acid base and fluid balance and abg interpretation

8/13/2019 Acid Base and Fluid Balance and ABG Interpretation

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Delicate balance of fluid and electrolytes

and acids and bases required to maintaingood health?



Homeostasis



Fluid within cells of body is known as?



ICF



K+



Fluid located outside of cell is known as?



ECF



Major cation of ECF?



Na+



Movement of H2O across cell membranes

from less concentrated to moreconcentrated?



Osmosis



Substances dissolved in a liquid are known

as?



Solutes



The concentration within a fluid is known as?



Movement of molecules in liquids from an

area of higher concentration to an areaof lower concentration is known as?



Diffusion



Fluid and solute move together across a

membrane from an area of psi to anarea of lower psi?



Filtration



Substance moves across cell membranes

from less concentrated solution to moreconcentrated solution – requires a

carrier?



Active transport



List some routes of fluid loss?



Urine

Insensible fluid loss Feces

Perspiration



List major electrolytes?



Sodium

Potassium Chloride

Phosphate

Magnesium

Calcium

Bicarbonate



Acid base balance is the regulation of ____

ions?



Hydrogen



The acidity or alkalinity of a solution is

measured as ____?



pH



The more ____ a solution the lower the pH?



Acidic



The more ____ the solution the higher the

pH?



Alkaline



7



The ____ hydrogen ions, the more acidic the

solution and the lower the pH?



More



The lower the hydrogen concentration, the

more ____ the solution and the higher thepH?



Alkaline



Most important buffer system?



Bicarbonate-carbonic acid buffer system?



Lungs help regulate acid-base balance by

eliminating or retaining ____?



Carbon dioxide



Normal CO2 level?



Kidneys are the ____ regulators of acid base

balance?



Long-term



Kidneys maintain pH balance by excreting or

conserving ____ and ____ ions?



Bicarbonate, hydrogen



Normal bicarbonate levels?



Factors affecting homeostasis?



Age

Gender Body size

Environment

Lifestyles



List the acid base imbalances?



Respiratory acidosis

Respiratory alkalosis Metabolic acidosis

Metabolic alkalosis



Signs and symptoms of respiratory acidosis?



Dyspnea

Disorientation Coma

Dysrythmias

Ph <7.35

PaCo2 >45

Hypokalemia Hyporemia



Treatment for respiratory acidosis?



Causes/etiology of respiratory acidosis?



Respiratory alkalosis may be caused by

hyperventilation due to?



Anxiety

Pain

Increased body temp

Overventilation with ventilator

Hypoxia

ASA overdose

Hypoxemia

CNS trauma/tumor

Emphysema Pneumonia



Signs and symptoms of respiratory alkalosis?



Tachycardia

SOB

CP

Syncope

Coma

Seizures

Numbness/tingling of extremities

Blurred vision

pH >7.45 CO2 < 35



Treatment for respiratory alkalosis?



Treat underlying cause

Assist client to breathe more slowly Breath in paper bag

Sedation



Conditions that may lead to metabolic

acidosis?



Renal failure

DKA Starvation

Lactic acidosis



____ diarrhea may lead to metabolic

acidosis?



Prolonged



Signs and symptoms of metabolic acidosis?



Kussmal’s respirations

Lethargy HA

Weakness

N/V

pH <7.35

Bicarb <22 CO2 >38



Acid loss due to vomiting and gastric suction

may lead to ____ alkalosis?



Metabolic



Overuse of ____ may lead to metabolic

alkalosis?



Signs and symptoms of metabolic alkalosis?



Hyperventilation

Dysrhythmias Dizziness

Hypertonic muscle tetany

pH >7.45

Bicarb >26

Hypokalemia

hypocalcemia



Treatment metabolic alkalosis?



Give K+

Treat underlying cause



List the normal values for

Ph

PaCO2

HCO3

PaO2

O2 sat



7.35-7.45

35-4522-26

80-100

95-98%



ROME stands for?



R – respiratory

O – oppositeM – metabolic

E – equal (arrows go same direction as pH

arrow)



ABG INTERPRETATION

Obj ti



Objectives

What’s an ABG?

Understanding Acid/Base Relationship

General approach to ABG Interpretation

Clinical causes Abnormal ABG’s

Case studies

Take home

Wh t is ABG



What is an ABG

Arterial Blood Gas

Drawn from artery- radial, brachial, femoral

It is an invasive procedure.

