1. Epidemiology & Incidence

Nausea and vomiting are highly prevalent and distressing symptoms in both intensive care unit (ICU) and oncology settings. Their presence significantly complicates patient management by interfering with nutrition and sedation, prolonging mechanical ventilation, and increasing the risk of aspiration.

Prevalence

• General Critical Illness & Oncology: Affects 20–70% of patients in these populations.
• Diabetic Gastroparesis: A contributing factor in 5–10% of ICU admissions for patients with diabetes.
• Postoperative Nausea & Vomiting (PONV): Occurs in over 30% of patients after abdominal or intracranial surgery, even with standard prophylaxis.

Clinical Impact

• Interrupts enteral feeding schedules and complicates sedation weaning.
• Associated with a 1–3 day increase in mechanical ventilation duration and ICU length of stay.
• Elevates the risk of aspiration events, which can lead to ventilator-associated pneumonia (VAP).

2. Pathophysiology

Vomiting is a complex reflex coordinated by the medullary emetic center, which integrates afferent signals from four primary sources: the chemoreceptor trigger zone (CTZ), peripheral vagal afferents from the gastrointestinal tract, the vestibular system, and higher cortical centers.

Neurotransmitter Roles

• Serotonin (5-HT3): A primary mediator of acute-phase emesis, especially from the GI tract.
• Substance P (NK1): Crucial for delayed-phase emesis, particularly in chemotherapy-induced nausea and vomiting (CINV).
• Dopamine (D2): Key receptor in the CTZ, activated by metabolic toxins and various drugs.
• Histamine (H1) & Muscarinic (M): Primarily involved in mediating signals from the vestibular system and higher brain centers.

3. Influence of Chronic Diseases

Chronic conditions such as renal failure, hepatic dysfunction, and metabolic disorders can significantly lower the threshold for nausea and vomiting. They achieve this by sensitizing central and peripheral emetic pathways, impairing GI motility, and altering the patient’s response to standard treatments.

Case Example: A patient on intermittent hemodialysis presents with persistent nausea despite scheduled ondansetron. Management should focus on addressing the underlying uremia and gastroparesis by considering continuous low-volume enteral feeds, adding a prokinetic agent like metoclopramide, and ensuring gradual correction of any electrolyte abnormalities.

4. Social Determinants of Health

The management of nausea and vomiting extends beyond pathophysiology to include social and economic factors. Barriers to medication access, low health literacy, and psychosocial stressors can substantially increase a patient’s symptom burden and undermine the effectiveness of treatment plans.

Medication Access & Cost

Financial constraints and limited insurance coverage can be significant barriers. Newer, more effective agents like neurokinin-1 (NK1) antagonists and branded 5-HT3 antagonists (e.g., palonosetron) may be prohibitively expensive, leading to reliance on older, potentially less effective therapies with more side effects.

Health Literacy & Adherence

A patient’s ability to understand and follow complex medication schedules is crucial for preventing breakthrough symptoms. Poor comprehension of dosing instructions, particularly for as-needed medications, can lead to under-treatment. Furthermore, patients may underreport early or mild nausea, delaying intervention until symptoms become severe.

Psychosocial Stressors

Anxiety and anticipatory nausea are powerful triggers, especially in patients undergoing chemotherapy. The psychological expectation of becoming sick can activate cortical pathways that induce emesis. In these cases, behavioral therapies (e.g., cognitive behavioral therapy, relaxation techniques) and anxiolytics can be valuable adjuncts to standard antiemetic therapy.

5. Clinical Implications & Controversies

Effective management requires a systematic approach that differentiates functional from organic causes, applies individualized risk frameworks, and acknowledges the limits of current diagnostic tools.

Functional vs. Organic Etiologies

A key diagnostic challenge is distinguishing between organic and functional causes.

• Organic causes are identifiable through testing and include structural issues (e.g., obstruction), toxic-metabolic derangements (e.g., uremia), or infections.
• Functional causes are diagnoses of exclusion, characterized by normal labs and imaging. They are thought to involve visceral hypersensitivity and autonomic dysregulation.

Individualized Risk Assessment

A one-size-fits-all approach to prophylaxis is often inadequate. Patients should be stratified into low, moderate, or high-risk categories based on a combination of clinical (e.g., type of surgery, history of PONV), laboratory (e.g., renal function), and social factors. High-risk patients should receive preemptive, multimodal prophylaxis bundles.

Advanced Diagnostics

For refractory cases suspected to be related to motility disorders, advanced testing may be considered. Gastric emptying scintigraphy is the gold standard for diagnosing gastroparesis, while electrogastrography (EGG) can assess gastric myoelectrical activity. Investigational biomarkers like substance P and inflammatory cytokines are being studied but are not yet in routine clinical use.