Physiology of Anaesthesia Flashcards
(99 cards)
1
Q
Name the part that is missing
A
Medulla Oblongata
2
Q
Name the part that is missing
A
Cerebellum
3
Q
Name the part that is missing
A
Spinal cord
4
Q
Name the 3 main systems that are most altered during Anaesthesia
A
- Central Nervous System (CNS)
- Cardiovascular system
- Respiratory system
5
Q
Name the 2 systems responsible for the metabolism and excretion of anaesthetic drugs
A
- Hepatic system
- Renal system
6
Q
Where are anaesthetic drugs metabolised in the body?
A
Liver
7
Q
Where are anaesthetic drugs excreted in the body?
A
Via the Urinary system
8
Q
What part of the brain is responsible for the control of Respiration?
A
The Hind-brain
9
Q
What are the 2 parts of the Hindbrain, responsible for the control of respiration?
A
- Pons
- Medulla Oblongata
10
Q
List the 3 things that the Pons + the Medulla Oblongata control, in terms of respiration?
A
- Inspiration
- Expiration
- Prevent over-inflation of the lungs
11
Q
What does the Hering-Breuer Reflex do?
A
- Collects information from the Stretch receptors in the Bronchioles
- Allowing respiratory system to recognise the inflation in the bronchial tree, at any time
Essentially - preventing over-inflation of the lungs!
12
Q
What am I?
- I am a reflex.
- I am controlled by the ANS + Vagus nerve.
- I collect information from stretch receptors in the Bronchioles
- I recognise over-inflation in the bronchial tree
A
The Hering-Breuer Reflex
13
Q
Name the 3 components of the Nervous System that is reponsible for the control of respiration, during anaesthesia
A
- The Hering-Breuer Reflex
- Respiratory Rate
- Chemoreceptors
14
Q
What part of the brain controls the Respiratory Rate?
A
Central Chemoreceptors, within the Medulla Oblongata
15
Q
How do the Central Chemoreceptors in the Medulla Oblongata control the RR?
A
- The Central chemoreceptors monitor blood pH (Indicator** of blood **CO2)
- If the patient has a slow or shallow RR, CO2 increases
- This decreases the blood pH
- Which stimulates the respiratory centre to increase the RR
- This removes CO2 from the blood + return the pH to normal
Low blood pH = Acidic = High CO2 levels
High blood pH = Alkaline = Low CO2 levels
16
Q
Also known as Respiratory Acidosis..
How does a low/acidic blood pH indicate high levels of CO2?
A
- When CO2 levels rises in the blood
- It reacts with water
- To form Carbonic Acid
- This increases the concentration of the Hydrogen ions (H+)
- As the H+ are acidic, it lowers the blood pH
17
Q
Also known as Respiratory Alkalosis…
How does a high/alkaline blood pH indicate low levels of CO2?
A
- When CO2 levels decrease in the blood
- It reacts with water
- To form Carbonic Acid
- This decreases the concentration of the Hydrogen ions (H+) further
- As the H+ are acidic, it increases the blood pH back up to normal
18
Q
What is the role of breathing?
A
To regulate CO2 levels in the blood
19
Q
Why is Hyperventilation not good, during anaesthesia?
A
- It causes rapid + deep breathing
- This removes excess CO2
- Raising the blood’s pH (Alkalosis)
20
Q
Why is Hypoventilation not good, during anaesthesia?
A
- It causes shallow + slow breathing
- This retains CO2
- Lowering the blood’s pH (Acidosis)
21
Q
The regulation of what is the main control mechanism involved in Respiration?
A
The regulation of CO2
22
Q
Where are Chemoreceptors found in the body, that aid in the control of Respiration?
A
Found in the walls of:
1. Aorta
2. Carotid arteries
23
Q
What do Chemoreceptors do?
A
Detect levels of Oxygen in the blood
24
Q
How do Chemoreceptors work?
A
- Located in the Aorta + Carotid arteries
- They respond to O2 tension in the blood
- They send signals to the Medullary centres
- Which stimulate or depress respiration
25
True or False.
**GA depresses** the **function** of the respiratory centres of the **CNS**. Making them **less sensitive** to **physiologial changes**.
