Anaesthesia Critical Care Flashcards
What abnormalities in the mouth that may contribute to difficult airway management?
Anatomical: small mouth, receding chin, high arched palate, large tongue
Acquired: burns, tumours, abscess, radiotherapy injury, restrictive scars, beard
Poor dentition: loose teeth and crowns, protruding teeth, gaps in the front teeth
Mechanical: temporomandibular joint disease (reduced mouth opening)
What physical actions could be used to relieve airway obstruction?
Airway obstruction may be relieved by lifting the chin and/or pulling the jaw forward (jaw thrust)
How might the patency of an airway be improved?
Patency may be improved by:
* Insertion of an artificial airway (oropharyngeal (Guedel) airway, nasopharyngeal airway, laryngeal mask airway, tracheal tube)
* Turning the patient from the supine to the lateral position (recovery position)
What is the nasal cavity lined by?
Respiratory mucosa - pseudostratified ciliated columnar epithelium containing numerous mucous and serous glands
What is the widest part of the nasal airway
Below the inferior turbinate
What are the advantages of nasal intubation?
Nasal intubation leaves the oral cavity clear for oral surgery.
For patients in the Intensive Care Unit, nasal intubation is more easily tolerated than oral intubation and less sedation is required.
What are the disadvantages of nasal intubation?
More difficult than oral intubation, may cause nose bleed due to the rich blood supply to the nasal mucosa
May create a false passageway, e.g. beneath the nasal mucosa or, in basal skull fractures, into the cranium
Long term nasotracheal intubation - infection of the paranasal air sinuses.
What are the afferent and efferent nerves of Gag Reflex
Afferent = glossopharyngeal
Efferent = vagal
What may become a site of bleeding following nasal intubation in children.
The adenoids
List the sensory nerve supply to the tonsil
the glossopharyngeal, maxillary and mandibular nerves
Describe the anatomical location of palatine tonsils
Collections of lymphoid tissue between the palatoglossal and palatopharyngeal arches, the ‘pillars of the fauces’.
How is aspiration during swallowing prevented
Closure of the laryngeal sphincter
upward movement of the larynx behind the base of the tongue
Reflex inhibition of breathing and channelling of liquid/food laterally by the epiglottis into the piriform fossae. The epiglottis act as a ‘lid’ to the larynx to prevent substances entering the trachea.
Describe the anatomical landmark of the larynx
Midline, opposite the 4th to 6th cervical vertebrae
List the articulating cartilages and paired cartilages of the larynx
Articulating cartilages
* Thyroid
* Cricoid
* Epiglottis
Paired cartilages
* Arytenoid
* Corniculate
* Cuneiform
What do the extrinsic muscles of the larynx do?
Work with other muscles attached to the hyoid to move the larynx up and down during swallowing.
What do the intrinsic muscles of the larynx do?
Open the vocal cords during inspiration
Close the cords and laryngeal inlet during swallowing
Alter the tension of the cords during phonation
What do posterior cricoarytenoids do?
Abduct the vocal cords on inspiration
- pulls the posterior ends of the arytenoid cartilages together medially. The resulting pivoting movement abducts the anterior ends of the cartilages, to which the vocal cords are attached
What do lateral cricoarytenoids, transvere arytenoids do?
adductors of the cords and close the vocal cords
What do aryepiglottics, thyroepiglottics do?
Laryngeal sphincters and close the laryngeal inlet during swallowing
What do cricothyroids do?
Tensors of the cords, acting by tilting the cricoid cartilage (and the attached arytenoids) on the thyroid cartilage
What do the thyroarytenoids, vocalis
The thyroarytenoids are relaxors of the cords.
The vocalis are responsible for the fine adjustment of the cords
Describe the nerve supply to the larynx
Superior laryngeal nerve - above the vocal cords
* The external laryngeal branch - motor supply to the cricothyroid muscle.
* The internal laryngeal branch passes beneath the piriform fossa mucosa, and provides the sensory supply to the interior of the larynx as far as the vocal cords
Recurrent laryngeal nerve - below the vocal cords
How does laryngoscopy induce vagal reflexes
Stimulation of the internal laryngeal nerve, which provides the sensory supply to the vallecula.
