Opioid-induced respiratory depression

Question 1

Control of breathing

Answer 1

Chemical control: input from peripheral and central chemoreceptors on blood oxygenation and CO2 levels influence minute ventilation- the main process in patients under anaesthesia
- Central receptors are in the medulla and are the majority of the response to hypercapnia
- Peripheral in the carotid bodies solely responsible for hypoxia and slightly hypercapnia

Behavioural control: dependent on eating, drinking, exercising, talking etc. Input mainly from the cortex

Medulla and pons integrate information from both and control the diaphragm and intercostal muscles.
Pre-Botzinger nucleus (resp rhythm generation), parabrachial (sustains upper airway patency) and Kolliker-Fuse nucleus

Question 2

Opioids effects on ventilatory control

Answer 2

Agonism of mu-opioid receptors in the brainstem activates B-arrestin signalling causing reduced hypercapnic ventilatory response

Question 3

RFx for Opioid-Induced Resp Depression

Answer 3

• Age >60
• Male
• Opioid naive
• Sleep-disordered breathing/ High STOP-BANG score
• Chronic heart failure
• Use of opioids with high affinity for the mu-opioid receptor- buprenorphine, sufentanil, remifentanil

Question 4

Limitations of naloxone for Opioid-Induced Resp Depression

Answer 4

• Short half-life
• Can precipitate acute withdrawal- which can lead to seizures
• Difficulty displacing high-affinity opioids such as sufentanil and buprenorphine