Respiratory Acidosis: This condition occurs when the lungs cannot remove all the carbon dioxide the body produces, leading to an increase in blood carbon dioxide levels. Nausea can be a symptom due to the acid-base imbalance affecting various bodily functions. The increased venous carbon dioxide (CO2) is a direct indicator of respiratory acidosis.

Chronic Obstructive Pulmonary Disease (COPD): COPD can lead to respiratory acidosis due to impaired lung function, resulting in increased CO2 levels and symptoms like nausea.
Pneumonia: Severe pneumonia can impair gas exchange in the lungs, leading to increased CO2 levels and symptoms such as nausea.
Sedative or Opioid Overdose: Overdose on sedatives or opioids can lead to respiratory depression, resulting in increased CO2 levels due to hypoventilation and may cause nausea.

Diabetic Ketoacidosis (DKA): Although primarily associated with metabolic acidosis, DKA can also lead to increased CO2 levels in severe cases due to respiratory compensation mechanisms. Nausea and vomiting are common symptoms. Missing this diagnosis can be fatal.
Cardiac Arrest or Severe Cardiac Dysfunction: These conditions can lead to inadequate circulation and ventilation, resulting in increased CO2 levels. Nausea might not be the primary symptom, but these conditions are critical and require immediate attention.

Mitochondrial Myopathies: Certain mitochondrial disorders can affect the muscles used for respiration, leading to respiratory failure and increased CO2 levels. Nausea might be a symptom due to the systemic nature of these diseases.
Malignant Hyperthermia: This is a rare but life-threatening medical emergency that can occur in response to certain anesthetics. It leads to increased CO2 production due to hypermetabolism and can cause nausea among other symptoms.