ch7 acid base balance

maintenance of a normal pH and homeostatic allows for what 3 things:

• Normal cellular function

• Enzyme activity

• Membrane stability

what are acids

substance that gives or donates hydrogen (H+) ions

what are volatile acids

acids that can be converted into gas form and eliminated via the lungs

what is the volatile acid we have and its equation

carbonic acid (HCO3)

H2CO3 ←→ CO2 + H20

how is the concentration of CO2 expressed

PaCO2

what is PaCO2

a measurement of partial pressure exerted by CO2 in the blood

how are volatile acids eliminated?

through the lungs as CO2

what are nonvolatile acids

products of metabolism

what are the 2 categories of sources nonvolatile/fixed acids come from?

exogenous and endogenous

what are exogenous sources of nonvolatile/fixed acids? (4)

ingestion of food

metabolism of protein (phosphoric acid, sulfuric acid)

fat (ketoacids)

carbs (pyruvic, lactic, and citric acid)

what are the endogenous sources of nonvolatile/fixed acids? (5)

• Starvation

• Fever

• Exercise

• Disease

• drugs

how are nonvolatile/fixed acids eliminated?

via the kidneys

what are bases?

can accept or receive H+ ions

define pH

ratio of base (HCO3-) to acids (H2CO3)

in a healthy state, what is the ratio of bases:acids

20 base: 1 acid

to maintain a steady pH, the ratio must remain

constant

what is the predominant base in human acid-base balance

bicarbonate (HCO3-)

how does bicarbonate appear in the ECF

NACHO3- , or with K or Mg

what organ provides primary regulation of bicarbonate regulation

kidney

high pH =

alkaline

low pH=

acidic

what is normal pH range

7.35-7.45

define acidosis

process leading to the accumulation of acid or loss of base

define acidemia

pH < 7.35

define alkalosis

process leading to accumulation of base or loss of acid

define alkalemia

pH > 7.45

In clinical practice, this distinction is generally not make, and the terms acidosis and alkalosis are used to refer to

abnormal pH

what regulates the concentration of HCO3

kidneys

which is the predominant base in the body?

bicarbonate

what are the 3 types of regulation of acid-base balance?

• Chemical buffering (cellular)

• Respiratory regulatory control of CO2 (lungs)

• Renal regulatory control of HCO3- (kidneys)

how do buffers work

Buffers don’t change the actual number of H+ but they limit the amount of free H+ including both extracellular and intracellular buffers

bicarbonate-carbonic acid buffer system is the primary buffer in

ECF

what does the bicarbonate-carbonic acid buffer system do?

buffers the fixed acid load (diet generated, etc)

does not work against carbonic acid changes

equation for bicarbonate-carbonic acid buffer system

H + HCO3 <--> H2CO3 <--> CO2 + H20

what is the role of the lungs for the Bicarbonate-carbonic acid buffer system

Lungs expel the excess CO2 by increasing rate and depth of breathing

the strength if the Bicarbonate-carbonic acid buffer system is related to the availability of

HCO3- (bicarbonate)

bicarbonate is regulated by the

kidneys

what are the other chemical buffer systems (4)

1. protein buffer system

2. hemoglobin buffer system

3. phosphate buffers

4. bone carbonate buffer

what is the protein buffer system (function and where)

• primary intracellular buffer

• proteins can operate as both acid and base buffering systems

what is the hemoglobin buffer system (what does it do, where?. primary buffer against what changes?)

• most important blood buffer

• primary buffer against carbonic acid changes

• CO2 + H2O <--> H2CO3 <--> H + HCO3 ---> Hbg binds to H+

what do the phosphate buffers do?

reduced acidity of urine --> protects kidneys

how does respiration (lungs) regulate acid base balance?

lungs have the ability to change the rate of respiration and depth of breathing to control the release or retain CO2

normal relationship between CO2 generated and CO2 released

equal

how do lungs regulate acid-base?

respond to changes in (H+) by changing rate or depth (or both)

which system has the best buffering ability?

respiration regulation (immediate and spontaneous)

1-2x > buffering power of all chemical buffers

In metabolic disturbances (high fixed acid load), what happens to the lungs

they cant excrete enough CO2 to maintain a normal pH BUT this is usually compensated to maintain a range compatible with life

renal regulatory control allows control for what 2 things

both free H+ and HCO3- (can impact both of these)

rate of renal regulation?

a lot slower than respiratory…

In normal healthy kidneys and normal pH how much bicarbonate (HCO3-) is resorbed?

