ABG and acid-base balance

normal arterial blood pH

7.35-7.45

what defines acidosis?

arterial pH < 7.35

what defines alkalosis?

arterial pH > 7.45

as [H+] increases in a system what happens to the pH?

pH decreases, becomes more acidic

as [H+] decreases in a system what happens to the pH?

pH increases, becomes more basic

in order for plasma pH to remain within the homeostatic range, the input of H+ blood must ___ the output of H+ from the blood

equal

where does H+ input come from

mainly via metabolic activities: lactic acid production, fat metabolism, CO2 loading into blood etc.

small amount via foods ingested

where does H+ output come from?

via secretion of H+ by the kidneys and blowing off CO2

what are buffer systems?

substance that can maintain the pH of a system

when a system is acidic, what does a buffer system do to H+?

binds H+

when a system is alkaline, what does a buffer system do to H+?

releases H+

what can buffers do and can’t do in ICF or ECF?

can lower H+ in ICF or ECF

cannot removed H+ from the body

buffers systems are the ___ to react to a shift in [H+], therefore the ___ to react to pH

first

most important buffer of ECF

carbonic acid-bicarbonate

most important buffer of ICF

proteins

hypoventilation leads to a ___ in plasma PCO2, ____ in H+, and ___ in pH

increase in plasma PCO2

increase in H+

decrease in pH

hyperventilation leads to a ___ in plasma PCO2, ____ in H+, and ___ in pH

decrease in plasma PCO2

decrease in H+

increase in pH

over what time frame are the respiratory mechanisms effective?

1-3 minutes

how do the renal mechanisms regulate [H+], and therefore pH?

increasing or decreasing their renal reabsorption of HCO3- and renal secretion of H+

increased renal reabsorption of HCO3- and increased renal secretion of H+ would cause plasma pH to ___

increase

decreased renal reabsorption of HCO3- and decreased renal secretion of H+ would cause plasma pH to ___

decrease

if plasma pH decreases, how would the kidneys react?

renal secretion of H+ increases and bicarbonate reabsorption increases

if plasma pH increases, how would the kidneys react?

renal secretion of H+ decreases and bicarbonate reabsorption decreases

over what time frame are the renal mechanisms effective?

24-48 hours

respiratory acidosis and alkalosis

pH imbalances caused by issues with respiratory function that lead to changes in plasma CO2

what are the indicators for respiratory acidosis and alkalosis?

out of range CO2 levels

metabolic acidosis and alkalosis

all pH imbalances NOT caused by too little or too much CO2 in the plasma

what are the indicators for metabolic acidosis and alkalosis?

out of range HCO3- levels

compensation

physiological response that attempts to normalize/correct arterial blood pH

compensation for metabolic alkalosis

hypoventilation

compensation for metabolic acidosis

hyperventilation

compensation for respiratory acidosis

increased renal absorption of HCO3- and increased renal secretion of H+

compensation for respiratory alkalosis

decreased renal absorption of HCO3- and decreased renal secretion of H+

what is an ABG test?

measures PaCO2, arterial blood pH, plasma HCO3- level, and PO2

uses these values to assess patient’s acid-base status: acidotic or alkalotic? Respiratory or metabolic in nature?

when is an ABG test performed?

can be used to:

• help diagnose suspected respiratory disease, e.g. COPD

• determine acid-base status in people with uncontrolled diabetes, kidney disease, drug overdose, for example

normal ranges for PCO2, HCO3-, PO2, and pH

PCO2 = 35-45 mmHg

HCO3- = 22-26 mEq/L

PO2 = 80-100 mmHg

pH = 7.35-7.45