Acid-Base Disorders Flashcards
pH, paCO2, HCO3,paO2, and oxygen saturation values
7.35-7.45, 35-45, 22-26, 80-100, >95%
Keys to Acid-Base balance
Dietary metabolism of glucose, proteins & fats
= 15,000 mmol of CO2 daily
Lungs = Regulation of CO2 Kidneys = Regulation of H+ and HCO3-
Major Buffering Pairs
increase in CO2 + water=H2CO3=H+ + HCO3-
Acid-Base Regulation with lungs and kidneys
Lungs : Hypoventilation or Hyperventilation of CO2
Kidneys: Increased or Decreased reabsorption of HCO3
pH < 7.35
acidosis
pH > 7.45
alkalosis
Arterial blood pH determinants
pH = 6.1 + log (HCO3/0.03 X PCO2)
HCO3 excess
Metabolic alkalosis - increased HCO3 and paCO2
HCO3 inadequacy
Metabolic acidosis
When does Respiratory compensation begin
begins within the first hour and
is complete by 12 to 24 hours
PaCO2 excess
Respiratory acidosis
PaCO2 inadequacy
Respiratory alkalosis - decreased HCO3 and paCO2
Renal compensation begins
begins within 24 hours and is complete in 5 days
Steps to Determining Acid-Base disorder
Evaluate the pH (acidotic or alkalotic?)
Determine Source of pH disturbance:
Exam PaCO2 and HCO3 on the ABG
- decreased pH = increased CO2 = respiratory acidosis
- decreased pH = decreased HCO3 = metabolic acidosis
- increased pH = decreased CO2 = respiratory alkalosis
- increased pH = increased HCO3 = metabolic alkalosis
Determine Compensatory Status of pH disturbance
compensatory mechanism is not yet active with no changes to pH
Uncompensated
Jan Doe is a 45 y/o female admitted for a
severe asthma attack. She has been experiencing
increasing shortness of breath since admission 3 hours ago.
Her ABG’s are as follows:
pH = 7.22 ; PaCO2= 55 mmHg; HCO3 = 25 meq/L
What type of disorder does the patient exhibit?
Uncompensated Respiratory acidosis
compensatory mechanism is active but has not fully corrected arterial blood pH
Partial
John Doe is admitted to the hospital. He is a kidney dialysis patient who has missed his last two appointments at the dialysis center.
His ABG’s are as follows:
pH = 7.32 ; PaCO2= 32 mmHg; HCO3 = 18 meq/L
What type of disorder does the patient exhibit?
Partially compensated Metabolic acidosis
compensatory mechanism has normalized arterial blood pH
Complete
Jane Doe is a 54 y/o female admitted for an ileus. She has been experiencing nausea and vomiting. An NG tube has been in place for the last 24 hours.
pH = 7.43 ; PaCO2= 48 mmHg; HCO3 = 36 meq/L
What type of disorder does the patient exhibit?
Compensated Metabolic alkalosis
Bicarbonate Reabsorption occurs where
Proximal Tubule
Gastric
Bicarbonate Secretion occurs
Pancreas
Metabolic acidosis
pH < 7.35: pH < 7.2 = Severe acidosis
pH < 6.7 = Incompatible with life
Deficiency in Serum HCO3/ Increase in Serum H ions
Causes of Metabolic Acidosis
Normal anion gap
Excessive Anion Gap
Causes of Metabolic acidosis:Normal anion gap
9 to 11 (AGap > 17 clinically relevant)
Represents a ↓HCO3- with ↑Cl- (keeps electroneutrality)
Termed “Hyperchloremic metabolic acidosis”
1) Excessive Diarrhea
Pancreatic secretions (GI) are rich with HCO3
Excessive loss of HCO3 results in excessive reabsorption of H+
Causes of Metabolic acidosis:Excessive Anion Gap
Anion Gap metabolic acidosis > 17
Presence of Organic acids (i.e. lactic acid) or toxins
These acids/toxins consume HCO3- becoming anions
See a ↓HCO3- with NO ↑Cl-
Causes of Increased Anion Gap (“MUDPILES”)Source of “Unmeasured Anions”
Methanol Uremia Diabetes ketoacidosis Propylene glycol Isoniazid Lactic acidosis Ethanol intoxication Salicylate overdose
GS has lab results as follows: Na 140 K 5.8 Cl 103 BUN 20 Scr 1.0 (0. Gluc 90 EtOH 25mg/dL No Ketones GS has a h/o alcohol abuse and type I DM pH = 7.16 ; PaCO2= 28 mmHg; HCO3 = 9 meq/L What is the source of this Acid-Base disorder?
Alcohol intoxication
Metabolic alkalosis
pH > 7.45: pH > 7.6= Severe alkalosis
pH > 7.7 = Incompatible with life
Excessive Serum HCO3 with loss of H+ ion
Causes of Metabolic alkalosis
- Increased HCO3 Retention:
Due to Loss of H+ ion (gastric or urinary)
i.e., Nasogastric suctioning/ vomiting - Contraction alkalosis
Excessive diuresis
promote loss of fluids with minimal or no loss of HCO3
RESULT: Increases Serum HCO3
Respiratory alkalosis
pH > 7.45: pH > 7.6= Severe alkalosis
pH > 7.7 = Incompatible with life
Inadequate Serum pCO2
Increased respiratory elimination of CO2
Causes of Respiratory alkalosis
Hyperventilation
Causes of Hyperventilation
CNS Mediated: Pain, Anxiety ,Fever, Head trauma, CVA
Medications: Theophylline, Nicotine, Catecholamines
Others: Severe anemia, High altitude, Hyperthyroidism
Respiratory acidosis
pH < 7.35: pH < 7.2 = Severe acidosis
pH < 6.7 = Incompatible with life
Failure of the lungs to eliminate CO2-
Excessive serum pCO2
Respiratory acidosis: Causes
Ventilatory failure :
Obstructive lung disease or Neuromuscular disease
i.e., Asthma, COPD versus Myasthenia gravis
Perfusion failure:
i.e., Massive Pulmonary embolism
Stepwise approach to Acid-Base
Determine acidosis or alkalosis
Determine primary disorder
Determine severity & if compensation present
* If pH < 7.2 or pH >7.6 = SEVERE
Determine the Cause (remove)
* If metabolic acidosis - ? Excess anion gap
