The Stephens Anesthetic Machine
Frequently Asked Questions
What size animals can be anesthetised with a Stephens?
Cats, small and large dogs as well as birds.
What anesthetic agent can be used in the Stephens?
Most volatile anesthetic agent, including Halothane, Isoflurane, Enflurane or Methoxyflurane
What maintenance is required on the Stephens?
Metal fittings are connected by pushing them together while turning them 1/2 turn and should be cleaned regularly by washing in warm, soapy water and dried thoroughly.
O - Ring grease should be used on all joints and “O” Rings.
Soda Lime inside the metal canisters needs to be changed regularly. You will get about 7.5 hours of operation for 25kg Dog from each canister. When filling the soda lime canisters, tap them gently to remove any dust from the soda lime, before attaching to the machine.
The O-Rings should be replaced periodically.
How can you tell when a soda lime canister is exhausted?
Soda lime gives off heat while it is absorbing carbon dioxide. To determine if a canister is exhausted feel it when in operation. The lower canister will exhaust first. If the lower canister is cold to the touch it may be removed from the circuit and be refilled. This can even be carried out during an operation. Remove the lower canister and re - connect the blow off valve and the expiratory hose to the bottom of the upper canister. When returning the fresh canister to the machine, always put it in the upper position. Seal the “Y” mount when the machine is not in use to prevent loss of soda lime activity.
Do you need to take the anesthetic agent out of the anesthetic jar after each day’s procedures?
A lid can be purchased to put on the anesthetic jar to prevent the anesthetic from vapourising. Store the jar on the bottom of the refrigerator.
How much dead space does the Stephens have?
The only dead space is at the end of the Y Piece approximately 3cc. The hoses and bag are part of the anesthetic circuit and do not contribute to the dead space.
Can you use a T - Piece on the Stephens?
A T-Piece or a Paediatric Set comprises a much smaller set of breathing hoses. A T - Piece connection may be used with the Stephens, we do not feel it is necessary, and its use is not supported by Blood Gas Studies.
Why do we use bakelite discs in the Unidirectional Valves instead of rubber?
The reason is that the bakelite discs create less resistance. Rubber is cheaper but will stick shut with moisture.
What stops the Stephens from heating up during a procedure?
The metal canisters and metal U D valves actually dissipate heat rather than retaining heat as plastic would. Heat is also lost from the rebreathing Bag.
What size rebreathing bag can be used on the Stephens?
Any size bag can be used, it really depends on the size of the animal. We find that a 4 Litre rebreathing bag is the most practical and commonly used bag, it also has a very low resistance.
From where do you read the oxygen flow?
The flow is read from the top of the red bobbin, which is located inside the flow metre.
When do you use the scavenger valve in the Stephens?
The scavenger valve is located at the bottom of the metal canisters. This is only used when you wish to dump the contents of the bag. For example at the end of a procedure, you may want to dispose of the anesthetic in the system, or if the flow rate is too high, the bag may be reduced by opening the valve and squeezing the bag, or if the concentration of anesthetic in the system is too high, it can be reduced by opening the blow off valve and squeezing the bag and re-filling with fresh oxygen.
What pre-meds can be used?
What precautions need to be taken with Pre-Meds?
Ideally if pre-meding with Ace, it should be administered 1 hour prior to the commencement of Anesthesia for its effect to be adequate. If given 15 minutes before the anesthesia, the animal will often go deeper 30 minutes into the anesthetic when the full effect of the Ace takes place. The original vapouriser setting which was adequate for the initial and subsequent maintenance phase of the anesthetic, will now, due to a deepening anesthetic plane, be too high. If pre-anesthetic agents are used - all settings should be drastically reduced (usually up to 30%).
Can you use Nitrous Oxide with the Stephens?
Yes you can, you will require another bank of monitors and regulators and much higher flow rates. Anesthetic usage will also quadruple.
How much anesthetic do you put in the anaesthetic jar?
There are lines indicating the level for Isoflurane, Halothane or Methoxyflurane.
When do you lower the sleeve in the vapouriser and what effect does it have on anesthetic concentration?
The sleeve in the vapouriser may be lowered in order to increase the anaesthetic concentration. For example when no pre-meds are used and you want to mask induce, a very small animal. If you create an open system with high flow rates, for example if anesthetising a bird then put the sleeve in the down position and this will help increase the anaesthetic concentration.
What happens to the anaesthetic concentration of an animal when it is hyperventilating and how do you correct the situation?
A hyperventilation on the Stephens machine occurs when an animal is too lightly anesthetised. The anaesthetic concentration is normally too LOW. The situation can be corrected by turning up the vapouriser to a higher setting. For a few breathers then returning to a lower setting usually the 3/8 or 1/4 setting.
What do you check when an animal is too lightly anesthetised?
-
Is the endo tube correctly positioned and inflated.
-
Does the vapouriser contain anaesthetic liquid?
-
Is the setting of the vapouriser main control correct?
-
Excess leakage from the system due to a loose connection.
-
Oxygen flow too high causing dilution of anaesthetic concentration.
What are the oxygen levels required when using the Stephens?
3 - 5ml per pound or 5 - 10ml per kilo body weight per minute.
What do you check if the bag overfills?
-
Excessive oxygen inflow.
-
Kink or obstruction has occurred in the breathing hose or endo tube.
-
A fall in body temperature with a resultant decrease in oxygen consumption.
-
A fall in cardiac output with a resultant decrease in oxygen uptake.
What do you check if the animal is too deeply anesthetised?
-
The position of the sleeve in the vapouriser, it should be in the “up” position.
-
Setting on the vapouriser control (may be too high).
-
Vapouriser over full (above the designated level for agent).
-
Soda Lime exhausted.
What may be causing a leak in the Stephens?
The connections are not fitting together properly. Check that the canisters are pushed together tightly and especially check around the vapouriser does the cork gasket need replacing. Check the cuff inflation on the endotracheal tube.
When do I remove the endotracheal tube?
When the swallowing reflex reappears, a little before this for cats.
What special precautions are needed for small animals?
On small animals where basal oxygen flow may be difficult to regulate, fill the rebreathing bag 2/3 full and almost shut off the oxygen flow. Refill the bag when the animal’s needs have reduced the bag to less than 1/2 full.
What procedures do I follow at the end of an anesthetic?
To terminate anesthetic, turn off the vapouriser, flush with oxygen to clear the machine of anaesthetic and allow the animal to breathe oxygen before detaching from the machine. To speed up anaesthetic recovery, turn off the vapouriser before the end of the surgery/anesthetic . After a long procedure, the machine should be dried to remove the water vapour, particularly with large dogs. This is due to the absorption of carbon dioxide within the soda lime canisters which produces both heat and moisture.
Related Information
Introduction to in-circle closed circuit Anesthesia
Low flow and closed circuit Anesthesia for veterinarians
Parts Diagram Of The Stephens
A detailed Diagram showing the components of the Stephens Anesthetic Machine
|
iM3 has designed a unique Oil Free portable Dental compressor. The advantage of the oil free is its quiet, easy to clean & easy to maintain. ...
Clear canine and feline dental model set with educational card only US$129.00 SET ...
iM3 is proud to support our local and international veterinary markets ...