Acid base balance
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Acid-Base Balance. Janis Rusin APN, MSN, CPNP-AC Pediatric Nurse Practitioner Lurie Children’s Transport Team. Objectives. Discuss the mechanisms for maintaining normal acid-base balance Define respiratory and metabolic acidosis and alkalosis

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Acid base balance

Acid-Base Balance

Janis Rusin APN, MSN, CPNP-AC

Pediatric Nurse Practitioner

Lurie Children’s Transport Team


Objectives

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


Acid base balance1

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


Chemistry flashback

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-


The bicarbonate buffer system

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


Balancing a ct

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


Clinical applications

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


Types of acid base disorders

Types of Acid Base Disorders

  • Metabolic Alkalosis

  • Metabolic Acidosis

  • Respiratory Alkalosis

  • Respiratory Acidosis


Metabolic alkalosis

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


Metabolic alkalosis1

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


Metabolic alkalosis2

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


Metabolic acidosis

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


Metabolic acidosis1

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


Metabolic acidosis2

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


Metabolic acidosis3

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


Anion gap

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


Anion gap1

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


Respiratory alkalosis

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


Respiratory acidosis

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


So how do we make the diagnosis

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)


Blood gas analysis

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


Blood gas analysis1

Blood Gas Analysis

26

HCO3

22

Blood Gas Interpretation

45

PaCO2

35

Normal Values

Respiratory

Acidosis

Metabolic

Alkalosis

Metabolic

Acidosis

Respiratory

Alkalosis

pH 7.35-7.45

AcidemiaAlkalemia


Mixed acid base disorders

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 present


Respiratory distress

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?


Respiratory failure

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


Respiratory failure causes

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


Indications for intubation

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


Goals of ventilation

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


Initial ventilator settings

Initial Ventilator settings


Correction of hypoxia and hypercarbia

Correction of hypoxia and hypercarbia


Match the gas

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


Match the gas1

Match the Gas

  • pH 7.09 PCO2 98 Po2 218 HCO3 30

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

    • Chronic Respiratory Failure

    • Uncompensated Respiratory Acidosis


Match the gas2

Match the Gas

  • Which patient does this gas belong to?

  • pH 7.55 PCO2 28PO2 63 HCO3- 23

    • 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


Match the gas3

Match the Gas

  • Which patient does this gas belong to?

  • pH 7.55 PCO2 28 PO2 63 HCO3- 23

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

    • Hyperventilation

    • Uncompensated Respiratory alkalosis


Match the gas4

Match the Gas

  • Which patient does this gas belong to?

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

    • 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


Match the gas5

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


Match the gas6

Match the Gas

  • Which patient does this gas belong to?

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

    • 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


Match the gas7

Match the Gas

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

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

    • Acute Respiratory Distress

    • Uncompensated Respiratory Acidosis


Questions

Questions?


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