Hypercarbia

Question 1

What is hypercapnia/hypercarbia?

Answer 1

-CO2 retention

Question 2

Hypercarbia is a reflection of either:

Answer 2

1. increased CO2 production

2. inadequate alveolar ventilation

Question 3

What does PACO2 mean?

Answer 3

Partial pressure of carbon dioxide in the the alveolus

Question 4

What does PaCO2 mean?

Answer 4

The partial pressure of carbon dioxide in the arterial blood

Question 5

What does PetCO2 mean?

Answer 5

It is the carbon dioxide partial pressure at the end of expiration

Question 6

What is hypercarbia?

Answer 6

The arterial blood partial pressure of carbon dioxide that is more than 6kPA/45mmHg

Question 7

What is the normal value of PaC02 in the arterial blood?

Answer 7

36-44mmHg or 5,-5,6 Kpa

Question 8

What is the normal pH at sea level?

Answer 8

7,36-7,44

Question 9

PaCO2>6 KpA is affected by?

Answer 9

Directly proportional to the CO2 production and inversely proportional to the alveolar ventilation

Question 10

What is the definition of hypoxemia?

Answer 10

Low amount of partial pressure of oxygen in the arterial blood

Question 11

What is the definition of hypoxia?

Answer 11

Low amount of oxygen perfusion to the tissues that does not meet metabolic needs

Question 12

What are the 3 sensors that regulate hypercarbia?

Answer 12

1. central chemo receptors
2. peripheral chemoreceptors
3. mechano receptors

Question 13

What are the central chemoreceptors?

Answer 13

They will be found in the medulla and respond to changes in hydrogen ion concentration due to the movement of these ions across the blood brain barrier
This stimulates the increase in Minute volume
Minute volume is rate multiplied by tidal volume
-central receptors facilitate about 70% of the response

Question 14

What are the peripheral receptors?

Answer 14

They are caused by the carotid and aortic body

• they respond to PaO2, pH and PaCO2
• facilitates 30% of the response

Question 15

What are the mechanoreceptors?

Answer 15

They are caused by stretch receptors, irritant receptors, muscles and joint receptors

Question 16

Why do we have increased ventilation with PaCO2?

Answer 16

Basically the body is trying to expel the CO2 and so respiration increases to reduce the PaCO2 and pH to back to normal

Question 17

What are the causes of increased VCO2?

Answer 17

The production of CO2 is increased by

• sepsis
• MH
• thyrotoxicosis
• shivering
• convulsions

Question 18

What are the decreases of central alveolar ventilation?

Answer 18

-central-IV induction drugs, IAA, Benzodiazepines, opiates

Neuro: CVA, prematurity, encephalopathy, hypothermia

Question 19

What are the decreases of peripheral alveolar ventilation?

Answer 19

1. Upper airway obstruction
2. Lungs: asthma, COPD from increased work of breathing
   Increased dead space pulmonary embolism, hypovolaemia, hypotension
3. pump mechanism: rib fractures, diaphragm paralysis, high spinals

Question 20

How can we clinically diagnose hypercarbia?

Answer 20

1. Blood gas is the gold standard

2. capnography- arterial alveolar gradient

Question 21

How does a patient present to us if they are hypercarbic?

under anaesthesia

Answer 21

1. Tachycardiac
2. confused/ mental obtunded
3. dysrythmias
4. hypotension/hypertension
5. tachypneo

Question 22

What is the management of a patient presenting with hypercarbia?

Answer 22

1. Airway- make sure there is no airway obstruction and do the head tilt, jaw thrust chin lift manouvre, put in oropharyngeal or nasopharyngeal airway if not responding
2. Breathing: chest movements(be worried if <10 ;>30 and check that tidal volumes are 5ml/kg
3. Circulation: pulses etc support if needed
4. Search for the cause

Question 23

What are the muscles of inspiration and expiration?

Answer 23

1. accessory muscles
2. intercostal muscles
3. abdominal muscles
4. diaphragm muscles

Question 24

What are the controllers?

Answer 24

1. pontine- pneumotaxic centre, apneustic centre

2. medulla- dorsal respiratory group, ventral respiratory group

Question 25

What are the adverse effects of hypocarbia?

Answer 25

1. Decreased cerebral blood flow
2. Decreased cardiac output
3. Respiratory depression