Definition and Prevalence
Nausea can either be acute, or chronic, and is not always associated with vomiting. In many cases it is possible to identify a cause, although in the palliative care population nausea is frequently multifactorial.
Palliative diagnosis that frequently cause nausea and / or vomiting include intra-abdominal or gastrointestinal malignancies - especially those which result in bowel obstruction; central nervous system malignancy - which may cause raised intracranial pressure, cerebellar or vestibular symptoms; and HIV AIDS.
Other factors that contribute to nausea and / or vomiting that should be considered, and treated where possible, include:
- Metabolic imbalance, including hypercalcemia, uraemia, liver failure
- Sepsis (including urinary tract and respiratory tract infection)
- Conditions affecting gastrointestinal motility, including constipation, previous surgery, gastroparesis, or autonomic failure
- Reflux or peptic ulcer disease
- Medication and treatment side effects, including opioids and other drugs, chemotherapy, and radiotherapy
- Anxiety and depression, anticipatory nausea
- Inappropriate presentation of food.
There are no widely accepted assessment tools for nausea and vomiting in palliative care, particularly for research. Nausea must be self-assessed by patients, whereas vomiting can be monitored objectively. Nausea is routinely assessed in Australian palliative care services using Symptom Assessment Scores (SAS) which is part of the PCOC dataset.
A systematic review has identified evidence to support the use of metoclopramide and 5HT3 antagonists in advanced cancer.  Other antiemetics are frequently used in palliative care, but at present lack a strong evidence base. The choice of an antiemetic for nausea may be either empirical, or aetiological - related to the likely main mechanism of nausea and / or vomiting. There is no evidence to support one approach over the other, based on a systematic review of randomised controlled trials. 
Nausea is a common side effect of opioid use and much of the research generated on opioid-induced nausea and vomiting comes from an acute and post-operative clinical setting. A recent systematic review of nausea and vomiting associated with opioids identified limited evidence to support the practice of opioid rotation or switching.  There are guidelines recommending clinical practice for treating nausea in cancer.  There is limited specific evidence for antiemetic choice in older people or paediatrics.
Use of antiemetics is examined in more detail in a separate section as is bowel obstruction related to gastrointestinal malignancy.
More on this topic:
Malignant Bowel obstruction
- There are no widely accepted assessment tools for nausea and vomiting in palliative care.
- Despite widespread use in palliative care, there is currently no high level evidence supporting the use of haloperidol as an antiemetic. 
- A recent meta-analysis of cannabis based medications did not find these medications superior to conventional anti-emetics. 
- A multisite randomised controlled trial studying antiemetics in palliative care is underway in Australia. It will firstly test whether prescribing according to clinical guidelines based on the presumed mechanism of nausea is effective, and secondly for patients with refractory nausea, will compare methotrimeprazine (levomepromazine) with either ondansetron or best supportive care using other antiemetics.
- The role of various complimentary therapies continue to be investigated.