by local, state, and federal agencies in most countries. In the United States, the Department of Transportation is the governing authority. Further, there are manufacturer guidelines to ensure that the cylinders have been tested and are safe. Some of the tests that cylinders undergo include tensile strength, hydrostatic testing, impact testing, burst testing, and pressure cycling. Once the cylinder is manufactured, it must have all the vital information permanently etched onto the cylinder.
Nursing, Allied Health, and Interprofessional Team Interventions
Knowledge of gas cylinders and proper management and utilization of gas cylinders is important.
It is most appropriate and ideal to maintain continuous closed-loop communication between all members of the perioperative care team regarding the need, technique, and potential management issues associated with gas cylinders.
It is necessary to obtain thorough and comprehensive informed consent from either the patient or their designated and authorized decision maker before anesthesia administration, as this will likely involve gas cylinders. It is most appropriate for all team members to feel empowered to state, to the team or the patient, any concerns that they might have regarding the process, as this ensures buy-in from all stakeholders as well as provide additional layers of review and insight into any problematic matters as soon as possible.
All team members have a duty to communicate their concerns, responsibilities, and activities with all other team members both contemporaneously and as indicated throughout the perioperative period based on their professional discretion.
All team members should respect the free flow of information and concerns among team members without allowing or producing an environment of hostility.
All team members should consider it their duty to neither disrupt the work done by other team members nor to, through their actions or inaction, create additional issues or increase the workload for other team members. [Level 4]