Anaesthesia - Airway Management, Oxygenation And Ventilation

Front 1

Ventilation

Back 1

Bulk flow of gas into and from the alveolar space

Front 2

Ventilation requirements

Back 2

Patent airway

Effective respiratory muscle activity

Responsive neural control

Front 3

Inadequate ventilation =

Back 3

CO2 retention

Lowering of blood O2 levels

Front 4

How does anaesthesia affect ventilation?

Back 4

Inhibits protective airway reflexes

Suppresses mucociliary escalator -> mucus clogging

Impairs ventilatory muscles

Alters chemoreceptor sensitivity

Abnormal body position may impair ventilation

Front 5

Advantages of endotracheal intubation

Back 5

Protects airway from foreign material

Effective means of providing positive-pressure ventilation

Reduces leakage of waste anaesthetic gases

Front 6

Disadvantages of endotracheal intubation

Back 6

Larnygeal trauma

Excessive mechanical dead space

Airway resistance (small diameter)

Endobronchial intubation -> increases in V/Q inequalities

Tube occlusion or kinking

Ischaemic tracheitis (high cuff pressures)

Chemical tracheitis (improper sterilisation technique)

Upper airway functions bypassed (humidification and warming of gases)

Fomite (carrying infectious particles)

Front 7

Why are pigs difficult to intubate?

Back 7

Larynx isn't linear and retained active laryngeal reflex (like cats)

Local anaesthetic spray or muscle relaxant

Front 8

Rabbits?

Back 8

Anatomically difficult - narrow mouth

Front 9

What is the relationship between PaCO2 and alveolar ventilation (VA)?

Back 9

Inversely proportional

Front 10

Which value varies the most?

Back 10

VA

(FiCO2 = concentration of inspired CO2

VCO2 = volume of CO2 produced by body per unit time)

Front 11

Hypoventilation -> PaCO2 levels

Back 11

Increase >45mmHg

Front 12

Why are CO2 inceased pH changes more dangerous than those caused by elevated acids like lactate?

Back 12

CO2 crosses cell membranes readily, influencing intracellular pH, widespread effects

Front 13

What types of hypercapnia are there?

Back 13

Decreased alveolar ventilation

Increased VCO2 - volume of CO2 produced by body

Increased FICO2 - concentration of inspired CO2

Front 14

What causes a decreased VA hypercapnia?

Back 14

Decreased respiratory rate, decreased tidal volume, increased dead space (anaesthetics, hypothermia, decreased thoracic compliance, thoracic pain, hypovolaemia)

Front 15

What causes an increased VCO2 hypercapnia?

Back 15

Surgical stimulation, pyrexia, malignant hyperthermia, hyperthyroidism

Front 16

What causes an increased FICO2 hypercapnia?

Back 16

Rebreathing

Front 17

Tidal volume

Back 17

Volume of air displaced between normal inhalation and exhalation when extra effort is not applied

Front 18

Clinical signs of hypercapnia

Back 18

Tachypnoea

Increased CO (tachycardia and bounding pulse, however anaesthetics may interfere with these)

Peripheral vasodilation (brick red mucus membranes, increased bleeding at surgical site)

Cardiac arrythmias

Extreme - respiratory and cardiac depression (narcotic)

Front 19

What is the effect of increased CO2 on the oxyHb dissociation curve?

Back 19

Right shift it - low affinity for O2

Front 20

Why does hypoxaemia still occur even if alveolar ventilation is adequate?

Back 20

Less soluble in blood than CO2 so processes other than ventilation are required to ensure adequate O2 blood levels

Front 21

Which factors influence O2 delivery to tissues?

Back 21

Decreased FiO2 (N2O, N2, FICO2)

Decreased VA

V/Q mismatch (disease, pregnancy, position, hypovolaemia)

Haemoglobinaemic (anaemia, methaemoglobinaemia, CO Hbaemia)

Stagnant (anaesthetic overdose, cardiac disease, hypovolaemia, polycythaemia)

Histiotoxic (left sided ODC, hydrogen cyanide, dinitrophenol)

Demand (pyrexia, increased workload, hyperthyroidism)

Front 22

Effects of hypoxia on organs

Back 22

Brain - increased intracranial pressure - irreversible neurological damage, convulsions, stupor

Myocardium - decreased contractility, dysrhythmias - severe dysrhythmias, cardiac arrest

Kidney - nephrosis, oliguria - pre-renal failure, anuria

Liver - increased enzymes - necrotizing hepatitis

Gravid uterus - fetal acidosis - death, abortion

Muscle - pain, compartmental syndrome, myositis

Front 23

Oxygenation and ventilation are not synonymous

Back 23

d

Front 24

Spontaneous ventilation

Back 24

Animal breathes by itself; anaesthetist exerts no control over tidal volume, respiratory rate and pattern

Front 25

Why is spontaneous ventilation more dangerous in anaesthetised animals?

Back 25

Chemoreceptor sensitivity reduced in anaesthetised animals -> hypoventilation

Front 26

Controlled ventilation or intermittent positive pressure ventilation

Back 26

R and Vt determined by anaesthetist

Manual - compression of rebreathing bag

Mechanical - mechanical ventilator

Front 27

SIghing

Back 27

Periodic delivery of abnormally large tidal volume - re-expands atalectic regions of lung

Front 28

Advantages of spontaneous ventilation

Back 28

Doesn't require mechanical ventilator or presence of anaesthetist

Alterations in respiratory pattern and rate in response to surgery provide useful info. on depth of anaesthesia

Beneficial effect on CV function as thocolumbar pump preserved

Front 29

Disadvantages

Back 29

Hypoventilation and hypercapnia almost inevitable

Energy for breathing supplied entirely by patient's own efforts

Front 30

For which operation is IPPV required?

Back 30

Thoracotomy

Front 31

Advantages of IPPV

Back 31

Fixed volume of anaesthetic reach lungs - stable level of anaesthesia

Rhythmic breathing pattern - useful for delicate operations

Neuromuscular block not needed

Front 32

Disadvantages

Back 32

Animal may fight ventilator -> adverse haemodynamic effects

Mechanical ventilators - complex and costly

Front 33

Adverse effects of PPV?

Back 33

Reduced cardiac output

Lung damage (volutrauma)

Increased ventilation/perfusion mismatches

Respiratory alkalosis

Front 34

Pulmonary volutrauma

Back 34

Lung rupture - only likely if done improperly or on animals with lung pathology

Front 35

Thoracolumbar pump

Back 35

Inspiration movements of diaphragm and thoracic wall caudally and outwardly produce an increased intathoracic volume and decrease in pleural pressure. Pressure gradient created from abdomen and head to right side of heart -> facilitates venous return and enhances cardiac output

Front 36

How does PPV affect intrathoracic pressure and venous return?

Back 36

Raises intrathoracic pressure and impedes venous return (expels blood from intrathoracic veins into neck and abdomen)

Decreased cardiac output and hypotension may occur

Front 37

What is the principle variable lowering cardiac output during PPV?

Back 37

Mean intrathoracic pressure

Front 38

In which animals is this a problem in?

Back 38

Animals with low compliance lungs -> increases intrathoracic pressure -> decreases CO

Front 39

How can IPPV be altered to reduce systemic vascular resistance caused by high levels of CO2 causing vasodilation?

Back 39

IPPV can be used to decrease CO2 -> may increase arterial pressure even if Qt is reduced