Acid-Base Imbalance Shu-Yi (Emily) Wang, PhD, RN, CNS gpwsy@hotmail.com Denver School of Nursing
ph Ranges Compatible With Life In blood, the ph represents the relationship between the respiratory and the metabolic systems. A normal ph in the human body is between 7.35-7.45
The first line of defense against ph disorders Chemical buffer systems
If too much acid is present, the bicarbonate ions take up the hydrogen ions released by the acid and become carbonic acid, which is then excreted through the respiratory system in the form of carbon dioxide and water
Homeostatic mechanisms attempt to maintain balance at a ratio of HCO 3 - to PCO 2 Represents the amount of bicarbonate present in the blood Renal tubules regulate balance of hydrogen ions and bicarbonate inos Acidosis: excrete hydrogen, reabsorb bicarb Alkalosis: retain hydrogen, excrete bicarb Represents METABOLIC component Partial pressure of CO 2 being carried in the blood to lungs for excretion Represents RESPIRATORY component
Metabolic Acidosis
Metabolic Alkalosis
Respiratory Acidosis
Respiratory Alkalosis
Figure 31.4 Acid-base imbalances.
An assessment to determine whether your patient s ulnar & radial arteries are patent. Ask patient to rest hands facing upwards so you can examine color changes Ask patient to make a tight fist to begin forcing the blood from his hand Using your middle & index finger compress both radial & ulnar arteries to obstruct arterial blood flow to the hand Ask patient to relax hand into a slightly flexed position Release pressure on the ulnar artery & continue to apply pressure to the radial artery. Note color. If they flush within 5 seconds, the ulnar artery is patent & Allen s Test is positive for the ulnar artery. Repeat for the radial artery
Basic Steps to ABGs Interpretation ph (7.35-7.45) PaCO 2 (35-45mmHg) HCO 3 (22-26 meq/l) PaO 2 (80-100mmhg) BE (±2 ) ph (7.35-7.45)
Using the Acid-Base Map Developed by Charles Peshkin of EKG Skillbuilders Represents 3 of the 4 elements of blood gas analysis ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 7.45 35 26 Normal 7.40 40 24 7.35 45 22 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99
Using the Acid-Base Map ph = hydrogen ions decrease The higher the ph, the lower the concentration of H and the more basic (alkalotic) the blood is. ph = hydrogen ions increase The lower the ph, the higher the concentration of H & the more acidic the blood. ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 7.45 35 26 Normal 7.40 40 24 7.35 45 22 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99 Normal ph is 7.40 The range is 7.35 to 7.45
PaCO ² = pressure of Carbon Dioxide Respiratory system lowers (hypoventilation) and raises (hyperventilation) CO ² to help maintain body ph to 7.40 breathing = CO ², acid and ph (hypoventilation) breathing = CO ², acid and ph (hyperventilation) ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 7.45 35 26 Normal 7.40 40 24 7.35 45 22 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99 Normal PaCO ² is 40 mmhg Normal range is 35-45 mmhg
HCO ³ = Bicarbonate Ion Buffer HCO ³ combines with acid and decreases its ability to lower the ph The kidneys excrete or retains the HCO ³ HCO ³ - acid = ph HCO ³ + acid = ph ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 7.45 35 26 Normal 7.40 40 24 7.35 45 22 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99 Normal HCO ³ is 24 meq Normal range is 22 to 26 meq
Example for Using The Map The CO ² is in the alkalotic range and this tells you that the respiratory system is contributing to the alkalosis The HCO ³ is in normal range and is not causing the alkalosis Interpretation respiratory alkalosis related to a low CO ² from hyperventilation ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 7.45 7.50 35 26 Normal 7.40 40 32 24 25 7.35 45 22 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99
Example for Using The Map The ph is alkalotic. The pco ² is normal The kidneys have released higher levels of HCO ³ to cause metabolic alkalosis ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 7.70 47 7.45 35 26 Normal 7.40 40 38 24 7.35 45 22 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99
If all 3 values are abnormal in the same direction on the map, the condition is called a combined problem
Example for Using The Map Combined means both the respiratory and metabolic systems are involved in the imbalance Combined respiratory and metabolic acidosis ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 7.45 35 26 Normal 7.40 40 24 7.35 45 22 60 6.83 Acidosis 6.80 75 5 10 Charles Peshkin/EKG Skillbuilders, 1996-99
Example for Using The Map All values in alkalotic range Combined respiratory and metabolic alkalosis ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 27 32 7.68 7.45 35 26 Normal 7.40 40 24 7.35 45 22 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99
If ph is abnormal; and PaCO ² + HCO ³ are abnormal in different directions on the map, this condition is called a partially compensated problem
Example for Using The Map Respiratory and metabolic values on opposite sides The value that is on the same side as the ph is the cause of the ph abnormality The value on the opposite side of the ph is trying to compensate Kidneys are trying to compensate by releasing more HCO ³ (balance through acidosis) Partially compensated respiratory alkalosis ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 7.66 15 7.45 35 26 Normal 7.40 40 24 7.35 45 22 17 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99
Example for Using The Map Two values on the same side is alkalosis The value at the opposite side is trying to compensate by decreasing breathing and increasing CO ² Partially compensated metabolic alkalosis ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 41 7.53 7.45 35 26 Normal 7.40 40 24 7.35 45 22 49 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99
Example for Using The Map ph and respiratory values are acidotic. Respiratory is from hypoventilation Kidneys respond by retaining HCO ³ in an effort to raise the ph. Partially compensated respiratory acidosis ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 29 7.45 35 26 Normal 7.40 40 24 7.35 45 22 7.28 62 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99
Example for Using The Map ph and metabolic are both acidotic The lungs are working to blow off CO ² and raise the ph Partially compensated metabolic acidosis ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 32 7.45 35 26 Normal 7.40 40 24 7.35 45 22 7.21 8 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99
If the ph is normal; and the PCO ² and HCO ³ are both abnormal this is a compensated problem Note: The ph will fall short a few hundredths of unit short of the 7.40 normal. The ph will be in the normal range. Which side of 7.40 determines acidotic or alkalotic
Example for Using The Map As the ph nears normal values, the compensatory mechanisms begin to cease This blood gas is slightly alkalotic. The renal system lowered the ph, as the ph entered normal range, the renal system ceased the compensatory mechanisms a few hundredths short of 7.40 This is compensated respiratory alkalosis ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 28 7.45 35 26 Normal 7.40 7.42 40 24 7.35 45 22 18 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99
Example for Using The Map As the ph nears normal values, the compensatory mechanisms begin to cease This blood gas is slightly alkalotic. The respiratory system highbred the ph, as the ph entered normal range, the respiratory system ceased the compensatory mechanisms a few hundredths short of 7.40 This is compensated metabolic alkalosis ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 46 7.45 7.45 35 26 Normal 7.40 40 24 7.35 45 22 67 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99
Example for Using The Map Compensated respiratory acidosis ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 31 7.45 35 26 Normal 7.40 40 24 7.38 7.35 45 22 53 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99
Example for Using The Map Compensated metabolic acidosis ph PCO2 HCO3 Resp. Metabolic Alkalosis 7.80 5 50 25 7.45 35 26 Normal 7.40 40 24 7.35 7.35 45 22 13 Acidosis 6.80 75 5 Charles Peshkin/EKG Skillbuilders, 1996-99