Principles of veterinary anaesthesia Flashcards
Which cavity is the brain located in?
The cranial cavity
What is the function of the brain?
To control and coordinate all the functions of a normal, healthy body
What different types of nervous tissue exist in the CNS?
The tissue may be white matter or grey matter.
What is grey matter?
A type of brain tissue that is normally centred in the cerebellum, medulla, and spinal cord. It contains areas of the neuron which are not covered in fat, so it is not white.
What is white matter?
Brain tissue that contains a high amount of myelinated fat. Usually found at the neuron’s axon
What is the hindbrain associated with?
Hearing, balance and taste
What is the forebrain associated with?
Smell
What is the midbrain associated with?
Sight
What are the components of the forebrain?
The telencephalon (the cerebrum), and the diencephalon
What is the cerebrum?
An area of the forebrain that is involves with voluntary movement, senses and memory
What is the diencephalon?
An area of the forebrain which is made up of three parts - the hypothalamus, the thalamus, and the epithalamus. They are all involved in circadian rhythms, and have control over endocrine functions
What are the three parts of the diencephalon?
The hypothalamus, the thalamus, and the epithalamus. It also contains the posterior and anterior pituitary glands.
Where is the pineal gland found?
In the epithalamus, which is part of the diencephalon, which is in the forebrain
Which part of the brain is the optic nerve associated with?
The diencephalon in the forebrain
What is the function of the pineal gland?
Related to stimulation during daylight. It helps to produce melanin and changes throughout the seasons and oestrus cycle
What is another name for the midbrain?
The mesecephalon
Where is the tegmentum?
The midbrain/mesencephalon. It is the main core of the midbrain
What is the tegmentum associated with?
Vision, hearing, motor control, alertness and thermoregulation
What is the hind brain comprised of?
The cerebellum, medulla oblongata and the pons
What are the general functions of the hindbrain?
Involved with complicated movements of the body, control of circulation and awareness of surroundings
What parts of the brain are involved in the control of respiration?
The medulla oblongata and the pons in the hindbrain
What is the cerebellum responsible for?
For CNS involvement with balance and coordination
What is the main cell of the nervous system?
The neuron
What is the function of a neuron?
To conduct a nerve impulse from one area to another
What does the function of the nervous system depend on?
The passage of electrical impulses (known as nerve impulses) to and from all parts of the body
What are the different components of a neuron?
The soma, the dendrites, the axon hillock, the myelinated sheath, the Schwann cells and the axon terminals
Where does the axon of each neuron eventually terminate?
The synapse, or synaptic cleft
What is the function of a synapse?
To transmit a nerve impulse from one neuron to another, or from a neuron to a muscle fibre at a neuromuscular junction, to bring about muscle contraction
What is the most common neurotransmitter?
Acetylcholine
What are some examples of neurotransmitters?
Dopamine, adrenaline, noradrenaline, serotonin, acetylocholine
How many pairs of cranial nerves are there?
12
What is the longest cranial nerve?
The vagus nerve (cranial nerve 10)
Which of the cranial nerves give only sensory (afferent) fibres?
These come from an organ to the brain - olfactory, optic, and vestibulocochlear
Which of the cranial nerves give only motor (efferent) fibres?
Oculomotor, trochlear, abducens, facial, accessory, hypoglossal
What are the mixed cranial nerves?
Trigeminal, glossopharyngeal, vagus
Name the cranial nerves from 1-12
Olfactory
Optic
Oculomotor
Trochlear
Trigeminal
Abducens
Facial
Vestibulocochlear
Glossopharyngeal
Vagus
Spinal accessory
Hypoglossal
What is the function of the olfactory nerve?
Carries the sense of smell from the olfactory bulb to the brain
What is the function of the optic nerve?
Carries information about sight from the eyes to both sides of the brain via the optic chiasma
What is the optic chiasma?
The point of the brain where the optic nerves cross
What is the function of the oculomotor nerve?
Supplies the extrinsic muscles of the eye
What is the function of the trochlear nerve?
Supplies the extrinsic muscles of the eye
What is the function of the trigeminal nerve?
Carries sensory fibres from the skin around the face and eyes and motor fibres to the muscles of mastication
What is the function of the facial nerve?
Supplies the muscles of facial expressions including those associated with the movement of the lips, ears, and skin around the eyes
What is the function of the abducens nerve?
Supplies the extrinsic muscles of the eye
What is the function of the vestibulocochlear nerve?
