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Principles of Anesthesia I - Summer 24 > Exam 2 - ABGs (Kane) > Flashcards

Exam 2 - ABGs (Kane) Flashcards

1
Q

Acidemia

A

Excess production of H+ (in relation to hydroxyl ions)

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2
Q

Alkalemia

A

Excess production of OH- (in relation to hydrogen ions)

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3
Q

What is pH measured as?

A

H+ concentration

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4
Q

What is pH managed by?

A
  1. CO2 enters/leaves via the lungs
  2. HCO3 enter/leaves the body via the kidneys proximal tubule
  3. H+ reabsorbed via distal tubule and collecting duct
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5
Q

Henderson-Hasselbalch Equation

A

pH = 6.1 + log (serum bicarb/0.03 x PaCO2)

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6
Q

Water is ________.

What does this mean?

A
  • amphoteric
  • it can act as an acid or a base
  • HCl (acid) donates a proton to water (base)
  • KOH receives a proton from water (acid)
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7
Q

What determines the strength of an acid/base?

A

The degree of dissociation in water

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8
Q

Is lactic acid a weak or strong acid?

A

Strong acid
* pKa 3.4
* completeley dissociates in water

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9
Q

Is carbonic acid a weak or strong acid?

A

Weak acid
* pKa 6.4
* incompletely dissociates in water

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10
Q

What are the 3 rules r/t substances in the body?

A
  1. Electrical neutrality
    – cations + anions should be equal
  2. Dissociation equilibria
    – a chunk of substance in water wants to break off into pieces (propensity to dissociate)
  3. Mass conservation
    – amount of substance remains constant in size (not amount)
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11
Q

How do strong ions dissociate?

A

Completely

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12
Q

What are the 2 most abundant ECF strong ions?

A

Na+, Cl-

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13
Q

What are other ECF strong ions?

A

K+, SO4(2-), Mg2+, Ca2+

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14
Q

How do you calculate strong ion difference?

A

Total Strong Cations - Total Strong Anions

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15
Q

What is the strong ion difference in the ECF?

A
  • it is always positive
  • we have more strong extracellular cations
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16
Q

The ability of ECF to maintain a more positive strong ion difference tells us what —–

A

it is an independent predictor of pH
-shows the importance of maintaing the right balance of fluid and electrolytes

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17
Q

What 2 things do we look @ to identify a disturbance in acid/base balance?

A
  1. is pH increased or decreased?
  2. is PaCO2 and/or HCO3- increased or decreased from normal?
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18
Q

PaCO2/HCO3- abnormalities

What is the problem if both change in the same direction?

A
  • primary disorder w/ secondary compensation
  • ex: respiratory acidosis w/ compensation by kidneys
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19
Q

PaCO2/HCO3- abnormalities

What is the problem if both PaCO2 and HCO3- change in different directions?

A
  • mixed acid/base disorder
  • 2 bad things going on
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20
Q

What are the cardiovascular consequences of acidosis?

A
  1. impaired contractility - 7.2
  2. decreased arterial BP
  3. sensitive to re-entry dysrhythmias
    – lack of repolarization time (Vtach)
  4. decreased threshold for v-fib (cardiac arrest)
  5. decreased responsiveness to catecholamines - 7.1 (epi, NE, etc.)
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21
Q

What are the nervous system consequences from acidosis?

A
  1. Obtundation
  2. Coma
    on a continuum
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22
Q

What are the pulmonary consequences from acidosis?

A
  1. Hyperventilation (increased Vm to blow off CO2)
  2. Dyspnea
  3. Respiratory muscle fatigue (exertion & resp. failure)
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23
Q

What are the metabolism consequencs from acidosis?

A
  1. Hyperkalemia
  2. insulin resistance
  3. inhibition of anaerobic glycolysis
    mainly affects big body systems - brain, heart, lungs
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24
Q

What is the most common acid/base abnormality we see?

