Intraoperative Inspired Oxygen Exposure and Mechanical Ventilation Recorded 24–48 Hours After Intracranial Neurosurgery: An INSPIRE Cohort Study

When a patient undergoes major brain surgery, the medical team faces a delicate balancing act long after the operation ends. The patient must wake up from anesthesia, clear their mind, and regain the ability to breathe on their own. Sometimes, this process is delayed. The patient remains on a ventilator, a machine that pushes air into the lungs, for hours or even days after the surgery is finished. This delay is not just a matter of waiting; it can signal deeper issues, such as swelling in the brain, weakness in the airway, or complications in the lungs themselves. For decades, doctors have known that the way a patient is managed during the surgery—how much oxygen they receive, how their lungs are supported—might influence whether they can breathe independently once they leave the operating room. Yet, the exact role of the oxygen itself has remained a mystery. Is giving more oxygen during the procedure a safety net that helps, or does it inadvertently stress the lungs, making it harder for the patient to recover?

A team of researchers from Tongji Hospital in Wuhan, China, set out to investigate this question using a massive collection of real-world data. They focused on adults who had undergone major intracranial neurosurgery, which involves operations on the brain or skull. The researchers were particularly interested in the amount of extra oxygen the patients received while they were asleep under general anesthesia. In a typical operating room, patients breathe a mixture of air and supplemental oxygen. The researchers wanted to know if the total amount of this extra oxygen, given while the patient's blood oxygen levels were already healthy, was linked to the need for breathing support later on. They did not look at whether the oxygen caused direct damage, but rather if a higher dose was a signal that the patient was more likely to need a ventilator between 24 and 48 hours after the surgery ended.

To find the answer, the team analyzed records from 1,602 patients who had undergone these complex brain surgeries. They used a sophisticated method to measure the "excess" oxygen each patient received. Instead of just looking at the average setting on the oxygen machine, they calculated the total amount of extra oxygen given only during the times when the patient's blood oxygen saturation was already above a safe threshold. This approach allowed them to isolate the deliberate administration of extra oxygen from the emergency treatment of low oxygen levels. They then checked the hospital records for every patient to see if there was a note indicating that the patient was still on mechanical ventilation between one and two days after the operation.

The results revealed a clear pattern. Patients who received a higher total amount of extra oxygen during their surgery were more likely to be recorded as needing mechanical ventilation in the 24 to 48-hour window after the procedure. Specifically, for every ten percentage-point increase in the amount of excess oxygen exposure, the odds of the patient still needing ventilation support rose significantly. The study found that this association held true even after the researchers adjusted for other factors that could influence the outcome, such as the patient's age, the urgency of the surgery, the type of brain procedure performed, and how long the operation lasted. When they looked at the data, they saw that patients with the highest levels of extra oxygen exposure were much more likely to have a ventilation record than those with the lowest levels.

However, the researchers were careful not to declare that the oxygen itself caused the need for the ventilator. In fact, their analysis suggested that the relationship was likely more complex. When they added details about how the lungs were managed during the surgery—such as the pressure settings used to keep the airways open and the size of the breaths delivered by the machine—the strength of the link between extra oxygen and postoperative ventilation weakened. This suggests that the amount of oxygen given was not acting alone as a harmful agent. Instead, it likely served as a marker for the overall condition of the patient or the complexity of the surgery. Doctors may have chosen to give more oxygen to patients who were already sicker, had more severe bleeding, or were undergoing longer, more difficult procedures. In this view, the extra oxygen was a response to the patient's vulnerability rather than the direct cause of their delayed recovery.

The study also addressed a specific question about the type of breathing support. Because the data did not always distinguish between invasive ventilation (where a tube is placed in the windpipe) and non-invasive support (where a mask is used), the researchers audited the timing of the records. They found that in the vast majority of cases where a ventilation record appeared 24 to 48 hours later, the patient had been on support continuously since the surgery ended, rather than being taken off and put back on. This pattern reinforced the idea that the surgery and the immediate recovery period were the critical factors. Yet, even with this detailed look, the data could not prove that lowering the oxygen levels during surgery would prevent the need for a ventilator later. The study explicitly stated that it did not establish a specific "safe" or "unsafe" level of oxygen for these patients.

Ultimately, this research provides a clearer picture of the landscape surrounding brain surgery recovery, even if it does not offer a simple solution. It confirms that the amount of extra oxygen a patient receives is tied to their likelihood of needing breathing support later, but it also highlights that this link is likely driven by the severity of the patient's condition and the nature of the surgery itself. The findings suggest that the extra oxygen is often a symptom of a challenging case rather than the culprit behind the delay in recovery. For the medical community, this means that while monitoring oxygen levels is important, the focus must remain on the broader picture of patient health and surgical complexity. The study serves as a reminder that in the intricate world of neurosurgery, the path to recovery is influenced by a web of factors, and simply adjusting one variable like oxygen concentration is unlikely to solve the puzzle of postoperative breathing difficulties on its own.