Intermittent Positive Pressure Ventilation (IPPV) + Neuro-muscular Blockade (NMB) Flashcards
Under what circumstances might we need to breathe for the patient?
- Patient is not breathing on its own: due to apnea or respiratory arrest
- Inadequate alveolar ventilation: CO2 levels too high in the lungs (ETCO2 > 7.5kPa)
- Thoracic surgery: lungs open to the atmosphere and they will collapse
- Diaphragmatic hernia repair: abdomen and thorax connected
- Administration of high dose opioid drugs: e.g. Fentanyl can cause major resp depression
- Raised intracranial pressure: must control CO2 levels
- Neuromuscular blockade: these agents paralyze all skeletal muscles including the muscles of respiration
What is the definition of Intermittent Positive Pressure Ventilation?
- Manual squeezing of the bag on a breathing system/ Ambu bag
- Mechanical ventilator breathing for the patient
Why might we want to abolish the patients own respiratory efforts?
If we want to start giving IPPV
e.g. they have apnea and are not breathing enough to support themselves, or we want to place them on a ventilator before the patient undergoes a thoracic or diaphragmatic hernia surgery
How can a patients respiratory efforts be abolished?
1) Use a respiratory rate that is slightly faster than the patients normal RR, by providing IPPV just before the patient would breathe itself, over a short period of time the patients respiratory efforts are abolished
2) Ventilate the lungs slightly more than the patients efforts
3) Drugs: Ketamine, Fentanyl or NMB agents
What is the Inspiratory : Expiratory ratio (I:E) used during IPPV, and why?
1:2 or 1:3
This allows for more exhalation, and therefore venous return is less likely to be compromised
How can anesthesia be maintained during IPPV?
1) volatile agents at a reduced vaporizer setting
2) TIVA e.g. propofol or alfaxalone
Both of the above must be supplemented with analgesia (opioids, medetomidine, ketamine)
and if CO2 is too high, then increase RR or TV, or both
Will a patient breathe again after undergoing IPPV?
Yes
Majority of cases will spontaneously breathe on their own, they just need a moment
It always helps to wait for sx to end, and have the drapes removed so you can visualize the movement of the chest
Always reverse any neuromuscular blockades
Why might a patient failt to breathe following IPPV?
1) Deep anesthesia: reduce iso or turn it off
2) Hypothermia: depresses respiration
3) Hypocapnia: reduces the patients respiratory drive
4) Pneumothorax: thoracic drain should be placed
5) Pain: patient may not want to take normal inhalation depths if in pain
6) Residual neuromuscular blockade: needs to be fully reversed
7) Severe brain injury
What are the 3 important points relating to Neuro-muscular Blocking agents?
1) ALL skeletal muscle is paralyzed: patient cannot breathe or move
2) NMB agents do NOT provide analgesia: patients can feel the entire sx
3) NMB agents do NOT provide hypnosis: the animal is therefore awake
What are the potential indications for the use of NMB’s?
- Provide full muscle relaxation in patients undergoing surgery where deep surgical access is needed
- To facilitate control of respiration and allow IPPV
- Ocular surgery: though nerve blocks can be used instead to get the same central position of the eye and abolish eye movement
note: NMB agents are RARELY used in vet medicine and is never used in general practice
If all movement, reflexes and respiratory function are abolished with the use of NMB’s, how do we assess the depth of anesthesia in a patient?
- Cardiovascular system: blood pressure, heart rate and pulse quality
How are NMB’s reversed/ what drugs are used?
- Competitive neuromuscular blocking agents can be reversed with Anticholinesterase drugs (e.g. Neostigmine or edrophonium): these act at the nicotinic and muscarinic receptors and will reverse the non-depolarizing agents
side effects include: decreased HR and increased salivation. Therefore they are often combined with atropine or glycopyrrolate to prevent the side effects
