Blood gas analysis, pt 1: why everyone needs to know about it

For those of you who have received referral histories from emergency or specialists hospitals, blood gas analysis is probably no stranger to you. For those who have never heard of them before, fear not – you are in for a treat.

In my emergency hospital, the blood gas analyser is arguably one of the most frequently used bench top lab machines, second only to centrifuge, and for good reasons…

Acid-base disturbances are common in critically ill and emergency patients, and it can help determine the severity of their condition and sometimes provide the answer. Tracking changes in blood gas parameters can provide information about the patient’s response to your interventions.

The information gained from pulse oximetry is very limited in patients with severe respiratory compromise, and the only way to accurately assess their oxygenation and/or ventilation status is by looking at their blood gas status.

So what does the blood gas analysis actually measure?

Most blood gas panels assess the pH of the blood, partial pressure of oxygen (PO₂) and partial pressure of carbon dioxide (PCO₂). From these, the machine is able to derive the percentage of haemoglobin saturated with oxygen (SO₂), bicarbonate (HCO₃^–) concentration and base excess of the extracellular fluid (BEecf).

In most machines, they are also able to measure other parameters, such as electrolytes (Na, K, Ca, Cl), glucose and lactate.

While arterial blood gas samples are required for determining the ability of the body to oxygenate the haemoglobin, venous samples are suitable for determining the ventilation status, assessing acid base balance, electrolytes, glucose and lactate levels.

So how can this help as a point-of-care test?

As mentioned previously, blood gas analysis can help assess the severity of a patient’s condition and help guide your diagnostic plan. It can also provide a diagnosis (such as diabetic ketoacidosis, typical hypoadrenocorticism and high gastrointestinal obstructions).

The changes in these parameters over time can be essential in managing critical patients in the emergency setting; it will help guide you in developing an appropriate IV fluid therapy regime and fluid choice, address the patient’s oxygenation and/or ventilation needs, correct any electrolyte and glucose abnormalities, and – although fallen out of favour – the administration of sodium-bicarbonate therapy.

In upcoming blogs, I will teach you how to interpret the blood gas results. At the end of this, I hope everyone will incorporate blood gas analysis as their standard point-of-care test for the better assessment and management of patients.

If given the choice between a biochemistry and a blood gas panel in a critical patient, I would hands down select blood gas every time.