DEAD SPACE
| A | 150 ml | |
| B |
200 ml |
|
| C | 250 ml | |
| D |
100 ml |
| A | 150 ml | |
| B |
200 ml |
|
| C | 250 ml | |
| D |
100 ml |
150 ml REF: Guyton physiology 11th edition page 478, http://en.wikipedia.org/wiki/Dead_space_%28p hysiology%29#Anatomical_dead_space
Indirect repeat from June 2009
“The normal dead space air in a young adult man is about 150 millilitres. This increases slightly with age”
Some of the air a person breathes never reaches the gas exchange areas but simply fills respiratory passages where gas exchange does not occur, such as the nose, pharynx, and trachea.This air is called dead space air because it is not useful for gas exchange.
TOTAL DEAD SPACE (also known as “PHYSIOLOGICAL” DEAD SPACE) can be divided into anatomical dead space and alveolar dead space.
- ANATOMICAL DEAD SPACE
Anatomical dead space is the gas in the conducting areas of the respiratory system, such as the mouth and trachea, where air does not come into contact with the alveoli of the lungs. Birds, which, relatively, have a far longer and wider trachea than mammals, have a higher proportion of dead space.
It is normally equal in milliliters to your body weight in pounds. A 150 lb (68 kg) male would have an anatomical dead space of about 150 mL. 1 mL per lb or 2.2 mL per kilogram of body weight. This is the same conversion of kilograms to pounds, except the final unit is in mL. This is about a third of the resting tidal volume (450-500 mL).
Anatomic dead space is the volume of the conducting airways. It may be measured by Fowler’s method, a nitrogen washout technique.
- ALVEOLAR DEAD SPACE
Alveolar dead space is caused by air contacting alveoli without blood flow in their adjacent pulmonary capillaries, i.e. ventilation without perfusion. As a result, no gas exchange can occur. Alveolar dead space is negligible in healthy individuals, but can increase dramatically in some lung diseases.
| A |
Anticholinergic drugs |
|
| B |
Standing |
|
| C |
Hyperextension of neck |
|
| D |
Endotracheal intubation |
| A |
Anticholinergic drugs |
|
| B |
Standing |
|
| C |
Hyperextension of neck |
|
| D |
Endotracheal intubation |
Endotracheal intubation [Ref : Ajay Yadav Anaesthesia 3″i/e p. 4]
|
ANATOMICAL DEAD SPACE Increased Decreased
|
The conducting airways are referred to as the anatomic dead space. TRUE about measurement of anatomical dead space is:
| A |
1 mL of dead space per pound of ideal body weight |
|
| B |
5 mL of dead space per pound of ideal body weight |
|
| C |
10 mL of dead space per pound of ideal body weight |
|
| D |
15 mL of dead space per pound of ideal body weight |
The conducting airways are referred to as the anatomic dead space. TRUE about measurement of anatomical dead space is:
| A |
1 mL of dead space per pound of ideal body weight |
|
| B |
5 mL of dead space per pound of ideal body weight |
|
| C |
10 mL of dead space per pound of ideal body weight |
|
| D |
15 mL of dead space per pound of ideal body weight |
- For a normal, healthy subject, the anatomic dead space can be estimated by referring to a table of standard values matched to sex, age, height, and weight or body surface area.
- A reasonable estimate of anatomic dead space is 1 mL of dead space per pound of ideal body weight.
- To determine the anatomic dead space in a particular patient, Fowler’s method is used.
In an normal adult, the ratio of physiological and anatomical dead space is:
| A |
2 : 1 |
|
| B |
1 : 3 |
|
| C |
3 : 1 |
|
| D |
1 : 1 |
In an normal adult, the ratio of physiological and anatomical dead space is:
| A |
2 : 1 |
|
| B |
1 : 3 |
|
| C |
3 : 1 |
|
| D |
1 : 1 |
In a normal healthy person physiological dead space almost equals anatomic dead space. Therefore the ratio is 1:1. In some respiratory disorders with non functioning alveoli the physiologic dead space may be ten times the anatomic dead space.
