Acid-Base Balance Janis Rusin APN, MSN, CPNP-AC Pediatric Nurse Practitioner Lurie Children’s...

Acid-Base BalanceJanis Rusin APN, MSN, CPNP-ACPediatric Nurse PractitionerLurie Children’s Transport Team

Objectives• Discuss the mechanisms for maintaining normal acid-

base balance• Define respiratory and metabolic acidosis and

alkalosis• Identify the common causes of acid base imbalance• Define and differentiate between respiratory distress

and failure• Discuss interventions on transport for a patient with

acid-base imbalance

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Acid-Base Balance• The human body must be maintained in a very narrow

range of acid-base balance• We use pH as our measure of acidity or alkalinity• pH stands for “power” of hydrogen• Normal pH is 7.35-7.45-Not a whole lot of wiggle

room!• Normal cellular metabolism occurs within this range• The 2 major organs responsible for maintaining acid

base balance are:– The lungs-Respiratory balance– The kidneys-Metabolic balance

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Chemistry Flashback!

• An acid is a substance that releases hydrogen ions (when it dissociates)

• A base is a substance that accepts the hydrogen ions

• A buffer is a substance that protects the pH from derangements by binding with hydrogen ions

HA H+ + A-

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The Bicarbonate Buffer System• The bicarbonate buffer system is what we monitor

clinically to assess acid base balance • This system works in the plasma• Relationship of carbon dioxide (CO2) to bicarbonate

(HCO3-)• CO2 is the acid and HCO3- is the base

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Balancing Act

• Lungs– CO2 is an end product of normal

cellular metabolism– The lungs regulate the CO2 level

through respiration– Rapid response-quick fix!– The lungs cannot regulate

bicarbonate levels

• Kidneys– The renal tubules reabsorb

bicarbonate– Excess hydrogen ions are

excreted in the urine– Slower process– The kidneys cannot regulate

CO2 levels

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Clinical Applications• Acidosis (blood pH < 7.35)

– A pathologic condition that causes an increase in the hydrogen ion concentration

• Alkalosis (blood pH > 7.45)– A pathologic condition that causes a decrease in the hydrogen

ion concentration

• A simple acid base disorder has just one disturbance• The respiratory and metabolic systems compensate

for each others deficiencies• If there is more than one disturbance, the patient is

said to have a mixed acid base disorder

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Types of Acid Base Disorders• Metabolic Alkalosis• Metabolic Acidosis• Respiratory Alkalosis• Respiratory Acidosis

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Metabolic Alkalosis• An elevation in the serum pH associated with a

decrease in hydrogen ion concentration and increase in bicarbonate ion concentration• Chloride plays a big role• 2 main categories

– Chloride Responsive• Chloride levels are < 10 mEq/L

– Chloride Resistant• Chloride levels are > 20 mEq/L

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Metabolic Alkalosis• Chloride Responsive

– Hydrogen ions are lost– Vomiting• Loss of HCL from stomach contents, as well as Na and K• Excessive NG suctioning• Loss of both Hydrogen and Chloride ions• The kidneys retain Na and K instead of H in order to maintain the

Na-K pump function

– Diuretics• Pull H2O from the extracellular space which is low in bicarb• Results in an increased concentration of bicarb• More bicarb available to bind with Hydrogen

– Post hypercapnia • Compensation by kidneys to retain bicarb in presence of

hypercapnia• Metabolic alkalosis occurs transiently once PaCO2 levels corrected

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Metabolic Alkalosis• Chloride Resistant

– Bicarbonate is retained• Hypokalemia

– Low serum K causes K to shift out of the cells and H to shift into the cells

• Excessive base intake– Antacids

• Hypertension– Aldosterone levels are elevated– Results in Na and H2O retention– Hydrogen and excess K are dumped by kidney– K shifts into cells

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Metabolic Acidosis• A decrease in pH associated with a low serum

bicarbonate concentration• Three primary mechanisms:

– Bicarbonate is lost form the body– Kidney function is impaired and acid cannot be excreted

properly– Endogenous or exogenous addition of acid to the body

• Common Diagnoses leading to MA– Diarrhea– Insulin Dependent Diabetes Mellitus (IDDM)– Lactic Acidosis • Poor perfusion and shock