True
26
Why is it particulary **dangerous** that the **Respiratory Centres** in the brain are **depressed** during anaesthesia?
* Because they are **less sensitive to physiological changes**
* So in states of deep anaesthesia, it can **easily lead to** **Hypoventilation** or **Hypotension**
* As it is **unable to respond** adequately
27
What can lead to **cell death**, leading to **diminished O2 levels** in the **bloodstream**?
**Inadequate** ventilation
28
What can **severe** **Hypovolaemia** + subsequent **reduced Cardiac Output**?
**Inadequate Ventilation**
* Due to cell death + diminished O2 levels in bloodstream
29
**How can indadequate ventilation** during anaesthesia **cause** **severe Hypovolaemia** + **reduced Cardiac Output**?
Disrupts the delicate balance of the circulatory system, by reducing venous return, preload + cardiac output.
1. Inadequate ventilation, especially during PPV
1. As **PPV Increases Intra-throacic pressure**
1. This **compresses** the **veins** + impedes blood flow
1. **Reducing venous return** to the heart
1. This **reduces preload**
2. **Decreases stroke volume** + **amount** of blood **ejected** w/each heartbeat
2. Thus **effecting Cardiac output**
## Footnote
**Stroke** volume = volume of blood pumped out of the left ventricle, during systolic cardiac conctraction (Systole)
30
What is **Stroke** Volume?
The **volume** of blood **pumped out of the left ventricle**, **during** systolic cardiac conctraction (**Systole**)
31
Why is it important to **undestand** + be **aware** of **how Hypoventilation occurs**, during anaesthesia?
Because Hypoventilation can lead to iminent **Cardiac Arrest**!
32
How can **Hypoventilation** **cause Cardiac Arrest**, during anaesthesia?
* The **respiratory system** **must** be able to **provide** the body with **fresh O2**
* **To** the **Alveoli**
* For **uptake into** the **bloodstream**
* **Whilst removing** excess **CO2**
If not it :
2. Leads to **Acidosis** >
1. Impairs cardiac **contractility** >
1. Vaso**dilation** >
1. **Impaired** **O2 uptake** >
1. **Altered** eletrical **conduction** >
1. **Damages** heart **muscle** >
1. **Arrest**
33
What is **Tidal** Volume?
* **Amount** of **gas passing into or out** of the lungs
* In **1 breath**
* Measured as **10 > 15 ml/kg**
34
What is **Minute** Volume?
* The **volume** of **air** **inhaled or exhaled**
* In **1 minute**
35
How is **MV** calculated?
MV = **TV x RR**
36
What is **TMF**, when referring to anaesthesia calculations?
1. T = Tidal volume
2. M = Minute volume
3. F = Fresh Gas Flow
37
What is **Dead Space**?
* **Gas** **passing down** the **respiratory tract**
* That **does not participate** in **gas exchange**
* I.e; last portion of inspiration
38
Give an example of **Anatomical** dead space
The **last portion** of **inspiration**
39
How is **Mechanical** dead space effectively enlarged during anaesthesia?
By the **attachment** of an anaesthetic **equipment**
40
What is **Alveolar** dead space?
* The **gas** that **does reach the alveoli**
* **But**
* **Doesn't participate** in gas **exchange**
41
Explain the difference in these types of Dead space:
1. Mechanical
2. Anatomical
3. Alveolar
1. **Mechanical** dead space is the space c**reated within the attachment of anaesthetic equipment**, that doesn't participate in gas exchange
2. **Anatomical** dead space is the **gas that passes down the respiratory tract** but does not partcipate in gas exchange
3. **Alveolar** dead space is the **gas that does reach the alveoli** but does not particpate in gas exchange
42
What does this mean?
Vd = Vd anat + Vd mech + Vd a
1. Vd = Dead space
2. Vd anat = Anatomical DS
3. Vd mech = Mechanical DS
4. Vd a = Alveolar DS
43
What is **Alveolar volume**?
The **volume** of **gas reaching** the **alveoli** for **gas exchange**
44
What is does this mean?
