A young man has suffered a head injury during a rugby match. Initially he was not knocked unconscious however he has become increasingly drowsy. On the way to hospital the paramedics have inserted an oropharyngeal airway and given him high flow oxygen.

Arterial blood gas analysis reveals:

Inspired oxygen   40% (FiO2 0.4)                  normal values

 

PaO2                  15.6 kPa                                >10 kPa on air

pH                      7.22                                        7.35 – 7.45

PaCO2               9.2 kPa                                   4.7 – 6.0 kPa

Bicarbonate     25.4 mmol l-1                         22 – 26 mmol l-1

 

  1. Assess the patient’s condition.

This patient has a reduced level of consciousness and an impaired airway which will probably both result in him not breathing out his carbon dioxide effectively. It may also mean that is oxygenation is poor. Because it is an acute situation the bicarbonate level is unlikely to have changed very much as the kidneys only respond relatively slowly.

 

  1. Assess the oxygenation.

As a rule of thumb the patients PaO2 should be no less than 10 points lower than the inspired oxygen that is being delivered. So in this case if there was no problem with the oxygenation you would expect the PaO2 to be around 30kPa. It isn’t, so there is some hypoxia occurring.

 

  1. Determine the pH concentration.

We next need to ask ourselves whether there is an acidaemia or an alkaleamia. In this case the pH is less than 7.35 so there is an acidaemia.

 

  1. Determine the respiratory component.

We then look at the PaCO2, remembering that values above 6 would indicate a respiratory acidosis, and values below 4.7 would indicate a respiratory alkalosis. In this example the PaCO2 is above 6 so the patient has a respiratory acidosis.

 

  1. Determine the metabolic component.

The final part of the process is to look at the bicarbonate to determine whether there is a metabolic disorder. The bicarbonate in this example falls within the normal range so there is no metabolic disorder at present.

So to summarise this blood gas we have an acidaemia caused by a respiratory acidosis and no metabolic compensation.

Jevon

Jevon

Possibly the book I most highly recommend for nurses to use as their pocket guide. Phil Jevon is a practitioner in Walsall and has produced an easily read, pocket sized tool. You can click on the picture above  to purchase this excellent book.
Talley and O'Conner
Slightly less 'weighty' than Macleods but still with lots of useful detail and information. The latest copies also have a CD with good, well narrated examples of clinical examination.
Macleods
This title is 'Highly Commended' in the 2006 British Medical Association Awards! 'an incredibly thorough book which is very well illustrated - a must in a book explaining how to perform examinations' - ("Medical Student Review"). This book will show you how to: talk with a patient; take the history from the patient; examine a patient; formulate your findings into differential diagnoses and rank these in order of probability; and, use investigations to support or refute your differential diagnosis.