Respiratory Flashcards
T/F - During pressure-cycled ventilation, inspiratory flow is constant
FALSE
Cycling = Variable a ventilator uses to end inspiration
Vent measures the variable during insp phase -> Once set parameter achieved, vent opens exp valve -> Exp begins
Time-cycled = Determined by set RR and I:E ratio -> Insp phase ends when predetermined time has elapsed
Flow-cycled = Vent cycles into exp phase once the flow has decreased to a predetermined value during insp (either fixed flow value L/min or % fraction of peak flow rate achieved)
Pressure-cycled = Insp ends when a predetermined peak insp pressure value is achieved -> Features a decelerating ramp pattern for the flow waveform
Volume-cycled = Insp ends when a predetermined volume has been delivered
T/F - PEEP can decrease LV afterload
TRUE
PEEP -> Increased intrathoracic pressure -> Decreased transmural pressure -> Decreased LV afterload
(Transmural pressure = Intraventricular pressure - intrathoracic pressure)
T/F - PEEP decreases total lung water
FALSE
Redistributes from interstitial alveolar areas to peribronchial and perihilar areas, but reduces thoracic duct drainage results in fluid retention in the interstitium.
T/F - CPAP can be achieved by partially closing the APL valve on a circle circuit
FALSE
Provides PEEP but not CPAP as it provides resistance but does not deliver a positive pressure flow. Does not reduce work of breathing but makes expiration harder.
T/F - PEEP or CPAP can increase LV transmural pressure
FALSE
PEEP -> Increased intrathoracic pressure -> Decreased transmural pressure
(Transmural pressure = Intraventricular pressure - intrathoracic pressure)
T/F - PEEP can increase RV volume
TRUE
Peep -> Increased lung volume -> Increased Pulm Vascular Resistance -> Increases RV Volume
T/F - During pressure support ventilation, cycling into expiration occurs when the inspiratory flow rate decreases to a pre-set level
TRUE
Insp pressure is constant -> Insp flow rate decreases throughout inspiration as the lung inflates and compliance decreases
T/F - Lung compliance is the change in alveolar pressure for a given change in lung volume.
FALSE
Lung compliance = Change in lung volume / Change in transpulmonary pressure
[Transpulmonary pressure = Alveolar Pressure (Palv) - Pleural Pressure (Ppl)]
T/F - Your ventilator screen displays a pressure-volume loop. It tells you the compliance is 50 mL/cmH20. This is LUNG compliance, and is normal for a healthy intubated patient
FALSE
It displays “Total Respiratory System Compliance”
Normal = 100mL/cmH20
Compliance of the lung and chest wall independently is 200mL/cmH2O
T/F - Deriving the compliance from a P-V loop during IPPV is an example of dynamic compliance.
TRUE
Dynamic compliance = Compliance measured during respiratory, using continuous pressure and volume measurements (includes the pressure required to generate flow by overcoming resistane forecs)
Static compliance = Compliance of the system at a given volume during periods without gas flow (e.g. inspiratory pause)
T/F - Static compliance is always higher (better) than dynamic compliance due to the variations in alveolar time constants.
FALSE
Static compliance IS always higher than dynamic compliance but it is due to airway resistance.
Variations in alveolar time constants only have an effect in cases of lung pathology that causes pendelluft
- Long time constant units may still be inhaling whilst the rest of the lung has stopped or begun exhalation
- Distribution of inspired gas is therefore dependent on respiratory rate
- Increased resp rate -> Proportion of Vt delivered to the region with long time-constant decreases -> Fast alveoli are preferentially inflated -> Decreased dynamic compliance further from static compliance
T/F - Increasing PEEP will always improve lung compliance
FALSE
Usually it will but not always.
Increasing PEEP to just above the lower inflection point of the static compliance curve will shift tidal breathing to the more compliance part of the pressure volume curve -> Decreased work of breathing
IF PEEP is increased above the upper inflection point, alveolar hyperinflation and barotrauma can occur causing inflammation and decreasing compliance
T/F - Increasing inspiratory time on the ventilator can improve ventilation of areas of lung with poor compliance, because their time constant will be slower
TRUE
Areas of poor lung compliance have slower time constants -> Require longer inspiratory time to facilitate flow
T/F - Shunt refers to the proportion of cardiac output which does not participate in gas exchange
TRUE
T/F - The peripheral chemoreceptors are located in the carotid sinus
FALSE
They’re located in the carotid body
T/F - Hypercarbia impairs the ventilatory response to hypoxaemia
FALSE
It enhances it
T/F - Volatile agents will mostly ablate the ventilatory response to hypoxaemia at low MAC values
TRUE
Significantly diminish even at 0.1 MAC
T/F - If you underwent bilateral carotid endarterectomy you would lose your ability to respond to hypoxaemia
FALSE
The aortic body in the aortic arch will also respond via CN X
T/F - Sustained hypoxaemia causes a triphasic response in the awake subject
TRUE
But only if the alveolar PCO2 is maintained (isocapnia).