Anatomic dead space in a non smoker under normal conditions is:
| A |
2.2 cc/kg |
|
| B |
5.1 cc/kg |
|
| C |
3.1 cc/kg |
|
| D |
1.5 cc/kg |
Anatomic dead space in a non smoker under normal conditions is:
| A |
2.2 cc/kg |
|
| B |
5.1 cc/kg |
|
| C |
3.1 cc/kg |
|
| D |
1.5 cc/kg |
Approximately 30% of each breath does not participate in alveolar gas exchange and is thus called dead space ventilation (VDS). Dead space ventilation is made up of anatomic dead space and alveolar dead space. Anatomic dead space is the volume of air that fills the conducting airways (trachea, bronchi, and bronchioles) and is estimated at approximately 2.2 cc/kg. The combination of alveolar and anatomic dead space is called the physiologic dead space.
In an normal adult, the anatomical dead space is approximately:
| A |
2.2 cc/kg |
|
| B |
1 cc/kg |
|
| C |
3 cc/kg |
|
| D |
1.5 cc/kg |
In an normal adult, the anatomical dead space is approximately:
| A |
2.2 cc/kg |
|
| B |
1 cc/kg |
|
| C |
3 cc/kg |
|
| D |
1.5 cc/kg |
Anatomical dead space is equivalent to:
| A |
1/3rd of tidal volume |
|
| B |
2/5th of tidal volume |
|
| C |
10 ml/kg of body weight |
|
| D |
15 ml/kg of body weight |
Anatomical dead space is equivalent to:
| A |
1/3rd of tidal volume |
|
| B |
2/5th of tidal volume |
|
| C |
10 ml/kg of body weight |
|
| D |
15 ml/kg of body weight |
Anatomic dead space refers to the volume of the conducting airways and is around 130 – 180ml (2ml/kg throughout life) in the adult i.e about 1/3rd of tidal volume.
Physiologic dead space: It refers to the proportion of the tidal volume that does not participate directly in gas exchange. It consists of the anatomic dead space and the alveolar dead space. It comprises 25 – 35% of of the normal tidal volume.
Which of the following statement is true about physiological dead space?
| A |
It is sometimes measured using the arterial PO2 |
|
| B |
It is generally smaller than the anatomic dead space |
|
| C |
It is often increased in lung disease |
|
| D |
It is determined primarily by the geometry of the branching airways |
Which of the following statement is true about physiological dead space?
| A |
It is sometimes measured using the arterial PO2 |
|
| B |
It is generally smaller than the anatomic dead space |
|
| C |
It is often increased in lung disease |
|
| D |
It is determined primarily by the geometry of the branching airways |
Physiological dead space in lung is
| A |
Zone 1 |
|
| B |
Zone 2 |
|
| C |
Zone 3 |
|
| D |
Zone 4 |
Physiological dead space in lung is
| A |
Zone 1 |
|
| B |
Zone 2 |
|
| C |
Zone 3 |
|
| D |
Zone 4 |
A i.e. Zone 1
The physiological dead space is decreased by:
| A |
Upright position |
|
| B |
Positive pressure ventilation |
|
| C |
Neck flexion |
|
| D |
a and b |
The physiological dead space is decreased by:
| A |
Upright position |
|
| B |
Positive pressure ventilation |
|
| C |
Neck flexion |
|
| D |
a and b |
C i.e. Neck flexion
Physiological dead space is decreased in – supine posture, neck flexionQ and use of bronchoconstrictors and artificial airway (eg. intubation, tracheostomy)
Anatomical dead space is increased by all /except
| A |
Atropine |
|
| B |
Halothane |
|
| C |
Massive pleural effusion |
|
| D |
Inspiration |
Anatomical dead space is increased by all /except
| A |
Atropine |
|
| B |
Halothane |
|
| C |
Massive pleural effusion |
|
| D |
Inspiration |
C i.e. Massive Pleural effusion
– Pleural effusion normally tends to decrease physiological dead space initially. However when massive it also decreases anatomical dead space.
Atropine, halothane are bronchodialators, so T anatomical dead space. Inspiration may also streatch airways to anatomical dead space.
True about endotracheal intubation is:
| A |
It reduces normal anatomical dead space |
|
| B |
It produces decrease in resistance to respiration |
|
| C |
Subglottic edema is most common complication |
|
| D |
All of the above |
True about endotracheal intubation is:
| A |
It reduces normal anatomical dead space |
|
| B |
It produces decrease in resistance to respiration |
|
| C |
Subglottic edema is most common complication |
|
| D |
All of the above |
A i.e. It reduces the normal anatomical dead space
– Endotracheal tube decreases the anatomical dead space (150 ml) to as less as 25 ml.
