Intraoperative Oxygenation in Adult Patients Undergoing Surgery (iOPS): a Retrospective Observational Study Across 29 UK Hospitals.

Morkane CM, McKenna H, Cumpstey AF et al.

Perioperative Medicine (2018) 7:17

Aim of Study

Characterise practice as regards to the administration of oxygen to patients undergoing major surgery and to describe intraoperative arterial oxygenation during general anaesthesia.

Design and Location

Retrospective observational study in 29 hospitals in London & Wessex.


Hospitals affiliated with two anaesthetic trainee audit networks (PLAN, SPARC) took part in this study. Those eligible were patients having general anaesthetic with an arterial catheter, except those undergoing cardiopulmonary bypass. Demographic and intraoperative oxygenation data, haemoglobin saturation and positive end-expiratory pressure were collected retrospectively from anaesthetic charts and arterial blood gases (ABGs) over five consecutive weekdays in April and May 2017.

Primary Outcome

To characterise practice as regards the administration of oxygen to patients undergoing major surgery and to describe intraoperative arterial oxygenation during general anaesthesia; to see if UK anaesthetists were following the World Health Organisation’s (WHO) 2016 guideline of an FiO2 of 0.8 for intubated patients undergoing surgery as evidence showed this decreased the risk of surgical site infections.


Data were examined for Normality using the Shapiro-Wilk test. Unpaired data were compared using the Wilcoxon-Mann-Whitney U test and Kruskal-Wallis tests. Correlation was tested with Spearman’s rank correlation coefficient. All tests were two-tailed, and significance was taken as p < 0.05. Cumulative oxygen dose was determined in patients for whom more than one ABG was recorded, by calculating the area under the curve between the times of the first and final ABGs


Data from 378 anaesthetic cases were contributed.

The median patient age was 66 years

Surgical duration ranged from 1 to 13 h with a median of 4 h. Estimated blood loss was > 1000 ml in 31 (8.2%) patients.

In total, 824 arterial blood gases were analysed. The number of ABGs recorded for each patient ranged from 1 to 13, with a median of 2. SpO2 of <96% was documented in 83 (22%) patients, with only 7 (1.9%) patients desaturating to < 88% at any point during the operation.

The median PaO2 and FIO2 for all analysed ABGs combined were 24.7 kPa (IQR 17.9–30.8) and 0.50 kPa (IQR 0.41–0.55) respectively.

The intraoperative FIO2 ranged from 0.25 to 1.0, and median PaO2/FIO2 ratios for the first four arterial blood gases taken in each case were 24.6/0.5, 23.4/0.49, 25.7/0.46 and 25.4/0.47 respectively.

Supraphysiological values for PaO2 (defined as >13.3 kPa) were observed in 734 (89%) ABGs. Of the 769 ABGs for which the corresponding FIO2 was recorded, an FIO2 ≥ 0.8 was administered on 32 (4.2%) occasions. Of these 32 occasions, 20 (62.5%) were at the time of taking the baseline arterial gas, closest to induction of anaesthesia.

The median cumulative oxygen dose, calculated for those patients for whom at least two ABGs were documented (n = 223), was 3824 kPa min (IQR 2121–6923) over a median time of 159 min (IQR 91–291). The administration of 13.3 kPa O2 over the same time period would have resulted in a median cumulative oxygen dose of 2088 kPa.

Positive end-expiratory pressure (PEEP) was recorded in 287 (75.9%) of cases, and the median PEEP administered was 5 cmH2O (range 0–12).


Intraoperative oxygenation currently varies widely. An intraoperative FIO2 of 0.5 currently represents standard intraoperative practice in the UK, with surgical patients often experiencing moderate levels of hyperoxaemia. This differs from both WHO’s recommendation of using an FIO2 of 0.8 intraoperatively, but compares with practice internationally.

An FiO2 of 0.5 is standard care in the UK and should be used in future research instead of the widely used FiO2 of 0.3.

Stated Limitations from the Study

Corresponding clinical outcomes could not be collected.

Data were collected from paper anaesthetic records. Previous studies have suggested a paper anaesthetic charts is not always the most accurate record of collecting intra-operative events.

In order to record PaO2 values only patients undergoing procedures necessitating arterial line insertion were included.

Discussion from Journal Club Meeting

Consensus agreement that there is wide variation in FiO2 delivered to patients. No-one routinely uses the WHO recommendation (FiO2 0.8) in an attempt to decrease surgical site infections.

Summary by Dr A Burt. Journal Club Meeting 13 September 2018.

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