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Anesthesia

Anesthesia is frequently a team effort consisting of the surgeon who may give a local anesthetic and/or a physician anesthesiologist and certified registered nurse anesthetist (CRNA) who may give sedation or a local, regional, spinal or general anesthetic.

  • Preparation for anesthesia
    1. Pre-admission testing - the patient is evaluated by the anesthesiologist prior to surgery. The patient's heart and lungs are examined. The patient's medications are evaluated to be sure that there is no conflict with the anesthetic to be used. Any allergies are determined. To facilitate this process the patient may complete the Pre-Surgery Information Form and take it to the hospital
    2. Laboratory tests such as blood count, urine analysis and pregnancy test (between ages 12 yrs to 50 yrs) may be obtained. Other tests may include blood clotting studies, EKG (heart tracing) and chest X-ray
    3. The patient is kept without food or fluids for at least 6 hours before surgery. This assures that the stomach is empty and the patient will not aspirate stomach content should he/she vomits
    4. A needle is inserted into a vein to give fluids usually a saline and dextrose (salt and sugar) solution
  • Local anesthesia - the injection of a drug into the skin or around a nerve in non-toxic concentrations to block pain impulses. (Figures 1,2) Sometimes the local anesthetic is mixed with a steroid (cortisone) to reduce inflammation. This is particularly so when used in a joint
    1. Local anesthesia is reversible with the length of the effect of the anesthetic varying depending on the drug used, the concentration of the drug and whether the drug is mixed with epinephrine
    2. Epinephrine causes the local blood vessels to constrict and thus slows the removal of the drug
    3. Some local anesthetics and their length of action when used for injecting in the skin or around a nerve are:
Local AnestheticLength of Action in HoursLength with Epinephrine (Hr.)
 Procaine  0.25 - 0.5   0.5 - 1.5
 Lidocaine  0.5 - 2.0  1-3
 Mepivacaine  0.5 - 2.0  1-3
 Bupivicaine  2 - 4 3 - 6
 Tetracaine  2 - 4  4 - 8
Figure 1 - Intercostal block. Local anesthetic is placed around the nerve lying between the ribs. Used for certain types of chest pain. © T. GravesFigure 2 - Anesthetic block of the sciatic nerve. © T. Graves
    1. Procedure
      • The skin over the site of injection is cleansed with antiseptic solution
      • The local anesthetic is placed in a syringe attached to a needle. The anesthetic is infiltrated into the skin or around the nerve to be anesthetized
      • The surgical procedure is then carried out
    2. Complications
      • Toxicity occurs when an excessive amount of drug enters the blood stream. This may cause confusion, dizziness, numbness around the mouth, metallic taste in the mouth, ringing in the ears, disturbances of vision and seizures. The drugs may also cause severe lowering of blood pressure and collapse of the heart and blood vessel system
      • Allergy to the drug may occur with itching, burning and formation of skin wheals; spasm of the bronchi (tubes to the lungs); low blood pressure and allergic shock
    3. Post-operative care - the patient usually may go home following a local anesthetic though this may be delayed as a result of the associated surgical procedure
  • Regional anesthesia - the injection of a local anesthetic into the tissues around a group of nerves such as the nerves exiting the spine in the neck, in the axilla (arm pit) for upper extremity blocks or the nerves in the region around the waist area for lower extremity blocks. (Figure 3)
    1. The drugs used and the possible complications are listed under local anesthesia
    2. The patient is usually kept NPO (nothing per os, nothing by mouth) because the regional anesthetic may have to be supplemented with sedation or a general anesthetic
  • Intravenous (IV) block anesthesia (Bier block anesthesia) - is a special form of regional anesthesia that is reserved for surgery of the arm or hand. A needle is placed in a vein of the arm and a tourniquet placed above the elbow. The tourniquet is inflated following which a local anesthetic is injected into the vein. The tourniquet keeps the anesthetic within the arm (Figure 4)
    Figure 3 - Brachial block. Local anesthetic is placed around the nerves that go to the arm. © T. GravesFigure 4 - IV block anesthesia. The anesthetic is injected into a vein and is limited to the arm by the tourniquet. © T. Graves

     

    1. This type of anesthesia is best reserved for procedures that can be done under one hour
    2. Some patients may have some numbness or tingling sensation in the arm for up to one hour after the anesthetic is completed
    3. The drugs used and the possible complications are listed under local anesthesia. A complication of particular concern is too early deflation of the tourniquet with release of the anesthetic into the bloodstream before the anesthetic is bound to the tissues of the arm. This can result in severe lowering of blood pressure and collapse of the heart and blood vessel system
  • Spinal anesthesia - the injection of a small amount of local anesthetic into the fluid that surrounds the nerve roots in the lumbar spine. (Figure 5)
    1. Anatomy
      • The spinal cord is an extension of the brain that lies in the center of the spinal canal. At each level along the spinal cord, nerve roots are given off that form the nerves of the body. The nerve roots at the end of the spinal cord form the nerves to the legs and together
        Local AnestheticLength of Action in HoursLength with Epinephrine (Hr.)