Caution must be taken with patient on anticoagulants.

Helps differentiate oxygen deficiencies from primary

ventilatory deficiencies from primary metabolic acid-base

abnormalities

What Is An ABG?



What Is An ABG?

pH [H+

]

PCO2 Partial pressure CO2

PO2 Partial pressure O2

HCO3 Bicarbonate

BE Base excess

SaO2 Oxygen Saturation



Case St d No 1



Case Study No. 1

60 y/o male comes ER c/o SOB.

Tachypneic, tachycardic, diaphoretic and

Cyanotic. Dx acute resp. failure and ABG’s

Show PaCO2 well below nl, pH above nl,

PaO2 is very low. The blood gas document

Resp. failure due to primary O2 problem.



Buffers



There are two buffers that work in pairs

H2CO3 NaHCO3

Carbonic acid base bicarbonate

These buffers are linked to the respiratory

and renal compensatory system

Buffers

Respiratory Component



Respiratory Component

function of the lungs

Carbonic acid H2CO3

Approximately 98% normal metabolites are in the form

of CO2

CO2 + H2O H2CO3

excess CO2 exhaled by the lungs

Metabolic Component



Metabolic Component

Function of the kidneys

base bicarbonate Na HCO3

Process of kidneys excreting H+ into the urine and reabsorbing

HCO3- into the blood from the renal tubules

1) active exchange Na+ for H+ between the tubular

cells and glomerular filtrate

2) carbonic anhydrase is an enzyme that accelerates

hydration/dehydration CO2 in renal epithelial cells

Acid/Base Relationship



H2O + CO2 H2CO3 HCO3 + H+

Acid/Base Relationship

Normal ABG values



Normal ABG values

pH 7.35 – 7.45

PCO2 35 – 45 mmHg

PO2 80 – 100 mmHg

HCO3

22 – 26 mmol/L

BE -2 - +2

SaO2 >95%

Acidosis Alkalosis



Acidosis Alkalosis

pH < 7.35

PCO2 > 45

HCO3 < 22

pH > 7.45

PCO2 < 35

HCO3 > 26

Respiratory Acidosis




Think of CO2 as an acid

failure of the lungs to exhale adequate CO2

pH < 7.35

PCO2 > 45

CO2 + H2CO3 pH

Causes of Respiratory Acidosis



Causes of Respiratory Acidosis

emphysema

drug overdose

narcosis

respiratory arrest

airway obstruction

Metabolic Acidosis



Metabolic Acidosis

failure of kidney function

blood HCO3 which results in availability of renaltubular HCO3 for H+ excretion

pH < 7.35

HCO3 < 22

Causes of Metabolic Acidosis



Causes of Metabolic Acidosis

renal failure

diabetic ketoacidosis

lactic acidosis

excessive diarrhea

cardiac arrest

Respiratory Alkalosis




too much CO2 exhaled (hyperventilation)

PCO2 , H2CO3 insufficiency = pH

pH > 7.45

PCO2 < 35

Causes of Respiratory Alkalosis



Causes of Respiratory Alkalosis

hyperventilation

panic d/o

pain

pregnancy

acute anemia

salicylate overdose

Metabolic Alkalosis



Metabolic Alkalosis

plasma bicarbonate

pH > 7.45 HCO3 > 26

Causes of Metabolic Alkalosis



Causes of Metabolic Alkalosis

loss acid from stomach or kidney

hypokalemia

excessive alkali intake

How to Analyze an ABG



How to Analyze an ABG1. PO2 NL = 80 – 100

mmHg

2. pH NL = 7.35 – 7.45

Acidotic <7.35

Alkalotic >7.45

3. PCO2 NL = 35 – 45 mmHg

Acidotic >45

Alkalotic <35

4. HCO3 NL = 22 – 26 mmol/L

Acidotic < 22

Alkalotic > 26



F t ABG I t t ti



Step 2:

pH acidosis <7.35alkalosis >7.45

Four-step ABG Interpretation

F st ABG I t t ti



Step 3:

study PaCO2 & HCO 3

respiratory irregularity if PaCO2 abnl & HCO3 NL

metabolic irregularity if HCO3

abnl & PaCO2

NL


F st ABG I t t ti



Step 4:

Determine if there is a compensatory mechanism working

to try to correct the pH.

ie: if have primary respiratory acidosis will have increased

PaCO2 and decreased pH. Compensation occurs when

the kidneys retain HCO3.