100% of HCO3- is resorbed (to be able to balance acids)

what does renal H+ secretion refer to?

H+ secretion refers to kidney pumping H+ ions from blood into the urine (to get rid of acid)

renal responses for acidosis (changes made):

• H+ secretion

• H+ excretion

• HCO3 reabsorption and addition to plasma

• HCO3 excretion

• pH of urine

• compensatory change in plasma pH (what is the goal)

• H+ secretion (increase)

• H+ excretion (increase)

• HCO3 reabsorption and addition to plasma (increase)

• HCO3 excretion (normal→ zero: all is reabsorbed)

• pH of urine (acidic)

• compensatory change in plasma pH (what is the goal) —> alkalinization toward normal

renal responses for alkalosis:

• H+ secretion

• H+ excretion

• HCO3 reabsorption and addition to plasma

• HCO3 excretion

• pH of urine

• compensatory change in plasma pH (what is the goal)

• H+ secretion (decrease)

• H+ excretion (decrease)

• HCO3 reabsorption and addition to plasma (decrease)

• HCO3 excretion (increase)

• pH of urine (alkaline)

• compensatory change in plasma pH (what is the goal)—> acidification towards normal

renal response to acidosis path?

• increase in H+ secretion —> increased excretion —> decrease H+ in plasma

• increase HCO3- conservation —> decreased excretion —> increase bicarbonate in plasma —> increased ability to buffer

H+ and bicarbonate are both considered

electrolytes

how do acid-base changes impact electrolytes

affect concentration of other electrolytes (potassium, chloride, sodium)

what are the main 4 base-acid disorders?

• respiratory acidosis

• respiratory alkalosis

• metabolic acidosis

• metabolic alkalosis

what does simple refer to? mixed?

simple is one acid-base disturbance event; mixed means more than one

A presence of a disturbance can affect what?

electrolytes (for example, shifts in K levels)

respiratory acid base disorders involve what compound

CO2

metabolic acid base disorders involve what compounds

HCO3 concentration by the kidneys OR nonvolatile acids

respiratory acidosis is caused how?

retention of CO2

why is ti hard to assess for acid base balance

Body attempts to self-correct changes in pH

If both acid and base increase or decrease within the same proportion, pH will remain steady

what are the 3 common types of labs measured?

• Arterial blood gas (ABG)

• Serum chemistries

• Anion gap: difference between unmeasured anions and cations

normal lab values for acid-base balance

what does compensated and uncompensated acid base status mean?

• Uncompensated means that the CO2 value changes without changes in bicarbonate

• Compensated means CO2 value changes and also bicarbonate

uncompensated respiratory acidosis

• pH

• CO2 (compared to normal)

• bicarbonate (compared to normal)

• HCO3/CO2 ratio

• decreased

• increased

• normal

• 20/2 (10/1)

compensated respiratory acidosis

• pH

• CO2 (compared to normal)

• bicarbonate (compared to normal)

• HCO3/CO2 ratio

• normal

• increased

• increased

• 40/2 (20/1)

uncompensated respiratory alkalosis

• pH

• CO2 (compared to normal)

• bicarbonate (compared to normal)

• HCO3/CO2 ratio

• increase

• decrease

• normal

• 20/0.5 (40/1)

compensated respiratory alkalosis

• pH

• CO2 (compared to normal)

• bicarbonate (compared to normal)

• HCO3/CO2 ratio

• normal

• decreased

• decreased

• 10/0.5 (20/1)

for respiratory acidosis, what are the common lab values

• pH

• pCO2

• bicarbonate

• Ca, K, Cl

• oxygen levels

• pH : decreased

• pCO2: increased

• bicarbonate: slightly elevated

• Ca, K, Cl: increase in serum

• oxygen levels: hypoxemia present

symptoms of respiratory acidosis (7)

restlessness

apprehension

lethargy

muscle twitching

tremors

convulsions

coma

what are common caused of respiratory acidosis (15)

• Hypoventilation (lack of CO2 excretion)

• Chronic obstructive pulmonary disease (COPD)

• Severe pneumonia or asthma

• Acute pulmonary edema

• Pneumothorax (collapse lung)

• Drugs: opiate, sedative, anesthetic overdose (acute)

• Excessive oxygen treating chronic hypercapnia

• Sleep apnea

• Neuromuscular disease (such as amyotrophic lateral sclerosis (ALS), Guillain-Barre syndrome, spinal cord injury)

• Morbid obesity, Pickwickian syndrome

• Chest wall injury or skeletal deformity

• Aspiration of foreign body or vomitus

• Laryngospasm, laryngeal edema, severe bronchospasm

• Excessive production of CO2

• Overfeeding, especially with high carb components of nutrition support

treatment for resp. acidosis?

