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CASE STUDIES IN ABGS

Mountain to Sound Chapter of AACN

Objectives

Review normal and abnormal arterial blood gas values

Discuss common acid/base imbalances and treatments

Analyze case examples with treatment strategies

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Blood gas acquisition

No need to ice the sample

Should be analyzed in < 30 minutes

Heparin syringe balanced to run electrolytes

Allen test prior to radial puncture

Arterial Blood Gases

Be methodical when assessing ABGs

Look at 3 main values to interpret:

pH PaCO2 HCO3

Lungs:Fast compensation

Kidney:Slow compensation

Homeostasis is achieved via the lungs, kidneys and blood buffers

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Compensation

Blood buffers provide immediate protection

The lungs excrete 13,000 mEq/day of volatile acid Carbonic acid

The kidneys excrete 40 – 80 mEq/day of fixed acid Sulfuric & phosphoric acids

ABG Interpretation

pH: 7.35 ----- 7.40 ----- 7.45

Acid Alkaline

PaCO2: 35 ----- 40 ----- 45

Alkaline Acid

HCO3: 22 ----- 24 ----- 26

Acid Alkaline

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ABG Interpretation

pH: 7.35 ----- 7.40 ----- 7.45

Acid Alkaline

PaCO2: 45 ----- 40 ----- 35

Acid Alkaline

HCO3: 22 ----- 24 ----- 26

Acid Alkaline

Normal Blood Gas values

Arterial Venous

pH 7.35 – 7.45 7.32 – 7.42

PaO2 80 - 100 28 - 48

PaCO2 35 - 45 38 - 52

HCO3 22 - 26 19 - 25

Base Excess/Deficit

- 2 to + 2

SaO2 95 – 100% 50 – 70%

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ABG Analysis

1. Always assess the pH first!

2. Is it normal?

3. Is there acidosis or alkalosis?

4. Which other value (PaCO2 or HCO3) is trending with the pH?

pH: 7.28 PaCO2: 54 PaO2: 196 HCO3: 26

If PaCO2 is the cause, it’s RESPIRATORY!

If HCO3 is the cause, it’s METABOLIC

Another tip…

Look at the pH & CO2

If the pH & CO2 are both up or both down:

saME = Metabolic

Example: pH: 7.32(↓) CO2: 32 (↓) HCO3: 18

REverse = Respiratory

Example: pH: 7.28 (↓) CO2: 54 (↑) HCO3: 26

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Compensation

If pH is normal & PaCO2 and HCO3

- are both abnormal, then the patient is compensated.

If pH is abnormal & PaCO2 and HCO3

- are both abnormal, then the patient is partially compensated.

If pH is abnormal, & either PaCO2 or HCO3

- are abnormal, then the patient is uncompensated.

Example:

pH 7.22 PaCO2 65 HCO3 24

Uncomp. Respiratory Acidosis

_______ _______ _______

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Respiratory Acidosis Causes

Over-sedation Late respiratory failure Drug overdoses that cause

resp. depression COPD Brain stem dysfunction Extreme V/Q mismatch

Pulmonary embolus, PNA

Guillain Barre’ K+ / PO-4 imbalances Excessive CO2 production

(Sepsis, TPN, Burns)

Think hypoventilation!

Example:

pH 7.52 PaCO2 26 HCO3 22

Uncomp. Respiratory Alkalosis

_______ _______ _______

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Respiratory Alkalosis Causes

Early respiratory failure

Anxiety or severe pain

Excessive tidal volume or rate on vent

ARDs

Heart failure

Neurologic disorders

Pulmonary embolus

Salicylate overdose (adults)

Decreased Cardiac Output/Shock

PaO2 < 60 (Cause & effect)

Think hyperventilation!

Example:

pH 7.16 PaCO2 35 HCO3 14

Uncomp. Metabolic Acidosis

_______ _______ _______

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Metabolic Acidosis Causes

Acute kidney injury

Drug overdoses

Diabetic Ketoacidosis

Sepsis

Lactic Acidosis

Toxins

Aspirin overdose

Liver failure

Calculate an anion gap!!!

