Acid Base Abnormalities Lecture Powerpoint Flashcards
Arterial blood gas measure functions (3)
A method to assess oxygenation of blood plasma***, evaluate acid base status, and monitor therapy
A-a gradient and how is it measured?
- Measure of lungs ability to transfer o2 from atmosphere to pulmonary circulation, if very high then not transferring (ventilating but not entering circulation), normal means it is.
- Measured normal = age/4
Increased A-a gradient can indicate these 3 pathologies
- congestive heart failure
- adult respiratory distress syndrome
- lobar pneumonia
Most common reason for a V/Q mismatch, and 2 other common causes
- Pulmonary emboli
- pneumonia
- pneumothorax
Alveolar hypoventilation is often due to…
….interstitial lung disease
Ways to attain ABG (2) and technique
- Radial artery stick
- Femoral artery stick (can’t be on any anticoag, need to put pressure on longer)
-use heparanized syringe, it fills passively, remove all air bubbles, transport on ice
Allyn test in attaining ABG using radial artery stick
Used to assess ulnar radial artery anastomosis before acquiring specimen for ABG by occluding both radial and ulnar artery, having patient pump fingers, then release the ulnar and watch entire hand refill - ensures that the hand is dual perfused so ABG stick in radial artery doesn’t cut off supply
PCO2 2 mech of removal from the body
- removal of bicarb
- exhalation of CO2
A ___ mmHg change of PCO2 is equivalent to a ___ change in pH which is equivalent to a ___ MEQ change in base
12, .1, 6
Definition of a volatile acid and example
Nonvolatile acids are typically…
An acid that readily dissociates in air, H2CO3
….nonvolatile acids
Strong vs weak acid/base
Completely dissolute in water while weak incompletely dissolute in water
buffer
A weak acid/base combo that will resist change in pH, predominantly proteins intracellularly and predominantly NaHCO3 (bicarb) extracellularly (weak base)
Treatment for respiratory acidosis
Increase ventilation to remove volatile acids from blood stream
Postprandial alkaline tide
Refers to how upon eating a meal there can be a slight alkalosis that occurs in the blood stream because HCl is used in digestion and intracellular Bicarb is released into the plasma to compensate
ABG stepwise approach (oh good lord 6 steps)
1) Is pH acidotic (<7.35) or alkalotic (>7.45) or normal? (May be normal in fully compensated condition)
2) Is PCO2 respiratory acidotic (>45), respiratory alkalotic (<35) or normal?
3) Is HCO3- metabolic acidotic (<22), metabolic alkalotic (>26), or normal?
4) Match the pCO2 and HCO3- with pH, find if the out of normal range one is going in same direction (High pCO2 with low pH and vise versa, low HCO3- with low pH)
5) If CO2 and HCO3- are going opposite direction of the pH, then this is compensation
6) Uncompensated pH is out of normal range, while partially compensated is 7.35-7.39 or 7.41-7.44
Gold standard test to determine pH and oxygenation of the bloodstream
Arterial blood gas
Hemoglobin and protein molecules in blood shift the physiologic pH of blood from ___ to ____ resting value
7, 7.35-7.45
Difference between arterial blood gas and pulse oximetry
Pulseox measures % sat of hemoglobin molecule which isn’t good indicator of overall oxygenation of blood (cause you might only have 10 hemoglobin molecules), arterial blood gas measures partial pressure of free O2 dissolved in plasma
An A-a gradient can still be normal in conditions that involve…
…hypoventilation
Base excess
A positive or negative measure of how much base is needed to bring pH back to physiologic limits (i.e. -8 means we need 8 more units of base to return to physiologic normal, +8 means we need 8 fewer units of base), more accurate than HCO3- levels
Normal acid base balance values
pH = 7.35-7.45 PaCO2=35-45 mmHg HCO3=22-26meq/L PAO2 and PaO2=80-106mmHg Base excess= +/-2
The anion gap and normal values
The difference between Na+ - (Cl- + HCO3-) and should normally be between 8-15 mEQ/L, but elevated levels indicate buildup of metabolic acids (metabolic acid)
Only time IV bicarb is given is what condition?
Metabolic acidosis to drive K+ back into cells
HCO3 is <24 in ____ acidosis or compensation for ____ alkalosis
metabolic, respiratory
Issue with giving a patient to high of O2 levels
The nitrogen conc of air is important as surfactant to keep alveoli from collapsing and therefore if not a large enough portion of the air content can see atelectasis of alveoli
30-60 rule and 60-90 rule
Refers to general rule that a PaO2 of 30=60% hemoglobin saturation, while a PaO2 of 60=90% saturation
Healthy satO2 in blood
> 94%
PaO2 levels interpretation and what does this indicate?
Normal 80-106
mild hypoxia 60-79
mod hypoxia 40-59
severe hypoxia <39
Determines need of oxygen therapy
Immediate treatment for carbon monoxide poisoning
Extreme O2 supplementation or use of a dive chamber
Despite good hem saturation, o2 might not be able to unload at the tissue if the blood pH is measured to be….
…alkalotic
Net result of left shift and right shift in oxy hemoglobin dissociation curve
- More O2 taken up by HGB but less released
- Less O2 taken up by HGB but more released at tissues
In patients with respiratory acidosis or alkalosis, we often do not see ___ because they are often COPD or other obstructive dz patients
Respiratory compensation
Respiratory and renal compensation
- Respiratory is achieved rapidly by elimination or retention of CO2 via hyper or hypoventilation
- Renal is achieved slowly by secretion or reabsorption of H+ and HCO3-
metabolic acidosis 2 subgroups
- Increased anion gap due to metabolic biproduct buildup
- normal anion gap seen with excessive bicarb loss
Extreme acidosis will see….
….removal of ca2+ from bone and excretion in urine resulting in wasting of skeletal structures
Metabolic alkalosis 2 subgroups
- Excessive gain of bicarb often thru ingestion
- Excessive H+ loss often from vomiting or hypokalemia
Standard in treatment of metabolic alkalosis
KCl and saline
Respiratory acidosis 3 subgroups
- depression of respiratory centers
- lung disease
- disorders of respiratory muscles
Respiratory acidosis treatment
Improve ventilation sometimes mechanically
respiratory alkalosis is usually caused by…
…anxiety or psychogenic source
