Disturbances in acid-base balance Flashcards
list (3) criteria for acid-base balance in body:
- arterial blood pH (7.35-7.45)
- arterial plasma [HCO3-] normal range (22-26 mM)
- arterial pCO2, normal range (35-45 mmHg)
normal values of arterial: pH, plasma HCO3-, and pCO2
- pH: 7.4
- arterial plasma HCO3-: 24mM
- arterial pCO2: 40mmHg
list (2) types of disturbances to acid base balance:
- respiratory og
- metabolic og
define respiratory disturbance:
- shift pH by altering pCO2
define metabolic disturbance:
- shift pH due to abnormal conc of HCO3-
changes in pCO2 what can’t buffer this? and new equation shifts
- carbonate buffers can’t cont to buffering
equation shifts to R:
CO2 + H2O H + HCO3
if HCO3- increases how about H+?
- doesn’t really affect it
- if double CO2, must double (HCO3- and H+)
H2CO3 will dissociate into
- noncarbonate buffers bind H+
general body compensation to disturbed acid base balance:
- ratio of [HCO3]/pCO2 towards normal = ECF pH returned to almost 7.4
- BUT these mechanisms won’t correct cause of change (abnormal pCO2, or [HCO3-] so acid base balance not restored
disturbance of acid base balance only corrected when:
- pH
- pCO2
- [HCO3-] all back to normal values
respiratory acidosis: how it forms
- insufficient CO2 excreted through lungs to balance that prod by cells of body
- pCO2 increases to >45 mmHg
respiratory acidosis: HH equation
when pH decreases, HCO3-/CO2 ration decreases
- arterial pH ~7.18
respiratory acidosis: non carbonate buffers involved
haemoglobin bind some additional H+
respiratory acidosis: how does HCO3- increase and result
- increased reab/regeneration of HCO3- by kidney tubules cause HCO3- in body
= if increase [HCO3-], increase CO2
respiratory acidosis: balance of initial rise of pCO2, and time taken
- nearly balanced by increase HCO3-
- pH nearly normal
- compensation slow (kidney) 2-5 days
respiratory acidosis: how is acid base balance properly fixed
- increased excretion of CO2 through lungs
respiratory acidosis: list causes (3)
- chronic lung diseases (bronchitis, emphysema = smokers)
- airway obstruction, chest injury
- inhibited central respiratory drive due to brain damage, anaesthetics, morphine (heroin), barbiturates
respiratory alkalosis: define
CO2 decreased, affecting ratio
respiratory alkalosis: if too much CO2 removed
- increases ratio = pH increases (7.62)
- noncarbonate buffers used (haemoglobin) releasing bound H+
- reduced reab/generation of HCO3- by kidney compensates increased pH = decreases ECF [HCO3-]
- so partially restoring pH (7.49)
- but normal breathing needed to return acid base balance to normal
respiratory alkalosis: list causes (3)
- hypoxia at high altitudes (>4500m) increase in alveolar ventilation -> resp alk reduced pCO2 on central chemoreceptors overridden by peripheral chemoreceptors in response to low pO2
- over breathing: due to sepsis, fever, brain damage, hysteria
- pregnancy: over breathing due to progesterone effect on brain, lowering pCO2 to 30mmHg, to compensate [HCO3-] decreases to 18-20mM returning pH to 7.44 ‘normal’ value
metabolic acidosis: define
- acidosis caused by low ECF [HCO3-]
metabolic acidosis: features
- addition of non carbonate acid to body
- HCO3- reduced by buffering excess acid
OR HCO3- lost directly
metabolic acidosis: effect on equation and time taken
- [HCO3-] decreases, so pH decrease (7.16)
- fall in pH detected, peripheral chemoreceptors breathing increases = lowering pCO2
- compensation within 12 hrs (7.29)
metabolic acidosis: what is needed to properly correct acid base balance
- increase in reabsorption and generation of HCO3-