        Lidocaine 5% (60 mg.) Hyperbaric0.75 - 1.5 1 - 1.5
        Bupivicaine 0.75%(9 mg) Hyperbaric2 - 42 - 4
        Tetracaine 1%(12 mg) Hyperbaric2 - 33 - 5
        is called the cauda equina (because the roots look like a horse's tail)
      • The spinal cord is bathed in a fluid called cerebrospinal fluid (CSF). The fluid is contained in a fibrous sac called the dura that lines the inside of the bony spinal canal
      • The segments of the spine are called vertebrae and are held together by tough fibrous bands called ligaments. The spine is surrounded by muscles
    2. Procedure
      • The skin over the vertebrae in the low back is cleaned with antiseptic solution
      • A thin, three inch needle (spinal needle) is inserted through the skin and directed through the muscles, ligaments and dura into the CSF
      • The local anesthetic drug is usually mixed with a concentrated sugar solution that is heavier than CSF (hyperbaric solution). This hyperbaric solution can be positioned by tipping the patient head up or down
      • A local anesthetic drug is injected into the CSF and the patient positioned to allow the drug to flow towards the head until the desired level of the body is anesthetized
      • Surgery is begun after the desired level of anesthesia is reached
    3. Length of action of local anesthetics for spinal anesthesia:
    1. Contraindications
      • Infection in the skin near the site of needle placement
      • Increased pressure inside the head (from head injury, brain tumor, etc.)
      • Bleeding tendency
      • Generalized infection in the body
      • Possible relative contraindications are low blood pressure, disease of the brain or spinal cord, chronic low back pain and aortic stenosis (See Heart Valve Surgery)
    2. Complications
      • Low blood pressure may occur because of paralysis of the nerves to the blood vessels in the area of anesthesia. This may be worse if the patient has associated heart disease
      • High spinal blockade occurs when the level of anesthesia goes too high. This may result in low blood pressure and loss of the ability to breath that may require assisted breathing
      • Headache may occur because of the loss of CSF through the needle hole in the dura. This is made worse by standing. The headache is relieved by fluids either by mouth of through a vein and pain medication
      • Infection, though rare, can cause meningitis
      • Epidural hematoma occurs when a blood clot forms between the ligaments and dura. It occurs rarely
      • Permanent nerve root injury may occur but is very rare
      • Inability to pass urine, which may require a catheter
  • Epidural anesthesia
    1. Epidural anesthesia is like a spinal anesthetic except that the needle is placed through the ligaments of the spine but not through the dura
    2. The anesthetic drug (see local anesthesia) is injected into the space between the ligament and dura (epidural space). This may be a single injection through the needle or, more commonly, a flexible catheter may be placed through the needle into the epidural space and anesthetic injected over a period of time for during and after surgery pain relief. This type of anesthesia is commonly used during delivery. (Figure 5)
    3. After the anesthetic is injected into the epidural space the anesthetic passes through the dura into the CSF and around the nerve roots of the cauda equinae. Epidural anesthesia develops more slowly than a spinal anesthetic because the drug must pass through the dura to work
    4. The degree and length of anesthesia is determined by which drug is use and the amount injected
    5. The anesthetic may be mixed with a steroid (cortisone) for treatment of back pain
    6. Complications are similar to those noted with spinal anesthesia
Figure 5 - Upper needle lies in the subarachnoid space for the injection of the anesthetic. Lower needle is in the epidural space. A small catheter is inserted through the needle into the epidural space after which the needle is removed leaving the catheter in place. © T. Graves
  • Sedation
    1. Degree of sedation
      • Minimal sedation is when drugs are used to relax the patient but the patient respond normally to spoken commands. Although thinking and coordination may be impaired, heart and lung function does not alter
      • Moderate sedation (sometimes called 'conscious sedation') is a drug produced decrease in consciousness during which the patient is able to respond to commands either alone or with light stimulation. The patient does not require any assistance in maintaining an airway and breathing is not assisted. Heart function is usually not affected
      • Deep sedation is when the drugs produce a decrease in consciousness during which the patient cannot easily be aroused but does respond to repeated or painful stimulation. The ability to maintain breathing may be impaired and the patient may require assistance in keeping the airway open and in breathing. Heart function is usually not affected
