abg seminar for pna cebu
TRANSCRIPT
Acid-base disorders and its implications: Therapy in a Nursing
Perspective(July 23, 2014)
EMILIANO IAN B. SUSON II, ED.D, USRN, MAN, RN
“SIR EYE”
Objectives
Describe physiology involved in acid base balance of the body
Review causes and treatments of acid base disorders
Identify normal arterial blood gas values
Interpret results of ABG samples
Interpret oxygenation state of a patient using reported ABG values
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Interpretation of ABG
» Very important for health care providers
» Usefulness of this tool depends on being able to interpret correctly the results
» Critically ill patients
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Acid base disorders
12000 to 15000 mEq of volatile acids are produced daily by body and excreted as CO2 by lungs
1 mEq / kg / day of non-volatile acids (sulfuric and phosphoric acids) are produced daily by body and excreted by the kidneys
The most important buffers in the body are, hemoglobin, plasma proteins and bicarbonate
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Acid base disorders
SIMPLE ACID BASE DISORDER: when there is only one primary disorder
MIXED ACID BASE DISORDER: when there are two or more primary disorders present at the same time
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Normal values
pH 7.35-7.45 7.40
PaCO2 35-45 mmHg 40
PaO2 70-100 mmHg
HCO3- 24±2 24
Met-Hb <2%
CO-Hb <3%
BE -2 to 2 mEq/L
CaO2 16-22 ml/dL
A gap 10±2 12
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Buffers
1. Protein Buffer Systems
Amino Acid buffers
Hemoglobin buffers
Plasma Protein buffers
2. Phosphate Buffer Systems
3. Carbonic Acid – Bicarbonate Buffer System
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12Bicarbonate buffer
Sodium Bicarbonate (NaHCO3) and carbonic acid (H2CO3)
Maintain a 20:1 ratio : HCO3- : H2CO3
HCl + NaHCO3 ↔ H2CO3 + NaCl
NaOH + H2CO3 ↔ NaHCO3 + H2O
13Phosphate buffer
Major intracellular buffer
H+ + HPO42- ↔ H2PO4-
OH- + H2PO4- ↔ H2O + H2PO4
2-
14Protein Buffers Includes hemoglobin, work in blood and ISF
Carboxyl group gives up H+
Amino Group accepts H+
Side chains that can buffer H+ are present on 27 amino acids.
The 10 essential amino acids are:(PVTMATHILL)
Phenylalanine, Valine, Tryptophan, Methionine, Arginine,
Threonine, Histidine, Isoleucine, Leucine, Lysine
10 Amino acids the body produces:
alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine and tyrosine
152. Respiratory mechanisms
Exhalation of carbon dioxide
Powerful, but only works with volatile acids
Doesn’t affect fixed acids like lactic acid
CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3-
Body pH can be adjusted by changing rate and depth of breathing
163. Kidney excretion
Can eliminate large amounts of acid
Can also excrete base
Can conserve and produce bicarb ions
Most effective regulator of pH
If kidneys fail, pH balance fails
17Rates of correction
Buffers function almost instantaneously
Respiratory mechanisms take several minutes to hours
Renal mechanisms may take several hours to days
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21Acidosis Principal effect of acidosis is depression of the CNS through ↓ in synaptic
transmission.
Generalized weakness
Deranged CNS function the greatest threat
Severe acidosis causes
Disorientation, Coma, Death
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Alkalosis
Alkalosis causes over excitability of the centraland peripheral nervous systems.