May lead to hyperkalemia

Suppresses myocardial contractility (↓ CO, ↓ BP)

Example:

pH 7.49 PaCO2 36 HCO3 29

Uncomp. Metabolic Alkalosis

_______ _______ _______

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Metabolic Alkalosis Causes

NG tube to suction Emesis Hypokalemia Antacid abuse Excessive sodium bicarb infusion Inadequate renal perfusion Diuretics Excessive albuterol use Hyperaldosteronism (d/t RAAS activation)

Practice:

pH 7.50 PaCO2 28 HCO3 24

Uncomp. Respiratory Alkalosis

_______ _______ _______

Causes: Hyperventilation, early respiratory failure, Anxiety, excessive tidal volume on vent

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Practice:

pH 7.24 PaCO2 87 HCO3 26

Uncomp. Respiratory Acidosis

_______ _______ _______

Causes: Hypoventilation, Late respiratory failure, over-sedation, brain stem dysfunction

Practice: Patient with bacterial infection

pH 7.49 PaCO2 28 HCO3 24

Uncomp. Respiratory Alkalosis

_______ _______ _______

Causes: Sepsis – Pneumonia with RR 30s

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Practice: PaO2: 44 COPD patient admitted with SOB

pH 7.36 PaCO2 49 HCO3 23

Compensated Resp. Acidosis

_______ _______ _______

Causes: COPD, CO2 retainer hypoxemic

Practice: Same COPD patient -12 hours later, more somnolent

pH 7.32 PaCO2 54 HCO3 30.6

Uncomp. Respiratory Acidosis

_______ _______ _______

Causes: COPD patient who is getting tired

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Practice: Aspirin overdose

pH 7.31 PaCO2 22 HCO3 18

Uncomp. Respiratory Acidosis

_______ _______ _______

Cause: Seen in aspirin OD

Practice: Post operative patient just admitted from the PACU

pH 7.28 PaCO2 62 HCO3 30

Uncomp. Respiratory Acidosis

_______ _______ _______

Causes: Hypoventilation, over-sedated

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Practice: Septic patient with lactate 4.8

pH 7.32 PaCO2 28 HCO3 17

Partially Metabolic Acidosis

compensated _______ _______

Causes: Hypo-perfused in the state of sepsis

Practice: Type 1 Diabetic presenting with sepsis

pH 7.26 PaCO2 28 HCO3 14

Uncomp. Metabolic Acidosis

_______ _______ _______

Causes: ketoacidosis, check a lactate for hypoperfusion

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Case

62 year old has the following ABG:pH: 7.36 PaCO2 58, PaO2 62, HCO3 28

The patient likely has:

Uncompensated respiratory acidosis Compensated respiratory alkalosis Acute kidney injury COPD Acute myocardial infarction

Case

You are assessing venous & arterial labs in your patient. You note the venous bicarb (CO2) = 29 mEq/L, while the arterial is only 25 mEq/L.

Why the difference?

It must be a lab error

This is actually expected

The labs were drawn at different times

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Case

58 year old admitted with pneumonia

HR 126, BP 84/52, RR 32, SaO2 85% on 4 L NC

Given fluids, antibiotics

Initial lactate 2.8

ABG: pH 7.48/ PaCO2 30/ PaO2 62/ HCO3 24

Your interpretation?

Uncompensated Respiratory Alkalosis

3 hours later…

The patient is tiring and getting more lethargic & sleepy

Repeat lactate 5.2 after a total of 5 L of fluid

ABG: pH 7.26/ PaCO2 58/ PaO2 52/ HCO3 20

Your interpretation?

Uncompensated Respiratory/Metabolic Acidosis

Moderate hypoxemia

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What should we do now?

Intubate/mechanically ventilate This patient is high risk for: ARDS!!!