What does damage to the superior laryngeal nerve result in:
A hoarse voice due to loss of function of the tensor of the cord (cricothyroid). The hoarseness is temporary as the muscle on the other side compensates
An increased risk of aspiration resulting from loss of sensation above the cords
What does unilateral recurrent laryngeal nerve damage result in:
Vocal cord palsy, with complete inability to abduct and a resulting cord position towards the midline.
* Produces a hoarse voice that is corrected to an extent as the other cord moves across to compensate.
* Glottis is unable to close tightly so that the patient cannot generate a positive intrathoracic pressure to cough effectively, which can lead to respiratory problems postoperatively.
The risk of aspiration is increased because of the infraglottic loss of sensation.
What does bilateral recurrent laryngeal nerve damage result in:
Severe respiratory distress, presenting as stridor as the flaccid vocal cords flap together.
How to manage bilateral recurrent laryngeal nerve damage
Urgent intubation is required acutely, with a tracheostomy likely to follow.
Why should Cricothyroidotomy only be used as a temporary airway
risk of subglottic stenosis
What is the airway of choice for a patient who requires continued use of an artificial airway postoperatively on the ward
nasopharyngeal airway
What is required for effective analgesia of the tonsils
Infiltration analgesia to the tonsillar bed
as the tonsils are supplied by branches of three nerves (mandibular, maxillary and glossopharyngeal).
What is the sensory supply to the larynx below the vocal cords
Recurrent laryngeal nerve
What provides the motor supply to the cricothyroid muscle
external laryngeal nerve
Where is the cricothyroid membrane located
Between the upper border of the cricoid cartilage and the lower border of the thyroid cartilage.
What is the narrowest part of the airway in adults.
The glottis
Where does the trachea extend from and to?
Extends from its attachment to the cricoid cartilage (C6) to the tracheal bifurcation at the carina (T5-6).
How is trachea patency maintained
C-shaped cartilages anteriorly
Completed posteriorly by the trachealis muscle.
Describe the relation of the thyroid isthmus to the trachea
thyroid isthmus overlies the 2nd to 4th tracheal rings.
In which bronchus are inhaled foreign bodies more likely to lodge?
Right bronchus
* The right main bronchus is shorter, wider and more vertically placed than the left. The right upper lobe bronchus arises 2.5 cm from the carina.
What is the lingula
the remnant of the left middle lobe
What is the pleural cavity and what does it contain?
The pleural cavity is the space between the visceral and parietal pleura.
It contains a few millilitres of serous fluid that allows free movement of the visceral and parietal pleura in relation to each other.
How much do the pleural margin and lung above the middle third of the clavicle
2-4 cm
During which common procedures may the pleural cavity be inadvertently opened to cause a pneumothorax?
Insertion of a central line, i.e. subclavian or internal jugular
Supraclavicular brachial plexus block
Intercostal nerve block
Surgery on the kidney or adrenal gland
What is each main bronchus divided into
10 functionally separate bronchopulmonary segments, each with its own bronchus, blood supply and distinct lung parenchyma
List the 10 separate bronchopulmonary segments
Left & right upper lobe
1. Apical
2. Posterior
3. Anterior
Left & right lower lobe
6. Apical
7. Medial basal
8. Anterior basal
9. Lateral basal
10. Posterior basal
Right middle lobe
4. Lateral
5. Medial
Left Middle lobe
4. Superior lingular
5. Inferior lingular
Which lung segment is most commonly affected by aspiration during anaesthesia?
The apical segment of the right lower lobe.
* The first segmental bronchus to arise posteriorly, most commonly affected in the supine patient.
What are bronchioles lined by
ciliated cuboidal epithelium
What are the alveoli lined by
single layer of non-ciliated cuboidal epithelium
What is a primary lung lobule
Each bronchiole, with its further subdivision
List the four mediastinal compartments
Anterior
Middle (containing the pericardium)
Posterior
Superior
List the nerve supply to the diaphragm
phrenic nerves (C3-5)
What effect does a damaged phrenic nerve have on the diaphragm?
How is it diagnosed?
