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BDS4 CDS Sedation Symposium > Physiology of Sedation > Flashcards

Physiology of Sedation Flashcards

1
Q

breathing mechanics

A
  • Diaphragm used for quiet breathing
  • Inspiratory muscles contract
  • Increase in thoracic volume
  • Reduction in thoracic pressure
  • Air pushed along pressure gradient
  • Expiration is passive
    • The intercostal and accessory muscles are used for more forceful breathing
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2
Q

contraction of diaphragm requires pressure on

A

abdominal cavity

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3
Q

air flow driven by

A

pressure gradients

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4
Q

intrapulmonary pressure during inspiration

A

less than atmospheric

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5
Q

intrapulmonary pressure during expiration

A

greater than atmospheric

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6
Q

intrapleural pressure during inspiration

A

falls during inspiration

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7
Q

intrapleural pressure during expiration

A

rises

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8
Q

TV

A

tidal volume

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9
Q

tidal volume represents

A

air moving in and out of lung during quiet breathing

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10
Q

force inspiration to maximum

A

air intake goes to IRV

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11
Q

IRV

A

inspiratory reserve volume

max inspiration

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12
Q

force expiration

A

ERV

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13
Q

ERV

A

expiratory reserve volume

forced breathe out

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14
Q

some of all reserve volumes

A

VC
vital capacity

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15
Q

sum of VC and RV =

A

TLC

total lung capacity

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16
Q

residual volume

A

RV

volume left in lung even after max expiration (ERV)

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17
Q

effect of posture on breathing

A

Movement facilitated in sitting position ?

Obesity can have an impact

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18
Q

FEV1

A

forced expiratory volume in 1 sec

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19
Q

COPD (restricted and obstructive types) affect on breathing

A

COPD reduces VC

Restrictive

  • e.g. affecting thorax – obesity, fibrosis, pneumonia, TB, asbestosis
  • VC and FEV similar, means small volumes are exchanged but occur at similar rate as normal pt

Obstructive

  • e.g. emphysema, asthma, bronchitis
  • Reduces VC and slows down expiration rate (lower FEV1
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20
Q

conductive zone in airway

A

trachea, bronchi, bronchiole terminals

no gas exchange = anatomical dead space

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21
Q

respiratory zone in airway

A

respiratory bronchiole, alveolar duct and sac

region of gas exchange

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22
Q

conducting zone and oral and nasal cavity are

A

DEAD SPACE

no gas exchange

150ml av

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23
Q

av tidal volume

A

450ml

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24
Q

av tidal volume is 450ml

so av breathe in takes in

A

300ml fresh air

as breathe in 150ml of dead space (conductive zone)

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25
Q

pulmonary gas exchange

A

Gas exchange occurs between the alveolar air and the pulmonary capillary blood

  • In close contact
  • 0.5-2 micrometers

Gases move across alveolar wall by diffusion

Diffusion is determined by partial pressure gradients (these are equivalent to conc gradients)

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26
Q

composition of air in atomsphere and alveoli

A
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27
Q

ventilation

A

amount of gasses passing into lungs

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28
Q

perfusion

A

amount of gasses travelling through pulmonary circulation

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29
Q

ventilation and perfusion

V:Q

A
  • Match
  • Upright person – vary in different parts of the lung
  • V and Q are greater at the base of the lung, reduce as go up
  • V:Q varies at different levels in the lung
    • Differences are less marked in a subject lying flat
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30
Q

gas transport in blood

A
  • Oxygen and CO2 transported in blood – erythrocytes (red blood corpuscles)
    • Haemoglobin most imp in O2 transport
  • Nitrous oxide does not bind to haemoglobin (carried in simple solution in blood)
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31
Q

haemoglobin structure

A
  • Globular protein​
  • MW = 68,000​
  • 2 alpha & 2 beta protein chains​
  • 4 haeme groups:​
    • Porphyrin ring​
    • Iron atom​
  • Fe reversibly binds O2​
  • 200-300 Hb molecules / RBC​

