Answer: A. Functional residual capacity

Pre-oxygenation is the administration of oxygen to a patient prior to intubation. It helps to extend the ‘safe apnoea time’. The ‘safe apnoea time’ is defined as the duration of time following cessation of breathing/ventilation that elapses until arterial desaturation occurs (SaO₂ reaches < 90%)

The primary mechanism by which pre-oxygenation works is by ‘denitrogenation’ of the lungs, however maximal pre-oxygenation is achieved when the alveolar, arterial, venous and tissue compartments are all filled with oxygen. Denitrogenation is achieved using oxygen to wash out the nitrogen contained in the lungs after breathing room air, resulting in a larger alveolar oxygen reservoir.

The functional residual capacity (FRC) is the volume of gas that remains in the lungs after a normal tidal expiration. It is the sum of the residual volume (RV) and the expiratory reserve volume (ERV). One method of measuring the FRC is the nitrogen washout technique.

The FRC is the most important store of oxygen in the body. The greater the FRC, the longer apnoea can be tolerated before critical hypoxia develops. Patients with reduced FRC (e.g. lung disease, kyphoscoliosis, pregnancy, and obesity) reach critical hypoxia more rapidly. The aim of pre-oxygenation is to replace nitrogen in the FRC with oxygen.

Answer: D. Give IV amiodarone 5-10 mg/kg

Supraventricular tachycardia (SVT) is the most common non-arrest arrhythmia during childhood and is the most common arrhythmia that produces cardiovascular instability during infancy.

The current APLS guidelines recommend that if the patient has no features of shock and remains haemodynamically stable then vagal maneovres should be attempted initially. If this is unsuccessful then:

• An initial dose of 100 mcg/kg of adenosine should be given.
• After two minutes another dose of 200 mcg/kg adenosine should be given is the child remains in stable SVT
• After a further two minutes another dose of 300 mcg/kg adenosine should be given

If the child remains in stable SVT despite these measures then the guidelines recommend that following be considered:

• Adenosine 400-500 mcg/kg
• Synchronous DC shock
• Amiodarone

Amiodarone, if given, should be administered initially at a dose of 5-10 mg/kg over 20 minutes to 2 hours, then by continuous infusion 300 mcg/kg/hour increased according to response by 1.5 mg/kg/hour. The infusion rate should not exceed 1.2 g in 24 hours.

If defibrillation is used for the treatment of SVT in children it should be as a DC synchronous shock at 1-2 J/kg.

Answer: B. Tetanus vaccination and 500 IU tetanus immunoglobulin

Tetanus prone wounds include:

• Puncture wounds
• Wounds over 6 hours old
• Dirty wounds
• Wounds with significant devitalized tissue
• Avulsions
• Open fractures
• Gunshot wounds
• Crush injuries
• Burns

Tetanus prone wounds only require tetanus immunoglobulin (TIG) if there is an unknown history of tetanus prophylaxis, less than 3 doses of tetanus toxoid have been given in the past or it is over 5 years since the last dose.

The preventative dose of tetanus immunoglobulin is 250 IU in most cases, unless over 24 hours have passed since the injury or the wound is heavily contaminated, then 500 IU should be given.

In this case the patient has a contaminated, tetanus prone wound that is over 24 hours old. He should therefore receive the higher dose of tetanus immunoglobulin and the vaccination. His GP should be also contacted to arrange the remainder of course as indicated.

For further information about tetanus prophylaxis please refer to the following reference:

https://www.gov.uk/government/Green-Book-Chapter-30

Answer: A. Transversalis fascia

From DEEP to SUPERFICIAL the structures in the anterior abdominal wall at this level are as follows:

• Parietal peritoneum (deepest)
• Extraperitoneal fat
• Transversalis fascia
• Aponeurosis of transverse abdominis and internal oblique
• Rectus abdominis muscle
• Aponeurosis of internal oblique and external oblique muscles
• Superficial fascia (most superficial)

The deepest structure in the given options in this case is therefore the transversalis fascia. This firm membranous sheet lines most of the abdominal wall and covers the deep surface of the transversus abdominis and its aponeurosis.

The parietal peritoneum is internal to the transversalis fascia and is separated from it by a variable amount of extraperitoneal fat.

The superficial fascia is divided into an anterior and posterior segment:

• Camper’s fascia (anterior part of the superficial fascia)
• Scarpa’s fascia (posterior part of the superficial fascia)

Answer: A. Haemostasis

After a wound occurs the first stage in the healing process is haemostasis.

Hemostasis is the process of the wound being closed by clotting. It begins with the leakage of blood from the body. The first step of hemostasis is when blood vessels constrict to restrict the blood flow. Next, platelets stick together in order to seal the break in the wall of the blood vessel. Finally, coagulation occurs and reinforces the platelet plug with threads of fibrin, which are like a molecular binding agent.

The hemostasis stage of wound healing happens very quickly. The platelets adhere to the sub-endothelium surface within seconds of the rupture of a blood vessel’s epithelial wall. After that, the first fibrin strands begin to adhere in about sixty seconds. As the fibrin mesh begins, the blood is transformed from liquid to gel through pro-coagulants and the release of prothrombin. The formation of a thrombus or clot keeps the platelets and blood cells trapped in the wound area.

Following haemostasis there are three phases of wound healing:

• The inflammatory phase (up to 48 hours after injury) – Blood vessels dilate to allow antibodies, white blood cells, growth factors, enzymes and nutrients to reach the wounded area. The characteristic signs of inflammation are seen. The predominant cell types seen are neutrophils and macrophages, which serve to autolyse devitalized necrotic tissue.

• The proliferative phase (up to 3 weeks after injury) – New granulation tissue, comprised of collagen and extracellular matrix develops. Epithelialisation occurs during this phase. During epithelialisation epithelial cells develop at the wound margins and then divide and migrate towards the centre of the wound. Angiogenesis occurs with fibroblasts and capillaries growing into the necrotic areas. Healing wound mass is greatest after 3 weeks.

• The maturation phase (up to 1 year after injury) – The final phase occurs when the wound has closed. This phase involves remodeling of collagen from type I to type III. Cellular activity reduces and the number of blood vessels in the wounded area regresses and decreases. Wound remodeling continues for up to 1 year.