Phrenic nerve palsy causes upward paradoxical movement of the diaphragm on that side during inspiration.
Diagnosis is made by screening the diaphragm by fluoroscopy.
What conditions may limit diaphragmatic movement?
(anything that distends the abdomen)
Pregnancy
Obesity
Ascites
Large tumours
Pneumoperitoneum
Describe the orientation of the internal and external intercostal muscles
The external intercostal muscles slope downward and forward.
The internal intercostal muscles slope downward and backward.
Describe the functions of the external intercostal muscles
Contract on inspiration to pull the ribs upward and outward, increasing the anteroposterior and lateral diameter of the thorax.
Describe the functions of the internal intercostal muscles
active expiration and pull the ribs downward and inward to decrease the volume of the thoracic cavity.
stiffen the intercostal spaces to prevent them from bulging during straining.
List the three types of intercostal muscles
External
Internal
Innermost
What do the innermost intercostals do
Link the ribs together to stabilize the chest wall.
Give the nerve supply to the intercostal muscles
Intercostal nerves, T1 – 11
What are the effects of intercostal nerve blocks on respiration?
Intercostal nerve blocks, or spinal or epidural anaesthesia for abdominal surgery (T4), do not affect respiration significantly, as the diaphragm is the more important muscle of respiration.
List the four groups of accessory muscles of respiration
Scalene
Sternomastoids
Alae nasi
Small muscles of the head and neck
What do scalene muscles do
elevate the first two ribs
What do the sternomastoid muscles do
elevate the sternum
List the muscles used in inspiration
Diaphragm
Small muscles of the neck
Alae nasi
Scalene muscles
Sternomastoids
External intercostal muscles
List the muscles used in expiration
Rectus abdominus
External, internal oblique
Transversus abdominus
Internal intercostal muscle
Where should the tracheal tube be ideally placed
Tip of the tube midway between the vocal cords and the carina
If a tracheal tube is inserted too far, which side is it more likely to enter and which areas of the lung are likely to collapse?
It is more likely to go down the right main bronchus.
The whole left lung and right upper lobe are prone to collapse (RUL bronchus is just past the carina).
How do patients in the ICU usually have CXR taken
on the bed in an ‘antero-posterior’ (AP) view
* In this case, the size of the heart is magnified and the lung fields are seen less clearly.
In which phase of respiration a chest x-ray is taken?
full inspiration
At least six ribs should be visible anteriorly and 10 ribs posteriorly.
What method of chest drain insertion is used for emergency relief of tension pneumothorax.
Describe the anatomical landmark
Needle thoracocentesis
A cannula should be inserted vertically into the second intercostal space (below the second rib) in the mid-clavicular line
What method of chest drain insertion is used for longer-term drain.
Describe the anatomical landmark
Formal chest drain
Inserted into the fifth intercostal space in the mid-axillary line
Immediately above the lower rib, to avoid the neurovascular bundle that runs in a groove under the rib.
What lung lobe is adjacent to the right heart border?
right middle lobe
Which lobar bronchus has its origin closest to the carina?
Right upper lobe
Give the anatomical landmark of the tracheal bifurcation
T5-6
What should the cardiothoracic ratio be in an adult on a PA film
Less than 50%
How to calculate cardiothoracic ratio
a/b where:
a = maximum transverse diameter of the heart
b = maximum internal diameter of the thorax
What can a misleadingly high cardiothoracic ratio result from?
Taking an A-P film rather than a P-A
The heart being pushed more horizontally by upward abdominal pressure, such as obesity or pregnancy
What is the sinoatrial (S-A) node arterial supply
right coronary artery in 65 % of people
What does the left anterior descending artery supply
Anterior aspect of both ventricles and the anterior two thirds of the ventricular septum.
Where does the posterior descending artery arise from
In 85% of people, arises from the right coronary artery (RCA) in the posterior interventricular groove (‘right dominance’).
In 15% of people, arises from the circumflex artery in the posterior interventricular groove (‘left dominance’).
What are the principle tributaries of the coronary sinus
great, small, middle and posterior LV cardiac veins
What are the parasympathetic nerve supplies of the heart
The vagus and recurrent laryngeal nerves send branches via the deep and superficial cardiac plexuses.
