Appeal from the Circuit Court of the 12th Judicial Circuit, Will County, Illinois. No. 98-L-374 Honorable Lawrence Gray, Judge, Presiding.
 The opinion of the court was delivered by: Justice McDADE
 Plaintiff, Phillip Matuszak, brought a medical malpractice action against his treating physician and hospital for damages allegedly sustained during a colonoscopy procedure. The trial court entered judgment on a jury verdict for defendants, and plaintiff timely appealed. In this appeal, plaintiff presents only one issue for review: Whether the trial court committed reversible error in allowing defendant's expert witness to render speculative opinions regarding the possible causes of his injury. We find the court did not err and we affirm.
 This present lawsuit arises from plaintiff's 1996 colonoscopy involving the use of the drug Versed. The record reveals that in July of 1996, plaintiff developed abdominal cramping and had blood in his stools. After he had been evaluated by his family physician, it was recommended that he undergo a colonoscopy in order to further assess his digestive tract.
 Colonoscopy is a procedure in which a flexible, lighted instrument connected to a video screen is inserted into the rectum and moved around to permit examination of a patient's large intestine. Plaintiff's colonoscopy was performed on July 26, 1996, by Dr. Gerald Cerniak at St. Joseph's Medical Center. Prior to the procedure, Dr. Cerniak ordered the administration of three drugs, Demerol, Phenergan and Versed, to induce conscious sedation, calming and anti-nausea effects to reduce patient discomfort during the procedure. Versed, which acts directly on the patient's central nervous system, causes respiratory depression, which in turn could lead to hypoxia, a lack of oxygen in the blood.
 During the procedure, the monitoring of oxygen saturation after the administration of Versed is a critical function, since a patient whose blood oxygen drops below a certain level for even a short period of time can suffer brain damage, and possibly death. Along with other devices for monitoring his vital signs, a pulse oximeter, a device attached to the patient's finger, was used during plaintiff's colonoscopy to record pulse as well as to determine oxygen saturation in the blood. The oximeter sounds an alarm if the blood oxygen falls below the critical 90% level.
 Judy Dunham and Barbara Scott, registered nurses employed by St. Joseph's Medical Center, monitored Matuszak's vital signs and oxygen saturation level at specific intervals during the colonoscopy. The first notation that the nurses made on plaintiff's medical chart showed that at 10:50 a.m., plaintiff had been given 75 milligrams of Phenergan and 50 milligrams of Demerol. A five-milligram dose of Versed was administered at 11:55 a.m. Plaintiff's chart showed that he had an oxygen saturation level of 98% at that time, a reading in the upper range of normal. At noon, plaintiff received another five milligrams of Versed; his oxygen saturation was recorded at 90%, the lowest point within the normal range. By 12:15 p.m., his blood oxygen had risen to 96%, and it remained at that level until the procedure was completed at 12:25 p.m. There was no evidence that the pulse oximeter alarm ever sounded.
 Plaintiff was discharged from St. Joseph's at 1 p.m. It was shown that he had lunch at a local restaurant, visited several stores and shops, and later that evening, engaged in sexual relations with his wife. Testimony at trial indicated that such sexual activity is not possible within 24 hours of an hypoxic event. Several days after the procedure, plaintiff became confused and disoriented, causing his wife to worry. Plaintiff was hospitalized in mid-August 1996, after a period of confusion, lethargy, and severe headaches.
 Plaintiff's wife Judy testified that plaintiff developed symptoms of confusion and disorientation immediately after the colonoscopy. She stated that plaintiff's prior medical impairments included headaches, dizziness, ear infections, and upper respiratory tract infections. Additionally, she testified that plaintiff had been using the drug Valium on a regular basis for relief from injuries he sustained in a 1968 automobile accident.
 Subsequent hospital examinations revealed decreased blood flow to both sides of plaintiff's brain. A Single Photon Emission Computed Tomography (SPECT) scan, performed at Loyola University Medical Center, provided evidence of diminished brain activity. The scan showed diminished blood flow in the temporal lobe and parietal area of plaintiff's brain. Following the initial tests and hospitalization, plaintiff continued to exhibit the above mentioned symptoms, plus angry outbursts, paranoia, and short-term memory problems.
 He was next examined at the Mayo Clinic in Rochester, Minnesota. Doctors at the Mayo Clinic performed a differential diagnosis, which accounts for or rules out other medical conditions that may cause or contribute to plaintiff's present symptoms and complaints. This diagnosis led them to conclude that plaintiff suffers from a "cognitive dysfunction of unknown etiology."
 The pertinent issue at trial was whether defendants deviated from the standard of care in failing to properly administer the appropriate amount of the drug Versed. Plaintiff therefore presented the testimony of various standard-of-care experts at trial, including Dr. William Cahill, who specializes in internal medicine and is board certified. Dr. Cahill testified that Dr. Cerniak gave plaintiff "too much Versed, which is a very dangerous drug. *** [H]e gave it too quickly. He didn't wait long enough in between the individual doses to be sure on what the effect of the drug was. He didn't know what it was. He gave it too quickly." Dr. Cahill further stated that the oxygen saturation level of 90% was below normal and subsequently caused irreversible damage to plaintiff's brain. He explained that, when a brain is deprived of oxygen, it will recover unless and until a threshold is reached, and after that time, permanent injury results. Dr. Cahill concluded that such a threshold was reached in this case.
 Plaintiff next presented the testimony of Dr. William Berger, a board-certified anesthesiologist. Dr. Berger described defendants' use of the medication as "way too much" throughout the colonoscopy procedure. He also opined that a "reasonable physician" should "guard against *** giving this much Versed." He further stated that the risk of brain injury existed in this case when plaintiff's oxygen saturation reading was recorded at 90%.
 However, it appeared that plaintiff's medical experts who testified on causation could not definitely conclude that the administration of Versed on July 26 caused either an hypoxic event or plaintiff's conditions. Dr. Ronald Petersen, plaintiff's treating physician at the Mayo Clinic, informed the jury that it was unlikely that hypoxia was the cause of plaintiff's conditions. Dr. Petersen examined plaintiff's SPECT scan results and concluded "that the SPECT blood flow pattern, interpretations, are nonspecific."
 Dr. Morris Fishman, plaintiff's treating physician during his hospitalization at Loyola, testified that the testing that had been performed on plaintiff could not conclusively establish the origin of his symptoms. Dr. Fishman stated that based on his examination and treatment of plaintiff, he could not find "clear evidence for any meaningful structural neurological injury. Nor could [Dr. Fishman] on the basis of the available evidence relate it to the colonoscopy in July." Both doctors relied on differential diagnosis to arrive at their conclusions. Each identified several possible causes for plaintiff's symptoms, including Alzheimer's disease, stroke, elevated urinary arsenic level, rheumatoid arthritis, depression, and an infectious disease process suggested by elevated protein levels found in plaintiff's cerebral spinal fluid. Both experts considered those ...