Lab 2 Acid base - Blood gas

Question 1

Isohydria

Answer 1

pH

The conc of H-ions in the body

Question 2

Normal pH in blood

Answer 2

7.35-7.45

Question 3

Isohydria is essential for two things in the body:

Any pH change can lead to:

Answer 3

Cell membranes
Enzyme activities

Electrolyte imbalance

Question 4

Why is a buffer system needed in the body

Answer 4

Because hydrogen ions are constantly produced from chemical reactions, these can lead to alterations in pH

Question 5

Definition of a buffer system

Answer 5

A solution that can maintain a nearly constant pH if diluted, or if small amounts of strong acids or bases are added: they resist pH changes

Question 6

What does a buffer solution typically consist of?

Answer 6

Weak acid/base and one of its salts
If H+ in the body starts to increase, the conjugate base can uptake this excess.
If H+ starts to decrease, more weak acids can dissociate

Question 7

What is the most important buffer system in all fluid compartments of the body?

Answer 7

Carbonic acid - bicarbonate system

Phosphate buffer, protein buffer

Question 8

Three most important buffer systems of blood plasma

Answer 8

Carbonic acid - bicarbonate system
Primary - secondary phosphate buffer
Albumin - albumin + H+

Question 9

Three most important buffer systems of RBCs

Answer 9

Carbonic acid - bicarbonate system
Primary - secondary phosphate buffer
Haemoglobin + O2 - haemoglobin - H+

Question 10

Three most important buffer systems of tissue cells

Answer 10

Carbonic acid - bicarbonate system
Primary - secondary phosphate buffer
Cytoplasmic proteins

Question 11

What does the vital buffer system consist of?

Answer 11

The kidneys and lungs

Question 12

Buffering capacity of lungs

Answer 12

Can retain or excrete CO2 to regulate pH acutely
Reduced ECF pH - hypercapnia
Ventilation is stimulated (huge capacity)
Kussmaul breathing is observed (deep exp/ins)

Question 13

Buffering capacity of kidneys

Answer 13

Can retain or excrete H+ and effectively regenerate the HCO3- via complex tubular mechanisms
Takes hours/days

Question 14

Acid base sample

Answer 14

Sample: Ca-equilibrated Li-heparinised blood
Arterial: shows respiratory function
Air contamination must be avoided (false high pO2)
CO2 can evaporate into air: false low pCO2
Long storage: metabolism of RBCs: false high pCO2

Question 15

Acid base method

Answer 15

ISE to measure pH and CO2
Based on the measured parameters, HCO3- and ABE can be calculated
Measured at 37 C
Solubility of gas is dependent on temp - has to be corrected according to temp of patient (hypo/hyper-thermia)

Question 16

Give respiratory parameters

Answer 16

pCO2

Question 17

Give metabolic parameters

Answer 17

HCO3- (depends on pCO2)
ABE
SBE

Question 18

TCO2

Answer 18

Total CO2
5% higher than plasma HCO3-
Gives no direct information about respiratory function

Question 19

SBE

Answer 19

Standard base excess

Same as ABE but calculated value

Question 20

ABE

Answer 20

Actual base excess

the amount of acid/base needed to equilibrate blood to pH 7.4

Question 21

Evaluation of Acid/Base state

Answer 21

1. Evaluate acidosis/alkalosis according to pH!
   Most important step
2. Search for cause of pH alteration
   Respiratory/metabolic changes
   Resp: pCO2 change Met: HCO3-, ABE change
3. Evaluate whether compensation effort is visible

Question 22

Compensated state

Answer 22

Within 7.35-7.45

Below or above and it is decompensated

Question 23

Respiratory background of pH alteration

Answer 23

pCO2 shows a strong shift in the same direction as pH

High pCO2 = bound to water = H2CO3 (carbonic acid)
= shift in acidic direction

Low pCO2: hyperventilation, too much CO2 is exhaled

Question 24

Metabolic background of pH alteration

Answer 24

Lactic acid production: acidic shift of both parameters

ABE: positive in alkalosis, negative in acidosis

Question 25

Evaluation of respiratory and metabolic parameters compared to pH

Answer 25

Evaluate whether the change of parameters correspond to the alteration of pH

Question 26

How to detect compensatory effect?

Answer 26

The given parameter is shifted in the opposite direction compared to the pH EXAMPLE: Metabolic acidosis, the lungs will try and compensate by Kussmaul breathing. Result: pH acidic CO2 alkaline

Question 27

Mixed acidosis

Answer 27

Advanced acidosis | All parameters are shifted significantly in the same direction as pH

Question 28

Metabolic acidosis causes (8)

Answer 28

``` HCO3- loss Increased acid intake Increased acid production Grain overdose in cattle (VFA overproduction) Increased ketogenesis Decreased acid excretion Ion exchange (hyperkalaemia) Ethylene-glycol toxicosis ```

Question 29

Metabolic acidosis effects (5)

Answer 29

``` Kussmaul breathing Hypercalcaemia: mobilization (long term) Vomiting, depression Hyperkalaemia Acidic urine ```