Numbness
Lightheadedness
It can cause : Nervousness
muscle spasms or tetany
Convulsions
Loss of consciousness
Death
23Respiratory Acidosis
Acute conditons:
Adult Respiratory Distress Syndrome
Pulmonary edema
Pneumothorax
24Compensation for Respiratory Acidosis
Kidneys eliminate hydrogen ion and retain bicarbonate ion
25Signs and Symptoms of Respiratory Acidosis
Breathlessness
Restlessness
Lethargy and disorientation
Tremors, convulsions, coma
Respiratory rate rapid, then gradually depressed
Skin warm and flushed due to vasodilation caused by excess CO2
26Treatment of Respiratory Acidosis
Restore ventilation
IV lactate solution
Treat underlying dysfunction or disease
27Respiratory Alkalosis
Conditions that stimulate respiratory center:
Oxygen deficiency at high altitudes
Pulmonary disease and Congestive heart failure – caused by hypoxia
Acute anxiety
Fever, anemia
Early salicylate intoxication
Cirrhosis
Gram-negative sepsis
28Compensation of Respiratory Alkalosis
Kidneys conserve hydrogen ion
Excrete bicarbonate ion
29Treatment of Respiratory Alkalosis
Treat underlying cause
Breathe into a paper bag
IV Chloride containing solution – Cl- ions replace lost bicarbonate ions
30Metabolic Acidosis
Bicarbonate deficit - blood concentrations of bicarb drop below 22mEq/L
Causes:
Loss of bicarbonate through diarrhea or renal dysfunction
Accumulation of acids (lactic acid or ketones)
Failure of kidneys to excrete H+
31Symptoms of Metabolic Acidosis
Headache, lethargy
Nausea, vomiting, diarrhea
Coma
Death
32Compensation for Metabolic Acidosis
Increased ventilation
Renal excretion of hydrogen ions if possible
K+ exchanges with excess H+ in ECF
( H+ into cells, K+ out of cells)
33Treatment of Metabolic Acidosis
IV lactate solution
34Metabolic Alkalosis Bicarbonate excess - concentration in blood is greater than
26 mEq/L
Causes:
Excess vomiting = loss of stomach acid Excessive use of alkaline drugs
Certain diuretics Endocrine disorders
Heavy ingestion of antacids
Severe dehydration
35Symptoms of Metabolic Alkalosis
Respiration slow and shallow
Hyperactive reflexes ; tetany
Often related to depletion of electrolytes
Atrial tachycardia
Dysrhythmias
36Treatment of Metabolic Alkalosis
Electrolytes to replace those lost
IV chloride containing solution
Treat underlying disorder
37Example
A patient is in intensive care because he suffered a severe myocardial infarction 3 days ago. The lab reports the following values from an arterial blood sample:
pH 7.3
HCO3- = 20 mEq / L ( 22 - 26)
pCO2 = 32 mm Hg (35 - 45)
38Diagnosis
Metabolic acidosis
With compensation
Acid base disordersMETABOLIC ACIDOSIS: HCO3 <24 OR Anion Gap
>12
METABOLIC ALKALOSIS: HCO3 >24
RESPIRATORY ALKALOSIS: PCO2 <40 or PCO2 less than expected for primary metabolic abnormality
RESPIRATORY ACIDOSIS: PCO2 >40 or PCO2 higher than expected for primary metabolic abnormality
HIGH ANION GAP (>12-20) always indicates primary metabolic acidosis
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Acid base disorders and compensatory response
pH HCO3- PaCO2
Metabolic acidosis
Metabolic alkalosis
Respiratory acidosis
Respiratory alkalosisCompensatory response never brings the pH back to normal if the pH is in acidic direction, it tells you that the process or processes in acidic direction are the primary disorders
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Anion Gap
Na-(Cl+HCO3)= 12±2
Estimates unmeasured anions
Normal is 12
Hypoalbuminemia:
Correct anion gap: 2.5 per gram of albumin below 4
Calculate osmolal gap if anion gap is elevated
OSM gap = measured OSM-2(Na)-glu/18-BUN/2.8 = <10
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Urinary anion gap
Useful in differential diagnosis of non gap acidosis
U anion gap= Na + K – Cl
A negative U. Anion Gap ie Cl >> Na + K suggests appropriate urinary NH4 excretion and G.I. loss of HCO3
A positive U. Anion Gap ie. Cl << Na + K suggests RTA with distal acidification defect and inadequate NH4 excretion in urine
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Acidosis (Low pH)
Lowering extracellular pH by rising concentration of hydrogen ions
Fall in bicarbonate concentration
