A 32-year-old male is admitted to your ICU after an appendicectomy for a perforated appendix. He has a background of schizoaffective disorder. On admission, he is receiving vasopressor support with noradrenaline at 7 mcg/min. and has a temperature of 41ºC. The first arterial blood gas on admission is given below:
Parameter | Patient Value | Adult Normal Range |
FiO2 | 50% | |
pH |
7.01* |
7.35 – 7.45 |
pO2 |
120.0 mmHg (16.4 kPa) |
|
pCO2 |
58.0 mmHg (9.6 kPa)* |
35.0 – 45.0 (4.6 – 6.0) |
SpO2 |
96% |
|
Bicarbonate |
14.0 mmol/L* |
22.0 – 26.0 |
Base Excess |
-15.0 mmol/L* |
-2.0 to +2.0 |
Lactate |
8.5 mmol/L* |
0.5 – 1.6 |
Sodium |
135 mmol/L |
135 – 145 |
Potassium |
5.2 mmol/L* |
3.5 – 5.0 |
Chloride |
99 mmol/L |
95 – 105 |
Glucose |
8.0 mmol/L* |
3.5 – 6.0 |
a) Comment on the acid base status. (10% marks)
b) List four likely explanations for these findings other than sepsis. (10% marks)
So: let's go through this ABG systematically.
In summary, this is a severe high anion gap metabolic acidosis as well as a respiratory acidosis.
Four likely explanations for this? The college examiners have loaded this SAQ with plenty of background information. Specifically, they've given this patient a history of mental illness. The expectation here, of course, is that the candidates would form the impression of somebody who is likely to be using illicit drugs while recovering from appendicectomy. Because that's clearly what mentally ill people always do.
Anyway, the hints are:
Inevitably, the following elements must be in your list of differentials:
These are the four most likely culprits. The college throws thyrotoxicosis and transfusion reaction in there, but the history and biochemistry do nothing to promote those differentials. So if we're going to just throw random causes of lactic acidosis around, then, dear reader, have at you:
Type A lactic acidosis: impaired tissue oxygenation
Type B1 lactic acidosis, due to a disease state
|
Type B2 drug-induced lactic acidosis
Type B3 : inborn errors of metabolism
|
Narins RG, Krishna GG, Yee J, Idemiyashiro D, Schmidt RJ: The metabolic acidoses. In: Maxwell & Kleeman's Clinical Disorders of Fluid and Electrolyte Metabolism, edited by Narins RG, New York, McGraw-Hill, 1994, pp769 -825
Luft FC. Lactic acidosis update for critical care clinicians. J Am Soc Nephrol 2001 Feb; 12 Suppl 17 S15-9.
Ohs manual – Chapter 15 by D J (Jamie) Cooper and Alistair D Nichol, titled “Lactic acidosis” (pp. 145)
Cohen RD, Woods HF. Lactic acidosis revisited. Diabetes 1983; 32: 181–91.
Reichard, George A., et al. "Quantitative estimation of the Cori cycle in the human." Journal of Biological Chemistry 238.2 (1963): 495-501.
Andres, Reubin, Gordon Cader, and Kenneth L. Zierler. "The quantitatively minor role of carbohydrate in oxidative metabolism by skeletal muscle in intact man in the basal state. Measurements of oxygen and glucose uptake and carbon dioxide and lactate production in the forearm." Journal of Clinical Investigation 35.6 (1956): 671.
Phypers, Barrie, and JM Tom Pierce. "Lactate physiology in health and disease." Continuing Education in Anaesthesia, Critical Care & Pain 6.3 (2006): 128-132.