◊ 4-Basal Narcosis ◊

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IV-Basal Narcosis

Definition: -

It is a stage during which the animals losses consciousness but still responding to painful stimuli, so it is of clinical importance for performing operations in horses and cattle under local or regional analgesia. Accordingly all anesthetics are narcotics but not all narcotic are anesthetics. Its administration should be limited to avoid interference with vital processes. The most common drug is chloral hydrate.

1-Chloral hydrate

Chloral hydrate can be considered sedative or hypnotic aside from it is being narcotic. However certain authors refuse its use due to its administration poses problems; and the ataxia, hypotension, and respiratory depression that associate sedation.

1-It is a white crystalline, easily soluble in water, and has penetrating odor

2-It is mainly used for equine and may be used for cattle

3-Detoxicated in liver and excreted by kidney

4-Can be used in different doses to induce three stages of narcosis

5-Can be used strictly IV, orally, or rectally

6-Hypnotic dose doesn’t affect respiration, but over dose predisposes to respiratory failure via affecting the respiratory center

Stages of narcosis, doses, and effect: -


Dose / 50 Kg





3-4 gm




The animal still in standing position with motor in coordination and reduced response to external stimuli, which facilitate examination of the animal.


4-5 gm



The animal becomes unable to stand, lies down, with reduced response to external stimuli


5-6 gm



The animal lies down in lateral recumbency, becomes on the border of general anesthesia, with reduced response to external stimuli


 Advantages: -

1-Easily dissolved in water

2-Wide safety margin

3-Detoxicated by liver and excreted by kidney

4-Easily absorbed from mucous membrane of GIT

5-The animal able to stand under effect of light and medium narcosis

Disadvantages: -

1-Very irritant, and can’t be injected IM or SC

2-Over dose causes hypotension and respiratory failure

Routs of administration: -


Dose /

50 Kg






3-4 gm

4-5 gm

5-6 gm




1-2 hours

The drug is highly irritant even after dilution to 10%, so it should be injected strictly intravenous into jugular vein, to avoid cellulites and phlebitis.


6-7 gm

About 6-8 L water

10-20 mins


It can be applied either by

1-In drinking water after fasting for 24 hours (1%)

2-By stomach tube after dilution in water (5%), to reduce its irritant effect.


8 gm

3-4 L water

20-30 mins


By rectal enema



It is used either as morphine sulfate or HCl, and mainly used in dogs

Dose,  rout, on set, and duration: -



On set


Up to 5 mg/ Kg

SC or IV

5-10 mins

(maximum is 30-45 mins)

12 hours

Effect: -

1-It depresses the higher functions of the brain

2-It stimulates then depresses medullary functions, and stimulates spinal reflexes

3-It produces depression, analgesia, and sleeping in dogs, but in large doses cause coma. Also it Produces pin-point pupil

4-It produces delirium or maniacal excitement in cat

5-It produces unreliable effect in horses, cattle, and pigs (narcosis or excitement), also it may cause sufficient excitement to dilate the pupil

Side effects: -

1-It is advised that the dose of morphine as a preanesthetic should not exceed 15 mg even in the large dogs because larger dose causes respiratory depression.

2-It crosses the placenta and reaches the fetus, depressing its respiratory center and making the initiation of breathing difficult after birth, but the analgesic doses of morphine do not affect normal uterine contractions at parturition, accordingly it shouldn’t be used for caesarian section.

3-The stimulant effect on the vagal center

a-Increases gastro-intestinal activity

b-Increases the tone of the visceral muscle (especially pyloric, ileo-colic and anal sphincters).

c-Increases segmenting contractions

d-Diminishes the truly propulsive movements.

e-Delays intestinal contents in the large bowel and allows an increased absorption of water

f-Inhibits the normal defecation reflex because the distended rectum no longer produces the usual discomfort.

4-In species with developed vomiting center, it stimulates then suppresses vomiting, and when vomiting occurs, it is not associated with the usual unpleasant emotional reactions, so that animals do not appear distressed.

5-Morphine also produces retention of urine, distension of the bladder

6-It affects respiratory system through the central nervous system and decreases respiratory activity (respiration becomes slow and deep), however the analgesic effect of morphine improves respiration when it is fast, shallow, and inefficient due to pleural pain or trauma, or when lungs are edematous, as in left ventricular failure.

7-Therapeutic doses have negligible effects upon the heart rate and blood pressure, but larger doses slow the heart by depressing conduction in the myocardium and stimulation of the vagal center.

3-Xylazine HCl (Rompun® or Xylaject®)

As we mentioned before under title pre-anesthetic medications

4-Pentobarbitone sodium

It will be discussed later under general anesthesia