Affinity to oxygen changes at different partial pressures (binds to Fe)

(Fetus has Hb-F (fetal form) stronger bind to O2)​

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32
Q

oxygen transport when breathing air

A
  • Attached to haemoglobin 97%
  • Dissolved in plasma 3%
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33
Q

oxygen transport when inc PO2 (e.g. breathing pure O2, hyperbaric O2_

A
  • Little inc in O2 bound to haemoglobin
  • Amount dissolved is increased in proportion to PO2
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34
Q

CO2 transport

A

Erythrocytes or plasma

  • As
    • Dissolved CO2 (10%)
    • Combined to protein: carbamino compounds (20%)
    • Bicarbonate ions (70%)
35
Q

Bohr shifts on PO2

A

Physiological conditions affecting curve

  • hypothermia as well as alkalosis will shift the curve to the left and increase haemoglobin affinity to oxygen
    • easier to harvest oxygen in the lung but harder to give that oxygen away in the tissues.​
  • increase in temperature, acidosis, and increase in 2,3 DPG (diphosphoglycerate) shift the curve to the right reducing the affinity of haemoglobin to oxygen
    • facilitate haemoglobin to give away oxygen when in the tissue.
    • 2,3 DPG is an alternative by-product of glycolysis and is part of a feedback loop that can prevent tissue hypoxia.
36
Q

IHS

why need to give pt 100% O2 until all N20 diffused out

A
  • As if straight normal air sudden drop in maintenance oxygen with the slowly diffusing N2O, would increase shift towards N2O

here it is 50:50 but room air O2 is just 21%

37
Q

breathing control

A

Breathing automatic process controlled by ‘voluntary’ (Skeletal) type muscles

  • But not autonomic process
  • Rhythm generated by respiratory centres in the brainstem
    • can be modified by signals from various ‘sensory’ receptors
38
Q

breathing rhythm can be increased by

A
  • conscious cerebral cortex
  • peripheral (arterial) chemoreceptors – reduction PO2, inc PCO2
  • central chemoreceptors – dec in pH, inc PCO2 (CSF)
39
Q

inc in breathing rhythm causes

A
  • lung stretch receptors detect and inflation and reduce resp centre rhythms
40
Q

increase in physical activity causes

A

inc in resp centre and breathing rhythm

41
Q

hypoxia

A

reduction in O2 delivery to tissues

hypoxic, anaemia, stagnant (ishaemic) or cytotoxic

42
Q

how does the partial pressure of oxygen and carbon dioxide affects breathing?​

A

low oxygen concentration, small variations of carbon dioxide have greater effect in pulmonary ventilation, when compared to higher concentrations of oxygen and vice versa.​

​

PCO2 and PO2 respiratory control of breathing are intertwined; a change in one will affect the respiratory response of the other.​

43
Q

hypoxic hypoxia due to

A

less O2 reaching alveoli or less O2 diffusion into blood

44
Q

anaemic hypoxia due to

A

reduction of O2 transport due to low Hb or ability of Hb to funtion as carrier (e.g. due to CO poisoning)

45
Q

stagnant (ishaemic) hypoxia due to

A

reduction in transport due to reduced flow

46
Q

cytotoxic hypoxia

A

reduction in o2 utilisation by cells

47
Q

cyanosis

A

Blue colour of skin and/or mucous membranes

Due to >5gm de-oxygenated Hb/dl of blood (deoxyhaemoglobin)

  • 1/3 of ‘normal’ (so 5 not 15gm Hb)

2 main forms

  • Central
    • Affects whole body, evident in oral tissues
    • Generally due to dec O2 delivery to blood, hypoxic hypoxia
      • Low atmospheric PO2
      • Dec airflow in airways (obstruction)
      • Dec O2 diffusion into blood
      • Dec pulmonary blood flow
      • ‘shunting’ (‘venous’ blood à arteries)
  • Peripheral
    • Due to dec O2 delivery to a localised and ‘peripheral’ part of body
    • Often due to red blood flow to tissues – stagnant hypoxia
      • Peripheral vascular diseases e.g. atherosclerosis

