[Hypoxemia after general anesthesia]

Studies conducted shortly after the implementation of pulse oximetry (PO) into clinical practice 20-25 years ago revealed that many patients breathing room air during transfer from the operating room (OR) to the post-anesthesia care unit (PACU) directly after general anesthesia (GA) had a peripheral oxygen saturation (S(p)O(2)) below 90%. Moreover, it was shown that the detection of hypoxemia by clinical criteria is extremely unreliable. Meanwhile, the use of PO has become part of the obligatory standard monitoring during GA in Germany and many other countries. Likewise, the use of PO is standard care in the PACU although there are no official recommendations. However, for the time period in between, i.e. immediately after GA during transportation of patients from the OR to the PACU, monitoring of the S(p)O(2) in patients breathing room air is neither obligatory in Germany nor are there any official recommendations or guidelines in this respect. Given the introduction of shorter acting anesthetic agents within the last 25 years, the main goal of this study was to explore whether the incidence of hypoxemia in the immediate period after GA is still so high. Additional aims of this study were to examine whether the detection of hypoxemia based on clinical criteria can be confirmed to be very unreliable, what the risk factors for hypoxemia following GA are and how common it is in Germany to transport patients from the OR to the PACU without PO and supplemental oxygen.

In a prospective observational study 970 patients who underwent a broad spectrum of elective surgery under GA in a university hospital setting were included. The S(p)O(2) was measured at the end of the transfer from the OR to the PACU immediately after the anesthetist who had taken care of the patient during the operation had estimated the S(p)O(2). The association between biometric, surgical and anesthesiological variables on the one hand and hypoxemia as well as a decrease of S(p)O(2) on the other hand were studied using multivariate methods. Finally, a survey including all university hospitals was carried out to find out about the use of PO and oxygen during patient transfer from the OR to the PACU.

Of the 959 patients who were eligible for analysis 17% had a S(p)O(2) < 90% and 6.6% a S(p)O(2) < 85%. Hypoxemia was not recognized in 82% of the patients in whom an assessment based on clinical grounds was carried out. Variables with an independent influence on hypoxemia and decrease of S(p)O(2) were as follows: saturation before induction of GA, body mass index, age, American Society of Anesthesiologists (ASA) physical status, difference between maximum and minimum inspiratory pressure, mode of ventilation, the choice of opioid and muscle relaxant as well as the use of nitrous oxide. Patient-dependent risk factors had the strongest impact on hypoxemia. In about 80% of the university hospitals neither PO nor supplemental oxygen is used during transportation of the patient from the OR to the PACU.

The use of opioids and relaxants with short duration of action may have favorable effects on preventing hypoxemia and decreases of S(p)O(2). These measures will, however, not be sufficient to solve this problem because the highest risk factors for hypoxemia are patient-related. Despite knowing risk factors for oxygen desaturation, it is currently not possible to reliably predict which patients will become hypoxemic or have a decrease of S(p)O(2). Therefore, transportation of patients breathing room air from the OR to the PACU directly after GA without use of PO or supplemental oxygen seems to be questionable in terms of patient safety.