An 84-year-old male with a recent diagnosis of myeloma and osteoarthritis is admitted to ICU following a three-day history of constipation followed by diarrhoea.
Parameter |
Patient Value |
Adult Normal Range |
FiO2 |
0.21 |
|
pH |
7.22* |
7.35 – 7.45 |
pO2 |
98 mmHg (13 kPa) |
|
pCO2 |
10.0 mmHg (1.3 kPa)* |
35.0 – 45.0 (4.6 – 6.0) |
SpO2 |
99.6% |
|
Bicarbonate |
4.0 mmol/L* |
22.0 – 26.0 |
Base Excess |
-22.0 mmol/L* |
-2.0 – +2.0 |
Lactate |
1.4 mmol/L |
0.5 – 1.6 |
Sodium |
133 mmol/L* |
135 – 145 |
Potassium |
5.7 mmol/L* |
3.5 – 5.0 |
Chloride |
113 mmol/L* |
95 – 105 |
Glucose |
4.4 mmol/L |
3.5 – 6.0 |
a) Describe the acid base abnormality. (10% marks)
b) Give a physiological rationale for the acid base abnormalities in this patient.
(20% marks)
Describe the acid base abnormality. (10% marks)
High anion gap metabolic acidosis, respiratory alkalosis, delta ratio of 0.2 suggesting associated normal anion gap metabolic acidosis.
Give a physiological rationale for the acid base abnormalities in this patient (20% marks)
HAGMA without elevated lactate in this scenario may be renal failure (multiple possible causes) or starvation ketosis
Coexisting NAGMA from diarrhoea
Respiratory alkalosis from hyperventilation secondary to pain/distress
Only one rationale per abnormality required.
Let us dissect these data;
This is weird. Irrespective of which formula you use, the delta ratio range associated with a mixed disturbance is probably 0.4-0.8 (according to Brandis), as the older 0.8-1.2 range had poorer sensitivity (according to Rastegar, 2007). Either way, delta ratio of 0.2 is not expected to be associated with a mixed disorder. Taken literally, this value suggests that the rise in the anion gap accounts for only 20% of the drop in the bicarbonate. Using updated values and incorporating the nontrivial potassium (5.7mmol/L) one arrives at a delta ratio of 0.5 or so, which is more consistent with a mixed disturbance.
Physiological rationale for the acid base abnormalities in this patient:
There are multiple possible causes for a mixed distrubance. Individually, the causes of metabolic acidosis are:
High anion gap |
Normal anion gap |
MUD PILES |
PANDA RUSH |
This old man with constipation and diarrhoea could potentially have any number of these causes, considering that we have zero history. Renal failure is a plausible cause of this acid-base disturbance because the acidosis is usually mixed in that setting, and the history suggests some fluid depletion.
Rastegar, Asghar. "Use of the ΔAG/ΔHCO3− Ratio in the Diagnosis of Mixed Acid-Base Disorders." Journal of the American Society of Nephrology 18.9 (2007): 2429-2431.
Dinubile, MarkJ. "The increment in the anion gap: overextension of a concept?." The Lancet 332.8617 (1988): 951-953.