The accuracy of postoperative, non-invasive Air-Test to diagnose atelectasis in healthy patients after surgery: a prospective, diagnostic pilot study

BMJ Open. 2017 May 29;7(5):e015560. doi: 10.1136/bmjopen-2016-015560.


Objective: To assess the diagnostic accuracy of peripheral capillary oxygen saturation (SpO2) while breathing room air for 5 min (the 'Air-Test') in detecting postoperative atelectasis.

Design: Prospective cohort study. Diagnostic accuracy was assessed by measuring the agreement between the index test and the reference standard CT scan images.

Setting: Postanaesthetic care unit in a tertiary hospital in Spain.

Participants: Three hundred and fifty patients from 12 January to 7 February 2015; 170 patients scheduled for surgery under general anaesthesia who were admitted into the postsurgical unit were included.

Intervention: The Air-Test was performed in conscious extubated patients after a 30 min stabilisation period during which they received supplemental oxygen therapy via a venturi mask. The Air-Test was defined as positive when SpO2 was ≤96% and negative when SpO2 was ≥97%. Arterial blood gases were measured in all patients at the end of the Air-Test. In the subsequent 25 min, the presence of atelectasis was evaluated by performing a CT scan in 59 randomly selected patients.

Main outcome measures: The primary study outcome was assessment of the accuracy of the Air-Test for detecting postoperative atelectasis compared with the reference standard. The secondary outcome was the incidence of positive Air-Test results.

Results: The Air-Test diagnosed postoperative atelectasis with an area under the receiver operating characteristic curve of 0.90 (95% CI 0.82 to 0.98) with a sensitivity of 82.6% and a specificity of 87.8%. The presence of atelectasis was confirmed by CT scans in all patients (30/30) with positive and in 5 patients (17%) with negative Air-Test results. Based on the Air-Test, postoperative atelectasis was present in 36% of the patients (62 out of 170).

Conclusion: The Air-Test may represent an accurate, simple, inexpensive and non-invasive method for diagnosing postoperative atelectasis.

Trial registration: NCT02650037.

Keywords: SpO2; adult anaesthesia; adult intensive & critical care; atelectasis; oxygenation; postoperative.

Publication types

  • Observational Study

MeSH terms

  • Adult
  • Aged
  • Air / analysis*
  • Anesthesia, General / adverse effects
  • Blood Gas Analysis
  • False Negative Reactions
  • Female
  • Humans
  • Linear Models
  • Male
  • Middle Aged
  • Oximetry
  • Oxygen Inhalation Therapy
  • Pilot Projects
  • Postoperative Complications / diagnosis*
  • Postoperative Complications / etiology
  • Postoperative Complications / therapy*
  • Prospective Studies
  • Pulmonary Atelectasis / diagnosis*
  • Pulmonary Atelectasis / etiology
  • Pulmonary Atelectasis / therapy*
  • Sensitivity and Specificity
  • Spain
  • Tertiary Care Centers
  • Tomography, X-Ray Computed

Associated data