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Hypoxemia - Approach to the Patient

General Information


  • hypoxemia - low partial pressure of oxygen (PO2) or partial pressure of arterial oxygen (PaO2) in the blood1
  • hypoxia - insufficient oxygen supply to meet oxygen demands of tissue1
  • hyperoxia/hyperoxemia - high oxygen content in tissue/blood1
  • histotoxic hypoxia - low intracellular oxygen content due to interruption of normal cellular metabolism1



General references used

  1. O'Driscoll BR, Howard LS, Earis J, Mak V; British Thoracic Society Emergency Oxygen Guideline Group. BTS Emergency Oxygen Guideline Development Group. BTS guideline for oxygen use in adults in healthcare and emergency settings. Thorax. 2017 Jun;72(Suppl 1):ii1-ii90
  2. Sarkar M, Niranjan N, Banyal PK. Mechanisms of hypoxemia. Lung India. 2017 Jan-Feb;34(1):47-60
  3. West J, Luks A. West's Respiratory Physiology: The Essentials. 10th ed. Philadelphia, PA: Wolters Kluwer; 2016

Recommendation grading systems used

  • British Thoracic Society (BTS) grading system
    • grades of recommendations
      • Grade A
        • at least 1 meta-analysis, systematic review, or randomized controlled trial (RCT) rated as 1++ and directly applicable to the target population, or
        • body of evidence consisting principally of studies rated as 1+, directly applicable to target population and demonstrating overall consistency of results
      • Grade B
        • body of evidence including studies rated as 2++, directly applicable to target population and demonstrating overall consistency of results, or
        • extrapolated evidence from studies rated as 1++ or 1+
      • Grade C
        • body of evidence including studies rated as 2+, directly applicable to target population and demonstrating overall consistency of results, or
        • extrapolated evidence from studies rated as 2++
      • Grade D
        • evidence level 3 or 4, or
        • extrapolated evidence from studies rated as 2+
      • Good Practice Point - recommended best practice based on clinical experience of guideline development group
    • levels of evidence
      • 1++ - high-quality meta-analyses, systematic reviews of RCTs, or RCTs with very low risk of bias
      • 1+ - well-conducted meta-analyses, systematic reviews of RCTs, or RCTs with low risk of bias
      • 1- - meta-analyses, systematic reviews of RCTs, or RCTs with high risk of bias
      • 2++
        • high-quality systematic reviews of case-control or cohort studies
        • high-quality case-control or cohort studies with very low risk of confounding or bias and high probability that relationship is causal
      • 2+ - well-conducted case-control or cohort studies with low risk of confounding or bias and moderate probability that relationship is causal
      • 2- - case-control or cohort studies with high risk of confounding or bias and significant risk that relationship is not causal
      • 3 - nonanalytical studies (for example, case reports, case series)
      • 4 - expert opinion
    • Reference - BTS guideline on oxygen use in adults in healthcare and emergency settings (28507176Thorax 2017 Jun;72(Suppl 1):ii1)
  • British Medical Journal (BMJ) Rapid Recommendations uses Grades of Recommendation, Assessment, Development, and Evaluation (GRADE)
    • strength of recommendation
      • Strong - most patients should receive recommended course of action; decision aids unnecessary as almost all informed patients will make same choice
      • Weak - clinicians should recognize that different choices will be appropriate for different patients and must help each patient arrive at management decision consistent with his or her values or preferences
    • quality of evidence
      • High - panel is very confident that true effect lies to close to estimate of effect
      • Moderate - panel is moderately confident in effect estimate; true effect is likely to be close to estimate of effect, but there is possibility that it is substantially different
      • Low - panel's confidence in effect estimate is limited; true effect may be substantially different from estimate of effect
      • Very low - panel has very little confidence in effect estimate; true effect is likely to be substantially different from estimate of effect
    • Reference - BMJ Rapid Recommendations clinical practice guideline on oxygen therapy for acutely ill medical patients (BMJ 2018 Oct 24;363:k4169), editorial can be found in BMJ 2018 Oct 24;363:k4436