Vent settings: AMV rate 14, ~8 cc/kg TV, +5 PEEP, 60% FiO2

Post intubation: ABG: pH 7.30/ PaCO2 52/ PaO2 68/ HCO3 24 Your interpretation? Uncompensated (or partially compensated)

respiratory acidosis

Next steps?

Vent settings: AMV rate 14, ~8 cc/kg TV, +5 PEEP, 60% FiO2

Post intubation: ABG: pH 7.30/ PaCO2 52/ PaO2 68/ HCO3 24

Increase the vent rate Increase the PEEP/FiO2

Calculate the P/F Ratio PaO2 68/FiO2 .60 = 113

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What therapy will improve the FiO2?

PEEP!

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Diagnosis:

Pulmonary infiltrates on CXR **P/F Ratio:

< 300 – Mild ARDS < 200 – Moderate ARDS < 100 – Severe ARDS

Predisposing conditions Absence of left heart failure or left

atrial HTN PAOP abandoned to assist diagnosis

Mimics pneumonia & cardiogenic pulmonary edema

Berlin Criteria - 2012

ARDS Severity PaO2/FiO2* Mortality**

Mild 200 – 300 27%

Moderate 100 – 200 32%

Severe < 100 45%

*on PEEP 5+; **observed in cohort

JAMA 2012

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Acute Respiratory Distress Syndrome (ARDS)

Inflammatory lung disease

It is not a primary disease, but a result of:

Sepsis

Trauma

Multiple blood transfusions

Pancreatitis

Cardiopulmonary bypass

Pulmonary contusion

Pneumonia/aspiration

Broncho-alveolar Lavage (BAL)

Diagnostic that is highly underutilized!

Small bronchoscope Lavage with Normal Saline Sample examined for

neutrophils & protein Neutrophils:

NL: 5% ARDS: Up to 80%!

Protein: < 0.5 – pulmonary edema > 0.7 - inflammation

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ARDS Treatment:

Mechanical ventilation

Lung Protective Ventilation (LPV):

Low tidal volumes (6 ml/kg)

Large tidal volumes over distend & rupture distal air space (volutrauma)

Pressure related (barotrauma)

ARDS Net trial – 9% reduction in mortality

Compared 6 ml/kg vs. 12 ml/kg

Use predicted body weight

End inspiratory plateau pressure < 30

ARDS Management Con’t

Low tidal volume (6 ml/kg) Permissive Hypercapnia

PEEP: Like a stent to keep the

alveoli open When increasing PEEP,

monitor for signs of decreased cardiac output!!!

Neuromuscular blockade if dysynchrony with the ventilator

PEEP Ladder from ARDSNet

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Other therapies:

Diuretics: FACTT Trial – Conservative

fluid management Some benefit Did not reduce inflammation

Improving O2 delivery: -Cardiac Output:

Dobutamine -PaO2: PEEP -Hemoglobin: Transfuse only

if necessary!

Steroids: No benefit from early steroids Some benefit days 7 – 14 Methylprednisolone 2 – 3

mg/kg/day Inhibits fibrinolysis Prone Therapy: New evidence of benefit Must be done early, not rescue

strategy

**Mortality increases with advanced age & multi-organ failure

Next steps?

ABG: pH 7.30/ PaCO2 52/ PaO2 68/ HCO3 24Vent settings: AMV rate 14, ~8 cc/kg TV, +5 PEEP, 60% FiO2

Changes: AMV rate 18, ~6 cc/kg TV, +10 PEEP, 70% FiO2

ABG after changes: ABG: pH 7.34/ PaCO2 48/ PaO2 72/ HCO3 26

Uncompensated Respiratory Acidosis Increase the vent rate or possibly hold

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Case study

Michelle is a 49 year old Type 1 Diabetic who is admitted with LOC changes.

Labs:

Na 152, K+ 6.5, glucose 483, + ketones blood & urine

ABG: pH 7.12/ PaCO2 24/ PaO2 85/ HCO3 14

Your interpretation?