Pulse oximeter providing early warning of falling PaO2

Alarm set higher than evidence of cyanosis

48
Q

central cyanosis

A
  • Affects whole body, evident in oral tissues
  • Generally due to dec O2 delivery to blood, hypoxic hypoxia
    • Low atmospheric PO2
    • Dec airflow in airways (obstruction)
    • Dec O2 diffusion into blood
    • Dec pulmonary blood flow
    • ‘shunting’ (‘venous’ blood à arteries)
49
Q

peripheral cyanosis

A
  • Due to dec O2 delivery to a localised and ‘peripheral’ part of body
  • Often due to red blood flow to tissues – stagnant hypoxia
    • Peripheral vascular diseases e.g. atherosclerosis
50
Q

pulmonary circulation volume %

A

20%

short to lungs

51
Q

systemic circulation volume %

A

80%

to body

52
Q

heart structure

A

4 chambers:​

  • -right atrium​
  • -right ventricle​
  • -left atrium​
  • -left ventricle

4 main valves:​

  • -tricuspid ​
  • -pulmonary​
  • -mitral (bicuspid)​
  • -aortic
53
Q

coronary vessels

A

Arterial blood supply to the myocardium is via the right & left coronary arteries and their branches​

Venous drainage is mostly via coronary veins into the right atrium​

54
Q

heart conducting system

A

Conducting system of heart

Electric signal

Not all chambers sim

Atrium first then ventricles

Sino-atrial SA node – pacemaker, define cardiac rhythm

  • Initiate contraction

Atrio-ventricular AV node next

  • atria contract, fill ventricle

Then down to apex of heart

  • right and left bundle of His
55
Q

heart innervation

A

Both Parasym and sym nervous system

Parasympathetic (vagus):​

  • Actions on SAN, AVN​
  • Via muscarinic cholinergic receptors​
  • Negative chronotropic and dromotropic effect​
    • slow down pacemaker and inc delay, reducing conduction velocity

Sympathetic :​

  • Actions on SAN, AVN, myocytes​
  • Via b-1 adrenoreceptors​
  • Positive chronotropic and dromotropic effect​ and Positive inotropic effect​
    • E.g noradrenaline, inc HR conduction velocity and contractility
56
Q

cardiac cycle

A
  • Ventricular systole:​
    • Isovolumetric contraction​
    • Ejection phase​
  • Ventricular diastole:​
    • Isovolumetric relaxation​
    • Passive filling​
    • Active filling (Atrial systole)​
  • Pressure changes and timing​
  • Volumes​
  • Mechanical events (valves)​
  • Electrical events (ECG)​
57
Q

ECG

A

electrocardiogram

P-wave: atrial depolarisation​

QRS-wave: ventricular depolarisation​

T-wave: ventricular repolarisation

58
Q

coronary blood flow

A
  • Coronary BF is greatest during ventricular diastole​
  • Coronary arteries are compressed during systole​
  • Coronary blood flow is decreased by:​
    • Increased heart rate​
    • Low aortic diastolic BP
59
Q

BP = CO x TPR

A
  • BP = Mean arterial Blood Pressure​
  • CO = Cardiac Output​
  • TPR = Total Peripheral resistance
60
Q

CO =

A

Stroke Volume x Heart Rate

61
Q

factors for stroke volume

A

end diastolic volume (preload)

  • venous return
  • HR

ventricular contractility

after load (TPR)

62
Q

heart rate determined by

A

SA node

63
Q

venous return

A
  • Blood returning to right atrium​
  • ‘Push’ forces: ​
    • momentum (from systole)​
    • muscle pump (limb muscles; venous valves)​
  • ‘Pull’ forces:​
    • Thoracic ‘pump’ (negative intrathoracic pressure)​
64
Q

pre-load (Stroke volume)

