Medical background:

Bronchial asthma is the most common chronic condition in children and is particularly prevalent in urban areas and industrialised countries. Chronic inflammation of the airways causes damage to the mucous membrane lining the bronchi, the production of thick mucus and difficulty breathing. During an asthma attack, mucus is coughed up; breathing often becomes very difficult and is accompanied by characteristic wheezing sounds. The thickened bronchial muscles become fatigued. Such an asthma attack results in an acute shortage of oxygen, which can be treated with inhalers or ventilation. Blood gas analysis is frequently carried out for monitoring purposes, as the uneven ventilation of the lungs and the difficulty in exhaling cause carbon dioxide to accumulate in the alveoli and be absorbed into the bloodstream to a greater extent, where the excess can lead to acidosis (acidosis).

Application of the context:

Learners are given the medical records of a patient who was placed on ventilation following a severe asthma attack and is now being monitored in hospital. The learners’ task is to establish a diagnosis for the patient’s persistent symptoms (dizziness, headache, nausea). The steps involved in reaching a diagnosis therefore form the central thread of the context.

Short brainstorming and information-gathering phases lead to the conclusion that a blood gas analysis is medically appropriate for examining the patient. Building on this, a three-step experimental procedure is proposed within the context:

1. Detection of carbon dioxide (lime water test) using two different breathing techniques, to identify differences in the carbon dioxide content of exhaled air between healthy individuals and those who have just had an asthma attack
2. A microscale experiment using a Luer-Lock system to test the reaction of carbon dioxide with a buffer solution (pH = 7.4 as a reference to human blood), in order to determine the solubility of carbon dioxide in aqueous solutions
3. Microscale experiment using a Luer-Lock system to demonstrate the reaction of carbon dioxide with a buffer solution coloured by an indicator (pH = 7.4 as a reference to human blood), in order to characterise the resulting reaction as the formation of an acidic solution

A diagnostic algorithm can then be used to arrive at the clinical diagnosis of ‘respiratory acidosis’ and to compare this with the patient’s actual blood gas analysis results.

Position within the curriculum and learning objectives:

This unit covers, in particular, the core concept of ‘chemical reactions’, as well as ‘properties of substances and their particles’. Through the use of model experiments and the exploration of donor-acceptor concepts, the focus is particularly on the competence areas of factual knowledge and knowledge acquisition. The overarching aim is to explain the connections between real-life situations and chemical processes. Specific objectives are listed in the lesson plan and can be adapted depending on the Federal State or curriculum.

The supporting materials and information/answers for teachers can be found at this link.

You can also view the information video on the topic of blood here .