A 43 year old man, with no history of previous illnesses is admitted with septic shock requiring administration of high dose vasopressor. His blood results on 40% oxygen, pressure support ventilation are as follows:
Parameter |
Value |
Normal range |
pH |
7.64 |
7.35-7.45 |
PaCO2 |
28 mmHg (3.7 kPa) |
35-45 mmHg (4.7-6.0 kPa) |
PaO2 |
189 mmHg (25.2 kPa) |
75-98 mmHg (10.0-13.0 kPa) |
Actual |
29 mmol/l |
22-26 mmol/l |
Sodium |
147 mmol/l |
134-145 mmol/l |
Potassium |
3.5 mmol/l |
3.5-5.1 mmol/l |
a. Describe the acid-base abnormality
b. List 3 likely causes of each acid-base abnormality in this patient.
a. Describe the acid-base abnormality
Respiratory and metabolic alkalosis
b. List 3 likely causes of each acid-base abnormality in this patient. Respiratory alkalosis: Hyperventilation – spontaneous or IPPV induced, septic
encephalopathy, pneumonia
Metabolic alkalosis: Diuretics, volume contraction, upper GI losses, steroids.
Let us dissect these results systematically.
What the hell is driving this derangement in this septic patient?
The disturbances are not connected. Each likely has a separate cause.
The respiratory alkalosis can be driven by spontaneous hyperventilation, or by excessive mechanical ventilation (i.e. somebody has increased the pressure support level to a point where the patient is generating unnecessarily massive tidal volumes). Alternative explanations include pain, encephalopathy (of whatever cause) and pneumonia.
The causes of metabolic alkalosis are numerous; those relevant to this question can include the following:
Sankaran, Ramkumar T., et al. "Laboratory abnormalities in patients with bacterial pneumonia."CHEST Journal 111.3 (1997): 595-600.