Va = TV - Vd
1. Va = Alveolar volume
2. TV = Tidal volume
3. Vd = Dead space
I.e; The **Alveolar volume** = **Tidal Volume - Dead Space**
45
If the **alveolar volume** is the **Tidal volume - the dead space**...
(I.e.
* The volume of gas that reaches the alveoli for gas exchange, is the amount of gas that passes into + out of the patient in 1 breath
* Minus
* The amount of gas that does not participate in gas exchange)
**What** does this **mean** if there is a **lot of dead space in** the **anaesthetic circuit**?
* If there is a **large amout of dead space**, this will **reduce alveolar ventilation**
* Therefore
* **Detrimental** for the patient to breath efficently
Thus...
1. **Large dead space = less air/gas taking place in gas exchange!**
46
Define the term **Hyperventilation**
Excessive ventilation
47
Define the term **Hypoventilation**
Inadequate ventilation
48
Define the term **Hypercapnia**
Abnormally high levels of blood CO2
49
Define the term **Hypocapnia**
Abnormally low blood CO2 levels
50
Define the term **Hypoxia**
Abnormally low O2 tension
51
Define the term **Respiratory Acidosis**
Decreased blood pH
52
Define the term **Respiratory Alkalosis**
Increased blood pH
53
What can cause **Hyper**ventilation?
1. **Excessive** **breathing** + **ventilation** (IPPV)
2. ***Light GA***
## Footnote
* Hyperventilation will cause decrease in CO2 levels
* Leading to Respiratory Alkalosis
54
What can cause **Hypo**ventilation?
1. **Decreased RR**
2. GA **overdose**
3. ***Increased** Dead space* + *TV*
## Footnote
* Hyperventilation will cause increase in CO2 levels
* Leading to Respiratory Acidosis
55
What can cause **Hyper**capnia?
**Hypo**ventilation
## Footnote
* Will result in Respiratory Acidosis
56
What can cause **Hypo**capnia?
**Hyper**ventilation
## Footnote
* Breathing will often stop
* Until CO2 levels rise again
57
During **Hyperventilation**, while may the patient often have **apnoea**?
1. Hyperventilation will **remove excess CO2**
1. Resulting in **low levels of CO2** in the **blood**
1. The **Central chemoreceptors** will **send signals to** the **hindbrain** (Medulla Oblongata) to **temporarily halt expiration**
1. To **allow** the body to gain/accumilate/**inspire more gases**
58
What can cause **Hypo**xia?
1. **Decreased O2 in inspired gas**
2. Under **GA**
3. Faulty/**empty O2 cylinder**
4. **Decreased RR**, **Dead space** + **TV**
5. Lung disease
6. **Anaemia**
7. Decreased Cardiac output
## Footnote
* **Tissue hypoxia** = causes **cell death**
* If heart becomes effect = cause cardiac arrest, as **myocardial cells are starved of O2**
59
Why can **Tissue Hypoxia** do to the body?
1. **Tissue hypoxia** causes **cell death**
2. Cell death is caused by lack of O2, as O2 is required for **breaking down glucose > energy (ATP)** to work!
1. If heart becomes effected it causes Cardiac Arrest
2. As the **myocardial cells are starved of O2**
60
What can cause Respiratory **Acidosis**?
**Increased** CO2
## Footnote
Causing **Hypercapnia**...
61
What can cause Respiratory **Alkalosis**?
**Decreased** CO2
## Footnote
Causing **Hypocapnia**...
62
What is the role of the **Cardiovascular system**, within the body?
1. It acts to **perfuse the tissues** of the body with **sufficent nutrients + metabolites**
2. To **support life + remove waste** products for elimination
63
Name the **3** components that **work syngeristically**, to **regulate** an optimum **perfusion** of O2 to the **tissues**
1. Heart
2. **Vascular network**
3. **Sympathetic Nervous System** (SNS)
## Footnote
* Remember that the SNS is part of the **ANS**
* So fight or flight, **Inc RR, HR**, slowing down digestion etc
64
What **3** things does the **Cardiovascular** system **regulate**?