~ PaCO – pH Relationship



~ PaCO2 – pH Relationship

80 7.20

60 7.30

40 7.40

30 7.50

20 7.60



ABG Interpretation



Compensated

Respiratory

Alkalosis

CO2

More Abnormal

Respiratory

Alkalosis

CO2

Expected

Mixed

Respiratory

Metabolic

Alkalosis

CO2

Less Abnormal

CO2 Change

c/w

Abnormality

Metabolic

Alkalosis

CO2

Normal

Compensated

Metabolic

Alkalosis

CO2 Change

opposes

Abnormality

Alkalosis

ABG Interpretation





pH 7.30

PaCO2 60

HCO3 26





pH 7.50

PaCO2 30

HCO3 22

Metabolic Acidosis



Metabolic Acidosis

pH 7.30

PaCO2 40

HCO3 15

Metabolic Alkalosis



Metabolic Alkalosis

pH 7.50

PCO2 40

HCO3 30

What are the compensations?



Respiratory acidosis metabolic alkalosis

Respiratory alkalosis metabolic acidosis

In respiratory conditions, therefore, the kidneys will

attempt to compensate and visa versa.

In chronic respiratory acidosis (COPD) the kidneys increase

the elimination of H+ and absorb more HCO3. The ABG

will Show NL pH, CO2 and HCO3.

Buffers kick in within minutes. Respiratory compensation

is rapid and starts within minutes and complete within 24

hours. Kidney compensation takes hours and up to 5 days.

Mixed Acid-Base Abnormalities



Mixed Acid Base Abnormalities

Case Study No. 3:

56 yo neurologic dz required ventilator support for several

weeks. She seemed most comfortable when hyperventilated

to PaCO2 28-30 mmHg. She required daily doses of lasix to

assure adequate urine output and received 40 mmol/L IV K+

each day. On 10th day of ICU her ABG on 24% oxygen & VS:

ABG Results



ABG Results

pH 7.62 BP 115/80 mmHg

PCO2 30 mmHg Pulse 88/min

PO2 85 mmHg RR 10/minHCO3 30 mmol/L VT 1000ml

BE 10 mmol/L MV 10L

K+ 2.5 mmol/L

Interpretation: Acute alveolar hyperventilation

(resp. alkalosis) and metabolic alkalosis with corrected

hypoxemia.

Case study No. 4



Case study No. 4

27 yo retarded with insulin-dependent DM arrived at ER

from the institution where he lived. On room air ABG & VS:

pH 7.15 BP 180/110 mmHg


PO2 92 mmHg RR 40/min

HCO3 9 mmol/L VT 800ml

BE -30 mmol/L MV 32L

Interpretation: Partly compensated metabolic acidosis.

Case study No. 5



Case s dy o. 5

74 yo with hx chronic renal failure and chronic diuretic therapywas admitted to ICU comatose and severely dehydrated. On

40% oxygen her ABG & VS:

pH 7.52 BP 130/90 mmHgPCO2 55 mmHg Pulse 120/min



BE 17 mmol/L MV 3.75L

Interpretation: Partly compensated metabolic

alkalosis with corrected hypoxemia.

Case study No. 6



s s y

43 yo arrives in ER 20 minutes after a MVA in which he

injured his face on the dashboard. He is agitated, has mottled,

cold and clammy skin and has obvious partial airway obstruction.

An oxygen mask at 10 L is placed on his face. ABG & VS:

pH 7.10 BP 150/110 mmHgPCO2 60 mmHg Pulse 150/min


HCO3 18 mmol/L VT ? ml

BE -15 mmol/L MV ? L

.Interpretation: Acute ventilatory failure (resp. acidosis) and

acute metabolic acidosis with corrected hypoxemia

Case study No. 7



s s y

17 yo, 48 kg with known insulin-dependent DM came to ERwith Kussmaul breathing and irregular pulse. Room air

ABG & VS:

pH 7.05 BP 140/90 mmHg




BE -30 mmol/L MV 48L

Interpretation: Severe partly compensated metabolic

acidosis without hypoxemia.