Has two branches: the vestibular and cochlear:
Vestibular branch - controls the balance from the semicircular canals
Cochlear branch - controls the hearing from the cochlea
What is the function of the glossopharyngeal nerve?
Carries the sensation of taste
What is the function of the vagus nerve?
Carries sensory fibred from the pharynx and larynx. Supplies motor fibres to the muscles of the larynx. Also has parasympathetic visceral motor fibres to the heart and various thoracic and abdominal
What is the function of the spinal accessory nerve?
Supplies the muscles of the neck and the shoulder
What is the function of the hypoglossal nerve?
Supplies the muscles of the tongue
What is the ventricular system?
Similar to an interconnecting rooms/tunnel. It is a system of interconnecting cavities
What is the ventricle linked to the hindbrain?
The 4th ventricle
What is the ventricle linked to the midbrain?
Cerebral aqueduct
What is the ventricle linked to the forebrain?
Ventricles 1-3
What are the ventricles of the brain filled with?
Cerebrospinal fluid
Where is CSF found?
In the ventricles of the brain, the central canal of the spinal cord and bathing the outer surface of the brain
What is CSF secreted by?
The choroid plexuses, within the ventricles of the brain. The majority is secreted by the choroid plexus in the 4th ventricle of the brain
What is cerebrospinal fluid?
Clear, quite viscous fluid that resembles plasma. It is an example of a transcellular fluid
What is the function of CSF?
- protects the brain and the spinal cord by acting like a shock absorber, especially for blunt trauma
- provides nutrients for neurons
Where does excess CSF collect?
In the cisterna magna, at the base of the skull
What is the dura mater?
The ‘outer layer’ of the meninges - means ‘ tough mother’ in Latin. It is the tough, fibrous layer
What does loss of CSF cause?
An increase in intracranial pressure - CSF samples should be taken via spinal tap and can be done with no problem
What are the meniges?
The membranes that surround the CNS. There are three layers of them: the dura mater, the arachnoid layer, and the pia mater
What are the three layers of the meninges?
The dura mater, the arachnoid layer, and the pia mater
What is the arachnoid layer?
The middle layer of the meninges - a network of collagen fibres and large blood vessels. Between this and the dura mater is the subdural space. Below the arachnoid layer is the subarachnoid space, which is filled with CSF
What is the pia mater?
The inner layer of the meninges. Means ‘sweet/gentle’ in Latin. A fine membrane closely applied to the brain following the gyri and sulci (the ridges and grooves of the brain respectively).
What is the autonomic nervous system?
A component of the peripheral nervous system that regulates involuntary physiological processes including heart rate, blood pressure, respiration, digestion, and sexual arousal.
What are the three divisions of the autonomic nervous system?
Parasympathetic, sympathetic, and enteric
What is the sympathetic nervous system? What does it control?
It contains afferent (sensory) and efferent (motor) fibres that provide input to the CNS. Activation of the sympathetic nervous system activates the ‘fight or flight’ response. It promotes active responses - blood pressure and heart rate increases, glycogenolysis ensues and gastrointestinal peristalsis ceases.
What is the parasympathetic nervous system? What does it control?
Promotes the ‘rest and digest’ processes - heart rate and blood pressure lower, gastrointestinal peristalsis restarts
What is the enteric nervous system?
A section of the autonomic nervous system, it can function independently of the remainder of the nervous system. It is chiefly responsible for the regulation of digestive processes. It controls muscle functions including contraction/relaxation, secretion/absorption, and blood flow
What are some characteristics of the parasympathetic nervous system?
- constricts pupils
- stimulates salivary glands
- slows heart rate
- constricts bronchi
- stimulates stomach and intestines and bile release
- contracts bladder
What are some characteristics of the sympathetic nervous system?
- dilates pupils
- inhibits salivary glands
- accelerates heart rate
- dilates bronchi
- converts glycogen to glucose for immediate energy
What is the somatic nervous system?
Contains both afferent and efferent nerves. The main function of the somatic nervous system is to connect the CNS with organs and striated muscle to perform daily functions
What is the somatic reflex arc?
These are the neural pathways that are responsible for the automatic response between a sensory and motor neuron. Sensory information is processed and creates a motor response - an example of this is a pain response, or the patellar reflex
What is the triad of anaesthesia?
It has 3 constituent parts:
- analgesia
- immobility/loss of consciousness
- muscle relaxation (complete loss of function)
What is the function of the somatic nervous system?
The main function of the somatic nervous system is to connect the CNS with organs and striated muscle to perform daily functions
Between which vertebrae is an epidural given?
