Anaesthetics - spinals, femoral blocks, GAs and everything else

[Josephine]

There is a difference between a spinal and an epidural.

Spinal

With a spinal, the anesthetic drug is injected into the spinal fluid below where the spinal cord itself terminates. Most of the time the drug will be placed at the L4/5 level, but this can be adjusted by the anesthesiologist in some cases to accommodate fusions. The drug is administered as a one shot and it usually lasts about 4-6 hours.

Epidural

In an epidural, the drug is injected into the space outside the dura. The dura is the membrane that surrounds the spinal cord and contains the cerebral-spinal fluid. Hence the term "epi" dural meaning "close to" the dura.

Sometimes a very fine catheter is placed in this spot and taped up the patient's back to be accessed at the shoulder so additional anesthetic can be administered if needed for procedures that might take several hours.

The anesthetic effect of both a spinal and an epidural is the same - numbness which is generally as high as T7 (7th thoracic vertebra) just under the breasts. Since this has a potential impact on the diaphragm, patients must stay under close supervision in recovery until the level reduces to around T12 when respiration is no longer compromised. Nurses typically will check the level of sensation at regular intervals using a cold spray.

Headaches

Headaches from spinals are quite rare, though headaches from epidurals are a little more common. This is because in an epidural, the needle and cannula go into the cerebrospinal fluid (CF). On occasion there can be some CF loss which inevitably lowers the pressure inside the ventricles (fluid spaces) in the brain and this is what causes the headaches. Spinals don't enter the CF space, so CF loss doesn't happen and therefore neither do the headaches.

Updated May 8, 2020 by Jamie

 

[Josephine]

Femoral block in knee surgery

A means of providing extra pain control in combination with either a general or spinal anaesthetic. It will last some hours longer than a spinal, generally up to 24hrs. Sometimes called a triple nerve block because of the way the nerve divides into three.The femoral nerve travels from the groin down the front of the thigh where it divides.

An injection is placed in the tissues very close to this nerve. The placement is checked using a small metre which registers neural activity. Small, fine electrodes are placed and adjusted until they are as close to the nerve as possible without actually penetrating it. Then the local anaesthetic is injected. This can be with a one-off injection or a fine cannula is sometimes placed so top-ups can be given if the period of anaesthesia needs to be extended.

Anaesthetist checking the position of the nerve with the nerve stimulator. The unit can be seen in part at the top of the picture.

Some people worry about this procedure being more difficult if your leg is heavy...it is not. The correct location is determined by the use of a little monitor attached to the needle. When the needle is inserted in the vicinity of the nerve, a very tiny electric impulse is sent down it which will only get a response when the tip of the needle is in the correct proximity to the nerve. If it is in the correct spot, the impulse makes nerve respond causing the adjacent muscle fibres to twitch which makes the needle twitch and this is what the anaesthetist is watching for! It also registers on the machine where a needle pings back and forth with the nerve responses. It's all clever stuff these days and success is almost always guaranteed!

The area of numbness is quite extensive and can result in loss of co-ordination and function until the block lifts.

As a result of this, it is usually necessary for the patient to remain in bed for 24hrs after a single dose block or longer if they have had a top-up.

 

[Josephine]

WILL I BE AWAKE DURING SURGERY?

Another issue people worry about is being awake during the surgery. This isn't routine. You can choose to stay awake if that's your preference or you can choose to be sedated so you sleep peacefully throughout. You will, however, be awake during the placement of the spinal/epidural and get sedation once it's working.

Most anaesthetists will sedate patients anyway but you should feel perfectly free to state your preference which you can do any time even up to point they are putting in your spinal or epidural!

It's no big deal and anaesthetists will happily comply with whatever you request.

 

[Josephine]

GENERAL ANAESTHETIC

PREPARATION
First thing is always to have an IV access created. This requires the insertion of an IV cannula, often called a Venflon though other brands are used! It's a bit like Biro or Hoover - those trade names that became the generic name for this kind of thing!

