Arterial Blood Gas

radial, femoral, PaO2, point, carboxyhemoglobin

Arterial Blood Gas (ABG) Introduction

-Arterial blood specimen is gathered often from the ______, brachial, or ______ artery via an arterial stick or an indwelling arterial line. The specimen is then taken on ice for immediate analysis.

-Information included on a typical ABG report are: pH, PaCO2, ____, base excess, HCO3-, and SaO2 (both are calculated)

-____ of care lab values are available upon request, as are abnormal hemoglobin values like ______________ (CO poisoning) and methemoglobin

oxygen, acid-base, compensate, clinical

Indications of ABG

-Assess issues with ________ exchange (oxygenation), carbon dioxide exchange (ventilation), ____-____ disturbances ± determine etiology, and abnormal hemoglobins

-Ongoing monitoring of above problems

-Assess patient’s ability to ___________ for above problems

-Assess effectiveness of _________ interventions

collateral, infection, Raynaud’s

Contraindications of ABG

-Inadequate _________ circulation of hand (Allen’s Test)

-Local _________, thrombus, or distorted anatomy at the puncture site

-Severe peripheral vascular disease of the artery selected for sampling

-Active ________’_ Syndrome

-Relative: coagulopathy

pain, bleeding, hematoma, infection, nerve

Complications of ABGs

-Common: local _____ and paresthesia, bruising, and local minor __________

-Less common: vasovagal response, local __________ from moderate or major bleeding, and artery vasospasm

-Rare: ________ at the puncture site, arterial occlusion from local hematoma, air or thrombus embolism, local anesthetic anaphylactic reaction, local ______ injury, pseudoaneurysm formation, and vessel laceration

regulated, 7.35

pH must be precisely __________ to maintain optimal cellular function (_.__-7.45)

<, acidosis

pH _ 7.35 = acidemia or ___________

>, alkalemia

pH _ 7.35 = ___________ or alkalosis

bicarbonate, carbon dioxide

The body’s pH is directly proportionate to its level of ____________ and indirectly to _______ _______ (CO2)

Kidneys, metabolic, lungs, respiratory

Acid-base balance is achieved mainly by the ___________, which regulate HCO3- (bicarbonate) and make up the __________ component. This process also relies on the _______, which regulate CO2 and make up the __________ component.

slower

The kidneys respond to an acid-base disturbance much ________ than the lungs can

increase, CO2

Respiratory Acidosis

-___________ in ___ (can be acute or chronic)

-Common causes: CNS depression (drugs, intoxication, CNS event), neuromuscular disorder, pulmonary disease, and OSA

decrease, CO2

Respiratory Alkalosis

-__________ in ___ (can be acute or chronic)

-Common causes: CNS process, drugs (particularly salicylates), progesterone, sepsis, pulmonary processes, and anxiety

decrease, GI, renal, endocrine, carbonic, renal

Metabolic Acidosis: Non-Anion Gap Acidosis

-___________ in bicarb (typically __ losses, _____ losses, or NaCl overload)

-Common Causes: USEDCAR

• Ureteroenterostomy

• Saline infusion (NaCl)

• _________ causes

• Diarrhea

• ________ anhydrase inhibitors (acetazolamide)

• Ammonium chloride

• _______ tubular acidosis

bicarb, methanol, isoniazid, lactic

Metabolic Acidosis: Elevated Anion Gap

-Decrease in _______

-Common Causes: MUDPILES

• ___________

• Uremia

• DKA

• Propylene glycol

• ___________ (hint: one of the TB meds)

• ______ acidosis

• Ethylene glycol

• Salicylates

increase, Cl, low, high, diuretic

Metabolic Alkalosis

-_________ in bicarb, typically driven by loss of __ (either renal or non-renal loss). If non-renal loss, urine Cl is ___. If renal loss, urine Cl is _____.

-Common causes: nausea/vomiting, ________ therapy (“contracture alkalosis”), posthypercapia, mineralocorticoid use, and hyperaldosteronism

immediately, CO2, days, bicarbonate, hydrogen

Compensatory Mechanisms

-Pulmonary system: occurs nearly _________. “Blows off” ___ by increasing respiratory rate and tidal volume.