Elevation in PCO2
Decreases force of cardiac contractions
Decreases vascular response to catecholamines
Decreases response of certain medications
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Alkalosis (High pH)
Elevation of the pH of the extra cellular fluid
Lowering hydrogen ion concentration
Elevation in plasma bicarbonate
Reduction in PCO2
Impairs oxygenation
Impairs muscular function
Impairs neurological function
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Metabolic acidosis
Anion Gap
Methanol
Uremia
DKA
Paraldehyde
INH
Lactic acidosis
Ethylene glycol
Salicylate
Non Gap
Hyperalimentation
Acetazolamide
Renal tubular acidosis
Diarrhea
Ureterosigmoidostomy
Pancreatic fistula
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Metabolic alkalosis
Gain of bicarbonate by abnormal renal absorption
Volume contraction (low urine chloride)
Vomiting: loss of H+
Diuretics: depletion ECF
Severe hypokalemia
Renal failure
Mineralocorticoid excess (high urine chloride)
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At a Glance Acid- Base Disorders
Acid-base
disorder
Causes Signs and
Symptoms
Respiratory
acidosis
Hypoventilation,
Neuromuscular
disorders, Airway
obstruction, CNS
depression
↑PR, ↑RR, ↑BP,
Mental
cloudiness,
Feeling of
fullness in the
Head, ↑ICP
Ventricular
Fibrillation, Papilledema,
Dilated
Conjunctival
Blood vessel,
Hyperkalemia,
Tachypnea,
Cyanosis
Acid-base
disorder
Causes Signs and
Symptoms
Respiratory
alkalosis
Hyperventilation,
Sepsis,
Pregnancy,
Mechanical
Ventilation, fever
Lightheadedness
Inability to
Concentrate,
Numbness and
Tingling, Tinnitus
Loss of
consciousness
At a Glance Acid- Base Disorders
Acid-base
disorder
Causes Signs and
Symptoms
Metabolic
acidosis
Diabetic
Ketoacidosis,
Renal failure
Methanol/aspirin
Overdose,
Renal tubular
Acidosis,
Diarrhea, Chronic
alcoholism
Headache, ↓ BP
Confusion
Drowsiness
↑ RR and depth
Nausea, Vomiting
↓Cardiac output
Cold and clammy
Skin, Shock,
Dysrhythmias
At a Glance Acid- Base Disorders
Acid-base
disorder
Causes Signs and
Symptoms
Metabolic
alkalosis
vomiting
diuretics
alkali ingestion
Tingling of fingers
and toes, Dizziness,
Hypertonic muscles,
Symptoms of
Hypocalcemia, ↓ RR,
Atrial tachycardia
Hypokalemia, Paralytic
Ileus, Dysrhythmia
At a Glance Acid- Base Disorders
Acid-Base Imbalances Management
TYPE OF
IMBALANCE
MANAGEMENT
Respiratory
Acidosis
- Improving ventilation
- Bronchodilators
- Antibiotics for infection
- Thrombolytics & anticoagulants
(pulmonary emboli)
- Pulmonary hygiene
- Mechanical ventilation
- Semi-Fowler’s position
Acid-Base Imbalances Management
TYPE OF
IMBALANCE
MANAGEMENT
Respiratory
Alkalosis
- Treatment of the underlying
cause
- Breathe into a paper bag
- Sedative
Acid-Base Imbalances Management
TYPE OF
IMBALANCE
MANAGEMENT
Metabolic
Acidosis
- Treatment is correcting the
underlying defect.
- Eliminating source of chloride
- Bicarbonate
- Alkalizing agents
- Hemodialysis
- Peritoneal dialysis
Acid-Base Imbalances Management
TYPE OF
IMBALANCE
MANAGEMENT
Metabolic
Alkalosis
- Treatment of underlying
disorder
- Chloride supply
- Sodium chloride fluids
- KCl
- H2-receptor antagonists
(Cimitidine)
- Carbonic anhydrase inhibitors
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Cases
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HEMOGLOBIN
PLT
WBC
HEMATOCRIT
SEGMENTERS
RBC
pH K
Na
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12-14
140k-440k
5k-10k
38-42
SEGMENTERS
4-8
7.35-7.45 4.0-5.1
135-145
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Hemoglobin – this is the part of your red blood cell which carries
oxygen all over the body. If your hemoglobin levels are decreased it
could pertain to anemia, bleeding, patients with chronic kidney
disease, or a possible blood dyscrasia. If your hemoglobin levels
are elevated we could consider polycythemia vera and dehydration.
Red Blood Cell (RBC) – this part of the CBC tells you the number
of cells that could carry oxygen in the body. Same with hemoglobin,
decrease levels of RBC could also be secondary to anemia or
bleeding and increase levels could also be secondary to
polycythemia or dehydration.