Phase 1: Acute hypoxic response = Simulation of ventilation within lung-to-carotid body circulation time (6 seconds) -> Increased minute ventilation for 5-10 mins
Phase 2: Hypoxic ventilatory decline = After reaching a peak, minute ventilation begins to decline and reach a plateau level (still above resting ventilation) after 20-30 mins
Phase 3: Ventilatory response to sustained hypoxia = Continued isocapnic hypoxia results in a second slower rise in minute ventilation over several hours (reaches plateau by 24 hours)
T/F - Hypoxic pulmonary vasoconstriction is markedly impaired by 1 MAC volatile
FALSE
All volatile anaesthetics inhibit HPV in a dose-dependent fashion although it is likely only a small effect
T/F - An increased PaCO2 is generally not caused by venous admixture
TRUE
The effect of venous admixture on arterial CO2 content is similar in magnitude to that of oxygen content. However, due to the steepness of the CO2 dissociation curve near the arterial point, the effect on arterial PCO2 is very small
T/F - The haemoglobin concentration needs to be known in order to calculate pulmonary shunt
TRUE
It is required to calculate the oxygen content of blood [Oxygen Content Equation = (1.34 x [Hb] x SaO2) + (PaO2 x 0.03)]
- 34 = Hufner’s constant at 37degC
- 03 = Solubility coefficient for O2 in water
T/F - Mixed venous PO2 can be measured using blood taken from the CVP lumen of a central line
FALSE
It CAN be for practicality sake, however it should only be sampled from a pulmonary artery catheter (in case of intracardiac shunt)
T/F - A healthy patient under general anaesthesia usually has a pulmonary shunt fraction of 10%
TRUE
In a conscious healthy subject, the shunt or venous admixture is 1-2%. Under GA, the alveolar/arterial PO2 difference usually increases to a value that corresponds with a shunt of 10%. Venous admixture increases steeply with age (0.17% per year) but this does not necessarily equate to a significant increase in pulmonary shunt fraction in these patients
T/F - Very high levels of PEEP may decrease SaO2
TRUE
High levels of PEEP -> Obstruction of filling of the right atrium -> Decreased RV filling pressures -> Decreased LV filling -> Decreased cardiac output ->
High levels of PEEP -> Constrict pulmonary capillaries -> Increase V/Q mismatch
T/F - 15-20% of lung volume may be atelectatic during an anaesthetic where IPPV is being used
FALSE
10%
T/F - Oxygenation is improved more when hypovolaemic patients are given PEEP compared to normovolaemic patients
FALSE
Hypovolaemia will worsen the effects of PEEP on reducing cardiac output and therefore oxygenation
T/F - Venous admixture may increase to 10% of cardiac output with IPPV and anaesthesia
TRUE
T/F - An increased BMI decreases atelectasis by increasing splinting of the chest wall
FALSE
Increased BMI will increase atelectasis
T/F - The Bohr equation is used to calculate physiological dead space
TRUE
Physiological dead space = the sum of all parts of the tidal volume that do not participate in gas exchange
VD/VT = (PaCO2 - PECO2)/PaCO2
T/F - End-tidal and mixed alveolar CO2 are very similar in the healthy subject
TRUE
End-tidal CO2 is slightly lower because it is diluted with the non-CO2 containing gas within the dead space
T/F - The Enghoff modification refers to substituting arterial CO2 for alveolar CO2
TRUE
With the invention of arterial blood gas measurements, Enghoff proposed that arterial PCO2 may be substituted for alveolar PCO2 (as alveolar PCO2 cannot be measured)
T/F - Anatomical dead space extends down as far as the fifteenth generation of airways
TRUE
Generation 0 (trachea) - Generations 12-14 (bronchioles) = Conducting Zone (anatomical dead space)
Generations 15-18 (respiratory bronchioles) - Generation 23 (alveoli) = Acinar airways
T/F - Intubation per se increases dead space
TRUE
Apparatus dead space (ETT/LMA etc) and their connections must be included when calculating the total dead spact - can increase to 50% of the total volume
T/F - The PAO2 with an FiO2 of 40% can be calculated by the formula = 0.4(760-47) - PaCO2/0.8
TRUE
Alveolar gas equation = FiO2(Pbaro - Psvp) - PaCO2/0.8
T/F - The calculated alveolar oxygen tension is altered depending on what you eat
TRUE
The respiratory quotient changes depending on diet:
- 7 - lipids
- 8 - proteins
- 0 - carbohydrates
T/F - EtCO2 decreases in hypotension because of increase anatomical dead space
FALSE
EtCO2 does decrease but due to an increase in alveolar dead space and therefore physiological dead space
T/F - Functional residual capacity is reduced during anaesthesia
TRUE
FRC is reduced 15-20% of the awake FRC in the supine position.