-Renal system: takes hours to _____. During acidosis, the kidneys generate __________ and add it to the blood. During alkalosis, Type B intercalated cells in the collecting duct will reclaim _________ ions

7.35-7.45, 24, 40, 90, 95

Important ABG Values: Standards

-pH: _.__-_.__

-HCO3-: __ mEq/L

-PaCO2: __ mmHg

-PaO2: __

-O2 saturation: > __%

pH, primary, compensation, maximal, mixed, etiology

8 Step Systematic Approach to ABG Interpretation

1. Identify __

2. Determine ________ process

3. Determine if ___________ occurred

4. Determine ________ compensation

5. Identify ______ disorders

6. Calculate serum anion gap

7. Assess pulmonary status

8. Determine underlying __________/most likely diagnosis

decrease, increase, increase, decrease

Primary Process: Metabolic vs Respiratory

-Acidemia: low pH < 7.35

• Metabolic acidosis = _________ in HCO3-

• Respiratory acidosis = ___________ in CO2

-Alkalemia: high pH > 7.45

• Metabolic alkalosis = _________ in HCO3-

• Respiratory alkalosis = _________ in PaCO2

Mixed Disorder

issue in both metabolic and respiratory components, intervene immediately

Metabolic and respiratory acidosis

What mixed disorder are these findings indicative of?

Metabolic and respiratory alkalosis

What mixed disorder are these findings indicative of?

respiratory, decrease, increase, metabolic, increase, decrease

Determine if Compensation Has Occurred

-Primary metabolic disturbance → ___________ compensation

• Metabolic acidosis = compensatory _________ in PaCO2

• Metabolic alkalosis = compensatory _________ in PaCO2

-Primary respiratory disturbance → __________ compensation

• Respiratory acidosis = compensatory _________ in HCO3-

• Respiratory alkalosis = compensatory _________ in HCO3-

drop, 1.5, 8

Compensatory Equations: Metabolic Acidosis

-With a compensatory _____ in PaCO2

-Expected PaCO2 = (_._ x actual HCO3-) + _ (±2)

-AKA Winter’s Formula

rise, 0.7

Compensatory Equations: Metabolic Alkalosis

-With a compensatory _______ in PaCO2

-Expected PaCO2 = (_._ x actual HCO3-) + 20

rise, 1, 10, 4, 10

Compensatory Equations: Respiratory Acidosis

-With a compensatory _______ in HCO3-

-Acute: Expected HCO3- = 25 + _ [(actual PaCO2-40) / __]

-Chronic (> 3 days): Expected HCO3- = 25 + _ [(actual PaCO2 - 40) / __] ± 2

drop, 2, 5

Compensatory Equations: Respiratory Alkalosis

-With compensatory _______ in HCO3-

-Acute ( < 3 days): Expected HCO3- = 25 - _ [(40-actual PaCO2) / 10]

-Chronic ( > 3 days): Expected HCO3- = 25 - _ [(40-actual PaCO2) / 10] ± 2

less, same, more, both

Identifying Mixed Disorders

-If the compensatory change is ____ than expected → mixed acid-base disorder of the ____ type

-If the compensatory change is ______ than expected → mixed disorder with ____ acidosis and alkalosis present

Na, etiology, plasma, 8-15

Anion Gap

-Anion Gap = __ - (Cl + HCO3)

-Helps identify _______, only in the setting of metabolic acidosis

-Often means that there are too many unmeasured anions in _______. Normal gap is = _-__ mEq/L

Osmolal Gap

-Used in patients with AGMA and concern for toxic alcohols or unexplained AGMA

-Formula: Measured Osm - Calculated Osm (2 x Na + Glucose/18 + BUN/2.8)

-Normal gap = < 10 mOsm/kg

-Anything higher than 10 indicates the possible presence of osmotically active substances like methanol, ethylene glycol, isopropanol, and mannitol

Delta Gap

-Purpose: used when an anion gap metabolic acidosis (AGMA) is identified to check for additional processes

-Formula: (Measured AG - Normal AG)

-If the value is greater than the change in HCO3-, consider concurrent metabolic alkalosis

lactic, diarrhea, vomiting, obesity, CNS

Identify Likely Etiology

-Metabolic acidosis

• AGMA: ____ acidosis, ketoacidosis, uremia

• NAGMA: _______, normal saline

-Metabolic alkalosis

• GI tract losses of acid: _______, NG suction

• Diuretics

-Respiratory acidosis: hypoventilation from any cause

• COPD, ________ hypoventilation syndrome, narcotic use, mechanical under-ventilation

-Respiratory alkalosis: hyperventilation from any cause

• Anxiety, pregnancy, mechanical over-ventilation, ___ disorder

VBG

venous blood gas

-cannot evaluate PaO2 or SaO2

-pH and CO2 are correlated but not identical