This blog follows on from the twitter thread from @gasnovice
PONV is defined as retching or vomiting within 24hrs of surgery. It is common - and could affect up to 30% of patients undergoing a general anaesthetic if we didn't take steps to address it. It’s the most common PACU complaint from patients and the commonest cause for delayed PACU discharge.
Patients dread it (more so than pain according to some surveys) especially if they've had it before.
As if this wasn't enough reason for us to intervene and try to prevent...PONV can also have serious implications:
Wound dehiscence
Dehydration
Elecrolyte imbalances (metabolic alkalosis)
Aspiration
Delayed nutrition (affect wound healing and immunity)
Prolonged hospital length of stay (cost and patient flow)
But it doesn't necessarily end after 24 hours. There is such a thing as post discharge nausea and vomiting (PDNV) which can affect patients when at home and potentially without access to prescribed therapies or support. see here https://doi.org/10.1097/ALN.0b013e318267ef31
Therefore, because of it's potential prevalence, impact on the patient experience and cost implications...guidelines of course exist. There are international consensus guidelines (https://bit.ly/3BScPTz) and you local departments will have a policy too.
Broadly speaking...all approaches are similar (and logical)
Step 1 - identify a patients risk of PONV.
Several scores exist. The most common in clinical practice for adults is the APFEL score
https://pubmed.ncbi.nlm.nih.gov/17236637/ consisting of 4 risk factors:
Female gender
History of PONV or motion sickness
Non-smoker
Perioperative opiate use
Each risk factor adding approximately 20% to your chances of getting PONV!
In children, the commonest is the POVOC score https://doi.org/10.1213/01.ane.0000135639.57715.6c :
Surgery duration >30mins
Age >3yrs
High risk surgery (strabismus)
History of PONV on child or relative
With these scores we can identify a patient's risk as low, medium (usually >40%) or high (>70-80%).
Step 2 - mitigate the risk of PONV
We can then reduce a patients risk of experiencing PONV through our anaesthetic/surgical choices:
Pharmacological therapy
Avoiding GA/volatiles
Using regional anaesthesia techniques
Using TIVA
Minimising opiate use
Minimising operative time
Adequate hydration
The higher the risk, the more interventions we are likely to employ and the more modifications we are likely to make.
Low risk patients will typically have 1 pharmacological agent
Medium risk patients will have 2 agents
High risk patients will have 2-3 agents AND have change in the anaesthetic technique
Step 3 - choose the right agents to use
There are A LOT of anti-emetic agents out there, some of whose mechanisms we do not yet fully understand. However a good working knowledge of them is essential.
Firstly, I want to direct you to a Cochrane review of antiemetic agents. It's a big document with a convenient summary table. The review looked at 44 drugs and ranks them by PONV risk reduction (RR) and side effect profiles.
Secondly its important to realise that these agents reduce risk in relative terms... So for example:
Patient A has a PONV risk of 80% (high)
Patient B has a PONV risk of 20% (low)
We give them both haloperidol 500mcg (risk reduction 49%)
Patient A now has a PONV risk of 40% (a 40% absolute RR)
Patient B now has a PONV risk of 10% (a 10% absolute RR)
The biggest gains are for Patient A, with the higher risk. This is really important, because it might affect the risk/benefit consideration. For only a 10% reduction in risk, we might not be so keen to expose to the potential side effects of extrapyramidal Sx, agitation and long QT.
Thirdly, There appears to be a ceiling effect for anti-emetics. They are not additive and the effect plates at around 80% RR
So we shouldn't over-prescribe these agents to try and beat the risk down to 0% (we won't manage it and we will expose patient to side effects and harm)
Step 4 - consider their post operative wellbeing
If you think someone has a high risk of PONV, then make sure there are agents available to use in recovery, on the ward and (if necessary) on discharge.