– Endotracheal intubation increases the resistance to respiration; obstruction from kinking, foreign body or secretions further increase resistance.
Subglottic edema, though a complication, is not the most common one.
How will you calculate that how much inspired air actually ventilates the alveoli ‑
| A |
Single breath N2 method |
|
| B |
Dalton’s law |
|
| C |
Bohr equation |
|
| D |
Boyle’s law |
How will you calculate that how much inspired air actually ventilates the alveoli ‑
| A |
Single breath N2 method |
|
| B |
Dalton’s law |
|
| C |
Bohr equation |
|
| D |
Boyle’s law |
Ans. is ‘a’ i.e., Single breath N2 method
Examiner is simply asking that how will you measure anatomical dead space.
When air is breathed in, only the air that reaches the alveoli participates in gas exchange. The air in the airways (Trachea, bronchi) is breathed out unchanged as air in them does not participate in gaseous diffusion. Hence the airway space behaves as functionally dead so far as gas exhange is concerned. This is called ‘anatomical dead space’. The volume of this space is 150 ml. That means only the first 350 ml of the 500 ml inspired with each breath (tidal volume) at rest mixes with the air in the alveoli. Conversely, with each expiration, the first 150 ml expired is gas that occupied the dead space, and only the last 350 ml is gas from the alveoli. So, normally dead space (Vd) : tidal volume (Vi) ratio is 0.30 (150: 500).
Anatomical dead space is calculated by single-breath N2 method.
About option ‘C’
Bohr equation is used to calculate physiological (total dead space).
Normally, 350 ml of air enters the alveoli, with each breath. However, not all the air that enters the alveoli necessarily participates in alveolar gas exchange. In disease states, no diffusion (exchange) may take place between the gas in some of the alveoli and blood, and some of the alveoli may be overventilated. Such spaces in the alveoli constitues ‘alveolar’ dead space. The sum of anatomical dead space and alveolar dead space is called the ‘physiological’ dead space. Hence, the physiological dead space is the volume of inspired air, in airways (anatomical dead space) and in the alveoli (alveolar dead space), that does not participate in gaseous exchange. In healthy individuals, anatomical dead space and physiological dead space are identical because all the air entering into the alveoli participates in gaseous exchange (as alveolar diffusion, ventilation and perfusion are normal in healthy individuals).
A child, known case of bronchial asthma, presents with respiratory distress with respiratory rate of 48/ min, can speak barely 2 words. Nebulized salbutamol was given and patient could speak a sentence but there was a fall in Sp02 from 95% to 85%. What could be the possible explanation?
| A |
Ventilation perfusion mismatch because of increased dead space ventilation |
|
| B |
Intra-thoracic shunting |
|
| C |
Due to salbutamol |
|
| D |
Faulty pulse oximete |
A child, known case of bronchial asthma, presents with respiratory distress with respiratory rate of 48/ min, can speak barely 2 words. Nebulized salbutamol was given and patient could speak a sentence but there was a fall in Sp02 from 95% to 85%. What could be the possible explanation?
| A |
Ventilation perfusion mismatch because of increased dead space ventilation |
|
| B |
Intra-thoracic shunting |
|
| C |
Due to salbutamol |
|
| D |
Faulty pulse oximete |
Ans. a. Ventilation perfusion mismatch because of increased dead space ventilation
Ventilation perfusion mismatch because of increased dead space ventilation could be the possible explanation for the child of bronchial asthma presenting with respiratory distress with respiratory rate of 48/min, speaking barely 2 words but patient could speak a sentence with a fall in SpO, from 95% to 85% when nebulized salbutamol was given
Ventilation Perfusion Mismatch
- A defect, which occurs in the lungs whereby ventilation (the exchange of air between the lungs and the environment) and perfusion (the passage of blood through the lungs) are not evenly matched, a finding typical of bronchial asthma.
- V/Q mismatch is the most common cause of hypoxemia and a component of most causes of respiratory failure.
- In a patient with V/Q mismatch, there will most likely be some areas of the lungs, which are better perfused that ventilated and some areas which are better ventilated than perfused. While this occurs to some degree in the normal lung, in V/Q mismatch, it is increased significantly to the point of being pathological.
- In asthma, bronchospasm, mucus plugs, inflammation and airway obstruction in general worsen ventilation disrupting the balance between ventilation and perfusion