Uncompensated (Partially compensated) Metabolic Acidosis

Anion gap: Normal < 11 - 12

Na++ Cl-

K+ (don’t count) HCO3-

>12 – Metabolic acidosis

M: Methanol P: Propylene glycolU: Uremia I: IsoniazidD: DKA L: Lactic acidosis

E: Ethylene glycolS: Salicylates

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Lack of insulin leaves too much

circulating glucose +

Ketone body production

Osmotic diuresis

profound water loss

Leads to glucosuria,

dehydration & electrolyte imbalance

Stress, infection, medications,

diet

In DKA & HHNS, always ask…

Is there something else going on?

Non-compliance?

Infection?

Sepsis?

Pancreatitis?

Myocardial infarction?

New medication? (steroids)

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DKA: Treatment Insulin + Fluids

Decreased Insulin

Serum & urine ketonesIncreased glucoseKetone body production

Osmotic diuresis & dehydrationAcidosis

Anion gap acidosis – Excess serum K+,

Total body depletion of K+/PO4

↑ K+ ↑ Crea nine

Renal Failure

INSULIN FLUIDS

Hyperglycemic crisis (BG 300 - 800)

Metabolic acidosis↓ pH: > 7.0 self correct, < 7.0 consider bicarb

Serum bicarb < 20 mEq/L

Anion gap >12*

Elevated serum ketones

Elevated urine ketones

Electrolyte imbalance: Increased K+ (acidosis causes K+ to shift out of cell)

decreased Na+/Ca++

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3 P’s: Polyuria (early), oliguria – (late) Polydipsia Polyphagia

Neuro:Headache↓ Deep Tendon Reflexes (DTRs) 

Visual disturbances

Hypo/hyperthermiaDecreased LOC – advancing to coma

CV:Tachycardia

Decreased CVP & PAOP

Pulmonary:Kussmaul’s breathing

Acetone/fruity odor to breath

GI:Nausea, vomiting

Abdominal painWeight loss

Fluid Replacement 0.9% Saline or Lactated Ringers (isotonic)

Add dextrose to IVF when BG reaches 250 mg/dL

Then, 0.45% saline @ 250-500 mL/hr

Correct total fluid deficit (~ 50 – 100 mL/kg deficit)

Depending on fluid deficit:

Administer 1-3 L during the first hour

Administer 1 L during the second hour

Administer 1 L during the following 2 hours

Administer 1 L every 4 hours, depending on the degree of dehydration

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Insulin Management - DKA

Insulin (Regular)Assess BG every 1 - 2 hours until goal is reached

Run infusion at 0.1 units/kg/hour

Then, insulin infusion goal: decrease glucose SLOWLY!!!

Do not drop BG by more than 50-100 mg/dL per hour

Transition to subcutaneous

2 hour overlap period – you don’t want the patient going without insulin

DKA – Insulin infusion

Transition to SQ insulin – Overlap by 2 hours

Goal is to shut down ketone production!!!

Electrolyte replacementPotassium Total body potassium depletion Serum is often normal or elevated Transcellular shifts of K+ with insulin therapy Begin K+ replacement at high normal ranges Monitor closely

PhosphateDepletion is common Routine replacement is not recommended (little impact on outcome

in DKA) If level < 1 mg/dL, replacement should be given

Bicarbonate Replacement not recommended unless pH < 7

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Acidosis in Hyperglycemia

For every 0.1 ↓ in pH

If pH is: 7.4

pH 7.3pH 7.2pH 7.1pH 7.0pH 6.9

0.6 ↑ in serum K+

And, K+ is 4.0

K+ 4.6K+ 5.2K+ 5.8K+ 6.4K+ 7.0

Lab values associated with DKA:

Lab Value

Blood glucose > 250 mg/dL

pH (arterial) ≤ 7.3

Anion gap > 10

Bicarb ≤ 18

Ketones Present in serum & urine

Creatinine Can be elevated

Sodium Normal or elevated

Potassium Normal or elevated

Phosphate Normal or elevated

WBC Often elevated

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Top 5 priorities in managing DKA:

Correction of fluid loss with intravenous fluids

Correction of hyperglycemia with insulin

Correction of electrolyte disturbances, particularly potassium loss

Correction of acid-base balance

Treatment of concurrent infection, if present

Discharge when they are stabilized on their home insulin regimen

Case Scenario

Marvin is a 68 year old patient with COPD who presents with SOB. He is given a nebulizer treatment, but remains SOB.