– Renal Failure

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Metabolic Acidosis

• Diarrhea– Most common cause of MA– Bicarbonate is lost in excessive

stool– The kidneys are unable to keep

up with the losses– Potassium is also lost in the

stool– Volume depletion results in

aldosterone release– Sodium is retained leading to

further loss of K– Hypokalemia results

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Metabolic Acidosis• Diabetic Ketoacidosis

– Insulin deficiency occurs stimulating the release of excess glucagon

– Glucagon stimulates the release of fatty acids from triglycerides

– Fatty acids are oxidized in the liver to ketone bodies, beta-hydroxybutrate and aceto-acetic acid

– These acids result in MA– In addition, the DKA patient become volume depleted due to

excessive urination– Shock develops and further exacerbates the acidosis

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Metabolic Acidosis

• Lactic acidosis– Hypoxia or poor tissue perfusion– Cells are forced into anaerobic

metabolism producing lactic acid• Shock• Excessive exercise• Ethanol toxicity

– Ethanol interferes with gluconeogenesis

– Anaerobic metabolism

• Renal Failure– Distal RTA• Failure of the distal tubule to

properly excrete hydrogen ions

– Fanconi syndrome• Failure of the proximal renal

tubule to reabsorb bicarbonate, phosphate and glucose

• Causes include:– Genetics– Medications such as

tetracycline and antiretrovirals

– Lead poisoning

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Anion Gap• Calculation that determines the gap between

concentrations of positive (cations) and negative (anions) ions• Useful in determining the cause of metabolic acidosis• Calculated by:

– (Na+ + K+) – (HCO3- + Cl-) = 10-12mEq/L

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Anion Gap

• Normal Anion Gap• The loss of bicarbonate is

compensated for by the retention of chloride

• Also known as Hyperchloremic Metabolic Acidosis– Diarrhea– Renal Failure, Proximal RTA

• Elevated Anion Gap• MA due to increased H+

load• MUDPILES

– Methanol– Uremia– DKA– Propylene Glycol– Isoniazid – Lactic Acid– Ethylene Glycol (antifreeze)– Salicylates

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Respiratory Alkalosis• A condition in which the carbon dioxide content is

significantly reduced (hypocapnia)• Caused by:

– Hyperventilation– Occurs within minutes of onset of hyperventilation– Pulmonary disease– CHF– Hypermetabolic states• Fever• Anema• Hyperthyroid

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Respiratory Acidosis

• Occurs when ventilation of CO2 is inadequate and CO2 is retained (hypercapnia)

• Causes include airway obstruction, respiratory depression, pneumonia, asthma, pulmonary edema, chest trauma

• The renal buffer system is not effective for acute RA

• Chronic respiratory acidosis can be well compensated for by the kidneys

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So, how do we make the diagnosis?

• Arterial Blood Gas-Normal Values

• pH (7.35-7.45)• PCO2 (35-45)• PO2 (80-100)• HCO3 (22-26)• Base Excess/Deficit (-2 to

+2)

• Venous Blood Gas-Normal Values

• pH (7.31-7.41)• PCO2 (40-50)• PO2 (35-40)• HCO3 (22-26)• Base Excess/Deficit (-2 to

+2)

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Blood Gas Analysis

• Step 1: Look at the pH– < 7.35 is acidic– > 7.45 is alkalotic

• Step 2: Look at the PCO2– <35 is alkalotic– > 45 is acidic

• Step 3: Look at the HCO3– < 22 is acidic– > 26 is alkalotic

• Step 4:Match the pH to either the PCO2 or HCO3 – Whichever one goes in the same

direction as pH determines the primary disorder

– Respiratory = CO2– Metabolic = HCO3

• Step 5:Which one goes in the opposite direction of the pH?– This is the compensatory

system

• Step 6: Look at the PO2– Determines presence of hypoxia

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Blood Gas Analysis

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Normal Values

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HCO3

22

45

PaCO2

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Blood Gas Interpretation

pH 7.35-7.45 Acidemia Alkalemia

Respiratory

Acidosis

MetabolicAlkalosis

Metabolic Acidosis

Respiratory

Alkalosis

Mixed Acid Base Disorders• When to suspect a mixed acid base disorder:

– The expected compensatory response does not occur– Compensatory response occurs, but level of compensation is

inadequate or too extreme– Whenever the PCO2 and HCO3 become abnormal in the

opposite direction. – In simple acid base disorders, the direction of the

compensatory response will always be in the same as the direction of the initial abnormal change.