It is reduced immeduately on induction, and reaches its final value in the first few minutes
It does not return to normal for some hours after anaesthesia
The reduction of FRC is greater in obese patients
T/F - Total respiratory system compliance is unchanged during anaesthesia
FALSE
Total respiratory system compliance is reduced during anaesthesia (approaches lower end of normal range). Both statis and dynamic measurements are reduced compared with the awake state.
T/F - Airway resistance during anaesthesia is unchanged compared to a supine awake patient
TRUE
The reduction in FRC that occurs during anaesthesia slightly increases airway resistance, however this is offset but the bronchodilatory effect of most anaesthetic agents. Therefore the total respiratory system resistance is only slightly greater under anaesthesia than in the awake supine patient.
T/F - Arterial PO2 is lower during anaesthesia in the lateral position than when supine
TRUE
Lateral positioning favours ventilation of the non-dependent (upper) lung and perfusion of the dependent *(lower) lung -> Increases V/Q mismatch -> Further fall in PO2 compared with the supine position
T/F - During anaesthesia, FRC is higher in the prone position than when supine
TRUE
Both FRC and PO2 are greater when prone compared with supine as it establishes better V/Q matching through ventilation of the dependent areas that is matched with perfusion of these areas.
PEEP >10 will redistribute ventilation and perfusion, and may worsen gas exchange
T/F - Atelectasis occurs in approximately 40% of patients undergoing anaesthesia with muscle paralysis
FALSE
Atelectasis occurs in 75-90% of patients having general anaesthesia with muscle paralysis.
It is more common in children due to compliant chest walls.
T/F - The V/Q ratio at the base of the upright lung is about 0.6, because there is more perfusion than ventilation
TRUE
V/Q Ratios when upright:
Base 0.6
Apex 2
Overall, V/Q ratio = 0.8
T/F - The V/Q ratio of infinity is an alveolar shunt
FALSE
Unventilated but perfused alveoli - V/Q Ratio = 0
Ventilated but unperfused alveoli - V/Q Ratio = infinity
T/F - In a conscious patient with left lower lobe collapse, hypoxaemia would be WORSE when lying on their left side
FALSE
There would be increased perfusion of the collapsed lung initially but HPV would redirect blood flow to the ventilated non-dependent upper lung
T/F - In an intubated ventilated patient with left lower lobe collapse, hypoxaemia would be WORSE when lying on their left side
TRUE
There will be preferential ventilation of the non-dependent lung and preferential perfusion of the dependent lung -> Worsens V/Q mismatch -> Worsens hypoxaemia (PO2)
T/F - Hypoxic pulmonary vasoconstriction can reduce the degree of hypoxaemia caused by V/Q mismatch - HPV is mediated by BOTH alveolar and mixed venous PO2
TRUE
HVP is the primary mechanism used to reduce V/Q mismatching.
T/F - The V/Q ratio at the apex of the upright lung is 3.3, because the apex receives most of the alveolar ventilation
FALSE
The base is better ventilated
T/F - in a conscious patient lying on their left side, the left lung will receive more ventilation AND perfusion than the right lung
TRUE
T/F - In an anaesthetised and ventilated patient lying on their left side, the left lung will receive more ventilation AND perfusion than the right lung
FALSE
The left lung will receive more perfusion while the right lung will receive more ventilation
T/F - Atelectasis results in an increase in alveolar dead space, which can cause hypercapnoea
FALSE
Atelectasis is a form of alveolar shunt where the alveoli are perfused but not ventilated (whereas alveolar dead space is ventilated but not perfused alveoli)
T/F - A decrease in cardiac output can decrease mixed venous PO2 - this will magnify the hypoxaemia produced by any alveolar shunt
FALSE
It will reduce mixed venous PO2 but this has minimal effect on PaO2
T/F - Most of the dissolved carbon dioxide in the blood is in the erythrocytes
FALSE
Most of the dissolved CO2 is in the plasma
T/F - Carbonic anhydrase is found in erythrocytes
TRUE
RBCs contain large amounts of carbonic anhydrase II
T/F - Carbonic anhydrase is found in pulmonary capillary endothelium
TRUE
Carbonic anhydrase IV is a membrane bound isozyme found in pulmonary capillaries
T/F - As temperature decreases, there is a lower pCO2 for a given mass of CO2 in the blood
TRUE
Decreased temperature -> Increased CO2 solubility -> Decreased pCO2 -> Maintenance of pCO2 under hypothermic conditions requires increased total CO2 content.
