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Blood gases: a dreadful combination of metabolic, respiratory and lactic acidosis


Arterial blood gases (ABGs) are the immediate, easiest, most reliable and cost effective bedside method of assessing an unstable patient. It portrays an array of functional reserves from the lungs to the kidneys and the blood cells in between. It also hints at the causes of hypoxia and hypercarbia. We applied the Henderson Hasselbalch Equation (PCO2 = HCO3 × 1.5 + 8) to interpret the blood gas and used it effectively to prognosticate the patient's outcome.


All patients with acidosis on blood gas were included. In addition, PCO2 was calculated independently using the Henderson Hasselbalch Equation. Patients are divided into three groups as shown in Table 1. Prototype ABGs of each group as shown in Table 2.

Table 1
Table 2


Group 1. Patients in blood gas group 1 did not have any problem, responded very well to the treatment and were stable. The PCO2 matches with the HCO3 according to the Henderson Hasselbalch Equation. In dehydrated patients, sodabicarb was given to replace the loss of carbonates.

Group 2. These patients came to the ICU deteriorated with multiorgan involvement, in an unstable condition needing mechanical support beside all medical strategies. The outcome was not that good in this group.

Group 3. Very poor outcome from this group. Patients did not survive after this combination of metabolic, respiratory and lactic acidosis occurred. This was much in evidence in a patient who had multiorgan failure and septic shock. The PCO2 in this group was always on the higher side then the calculated value as is in evidence in sample number 3.


1. The Henderson Hasselbalch Equation is very useful in the interpretation of blood gases and guides us about the severity of illness and prognosis of the patient.

2. If soda-bicarbonate has to be used, the equation can be used to guide us of its effect on the patient.

3. The combination of metabolic, lactic and respiratory acidosis is a dreadful combination usually culminating in death. Commonly patients had multiorgan dysfunction and irreversible shock.

4. It is imperative that we adopt an aggressive approach early on in treatment of metabolic and lactic acidosis combination and should not allow patients to go in to Group 3.

5. To begin with, patients presenting in group 3 were more severely ill and warranted an aggressive approach irrespective of the blood gas.

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Aaron, A., Bachwani, A. Blood gases: a dreadful combination of metabolic, respiratory and lactic acidosis. Crit Care 7, P016 (2003).

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  • Septic Shock
  • HCO3
  • Lactic Acidosis
  • Unstable Condition
  • Multiorgan Failure