A
  • The tension in the heart wall as a result of filling​
  • Determined by end-diastolic volume​
  • Starling’s law of heart​
    • increase EDV then increase stroke volume​
    • Length-tension relationship (overlap of actin and myosin filaments)
65
Q

contractility impact on SV

A

compared to a normal contractility for instance by increasing the inotropic activity and thus increasing force and contraction of the cardiac muscle, the heart will increase its end diastolic volume for the same stroke volume. It becomes more efficient pumping blood.​

However, in heart failure and diseases that limit contractility the opposite is true and the heart becomes less efficient pumping blood

66
Q

after load (stroke volume)

A
  • Force that heart must develop to pump blood against the arterial BP and peripheral resistance​
  • After-load is increased in patients with hypertension:​
  • Increased cardiac ‘work-load’​
  • Can affect coronary blood flow​
67
Q

blood pressure

typical value

dependent on

A

In systemic circulation the ideal 120/80 drops at the arterioles level until reaches below 35mm mercury at the venules and the difference between systolic and diastolic disappears

  • depends on level you measure at what normal readings should be

The systolic and diastolic pressure from the pulmonary circulation is much lower

68
Q

7 pulses

A

Arterial​

  • External carotid artery​
  • Facial artery​
  • Superficial temporal artery​
  • Radial artery​
  • Accessibility​
  • Continuous monitoring​

Jugular venous pulse

69
Q

blood flow

A

Blood flow to an organ is determined by various factors​ – Poiseuille’s Law

  • Delta P = pressure difference
  • Radius – large impact
  • Small change in it – big change in flow
70
Q

local blood flow is determined by

A

arteriolar radius

71
Q

arteriolar radius determined by (3)

A

local factors - O2, CO2, pH, temp, vascoactive agents

sympathetic nerves (alpha and beta effects)

hormones - adreanline, ADH, angiotensin II

72
Q

total peripheral resistance

A

TPR = the combined resistance of systemic vessels

BP = CO x TPR

73
Q

changes can occur in vascular beds but TPR and MAP stay the same

how

A

No change in TPR so no change in arterial blood pressure

  • Dilation in some vascular beds can occur without changing the mean arterial BP
    • there is ‘compensatory’ vasoconstriction in other vascular beds
74
Q

postural effects on blood vessels

A

Standing

  • Additional hydrostatic pressure due to gravity = 80 mmHg
    • Veins are more compliant than arteries​

Veins distend = ‘venous pooling’​ =Reduced venous return

75
Q

hypovolemia

A

when loose blood – dec intravascular volume

reduce – SV, CO, MAP

Inc HR and inc TPR by vasoconstriction

76
Q

2 most commonly used cannulation sites

A

cubital fossa of forearm

dorsum of hand

77
Q

4 adv of dorsum of hand as cannulation site

A
  • access​
  • no nearby arteries​
  • no nearby nerves​
  • no joints
78
Q

4 disadv of dorsum of hand for cannulation

A
  • small veins​
  • susceptible to cold/anxiety​
  • mobile veins​
  • more painful ​
79
Q

cubital fossa of forearm cannulation site

A

Mainly use CEPHALIC VEIN, BASILIC VEIN & MEDIAN CUBITAL VEIN​

  • cannulate lateral to biceps tendon

Larger veins more predictably sited​

Better tethered to underlying connective tissue​

80
Q

3 adv of cubital fossa as cannulation site

A
  • Big well tethered veins
  • Less painful
  • Less venoconstriction
81
Q

4 disadv of cubital fossa cannulation site

A
  • Access
  • Potential nerve damage
  • Potential intra arterial injection
  • Joint immobilisation
82
Q

veins in cubital fossa

A

used

  • median cepahlic (or cubital) vein
  • cephalic vein
  • basilic vein

other structures

  • brachial artery
  • median basilic vein

Cannulate lateral to biceps tendon​

83
Q

veins in dorsum of hand

A

basilic vein

cephalic vein

dorsal venous network

BDS4 CDS Sedation Symposium (8 decks)

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