General anesthetics

General Anesthetics

Definition
Drug induced absence of perception of all sensation allowing surgery or other painful procedure to be carried out

Triad of General anaesthesia

Hypnosis
Analgesia
Muscle relaxation

Pre anesthetic medication

It is the use of drugs prior to anesthesia to make it more safe and pleasant.To relieve anxiety – benzodiazepines.To prevent allergic reactions – antihistaminics.To prevent nausea and vomiting – antiemetics.To provide analgesia – opioids.To prevent Bradycardia and secretion – atropine.

Stages

Stage I: Analgesia: characterized by development of analgesia, reduce pain sensation, reflex are present, respiration remain and regular. Stage II: Delirium or Excitement: Begin with unconciousness, involuntory movement, excitement, irregular respiration and increase muscle tone. Sympathetic stimulation produce tachycardia, mydriasis and hypertention


Stages
3. Stage III: Surgical Anesthesia Return to regular respiration, muscle relaxation and normal H.R and pulse rates, eye reflexes disappear. 4. Stage IV: Respiratory or Mudullary paralysis: Complete cessation of respiration and circulatory failure and death.

Ketamine

Short acting, induce dissociated state in which the patient is unconscious but appears to be awake and doesn't feel pain. Provide sedation, amnesia, immobility and catalepsy (excitotory state) : Eye remain open with slow nystagmus .

Mechanism of action

It is bind and block to NMDA (N-methyl-D-aspartate receptor ) (excitatory receptor )and also stimulate the central sympathetic outflow which cause heart stimulation, increased blood pressure and cardiac output. Rapid onset of action. and last for 5-10 min.(short acting)

Xylazine

It is used in veterinary medicine for many diagnostic and surgical procedures.Mechanism of action : It is α2 sympathomimedtic agent, it act by activation of central α2 receptors which will cause reduction or depression in release of dopamine and norepinephrine.

Pharmacological effects

CNS depression and sedation (30-90 min). Analgesia which last (15-30 min). Muscle relaxation. Emesis Hypotension and bradycardia Decreased respiratory rate. recovery from effect usually takes 2-4 hr.

Methodology

recovery
Duration of anesthesia
Duration of analgesia
onset
agents
Ketamine Alone
Ketamine& xylazine