Acid + Base Flashcards
Normal plasma pH?
• ph range compatible with life?
7.35-7.45
ph range compatible with life=6.8-7.8 this represents a 10 fold difference in H+ conc in plasma (its logarithmic scale)
How do buffer systems work?
prevent major changes in pH by removing or releasing H+
- Can act quick to prevent excess H+ conc changes
- H+ buffered by intracellular and extracellular buffers
• The major extracellular buffer is
What ratio should be seen in this buffer?
the bicarbonate-carbonic acid buffer system
this is assessed when ABGs are measured
• There should be 20 parts bicarbonate (HCO3-) to one part carbonic acid (H2CO3) and if the ratio is altered ph changes. The ratio, not the values are important. A shift in either leads to imbalance
• Intracellular buffers include proteins
proteins, organic and inorganic phosphates, and (in RBCs) haemoglobin
how do kidneys buffer?
- Regulate bicarbonate level in ECF
- Can regulate bicarbonate ions and reabsorb them from renal tubular cells
- In resp acidosis and most cases of metb acidosis the kidneys excrete H+ and conserve bicarbonate ions to help restore balance
- In resp and metb alkalosis the kidneys retain H+ ions and excrete bicarbonate
When can the kidneys not compensate for metb acidosis?
when the acidosis is caused by kidney failure…
What part of the brain responds to changing acidity and how?
• The medulla controls the CO2 and therefore the carbonic acid content of ECF by adjusting ventilation in response to amount of CO2 in blood
What do you see in the blood with metb acidosis + alk?
- Metb acidosis is common and characterized by low PH (inc H+ conc) and low plasma bicarbonate conc
- Can be caused by gain of H+ or loss of bicarb
*Why are ABG’s measured?
To evaluate respiratory and renal function
A method to determine Acid-Base and electrolyte imbalances
*Where are ABG’s taken from?
Radial artery (most common) Brachial or Femoral artery Arterial line ( Artline)
*Nursing considerations for taking ABGs?
More painful procedure than regular blood test
Increased risk of bleeding
Increased risk of hematoma at puncture site
*ABG’s can also measure what?
- Electrolytes (sodium and potassium)
- Hemoglobin
- Glucose
- Lactate
*What Exactly Do ABG’s Measure
1) pH (The number of free H+ ions in the body)
2) PaCO2/PC02
3) PaO2/P02
4) HCO3-
5) BE
Base Excess (the amount of blood buffer that exists)
Low values indicate acidosis
High values indicate alkalosis
*What blood values indicate acidosis and alkalosis?
Less than 7.35 is considered acidosis
Greater than 7.45 considered alkalosis
*Normal PaCO2 levle?
Normal range 35 to 45 mm Hg
*Normal HCO3- level?
22-26mmol/L
Used to look at the metabolic side of acid-base balance
*Normal range of PaO2?
How does this change with age?
What value indicates hypoxemia?
80-100 mm Hg
There is a normal decline in pO2 of older adults
Below 60 indicates hypoxemia
*What are the causes of resp acidosis?
Any disease process or problem that cause impaired ventilation could potential cause respiratory acidosis
Examples:
-Drug Overdose
-Pneumonia
-Pulmonary edema
-Chest injuries
Asthma
COPD
*Causes of resp alk?
Any disease process or problem that causes increased ventilation could potentially cause respiratory alkalosis
The patient “blow offs”
the CO2
Examples:
-Hyperventilation
-Fever
PE
Pulmonary Edema
Mechanical Ventilation
*What causes metb acidosis?
A disease process or problem that causes a decrease in base bicarbonate
Examples:
- Diabetic Ketoacidosis
- Lactic acidosis
- ASA , ethanol, ethylene glycol poisoning
- Excessive diarrhea
- Renal failure
*Causes of metb alkalosis?
A disease process or problem that causes an increase in base bicarbonate.
Examples:
-Vomiting
-NG suctioning
-Diuretic therapy and resulting potassium loss
(the kidneys try to retain K+ and thus excrete H+)
*General Signs & Symptoms of Acidosis
General Signs & Symptoms of Alkalosis:
ACID Headache Confusion Decreased LOC SOB Tachycardia Seizures Muscle weakness
ALK Headache Confusion Irritability Lethargy Seizures N & V
*Outline compensation for resp acidosis?
Respiratory Acidosis:
- Initial event: inc PaCO2, inc or normal HCO3-, dec pH - Compensation: Kidneys eliminate H+ and retain HCO3-
Outline compensation for Respiratory Alkalosis:
Initial Event: dec PaCO2, dec or normal HCO3-, inc pH
-Compensation: Kidneys conserve H+ and excrete HCO3-
*Metb acidosis compensation?
- Initial Event: dec or normal PaCO2, dec HCO3-, dec pH
- Compensation: Lungs eliminate CO2 and conserve HCO3-
*Metabolic Alkalosis compensation?
-Initial Event: inc or normal PaCO2, inc HCO3-, inc pH
-Compensation: Lungs inc ventilation to inc PaCO2, kidneys
conserve H+ to excrete HCO3-
*How do you tell if acid/alk is compensated or not?
If you’re seeing a pH outside the normal range, your disorder eitheruncompensatedor partially compensated
Fully compensated: pH seen within normal range of 7.35-7.45
*How to determine what kind of acid/alk you have and whether it’s compensated?
1) look at ph
2) look at PaCO2 (to see resp status)
3) Look at HCO3 (to see metb status)
4) Determine the disorder based on these
5) Look at PaO2 - if below normal, indicates hypoxemia!
