A 25-year-old female with a 5-day history of anorexia, nausea and vomiting presents to hospital after a convulsion and is transferred immediately to your ICU. She is G3P2 and 30/40 gestation.The following blood results are obtained: 

Parameter               Patient Value           Adult Normal Range
Fi02               0.28                      
pH               7.54*                 7.35 - 7.45
p02               87 mmHg (11.6 kPa)              
pC02               33.0 mmHg (4.4 kPa)*       35.0 - 45.0 (4.6 - 6.0)
Sp02               94%                      
Bicarbonate             28.0 mmol/L*             22.0 - 26.0
Base Excess             4.5 mmol/L*             -2.0 - +2.0
                                         
Sodium               127 mmol/L*             135 - 145
Potassium               2.3 mmol/L*             3.5 - 5.0
Chloride               84 mmol/L*             95 - 105
Glucose               4.8 mmol/L             3.5 - 6.0
Creatinine               354 µmol/L*             45 - 90  
Urea               29.0 mmol/L*             3.0 - 8.0
                                         
Haemoglobin             177 g/L*             120 - 160
White Cell Count             25.4 x 109/L*   j         4.0 - 11.0
Platelet count             29 x 109/L*   I         150 - 350
                                         
Prothrombin time             15.0 sec               12.0 - 16.5
INR               1.1                 0.9 - 1.3
APTT               28.0 sec               27.0 - 38.5
Fibrinogen               5.7 g/L*   ,           2.0 - 4.0
D-Dimer               16.8 mg/L* /           < 0.5    

Describe the important metabolic abnormalities and give one explanation for each.

(40% marks)

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College answer

Describe the important abnormalities and give one explanation for each?                

  • Raised Aa gradient (aspiration, pneumonia, any plausible)
  • Metabolic alkalosis   -dehydration, vomiting                                       
  • Raised anion gap – sepsis, seizures, renal failure   
  • Respiratory alkalosis- pain, anxiety, post ictal                                                                       
  • Hypokalaemia, hyponatraemia : dehydration                                                 
  • AKI – sepsis, TTP, dehydration,eclampsia                                                     
  • Haemoconcentration – dehydration
  • Leucocytosis – sepsis
  • Thrombocytopenia –sepsis, TTP, HELLP       
  • Elevated fibrinogen, D-Dimer – sepsis

Discussion

Systematically:

  • The patient is alkalaemic. This pH is in excess of what would normally be expected in pregnancy
  • There is normoxia (PaO2 is satisfactory) but the A-a gradient is raised. 
  • The CO2 is within normal limits for this stage in pregnancy
  • Oxygen saturation is lower than would be expected for this level of alkalosis (i.e. there is an unexplained right-shift of the oxyhaemoglobin dissociation curve).
  • Base excess and bicarbonate present a metabolic alkalosis. In pregnancy, one would conventionally expect to normally have a lower bicarbonate level because of the chronic respiratory alkalosis. Ergo, in this scenario, the metabolic alkalosis from vomiting and dehydration is even worse than it seems. 
  • The patient is hyponatremic, though it is not so severe as to produce the seizures. One possible explanation for this is the fluid overload and water retention related to the renal failure.
  • Potassium is severely depleted, which is likely related to the nausea and vomiting
  • The low chloride is due to the vomiting
  • The creatinine and urea are raised, indicating acute kidney injury
  • The haemoglobin is significantly higher than would be expected at this stage of pregnancy, which suggests significant dehydration
  • The white cell count is elevated, which may be a combination of haemoconcentration and infection
  • There is thrombocytopenia, consistent with HELLP - but it could also be consumptive, eg. in the context of thrombosis or something like TTP/HUS.
  • The coags are normal, which virtually excludes hepatic involvement 
  • The D-dimer is elevated, which might represent thrombosis and consumption (of particular interest would be cerebral venous sinus thrombosis).

References