Patho Lecture 13: Acid-Base Balance

7.35 - 7.45

what is the normal pH range in the bloodstream?

20 parts to a base to every 1 part of an acid

how many parts base are there to parts of acid?

hydrogen

the main component that determines acidity and alkalinity

acid

releases H+; substance that dissociates into H+ ion and conjugate base

base

substance that takes up H+ ions

- greater the H+ = more acidic = lower pH

- lower the H+ = more alkaline = higher pH

what is the relationship between the H+ concentration and pH

HCO3 (bicarbonate)

what is considered the most important base in the body?

-protein metabolism

-carbohydrate metabolism

-fat metabolism

body acids are formed as end products of what 3 types of metabolism?

-lungs

-kidneys

-bone

what are some major organs involved in regulating the acid-base balance?

1. volatile (weak acids)

2. nonvolatile (strong acids)

what are the 2 forms of body acids?

carbonic acid (H2CO3)

what is an example of a volatile acid?

eliminated as CO2 gas, which we can exhale

what can carbonic acid (H2CO3) be eliminated as?

-sulfuric (H2SO4)

-phosphoric (H3PO4)

-lactic acid

what is an example of a nonvolatile acid?

can be eliminated by kidneys/urination

how are nonvolatile acids eliminated by the body?

metabolic acid

general term that includes all acids except carbonic acid

during aerobic metabolism

when is carbonic acid (H2CO3) formed?

CO2 and H2O

what is carbonic acid (H2CO3) derived from?

buffered and excreted by kidneys

how are metabolic acids eliminated from the body?

buffer

minimizes changes in pH when extraneous acids or bases are added to the solution; a pair of chemicals (weak acid and base)

circulates throughout the body

where does bicarbonate circulate in the body?

buffers metabolic acid produced by cells --> can release H+ if too little acid present (reverse if there is too much)

what is the role of bicarbonate in the body?

bicarbonate circulates in body --> picking up H+ when we need it --> takes it to the kidney --> attaches it to ammonia --> ammonia is excreted

what is the relationship between bicarbonate and ammonia?

excretes carbonic acid (gas form)

what type of acids does the respiratory system excrete?

excretes all other metabolic acids

what type of acids do the kidneys excrete?

not overwhelmed by amount of acid generated

when optimal acid-base balance occurs, what is true of buffers?

-carbonic acid

-metabolic acid

what types of acids can be excreted via acid excretion?

body excretes more acid

during hyperventilation, what happens to carbonic acid?

body holds onto more acid

during hypoventilation, what happens to carbonic acid?

chemoreceptors

receptors that focus on CO2 and H+ level and adjust rate and depth accordingly

exhaled through the lungs

where is carbonic acid exhaled through?

excreted out of the kidneys

where are metabolic acids excreted out of?

H+ combines with NH3 --> becomes NH4+ --> excreted in urine

how is ammonia excreted and where is it excreted?

-respiratory system

-renal system

-phosphate system

-plasma protein system

what are some of the most prominent buffer systems in the body?

phosphate buffer system

buffer system that functions similarly to bicarbonate system; maintains intracellular pH; in extracellular fluid

plasma protein system

buffer system that allows hemoglobin and other plasma proteins to buffer H+; maintains intracellular pH

tissue perfusion

must have this to bring blood, oxygen, and nutrients to the cells and get rid of waste products

-ensure blood flow carries away CO2

-ensure oxygen/nutrients get to cells to maintain aerobic metabolism

-preventing accumulation of lactic acid

what is tissue perfusion essential for in the body?

potassium and calcium

changes in H+ concentration impact which minerals that ultimately impact smooth muscle contraction in vessels?

↓ cardiac contractility (cannot pump effectively)

what effect does acidosis have on cardiac contractility?

- decreases cardiac contractility

- ↑ vasoconstriction of blood vessels

what effect does alkalosis have on cardiac contractility?

alters ability of hemoglobin to bind and transport and release O2

what effect does H+ concentration have on hemoglobin?

describes the unloading/unbinding of O2 from hemoglobin

what is the purpose of the oxyhemoglobin dissociation curve?

-shift to right

-decreased affinity for O2

-doesn’t hold onto O2 very well

describe the effect that acidosis has on the oxyhemoglobin dissociation curve

-shift to the left

-↑ affinity for O2

-hemoglobin doesn't like to let go of O2 and holds onto it

describe the effect that alkalosis has on the oxyhemoglobin dissociation curve

more H+ binds to protein

↓

fewer sites open for calcium to bind

↓

hypercalcemia in the bloodstream

in a state of acidosis, what is the relationship between H+ and calcium?

blocks sodium channels (in nerves & muscles) --> muscle weakness

when there is increased levels of calcium in the bloodstream as a result of acidosis, what is the effect on the body (neuromuscular)?

calcium is able to bind everywhere to the protein sites

↓

H+ is not

↓

hypocalcemia in the bloodstream

in a state of alkalosis, what is the relationship between H+ and calcium?

associated with positive symptoms (hyperactive muscle response)

when there is decreased levels of calcium in the bloodstream as a result of alkalosis, what is the effect on the body (neuromuscular)?

-Chvostek's sign

-Trousseau's sign

-paresthesia

-convulsions

-laryngospasm

-tetany

what are some positive symptoms that result from decreased levels of calcium in the bloodstream (in a state of alkalosis)?

