Special Techniques Ch.7 Objectives Flashcards
Define or explain the term sensory neuron
The primary targets of local anesthetic drugs are the neurons that convey sensations (i.e., pain, heat, cold, and pressure) from the skin, muscles, and other peripheral tissues to the brain. These neurons (called sensory neurons) are affected by even small amounts of local anesthetic, provided the drug is deposited in proximity to the neuron.
Define or explain the term local anesthesia
Local anesthesia is a method of pain management that temporarily numbs a specific area of the body by blocking nerve signals, allowing procedures to be performed without the patient feeling pain, while remaining conscious.
Define or explain the term motor neuron
Motor neurons (MNs) are specialized type of nerve cells in the central nervous system (CNS) that regulate voluntary and involuntary movements via transmitting signals from the brainstem and sensory systems to muscle cells.
Define or explain the term infiltration
In a veterinary context, “infiltration” typically refers to the leakage of a fluid or substance (like a medication) from a blood vessel into the surrounding tissues, which can occur during intravenous (IV) therapy or injections.
Define or explain the term line block
a line block, consisting of a continuous line of local anesthetic, can be placed in the subcutaneous or subcuticular tissues immediately proximal to the target area (Figure 7-2, A). If the line of local anesthetic completely encircles an anatomic part, such as a digit or teat, it is called a ring block.
Line blocks should be positioned between the target area and the spinal cord because this will block the sensory neurons most effectively. As with nerve blocks, the area is clipped and the skin prepared. A line block is performed by inserting the needle along the proposed line of infiltration, then gradually withdrawing the needle while simultaneously injecting a small amount of local anesthetic.
Define or explain the term nerve block
A nerve block is achieved by injecting local anesthetic in proximity to a nerve to desensitize a particular anatomic site. One familiar example is the use of Novocain (procaine) in human dentistry. Nerve blocks are used commonly in anesthesia of large animals and also may be used in small animals provided the location of the target nerve is known exactly. Reference texts contain illustrations that indicate the location of nerve blocks for different species and particular areas of the body. Before a nerve block is performed, the nerve is palpated to determine its location, although this may not always be possible if the nerve is small.
Define or explain the term ring block
If the line of local anesthetic completely encircles an anatomic part, such as a digit or teat, it is called a ring block.
Define or explain the term splash block
The use of sprays or soaked gauze sponges is called a splash block. The efficacy of this technique has not been well established, but it appears to be most effective if the surgical field is relatively dry, with minimal bleeding.
Define or explain the term epidural anesthesia
Epidural anesthesia is a regional anesthesia technique that is commonly used in both large and small animal patients. The procedure is not difficult (Procedure 7-3, p. 224) and, once mastered, allows the anesthetist reliably to block sensation and motor control of the abdomen, pelvis, tail, pelvic limbs, and perineum. The technique is useful for tail amputation, anal sac removal, perianal surgery, urethrostomies, obstetric manipulations, cesarean sections, and some hind limb operations.
Define or explain the term cauda equina
The spinal cord itself terminates in a group of neurons collectively called the cauda equina.
Define or explain the term tidal volume
The amount of air that passes into or out of the lungs in a single breath is the tidal volume (VT). Animals that are breathing deeply have a relatively large VT, whereas animals that have shallow breathing or that are panting have a relatively small VT. Normal VT in the awake animal is 10 to 15 mL/kg.
Define or explain the term respiratory minute volume
The respiratory rate or frequency is the number of breaths that occur in 1 minute. The respiratory minute volume is the total amount of air that moves into and out of the lungs in 1 minute. This value can be found by multiplying the average VT by the respiratory rate.
Define or explain the term atelectasis
In an anesthetized animal, VT is reduced and consequently the alveoli do not expand as fully as normal on inspiration. The alveoli in some sections of the lung, particularly those that are lower in the animal’s body, may partially collapse (a condition called atelectasis).
Define or explain the term controlled ventilation
In controlled ventilation, the anesthetist delivers all of the air or anesthetic gases required by the patient, and the patient usually does not make spontaneous respiratory efforts. The anesthetist controls the respiratory rate and the volume and pressure of gas delivered to the animal.