– pH is normal but PCO2 or HCO3- is abnormal

• General rule:– If the pCO2 is elevated and HCO3 is reduced, then both

respiratory and metabolic acidosis are present– If the pCO2 is reduced and the HCO3 is elevated, then both

respiratory and metabolic alkalosis are present23

Respiratory Distress

• A compensated state in which oxygenation and ventilation are maintained– Define oxygenation and

ventilation– How will the blood gas look?• Characterized by any

increased work of breathing– Flaring, retractions, grunting– What is grunting?

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Respiratory Failure

• Compensatory mechanisms are no longer effective• Inadequate oxygenation

and/or ventilation resulting in acidosis– Abnormal blood gas with

hypercapnia and/or hypoxia– Will begin to see decreasing

LOC due to hypercapnia• Medical emergency! Must

protect airway!• Strongly consider

intubation

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Respiratory Failure-Causes

• Pulmonary Causes– Diffusion impairment– Atelectasis– Pneumonia– Bronchiolitis– Acute lung injury– Pulmonary edema– Shunting and V/Q mismatch

• Non-Pulmonary Causes– Respiratory muscle compromise

or fatigue– Impairment of the nervous

systems control of breathing• Guillain-Barre• Muscular Dystrophy• Central hypoventilation

syndrome– Sedatives– Head injury– Upper airway obstructions

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Indications for intubation

• Inability to protect airway– No cough or gag

• Decreasing LOC• GCS < 8• Cardiac or respiratory arrest• Acute respiratory acidosis• Refractory hypoxemia

despite 100% FiO2

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Goals of ventilation

• Correct acidosis• Rest the respiratory

muscles• Correct hypoxemia

– Allows for delivery of high FiO2– PEEP

• Improves cardiac function– Decreases preload– Decreases metabolic demand

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Initial Ventilator settings

Volume Control Pressure Control

Rate Normal for age Normal for age

Tidal Volume 8-10 cc/kg

PEEP Start at 5cm H2O and increase as clinically

indicated

Start at 5cm H2O and increase as clinically

indicated

i-Time1:2

(Must increase E-time in obstructive processes to

avoid air trapping)

Pressure ControlSet pressure to

produce adequate chest rise and TV’s (8-

10/kg) 29

Correction of hypoxia and hypercarbia

To increase PaO2 To decrease PaCO2

Increase FiO2 Increase Rate

Increase PEEP Increase Tidal Volume orPressure control

Increase I-Time

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Match the Gas• Which patient does this gas belong to?

• pH 7.09 PCO2 98 PO2 218 HCO3 30

– A) 22 y/o with Muscular Dystrophy. Severe and worsening muscle weakness

– B) 9 y/o with new onset Diabetic Ketoacidosis– C) A 30 y/o patient presenting with a panic attack– D) A 25y/o in a skiing accident presenting in respiratory

distress

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Match the Gas

• pH 7.09 PCO2 98 Po2 218 HCO3 30


– Chronic Respiratory Failure– Uncompensated Respiratory Acidosis

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• pH 7.55 PCO2 28 PO2 63 HCO3- 23



distress

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• pH 7.55 PCO2 28 PO2 63 HCO3- 23

– C) A 30 y/o patient presenting with a panic attack

– Hyperventilation– Uncompensated Respiratory alkalosis

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• pH 6.94 PCO2 26.6 PO2 55.7 HCO3 5.7 BD -27



distress

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Match the Gas

• pH 6.94 PCO2 26.6 PO2 55.7 HCO3 5.7 BD -27

– B) 9 y/o with new onset Diabetic Ketoacidosis

– DKA– Uncompensated Metabolic Acidosis

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• pH 7.27 PCO2 54.8 PO2 70 HCO3 26 BD -1



distress

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Match the Gas

• pH 7.27 PCO2 54.8 PO2 70 HCO3 26 BD -1

– D) A 25y/o in a skiing accident presenting in respiratory distress

– Acute Respiratory Distress– Uncompensated Respiratory Acidosis

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Questions?

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Acid-Base Balance Janis Rusin APN, MSN, CPNP-AC Pediatric Nurse Practitioner Lurie Children’s...

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