A
  • respiratory acidosis
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25
Q

What is the definition of respiratory acidosis?

A
  • acute decrease in alveolar ventilation that results in an increase in PaCO2
  • pH < 7.35
  • “respiratory failure”
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26
Q

What are the 3 main issues that lead to respiratory acidosis?

A
  1. Central ventilation control problems
  2. Peripheral ventilation control problems
    – myasthenia gravis
  3. V/Q mismatch
    – pulmonary edema/pleural effusion

can be more than 1 cause that we need to think about what is going on w/ our patient!

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27
Q

9 causes of respiratory acidosis

A
  1. drug-induced ventilatory depression
  2. permissive hypercapnia
    –vent settings not right for pt
  3. Upper airway obstruction
  4. status asthmaticus
  5. restriction of ventilation (rib fracture, flail chest)
  6. disorder of NM function
  7. Malignant Hyperthermia
  8. pneumonia/pulmonary edema/pleural effusion
  9. inadequate NMBD reversal, opioid excess, CO2 insufflation
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28
Q

What are the most common causes of respiratory acidosis that we see in anesthesia?

A
  1. drug induced
    – propofol/versed/NMBD
  2. inadequate NMBD reversal
    – neostigmine/glycopyrrolate
  3. opioid excess
  4. CO2 insufflation
    – laparoscopic cases: insufflating w/ CO2 & absorbs into vessels & blown off via lungs
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29
Q

Causes of Respiratory Acidosis Chart:

A
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30
Q

How do we know when compensation for acid/base problems has occurred?

A
  • when CO2 & HCO3- change enough to where pH will change
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31
Q

Acute Hypercarbia Compensation formula

A
  • increase of PaCO2 by 10mmHg = increase in plasma HCO3- of 1mmol/L (1meq/L)
    to be compensated/well adjusted

ex: PaCO2 goes from 40-50 then HCO3- should go from 24-25

32
Q

Chronic Hypercarbia Compensation Formula

A
  • increase of PaCO2 by 10mmHg = increase plasma HCO3- by 3mmol/L (3meq/L)
  • body has had more time to get used to it - retaining more HCO3-
  • ex: PaCO2 goes from 40-50; HCO3- goes from 24-27 to be compensated
33
Q

Respiratory Acidosis Treatment

A
  1. wake the pt up
    – let them be more stimulated to breathe/follow commands
  2. Mechanical Ventilation
    – increase minute volume (increased Vt/RR)
    – figure out ideal Vt (6-8mL/kg)
  3. HCO3-
    – caution in chronic hypercarbia b/c its already high
    – excess HCO3- can cause CNS irritability & seizures
34
Q

When can we give pts HCO3-?

A
  • if we prove that they have metabolic acidosis w/ low HCO3-
35
Q

What is metabolic acidosis?

A
  • lowered blood pH signifying an underlying condition
  • where respiratory compnesation does not fully counter excessive acid production
  • this is an underlying body process that needs to be fixed
36
Q

Causes of metabolic acidosis

A
  1. increased production of acid
  2. decreased excretion of acid
  3. acid ingestion - poison
  4. renal/GI bicarbonate loss (altered cation/anion balance)
37
Q

What 3 things is metabolic acidosis associated with?

A
  1. alterations in transcellular ion pumps
    – all of the cellular processes in the body (Na/K pump, Ca exchange)
  2. increased ionized Calcium
  3. rightward shift of O2Hb curve
    – changes in the affinity of O2 in metabolic acidosis
38
Q

What are the causes of a Left shift in the O2Hb curve?

A

increased affinity for O2
1. decreased PCO2
2. decreased H+
3. decreased 2,3 DPG
4. decreased temp
5. HbF

39
Q

What are the causes of a Right shift in the O2Hb curve?