Define or explain the term assisted ventilation
In assisted ventilation, the anesthetist ensures that an increased volume of air, or, more commonly, oxygen and anesthetic gases, is delivered to the patient, although the patient initiates each inspiration. In controlled ventilation, the anesthetist delivers all of the air or anesthetic gases required by the patient, and the patient usually does not make spontaneous respiratory efforts. The anesthetist controls the respiratory rate and the volume and pressure of gas delivered to the animal.
Define or explain the term manual ventilation
The patient’s lungs are ventilated by the anesthetist using the anesthetic machine breathing circuit; this technique is referred to as manual ventilation. A common term that is also used to indicate manual ventilation is “bagging.” In this type of PPV, the lungs are filled with oxygen by the pressure of gas entering the airways as the anesthetist squeezes the reservoir bag with the pop-off valve fully or partially closed. Exhalation is passive and occurs when the positive pressure is discontinued and the pop-off valve is opened fully, allowing the lungs to empty.
Define or explain the term mechanical ventilation
The patient’s lungs are ventilated by a machine; this technique is called mechanical ventilation. In this type of PPV, the lungs are filled with oxygen by the pressure of gas from a special apparatus called a ventilator. As with manual ventilation, exhalation is passive and occurs when the positive pressure is discontinued.
Define or explain the term sympathetic blockade
This is most important in the sympathetic nervous system, and the loss of function of these neurons is called a sympathetic blockade. The main effect in the peripheral tissues is vasodilation, resulting in flushing and increased skin temperature of the affected area. If severe, vasodilation may cause blood pressure to fall, leading to hypotension. Sympathetic blockade can also be seen after epidural blocks with lidocaine and other local anesthetics, because sympathetic ganglia adjacent to the vertebrae are affected. If sympathetic blockade occurs within the thoracic spinal cord (as may occur if local anesthetic 217is allowed to diffuse into the thoracic spinal canal), sympathetic innervation to the heart may be blocked, resulting in bradycardia and impaired ventricular contractions, both of which are undesirable.
List the advantages and disadvantages associated with the use of local anesthetic agents.
Local anesthetic agents offer pain relief during procedures with minimal systemic effects and quick recovery, but carry risks like allergic reactions, nerve damage, and potential toxicity if overdosed.
Advantages:
Targeted Pain Relief:
Local anesthetics numb a specific area, allowing procedures to be performed without general anesthesia.
Reduced Systemic Effects:
Local anesthesia generally has fewer systemic side effects compared to general anesthesia.
Faster Recovery:
Patients usually recover quickly from local anesthesia and can return to normal activities sooner.
Simpler Administration:
Local anesthesia often requires less preparation and monitoring than general anesthesia.
Reduced Risk of Nausea and Vomiting:
Side effects like nausea and vomiting are less common with local anesthesia compared to general anesthesia.
Disadvantages:
Allergic Reactions:
Although rare, allergic reactions to local anesthetics can occur, potentially causing serious problems.
Nerve Damage:
In rare cases, local anesthesia can cause temporary or permanent nerve damage, leading to numbness, weakness, or pain.
Toxicity:
If too much local anesthetic enters the bloodstream, it can cause toxicity, leading to seizures, heart problems, or even death.
Pain at Injection Site:
Some patients experience pain, tenderness, or bruising at the injection site.
Prolonged Anesthesia:
In some cases, the numbness from local anesthesia can last longer than expected, causing discomfort or difficulty.
Incomplete Anesthesia:
In some cases, local anesthesia may not provide complete pain relief, requiring additional measures.
Infection:
Although rare, there is a risk of infection at the injection site.
Describe the ways in which local anesthetic agents may be used, including topical, infiltration, regional, intraarticular, epidural, and intravenous administration.
Local anesthetic agents can be administered via topical, infiltration, regional, intraarticular, epidural, and intravenous routes, each with specific applications and mechanisms of action.
Here’s a breakdown of each method:
1. Topical Application:
Mechanism: Local anesthetic agents are applied directly to the skin or mucous membranes to numb the surface area.
Examples: Creams, gels, ointments, sprays, or liquids.
Uses: Numbing the skin before injections, minor procedures, or painful procedures.
Examples of agents: Benzocaine, lidocaine.
2. Infiltration:
Mechanism: Local anesthetic agents are injected into the tissues surrounding a surgical site or area of pain to numb the nerves in that area.
Uses: Minor surgical procedures, dental procedures, suturing, and wound care.
Examples of agents: Lidocaine, bupivacaine.
