Table of Contents
The word anaesthesia stems from the Greek term anaistesia (Gr. numbness). Anaesthesia refers to numbness, in particular the lack of any sense or perception.
General Anaesthesia vs. Local Anaesthesia
- General anaesthesia temporarily cancels out all sensations and, therefore, also affect the pain perception of the brain. This form of anaesthesia is used in operations that are not bearable for patients when they are awake.
- Local- or regional anaesthesia prevents the transmission of pain from a certain point in the body to the brain. Here specific peripheral nerves get blocked reversibly with a local anaesthetic, sensations from other areas of the body, however, are maintained. The patient is awake and can react adequately.
General Anaesthesia – The “Full Anaesthesia”
The goal of general anaesthesia is to bring the patient into a temporary state under which the operation can be performed most successfully, both for the patient and the operator:
- Unconsciousness (hypnosis), freedom from pain (alganaesthesia), dullness of vegetative reflexes (patient)
- Muscle relaxation and, therefore, good access to the area that is being operated (operator) as well as a simplified intubation (anaesthesiologist)
At the same time, the procedure needs to be technically safe and influence the patient’s vegetative functions (breathing and circulation) in the least possible way.
Normally, general anaesthesia is initiated intravenously and then continued via an inhalational anaesthetic (balanced anaesthesia) or an intravenous anaesthetic (total intravenous anaesthesia, TIVA). Both procedures can be viewed as equally effective in principle.
Respiratory System Protection
The medications that are used for general anaesthesia lead to a respiratory depression up to a complete stagnancy of respiration of the patient. Patients are therefore given artificial respiration during narcosis. There are various procedures with different indications for a patient’s artificial respiration.
- Narcosis with a mask: This least invasive procedure is being used for initiation of narcosis as well as for very short interventions in supine or lithotomy position. Some of the disadvantages of this procedure are the lack of separation of respiratory system and gastrointestinal tract as well as the fact that the anaesthesiologist needs to hold the mask and breathing bag throughout the entire operation, making the presence of an assistant indispensible.
- Larynx mask narcosis: This mildly invasive procedure makes use of a lens tube with an inflatable mask that is inserted in the throat up to the larynx. The air filled mask nestles up against the pharynx and around the epiglottis. The mask, however, does not offer a safe aspiration protection, which is why artificial respiration via a larynx mask may only be applied to sober patients. The larynx mask is used for surgical interventions on body surface or extremities, ENT- and eye surgery as well as ultima ratio in childbirth (emergency sectio).
- Intubation narcosis: Artificial respiration with an endotracheal tube is the safest and most invasive technique. The tube is inserted either through the mouth (oreotrachial intubation) or the nose (nasotracheal intubation) and ends in the trachea via the glottis. One of the advantages of the endotracheal intubation is that the patient is protected from aspiration of foreign bodies (saliva, blood, stomach contents). The patient can be attached to a respirator. It is strongly recommended that patients who are not sober, pregnant, receive lung, stomach or thorax surgery or have strong adiposity do not receive an intubation.
Procedure of Inhalational Anaesthesia
After initiation of narcosis through a quickly acting inhalational or IV analgesic (e.g. the intravenously injected Propofol), the anaesthesia can be continued by means of inhalational anaesthetics such as Isofluran, Sevofluran or Desfluran. The medication is added to a gas mixture consisting of O2 and ambient air or nitrous oxide (N2O).
The inhalational anaesthesia can be executed as mask (larynx mask) or intubation narcosis.
Balanced Anaesthesia Procedures
Additionally, short- and long-term effective opioids can be added to the analgesic effect. The combination of inhalational narcotics and intravenously injected opioids is formally known as balanced anaesthesia. It represents the most common form of anaesthesia and is characterised by good controllability with regard to surging of the anaesthetic, control of narcotic depth and elimination.
Evaluation of the Narcosis
The patient’s blood pressure response is monitored for the evaluation of the anaesthetic’s depth. A too shallow level can express itself through an increase in blood pressure and heart rate, a deepened spontaneous respiration for spontaneously breathing patients, and through defensive movements by non-muscle relaxed patients. The reason for this is the release of catecholamine due to pain.
A good narcosis management is marked by the fact that the narcosis is being held as shallow as possible without displaying the symptoms of a too shallow narcosis mentioned above. To achieve this state, it is important to have knowledge about the exact course of the operation and to closely observe it in order to adjust the depth of narcosis to the respective phase (e.g. painful cut). As the inhalational anaesthetic’s onset of action occurs out of phase, the anaesthesiologist needs to know the course of the operation in order to adjust the alveolar concentration of the anaesthetics to the surgical stimulation.
|Advantages of inhalational anaesthesia||Relatively stable haemodynamics and only mild post operative respiration depression|
|Disadvantages/dangers of inhalational anaesthesia||Insufficient post operative analgesics have been noticed after purely inhalational narcoses because quick surging often causes muscle spasms and nausea/vomiting (“postoperative nausea and vomiting” – PONV)|
TIVA – Total Intravenous Anaesthesia
General anaesthesia can also be conducted with purely intravenously administered substances. This case is known as total intravenous anaesthesia (TIVA).
