Case 2 : A sick diabetic patient
A 19 year old pregnant insulin dependent diabetic patient was admitted with a history of polyuria
and thirst. She now felt ill and presented to hospital. There was a history of poor compliance with
She was afebrile. Chest was clear. Circulation was adequate. Perioral herpes was
present. Urinalysis: 2+ ketones, 4+ glucose. Biochemistry on admission: Na+ 136, K+ 4.8, Cl- 101,
'total CO2' 10, glucose 19.0, urea 8.1 and creatinine 0.09
(all biochem results in mmol/l). Arterial blood gases were collected on arrival:
Arterial Blood Gases
pCO2 16 mmHg
pO2 128 mmHg
HCO3 7.1 mmol/l
First: Initial clinical assessment
The diagnosis is obvious on history: the patient has a severe diabetic ketoacidosis.
If the diagnosis is so obvious on the history then why do we need to bother with the systematic approach?
Because the 3 step systematic approach has several advantages:-
- The first step incorporates all this clinical expectation (ie in "the initial clinical assessment" stage) so there
is nothing lost. Indeed the clinician should learn to spot the obvious diagnosis because this becomes
in effect a hypothesis which is tested in the rest of the analysis. In this case, the hypothesis is
"This patient has a diabetic ketoacidosis". Now we have to confirm the diagnosis.
- The approach will generally detect the presence of all other acid-base disorders
- It provides a framework to synthetize the acid-base results with the overall clinical situation
(ie 'the clinical diagnosis' step)
In this case then, the patient has a diabetic ketoacidosis. Our clinical knowledge leads us to
the need to consider other acid-base disorders that can occur in such patients. In particular:
- a co-existent lactic acidosis (related to poor tissue perfusion)
- a hyperchloraemic metabolic acidosis (due replacement of keto-anions lost in the urine with
chloride by the kidney & as a result of saline resuscitation fluids)
- a respiratory acid-base disorder is possible if for example pulmonary infection is the
cause or if there is a decreased level of consciousness
Second: The acid-base diagnosis
- pH: The acidaemia indicates the presence of an acidosis
- Pattern: The low bicarbonate & the low pCO2 are typical of a metabolic acidosis
- Clues: The hyperglycaemia, glycosuria & ketonuria indicate the presence of a diabetic
ketoacidosis. The anion gap is elevated (at 25) supporting a diagnosis of a high anion gap
disorder. There is no evidence of renal failure. The delta ratio is (25-12)/(24-7) = 0.76 and
the chloride level is normal (as is [Na+])
- Compensation: The appropriate rule to assess compensation for a metabolic acidosis
is the 'one & a half plus 8' rule (rule 5). The expected pCO2 is (1.5 x 7.1 + 8) = 18.5mmHg.
The actual pCO2 is only 2 mmHg different so there is no evidence of a co-existing respiratory
acid-base disorder. Sufficient time (12-24 hours) has passed so compensation would be expected
to have reached its maximum value. Note that this 'maximal compensation' is rarely if ever enough
to return the pH completely to normal
- Formulation: A severe metabolic acidosis (diabetic ketoacidosis) is present. There is
no evidence of any other acid-base disorder. The delta ratio is not low enough nor the chloride
level high enough to indicate a definite hyperchloraemic acidosis but this commonly develops
during treatment. A lactic acidosis component cannot be totally excluded as no lactate result
has been recorded but the fact that the urine test for ketones was reactive argues against a
major component of lactic acidosis
- Confirmation: A lactate level would be useful but this unfortunately is often not done
in such cases
Finally: the Clinical Diagnosis
Diabetic ketoacidosis due to poor compliance with diabetic treatment.
This case history is of a patient with a high anion gap metabolic acidosis. The overview of
causes in the table below is what a clinician should have a mental picture of as she/he
approaches the differential diagnosis of a high anion gap acidosis.
Diabetic ketoacidosis is the commonest severe acid-base disorder that presents to hospital
so you should be particularly familiar with this diagnosis.
The approach will be to follow the following steps:
- Low pH => significant acidaemia => therefore an underlying acidosis is present
- Both pCO2 and HCO3 are low => therefore a metabolic acidosis is present
- The Anion Gap is elevated => therefore a high anion gap metabolic acidosis (HAGMA) is present
A high anion gap alerts to the presence of an underlying HAGMA.
This is particularly useful in patients with the combination of a HAGMA & a metabolic alkalosis
So the diagnosis so far is that a HAGMA is present. Now determine the cause among the following 4 groups:
- Ketoacidosis - Diagnosis is supported by history, hyperglycaemia, glycosuria & ketouria
- Lactic acidosis - Often a diagnosis of exclusion but should be diagnosed based on a lactate
level. Then consider whether the cause is poor perfusion (type A) or not (type B)
- Acidosis due to renal failure - Diagnosis suggested by creatinine > 0.30 to 0.35 mmol/l
- Acidosis due to toxins - This is often a diagnosis based on history and/or CNS signs
In this case, the patient recovered with management but compliance with diabetic therapy continued to be
poor. An intrauterine foetal death occurred four months after this admission.
This patient had had several previous admissions with diabetic ketoacidosis. Results on
presentation five months prior to the admission discussed in the example were:
Arterial Blood Gases
pCO2 10 mmHg
pO2 138 mmHg
HCO3 2 mmol/l
Other biochemistry: Na 140, K 4.3, Cl 111, glucose 24.8, urea 4.6 mmol/l.
What is your analysis in this case? Try your hand at the following questions:
Question 1: The delta ratio here is about 0.68 - What does this indicate in this case?
Question 2: Is respiratory compensation appropriate or is there a mixed disorder present?