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

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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

  • 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 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!

  • 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 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 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

  • 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

  • Metabolic Alkalosis

  • Metabolic Acidosis

  • Respiratory Alkalosis

  • Respiratory Acidosis


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 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 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

  • 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 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 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 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

  • 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 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

  • 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

  • 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?

  • 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

  • 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 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

  • 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

  • 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

  • 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

  • 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

  • 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

  • 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


Correction of hypoxia and hypercarbia


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 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 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 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 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 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 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 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?


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