acid-base balance

normal physiological processes of acid & bases

• ph=concentration fo H+

• acid→ H, CO2

• base→ HCO3-

body systems buffer to maintain pH(7.35-7.45)

• respiratory(lungs): CO2

• metabolic(kidneys): H+ and HCO3

• acid poduction: carbonic acid & metabolic acid

• acid excretion: carbonic acid(lungs) & metabolic acid(kidney)

acid buffering

chemicals that take H+ or release it

• a pair of chemicals weak acid and a base e.g. H2CO3 and HCO3

compensation

compensatory mechanism by the body in order to return pH to normal range

compensation via lungs=CO2

compensation via kidneys=HCO3

respiratory compensation:

• changes rate and rhythm of breathing

• acidosis→ offload CO2 by increasing respirations

• alkalosis→ retain CO2 by decreasing respirations

renal mechanism:

• acidotic→ kidneys retain HCO3

• alkalosis→ kidneys excrete HCO3

degrees of compensation

• uncompensated→ body has made no attempt to correct acid-base imbalance

• partially compensated→ pH remains abnormal, body is attempting to correct the imbalance

• fully compensated→ pH is normal, body is correcting the imbalance

acidosis vs alkalosis on CNS

• acidosis→ decreases the level of consciousness

• alkalosis→ decreases LOC, may cause dysrhythmias

acid-base balance and potassium

when changes in H+ concentration happen, the cell will try to maintain the same number of ions intracellularly to maintain an electrical charge

• so H+ ions will be traded for K+ ions

• acidosis= risk of hyperkalemia

• alkalosis=risk of hypokalemia

causes of metabolic acidosis

decreased ability of kidneys to excrete acid or convert bases

• any form of ketoacidosis: DKA, starvation ketoacidosis, alcohol

• lactic acidosis

• thyroid storm

• ASA overdose

• diarrhea(loss of HCO3)→ laxatives

S&S metabolic acidosis

• changes in LOC

• kussmaul respirations

• hyperkalemia

• warm, flushed skin

• nausea, vomiting, diarrhea

• muscle

metabolic alkalosis

causes:

• gain of base(antacids)

• ingestion or infusion of NaHCO3

• massive blood transfusion

• diuretic(non-potassium sparing)

• repeated vomiting

S&S of metabolic alkalosis

• confusion, irritability, dizziness

• dysrhythmias

• hypokalemia

• tremors, muscle cramps

• tinging of fingers and toes

• nausea, vomiting, diarrhea

causes of respiratory acidosis

• consider things that may obstruct the airway or trap CO2

• hypoventilation→ bronchitis, emphysema, severe, asthma, pneumonia

• guillain—barre syndrome

• CNS

• neuromuscular disorder

• acute airway obstruction

• severe pneumonia, pulmonary edema

• obstructive sleep apnea

S&S of respiratory acidosis

• hypoventilation

• shallow, rapid respirations

• low blood pressure

• hyperkalemia

• disorientation, drowsiness, dizziness

causes of respiratory alkalosis

• hyperventilaton

• Myocardial infarction

• lung disease

• pulmonary embolism

• drug use

• high altitude

• drug use- catecholamines

S&S of respiratory alkalosis

• hyperventilation(increase in depth and rate)

• tahcycardia

• low or normal BP

• hypokalemia

• numbness and tingling

scid-base normal ranges

• pH= 7.35-745

• PaCO2= 35-45 mmHg

• HCO3= 22-26

• O2 stat=95-100%

• anion gap=3-10 mEq/L

• base excess: -2 to +2 mmol/L (negative means too much acid)

relationship between pCO2 and HCO3

• if PH and CO2 are going in opposite direction→ respiratory

• if pH and CO2 are going in the same direction→ metabolic

e.g. respiratry acidosis= low pH, high CO2

metabolic acidosis= low ph, low CO2

prevention for acid-base issues

treat the underlying cause

steps for ABG analysis

• top column= categoires(acidsos, normal, alkalosis)

• remaining rows underneath are for pH, CO2, HCO3

1. classify the pH

2. classify the CO2 and classify the HCO3

3. determine if the problem is respiratory or metabolic

• if CO2 and pH are the same direction(both low or both high) = metabolic

• CO2 and ph are different(e.g. low ph, and high CO2= respiratory

4. determine compensation→ if CO2 or HCO3 fall within normal there is no compensation, if pH is normal there is full compensation, if CO2 or HCO3 are opposite of each other then there is partial compensation