Question 30

Metabolic acidosis treatment:

Answer 30

Adequate ventilation | if pH <7.2: alkaline (NaHCO3) infusion therapy (based on ABE calculation)

Question 31

Anion gap

Answer 31

Cations:anions | Useful when attempting to determine cause of metabolic acidosis

Question 32

Maintaining electroneutrality (anion gap)

Answer 32

Conc of cations and anions must be equal in plasma Decrease in HCO3- has to be balanced by an increase in Cl- or Unmeasured anions Direct HCO3- loss: Cl- replaces HCO3- Normal anion gap: hyperchloraemic metabolic acidosis If reduction of HCO3- is due to acc of Ua, Cl- stays normal Increased anion gap: normochloraemic metabolic acidosis

Question 33

Normal anion gap: hyperchloraemic metabolic acidosis | CAUSES

Answer 33

Diarrhea Early kidney failure Renal tubular acidosis Acidifying substances

Question 34

Increased anion gap: normochloraemic metabolic acidosis | CAUSES

Answer 34

Azotaemia/uraemia Lactoacidosis Ketoacidosis Toxicosis (basically substances in the blood that aren't measured)

Question 35

Metabolic alkalosis causes (5)

Answer 35

Increased alkaline intake (rotten/bicarbonate) Increased ruminal alkaline prod (high prot, low carb) Decreased hepatic ammonia catabolism (liver failure) Increased acid loss: vomiting, GDV, abomasal displacement Ion exchange: hypokalaemia (HCO3- retention)

Question 36

Metabolic alkalosis effects (4)

Answer 36

``` Breathing depression Muscle weakness - hypokalaemia Hypocalcaemia (ø bind to albumin) Ammonia toxicosis Arrythmia ```

Question 37

Metabolic alkalosis treatment

Answer 37

Treatment of underlying electrolyte imbalance

Question 38

Respiratory acidosis causes (7)

Answer 38

Upper airway obstruction Pleural cavity disease Pulmonary disease Depression of central control of respiration Neuromuscular depression of respiratory muscles Muscle weakness Cardiopulmonary arrest

Question 39

Respiratory acidosis effects (5)

Answer 39

``` Dyspnoea Cyanosis Suffocation Muscle weakness Tiredness ```

Question 40

Respiratory acidosis treatment

Answer 40

Assisting ventilation Treatment of cause (oedema of lungs) Milk anxiolytic/sedating drugs to decrease fear/excitement caused by hypoxia

Question 41

Respiratory alkalosis causes (5)

Answer 41

``` Hyperventilation: Excitation Forced ventilation (anaesthesia) Epileptic seizures Fever, hyperthermia Interstitial lung disease ```

Question 42

Respiratory alkalosis effects

Answer 42

Hyperoxia, decreased pCO2:pO2 ratio | Increased elimination of HCO3- by kidneys

Question 43

Respiratory alkalosis treatment

Answer 43

Anxiolytic drugs | Breathing into paper bag

Question 44

Why do we analyse blood gas?

Answer 44

Assess effectiveness of gas exchange (esp during dyspnoea or anaesthesia

Question 45

Blood gas analysis sample

Answer 45

``` Arterial blood (venous blood only gives indication of how much oxygen was consumed by body) Ca-equilibrated Li-heparinised plasma Closed sampling method (Avoid air contamination) ```

Question 46

Blood gas analysis method

Answer 46

ISE | Standardized temp 37C (must be temp corrected!)

Question 47

paO2

Answer 47

Arterial partial pressure of oxygen | Indicates the lungs ability to oxygenate blood

Question 48

paCO2

Answer 48

Arterial partial pressure of carbon dioxide | Indicates the ability of alveolar gas exchange to remove CO2

Question 49

SAT/SatO2

Answer 49

Oxygen saturation % Indicates fraction of oxygen-saturated hemoglobin relative to total hemoglobin in the blood Venous: 75-80% Arterial: 90-100%

Question 50

FiO2

Answer 50

Fraction of inspired oxygen The assumed % of O2 concentration participating in gas exchange in the alveoli Room air: 20.9% >0.5 risk of O2 toxicity

Question 51

What can be the case when paO2 is under 40-50 mmHg?

Answer 51

Cyanosis

Question 52

Which is higher, pvCO2 or paCO2

Answer 52

pvCO2

Question 53

Hypoventilation causes (5)

Answer 53

Upper airway obstruction Pleural effusion Disturbance to central control of respiration Neuromuscular disease which affects resp system Overcompensation of metabolic alkalosis

Question 54

Hypoventilation effects

Answer 54

Dyspnoea, cyanosis

Question 55

Hypoventilation treatment

Answer 55

Assisting ventilation Diuretic treatment (fluid acc in lungs or thoracic cav) Mild anxiolytic/sedative treatment

Question 56

V/Q

Answer 56

Ventilation-perfusion mismatch

Question 57

Hyperventilation causes

Answer 57

Iatrogen Seizures Excitation (mild/extreme) Compensation of severe metabolic acidosis