Hematocrit – this measures the amount of space in the blood
being occupied by your red blood cells. Causes for the increased
and decreased of hematocrit are the same with your hemoglobin
and red blood cells.
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White Blood Cell (WBC) – this are the cells in the body that fight
off invaders like infections. An increase or decrease in WBC count
could represent an ongoing infection or a malignancy like your
leukemia. Also included in the CBC is the 5 differential count for
your WBC, namely:
Neutrophils or segmenters – this type of WBC are the primary
cells that respond to a bacterial infection. High levels of your
neutrophils usually represent and ongoing infection, an
inflammation, malignancy, cause by some drugs, etc. Low levels of
your neutrophils could be seen in patients with viral infection,
autoimmune diseases, some medications and malignancy.
Lymphocytes – this type of WBC represent 20-40% of your
circulating WBC in the blood. An increased in lymphocyte count
usually represents an acute infection especially viral infections,
leukemia, smoking, etc. Low lymphocyte count is usually not
significant.
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Monocytes – this comprises 3-8% of all white blood cells in the
body. An increase in monocyte could signify a chronic infection like
your tuberculosis or a chronic inflammation condition like your
inflammatory bowel disease and malignancy. Low levels of
monocytes are usually none significant if other cells are normal.
Basophils – this comprises only 0.01-0.3% of all white blood cells
in the blood. This type could produce histamine. Increased
numbers could represent a myeloproliferative disorder.
Eosinophils – comprises 1 – 6% of all white blood cells in the
blood stream. They are usually increase in cases of allergy, asthma
and in parasitic infections. Low levels are usually not significant.
Platelet Count – the normal platelet count ranges from 150,000 –
400,000 /L and this cell is involved in the clotting cascade of the
body. Low levels of this cell could cause easy bruising and
bleeding. Causes of low platelet count include infections (ex:
dengue fever), autoimmune disease, liver disease, idiopathic
thrombocytopenic purpura, etc.
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Red Cell Indices – this are investigated when considering
diseases like your thalassemia or sickle cell anemia.
MCV (mean corpuscle volume) – telling you the average size of
the red blood cell (80-100)
MCH (mean corpuscle hemoglobin) – shows the average
amount of hemoglobin in each red blood cell (26-34)
MCHC (mean corpuscle hemoglobin concentration) – average
amount of hemoglobin in the red blood cell compared to their
average size. (31-37)
RDW – (11.5 -14.5)
ABG SHORTCUT
Laboratory studies
ABG: pH/PaCO2/PaO2/HCO3/O2sat
ABG: 7.38-7.44/35-45/80-100/22-26/95-100
What is the acid base disturbance and what is the cause
Na135-145
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K3.5-5.1
AG7-16
CO222-30
BUN5-25
Crea0.6-1.2
Glu70-110
Ca8.5-10.1
Cl98-107
CHEMICAL COMPOSITIONS OF BODY FLUIDS
Extracellular Fluid Intracellular Fluid
Na+ 142 mEq/L 10mEq/L
K+ 4mEq/L 140 mEq/L
Ca2+ 2.4 mEq/L 0.0001 mEq/L
Mg2+ 1.2 mEq/L 58 mEq/L
Cl- 103 mEq/L 4 mEq/L
HCO3- 28 mEq/L 10 mEq/L
Phosphates 4 mEq/L 75 mEq/L
SO42- 1 mEq/L 2 mEq/L
Glucose 90 mg/dl 0-20 mg/dl
Amino Acids 30 mg/dl 200 mg/dl
CHEMICAL COMPOSITIONS OF BODY FLUIDS
Extracellular Fluid Intracellular Fluid
Cholesterol 0.5 g/dl 2-95 g/dl
Phospholipids 0.5 g/dl 2-95 g/dl
Neutral fat 0.5 g/dl 2-95 g/dl
PO2 35 mm Hg 20 mm Hg
PCO2 46 mm Hg 50 mm Hg
pH 7.4 7.0
Proteins 2 g/dl 16 g/dl
5 mEq/L 40 mEq/L
Arterial Blood Sampling
NURSE PHLEBOTOMIST
Indications
To assess.
Respiratory Status
Assess oxygenation and ventilation
Acid Base Balance
Phlebotomy. Used if venous route is unavailable or inaccessible due to trauma or burns. Usually a femoral puncture, uncommon variation.