• Focuses on correcting the underlying condition

• Focuses on increasing oxygenation (Through mechanical ventilation)

The lungs work to get rid of an increased amount of acid by

Increasing rate and depth of breathing

what is respiratory alkalosis?

Increase in base (HCO3) as a result of increased CO2 release via hyperventilation

what is the acute response for respiratory alkalosis

shift of acid from ICF to ECF with the movement of bicarbonate into cells in exchange for chloride

uncontrolled respiratory alkalosis presents what in terms of

• pH

• paCO2

• K, Ca, Cl

• pH >7.45

• paCO2 decreased

•  ↓K, Ca, and ↑Cl

what is the compensatory response for respiratory alkalosis

Kidneys retain H+ and excrete HCO3-

in order to lower pH (more acidic)

what are common causes of respiratory alkalosis? (9)

• Hyperventilation (increase in CO2 excretion)

• Respiratory infection (Pneumonia)

• Asthma

• Change in altitude environment (ex: high altitude)

• Drugs that stimulate respirations (ex: theophylline, catecholamines)

• Anxiety and cerebrovascular accident

• Fever and sepsis

symptoms of alkalosis (lab)

• pH

• plasma HCO3 in chronic

• PaCO2 in acute

• pH > 7.45

• Plasma HCO3 is low in chronic

• PaCO2 is low in acute

respiratory alkalosis includes what system symptoms?

 cardiovascular, central nervous, and respiratory symptoms

treatment for respiratory alkalosis

• Sedative, anti-anxiety agents for hyperventilation related anxiety

• Hyperventilation related to other medical causes will be focused on treatment of those conditions (fever, pulmonary embolism, etc.)

what is metabolic acidosis

Refers to all types of acidosis that are not causes by excessive CO2

what is the most common cause of metabolic acidosis

diarrhea

common causes of metabolic acidosis? (9)

• Ileostomy or pancreatic, biliary, or intestinal fistulas

• Kidney loss of HCO3-

  • Chronic kidney disease

  • Systemic loss of HCO3-

  • Diarrhea and fistula drainage

• Excessive production of acid

• Ketoacidosis secondary to conditions such as diabetes mellitus, alcoholism, or starvation

• Lactic acidosis secondary to conditions such as diabetes mellitus, salicylate overdose (form of aspirin)

signs and symptoms of metabolic acidosis

Tachypnea leading to Kussmaul respirations, hypotension, cold and clammy skin, coma

what is the primary compensatory response for metabolic acidosis?

Lungs increase the release of CO2 by increasing the rate and depth of breathing to deepen respiration

what is the secondary compensatory response for metabolic acidosis?

Kidneys increase excretion of H+ and retention of HCO3 --> effectiveness is decreased if renal disease is present

treatment for metabolic acidosis focuses on what and has goal of what ?

•  the underlying cause

• Goal: raise systemic pH to safe level

examples of treatments (3)

• Ketoacidosis --> insulin therapy

• Hyperosmolality --> rapid rehydration

• Bicarbonate replacement

Why does diabetic ketoacidosis result in metabolic acidosis?

Ketones are strong acids and a buildup will result in lack of bicarbonate to neutralize them, resulting in lowering the pH. They cause metabolic acidosis when there is a severe lack of insulin forces for the body to break down fat for energy (use the ketone bodies )

what is metabolic alkalosis

Due to excessive amount of base

metabolic alkalosis relation with fluid balance?

• Fluid imbalance: alkalosis with volume decrease

• Without fluid imbalance: alkalosis without volume contraction

Initiation of metabolic alkalosis begins with the underlying event that causes either what or what?

an excessive loss of acid or accumulation of base

common causes of metabolic alkalosis (7)

• Loss of acid

• Vomiting

• Nasogastric suctioning

• Hypokalemia

• Intravenous therapy

• Blood transfusion

• Excessive or chronic use of antacids

signs and symptoms of metabolic alkalosis?

No specific signs and symptoms

lab values that could show metabolic alkalosis?

Indicated pH > 7.45 and elevated levels of HCO3-

treatment for metabolic alkalosis focuses on

correction of underlying cause

how is volume imbalances with metabolic alkalosis corrected?

 isotonic saline with KCL

In severe conditions what is used to enhance HCO3 excretion?

carbonic anhydrase inhibitor (rmb that this enzyme allows for Hgb to bind to H+; so inhibiting it will allow for more acid in the blood)