A previously well 23-year-old male has been an inpatient on your ICU for six days following an isolated traumatic brain injury. He has been extremely agitated and required constant infusions of propofol and fentanyl. A full workup has confirmed there are no other injuries, and he has been stable from a haemodynamic, respiratory and metabolic standpoint since admission. This morning he has become hypotensive, and the following results are available.
|
Parameter |
Patient Value |
Adult Normal Range |
|
FiO2 |
0.4 |
|
|
pH |
7.16* |
7.35 – 7.45 |
|
pO2 |
120 mmHg (16 kPa) |
|
|
pCO2 |
35.0 mmHg (4.7 kPa) |
35.0 – 45.0 (4.6 – 6.0) |
|
SpO2 |
97% |
|
|
Bicarbonate |
12.0 mmol/L* |
22.0 – 26.0 |
|
Base Excess |
-15 mmol/L* |
-2.0 – +2.0 |
|
Lactate |
9.2 mmol/L* |
0.5 – 1.6 |
|
Sodium |
145 mmol/L |
135 – 145 |
|
Potassium |
6.3 mmol/L* |
3.5 – 5.0 |
|
Chloride |
98 mmol/L |
95 – 105 |
|
Bicarbonate |
12.0 mmol/L* |
22.0 – 26.0 |
|
Glucose |
10.2 mmol/L* |
3.5 – 6.0 |
|
Urea |
6.7 mmol/L |
3.0 – 8.0 |
|
Creatinine |
70 μmol/L |
45 – 90 |
|
Creatinine Kinase |
43,500 U/L* |
55 – 170 |
a)
High anion gap metabolic acidosis
Associated respiratory acidosis
Delta ratio 1.9 suggesting pure HAGMA
Elevated Aa gradient
Rhabdomyolysis
b)
Diagnosis:
Propofol Infusion Syndrome
To approach this systematically:
1) The A-a gradient is raised; (0.4 × 713) - (35 / 0.8) - 120 = 121.5 mmHg.
2) There is severe acidaemia.
3) There is a severe metabolic acidosis (SBE is -15)
4) There is minimal effort at respiratory compensation - the expected CO2 is 25 mmHg by the Copenhagen SBE rules, or 26 using Winter's rule where expected CO2 = (1.5 ×12)+ 8. Thus, there is also a respiratory acidosis.
5) The anion gap is elevated; it is 35 if you omit potassium from the equation, or 41.3 if you do not. The delta ratio therefore also changes. Assuming a normal albumin of 40g/L, the delta ratio is either 2.4 (with potassium) or 1.9 (without). Thus, depending on whether or not you include that electrolyte in your anion gap equation, you'd either develop the impression that there is a co-existing metabolic alkalosis, or that this is a pure HAGMA. The evils of the anion gap and whether or not one ought to involve the potassium ions are debated elsewhere.
Other abnormalities which can be seen:
The diagnosis of propofol infusion syndrome is suggested by the story, where this young man is pickled in propofol for some days following his traumatic brain injury. Other features of PRIS are :
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Marinella, Mark A. "Lactic acidosis associated with propofol." CHEST Journal109.1 (1996): 292-292.
Vasile, Beatrice, et al. "The pathophysiology of propofol infusion syndrome: a simple name for a complex syndrome." Intensive care medicine 29.9 (2003): 1417-1425.
Schenkman KA, Yan S. Propofol impairment of mitochondrial respiration in isolated perfused guinea pig hearts determined by reflectance spectroscopy. Critical Care Medicine 2000; 28: 172–7.