Contraindications
Overlying infection or burn at insertion site.
Absent collateral circulation.
Arteriovenous shunt. Often radial or brachial.
Severe atherosclerosis
Raynauds disease.
Coagulopathy.
Sites
Preferred radial or femoral arteries.
Less common. Dorsalis pedis and posterior tibial.
Avoid. Branches without collateral supply. Example is the brachial artery.
Complications
Bleeding causing hematoma.
Arterial occlusion causing thrombus or dissection.
Infection causing arteritis or cellulitis.
Embolization
Last 3 uncommon.
Normal Values
pH, 7.36 to 7.44. For acid base status of blood.
pCO2, 38 to 44 mmHg. Reflects ventillation.
pO2, 85 to 95 mmHg. Reflects oxygenation.
HCO3, 21 to 27 meq per litre. Key blood buffer.
Base excess, plus or minus 2 meq per litre
ABG quiz. http://www.vectors.cx/med/apps/abg.cgi
Pathophysiology
Metabolic alkalosis
Metabolic acidosis
Respiratory alkalosis
Respiratory acidosis
Initial Preparation
Wash hands
Gloves
Protective eye wear
Iodine swab. Povidone-iodine, betadine. Followed by alcohol swab
Arterial blood gas sampling kit
2 x 2 cm gauze
Bag of ice. To store sample
Allens Test
Indicates collateral circulation to hand.
Radial artery on non dominant hand.
Palpate radial artery.
Simultaneouslys palpate ulnar artery, or as close to that area as possible.
Patient makes a fist. Palpate both arteries for10 seconds.
Release ulnar artery and witness blood flow and pinking of the hand via collateral radial artery
Radial artery is now a candidate for testing.
Set Up
Patient seated on stretcher
Rolled up towel under wrist. That hyperextends wrist, bringing artery closer to surface.
Clean area in a cicular motion with iodine. Allow to dry.
Wipe away iodine with alcohol. While drying, open sampling kit.
Sampling Kit
3 pieces
1. Orange air ball or cube. Used to expel excess air from the syringe.
2. Black cap for syringe, used for transport.
3. 3 cc, cubic centimetres heparinised syringe. With needle attached.
Sampling Kit Use
Pull back slightly on plunger, so once needle is in artery, natural pulsations will fill the syringe.
Remove clear needle cap. Locate the bevel. Bevel is a slanted opening on one side of the needle tip. We want bevel facing upward, so you can see it.
Syringe Use
45 degrees, sharper angle.
Hold like a dart or pen.
Feeling pulse under non syringe finger is the only landmark for orientation.
Before piercing skin, roll finger back slightly from artery, so you dont stab yourself in the finger.
Flash of blood into hub of needle. Artery has been accessed.
Blood will pulse into syringe. 1.5 to 2.0 cc required.
Cover needle with gauze. Quickly remove needle.
After Care
Physician applies pressure to gauze for 5 minutes. 10 minutes if patient is on anticoaggulant therapy.
Optional to ask patient to do this instead.
Blood Care
Insert needle into orange air cube or ball. Want bevel covered, dont want needle to go through cube.
Push down on plunger to expell excess air. So it doesnt affect results. Key point because we are measuring air component levels in blood.
Remove cube and needle as one.
Attach black cap to syringe.
Roll test tube between hands, to ensure blood heparinisation.
Place in iced bag. Send to lab.
Needle and cube to sharps container.
THANK YOU
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References
Bishop, M., Fody, E., & Schoeff, l. (2010). Clinical Chemistry: Techniques, principles, Correlations. Baltimore: Wolters Kluwer Lippincott Williams & Wilkins.
Carreiro-Lewandowski, E. (2008). Blood Gas Analysis and Interpretation. Denver, Colorado: Colorado Association for Continuing Medical Laboratory Education, Inc.
Sunheimer, R., & Graves, L. (2010). Clinical Laboratory Chemistry. Upper Saddle River: Pearson .
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Resources to learn more
www.acid-base.com
www.acidbasedisorders.com
Haber RJ. A practical approach to acid-base disorders. West J Med 1991; 155: 146
www.postgradmed.com/issues/2000/03_00/fall.htm
http://medicine.ucsf.edu/housestaff/handbook/HospH2002_C5.htm