My 75 year old patient has an arterial oxygen tension (Pa02) less than 90 mmHg on room air. Does age affect PaO2?

Short answer: Yes! Most studies of blood gas concentrations have demonstrated a decrease in oxygen tension with age.1

Earlier studies have demonstrated a linear decrease in oxygen tension based on observations that included relatively small number of patients over the age of 60. 1 More recently, however, in a study of 532 consecutive patients admitted for elective surgery without overt cardiac, pulmonary, or metabolic disease, obesity or smoking, the mean PaO2 differed by age group as follows:

  • <30 years: 98.4 mmHg
  • 30-50 years: 88.7 mmHg
  • 51-70 years: 81.0 mmHg
  • >70 years: 76.5 mmHg

After age 70 years, decline in Pa02 may slow down or actually reverse, likely related to the “survival of the fittest” in more advanced years. 1,2 Some have suggested accepting a PaO2 80-85 mmHg as normal for subjects > 65 years of age. 3

The decrease in PaO2 with age is a result of increased heterogeneity of ventilation/perfusion ratio, especially reduced ventilation in the dependent parts of the lung. 3 Aging is also associated with a decrease in chest wall compliance, muscle (including the diaphragm) strength, forced expiratory volume in 1 second (FEV1), vital capacity, and diffusing capacity of carbon monoxide (DLC0)/alveolar volume.  

In addition, aging is associated with a reduction in response to hypoxia and hypercarbia, making older patients particularly vulnerable to complications from  heart failure and pneumonia4, especially in the current Covid-19 era.

Bonus Pearl: Did you know that poor response to hypoxic or hypercarbic states in the elderly is likely related to an age-related decline in efferent neural output to respiratory muscles?4

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References

  1. Blom H, Mulder M, Verwej W. Arterial oxygen tension and saturation in hospital patients: effect of age and activity. BMJ 1988;297:720-2. Doi:10.1136/bmj.297.6650.720 https://www.bmj.com/content/297/6650/720   
  2. Delclaux B, Orcel B, Housset B, et al. Arterial blood gases in elderly persons with chronic obstructive pulmonary disease (COPD). Eur Respir J 1994;7:856-61. https://www.researchgate.net/publication/15147788_Arterial_blood_gases_in_elderly_persons_with_chronic_obstructive_pulmonary_disease_COPD
  3. Janssens JP, Pache JC, Nicod LP. Physiological changes in respiratory function associated with ageing. Eur Respir J 1999;13:197-205. https://www.researchgate.net/publication/12689073_Physiological_changes_in_respiratory_function_associated_with_ageing
  4. Sharma G, Goodwin J. Effect of aging on respiratory system physiology and immunology. Clin Interventions in Aging 2006;1:253-60. https://pubmed.ncbi.nlm.nih.gov/18046878/

 

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

 

 

My 75 year old patient has an arterial oxygen tension (Pa02) less than 90 mmHg on room air. Does age affect PaO2?

What is the role of prone ventilation in patients with Covid-19 and ARDS?

A 2017 guideline strongly recommends the use of prone ventilation for 12+ hours daily in individuals with severe ARDS (1). A JAMA article gave similar recommendations for critically ill patients with COVID-19 (2).

The recommendations are often based on a NEJM 2013 randomized-controlled study involving 466 patients with severe ARDS (3). While previous research had demonstrated improved oxygenation in the prone position (4), this study demonstrated a significant survival benefit (3).  Mortality at 28 days was 16.0% in prone patients versus 32.8% in supine patients (p<0.001; HR 0.39 with 95% CI, 0.29 – 0.67) (3). Mortality was also lower in prone patients at 90 days (3).  A meta-analysis of 4 additional randomized-controlled trials confirmed the survival benefits (1). 

In patients with Covid-19 and ARDS, a small retrospective study involving 12 patients showed a significant association between prone positioning and lung recruitability (ie, lung tissue in which aeration can be restored) (p = 0.020) (5).

Physiologically, numerous mechanisms have been proposed for these findings, including the possbility that while blood flow consistently favors the dorsal alveoli regardless of position, the prone position allows dorsal alveoli to reopen, improving ventilation/perfusion matching (6). 

Of note, some institutions find difficulties with prone positioning, including higher rates of pressure sores and endotracheal tube obstruction (1).

 

Contributed by Grant Steele, Harvard Medical Student, Boston, MA.

 

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References:

1. Fan E, Del Sorbo L, Goligher E, et al. An official American Thoracic Society/European Society of Intensive Care Medicine/Society of Critical Care Medicine clinical practice guideline: mechanical ventilation in adult patients with acute respiratory distress syndrome.” Am J Respir Crit Care Med 2017;195:1253-1263. https://www.atsjournals.org/doi/abs/10.1164/rccm.201703-0548ST 
2. Murthy S, Gomersall C, & Fowler R. Care for critically ill patients with COVID-19. JAMA – Published online March 11, 2020. doi:10.1001/jama.2020.3633 https://jamanetwork.com/journals/jama/fullarticle/2762996
3. Guérin C, Reignier J, Richard J-C, et al. Prone positioning in severe acute respiratory distress syndrome. N Engl J Med 2013;368:2159-2168. https://www.nejm.org/doi/full/10.1056/nejmoa1214103
4. Abroug F, Ouanes-Besbes L, Elatrous S, et al. The effect of prone positioning in acute respiratory distress syndrome or acute lung injury: a meta-analysis. Areas of uncertainty and recommendations for research. Intensive Care Medicine – Published online March 19, 2008. doi: 10.1007/s00134-008-1062-3 https://link.springer.com/article/10.1007/s00134-008-1062-3
5. Pan C, Chen L, Lu C, et al. Lung Recruitability in SARS-CoV-2 Associated Acute Respiratory Distress Syndrome: A Single-center, Observational Study. Am J Respir Crit Care Med – Published online March 23, 2020. doi: 10.1164/rccm.202003-0527LE. https://www.atsjournals.org/doi/pdf/10.1164/rccm.202003-0527LE 
6. Nyrén S, Mure M, Jacobsson H, et al. Pulmonary perfusion is more uniform in the prone than in the supine position: scintigraphy in healthy humans. J Appl Physiol 1999;86:1135-1141. https://www.physiology.org/doi/abs/10.1152/jappl.1999.86.4.1135

 

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

What is the role of prone ventilation in patients with Covid-19 and ARDS?