**ABG ANALYSIS

**Purpose of ABG Analysis:

To evaluate how effective the lungs are in bringing oxygen to the blood and removing carbon dioxide from it.

**Radial artery is the most frequently used artery for ABGs

**Allens TestPatient clenches fistApply firm pressure to radial & ulnar arteriesPatient relaxes handRelease pressure on the ulnar arteryPalm should flush within 5-15 secs

**Arterial Blood SamplingPrep sitePierce skin over arterial at a 60-90 angleObtain 3 mL of blood without air bubblesTwirl syringe to mix heparin with samplePlace in iceHold pressure for 5-10 minutesWait 30 minutes before drawing sample if O2 setting changed

**DocumentationMust Include:Presence of positive Allens TestDate and time of procedureSite chosenPatients tolerance to procedureFiO2 patient is on at the time the sample is drawnChart By Exception:Adverse side effects of procedureLength of time pressure applied, if greater than 5 minutesNegative Allens Test

**Key to bodys response to acid-base imbalance is: Hydrogen Ion Concentration

When H+ HCO3- + H+ H2CO3 CO2 + H2O

When H+ CO2 + H2O H2CO3 HCO3- + H+

**

**Components of ABGpH- Hydrogen ion concentration in plasmaPaCO2- Partial pressure of CO2 dissolved in plasmaHCO3- Bicarbonate concentration in plasmaPaO2- Partial pressure of O2 dissolved in plasmaBase Excess- The amount of base

**Interpretation of ABGs

**pHpH reflects the hydrogen ion (H+) concentration of plasmapH range0= pure acid14= pure base7.0 =neutral (equal parts acids/base)Normal pH in the blood = 7.35- 7.45

**AcidosisDecrease in pH resulting from an increase in hydrogen ion concentrationH+

**AlkalosisIncrease in pH resulting from a decrease in hydrogen ion concentration

**FOUR STEPS to evaluate ABGs 1.Evaluate each number2.Check pH to determine cause of imbalance3.Find value that matches acid-base status of pH4.Determine extent of compensation:AbsentPartialComplete

**Step 1 evaluating each numberIs the pH on the acid or alkaline side?What does the PaCO2 show?What does the HCO3 show?Does the PaO2 show hypoxemia?

BufferBaseHCO3phacidCO2PO2hgb

**

Step 2 Is the pH on the acid or alkaline side?Normal pH 7.35 - 7.45

pH < 7.40 = acidosis

pH > 7.40 = alkalosis

**Step 3 Does the PaCO2 match the pH?Normal PaCO2 35-45 mm Hg

PaCO2 > 45

PaCO2 < 35

**Step 3Does the HCO3 match the pH?Normal HCO3 22 - 26 mEq/L

HCO3 < 22

HCO3 > 26

**Which System is Involved?Lungs(Respiratory)

Kidneys(Metabolic)

**Step 4What is the extent of compensation?Absent - value that doesnt match the pH is normalPartial - value that doesnt match the pH & pH are above or below normalComplete - value that doesnt match the pH is above or below normal, but the pH is normal

**Metabolic System compensates for the Respiratory SystemRespiratory acidosis Kidneys re-absorb more bicarbonate

Respiratory alkalosisKidneys excrete more bicarbonate

**Respiratory System compensates for Metabolic abnormalitiesMetabolic acidosisHyperventilation lowers PaCO2 so the ratio of Bicarbonate to Carbonic acid returns to normal

Metabolic alkalosisHypoventilation so the PaCO2 rises and the ratio of Bicarbonate to Carbonic Acid returns to normal

**OxygenOxygen is carried in the blood in two ways:In combination with hemoglobinDissolved in plasma97% bound by Hgb3% dissolved in plasma

**PaO2Normal on room air 80-100 mm HgMild hypoxemia = 60-80 mmHgModerate hypoxemia = 40-60 mmHgSevere hypoxemia =below 40 mmHg

**Does the PaO2 show hypoxemia?

Is the client hypoxemic?Is the clients PaO2 or SaO2 low?Is the client anemic?Normal PaO2 is 80-100Normal SaO2 is 95-100