1. Cardiac **Output**
2. Blood pressure
3. **Systemic Vascular Resistance**
## Footnote
SVR = Resistant the heart must overcome to pump out blood
65
What is **Systemic Vascular Resistance**?
The **resistance** the **heart must overcome**, in order **to pump blood** around the rest of the body
* That is used to **create**:
1. **Blood pressure**
1. **Flow** of blood
1. Component of **Cardiac function**
66
What is **Cardiac Output** defined as?
1. The **volume of blood ejected** by the heart
1. **Per minute** + **beat**
67
What **2 factors affect** the Cardiac **Output**?
1. Heart Rate (**HR**)
2. **Stroke Volume** (SV)
68
What does this mean?
CO = SV x HR
Cardiac Output = Stroke Volume x Heart Rate
69
What are the **2 main factors** that **influence BP**?
1. Cardiac Output
2. **Systemic Vascular Resistance**
70
# 10 steps..
How is **BP regulated** in the body?
BP is regulated using the SNS + PNS feedback mechanisms.
1. Blood pressure is **detected** by the **Baroreceptors** (pressure receptors)
2. **In the walls** of the major arteries, especially the **Carotid arteries**
3. When BP is **elevated**, the **arterial wall enlarges** + the **Baroreceptors send signa**l to the **Medulla Oblongata**
4. The Medulla **decreases** the **Sympathetic Nervous stimulation**
5. Leading to a **reduction in HR** + **force** of **contractions**
6. At the *SAME TIME* - the **Parasympathetic Nervous System** is **stimulated**, to further **reduce** the **HR**
7. The **Baroreceptors suppresses** the **Vasomotor Centre** in the **Medulla**
8. Which causes **vasoconstriction** of the **pre-capillary sphincters**
9. Leading to **vasodilation** in the **capillary beds**
10. Which **reduces** the **Systemic Vascular Resistance** (SVR)
71
Name the **receptors** that detect a rise or fall (pressure) in **blood pressure**?
**Baro**receptors
72
What is **Systemic Vascular Restistance**?
* The SVR is the **resistance to the flow of blood** **through** the body's blood **vessels**
* The **left ventricle must overcome** this pressure in order **to pump blood around** the body
1. It **increases**, **as the** **vessels constrict**
2. It **Decreases**, when the **vessels dilate**
73
True or False.
SVR increases when the vessels dilate and decreases whent he vessels constrict
False.
The SVR **increases** when the **vessels constrict** + **decrease** when the vessels **dilate**
74
What is Systemic Vascular Resistance controlled by?
A **network** of **pre-capillary sphincters**
75
What controls SVR + What are they?
1. A **network of pre-capillary sphincters** control the SVR
2. These are essentially **small muscles**
3. That are **located** at the **arterial end** of the **capilaries**
76
What **3** components **determine** the **Relaxation + Constriction** of the **pre-capillary sphincters**, that **control** the **SVR**?
1. **Local metabolic factors**
2. ***Tonic Vasconstrictor Discharges***
3. Hormones
77
How can **Local Metabolic Factors** influence **SVR**?
1. If **local metabolic requirements** are **high**
1. **O2** levels **decrease**
1. **CO2 accumilates**
1. Local **hypoxia + hypercapnia causes relaxation** of **pre-capillary sphincters**
1. Which **reduces BP**
78
True or False.
Local Metabolic Factors cause an increase in BP > leads to an increase in SVR.
False.
Local Metabolic Factors cause a **decrease** in **BP** > leading to **subsequent decrease** in **SVR**.
79
What are Tonic Vasconstrictor Nerve **Discharges**?
Nerve **impulses/discharges from** the **Tonic Vasconstrictor Nerves**
80
What do the **Tonic Vasconstrictor Nerves** do?
1. Also known as '***Sympathetic Noradrenergic Vasoconstrictor nerves***'
2. **Constrict blood vessels** to **regulate** blood **flow**
3. In the skin
4. **Releasing Norepinephrine** + **Neuropeptide Y**
81
What is **SVR** primarily determined by?
**Changes** in blood **vessel diameters**
82
How can **Tonic Vasconstrictor Nerve Discharges** influence **SVR**?
