Chapter 25: Acid Base Homeostasis and imbalances Flashcards Preview

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Flashcards in Chapter 25: Acid Base Homeostasis and imbalances Deck (25):

The four primary acid base disorders

- Metabolic and respiratory acidosis ( pH 7.45)



the presence of a condition that tends to decrease pH of the blood making it more acidic



the presence of a factor that increases the pH of blood above normal, making it more alkaline


Metabolic Acidosis

- a relative excess of any acid except carbonic acid (renal failure, decrease in bicarbonate)

- may be caused by an increase in acid, an excess removal or decrease in base, or a combination of the both

- Results in the decrease of the normal 20:1 ratio of HCO3(carbonic acid) to H2CO3(bicarbonate)


Metabolic Acidosis (Increase in Acid)

- decrease in the normal ratio of bicarbonate to carbonic acid because bicarbonate ions are used up in buffering the excess acid

- Examples include Starvation Ketoacidosis (caloric and glucose intake is insufficient), any ketoacidosis (breath will smell fruity and also have coolsmal), severe hyperthyroidism, burns, circulatory shock, tissue anoxia, oliguric renal failure, and intake of acid precursors


Metabolic Acidosis (Removal or Decrease in Base)

- anything that causes a removal/decrease in bicarbonate

- examples include diarrhea, gastrointestinal fistula, renal tubular acidosis


Clinical Manifestations of Metabolic Acidosis

- Headache

- abdominal pain

- central nervous system depression

- Severe metabolic acidosis shows tachycardia, ventricular dysrhythmias, decreased cardiac contractility, and death from brain failure if pH falls below 6.9

- Uncompensated ABG (below normal bicarbonate concentration, pH below normal, normal PaCO2)

- causes lungs to try and compensate to correct pH, results in very fast breathing which causes Kussmaul's respirations (breathing very deep and fast)


Compensatory Responses of Metabolic Acidosis

- Hyperventilation due to low pH

- non removal of metabolic acids from the body (trying to equalize acidity of blood)

- change in the ratio of bicarbonate ions to carbonic acid - compensatory increase in pH

- shows decreased bicarbonate concentration, decreased PaCO2, and decreased or even normal pH 


Normal Levels of HCO3 and PaCO2

- PaCO2 = 35-45 mmHg - HCO3 = 22-28 mmHg


Respiratory Acidosis 

- brain stem condition 

- any condition that causes an excess of carbonic acid

- caused by impaired removal of carbonic acid by the lungs (impaired gas exchange, inadequate nuromuscular function, impairment of respiratory control in brainstem) 

- Decrease in the normal 20:1 ratio  of biarbonate ion to carbonic acid 


Respiratory Acidosis (Impaired Gas Exchange)

- Chronic obstructive pulmonary disease (COPD) 

- Pneumonia 

- severe asthma 

- pulmonary edema

- acute respiratory distress syndrome


Respiratory Acidosis (Inadequate Neuromuscular Function)

- guillian-Barre Syndrome 

- chest injury or surgery 

- Hypokalemic respiratory muscle weakness 

- Severe kyphoscoliosis (at top of spine and bottom, which causes decreased lung movement) 

- Respiratory Muscle Fatigue 


Respiratory Acidosis (impaired respiratory control)

- respiratory depressants drugs (opiods, barbiturates) 


Clinical Manifestations of Respiratory Acidosis 

- headache 

- tacchycardia 

- cardiac dysrhythmias 

- Neurologic Abnormalities (blurred vision, tremors, vertigo, disorientation, lethargy, somnolence) 

- Severe respiratory acidosis causes peripheral vasodialtion with hypotension

- Uncompensated ABG (PaCO2 above normal, pH below normal, Bicarbonate normal) 


Compensatory Response of Respiratory Acidosis 

- increased renal excretion of metabolic acid which results in an increase of bicarbonate ion movement of pH towards normal 

- compensated respiratory acidosis will show increased PaCO2 (primary imbalance) , increased bicarbonate concentration (compensation), and decreased or normal pH


Metabolic Alkalosis

- Any condition that tends to cause a relative deficit of any acid (except for carbonic acid) - causes include and increase in base, decrease in acid, or a combination of the two


Metabolic Alkalosis (increase in base)

- intake of bicarbonate or bicarbonate precursors (acetate, lactate, citrate) - massive transfusion with citrated blood - mild or moderate extracellular fluid volume deficit


Metabolic Alkalosis (decrease in acid)

- emesis (vomiting) - gastric suction - mild or moderate extracellular volume deficit (contraction alkalosis) - hyperaldosteronism - Hypokalemia


Clinical Manifestations of Metabolic Alkalosis

- Postural Hypotension 

- hypokalemia may coexist 

- Increased neuromuscular excitability (tingly fingers and toes, signs of tetany(sustained muscle contraction), ionized hypokalemia) 

- increased excitablity of nerve cell membranes 

- beligerence 

- Severe metabolic alkalosis causes central nervous system depression, confusion, lethargy, and coma. Death occurs at pH 7.8 

- Uncompensated ABG shows elevated bicarbonate concentration, normal PaCO2, above normal pH 


Compensatory Response of Metabolic Alkalosis 

- hypoventilation 

- usually incomplete (need for oxygen drives ventilation and prevents complete compensation) 

- compensated Metabolic Alkalosis shows increased bicarbonate concentration (primary imbalance), increased PaCO2 (compensation), slightly increased pH 


Respiratory Alkalosis

- any condition that tends to cause a carbonic acid deficit 

- caused by hyperventilation 


Respiratory Alkalosis (hyperventialtion)

- hypoxemia

- acute pain 

- anxiety, psycholigical stress

- prolonged sobbing 

- alcohol withdrawls 

- stimulations of the brainstem 


Clinical Manifestations of Respiratory Alkalosis

- Increased neuromuscular excitability

- increased central and peripheral membrane excitability 

- increased pH of cerebrospinal and cerebral interstitial fluid alters brain cell function

- cerebral vasoconstriction 

- uncompensated ABGs show abnormally low PaCO2, abnormally high pH, and a normal bicarbonate level 


Compensatory Response of Respiratory Alkalosis

- decreased renal excretion of metabolic acid 

- decrease in bicarbonate ion concentration 

- renal compenstation tends to return the ratio of bicarbonate ions to carbonic acid, moving pH towards normal 

- Compensated respiratory ABGs show decreased PaCO2 (primary imbalance), decreased bicarbonate concentration (compensation), increased somewhat high pH 


Mixed Acid Base Imbalances 

- 2 primary imbalances occur simutaneously 

- 2 types of primary acidosis or alkalosis may impair effectiveness of usual compensatory mechanisms 

- pH will reflect primary mechanism 

- may also occur with a nearly normal pH if a primary acidosis and a primary alkalosis are involved 

- if bicarbonate is the main problem it is acidosis, if PaCO2 is the main problem it is alkalosis