acid base lecture (1)

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.