1. Tonic Vasoconstrictor Nerve Discharges (impulses) **from** the **Sympathetic Nervous System** (SNS)
2. **Increasing BP**
3. These **Vasoconstrictor nerve fibers** mainly **supply** **non-vital organ tissues**
4. Such as **GI tract + Skin**
83
How do **Hormones** influence SVR?
1. **Hormones** such as **Adrenaline** can **increase** SVR
1. Whereas **drugs**, such as **Sedatives + Anaesthetics**, can **decrease** this
84
# 3..
What does **GA** do to the **Vasomotor function**?
1. It **suppresses** the Vasomotor functions
2. Leading to a **reduction in SVR**
3. Subsequent a **drop in BP**
85
True or False.
Any **fall in Cardiac Output**, as a result of anaesthesia, can **result** in **reduced blood flow** **to** the **liver** tissue
True
86
True or False.
Some GA agents can affect the reciprocal mechanisms that regulate blood supply to the liver.
But not via the Hepatic arteries or Portal veins.
False.
Some **GA agents do have reciprocal mechanisms** that **regulate blood supply to** the **liver**.
However, t**his does occur via the Hepatic Artery + Portal veins**.
87
True or False.
Anaesthetic drug selection doesn't need to be based on Liver function.
False.
As the Liver metabolises anaesthetic drugs, it's **vital** that **drugs** are **chosen** that are easily **metabolised by the liver**, not overworking it, if the patient has impaired liver function or disease.
88
What is the **minimum** **%** of **Cardiac Output** is **required** **for** the **Kidney** to **maintain** **normal functions + Glomerular Filtration Rate**?
20%
89
Why is it important to **provide supportive measures** during the anaesthetic period for patient's with **Kidney disease or impaired functions**?
1. Because **Anaesthesia + Anaesthetic drugs cause** a **fall in CO2 or Blood Pressure**
2. Which will **lead** to a **reduced Glomerular blood flow** + **corresponding reduction in GFR**
2. And if the kidney requires a minimum Cardiac Output of 20%
3. So measures such as **IV fluid replacement will prevent** this from occuring!
90
True or False.
Liver is the main organ in the excretion of anaesthetic drugs, but Propofol + Ketamine are also excreted by the Kidneys.
True!
91
# 5 ...
What is the ideal aim when providing anaesthesia to a patient?
1. To provide **high quality anaesthesia**
1. Whilst **minimising the total doses of agents** used
1. Thereby **reducing potential side effects**
1. This is achieved by using **multiple drugs in combination**
1. To provide ***Balanced Anaesthesia***
92
Which areas of the brain are responsible for control of respiration?
1. Pons
2. Medulla oblongata
93
Explain the mechanism by which slow or shallow respiration stimulates a fall in blood pH and how the body responds in a non-anaesthetised animal
1. Slow or shallow respiration leads to accumulation of CO2 in the blood
1. Which lowers pH , this is detected by chemoreceptors in the Medulla Oblongata
2. Which stimulates an increased respiratory rate
3. To remove more CO2 from the respiratory system + lower blood levels
94
Explain the meaning of the term Tidal volume and how it would be calculated for a patient who weighs 14kg
* Tidal volume is the volume of gas passing in or out of the lungs in one breath.
* For a patient of 14kg tidal volume would be:
* 14kg x 10ml/kg = 140ml
95
Explain what is meant by the term ‘dead space’
* This is where gas passes into the respiratory tract
* But
* Does not participate in actual gas exchange
96
Give one cause of hypoxia that may be related to anaesthetic equipment
1. Cylinder empty
2. Faulty O2 supply
3. Obstruction of ET tube or circuit
97
List the factors that might affect heart rate and therefore cardiac output in an anaesthetised patient
1. Drugs used
2. Pre-existing health condition
3. Depth of anaesthesia
4. Pain
98
List 3 factors that affect systemic vascular resistance in a patient
1. Local Metabolic
2. Sympathetic Nervous System > increasing > Vascular tone
3. Hormones
4. Drugs
99
Explain why the doses of some drugs may need to be lowered when administered to a patient with known hepatic disease
The liver is responsible for the metabolism of many anaesthetic drugs
