Hypoxemia laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:
Overview
An elevated/reduced concentration of serum/blood/urinary/CSF/other [lab test] is diagnostic of [disease name].
OR
Laboratory findings consistent with the diagnosis of [disease name] include [abnormal test 1], [abnormal test 2], and [abnormal test 3].
OR
[Test] is usually normal among patients with [disease name].
OR
Some patients with [disease name] may have elevated/reduced concentration of [test], which is usually suggestive of [progression/complication].
OR
There are no diagnostic laboratory findings associated with [disease name].
Laboratory Findings
PaO2/FiO2 ratio
The PaO2/FiO2 ratio (PF ratio) A higher ratio indicates better gas exchange:
- Normal is 500
- ARDS is < 200
Comparative studies suggest this measure correlates better with pulmonary shunts than does the A-a gradient.[1][2][3]
AVO2D
The alveolar-arterial oxygen (A-a) difference (AVO2D) or A-a gradient is The A-a gradient is harder to calculate, but accounts for changes in respiration as measured by the partial pressure of carbon dioxide. However, this calculation relies on the respiratory quotient being constant in the prediction of alveolar CO2.
When compared to the PF ratio, the A-a gradient is found to correlate less well with pulmonary shunting.[1][2][3]
Among outpatients with possible pulmonary embolism, the A-a gradient may be a better test.[4]
An online calculator for the A-a gradient is at http://www.mdcalc.com/aagrad.
Tissue perfusion
- Central venous oxygen saturation (ScvO2)
In patients with septic shock, maintaining the central venous oxygen saturation (ScvO2) > 70% is a health care quality assurance measure for the Institute for Healthcare Improvement.[5] This is measured from the superior vena cava. This is hard to predict by physical examination.[6]
- Mixed venous oxygen saturation (SvO2)
In patients with septic shock, maintaining the mixed venous oxygen saturation (ScvO2) > 65% is a health care quality assurance measure for the Institute for Healthcare Improvement that is an alternative to the central venous oxygen saturation.[7] This is measured from a pulmonary artery catheter. This is hard to predict by physical examination.[6]
The mixed venous pressure may be lower than the central venous pressure due to mixing with blood from the splanchnic circulation or carotid sinuses that has lower oxygen content.[8]
- Tissue oxygen saturation (StO2)
Tissue oxygen saturation (StO2) at the thenar eminence may be an alternative, non-invasive measurement.[9][10]
- Lactate clearance
Maintaining lactate clearance about 10% may be an easier alternative than invasive measurements of oxygenation according to a randomized controlled trial by EMShockNet.[11]
- Capnography
Capnography, which is "continuous recording of the carbon dioxide content of expired air,"[12] may detect respiratory depression before hypoxemia occurs.[13] Proposed criteria for respiratory depression are:[13]
- End tidal CO2 (ETCO2) level 50 mm Hg
- ETCO2 change from baseline of 10%
- Loss of waveform for 15 seconds
References
- ↑ 1.0 1.1 Covelli HD, Nessan VJ, Tuttle WK (1983). "Oxygen derived variables in acute respiratory failure". Crit. Care Med. 11 (8): 646–9. PMID 6409506.
- ↑ 2.0 2.1 El-Khatib MF, Jamaleddine GW (2004). "A new oxygenation index for reflecting intrapulmonary shunting in patients undergoing open-heart surgery". Chest. 125 (2): 592–6. PMID 14769743.
- ↑ 3.0 3.1 Cane RD, Shapiro BA, Templin R, Walther K (1988). "Unreliability of oxygen tension-based indices in reflecting intrapulmonary shunting in critically ill patients". Crit. Care Med. 16 (12): 1243–5. PMID 3191742.
- ↑ McFarlane MJ, Imperiale TF (1994). "Use of the alveolar-arterial oxygen gradient in the diagnosis of pulmonary embolism". Am. J. Med. 96 (1): 57–62. PMID 8304364.
- ↑ Maintain Adequate Central Venous Oxygen Saturation Institute for Healthcare Improvement
- ↑ 6.0 6.1 Grissom CK, Morris AH, Lanken PN, Ancukiewicz M, Orme JF, Schoenfeld DA; et al. (2009). "Association of physical examination with pulmonary artery catheter parameters in acute lung injury". Crit Care Med. 37 (10): 2720–6. PMID 19885995.
- ↑ Maintain Adequate Central Venous Oxygen Saturation Institute for Healthcare Improvement
- ↑ Kopterides P, Mavrou I, Kostadima E (2005). "Central or mixed venous oxygen saturation?". Chest. 128 (2): 1073–4, author reply 1074-5. doi:10.1378/chest.128.2.1073. PMID 16100219.
- ↑ Podbregar M, Mozina H (2007). "Skeletal muscle oxygen saturation does not estimate mixed venous oxygen saturation in patients with severe left heart failure and additional severe sepsis or septic shock". Crit Care. 11 (1): R6. doi:10.1186/cc5153. PMC 2147710. PMID 17227587.
- ↑ Leone M, Blidi S, Antonini F, Meyssignac B, Bordon S, Garcin F; et al. (2009). "Oxygen tissue saturation is lower in nonsurvivors than in survivors after early resuscitation of septic shock". Anesthesiology. 111 (2): 366–71. doi:10.1097/ALN.0b013e3181aae72d. PMID 19602965.
- ↑ Jones AE, Shapiro NI, Trzeciak S, Arnold RC, Claremont HA, Kline JA; et al. (2010). "Lactate clearance vs central venous oxygen saturation as goals of early sepsis therapy: a randomized clinical trial". JAMA. 303 (8): 739–46. doi:10.1001/jama.2010.158. PMID 20179283.
- ↑ Anonymous (2025), Capnography (English). Medical Subject Headings. U.S. National Library of Medicine.
- ↑ 13.0 13.1 Deitch K, Miner J, Chudnofsky CR, Dominici P, Latta D (2010). "Does end tidal CO2 monitoring during emergency department procedural sedation and analgesia with propofol decrease the incidence of hypoxic events? A randomized, controlled trial". Ann Emerg Med. 55 (3): 258–64. doi:10.1016/j.annemergmed.2009.07.030. PMID 19783324.