2. اﻟﺮﺣﯿﻢ اﻟﺮﺣﻤﻦ ﷲ ﺑﺴﻢ
♻ This is a summarized presentation about
acid base balance & its practical application
in the ICU.
♻ I hope this will help in simplifying this
important ICU topic.
♻ All comments are welcome & highly
appreciated.
1a
3. 1b
Dr. Sherif
Badrawy
Digitally signed by Dr.
Sherif Badrawy
DN: cn=Dr. Sherif Badrawy,
o=KKUH, ou=Critical Care,
email=sherif_badrawy@ya
hoo.com, c=SA
Date: 2015.08.25 18:40:56
+03'00'
5. Screening test for detecting abnormal
low MW solutes (e.g. ethanol, methanol
& ethylene glycol [Normal is < 10]
↑Osmolar Gap ➜ >10 ➜ indirect
evidence for the presence of an abnormal
solute in significant amounts
2b
24. Working out a Metabolic
Acidosis
◒ Calculate AG or AGc, if:
◒ High:
12a
25. ◒ Unmeasured anions likely ➜ measure osmolality.
➜ If there is no obvious cause for an elevated AGc, ➜
specific assays (glucose, renal function,
rhabdomyolysis, L-lactate, D-lactate, β-
hydroxybutyrate, salicylate)
◒ Calculate osmolar gap. If high AG and high OG
then ketones, lactate, ethanol, ethylene glycol,
methanol, mannitol.
12b
26. Working out a Metabolic
Acidosis
◒ Calculate AG or AGc, if:
◒ Normal:
13a
31. 【U S E D C A R PAR T S】
✺ U ⇨ Ureterosigmoidostomy
✺ S ⇨ saline administration (in the face of renal dysfunction)
✺ E ⇨ Endocrine〘Addisons〙
✺ D ⇨ Diarrhea
✺ C ⇨ Carbonic anhydrase inhibitors
✺ A ⇨ Ammonium chloride
✺ R ⇨ Renal tubular acidosis
✺ PAR ⇨PARathyroid Adenoma
✺ T ⇨ Triamterene, amiloride
✺ S ⇨ Spironolactone
15b
41. albumin is the major unmeasured anion
in plasma. This means that a decrease in
serum albumin will decrease the
AG,(e.g., a high AG metabolic acidosis
can present with a normal AG in the
presence of hypoalbuminemia).
20b
45. In the presence of a high AG metabolic
acidosis, it is possible to detect another
metabolic acid-base disorder (a
normal AG metabolic acidosis or a
metabolic alkalosis)
by comparing the AG excess to the HC03
deficit
22b
49. ☼ Mixed Metabolic Acidoses
↑AG metabolic acidosis the ↓in serum HC03 = the ↑in
AG, and the AG excess/HC03 deficit ratio is unity
(=1) when a hyperchloremic acidosis appears, the↓in
HCO3 is > ↑in the AG, and the ratio (AG
excess/HCO3 deficit) falls below unity (<1),( as 24-
HCO3 ➜ will be a bigger number dt ↓in HCO3).
∴Gap-Gap <1 indicates the coexistence of a ↑AG
metabolic acidosis + normal AG metabolic acidosis
24b
51. ☼ Metabolic Acidosis and Alkalosis
When alkali is added in the presence of a ↑AG
metabolic acidosis, the ↓in HCO3 is < the ↑in
AG, and the gap-gap (AG excess /HCO3
deficit) is greater than unity (>1).
∴Gap-Gap > 1 indicates the coexistence of a
↑AG metabolic acidosis + normal AG
metabolic Alkalosis
25b
57. - when levels are greater than 5 mmols/l
- As levels rise above 5mmols/l, the associated mortality
rate can become very high.
- The brief and often very high lactate levels that occur
with severe exercise or generalised convulsions (eg up to
30 mmol/l) are associated with an extremely low
mortality rate so the absolute lactate level (alone) is not a
good predictor of outcome unless the cause of the high
level is also considered.
28b
61. - Lactate is produced from pyruvate in a
reaction catalysed by lactate
dehydrogenase
This reaction considered to be always in
an
equilibrium situation. Normally the ratio
of lactate to pyruvate in the cell is 10 to 1.
30b
65. - If hypoxaemia is the only factor present, it
needs to be severe (eg paO2 < 35mmHg) to
ppt lactic acidosis dt protection afforded by
the body's compensatory
mechanisms which ↑tissue blood flow.
Similarly anaemia needs to be severe (eg
[Hb] <5g/dl) if present alone because tissue
blood flow is increased in compensation.
32b
73. Assoc with inborn errors of
metabolism (eg congenital forms of
lactic acidosis with various enzyme
defects eg pyruvate dehydrogenase
deficiency)
36b
75. D-lactate generated by bacterial fermentation in the
bowel can enter the systemic circulation and produce
a metabolic acidosis, often combined with a
metabolic encephalopathy, 【after extensive small
bowel resection or after jejunoileal bypass】 for
morbid obesity, can ↑anion gap, but the standard lab
assay for lactate measures only l-lactate. If d-lactic
acidosis is suspected, you must request a specific d-
lactate assay.
37b
76. The principles of management
of patients with lactic acidosis
are:
38a
77. (i) Diagnose and correct the underlying
condition (if possible)
(ii) Restore adequate tissue oxygen
delivery (esp restore adequate perfusion)
(iii) Ensure appropriate compensatory
hyperventilation where possible
38b
78. patients with severe acidosis (pH
<7.1), HD unstable, a trial infusion
of HCO3 can be attempted by
administering 1/2 of the estimated
bicarbonate deficit
39a
83. (i) acute hypercapnia
(ii) ionised hypocalcaemia
(iii) intracellular acidosis due to CO2 crossing cell
membranes rapidly
(iv) acute intravascular overload
(v) bicarbonate ↑lactate production by ↑activity of
the rate limiting enzyme phosphofructokinase, ➜
shifts Hb-O2 dissociation curve, ↑O2 affinity of Hb
➜ ↓DO2 to tissue
41b
87. ☼ Lactate is a question not any
answer: exclude occult sepsis,
inadequate resuscitation, localised
ischaemia or CVS failure
☼ Stop NRTIs in HIV
43b
99. ✪ Activation of (RAAS) is a key factor
✪ Aldosterone ➜ reabsorption of Na+ in exchange
for H+ in the DCT
✪ ECF depletion (vomiting, diuretics) ➜ Na+ and
Cl- loss activation of RAAS➜ ↑ aldosterone levels
✪ In Hypokalemia, K+ shift from cells ➜ ECF.
Alkalosis is caused by shift of H+ into cells to
maintain neutrality
49b