CONTROL OF RESPIRATION AND BREATHING ANESTHESIA

CONTROL OF RESPIRATION AND BREATHING

1. CONTROL OF RESPIRATION /BREATHING Daniel Kithome -RCOA 31/10/2017

2. Anaesthesia affects respiratory function in different ways. Physiological control systems involving the nervous system usually have three components. These are; A central controlling area. An afferent pathway An efferent pathway .

3. Has 2 neurons –inspiratory and expiratory. The neurons of the controlling area integrate the information from other parts of the body and produce a coordinated response. The 2 neurons automatically maintain a rhythmic cycling pattern of inspiration and expiration. This response from the central controlling area is carried to various organs and muscles along efferent pathways. The input to the central controlling are via afferent.

4. Central controlling area Called the respiratory centre. Is in the lower part of the brain stem, in medulla oblangata. There are inspiratory neurons which are active during inspiration and inactive during expiration. The two groups of neurons automatically maintain rhythmic cycling pattern of inspiration and expiration

5. Afferent supply (a) Central chemo receptors. Chemo receptors are cells that respond to chemical stimuli. Cells in the floor of the fourth ventricle that respond to the acidity of the CSF and the output from these cells influences breathing. The acidity of any fluid is measured by PH. Normal PH 7.35-7.45. A higher PH represents alkaline conditions.

6. Low pH= acidic conditions. The cells in the floor of the ventricle respond to the pH of the CSF. An acidic CSF causes the reason for hyperventilation- the reason for dyspnoe with conditions such as diabetic keto acidosis. An alkaline CSF inhibits respiratory centers.

7. If the CO2 in the blood increases e.g during exercise then the CO2 increase in the CSF. This causes hyperventilation which lowers the CO2 . Hypocarbia has the opposite effect . It may occur following controlled ventilation during anaesthesia . This may delay return of spontaneous breathing at the end of surgery.

8. (b) Peripheral chemoreceptors The carotid and aortic bodies are small pieces of tissue that contain chemoreceptors which respond to O2 and CO2 concentration in the arterial blood. The carotid body is the more important of the two and is situated at the division of the common carotid artery into the external and internal carotid arteries in the neck.

9. The aortic body is found in the aortic arch. The information from the carotid body is carried along the glossopharyngeal and the vagus nerve to the respiratory centre. Increase of CO2 leads to an immediate and marked increase in breathing. These limits can be modified by disease or age for example bronchitis .

10. ( c ) Brain We can all consciously breathe deeply and more rapidly and this can happen during exercise, intense emotional situations for example distressing sights. Hyperventilation is also part of the response to massive blood loss. This response is coordinated by the autonomic nervous system in the hypothalamus and the vasomotor centre in the brainstem

11. (d) Lungs Various receptor in the lung that modify breathing. Receptors in the wall of the bronchi respond to irritant substances and cause coughing, breath holding and coughing. There are stretch responses that occur when the lung and chest wall are distended this is to avoid over distension of the lungs.

12. EFFERENT SUPPLY The efferent nerves from the respiratory centre pass down the spinal cord to the diaphragm, intercostal muscles and acessory muscles of inspiration in the neck. The diaphragm is supplied by the phrenic nerve that is formed in the neck from the spinal nerves C3,4 and 5. The intercostal muscles are supplied by the segmental intercostal nerve that leave the spinal cord between T1 and T12.

13. The accessory muscles in the neck are supplied from the cervical plexus. During normal breathing inspiration is an active process while expiration is passive. The most important muscles for inspiration is the diaphragm. Any disease that affects the efferent pathways may cause severe difficult breathing. Trauma to the cervical cord is normally fatal.

14. ANAESTHETIC DRUGS AND RESPIRATION Opiods drugs such as morphine or fentanyl depress the respiratory centres response to hypercarbia. These effects can be reversed by naloxone . Volatile anesthetic agents depress the respiratory system as well. When oxygen is not available respiration should always be supported during anesthesia.

15. Thank you.