arterial blood gasses

gold standard of gas exchange analysis

ABG

what site is used to draw blood from

usually radial but other sites can be used (just not prefered)

how is an allens test performed

• The patient is asked to open and close the hand into a fist several times with both radial and ulnar arteries compressed

• Release the ulnar artery

• The entire hand and digits should fill with blood

• This indicates that there is good collateral flow into the radial artery system

positive allans test= ulnar circulation bad. dont use radial!!! dont use wrist!!!

Disorders that may require ABG’s

• respirtroy failure

• kidney disease 

• shock

• trauma 

• uncontroled diabtes 

• durg overdose*

• asthma 

• COPD

• hemorage 

• metabolic disease chemical poisioning

contraindications for ABG

• bleeding risk 

  • clotting disorder 

  • anticoagulants 

• failed allen's test 

• arterial puncture should not be performed through a lesion, scar tissue, burns, through or distal to a surgical shunt/fistula

• PAD

complication of ABG sampling

• bleeding 

• infection 

• arterial vasospasm 

• hematoma 

• air or thrombus embolism 

• vessel laceration 

• local pain 

• arterial occlusion 

normal blood pH

7.35-7.45

normal PaO2

• PaO2: 75-100mmhg

normal PaCO2

35-45mmhg

normal HCO3

22-26meq/l

normal SaO2

95-99%

If blood pH falls below 7.35, it is

acidic

If blood pH rises above 7.45, it is

alkalotic 

is CO2 an acid or a base

acid

PaCO2 below 35 is

alkalotic

PaCO2 above 45 is

acidic

in most acute problems blood pH will be

low

Failure of lungs or kidneys results in acidic or alkalotic 

acid build up

too much CO2 causes

acidosis

If the HCO3 is below 22, the patient is

acidotic

If the HCO3 is above 26, the patient is

alkalotic

bicarb is a

base

HCO3 is regulated by

kidneys

If both CO2 and HCO3 values are outside of normal limits

could indicate compensation.

which is quicker: respirotry or renal compensation

Respiratory compensation is immediate. (minutes)

Renal compensation takes time. (hours or days)

hypoxia vs hypoxemia

Hypoxia = low oxygen content in tissues

Hypoxemia = low oxygen content in the blood

Acute Respiratory Acidosis

The decrease in pH is accounted for entirely by the increase in pCO2

Bicarbonate and base excess will be in the normal range because the kidneys have not had adequate time to establish effective compensatory mechanisms

Acute Respiratory Acidosis causes

• Respiratory pathophysiology - airway obstruction, severe pneumonia, chest trauma/pneumothorax

• Acute drug intoxication (narcotics, sedatives)

• Residual neuromuscular blockade (anesthesia)

• CNS disease (MG, head trauma)

Respiratory depression can lead to

CO2 builds up as body not able to excrete it, lungs can’t blow it off (acidosis)

Respiratory Acidosis symptoms 

• suddenly increased pulse, respiratory rate, and BP; drowsiness, mental changes; feeling of fullness in head 

  • Potential increased intracranial pressure

Respiratory Acidosis treatment is centered around

improving ventilation

Chronic Respiratory Acidosis

• pCO₂ is elevated with a pH in the acceptable range

• Renal mechanisms increase the excretion of H⁺ within 24 hours and may correct the resulting acidosis caused by chronic retention of CO₂ to a certain extent

Chronic Respiratory Acidosis causes

• Chronic lung disease (COPD)

• Neuromuscular disease

• Extreme obesity

• Chest wall deformity

Acute Respiratory Alkalosis

• The increase in pH is accounted for entirely by the decrease in pCO₂

• Bicarbonate and base excess will be in the normal range because the kidneys have not had sufficient time to establish effective compensatory mechanisms

Acute Respiratory Alkalosis causes

• Pain/Anxiety

• Hypoxemia

• Restrictive lung disease

• Severe congestive heart failure

• Pulmonary emboli

• Sepsis

• Overaggressive mechanical ventilation

hyperventilation can lead to

Hyperventilation – lungs get rid of too much CO2 (alkalosis)

Respiratory Alkalosis manifestations

• Manifestations: lightheadedness, inability to concentrate, numbness and tingling, sometimes loss of consciousness

• Tachypnea, tachycardia, dysrhythmias

chronic Metabolic Acidosis causes

Renal failure – Chronic Acidosis

acute Metabolic Acidosis causes 

• Diabetic ketoacidosis 

• Excessive EtOH use

• ASA overdose

• Excessive diarrhea

• Cardiac arrest

• Hypothermia

• Lactic acidosis

lactic acidosis can be related to

heavy exercise, seizure activity

excessive diahrrea can lead to

loss of HCO3

Metabolic Acidosis manifestations 

• drowsiness, increased respiratory rate and depth, decreased blood pressure, decreased cardiac output, dysrhythmias, shock

• Patient may be asymptomatic until bicarbonate is 15 mEq/L or less

acidosis effect on electrolytes

With acidosis, hyperkalemia may occur as potassium shifts out of cell

As acidosis is corrected, potassium shifts back into cell, potassium levels decrease

Serum calcium levels may be low with chronic metabolic acidosis

Must be corrected before treating acidosis

metabolic alkalosis may be caused by 

Loss of acid from stomach or kidneys

• Vomiting, NG tube suctioning

• 
  

  • Hypokalemia – Chronic Alkalosis = long-term diuretic use

  • Excessive alkali intake (antacids)

  • Large amounts of blood transfusions

  • TPN