Hypoxämie nach Allgemeinanästhesie

Zusammenfassung

Hintergrund

Studien aus den Zeiten der klinischen Einführung der Pulsoxymetrie zeigten, dass nach Allgemeinanästhesien ein großer Anteil der Patienten auf dem Weg vom OP in den Aufwachraum (AWR) unter Atmung von Raumluft hypoxämisch [pulsoxymetrisch gemessene Sauerstoffsättigung (S_pO₂) < 90%] war und dass das Erkennen der Hypoxämie anhand von klinischen Kriterien sehr unzuverlässig ist. Unklarheit besteht darüber, ob die Inzidenz von Hypoxämien trotz modernerer Anästhesieverfahren immer noch so hoch ist, ob sich die Unzuverlässigkeit der Detektion von Hypoxämien nach klinischen Kriterien bestätigt und was die Risikofaktoren für Hypoxämien nach Allgemeinanästhesie sind.

Methoden

Bei 970 in Allgemeinanästhesie operierten Patienten wurde nach dem Transport vom OP in den AWR unter Atmung von Raumluft die S_pO₂ gemessen, nachdem der betreuende Anästhesist eine Schätzung der S_pO₂ vorgenommen hatte. Zusammenhänge zwischen biometrischen, operativen und anästhesiologischen Variablen einerseits sowie Hypoxämie andererseits wurden multivariat untersucht.

Ergebnisse

Es hatten 17% der 959 ausgewerteten Patienten eine S_pO₂ < 90%; hierbei wiesen 6,6% der Patienten eine S_pO₂ < 85% auf. Die Hypoxämie wurde in 82% der Fälle nicht erkannt. Unabhängige Einflussfaktoren auf eine Hypoxämie waren: Ausgangssättigung, Body-Mass-Index, Alter, körperlicher Status gemäß Klassifikation der American Society of Anesthesiologists, Differenz zwischen maximalem und minimalem Beatmungsdruck, Beatmungsmodus, Wahl des Opioids, des Relaxans und Verwendung von Lachgas.

Schlussfolgerung

Durch die Wahl von Anästhetika können Hypoxämien und Sättigungsabfälle günstig beeinflusst werden, ohne dass dadurch diese Problematik vollständig gelöst werden kann, weil die stärksten Risikofaktoren patientenassoziiert sind. Da bislang selbst bei Kenntnis von Risikofaktoren nicht vorherzusagen ist, wer nach Allgemeinanästhesie eine S_pO₂ < 90% haben wird und überdies die Abschätzung der S_pO₂ anhand klinischer Kriterien höchst unzuverlässig ist, erscheint der Transport von spontan-atmenden Patienten nach Narkose ohne Überwachung der S_pO₂ bzw. ohne O₂-Gabe überdenkenswert.

Abstract

Background

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_pO₂) 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_pO₂ 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.

Methods

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_pO₂ 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_pO₂. The association between biometric, surgical and anesthesiological variables on the one hand and hypoxemia as well as a decrease of S_pO₂ 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.

Results

Of the 959 patients who were eligible for analysis 17% had a S_pO₂ < 90% and 6.6% a S_pO₂ < 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_pO₂ 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.

Conclusions

The use of opioids and relaxants with short duration of action may have favorable effects on preventing hypoxemia and decreases of S_pO₂. 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_pO₂. 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.