Synthesized Recommendation Grading System for DynaMed Content

  • The DynaMed Team systematically monitors clinical evidence to continuously provide a synthesis of the most valid relevant evidence to support clinical decision-making (see 7-Step Evidence-Based Methodology).
  • Guideline recommendations summarized in the body of a DynaMed topic are provided with the recommendation grading system used in the original guideline(s), and allow users to quickly see where guidelines agree and where guidelines differ from each other and from the current evidence.
  • In DynaMed content, we synthesize the current evidence, current guidelines from leading authorities, and clinical expertise to provide recommendations to support clinical decision-making in the Overview & Recommendations section.
  • We use the Grading of Recommendations Assessment, Development and Evaluation (GRADE) to classify synthesized recommendations as Strong or Weak.
    • Strong recommendations are used when, based on the available evidence, clinicians (without conflicts of interest) consistently have a high degree of confidence that the desirable consequences (health benefits, decreased costs and burdens) outweigh the undesirable consequences (harms, costs, burdens).
    • Weak recommendations are used when, based on the available evidence, clinicians believe that desirable and undesirable consequences are finely balanced, or appreciable uncertainty exists about the magnitude of expected consequences (benefits and harms). Weak recommendations are used when clinicians disagree in judgments of relative benefit and harm, or have limited confidence in their judgments. Weak recommendations are also used when the range of patient values and preferences suggests that informed patients are likely to make different choices.
  • DynaMed synthesized recommendations (in the Overview & Recommendations section) are determined with a systematic methodology:
    • Recommendations are initially drafted by clinical editors (including ≥ 1 with methodological expertise and ≥ 1 with content domain expertise) aware of the best current evidence for benefits and harms, and the recommendations from guidelines.
    • Recommendations are phrased to match the strength of recommendation. Strong recommendations use "should do" phrasing, or phrasing implying an expectation to perform the recommended action for most patients. Weak recommendations use "consider" or "suggested" phrasing.
    • Recommendations are explicitly labeled as Strong recommendations or Weak recommendations when a qualified group has explicitly deliberated on making such a recommendation. Group deliberation may occur during guideline development. When group deliberation occurs through DynaMed Team-initiated groups:
      • Clinical questions will be formulated using the PICO (Population, Intervention, Comparison, Outcome) framework for all outcomes of interest specific to the recommendation to be developed.
      • Systematic searches will be conducted for any clinical questions where systematic searches were not already completed through DynaMed content development.
      • Evidence will be summarized for recommendation panel review including for each outcome, the relative importance of the outcome, the estimated effects comparing intervention and comparison, the sample size, and the overall quality rating for the body of evidence.
      • Recommendation panel members will be selected to include at least 3 members that together have sufficient clinical expertise for the subject(s) pertinent to the recommendation, methodological expertise for the evidence being considered, and experience with guideline development.
      • All recommendation panel members must disclose any potential conflicts of interest (professional, intellectual, and financial), and will not be included for the specific panel if a significant conflict exists for the recommendation in question.
      • Panel members will make Strong recommendations if and only if there is consistent agreement in a high confidence in the likelihood that desirable consequences outweigh undesirable consequences across the majority of expected patient values and preferences. Panel members will make Weak recommendations if there is limited confidence (or inconsistent assessment or dissenting opinions) that desirable consequences outweigh undesirable consequences across the majority of expected patient values and preferences. No recommendation will be made if there is insufficient confidence to make a recommendation.
      • All steps in this process (including evidence summaries which were shared with the panel, and identification of panel members) will be transparent and accessible in support of the recommendation.
    • Recommendations are verified by ≥ 1 editor with methodological expertise, not involved in recommendation drafting or development, with explicit confirmation that Strong recommendations are adequately supported.
    • Recommendations are published only after consensus is established with agreement in phrasing and strength of recommendation by all editors.
    • If consensus cannot be reached then the recommendation can be published with a notation of "dissenting commentary" and the dissenting commentary is included in the topic details.
    • If recommendations are questioned during peer review or post publication by a qualified individual, or reevaluation is warranted based on new information detected through systematic literature surveillance, the recommendation is subject to additional internal review.

DynaMed Editorial Process

  • DynaMed topics are created and maintained by the DynaMed Editorial Team and Process.
  • All editorial team members and reviewers have declared that they have no financial or other competing interests related to this topic, unless otherwise indicated.
  • DynaMed content includes Practice-Changing Updates, with support from our partners, McMaster University and F1000.

Special acknowledgements

  • DynaMed topics are written and edited through the collaborative efforts of the above individuals. Deputy Editors, Section Editors, and Topic Editors are active in clinical or academic medical practice. Recommendations Editors are actively involved in development and/or evaluation of guidelines.
  • Editorial Team role definitions
    Topic Editors define the scope and focus of each topic by formulating a set of clinical questions and suggesting important guidelines, clinical trials, and other data to be addressed within each topic. Topic Editors also serve as consultants for the internal DynaMed Editorial Team during the writing and editing process, and review the final topic drafts prior to publication.
    Section Editors have similar responsibilities to Topic Editors but have a broader role that includes the review of multiple topics, oversight of Topic Editors, and systematic surveillance of the medical literature.
    Recommendations Editors provide explicit review of Overview and Recommendations sections to ensure that all recommendations are sound, supported, and evidence-based. This process is described in "Synthesized Recommendation Grading."
    Deputy Editors oversee DynaMed internal publishing groups. Each is responsible for all content published within that group, including supervising topic development at all stages of the writing and editing process, final review of all topics prior to publication, and direction of an internal team.

How to cite

National Library of Medicine, or "Vancouver style" (International Committee of Medical Journal Editors):

  • DynaMed [Internet]. Ipswich (MA): EBSCO Information Services. 1995 - . Record No. T920488, Hypoxemia - Approach to the Patient; [updated 2018 Nov 30, cited place cited date here]. Available from Registration and login required.

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EBSCO Information Services accepts no liability for advice or information given herein or errors/omissions in the text. It is merely intended as a general informational overview of the subject for the healthcare professional.


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