What HCO3 values indicate alk and acid?
Acidosis: Below 22
Alkalosis: Above 26
Cardinal feature of metb acidosis?
Low bicarb
How might K levels change with metb acidosis?
• Hyperkalemia may occur w metb acidosis as K leaves the cells, once the acidosis is corrected the K goesback into cells and HYPOkalemia may occur
How might metb acidosis be treated?
- May give alkalizing agents
* May use hemodialysis or peritoneal dialysis
Most common cause of metb alk
Other causes?
• Most common cause is vomiting or gastric suction w loss of H+ and Chloride ions
- Chronic metb alklaosis can occur w long term diuretic therapy (thiazides or furosemide)
- Also pyloric stenosis–>loss of gastric fluid which is acidic pH 1-3
- Potassium loss eg from diuretics and excess adrenocorticoid hormones (like hyperaldosteronism and Cushing’s ) can predispose pt to metb alkalosis
- Excess alkali ingestion of sodium bicarb during CPR or ingestion of antacids w bicarbonate also cause metb alklaosis
How does hypokalemia cause alkalosis (2 ways)?
- Kidneys conserve potassium nd H+ excretion inc
- Cellular potassium moves out of cells into ECF to try to maint near-normal serum levels (as K moves out from cells H+ enters to maint electroneutrality)
Manifestations of metb alkalosis?
- Mostly manifests w symptoms r/t dec calcium ionization (hypocalcemia) eg tingling of fingers and toes, dizziness, hypertonic muscles
- W alkalosis the calcium combines w serum proteins and pt can be hypocalcemic
- Dec resp rate to compensate (this is more pronounced in unconscious or semi conscious pts). May result in hypoxemia
- Atrial tachy possible. As pH inc and hypokalemia develops, ventricular disturbances may occur. (the lack of potassium may cause ECG changes)
- Dec motility and paralytic ileus may be evident
- Chronic and acute s/s are same\
- Kozier: dizziness,hypertonic muscles, tetany
How can urine chloride levels be used to find cause of metb alkalsosi?
• Can look at urine chloride levels to figure out cause of metb alkalosis. Chloride conc may give better indication of fluid volume thatn urine sodium conc. Chloride levels help to differentiate between vomiting, diuretic therapy, and excess adenocorticosteroid sec as the cause of metb alkalaosis
Med management of metb alk?
- d/t volume depletion from GI loss the pts fluid balance and I&O are carefully monitored
- give pt sufficient chloride so the kidneys can absorb sodum with chloride (allowing the excretion of exces bicarb)
- give fluids (NaCL) as volum depletion makes alkalosis worse
- may give K+
- H2RA if pt has gastric suction
- CAI (carbonic anhydrase inhibitors) for those who cant tolerate rapid volume expansion
What ABG findings indicate resp acid
• Respiraory acidosis =pH 42mmHg
Causes of resp acidosis?
• Always d/t inadequate excretion of CO2 w inadequate ventilation that leads to inc plasma CO2 conc and inc levels of carbonic acid
• Hypoventilation usually ->dec PaO2
• Acute respiratory acidsis occurs w emergency situations
o Acute pulm edema
o Aspiration of a foreign object
o Atelectasis
o Pneumothorax
o OD of sedatives
o Sleep apnea
o Admin of oxygen to pt w chronic hypercapnia
o Sever pneumonia
o Acute resp distress syndrome
o Can also occur in diseases that impair resp muscles eg myasthenia gravi, guillain barre syndrome
o If mechanical ventilation rate is wrong and CO2 is retained
Medical management of resp acidosis?
- Tx aims to improve ventilation
- Pulm hygiene measure may be done to clear resp tract of mucus and purulent drainage
- Adequate hydration
- O2?
- May use mechanical ventilation. PaCO2 must be dec slowly. If CO2 is too rapidly excreted kidneys cant remove excess bicarb fast enough can→seizures
- Semi fowlers to promote chest wall expansion
Explain the importance of using O2 judiciously
- If PaCO2 is chronically >50mmHg the resp centre becomes relatively insensitive to CO2 as a stimulant for respiration, leaving hypoxemia as major drive for respiration
- Oxygen admin may remove the stimulus of hypoxemia and the pt develops “carbon dioxide narcosis” unless quickly reversed
- Only use O2 w caution in these pts
Causes of resp alkalosis
• Always caused by hyperventilation “blowing off CO2 (means theres dec of carbonic acid)
• Causes eg
o extreme anxiety,
o hypoxemia,
o early phase of salicylate intoxication,
o gram negative bacteremia,
o inapprop ventilator settings that don’t match pts needs
Manifestations of resp alkalosis?
- Lightheaedness d/t vasoconstriction and dec cerebral blood flow
- Inbility to concentrate
- Numbness and tingling from dec calcium ionization,
- tinnitus
- Can have l/o consciousness
- Can have tachy and ventricular or atrial dysrhythmia
- Kozier: SOB, chest tightness, blurred vision
Assessment and dx finding in resp alkalosis
- Acute: PH is above normal d/t low PaCO2 and normal bicarb
- Look at lytes for dec in K+ as H+ is pulled from cells in exchange for K+
- Dec calcium (severe alkalosis inhibits calcium ionization)
- Dec phosphate d/t alkalosis→phosphate uptake by cells
Medical/nurse interventiosn of resp alk?
• Try to calm anxious pt. May use sedative
- Monitor vitals and ABGs
- Help pt breathe into paper bag or apply rebreather bag
- Assist pt to breathe more slowly