Post-ganglionic fibres pass to the S-A and A-V nodes, with minimal distribution to the ventricles. Vagal stimulation reduces the rate and force of contraction and constricts the coronary arteries.
The vagus nerves carry afferent fibres concerned with cardiac reflexes.
What are the sympathetic nerve supplies of the heart
The sympathetic supply originates from the lateral horns of the spinal cord (T1-4).
Post-ganglionic fibres arise from the three cervical ganglia and upper thoracic sympathetic ganglia.
Sympathetic stimulation increases the rate and force of contraction and dilates the coronary arteries.
Where does the internal jugular vein run from and to
The internal jugular vein runs from the jugular foramen at the base of the skull to join the subclavian vein behind the clavicle
Where is the internal jugular vein in the carotid sheath
Lateral to the carotid artery
What is the subclavian vein a continuation of
Axillary vein
Where does the subclavian vein join the internal jugular vein
Behind the sternoclavicular joint, to form the brachiocephalic vein
What does subclavian vein receive on the left side
Thoracic duct
Describe the relationship between the vein, artery and nerve in the femoral triangle
(Medial to lateral)
femoral vein - femoral artery - femoral nerve
where does the femoral artery lie
mid-way between the anterior superior iliac spine and the pubic symphysis.
where does the brachial artery lie
medial in the antecubital fossa deep to the bicipital aponeurosis.
2% of the population have an anomalous superficial ulnar artery that passes superficial to the bicipital aponeurosis.
Where are peripherally inserted central catheters inserted
via the basilic vein or the median cubital vein, which drain directly into the axillary vein.
on a normal P-A CXR, what forms most of the anterior surface of the heart
right ventricle
on a normal P-A CXR, what forms the posterior surface of the heart
The left atrium and the pulmonary veins.
on a normal P-A CXR, what forms the right heart border
the right atrium and the caval vessels
Where does the left coronary artery arises from
left posterior aortic sinus
What is the AV node supplied by
right coronary artery in 80% of people
MI affecting which area will commonly result in complete heart block
Inferior MI (associated with right coronary artery disease, supplies AVN)
What supplies the anterior two thirds of the ventricular septum
left anterior descending coronary artery
What muscle does the IJV pass deep to
sternocleidomastoid muscle, anterior to the anterior scalenus muscle.
Where does the IJV pass anterior to the phrenic nerve
as it crosses the scalenus anterior muscle.
Why is the cephalic vein not preferred for insertion of a PICC line
The cephalic vein passes deep to the clavipectoral fascia at the shoulder.
This acute angle and the presence of a valve where the cephalic vein joins the axillary vein tend to impede the passage of a PICC line.
What is the term used to describe the volume of blood pumped round the circulation by the left ventricle per minute?
How much?
Cardiac output: approximately 5L/min at rest.
What is the name used for the quantity of blood pumped out by the heart with each beat?
How much?
Stroke volume: approximately 70mL
Cardiac output = stroke volume * heart rate
What equation links pressure, flow and resistance?
What are the equivalent values for the circulation?
Pressure = flow x resistance.
BP = CO x SVR.
(BP: blood pressure, CO: cardiac output, SVR: systemic vascular resistance.)
Describe the descending part of the arterial blood pressure waveform
The change in shape during the descending part of the wave is the dicrotic notch.
It is generally thought to represent the elastic recoil of the aortic wall immediately after aortic valve closure.
Why is mean arterial pressure approximately one-third of the way between the diastolic and systolic values?
At rest, the cardiac cycle spends about two-thirds of the time in diastole and one-third in systole. The mean blood pressure reflects their respective contributions.
List the normal pressures of heart chambers
LA - 6/3
RA - 5/2
LV - 120/0
RV - 25/0
What are the resistance vessels
arterioles
When is the volume of blood in the veins reduced?
In hypovolaemia, when the body’s responses lead to vasoconstriction, particularly in the skin or gut with most of the blood kept in the central circulation to perfuse the vital organs.
How does the anatomy of the coronary arteries help maintain perfusion?