3. Regional Anesthesia:
Mechanism: Local anesthetic agents are injected near a nerve or nerve plexus to block nerve transmission and numb a larger area of the body.
Types:
Nerve Block: Injection near a specific nerve or nerve plexus.
Spinal Anesthesia: Injection into the subarachnoid space surrounding the spinal cord.
Epidural Anesthesia: Injection into the epidural space outside the dura mater of the spinal cord.
Uses: Major surgeries, pain management, and childbirth.
Examples of agents: Lidocaine, bupivacaine, ropivacaine.
4. Intraarticular Administration:
Mechanism: Local anesthetic agents are injected directly into a joint space to numb the joint and surrounding tissues.
Uses: Pain management in conditions like arthritis, and before or after joint procedures.
Examples of agents: Lidocaine, bupivacaine.
5. Epidural Administration:
Mechanism: Local anesthetic agents are injected into the epidural space, which surrounds the spinal cord, to block nerve signals.
Uses: Pain management during childbirth, surgery, and chronic pain conditions.
Examples of agents: Lidocaine, bupivacaine, ropivacaine.
6. Intravenous Regional Anesthesia (Bier Block):
Mechanism: Local anesthetic agents are injected into a vein in a limb, and a tourniquet is used to prevent the anesthetic from entering the systemic circulation.
Uses: Surgical procedures on extremities, particularly for shorter procedures.
Examples of agents: Lidocaine, prilocaine
Outline the methods for performing a nerve block and a line block, and list clinical situations in veterinary practice in which these blocks are used.
In veterinary practice, nerve and line blocks use local anesthetic injection to temporarily block nerve signals, providing pain relief. Nerve blocks target specific nerves, while line blocks create a “wall” of analgesia along a planned incision.
Nerve Block Methods:
Identification: Locate the target nerve using anatomical landmarks or nerve stimulators.
Injection: Inject local anesthetic solution around the nerve, aiming to block nerve conduction.
Examples:
Dental Blocks: Block nerves innervating teeth and surrounding tissues for dental procedures.
Paravertebral Blocks: Block nerves along the spine for procedures like flank surgeries in large animals.
Peripheral Nerve Blocks: Block nerves in limbs for procedures like amputations or fractures.
Epidural Blocks: Inject local anesthetic into the epidural space for analgesia along the caudal half of the body.
Line Block Methods:
Infiltration:
Inject local anesthetic solution along the planned incision line, creating a “wall” of analgesia.
Examples:
Flank Coeliotomy: In cattle and sheep, two linear infiltrations are made cranial and dorsal to the incision line.
Limb Procedures: Ring blocks can be used to block nerves around an extremity.
Clinical Situations:
Pain Management:
Post-operative pain: Nerve and line blocks can effectively manage pain after surgeries.
Chronic pain: Nerve blocks can provide long-term pain relief by reducing nerve irritation.
Acute pain: Nerve blocks can provide immediate pain relief.
Surgical Procedures:
Dental procedures: Nerve blocks are used to numb the area for tooth extractions or other dental work.
Laparotomies: Line blocks can provide analgesia for abdominal surgeries.
Orthopedic procedures: Nerve blocks can be used to numb limbs for fracture repair or other orthopedic procedures.
Eye enucleation: Nerve blocks can be used to numb the eye and surrounding tissues.
Describe the technique for performing an epidural block, and give examples of clinical situations in which this block could be used.
In veterinary medicine, an epidural block involves injecting local anesthetic or analgesic medication into the epidural space around the spinal cord for pain management, typically used for procedures caudal to the diaphragm, especially those involving the hind limbs, pelvis, or perineal region.
Surgical Procedures:
Hind limb orthopedic surgery
Pelvic fractures
Perineal or hind limb surgical procedures in cats
Gastrointestinal surgeries
Urethral catheterization in cats with urinary obstruction
Explain the risks involved and the adverse effects that may be seen with the use of local anesthetic agents.
Local anesthetic use, while generally safe, carries risks and potential adverse effects, including local complications like pain or nerve damage, and systemic effects like seizures, arrhythmias, or hypotension if the anesthetic is absorbed into the bloodstream.
Explain the difference between assisted and controlled ventilation.
In mechanical ventilation, controlled ventilation means the ventilator completely controls the breathing process, while assisted ventilation allows the patient to initiate breaths, with the ventilator providing support.
