acid base lecture (1)
DESCRIPTION
A simplified description of the acid-base balance. Designed as an intro to acid-base for the healthcare provider.TRANSCRIPT
Acid-Base Balance
What
is an Acid-Base Status?
It’s as simple as the Henderson-Hasselbalch Calculation…
Let’s UNcomplicate the complicated
Acid-Base is about 2 things:
The patient’s pH &
what is causing it
WHY DOES A PATIENT’S
Acid-Base Status MATTER?
IT SHOULD
AFFECT YOUR
PATIENT CARE!
So let’s learn how to do what we do BETTER.
What is pH?
pH is the potential for Hydrogen
pH = Hydrogen = H+
So, when you think pH, think H+
What is normal?
pHpH
pH
pH
pH
pH
pH
pH pH
pH < 7.35 = Acidosis
pH > 7.45 = Alkalosis
So, pH < 7.35 = acidosis pH > 7.45 = alkalosis
Now the money question:
What is causing the imbalance?
CAUSES OF DISTURBANCE:
Metabolicor
Respiratory
Four Categories of Disturbance
Metabolic Respiratory
MetabolicAcidosis
RespiratoryAlkalosis
MetabolicAlkalosis
RespiratoryAcidosis
MetabolicAlkalosis
MetabolicThe most basic way to determine metabolic disturbance is
to look at a patient’s bicarb level.
Metabolic = HCO3-
Metabolic
Normal HCO3
- = 22-26
Metabolic
HCO3- is a base.
So, if a patient’s HCO3- is
low, what is their acid-base disturbance?
Metabolic AcidosisThe patient’s body has a deficit of bicarbonate.
HCO3- < 22
Causes of Metabolic Acidosis
• Ketones (Diabetic, Alcoholic, Starving)
• Uremia• Lactic Acidosis• Glycols• Salicylates• Rhabdomyolysis• Various Toxins
Metabolic AlkalosisThe patient’s body has an excess of bicarbonate.
HCO3- > 26
Causes of Metabolic Alkalosis
• Renal Failure• Excessive Vomiting• GI Suctioning• Overuse of Antacids (Calcium
Carbonate)• Diuretics, Laxative Abuse• Hypo-kalemia, calcemia, chloremia• Hyperaldosteronism
RespiratoryThe most basic way to determine respiratory
disturbance is to look at a patient’s PaCO2.
Respiratory = PaCO2
Respiratory
Normal PaCO2
= 35-45
Respiratory
CO2 is an acid.
So, if a patient’s PaCO2 is
high, what is their acid-base disturbance?
Respiratory Acidosis
Respiratory acidosis is an excess of carbon dioxide.
PaCO2 > 45
Causes of Respiratory Acidosis
Anything that causes decreased ventilation.- COPD, Asthma, CHF, Pneumonia, Aspiration, Flail Chest, Pneumothorax, Pleural Effusion, etc…
Anything that causes decreased respiratory rate.
- Narcotics, Sedatives, Brainstem Injury, Cardiac Arrest, etc.
Practically every Respiratory Disorder known in Medicine
Respiratory AlkalosisRespiratory alkalosis is a deficit of carbon dioxide.
PaCO2 < 35
Causes of Respiratory Alkalosis
Pulmonary Embolism
Alcohol Fever Head Trauma CVA’s Pneumonia
Hyperthyroidism Exercise Anxiety Overaggressive
Mechanical Ventilation
Anything that can cause increased minute volume.
Four Categories of Disturbance
Metabolic Acidosis
Respiratory Acidosis
MetabolicAlkalosis
Respiratory Alkalosis
To Sum it Up:
HCO3- = Metabolic Acidosis
HCO3- = Metabolic Alkalosis
PaCO2 = Respiratory Acidosis
PaCO2 = Respiratory Alkalosis
Simple Disturbance
Cases
Simple Disorders: Case 1
65 y/o Female
Carbon Monoxide Poisoning
pH: 7.20 torrHCO3: 12 mEq/LPaCO2: 38 torr
What is her acid-base status?
Simple Disorders: Case 2
32 y/o Male
Acute Asthma
pH: 7.08 torrHCO3: 26 mEq/LPaCO2: 60 torr
What is his acid-base status?
Simple Disorders: Case 3
21 y/o Male
Suspected Pulmonary Embolism
pH: 7.48 torrHCO3: 22 mEq/LPaCO2: 20 torr
What is his acid-base status?
Simple Disorders: Case 4
28 y/o Pregnant Female
Excessive Vomiting X4 days
pH: 7.58 torrHCO3: 32 mEq/LPaCO2: 35 torr
What is her acid-base status?
well, that was easy.
we aren’t quite there yet…
Well,
Keep Going
Let’s talk about exceptions.
Sometimes a pH is normal, but there is still a disturbance.
Sometimes there is more than one disorder at play.
Mixed Acid-Base Disorders
The Body STRIVES for a pH of about
7.40
THROUGH 3 SYSTEMS:
Blood
Lungs Kidneys
1st
2nd 3rd
Buffer System
• Activates in Seconds• Fastest & First Line of
Defense• The MOST important
buffer system is the bicarbonate-carbonic acid system.
• Hemoglobin and Oxyhemoglobin, Protein, and Phosphate Buffer Pairs
TENACITY
RespiratorySystem
• Activates in Minutes to Hours
• Second Defense to Activate
• H+ concentration stimulates breathing center
Renal System• Activates in Days
• Works by conserving or excreting H+ and HCO3-
• Strongest mechanism for control.
When the body uses these systems to attempt to maintain a pH that is NORMAL,
this is called
COMPENSATION
Example:
Pt has Respiratory Acidosis
Buffer System increases HCO3- in Blood
Increase in pH
Example:
Pt has Metabolic Acidosis
Increases Respiratory Rate
Decreases CO2
Increase in pH
Compensation
If changes in pH don’t normalize, the disturbance is called
Partially Compensated
If changes in pH normalize, it is called Fully Compensated
Compensation:
pH normal = Fully Compensated
pH abnormal = Partially Compensated
Compensated Disorder
Cases
Compensated Disorders: Case 1
65 y/o Female
COPD Exacerbation
pH: 7.35 torrHCO3: 18 mEq/LPaCO2: 60 torr
What is her acid-base status?
Compensated Disorders: Case 2
18 y/o Female
Type I Diabetic Patient
pH: 7.30 torrHCO3: 18 mEq/LPaCO2: 24 torr
What is her acid-base status?
Compensated Disorders: Case 3
18 y/o Male
Traumatic Brain Injury
pH: 7.45 torrHCO3: 18 mEq/LPaCO2: 22 torr
What is his acid-base status?
Extra Bad Mixed
Disorders
Extra Bad Mixed Disorders
Sometimes you have two independent disorders that drive the pH in the same direction.
This is extra BAD.
Example: COPD patient in Shock (Respiratory and Metabolic Acidosis)
One Disorder
is BAD.
Two Disorders are
Extra Bad!
Summary
Summary• Determine the pH
Summary• Determine the pH• Determine the category of disorder
Summary• Determine the pH• Determine the category of disorder• Is it a mixed disorder?
Summary• Determine the pH• Determine the category of disorder• Is it a mixed disorder?• Is it fully or partially compensated?
Treat the patient you have, not the one you wish you had.