Fundamentals of Pharmacology for Paramedics - Группа авторов

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a drug needs to be able to penetrate to its sites of action relatively quickly. If the drug was an antimicrobial being used to treat an infection of the blood, then getting enough drug into the bloodstream for long enough would be all that was required. However, if the drug were required to penetrate the central nervous system, for example, or get into joint spaces or some other protected body compartment, then it would also have to be able to move out of the bloodstream and travel through the cellular walls that form those body compartments. This presents another challenge to a molecule; in order to get through cell membranes, a drug molecule either needs to be soluble in lipids (lipophilic) or, if it is more water soluble (hydrophilic), then it would have to be a very small molecule. Drugs that are highly lipid soluble are generally able to move readily through cellular compartments without difficulty, and will therefore leave the bloodstream and enter the tissues, often concentrating there. Drugs that readily cross the blood–brain barrier, such as those used in general anaesthesia, are highly lipid soluble, allowing them to pass very rapidly into the protected environment of the brain, which explains their ability to produce general anaesthesia in a matter of seconds after being introduced into a vein.

      The dose, route and timing of administration will all play key roles in the effectiveness of the drug. This is discussed in greater detail in Chapter 5.

      Episode of care

      You are treating 94‐year‐old Nelida, who has fallen in her residential aged care facility while going to the bathroom. She has a large bruise on the side of her head (temporal region) and a shortened and rotated left leg, as well as a deep laceration to her left upper thigh caused by the shard of a mirror that broke during the fall. Staff report that the patient has dementia but can still converse appropriately most days. The patient is in extreme pain but her heart rate is not elevated. You realise this is probably due to her being on a beta‐blocker for hypertension. You administer intranasal fentanyl repeatedly en route to hospital to treat her pain. On arrival, her level of consciousness has decreased. Reflecting on what might have caused this, you consider that the combination of blood loss and a blunted compensatory response due to the beta‐blockers, along with a reduced renal capacity due to her age, and the fact that the repeated fentanyl doses have not been cleared as rapidly as expected has resulted in an accumulation of medication, leading to adverse effects.

      While this is not a contraindication of fentanyl, it is important to remember that older patients often clear medications much more slowly than younger patients, and dosing may need to be adjusted to account for this, to avoid adverse effects.

      Skills in practice

      Medications can come in varying concentrations and formulations for different modes of delivery. Adrenaline is a naturally occurring catecholamine hormone produced by the adrenal glands and is often also administered in the management of life‐threatening presentations such as cardiac arrest, anaphylaxis and croup.

      The concentration of adrenaline can be expressed as 1:1000 or 1:10 000. This is expressed verbally as ‘one in one thousand’ and ‘one in ten thousand’ respectively. This ratio refers to the medication mass per volume of solution:

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      Adrenaline concentrations can and do vary, but the following is a guide to concentrations and routes of administration for various indications:

Concentration Route of administration Indication
Adrenaline 1:1000 Intramuscular Nebulised Anaphylaxis Croup Asthma
Adrenaline 1:10 000 Intravenous Cardiac arrest Cardiogenic shock

      Administering medication to children

      Historically, children were considered small adults, with the same physiology and metabolic requirements as an adult, but on a smaller scale. This is now known not to be the case, but many medications are still not tested on children, so safe doses in this patient group are not established empirically. A basic understanding of the differences between adult and child anatomy and physiology will ensure safer administration of medication to children. For example, the child’s heart does not have the same capacity to raise cardiac output by increasing its force of contraction and relies on increasing the heart rate to compensate for increased demand. As a result, peripheral vasoconstriction usually occurs more readily, in order to maintain blood pressure.

      Medications which cause peripheral vasoconstriction need to be used with extra caution in children because of this. Adrenaline will cause peripheral vasoconstriction when used to treat anaphylaxis or asthma, and the beta‐2 agonist salbutamol (albuterol) is also often contraindicated in children because of the possibility of tachycardia. Using medications that cause tachycardia will place further demands on a child’s heart, possibly at a time when it is already working hard to compensate. These medications have to be dosed and administered with extreme care in children, and some may be contraindicated.

      Reflection

      How is dosing calculated for children? If you don’t know the weight of the patient and there is no one to give you the weight, how would you estimate it, to ensure you give a safe and effective dose?

      What special considerations need to be borne in mind when giving medications intranasally to children?

      When administering medications to a child, ensure consent is gained from the parent, caregiver or a response given by the child is appropriate for their age and presentation. Ensure your approach to treating a child extends to providing oversight to the parent/caregiver as well.

      The out‐of‐hospital setting is not the same as the controlled environment of the hospital and the unpredictable and uncontrolled nature of paramedicine requires that the practising paramedic performs the work that would be done by three different health professionals in a hospital. This places a great responsibility on the paramedic when it comes to the safe and effective use of medicines. The paramedic must be an expert in both the correct choice and administration of medications. In addition, because the environment in which the paramedic is operating is particularly conducive to making errors, the paramedic must also be constantly vigilant and ensure the stringent and consistent checking of medication route, dose, time, expiration date and patient. As the scope of paramedic practice increases and more medications are administered in the prehospital setting, the need for paramedics to have a mastery of medicines becomes even greater.

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