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Anaesthetics > Physiology > Flashcards

Physiology Flashcards

1
Q

What effect do anaesthesia and surgery have on the CVS?

A

Cardiovascular depressant effect of many of the anaesthetic agents
Stress response to surgery (neural and humoral component)
Potential blood and fluid loss during surgery

(All negatively affect systemic circulation and CO)

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2
Q

List the indices of cardiovascular function.

A 
Cardiac output
Stroke volume
Cardiac Index
Blood pressure
Ventricular filling
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3
Q

Explain cardiac output (CO)?

A

CO = HR X SV
The volume of blood leaving the heart each minute
Average adults at rest: 5 L/min
CO is a measure of flow

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4
Q

Explain stroke volume (SV)?

A

Stroke volume is the volume of blood leaving the heart with each beat
It is determined by
1) Preload - venous return
2) Contractility
3) Afterload - systemic vascular resistance

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5
Q

Explain cardiac index (CI)?

A

CI = CO/BSA(body surface area)
Approximately 3,2 L/min/m2 in the average adult at rest
Adjusts the cardiac output for the patients size

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6
Q

Explain blood pressure (BP)?

A

MAP (mean arterial pressure) = CO X SVR

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7
Q

Explain ventricular filling?

A

Atrial systole normally contributes less than 15% towards ventricular filling, remainder of ventricular filling occurs passively
AF results in less ventricular filling and thus less preload

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8
Q

Explain the physiological control of heart rate?

A

Sympathetic innervation of SA node (via B1 recepeptors - increases HR)
Parasympathetic innervation of SA (via vagus nerve - slows HR)
Sympathetic and parasympathetic innervation normally balances each other out, but overall parasympathetic system predominates

SA node receives further input from baroreceptors in carotid sinus
Sudden increase in BP = increased baroreceptor firing = increased vagal stimulation = vasomotor system inhibition = fall in BP
Sudden fall in BP = decreased baroreceptor firing = decreased vagal stimulation = increased sympathetic outflow from vasomotor centre = increased HR and CO

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9
Q

CO is affected by which changes?

A

HR
Preload
Contractility
Afterload

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10
Q

What are the factors that decrease preload?

A 
Hypovolaemia
Haemorrhage
GA
Neuraxial anaesthesia
IPPV
Autonomic neuropathy
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11
Q

What are the factors that affect myocardial contractility?

A 
Increase contractility: 
Increase preload
Decrease afterload
Sympathetic stimulation
Inotropes
Decrease contractility:
Decrease preload
Myocardial ischaemia
Cardiac failure
Hypokalaemia, hypoclacaemia
Acidosis
Hypoxia, hypercapnia
Uraemia
Sepsis
Drugs
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12
Q

What are the factors that affect afterload?

A 
Decrease afterload:
Anaemia
Hyperthyroidism
Vasodilators
AV shunts
Exercise
Increased afterload:
Polycythaemia
Hypothyroidism
Vasoconstrictors/vasopressors
Hypothermia
Surgical tourniquets
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13
Q

Describe the physiological control of BP?

A

Intrinsic regulatory properties of heart (Frank-Starling)
Autonomic pathways
Hormonal mechanisms (RAAS, vasopressin, adrenaline and noradrenaline)

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14
Q

Effects of AA on CO?

A 
Propofol, etomidate and thiopentone: reduce CO
Ketamine: increase CO
Inhalational AA: decrease CO
Pancuronium: may increase CO
Vecuronium: may decrease CO
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15
Q

List the functions of the lung?

A 
Gas exchange
Phospholipid synthesis (surfactant)
Synthesis of PG's and histamine
Metabolism and de-activation of certain compounds
Intrinsic component of the immune system
Reservoir for blood (500-900ml)
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16
Q

Function of breathing?

A

To enable O2 delivery to cells (for oxidative phosphorylation and ATP production)
To eliminate CO2

17
Q

Values of oxygen consumption at rest?

A

Adults: 3-4 ml/kg/min

Young children: 7-9 ml/kg/min

18
Q

Values for respiratory failure I and II?

A

Type I: PaO2 less than 8kPa, PaCO2 low/normal
Type II: PaO2 less than 8kPa, PaCO2 greater than 6,5kPa

(1kPa = 10cm H20 = 7,5mmHg)

19
Q

Where is the respiratory centre housed?

A

Medulla Oblongata (brainstem)

20
Q

What is the major controller of ventilation?

A

PaCO2

PaO2 less than 8kPa also contributes

21
Q

Tidal volume definition and normal values?

A

The amount of air inhaled and exhaled during each respiratory cycle
Normally 6-10 ml/kg

Opiates and AA decrease tidal volume

22
Q

Minute ventilation/volume definition and normal values?

A

MV = VT X RR (tidal volume x RR)

Normally: 100 m/kg/min

23
Q

Classification and definition of dead space?

A

Anatomical dead space: volume of respiratory passages NOT involved in gas exchange (i.e. nose, trachea)
Normally 150-200 ml in adults

Physiological dead space: combination of anatomical dead space and alveolar dead space (alveoli that are ventilated but not perfused)

24
Q

Formula for alveolar ventilation?

A

Alveolar ventilation = alveolar MV = (tidal volume - phsysiological dead space) x RR

25
Q

Residual volume definition?

A

The volume of air that remains in the lungs after a MAXIMAL exhalatory effort

26
Q

Functional residual capacity definition?

A

The volume of air that remains in the lungs after a NORMAL tidal exhalation
FRC = residual volume + expiratory reserve volume (volume between normal tidal exhalation and maximal exhalation)
Normally 2,5-3,5 L in the average adult

27
Q

Why is function residual capacity (FRC) so important in anaesthesia?

A

With pre-oxygenation, the FRC can be denitrogenated (all nitogen-containing air replaced with 80-100% O2)
Serves as a reservoir during periods of apneoa during induction or intubation difficulties

28
Q

What factors reduce the functional residual capacity (FRC)?

A 
Supine position
Lithotomy (legs up)
Trendelenburg (head down)
Abdominal distension
Morbid obesity
Pregnancy
Restrictive lung disease
LVF
Upper abdominal surgery
GA agents
Loss of muscle tone/muscle relaxants
Intubation
29
Q

Forced volumes definitions?

A

FEV1: volume exhaled in the first second of a FVC (forced vital capacity) breath
Normally 75-80% of FVC

30
Q

FEV1:FVC ratio in obstructive and restrictive lung diseases?

A

FEV1:FVC ratio reduced less than 70% = obstructive
FEV1:FVC ratio normal or high = restrictive

31
Q

O2 delivery formula?

A 
DO2 = CO x CaO2 (arterial O2 content)
CaO2 = (Hb x 1,36 x SaO2) + (0,0031 x PaO2)
32
Q

Normal PaO2?

A

13,3kPa

33
Q

Normal PaCO2?

A

5,3kPa

34
Q

Definition and causes of hypoxia?

A

Hypoxia: An intracellular mitochondrial O2 tension below the critical level to sustain oxidative phosphorylation
Hypoxaemia: arterial O2 tension less than 8kPa

Causes of hypoxia?
Stagnant hypoxia (not enough blood flow)
Anaemic hypoxia (not enough Hb sufficient to carry O2)
Hypoxaemic hypoxia (no O2)
Cytotoxic hypoxia (poisoning - unable to utilise O2 despite adequate delivery)
35
Q

Causes of hypoxaemic hypoxia?

A 
Low fiO2
Hypoventilation
Diffusion abnormality
V/Q mismatch
Shunt
Decreased in mixed venous O2 tension

Anaesthetics (16 decks)

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