Question 28

College Answer

a)

High anion gap metabolic acidosis

AG 23 not accounted for by just rise in lactate

Marked lactic acidosis

Respiratory acidosis

Hypoxaemia with A-a DO2 145

Anaemia

b)

Septic shock (intra-abdo, lung, other)

Hypovolaemic shock with intra-abdominal bleeding

Ischaemic gut

Cardiogenic shock (myocardial ischaemia or septic ardiomyopathy)

PE less likely with PO2 84 on FiO2 0.4 but cannot be excluded

c)

Resuscitation with simultaneous focussed assessment (history, examination, investigations) to ascertain diagnosis and institution of treatment (supportive and definitive)

Resuscitation – ensure adequate airway and ongoing adequate oxygenation and ventilation. Intubation and IPPV if needed. IV access and fluid resus plus/minus vasopressors.

Focussed assessment – differential diagnosis as above. Look for signs of bleeding, sepsis, intra-abdominal catastrophe, assess myocardial function

Investigations – FBC, U&E, coags, Troponin, septic screen, ECG, CXR, CT abdo (if stable) ± CTPA, bedside echo

Broad-spectrum antibiotics if sepsis suspected

Surgical review, consider proctoscopy, with urgent return to theatre if indicated (anastamotic leak, ischaemic gut)

Other urgent specific treatment as indicated eg stop bleeding, treat myocardial ischaemia Monitoring and transfer to ICU/HDU

Discussion

Let us dissect these results systematically.

1. The A-a gradient is high:
   PAO2 = (0.4 × 713) - (45 × 1.25) = 157.55
   Thus, A-a = ( 157.55 - 84) = 73.55mmHg.
2. There is acidaemia
3. The PaCO2 is contributing to the acidosis
4. The SBE is -19, suggesting a severe metabolic acidosis
5. The respiratory compensation is inadequate - the expected PaCO₂(11 × 1.5) + 8 = 24.5mmHg, and thus there is also a respiratory acidosis.
6. The anion gap is raised:
   (138) - (104 + 11) = 23, or 28.4 when calculated with potassium
   The delta ratio, assuming a normal anion gap is 12 and a normal bicarbonate is 24, would therefore be (23 - 12) / (24 - 11) = 0.84
   The delta ratio suggests that there is a mixed high anion gap and normal anion gap metabolic acidosis here.
    

The lactate is 13, which can actually account for all of the increase in the anion gap. The anion gap is 23, which means it has increased by 11. The lactate is 13. What other anions do you need here?

Perhaps they want a better explanation for the change in SBE? True, there is a very large base deficit.  Taking the simplistic view that lactate is a fully dissociated ion and for every mole of lactic acid there should be a mole of hydrogen ions, one would still fall short of explaining the SBE of -19. 

Anyway: why is the lactate so high, the college asks?

Differentials relevant to this case might include the following:

• Ischaemic gut
• Sepsis with intra-abdominal collection
• Cardiogenic shock
• Haemorrhagic shock
• "Obstructive" shock - PE or cardiac tamponade

Approaching the management systematically, one might respond to the last question in the following fashion:

• Attention to the ABCS, with management of life-threatening problems simultanous with a rapid focused examination and a brief history
• Airway
  • Assess the need to control the airway
  • This patient will probably require intubation
• Breathing/ventilation
  • Aim for a lower PaCO₂ to help correct the acidosis
  • Apply PEEP to improve oxygenation
  • A CXR would be helpful
• Circulatory support
  • Fluid resuscitation should commence
  • Vasopressors will likely be required
  • Central venous access needs to be established
  • Invasive hemodynamic monitoring will be required
  • a TTE would be helpful
• Specific investigations
  • A CT of the abdomen is required
  • A septic screen should be sent
• Specific management
  • A surgical opinion is required
  • Broad-spectrum antibiotics cannot be delayed

Oh's Intensive Care manual: Chapter   45   (pp. 520) Abdominal  surgical  catastrophes by Stephen  J  Streat

Marshall, John C., and Marilyn Innes. "Intensive care unit management of intra-abdominal infection." Critical care medicine 31.8 (2003): 2228-2237.

Gajic, Ognjen, et al. "Acute abdomen in the medical intensive care unit."Critical care medicine 30.6 (2002): 1187-1190.