Here, no inhalational anaesthetic is being used. Instead, an intravenously injected hypnotic (e.g. Propofol) in combination with an opioid (e.g. Remifentanil, which has a very short half-life) and perhaps a muscle relaxer is applied. Artificial respiration of the patient is carried out through an O2-mixture. Laughing gas is not used.
The goal of the TIVA procedure is to quickly reach a Steady State with constant plasma levels of the drugs. The depth of the narcosis should be directly adjusted to the surgical phase, which is why substances with a quick elimination (e.g. the combination of Propfol/Ramifentanil) are used.
Indications of TIVA
The TIVA is especially handy for short surgical interventions with a consistent depth of narcosis (e.g. minimally invasive surgery, ambulant anaesthesia). When anamnestic cues for malignant hyperthermia are present, a TIVA without the usage of trigger substances may be conducted.
Advantages of TIVA
The patients wake up quickly after the operation, which is why total intravenous anaesthesia is preferred in the ambulant field. The frequently used Propofol shows an antiemetic effect so that postoperative nausea occurs less frequent.
Pain transfer from a specific body region up to the brain is selectively prevented in regional anaesthesia. In this procedure, the respective peripheral nerves are selectively disabled using a local anaesthetic. Local anaesthetics are drugs that prevent the depolarisation of nerve cells by blocking their sodium channels. Due to the so-achieved membrane stabilisation, no depolarisation and therefore no transmission of impulses can occur. Most of the time, local anaesthetics are injected close to the peripheral nerves and then diffuse to the nerves.
Complications of Local Anaesthesia
The drugs can, however, also diffuse into the bloodstream and, thus, develop side effects in the brain and the heart. At high concentrations, local anaesthetics can surge e.g. in the brain and unfold a toxic effect by creating an unwanted stabilization of the membrane there.
The heart’s conduction system can be negatively influenced by a toxic blood concentration caused by a local anaesthetic. This leads to a decreased heart rate, AV blockage, decrease in heart strength and blood pressure as well as a possible cardiac arrest.
Anaphylactic reactions to local anaesthetics are also possible, which may express themselves through urticaria, an asthma attack or a decline in blood pressure up to an anaphylactic shock.
Advantages of Local Anaesthesia
Altogether, local anaesthesia presents low strains for the entire organism, fewer incidents, an easier medical attendance after the operation and the possibility of treating non-sober patients.
Local And Regional Anaesthesia Procedures
- Surface anaesthesia (mucosal anaesthesia): A local anaesthetic is applied onto the mucous membrane area, causing the sensitive nerve ends lying there to be blocked. Application: e.g. before the male urethral catheterization in form of a local anaesthetic containing lubricant, EMLA-crème for siting of peripheral venous adituses in child anaesthesia.
- Infiltration anaesthesia: Local (intradermal, subcutaneous or intramuscular) injections of local anaesthetics into the area of operation, blocking the sensitive nerve endings in this area. Application: e.g. for wound treatment. A local anaesthetic with adrenaline supplementation may be used, which leads to a local vasoconstriction. This has the advantage of a slower resorption and an increased duration of action, while systematic-toxic side effects can be reduced.
Conduction and local anaesthesia
- Peripheral nerve blockage (injection CA close to the nerve, diffusion into the nerve): Simultaneous deactivation of the nerve’s supply zone. Application: e.g. alveolaris inf.-blockage at the dentist
- Plexus anaesthesia, “blockage of axilliaris”: Plexus brachialis blockage in the area of the arm pit enables pain blockage in the hand, forearm and parts of the upper arm; “snatch block” of the plexus lumbosacralis
- Conduction anaesthesia close to the spinal cord
- Spinal anaesthesia: Inserting local anaesthetic into the spinal canal, enabling blockage of pain in the lower half of the body
- Peridural/epidural anaesthesia: The local anaesthetic is being placed in the peridural area for the peridural anaesthesia (PDA). The peridural area lies behind the ligamentum flavum of the spine and contains fat and connective tissue as well as tender venous plexuses. The dura mater is not damaged during the PDA.
Indications and Contraindications of Local Anaesthesia
- Advantage: Problems of day-to-day anaesthesia, such as unsatisfying soberness of patient or difficulties in securing the respiratory system can be bypassed.
- Disadvantage: Regional anaesthesia are often unsuitable for ambulant anaesthesia due to the time-consuming procedure and the long duration.
|Contraindications of regional pain blockage:||
|Contraindications of a plexus blockage:||
Procedures Close to the Spinal Cord
- Spinal anaesthesia: Placing the local anaesthetic in the spinal canal and into the cerebral fluid interspaces makes it possible to block pain in the lower half of the body and is therefore used as anaesthetic for operations of legs, hips, abdomen and the groin area. Spinal anaesthesia has also become the standard procedure with C-sections (section caesarea).