**ABG ExamplepH 7.48PaCO2 32HCO3 22Normal Uncompensated Respiratory Alkalosis

**Acid-Base Disorders

ABG DisorderPossible CausesSigns and SymptomsRespiratory AcidosisCNS depression (barbiturate or sedative OD)AsphyxiaHypoventilationCOPD Respiratory muscle weakness (Guillain-Barre)Chest wall abnormality (obesity)DiaphoresisHeadacheTachycardiaConfusionRestlessnessApprehension

**Acid-Base Disorders

ABG DisorderPossible CausesSigns and SymptomsRespiratory AlkalosisHyperventilationRespiratory stimulation (septicemia, encephalitis, brain injury, salisylate poisoning)Gram-negative bacteremiaRapid, deep respirationsParesthesiasLight-headednessTwitchingAnxietyFear

**Acid-Base Disorders

ABG DisorderPossible CausesSigns and SymptomsMetabolic AcidosisHCO3- depletion from diarrheaExcessive production of organic acidsInadequate excretions of acids from renal diseaseDKA, Lactic acidosisShock, GI fistulasRapid, deep breathingFruity breathFatigueHeadacheLethargyNauseaVomitingComa

**Acid-Base Disorders

ABG DisorderPossible CausesSigns and SymptomsMetabolic AlkalosisLoss of hydorchloric acid from vomiting or NG suctioningLoss of hydrogen ions due to increased renal excretion from diuretic therapyExcessive alkali ingestionSlow, shallow respirationsMuscle twitchingHypertonic musclesRestlessnessTetany (convulsion)Coma

**ABG Case StudiesExercises

**A patient was admitted to the ICU after suffering a stroke. The third day, the patient is more lethargic than the day before. His lung sounds are diminished in the lower lobes. ABGs are drawn and the following results were obtained. pH 7.33PaCO2 55HCO3 29PaO2 60

**What is the ABG result for the CVA patient? Comp. resp. acidosis with mild hypoxemiaPart. Comp. resp. acidosis with mild hypoxemiaPart. Comp. metabolic acidosis with mod. hypoxemia Comp. metabolic alkalosis with mod. hypoxemia

**A postop cholecystectomy patient is hyperventilating due to anxiety and pain. She complains of tingling and numbness in her fingers. Her ABG values are as follows: pH 7.55PaCO2 28HCO3 24PaO2 90

**

What is the ABG result for the S/P cholecystectomy patient?Comp. resp. alkalosis with normal oxygenationPart. comp. resp. alkalosis with mild hypoxemiaUncomp. Resp. alkalosis with normal oxygenationComp. metabolic alkalosis with mild hypoxemia

**A patient has acute tubular necrosis, brought on by cardiopulmonary arrest. His ABG results are as follows: pH 7.32PaCO2 34HCO3 17PaO2 95

**What is the ABG result for the ATN patient?Comp. resp. acidosis with normal oxygenationComp. metabolic alkalosis with normal oxygenationUncomp. metabolic acidosis with mild hypoxemiaPart. comp. metabolic acidosis with normal oxygenation

**A patient has a history of pancreatitis. He has been vomiting for several days PTA. He presently has a NGT to suction. His ABG values are as follows:pH 7.52PaCO2 49HCO3 40PaO2 93

**What is the ABG result for the patient with pancreatitis?Part. comp. metabolic alkalosis with normal oxygenationComp. metabolic acidosis with normal oxygenationComp. respiratory alkalosis with normal oxygenationPart. comp. resp. alkalosis with normal oxygenation

**A patient has a history of smoking three packs of cigarettes for 40 years and has a history of COPD. His ABGs are as follows:pH 7.35PaCO2 70HCO3 30 PaO2 55

**What is the ABG result for the COPD patient?Part. comp. resp. acidosis, mod. hypoxemia Comp. metabolic alkalosis, mod. hypoxemiaComp. resp. acidosis, mod. hypoxemiaPart. comp. metabolic acidosis, mod. hypoxemia

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****Purpose of the test is to check for patency of the ulnar artery to make sure there is adequate palmar collateral circulation should the radial artery become occluded.

Youre looking for a positive Allens Test.***When H+ increases, HCO3 combines with H+ to form H2CO3 (carbonic acid), The carbonic acid breaks down to CO2 and H20. The lungs react first to blow off the excess CO2. The kidneys react last by excreting H+ and retaining HCO3.

