Nausea and vomiting is your body’s mechanism for eliminating foreign substances that might cause harm or damage. Most researchers agree that Post-Operative Nausea and Vomiting (PONV) is triggered when the brain detects the presence of anesthesia and/or opiates, then responds with protective reflexes meant to stop the absorption of toxins or poisons.

Opiate pain killers, such as morphine, are known to cause to nausea and vomiting, and to delay digestion and gastric emptying. Many anesthetics (especially general anesthesia inhalants) are also known to cause PONV in the recovery room.

The Anatomy

The Physiology

When you go into a hospital for surgery requiring more than a local anesthetic, you will often be given medication prior to the operation to sedate you, relieve pain, and prepare you for the anesthesia. Morphine and its derivatives are probably used most frequently for pre-medication and for pain control after the procedure. The anesthesia itself is used to block any feeling or sensation while the surgery is being done.

Both the opiates (morphine) and the anesthesia enter the bloodstream and work their way into the spinal fluid. The Chemoreceptor Trigger Zone, located in the Medulla, monitors the bloodstream and the cerebrospinal fluid for signs of foreign toxins in the body. When the CTZ detects the continued presence of opiates or anesthetics in the system, it activates the Vomiting Center (also located in the Medulla).

The Vomiting Center is the coordinator for your body’s vomiting reflex, used to eliminate possible toxins by forcefully expelling the contents of your stomach. This reflex mechanism begins with signals of discomfort to the stomach, followed by the awareness of the urge to vomit (feeling nauseous). It can then continue on to the involuntary abdominal muscle contractions that result in the actual vomiting of the stomach contents.