Case No. 7 cont’d



s

This patient is in diabetic ketoacidosis.

IV glucose and insulin were immediately administered. A

judgement was made that severe acidemia was adversely

affecting CV function and bicarb was elected to restore pH to

7.20.

Bicarb administration calculation:Base deficit X weight (kg)

4

30 X 48 = 360 mmol/L Admin 1/2 over 15 min &4 repeat ABG



Case study No. 8



y

47 yo was in PACU for 3 hours s/p cholecystectomy. She

had been on 40% oxygen and ABG & VS:

pH 7.44 BP 130/90 mmHgPCO2 32 mmHg Pulse 95/min, regular



BE -2 mmol/L MV 7LSaO2 98%

Hb 13 g/dL

Case No. 8 cont’d



Oxygen was changed to 2L N/C. 1/2 hour pt. ready to be D/C

to floor and ABG & VS:

pH 7.41 BP 130/90 mmHgPCO2 10 mmHg Pulse 95/min, regular



BE -17 mmol/L MV 7LSaO2 99%

Hb 7 g/dL

Case No. 8 cont’d



What is going on?

Case No. 8 cont’d



If the picture doesn’t fit, repeat ABG!!

pH 7. 45 BP 130/90 mmHg


PO2

87 mmHg RR 20/min


BE -2 mmol/L MV 7L

SaO2 96%

Hb 13 g/dL

Technical error was presumed.

Case study No. 967 yo who had closed reduction of leg fx without incident.



67 yo who had closed reduction of leg fx without incident.

Four days later she experienced a sudden onset of severe

chestpain and SOB. Room air ABG & VS:

pH 7.36 BP 130/90 mmHg

PCO2

33 mmHg Pulse 100/min


HCO3 18 mmol/L

BE -5 mmol/L MV 18L

SaO2 88%

Interpretation: Compensated metabolic acidosis with

moderate hypoxemia. Dx: PE

Case study No. 1076 yo with documented chronic hypercapnia secondary to



76 yo with documented chronic hypercapnia secondary to

severe COPD has been in ICU for 3 days while being tx for

pneumonia. She had been stable for past 24 hours and wastransferred to general floor. Pt was on 2L oxygen & ABG &VS:

pH 7.44 BP 135/95 mmHg

PCO2 63 mmHg Pulse 110/minPO2 52 mmHg RR 22/min

HCO3 42 mmol/L

BE +16 mmol/L MV 10L

SaO2 86%

.Interpretation: Chronic ventilatory failure (resp. acidosis)

with uncorrected hypoxemia

Case No. 10 cont’d



She was placed on 3L and monitored for next hour. She

remained alert, oriented and comfortable. ABG wasrepeated:

pH 7.36 BP 140/100 mmHg


PO2 65 mmHg RR 24/minHCO3 42 mmol/L

BE +16 mmol/L MV 4.8L

SaO2 92%

.

Pt’s ventilatory pattern has changed to more rapid and shallow breathing. Although still acceptable the pH and

CO2 are trending in the wrong direction. High-flow

oxygen may be better for this pt to prevent intubation

Take Home Message:



Valuable information can be gained from an

ABG as to the patients physiologic condition

Remember that ABG analysis if only part of the patient

assessment.

Be systematic with your analysis, start with ABC’s as always

and look for hypoxia (which you can usually treat quickly),

then follow the four steps.

A quick assessment of patient oxygenation can be achievedwith a pulse oximeter which measures SaO2.

It’s not magic understanding



It’s not magic understanding

ABG’s, it just takes a littlepractice!

Any Questions?



References



1. Shapiro, Barry A., et al; Clinical Application of Blood

Gases; 1994

2. American Journal of Nursing1999;Aug99(8):34-6

3. Journal Post Anesthesia Nursing1990;Aug;5(4)264-72

4. Irvine, David;ABG Interpretation, A Rough and Dirty

Production



Answers to Practice ABG’s



1. Respiratory alkalosis

2. Respiratory acidosis

3. Metabolic acidosis4. Compensated Respiratory acidosis

5. Metabolic alkalosis

6. Compensated Respiratory acidosis

7. Compensated Metabolic alkalosis

8. Metabolic acidosis

9 Respiratory acidosis

acid base and fluid balance and abg interpretation

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