A

decreased affinity of Hb for O2
1. increased PCO2
2. increased H+ (decreased pH)
3. increased 2,3 DPG
4. increased temp
5. metabolic acidosis

40
Q

Formula for Acute metabolic acidosis compensation

A
  • 1.5 x HCO3- + 8
  • ex: if HCO3- is 24 then the CO2 should be 44 **(1.5 x 24 + 8)
41
Q

Example of metabolic acidosis compensation

A
  • HCO3 of 12mEq/L
  • 1.5 x 12 + 8 = 26mmHg expected PCO2
  • If PaCO2 is higher than 26mmHg then compensation is inadequate
42
Q

How can we determine adequacy of compensation with BE & PaCO2?

A
  • for every 1mEq/L drop in BE = PaCO2 should fall 1.2mmhg
  • otherwise compensation is inadequate
43
Q

What are the 2 ways we can assess metabolic acidosis?

What does this help us determine?

A
  1. metabolic acidosis w/ normal anion gap
  2. metabolic acidosis w/ high anion gap

helps us determine the cause of the metabolic acidosis

44
Q

Metabolic Acidosis w/ Normal Anion Gap

A
  1. bicarb loss is countered by net gain of Cl- ions (hyperchloremic metabolic acidosis)
    – balance b/w HCO3 loss & Cl gain
  2. electrical neutrality maintained
    – Na balanced by sum of HCO3 and Cl
45
Q

What are the 3 main causes of Normal Anion gap Metabolic Acidosis?

A
  1. NaCl infusions
    – fluid resuscitation: hemorrhagic shock, GSW, ruptured/bleeding abscess
    – if we are going to give crystalloids don’t use NS
  2. Diarrhea
  3. Early renal failure
46
Q

How to figure out a normal anion gap

Simple Anion Gap

A

Na - (Cl + HCO3) = 12-14mEq/L

**140mEq - (105+24) = 140-129 = 11

47
Q

How to figure out a normal anion gap

Conventional Anion Gap

A

(Na + K) - (Cl + HCO3) = 14-18mEq/L

added both of the 2 main cations = higher result

48
Q

Metabolic Acidosis

Why does an anion gap frequently underestimate the extend of the disturbance?

A
  • it underestimates all other electrolytes/substances
  • ignores all other cations/anions that play a minor role (albumin, phosphates)
  • complicated by hypoalbuminemia & hypophosphatemia
49
Q

What happens w/ high anion gap metabolic acidosis?

A
  1. additional acid is added to the extracellular space
  2. The acid dissociates
  3. H+ ion combines w/ HCO3 in the body
  4. Carbonic Acid is formed
  5. more acid/less HCO3 = compounding problem
50
Q

Causes of High Anion Gap Metabolic Acidosis

A
  1. Lactic Acidosis
  2. Ketoacidosis
  3. Renal Failure
  4. Poisoning
51
Q

What anion gap is considered a high anion gap metabolic acidosis?

A
  • Anion gap > 20mEq/L
52
Q

mneumonic for anion gap acidosis

CAT
MUD
PILES

A

C - Cyanide & CO
A - Arsenic
T - Toluene
M - Methanol, Metformin
U - Uremia
D - DKA
P - Paraldehyde
I - Iron
L - Lactate
E - Ethylene Glycol
S - Salicylates

53
Q

High Anion Gap Acidosis

What are the 2 main causes of lactic acidosis?

A

marker of critical illness
* overproduction
* inadequate clearance

54
Q

When does lactic acidosis become more concerning?

A
  • when the pt remains acidotic despite intervention
55
Q

lactate is a degradation product of what?

A
  • glucose metabolism
  • excess catecholamines
  • degrades to lactate
  • degrades to pyruvate
  • causes gluconeogenesis so we can produce more sugar for energy
56
Q

Metabolic acidosis tx

Treatment of ketoacidosis:

A
  • insulin & fluids
57
Q

Metabolic Acidosis Tx

Lactic Acidosis Treatment

A
  • improve tissue perfusion: add O2 and switch anaerbocic process to aerobic
  • fluid resuscitation
  • discontinue metformin
58
Q

Metabolic Acidosis Tx

Renal Failure & Acidotic

59
Q

What happens if you do not stop metformin early enough before surgery?