- Peridurial anaesthesia (= epidurial anaesthesia): Injection of the local anaesthetic in the epidural space around the dura mater (but not in the venous plexus). In opposition to spinal anaesthesia, the dura mater does not get pierced here. Theoretically, the PDA can be applied at any point on the spinal cord, as the dura does not get injured. A thoracic PDA demands highest caution and expertise due to the risk of injuring the spinal cord.
|Advantages of epidural anaesthesia over spinal anaesthesia:||
|Disadvantages of epidural anaesthesia:||
Procedure of Spinal Anaesthesia
Spinal anaesthesia may only be conducted below the third lumbar vertebra to avoid injury of the spinal cord (usually the spinal cord ends at L1/L2 under which the nerve fibres form the cauda equina, which easily dodge the incoming cannula).
Spinal punctuations can be applied to both sitting and procumbent patients. The patient’s posture is important – he/she needs to form a humpback (“a cat’s arched back”) in order to enlarge the spaces between the acanthae of the spine.
The most widely used point of injection is positioned at L3/L4. The punctuation spot is found by placing the hands flat on the patient’s iliac crests; that way both thumbs meet about where the acanthi of L4 is. The punctuation location should be marked (e.g. by applying pressure with thumb nails) in order to still be visible after disinfecting.
Procedure of a spinal anaesthesia:
- Once disinfected, a sterile fenestrated drape my be affixed.
- Skin and deeper band structures are numbed with a local anaesthetic. Subsequently, a guide cannula is pierced through the lig. Interspirale.
- The thin spinal cannula may now be inserted through the guide cannula. The fibers of the dura mater are pushed apart by the spinal cannula’s polish if held correctly, instead of poking a hole in the dura mater. The duraperforation can often be felt as a small “click”. By removing the mandrin from the spinal cannula, one can make sure that the needle syringe lies in the cerebral fluid interspaces: If it lies correctly, clear liquor will drop out of the cannula.
- Now, the local anaesthetic may be injected. A small amount of liquor should be aspirated beforehand to be absolutely sure that the tip of the needle is still in the correct cerebral fluid interspace.
- After removing the cannula, the location of punctuation may be covered with a sterile bandage.
Possible Complications with Spinal Anaesthesia
“Post-punctual headache” (ICD10-Code: G97.1 – Further reactions to spinal and lumbar punctuation)
Liquor may flow through the hole in the dura from the spine into the peridural area. This results in losing a small amount of liquor, which may bear small displacements of the brain and spinal cord as consequence. Ultimately, a dragging pain at the meninges results, which probably leads to strong, mostly analgesic-incompatible headaches.
Therapy of post-punctual headache
Positioning the patient horizontally for the first 24 hours after the punctuation can delay the post-spinal headache, but does not prevent them completely. Caffeine and theophylline may be administered pharmacotherapeutically. Usually the headache wears off after a few days. If this does not happen, one can execute a peridural blood patch. Here the patient’s blood is gathered and injected into the peridural space at the point of punctuation. The clotting blood seals the hole in the dura, which usually results in a quick enhancement of symptoms.
Further possible complications
- Hypotension (due to the quick onset of the sympathetic blockage),
- Cranial nerve lesions (nervus abducens -> double pictures),
- Injuries of the spinal cord when punctuating too high, spinal anaesthetic may rise up too high and inhibit the intercostal respiratory muscles and heart sympathetic,
- Bacterial infection (->meningitis),
- Peridural hematoma (due to injury of venous vessels in peridural area, difficult to avoid) for existing clotting problems; In the worst case a compression of the spinal cord up to paraplegic symptoms may result from the forming hematoma. Therefore, it is absolutely necessary to perform a prior anamnesis and a test of blood clotting and to check for possible clotting complications or medication that may interfere with clotting.
Contraindications of the Spinal Anaesthesia
- Refusal by the patient or uncooperative patient who cannot hold still
- Allergy of LA
- Local infection at the point of punctuation, systemic infection (sepsis)
- CNS diseases
- Shock state (lack of volume)
- Complications with clotting, consumption of coagulation-inhibiting drugs (check quick-value / INR, PTT, thrombocytes)
- Suspicion of elevated intracranial pressure
- Headache anamnesis (relative contraindication)
- Anatomical changes at spine, perhaps juvenile age (relative contraindication due to the many post-punctual headaches
Possible Exam Questions on Anaesthetic Procedures
The answers can be found below the references.
1. In what area is the anaesthetic injected for the peridurial anaesthesia?
- Between dura mater and arachnoidea
- In the peridural venous plexus
- Between lig. flavum and dura mater
- Between pia mater and arachnoidea
- Between pia mater and spinal cord
2. Which procedure is not one of the common regional anaesthesia procedures?
- Infiltration anaesthesia
- Peridurial anaesthesia
- Spinal anaesthesia
- “Axillaris blockage”
3. Which of the following is not one of the contraindications of spinal anaesthesia?
- Skin infection at the third lumbar vertebra
- Allergy of local anaesthesia
- Hypovolemic shock
- Elevated intracranial pressure
Kretz, Schäffer: Anästhesie Notfallmedizin Schmerztherapie, Springer 2008
Striebel: Anästhesie, Intensivmedizin, Notfallmedizin für Studium und Ausbildung, Schattauer 2013
Angstwurm, Kia: Mediscript StaR Skriptenpaket Hammerexamen, Elsevier 2014
Correct answers: 1C; 2B; 3D