20th March 2024

Prescribing guidelines

Anaphylaxis

Anaphylaxis is a systemic IgE-mediated hypersensitivity reaction which results in life-threatening airway and circulatory problems after exposure to an allergen. It is caused by release of inflammatory mediators after degranulation of basophils and mast cells. The initial management is IM adrenaline and in adults the concentration is 1mg/mL (1:1000) concentration. The intramuscular dose of adrenaline is 500 micrograms (0.5mL). Anaphylactic reactions may be confirmed by measuring mast cell tryptase levels. Ideally, three samples should be taken. These should be taken as soon as feasible after suspected anaphylaxis (but do not delay treatment to measure tryptase levels), 1–2 hours (but no later than 4 h) after onset of symptoms and at least 24 hours after complete resolution or in convalescence.

Cardiac arrest

In cardiac arrests, certain drugs are given at specific times depending on whether you are on the shockable or non-shockable side of the cardiac arrest management algorithm. When managing non-shockable rhythms, adrenaline 1mg IV/IO (concentration 1:10000) should be given as soon as a non-shockable rhythm is recognised on the defibrillator. It should then be given every alternate cycle. In shockable rhythms, adrenaline 1mg IV/IO (concentration 1:10000) should be given after the third shock. Once the first dose of adrenaline is given, further doses should be given every 3-5 minutes. Amiodarone 300mg IV/IO should be given after 3 shocks. A further dose of 150mg IV/IO should be considered after 5 shocks.

Diabetic Emergencies

Hypoglycaemia

Conscious patients who can swallow should be treated with oral fast-acting carbohydrates such as glucose tablets, Glucogel® or pure fruit juice. Once the blood glucose levels normalise, then a long-acting carbohydrate should be given to prevent blood glucose levels from falling again. This can include two biscuits or a slice of bread. In patients who are unconscious and hypoglycaemic, then either 200mls of 10% IV glucose or 100mls of 20% IV glucose should be given over 15 minutes. If intravenous access is not feasible, then 1mg of IM glucagon can be given.

Diabetic ketoacidosis

Patients who have diabetic ketoacidosis (DKA) require strict fluid resuscitation. If the systolic blood pressure (SBP) is below 90mmHg, then 500mls of 0.9% sodium chloride should be infused over 10-15 minutes. This should be repeated if SBP remains below 90mmHg. If it becomes difficult to raise the SBP, then consider contacting the critical care team. Once the SBP is above 90mmHg then infuse 1L of 0.9% sodium chloride over 1 hour. As an example, subsequent fluid administration can be as follows:

0.9% sodium chloride 1L with potassium chloride over the next 2 hours
0.9% sodium chloride 1L with potassium chloride over the next 2 hours
0.9% sodium chloride 1L with potassium chloride over the next 4 hours
0.9% sodium chloride 1L with potassium chloride over the next 4 hours
0.9% sodium chloride 1L with potassium chloride over the next 6 hours

The fixed-rate intravenous insulin infusion (FRII) is calculated as 0.1 units/kg/hour. Once the glucose drops to <14 mmol/L, then in addition to adding a 10% dextrose infusion, consider reducing the rate of intravenous insulin infusion to 0.05 units/kg/hr to avoid the risk of developing hypoglycaemia and hypokalaemia.

Hyperglycaemic hyperosmolar state

The hyperglycaemic hyperosmolar state (HHS) is a life-threatening metabolic decompensation of diabetes which presents with severe hyperglycaemia and profound dehydration, typically accompanied by alteration in consciousness ranging from lethargy to coma. It usually presents with those with Type 2 diabetes mellitus (T2DM). Unlike DKA, it usually does not present with significant hyperketonaemia or acidosis, but this may not always be the case. It usually presents in those over 45 years but it is known to present in younger groups of patients. The predominant cause of HHS is either a chest or urinary tract infection. HHS has a high mortality because it may be due to, or complicated by, vascular events such as myocardial infarction, stroke or peripheral arterial thrombosis. The aims of treatment are to normalise blood glucose levels, normalise osmolality and replace fluid and electrolyte losses.

The main type of fluid used in treating HHS is 0.9% sodium chloride. Only switch to 0.45% sodium chloride solution if the osmolality is not declining despite adequate positive fluid balance. The fall in osmolality should not be more than 3.0-8.0 mOsm/kg/hr. The fall in glucose should not be more than 5.0 mmol/L/hr. Insulin infusions should be commenced in the following situations:

If there is HHS and ketonaemia (blood ketones 3ß-hydroxybutyrate >1.0 – ≤3.0
mmol/L or urine ketones < 2+) and not acidotic (venous pH >7.3 and bicarbonate
>15.0 mmol/L) then use 0.05 units/kg/hr OR
If there is significant ketonaemia (3ß-hydroxybutyrate >3.0 mmol/L) or ketonuria
(≥ 2+) with a pH <7.3 and bicarbonate <15 /mmoL, then use the DKA guidelines at 0.1 units/kg/hr

The underlying precipitant of HHS should be identified and treated.