A
  • Can cause metabolic acidosis
60
Q

Metabolic Acidosis

When is it acceptable to give NaHCO3 to an acidotic pt?

A
  • pH < 7.1 & HCO3 <10mEq/L
  • the body cannot compensate fast enough to fix this
61
Q

What happens when to NaHCO3 in the body after you give it?

A
  • it reacts w/ H+
  • generates CO3
  • diffuses intracellularly & decreases pH more
62
Q

What happens when you give NaHCO3 to patients with chronic metabolic acidosis?

A
  • acute pH changes prevents a right shift in the O2Hb (prevents Bohr Effect)
  • causes tissue hypoxia
63
Q

How do we calculate the correction dose for NaHCO3 admin?

A

0.3 x BE (base deficit mmol/L) x wt (kg)
give 1/2 the dose & reassess

64
Q

Anesthesia management for metabolic acidosis

A
  • Elective surgery: postpone
  • Urgent/Emergent: use all hemodynamic monitoring
    – guide fluid admin
    – monitors cardiac function (CO, contractility)
    – frequent labs
65
Q

What is respiratory alkalosis?

A

an acute increased alveolar ventilation
* decreased PaCO2
* pH > 7.45

66
Q

Causes of respiratory alkalosis

A
  • pregnancy
  • high altitude
  • iatrogenic hyperventilation (periop period - anxiety, diagnosis)
  • salicylate OD
67
Q

Symptoms of respiratory alkalosis

A
  • vasoconstriction
    – light headed
    – visual disturbance
    – dizziness
    greater binding of Ca to albumin - less free Ca
    – paresthesia, muscle spasm, cramps, tetany, circumoral numbness, seizures
    – trousseau’s & chvostek’s
68
Q

What is Trousseau’s sign?

A
  • BP cuff on the arm pumped up - get tremors in hand/wrist
69
Q

What is Chvostek’s sign?

A
  • tap facial nerve & get irritability
70
Q

Anesthesia management for respiratory alkalosis

A
  • get rid of the underlying cause
  • consequence of pain, anxiety, full bladder, agitation
  • poor mechanical ventilation strategy
  • therapeutic hyperventilation?
71
Q

What is metabolic alkalosis?

A

marked increase in plasma bicarb, usually compensated for by an increase in CO2
* not a reason the body usually does this on its own

72
Q

What elevated lab value usually leads to metabolic alkalosis (HCO3 high)

A
  • increased PaCO2 - usually a slow response over a couple of days
73
Q

What are the iatrogenic causes of metabolic alkalosis?

A
  1. renal or extra renal causes
    * net loss of H+ or net gain of HCO3
    * too much NaHCO3 resuscitation
    * too much citrate
  2. happens as a natural effect for some things the pt was being treated for
74
Q

What else is iatrogenic metabolic alkalosis called?

A
  • volume depletion or volume overload alkalosis
75
Q

What are 6 causes of metabolic alkalosis?

A
  1. Hypovolemia
  2. vomiting
  3. NG suction - no continous suction
  4. diuretic therapy
  5. bicarb admin
  6. hyperaldosteronism
75
Q

Symptoms of metabolic alkalosis?

A

Ca inhibited (ion transport)
* lightheadedness
* tetany
* paresthesia

76
Q

Treatment of metabolic alkalosis

A

d/o the cause
* volume depletion - saline fluid resuscitation (caution can lead to hyperchloremic acidosis)
* gastric loss: PPIs, anti-emetics
* Loop diuretics:
– decrease dose & add K+ sparing diuretics to keep cation/anion balance better (spirinolactone)

Principles of Anesthesia I - Summer 24 (15 decks)

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