Chvostek's sign

spasm of the facial muscles produced by sharply tapping over the facial nerve; suggestive of hypocalcemia

Trousseau's sign

hand/finger spasms with sustained blood pressure cuff inflation; suggestive of hypocalcemia

-acidosis = cerebral vasodilation

-alkalosis = cerebral vasoconstriction

what effect does acidosis and alkalosis have on the CNS?

cerebral vasodilation --> ↑ blood flow --> ↑ ICP

(try to get more O2 and blood flow to the brain)

explain what happens during cerebral vasodilation as a result of acidosis

cerebral vasoconstriction --> ↓ blood flow --> ↓ O2 delivery to brain

(brain is getting more than enough O2 so blood flow is decreased)

explain what happens during cerebral vasoconstriction as a result of alkalosis

H+ likes to swap places with K+

regarding electrolyte levels, what does H+ like to switch places with in a state of acidosis?

H+ enters cells and K+ moves out --> results in hyperkalemia

what happens in a state of acidosis with H+ and K+?

mainly affects the heart

what part of the body is mainly affected by potassium imbalances?

↓ cardiac contractility

what effect does potassium have on the heart when the body is in acidosis?

some H+ moving out of cells with K+ moving in --> results in hypokalemia

what happens in a state of alkalosis with H+ and K+?

-cardiac dysrhythmias

-contractility will ↑, but then will rapidly drop

what effect does potassium have on the heart when the body is in alkalosis?

↓ in contractility

what is the relationship between acidosis and cardiac contractility?

↑ contractility (up to pH 7.7), then rapidly ↓

what is the relationship between alkalosis and cardiac contractility?

something going on w/ the lungs

in respiratory types of acidosis/alkalosis, what is the main part of the body impacted?

something wrong w/ the bicarbonate level

in metabolic types of acidosis/alkalosis, what is the main part of the body impacted?

respiratory acidosis

too much carbonic acid (CO2)

respiratory alkalosis

too little carbonic acid (CO2)

-cause: hypoventilation (not getting enough O2)

-correction: hyperventilation (brain tries to blow off more CO2 and bring in more oxygen)

what is the cause and correction for the problem of respiratory acidosis?

-cause: hyperventilation

-correction: hypoventilation

what is the cause and correction for the problem of respiratory alkalosis?

- ↑ secretion of H+

- ↑ NH3 (ammonia) production

describe some compensation methods for respiratory acidosis

- ↓ secretion of H+

- ↓ NH3 (ammonia) production

describe some compensation methods for respiratory alkalosis

metabolic acidosis

too much metabolic acid

metabolic alkalosis

too little metabolic acid

-cause: ↑ metabolic acid than kidneys can excrete

-correction: ↑ secretion of H+ and NH3 production

what is the cause and correction for the problem of metabolic acidosis?

-cause: ↑ bicarbonate than kidneys can excrete

-correction: ↓ secretion of H+ and NH3 production

what is the cause and correction for the problem of metabolic alkalosis?

hyperventilation (get rid of CO2 gas)

describe some compensation methods for metabolic acidosis

hypoventilation (hold onto more CO2 bring back balance)

describe some compensation methods for metabolic alkalosis

pH is too low or on lower range of normal

what is characteristic of the pH in acidosis?

-↓ excretion of metabolic acid

-excessive excretion of bicarbonate

-excessive production/intake of metabolic acids

what are some causes of metabolic acidosis?

-renal disease

-oliguria

-kidneys not working as they should

in regard to metabolic acidosis, what happens when there is reduced excretion of metabolic acid?

prolonged diarrhea

what is the main cause associated with the excessive excretion of bicarbonate?

-body cannot keep up

-HHS

-DKA

-Kussmaul breathing

in regard to metabolic acidosis, what can happen in the body when there is excessive production/intake of metabolic acids?

DKA

abnormal cellular metabolism caused by lack of insulin produced ketoacids faster than kidneys able to excrete

hypoventilation

accumulation of too much carbonic acid; usually a result of not getting enough oxygen to the alveoli

1. acute

2. chronic

what are the 2 types of alveolar hypoventilation (respiratory acidosis)?

-pneumonia

-asthma exacerbation

-ARDS

what are some types of acute alveolar hypoventilation?

-COPD

what are some types of chronic alveolar hypoventilation?

look at compensation in ABGs

how do we determine if someone has acute or chronic alveolar hypoventilation?

the alveoli cannot perform gas exchange = holding onto CO2

what happens during acute alveolar hypoventilation?

-chronically retaining CO2

-body has to get used to ↑ CO2 levels

what happens during chronic alveolar hypoventilation?

greater than 45 (hypercapnia)

what is considered a high CO2 level (PaCO2)?

pH is too high or on high range of normal

what is characteristic of the pH in alkalosis?

-massive blood transfusions

-diuretic therapy

-holding onto too much bicarbonate

what are some situations in which we might see high levels of a base in one's body?

-prolonged vomiting

-nasogastric suctioning

-mineralocorticoid excess

what are some situations in which we might see too little metabolic acid in one's body?

a lot bicarbonate in the blood = alkalosis

what is the relationship between high amounts of bicarbonate in the blood and pH?

less than 35 (hypocapnia)

what is considered a low CO2 level (PaCO2)?

-hyperventilation in times of acute hypoxia or pain

what happens during respiratory alkalosis?

in times of acute anxiety or emotional distress

when can respiratory alkalosis occur?

-hypoventilation (cause of problem)

-cardiac dysrhythmias

-↓ LOC, confusion

what are the common clinical findings associated with too much carbonic acid (respiratory acidosis)?

-pH: ↓

-PaCO2: ↑

-HCO3: may be ↑ if compensation is present

what are the common blood gas findings associated with too much carbonic acid (respiratory acidosis)?

-hyperventilation (compensatory mechanism)

-abdominal pain

-nausea/vomiting

-cardiac dysrhythmias

-↓ LOC, confusion

what are the common clinical findings associated with too much metabolic acid (metabolic acidosis)?