Hypothermia -> Reduces ionisation of water into H+ and OH- -> pH increases (more alkalotic) by 0.016 per degree Celcius fall in temperature -> Hypoventilation increases PCO2 to maintain normal pH (pH-stat hypothesis)
T/F - Reduced Hb has a tenfold ability to carry CO2 over oxyhaemoglobin
FALSE
Reduced haemoglobin is 3.5x as effective as oxyhaemoglobin at carrying carbamino compounds
T/F - 1 Joule of work is done when 1 litre of gas moves in response to a pressure gradient of 1kPa
TRUE
Work of breathing = the energy used by the muscles for respiration
Work = Pressure x Volume (Joules)
T/F - Breathing at rest is responsible for approximately 0.5% of the body’s oxygen consumption
FALSE
O2 Consumption by respiratory muscles = 3mL/min = <2% of BMR.
The efficiency of the respiratory muscles is only about 10%.
T/F - Work is calculated by integrating a pressure volume curve
TRUE
T/F - Half of the energy created in inspiration is stored as heat to be used for expiration
FALSE
Heat cannot be stored. Elastic potential energy is stored for passive expiration, while resistive work forms heat which is wasted and dissipated.
T/F - At end expiration, apical alveoli are larger
TRUE
The alveoli in the upper part of the lung have a larger volume than those in the dependent part - except at total lung capacity.
T/F - Perfusion of the lung base is greater than the apex
TRUE
Due to gravitational effects on regional pulmonary blood flow
T/F - Ventilation of the lung base is greater than that of the apex
TRUE
In the upright position, the apices of lung have a ventilation of around one-third that of the bases
T/F - PCO2 of apical alveoli is similar to that in the conducting airways
TRUE
T/F - The overall V/Q ratio of the lung is about 0.8
TRUE
T/F - The V/Q ratio in the lung apex is about 3.3
TRUE
T/F - In the supine position all the regional differences in lung perfusion become insignificant and it functions as a homogeneous unit
TRUE
In horizontal positions, there is no major difference in V/Q ratio between cranial and caudal, or dependent and non-dependent lung regions
T/F - Dynamic airways closure may occur during normal tidal breathing
TRUE
Not in normal healthy invidividuals, however it may in obese/elderly patients where closing capaacity > FRC -> Airway closure during normal tidal breathing
T/F - Dynamic airway closure accounts for the effort-dependent portion of the expiratory limb of the flow-volume loop
FALSE
T/F - During forced expiration, positive pressure generated will be transmitted equally across the respiratory system
TRUE
T/F - The trachea is never subject to dynamic airway closure
FALSE
Cough reflex will close the trachea
T/F - During the effort independent part of an expiratory flow volume loop, maximum air flow rate is determined by lung volume
TRUE
T/F - Nasal breathing provides better humidification than mouth breathing
TRUE
Humidification by the nose is highly efficient because the nasal septum and turbinates greatly increase the surface area of mucosa available for evaporation and product turbulent flow -> Increased contact between the mucosa and air
T/F - The afferent impulses for lung reflexes are mediated via the vagus nerves
TRUE
The upper and lower airway afferent impulses are transmitted via the vagus nerves. There are some phrenic nerve afferents that arise from muscle spindles and tendon organs of the chest wall,
T/F - Pharyngeal dilator muscles contract reflexively during normal inspiration to prevent pharyngeal obstruction
TRUE
Reflex contraction of the pharyndeal dilator mnuscles during inspiration prevents pharyngeal obstruction occurring as a result of subatmospheric pressure in the pharynx.
Mechanoreceptors in the pharynx/larynx detect subatmospheric pressure -> Afferent impulses via vagus nerve -> Pharnyngeal dilator muscle contraction
T/F - The expiration reflex may be stimulated at the larynx and sites lower in the airway
FALSE
The expiration reflex originates in the larynx - prevents material from being aspirated into the upper airway. There is no preceding inspiration (eg with cough) and the compressive and expulsive phases occur immediately and from the lung volume that is present at the time the larynx is irritated
T/F - Pharyngeal reflexes are maintained, unchanged, during sleep
FALSE
