Aging;

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

FA Manian MD, MPH, , , , , , , , , , , , , Leave a comment

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?

Why is my relatively healthy elderly patient so prone to hyperkalemia?

FA Manian MD, MPH, , , , , , , , , , , , , , , , , , , , , , , Leave a comment

Hyporeninemic hypoaldosteronism (HH)—without impairment of cortisol synthesis— is associated with hyperkalemic (type IV) renal tubular acidosis (RTA) and is not uncommon among older patients despite glomerular filtration rates (GFRs) >20 ml/min, and absence of diabetes mellitus or chronic tubulointerstitial disease (1-7).  

Hyperkalemia due to HH in the elderly should come as no surprise because the renin-angiotensin-aldosterone system (RAAS) function declines with age, reaching its lowest level by age 60. 1-4   In fact, older people have comparatively lower mean levels of plasma renin and aldosterone at baseline and have an impaired ability to mount appropriate responses to RAAS stimuli, such as upright posture, volume depletion, catecholamines, or potassium administration (3-5).

The impaired RAAS capacity in the elderly often becomes more obvious when they are prescribed medications that further suppress RAAS (3). These include angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, beta-blockers, calcium-channel blockers, nonsteroidal anti-inflammatory agents and heparin (3,7). 

Drugs that increase aldosterone resistance, including potassium-sparing diuretics (eg, spironolactone, amiloride, triamterene, eplerenone) and certain antibiotics (eg, trimethoprim, pentamidine) may also aggravate hyperkalemia associated with HH (7). 

A variety of mechanisms leading to HH with aging have been proposed. These include impaired conversion of prorenin to renin, prostaglandin deficiency, sympathetic nervous system dysfunction and increased plasma levels of atrial natriuretic factors as found in congestive heart failure (1,7). 

Bonus pearl: Did you know that the first case of “pure hypoaldosteronism” was described in 1957 in a 71 year old non-diabetic patient with hyperkalemia in the setting of congestive heart failure? (8)

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References

  1. Bauer JH. Age-related changes in the renin-aldosterone system. Physiological effects and clinical implications. Drugs & Aging 1993;3:238-45. https://www.ncbi.nlm.nih.gov/pubmed/8324299
  2. Musso CG, Jauregui JR. Renin-angiotensin-aldosterone system and the aging kidney. Expert Rev Endocrinol Metab 2014;9:543-46. https://www.tandfonline.com/doi/full/10.1586/17446651.2014.956723
  3. Yoon HE, Choi BS. The renin-angiotensin system and aging in the kidney. Korean J Intern Med 2014;29:291-95. https://www.researchgate.net/publication/262530577_The_renin-angiotensin_system_and_aging_in_the_kidney
  4. Nadler JL, Lee FO, Hsueh W, et al. Evidence of prostacyclin deficiency in the syndrome of hyporeninemic hypoaldosteronism. N Engl J Med 1986;314:1015-20. https://www.ncbi.nlm.nih.gov/pubmed/3515183
  5. Williams GH. Hyporeninemic hypoaldosteronism. N Engl J Med 1986;314:1041-42. https://www.ncbi.nlm.nih.gov/pubmed/3515186
  6.  Block BL, Bernard S, Schwartzstein RM. Hypo-hypo: a complex metabolic disorder. Ann Am Thorac Soc 2016;13:127-133. https://www.ncbi.nlm.nih.gov/pubmed/26730868
  7. Michelis MF. Hyperkalemia in the elderly. Am J Kid Dis 1990;16:296-99.https://www.ajkd.org/article/S0272-6386(12)80005-9/pdf
  8. Hudson JB, Chobanian AV, Relman AS. Hypoaldosteronism. A clinical study of a patient with an isolated adrenal mineralocorticoid deficiency, resulting in hyperkaliemia and Stokes-Adams attack. N Engl J Med 1957;257:529-36. https://www.ncbi.nlm.nih.gov/pubmed/13464977

 

Why is my relatively healthy elderly patient so prone to hyperkalemia?