Medical background:

Bronchial asthma is the most common chronic disease in children and is particularly prevalent in urban regions and industrialised countries. Chronic inflammation of the airways leads to damaged mucous membranes in the bronchial tubes, the formation of thick mucus and difficult breathing. During an asthma attack, mucus is coughed up, breathing is often very difficult and is accompanied by characteristic whistling noises. 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. A blood gas analysis is often performed 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 increasingly absorbed into the bloodstream, where the excess can lead to acidosis.

Realisation of the context:

Learners are given a file of a patient who has been ventilated after a severe asthma attack and is being monitored in hospital. The learners' task is to find a diagnosis for the patient's persistent symptoms (dizziness, headaches, nausea). The steps to diagnosis therefore form the central theme of the context.

Brief brainstorming and information phases lead to the decision that a blood gas analysis makes medical sense to examine the patient. Following on from this, a three-step experiment is proposed in the context:

1. Carbon dioxide detection (lime water sample) using two different breathing techniques to reveal differences in the carbon dioxide content in the air breathed by healthy people and after an asthma attack
2. Microscale experiment with Luer-Lock system for the reaction of carbon dioxide with a buffer solution (pH = 7.4 as a reference to human blood) in order to work out the solubility of carbon dioxide in aqueous solutions
3. Microscale experiment with Luer-Lock system for 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 reaction as the formation of an acidic solution

The specialist diagnosis "respiratory acidosis" can then be found using a diagnostic scheme and compared with the patient's real blood gas analysis values.

Classification in the curriculum and learning objectives:

The unit covers the basic concept of "chemical reaction" in particular, but also "properties of substances and their particles". The use of model experiments and the thematisation of donor-acceptor concepts focus in particular on the competence areas of factual and knowledge acquisition competence. The overarching goal is to explain the relationships between facts from the real world and chemical processes. Detailed objectives are listed in the course plan and can be adapted depending on the Federal State/curriculum.

The accompanying materials and information/solutions for teachers can be found under this link.

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