An ABG reveals the following: pH 7.22/PaCO2 92/ PaO2 103/ HCO3 28. This ABG confirms:

A. Uncompensated metabolic acidosis

B. Compensated metabolic alkalosis

C. Uncompensated respiratory acidosis

D. Compensated respiratory alkalosis

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Case Scenario:

A patient with ESKD presents with mental status changes after he skipped dialysis for 3 days. His ABG reveals the following: pH 7.12/ PaCO2 32/ PaO2 180/ HCO3

18. After analyzing the results, you know the patient has:

A. Uncompensated respiratory alkalosis

B. Uncompensated respiratory acidosis

C. Uncompensated metabolic alkalosis

D. Uncompensated metabolic acidosis

Case Scenario:

You are caring for a 46 year old patient with pneumonia and sepsis. He was treated with 4 days of antibiotics and IV fluids. He is increasingly short of breath and is now on 100% FiO2 via non-re-breather mask.

You obtain an ABG with the following results: pH 7.20 / PaCO2 68/ PaO2 102/ HCO3 28. A chest x-ray reveals bilateral pulmonary infiltrates.

The patient is likely developing: A. Worsening pneumonia

B. Acute Respiratory Distress Syndrome

C. Pulmonary embolus

D. Atelectasis

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Case Scenario:

The next course of anticipated action is to:

A. Intubate & place on low PEEP with high tidal volume (12 cc/kg)

B. Initiate non-invasive CPAP

C. Administer additional nebulizer treatments

D. Intubate & place on PEEP with low tidal volume (6 cc/kg)

Case Scenario:

When increasing the level of PEEP, you should monitor for which of the following adverse effects?

A. Hypotension

B. Hypercapnia

C. Worsening acidosis

D. Increased lactate level

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Case Scenario:

You are caring for a patient who developed ARDS after bacterial pneumonia. The CXR shows diffuse patchy infiltrates with progressive worsening hypoxemia. Vent settings: TV 6 cc/kg (540 cc), Rate 24, FiO2 100%, PEEP 10.

An ABG reveals the following: pH 7.22, PaCO2 56, PaO2 42, HCO3 28.

Which of the following interventions would be appropriate at this time?

A. Decrease the set ventilation rateB. Increase the tidal volumeC. Decrease the inspiratory hold timeD. Increase the PEEP

Review question:

pH PaCO2 PaO2 HCO3

7.35/ 54 / 72/ 26

7.49 / 28 / 58 / 24

7.38 / 56 / 44 / 23

Compensated Resp. Acidosis

Pre-Bariatric Surgery –Hypoventilation Syndrome

Uncompensated Resp. Alkalosis

Sepsis – Pneumonia with RR 30s

Compensated Resp. Acidosis

COPD with hypoxia – give O2

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Review question:

pH PaCO2 PaO2 HCO3

7.32 / 62 / 40 / 30.6(same patient)

7.31 / 22 / 98 / 18

Respiratory Acidosis with partial compensation

Same COPD patient, now failing, using accessory muscles

Uncompensated metabolic acidosis

(ASA OD)

Review question:

pH PaCO2 PaO2 HCO3

7.28 / 62 / 52 / 30

7.32 / 28 / 98 / 18

Respiratory Acidosis with partial compensation

Post-op patient, very sleepy, over-sedated

Metabolic acidosis with partial compensation

Septic patient Lactate 6.2