Between L7 and S1 - the patient must be anaesthetised for this.
What is the process for spinal anaesthesia?
Also called an epidural - it is a form of regional anaesthesia. Injected using a large spinal needle, it is used to relax the muscles of the hind limbs and deaden any pain. The animal must be anaesthetised for this.
What are some of the risks of sedation?
Generally there is less support available for cardiovascular and respiratory systems, particularly in respect to control of the airway. GA vs sedation should be considered holistically
What is dissociative anaesthesia? Give an example
A state in which the patient is less aware of what is happening around them - drugs in this category produce a feeling of detachment from the environment
An example is ketamine
What is dissociative anaesthesia categorised by?
4 aspects:
- catalepsy
- catatonia
- analgesia
- amnesia
Define CATALEPSY
Trance with rigidity - it is one of the characteristics of dissociative anaesthesia
Define CATATONIA
Disruption of how the patient perceives the world around them. It is one of the characteristics of dissociative anaesthesia
Define AMNESIA
Memory loss - it is one of the characteristics of dissociative anaesthesia
Which reflexes do patients retain when under dissociative anaesthesia?
Pharyngeal, laryngeal, corneal, palpebral, swallowing. This means they may not need to be intubated, however there is more limited support for the patient.
Define a NOCICEPTOR
A sensory receptor that responds to pain or noxious stimuli
What is the pain pathway?
The nerve impulse that is produced and sent to the brain when a noxious stimuli is detected
What are the stages of the pain pathway?
- The nociceptors translate the information into an electrical signal, like a message. This is TRANSDUCTION
- The signal is then passed up different nerves fibres (called A delta or C fibres) to the spinal cord. This is TRANSMISSION
- When the signal reaches the dorsal horn in the spinal cord a decision is made whether to pass the message to the brain or not. This is MODULATION
- Once the message arrives at the brain, perception occurs
At what stage of the pain pathway does local anaesthesia interrupt?
Transmission level, so the second part of the pathway
Define ALLODYNIA
A pain response to something that isn’t normally painful
Define HYPERALGESIA
Excessive pain responses - increased sensitivity to pain
Define BASAL NARCOSIS
Unconsciousness, usually associated with opioid induction prior to GA
Define the BLOOD BRAIN BARRIER
The semipermeable membrane that separates the brain from general blood flow. Anaesthetic drugs must be able to pass over it to be effective
Define NEUROLEPTANALGESIA
The combination of an antipsychotic (e.g. phenothiazines such as ACP) and opioid analgesia
Define a PREMEDICANT
A precursor sedation prior to induction to GA.
What is cardiac output?
The volume of blood pumped from each ventricle per minute
Stroke volume of the heart (amount in ml pushed out per stroke) x heart rate
What is anatomical dead space?
Anywhere within the body where gaseous exchange does not take place
What is mechanical dead space?
Excess length in equipment (e.g. circuits and ET tubes) that increases the total amount of dead space
Define HYPOCAPNIA
Not enough CO2 in the blood. Patient will be hyperventilating. Results in increased blood pH and respiratory alkalosis
What are some of the causes of hypocapnia?
- hypercapnia (may be due to pain or positioning)
- hypothermia
- hypoxaemia
- poor perfusion (decreased cardiac output, hypotension)
- inadequate gas sample size (very small patient)
Define HYPERCAPNIA
Elevated levels of CO2 in the blood. Lowers pH and results in respiratory acidosis
What are some of the causes of hypercapnia?
- hypoventilation
- hyperthermia
- exhausted CO2 absorbent
- airway obstruction
- excessive dead space
Define HYPERVENTILATION
High respiratory rate. Can lead to hypocapnia and respiratory alkalosis
Define HYPOVENTILATION
Low respiratory rate -shorter ad usually shallower. Leads to hypercapnia and respiratory acidosis
Define HYPOTHERMIA and HYPERTHERMIA
Low and high patient body temperature
Define a HYPNOTIC
‘To sleep’
The primary function of a hypnotic drug is to induce sleep for anaesthesia
Define HYPOXIA
Low levels of oxygen perfusing into tissue
Define HYPERTENSION/HYPOTENSION
Elevated blood pressure/low blood pressure
Define HYPOXAEMIA
Low oxygen levels in the blood - can lead to hypoxia
Define TIDAL VOLUME
The volume of air moved in/out of the lungs in a single breath
Define MINUTE VOLUME
The volume of gas breathed in/out in a single minute
