A 38-year-old female presents to the Emergency Department with complaints of lower abdominal pain and vaginal bleeding. On examination, she is confused and, with cool peripheral perfusion and patchy ecchymoses over her extremities. Vaginal examination reveals clots, with tissue resembling products of conception. She is tachypneic, tachycardic with a non-invasive blood pressure of 88/42 mmHg.
(Parts 24.1 and 24.2 of the question are related to the initial blood results obtained from this patient.)
A peripheral venous blood sample including a venous blood gas analysis shows the following results:
| Parameter | Patient Value | Adult Normal Range | |||||||||||||
| FiO2 | 0.21 | ||||||||||||||
| pH | 7.36 | 7.35 – 7.45 | |||||||||||||
| pO2 | 46.0 mmHg (6.0 kPa) | ||||||||||||||
| pCO2 | 20.0 mmHg (2.6 kPa)* | 45.0 – 51.0 (5.5 – 6.8 KPa) | |||||||||||||
| SpO2 | 82% | ||||||||||||||
| Bicarbonate | 11.0 mmol/L* | 23.0 – 29.0 | |||||||||||||
| Base Excess | -12.0 mmol/L* | -2.0 – +2.0 | |||||||||||||
| Sodium | 134 mmol/L* | 135 – 145 | |||||||||||||
| Potassium | 2.9 mmol/L* | 3.5 – 5.0 | |||||||||||||
| Chloride | 100 mmol/L | 95 – 105 | |||||||||||||
| Glucose | 5.4 mmol/L | 3.5 – 6.0 | |||||||||||||
a) Explain the acid base status, including your mathematical calculations where appropriate.
(20% marks)
b) List the most likely source of the metabolic acidosis in this patient. (10% marks)
c) List the most likely clinical diagnosis and underlying pathophysiology in this patient.
(10% marks)
d) Outline the advantages and disadvantages of a peripheral venous blood gas in critically ill patients.
(20% marks)
Not available.
"Including your mathematical calculations where appropriate"? I thought you'd never ask!
Now, this could well be a triple disorder (mixed high and normal anion gap metabolic acidosis as well as a respiratory alkalosis), but this is a venous gas, which really should not be used to assess compensation in a patient with such a terrible circulatory failure. The venous CO2 could be raised because of the extremely poor cardiac output, with an increased arteriovenous CO2 gradient, i.e. the respiratory alkalosis might be even more severe if you had an arterial sample.
Now:
b) List the most likely source of the metabolic acidosis in this patient.
They did not give us a lactate, but it's probably raised, and - not to cheat or anything - but on the same page, the next question about the same stem gives us a set of haematology values which is clearly demonstrating DIC. Thus, this looks like septic shock, and lactate is the most likely reason for the acidosis.
c) List the most likely clinical diagnosis and underlying pathophysiology in this patient.
The patient is falling apart from septic shock, in DIC, and there's "tissue resembling products of conception" in her vagina? What else could this be, if not septic abortion. There's barely anything to list. If it were not for those products, one could also consider toxic shock syndrome, eg. from a retained tampon. The pathophysiology is usually a polymicrobial infection by the normal flora of the vagina and endocervix.
d) The advantages and disadvantages of a peripheral venous blood gas in critically ill patients, in two minutes (because that's how long you have for this little 20% fragment), would have to be pretty brief:
Finkielman, Javier Daniel, et al. "The clinical course of patients with septic abortion admitted to an intensive care unit." Intensive care medicine 30.6 (2004): 1097-1102.
Stubblefield, Phillip G., and David A. Grimes. "Septic abortion." New England Journal of Medicine 331.5 (1994): 310-314.
Awasthi, Shilpi, Raka Rani, and Deepak Malviya. "Peripheral venous blood gas analysis: An alternative to arterial blood gas analysis for initial assessment and resuscitation in emergency and intensive care unit patients." Anesthesia, essays and researches 7.3 (2013): 355.