They run on the outside of the heart initially and are not compressed by LV contraction during this part of their course.
In which phase of the cardiac cycle does most of the coronary blood flow to the LV occur?
Diastole, when the LV is relaxed.
What change lowers the proportion of time spent in diastole, thus reducing the time for LV perfusion?
An increase in heart rate.
What activates the carotid sinus baroreceptors?
Stretch produced by a rise in blood pressure.
Because they respond to stretch, activation of the baroreceptors results in an inhibitory effect on the cardiovascular system, causing a fall in heart rate and vasodilatation.
Vasoconstriction and tachycardia result from a decrease in activity in the baroreceptors when the blood pressure falls.
What measurements might be useful to identify hypovolaemia?
Urine output, respiratory rate, central venous pressure (CVP).
Arterial blood pressure does not fall until nearly one-third of the circulating volume has been lost.
List the physiological changes in class 1 to 4 hypovolaemic shock
Blood loss (mL / %)
Heart rate
Capillary refill
Blood pressure
Blood loss (mL)
1. <750
2. 750-1500
3. 1500-2000
4. >2000
Blood loss (%)
1. <15
2. 15-30
3. 30-40
4. >40
Heart rate (BPM)
1. <100
2. 100-120
3. 120-140
4. >140
Capillary refill
1. normal
2. >2
3. >5
4. not detectable
Blood pressure
1. normal
2. normal
3. reduced
4. very low
How does the heart achieve simultaneous contraction of all fibres
the specialised conduction system
the syncitial nature of cardiac muscle
prolonging the action potential via slow Ca2+ inflow through L-type channels, thus ensuring total ventricular depolarisation
How much longer is the cardiac action potential than that of a nerve cell?
200 times (300ms vs 1ms to 2ms)
Describe the ionic sequence in the atrial pacemaker activity
continuous slow inward leak of Na until the threshold potential of -40mV is reached
main depolarisation brought about by Ca2+ (not Na+) inflow through L-type channels
repolarisation from K+ outflow
How is the heart rate changed?
The slope of phase 4 is altered to make the cycle length shorter or longer. This is brought about by increases in permeability to Na (tachycardia) or K (bradycardia).
Give the equations for BP and CO
BP = CO x SVR
CO = SV x HR
Give the cardiovascular changes that would be expected acutely in anaphylaxis, hypovolaemia, and early septic shock
Anaphylaxis: CO low; SVR low
Hypovolaemia: CO low; SVR high
Early septic shock: CO high; SVR low
Give the normal cardiovascular values in a healthy adult at rest:
Bloodpressure
Heart rate
Stroke volume
Cardiac output
Pulmonary blood flow
Blood pressure 120/70mmHg
Heart rate 70 beats/min
Stroke volume 70mL
Cardiac output 5L/min
Pulmonary blood flow 5L/min
At what pressure does the mitral valve normally open?
3mmHg
At which left atrial pressure is greater than left ventricular pressure.
How big is the area for alveolar gas exchange in an adult?
80m2 to 90m2, approximately half the size of a singles tennis court.
What is the normal tidal volume at rest and what is it divided into?
~500mL
anatomical dead-space (150mL) limited to the conducting airways
alveolar ventilation (350mL) reaches the lower airways
How to calculate the minute volume (Vmin)
VT x RR = Vmin
500 x 14 = 7000mL/min (7L/min)
Inspiration normally lasts half as long as expiration: an I:E ratio of 1:2.
How to calculate the alveolar minute volume
Alveolar ventilation x respiratory rate
350 x 14 = 4900mL/min (~5L/min).
What is functional residual capacity
the quantity of gas in the lungs at the end of a normal expiration.
why is functional residual capacity important to the anaesthetists
- during apnoea it provides the reservoir in the lungs from which oxygen can be taken to maintain arterial oxygenation; the greater the oxygen reservoir, the longer the time before hypoxaemia develops
- influences the distribution of ventilation within the lung by determining where the starting position of each area of the lung is on the compliance curve
What conditions may reduce the functional residual capacity?
General anaesthesia
Moving from standing to supine
Obesity
Pregnancy
In what structures does gas exchange first take place?
Respiratory bronchioles.
