Introduction to Anaesthesia | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Pre-Anaesthetic Medication

Pre-anaesthetic medication involves the use of sedatives and tranquilizers to reduce excitement and struggling during both the induction and recovery phases of anesthesia. These medications enhance the safety and comfort of the anesthesia process for the patient.

Preliminary sedation before surgical anesthesia is a widely accepted practice. It results in a smoother and less distressing induction stage, with patients more readily accepting the anesthesia, particularly in humans, as pre-operative anxiety is alleviated.

Considerations for Premedication

• The patient's physical condition plays a crucial role. A muscular, well-developed patient typically requires more sedation compared to a slightly built patient. Debilitated and obese patients usually need smaller doses. Women generally require less sedation than men.
• Anxious patients may necessitate higher levels of sedation. Increased sedation is often needed when administering spinal or regional anesthesia.
• Patients receiving thiopental should not be overly sedated to prevent complications.
• Special attention is required to avoid respiratory depression, especially in patients with chest diseases.

These considerations are vital in tailoring premedication to individual patients to ensure a safe and effective anesthesia process.

Pre-Anaesthetic Agents

• Barbiturates with scopolamine or atropine
• Morphine with atropine
• Meperidine with atropine
• Chlorpromazine (not commonly used due to hypertension risks)

Barbiturates with Scopolamine or Atropine

Barbiturates, such as secobarbital or pentobarbital, are commonly used for sedation before anesthesia. They act quickly and provide excellent sedation. When combined with scopolamine or atropine, the sedative effects are enhanced.

Morphine with Atropine

Combining morphine sulfate with atropine sulfate leads to sedation and reduction of saliva flow. Morphine acts on the central nervous system, while atropine contributes by resembling its effects on the parasympathetic division of the autonomic nervous system.

Meperidine with Atropine

The combination of meperidine with atropine also provides pre-anaesthetic effects, contributing to sedation and other necessary effects before anesthesia.

Chlorpromazine

Chlorpromazine was previously used but is now avoided due to the high incidence of hypertension associated with its use.

It is important to note that different pre-anaesthetic agents have varying effects on patients. For example, secobarbital tends to induce calmness, unlike narcotics that may cause drowsiness and apprehension. Pre-medication with narcotic medications can lead to post-operative vomiting, a side effect that is absent when using secobarbital.

Action and doses of some drugs used for pre-medication

• Atropine

  Atropine is administered to reduce mucous and salivary secretions. It should be avoided in ruminants as it thickens secretions. The dosage is 0.01 mg per kg of body weight.

• Largactil (Chlorpromazine hydrochloride)

  Largactil acts as a tranquilizer, antiemetic, and antiadrenaline agent. Dosage: Horse - 0.4 mg/kg intramuscularly, Dog and Cat - 1 mg/kg intramuscularly.

• Siquil (Trifluopromazine hydrochloride)

  Siquil, when administered before anesthesia, decreases the required dose of barbiturates. Dosage: Horse - 1 to 1.5 mg per 5 kg intravenously, Cattle - 0.5 mg per 5 kg intramuscularly, Dog and Cat - 1 mg/kg.

• Local Anaesthesia

  Local anesthesia blocks sensory nerve impulses reversibly without affecting consciousness or causing permanent nerve damage. It involves applying the drug around nerve terminals or fibers to prevent impulse conduction. Field block is desensitizing an area by injecting analgesics around its borders.

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  • Local Anaesthetics

    Local anesthetics like Procaine HCl and Lignocaine HCl are commonly used for different types of anesthesia.

  • Procaine HCl

    Procaine HCl is typically used in 2-2.5% solution for infiltration and nerve block. It can also be used in 1-2.5% solution for epidermal analgesia combined with adrenaline. It takes about 5 minutes for anesthesia to develop and lasts for approximately 1 hour.

  • Lignocaine HCl

    Lignocaine HCl is effective for both surface application (4%) and local infiltration (2%).

  • Cocaine

    Cocaine is used for surface anesthesia on mucous membranes. The solutions vary for different applications, such as 4% for the eye and 10-20% for nasal and laryngeal mucous membranes.

General Anaesthesia

• General anaesthesia involves inducing unconsciousness, insensitivity, and reduced motor response through controlled reversible central nervous system intoxication.

• Stages of General Anaesthesia:

  • Stage 1 - Induction:

    At this stage, the animal is conscious and excited, showing accelerated pulse and respiration rates.

  • Stage 2 - Involuntary Excitement:

    Consciousness is lost, respiration becomes regular, and there are exaggerated responses to stimuli followed by muscle relaxation.

  • Stage 3 - Surgical Anaesthesia:

    This stage is divided into three planes:

    • Plane 1 - Light Anaesthesia:

      Breathing is regular, limb movements cease, reflexes become sluggish, and pedal reflex persists.

    • Plane 2 - Medium Anaesthesia:

      Respiration remains similar to Plane 1, reflexes are sluggish, and muscular relaxation intensifies.

    • Plane 3 - Deep Anaesthesia:

      Respiration rate increases, pedal reflex vanishes, eye movement may change, and muscle relaxation is notable.

  • Stage 4 - Medullary Paralysis:

    This stage occurs with an anaesthetic drug overdose, leading to rapid pulse, dilated pupils, and paralysis of thoracic muscles, potentially resulting in respiratory and heart failure.

Regional Anaesthesia

• Regional anaesthesia involves injecting an analgesic near the primary nerve trunk supplying a specific area or region.

Paravertebral Block

• To induce paravertebral block, a local anaesthetic is injected close to where the cutaneous and ventral branches of certain spinal nerves emerge.
• This method can be used to anaesthetize the flank of a bovine during procedures like caesarean sections and rumenotomy.

Epidural Analgesia

• In cattle, epidural analgesia is achieved by administering a local anaesthetic drug into the spinal canal through a specific intervertebral space near the tail.
• It is performed while the animal is either standing or lying down and is useful for procedures like tail amputation and managing straining during rectal, vaginal, or uterine prolapse.

Cornual Nerve Block

• This type of nerve block is utilized for painless dehorning operations by using a local anaesthetic.
• The nerve is positioned slightly lateral and ventral to a particular edge of the frontal bone, aiding in blocking the nerve effectively.

Retrobulbar Block

• During this procedure, the maxillary and ophthalmic branches of certain nerves are desensitized to facilitate surgical eye removal.
• The desensitization occurs at the points where these nerves emerge, such as the foramen rotundum.