    2. Uses for sedation
      • Supplement to local anesthesia - under some circumstances in which local anesthetics are used the surgeon may have sedation administered by a nurse without the presence of an anesthesiologist or CRNA
      • Monitored anesthesia care in which an anesthesiologist or CRNA is present to administer the sedation and monitor the progress of the patient
    3. Drugs used for sedation
      • Benzodiazepines - the drugs in this group are midazolam (Versed) and diazepam (Valium)
      • Narcotics - some of the longer acting drugs in this group are meperidine (Demerol) and morphine. Shorter acting narcotics such as fentanyl are also used
      • Intravenous (I.V.) short acting anesthesia - this group of drugs, such as propofol (Diprivan), produce anesthesia as long as the drug is being given I.V. Once the drug is stopped the patient arouses rapidly
    4. Complications
      • Respiratory depression - this may result in inadequate breathing and lack of oxygen in the blood
      • Depressed airway reflexes - this may reduce coughing and removal of secretions from the lungs
      • Low blood pressure
      • Death may result if inadequate respiration or shock occurs
  • General anesthesia is total loss of consciousness as a result giving drugs. Patients usually loose the ability to maintain their airway and require assistance in breathing. A general anesthetic provides analgesia (loss of pain), amnesia (memory loss) and relaxation of muscles
    1. Monitoring - the patient is monitored for heart rhythm, blood pressure and the concentration of oxygen and carbon dioxide in the blood (Figure 6)
Figure 6 - Modern anesthesia machines accurately meter the appropriate anesthetic gas mixtures. Blood oxygen and airway carbon dioxide concentrations are continuously monitored, as are the EKG (electrocardiogram) and blood pressure
    1. Induction (starting) of anesthesia is usually with a rapidly acting drug given I.V. such as thiopental, propofol or etomidate
    2. Airway management
      • The patient may be allowed to breath spontaneously particularly if a muscle relaxant does not have to be used
      • Intubation is used to protect the airway, control ventilation and prevent aspiration of mucous or stomach contents. The tube is placed through the vocal cords into the trachea. (Figure 7) See Laryngectomy
Figure 7 - During a general anesthetic, the airway is protected by the insertion of a tube (endotracheal tube) through the mouth and into the trachea (windpipe). A low pressure balloon is inflated between the tube and trachea wall to prevent secretions or stomach contents from getting into the trachea. © T. Graves
    1. Muscle paralysis is used to help in intubation and may be required for certain surgical procedures. There are a number of drugs used for this purpose some that are short acting while others may last hours
    2. The anesthesia is maintained by:
      • Inhalation agents (volatile anesthetics, gas) such as isoflurane, desflurane, sevoflurane and nitrous oxide alone or in combination; are frequently used to maintain anesthesia
      • Drugs given I.V. such as narcotics and strong sedatives
    3. Other medications may be necessary to control blood pressure and heart rhythm
    4. After surgery is completed the anesthetic is stopped and the patient is allowed to awake. Care is taken to be sure that the airway is maintained until the patient is fully awake
    5. Complications
      • Laryngospasm may occur if the vocal cords are stimulated when the patient is coming out of anesthesia. The vocal cords are brought together forcefully, which obstructs the airway
      • Nausea and vomiting may occur in 1/3 of patients
      • Urinary retention (inability to urinate) occurs in about 3% of patients particularly those that have pelvic operations
      • Hypothermia (low body temperature) may occur because the muscle action that produces heat is lost. This is especially so in children. Special heat blankets may be used to prevent heat loss
      • Malignant hyperthermia is a marked rise in body temperature associated with rapid heart rate, rapid breathing, high blood pressure and muscle rigidity. This must be treated rapidly to prevent brain damage
      • Dental injury may occur. A loose tooth may have to be removed for fear that the tooth fall into the windpipe. A tooth or permanent bridge may be chipped or broken during a difficult intubation
      • Nerve injury
      • Death with any anesthesia is a possible and must always be considered before consenting for surgery
    6. After surgery the patient is taken to the post-anesthetic recovery room where nurses under the direction of the anesthesiologists carefully monitor the patient and then patient sent back to the room or home in case of an outpatient surgery