When H+ decreases, CO2 and H2O combine to form carbonic acid, which then breaks down into H+ and HCO3. The lungs retain CO2 making it available to the buffer system and the kidneys excrete HCO3 and recirculate H+.

PH os solutions is 1-14 (7 is considered neutral). Blood is slightly alkaline 7/35-7.45 Buffers in the body: carbonic acid, monohydrogen-dehydrogen, phosphate excrete sodium biphosphate in urine, a weak acid), intracellular plasma protein, hgb buffers(shift CL in & out of RBCS in exchange for bicarb*Normal ph is maintained by 1 part carbonic acid to 20 pts bicard*Normal values:Ph 7.35-7.45PCO2 35-45HCO3 22-26PO2 80-100Saturation 96-100BE +_ 2

Venous: 7.35-7.45PCO240-45HCO3 20-30PO2 40-50Sat 60-85

***Reverse relationship: Low ph, high H+ ions***What is the normal acid to base balance in the body? 1-20*pH levels below 6.8 and above 7.8 are considered incompatible with life.Normal ph 7.35-7.45***The system that is the problem has the value that matches the pH.

The other value that doesnt match the pH, corresponds to the system that will compensate for the imbalance. *Partial= the value that doesnt match is moving in the opposite direction,but the PH still isnt normal***PaO2 is the measurement of dissolved oxygen in the arterial blood.

PaO2 is not necessary for the 4 step ABG analysis, but you should always check your patients PaO2.

The most important thing to remember about PaO2 is that hypoxemia kills. Decrease PaO2 will ultimately result in acid-base imbalance. Without oxygen, anaerobic metabolism takes place and large amounts of lactic acid accumulates causing acidosis.**For every year > 60 y.o. PaO2 decreases by 1 mm Hg.No one should have a PaO2 < 50.**Resp acidosis occurs whenever there is hypoventilation. A build up of CO2 causes carbonic acid to accumulate in the blood (CO2 + H2O=H2CO2=H+ HCO3-)CNS depression from drugs, injuryHypoventilation due to pulmonary, cardiac, musculoskeletal, or neuromuscular disease

COPD, Barbituate or sedative OD, atelectasis, Guillain-Barre), pneumonia, chest wall abnormality, mechanical ventilationTreat; make them breath! Narcan, Ventilator CDB*Hyperventilation from anxiety, pain or improper ventilator settings; sepsis. Have a carbonic acid deficit

Hyperventilation from hypoxia, PE, fear pain, exercise, feverStimulated respiratory center caused by septicemia, encephalitis, brain injury, ASA poisoningTreat: adjust vent settings, treat sepsis or anxiety

*Have a base bicarbonate deficit. Occurs when an acid other than carbonic acid accumilates in the body, or when bicarbonate is lost by body fluidsExcessive production of organic acids from hepatic disease, endocrine disorders, shock or drug intoxication

DKA, Lactic adic, starvation, severe diarrhea, renal tubular disease, renal failure GI fistulas shock*Base bicarbonate excess. Occurs when a loss of acid (prlonged vomiting or gastric suction), or a gain in bicarbonate (ingestion of baking soda)

Severe vomiting, Excess if gastric suctioningDiuretic therapy, potassium deficit, Excess intake NAHCO3, excessive mineralcorticoids **Partially compensated respiratory acidosis.

Caused by alveolar hypoventilation so paCO2 increased.

Treatment is TCDB, chest physiotherapy, aerosol therapy or nasotracheal suctioning.*Partially compensated respiratory acidosis.*Uncompensated respiratory alkalosis.

Caused by alveolar hyperventilation which decreases paC02.

Treatment is administer pain medication and have patient breathe regularly and deeply.**Partially compensated metabolic acidosis.

Caused by the fact the kidneys cant synthesize ammonia and ammonia is needed to excrete H+. Also HCO3 decreases because its used up to buffer the H+.

Treatment is IV NaHCO3 and directic therapy.

**Uncompensated metabolic alkaosis.

Volume depletion from vomiting or NGT suctioning causes loss of H+, Cl- and K+.

Treatment is NaCl and KCl replacement.****