This cannula will have an IV bag attached to it to give the patient fluids during the procedure but more importantly to keep a working IV access open to the anaesthetist at all times. The little pink port pointing upwards can be flipped open and a syringe attached so he can administer drugs any time and, in the anaesthetic room, often without you even knowing! Hence the sudden descent into sleep that people often remark upon.

FACE MASKS
Before anything else, an anaesthetist might require the patient to be pre-oxygenated which means a mask will be placed over the face with nothing but pure oxygen running through it. Some people might find this a bit claustrophobic, but just remember that any anaesthetic drugs will be given via the Venflon and not the mask, so you can rest assured that you are only breathing pure oxygen!

INTUBATION WITH AN ENDOTRACHEAL TUBE
For use of an endotracheal tube, an IV muscle relaxant called suxamethonium must be given in order to intubate. It is essential that the vocal chords and larynx are paralysed during this procedure which requires the use of a laryngoscope to get direct vision of the vocal chords for correct placement.

To maintain total relaxation further doses are given in small quantities throughout the surgery, just enough to keep the patient totally relaxed. This is in addition to other drugs and inhalation agents given to maintain unconsciousness. Because is this, the patient is unable to breathe and is therefore attached to a ventilator. Once the surgery is reaching its conclusion, the anaesthetist will commence the reversal of the suxamethonium so the patient starts breathing spontaneously again. It is at this point that the tube is removed and very shortly thereafter, the patient will begin to regain consciousness and be transferred to the recovery room, often before they are fully awake.

LARYNGEAL MASKS (which staff often called "larry masks" for short)
This device is a cross between a tube and a face mask and no paralysing agent is required to insert it. It goes into the throat, beyond the tongue into the larynx and closes off both the oesophagus and the trachea, protecting the airway should any fluid be regurgitated from the stomach. It's very soft, with an inflated ring which causes no irritation to the throat at all.

Removal occurs as the patient is regaining consciousness but before they are even aware of their surroundings. That phase can take about 4-5 minutes in all. Once the larry mask is out and the patient is made comfortable in their bed, they will likely relax and sleep again until taken into recovery where the nurses will rouse them again!

That's the bit everyone remembers, saying they knew nothing until they woke up in recovery!

 

[Josephine]

Cricoid pressure

Sometimes in an emergency, it's not possible to starve a patient to ensure an empty stomach. This may be in A&E/ER after accidents or in the operating theatre if sudden serious illnesses require emergency surgery. The safety procedure employed here is known as cricoid pressure.

The cricoid cartilage is more commonly known as the Adam's apple, the hard prominent structure in the neck of males. Women have these too, they're just not as prominent! As you can see in the image, the oesophagus lies directly behind this ring of cartilage so pressing on it closes the oesphagus and prevents any stomach contents regurgitating into the throat where they risk being inhaled.

Cricoid pressure is applied by the anaesthetic assistant just immediately prior to the administration of the intravenous anaesthetic and maintained until either the endotracheal tube or laryngeal mask is safely in place. The assistant should gently inform the patient that s/he is going to "just hold the front of your neck while you go to sleep" so they are not alarmed.

Very often the patient will be pre--oxygenated by mask in the minutes before the anaesthetic is administered.

 

[Josephine]

Saphenous Nerve Block vs. Femoral Nerve Block for Total Knee Arthroplasty
Hospital for Special Surgery, New York December 2013

Currently, the regional anesthetic standard of care for total knee replacement surgery is combined spinal/epidural to provide long-lasting pain relief with or without a femoral nerve block (FNB). The femoral nerve block refers to a technique that your anesthesiologist can use to numb the thigh muscle for approximately 18 hours after surgery. While this technique offers significant pain relief, it is possible it may cause muscle weakness and increase patients' recovery times. Hence there is a need for an alterative anesthetic technique, one that may help minimize postoperative pain as effectively as a femoral nerve block, while not causing weakness of the thigh muscle.

The saphenous nerve, a branch of the femoral nerve, provides sensation to the knee. Thus it is hypothesized by "blocking" or anesthetizing the saphenous nerve with local anesthetic closer to where it branches off, the area around and below the knee will feel numb. Yet unlike the femoral nerve block, the thigh muscle itself will still be able to function.

Upated July 26, 2017 Josephine