Additional notes from anaesthetics - drugs Flashcards
When we are talking about ionotropes what are we talking about ?
Positive inotropes i.e. drugs which increase the force of cardiac muscular contraction
When are ionotropes indicated?
In the hypotensive patient who is adequately fluid resuscitated in whom the principal reversible cause for hypotension is poor cardiac contractility
What is the only way to safely administer ionotropes ?
By infusion through a central venous catheter
Give the 2 main examples of ionotropes
- Adrenaline (epinephrine)
- Dobutamine
What is the mechanism of action of adrenaline ?
- Catecholamine, agonist at both alpha and beta receptors.
- In low doses beta-1 mediated vasodilatation is prominent, but the blood pressure rises because of the beta-1 mediated increase in the force and rate of myocardial contraction.
- At high doses alpha-1 vasoconstriction predominates, thus the optimal dose for cardiac output is not necessarily the highest dose possible.
What is the mechanism of action of dobutamine ?
- Synthetic catecholamine. Predominantly beta-1 adrenoceptor agonist, with dose-dependent effects at beta-2 and alpha-1 receptors.
- It increases myocardial contractility with minimal effects on heart rate and little direct effect on vascular tone
What are vasopressor drugs ?
A substance which increases the systemic vascular resistance ==> increase BP
Give the main examples of vasopressors
- Noradrenaline (Norepinephrine)
- Metaraminol
- Ephedrine
- Adrenaline (Epinephrine)
What is the mechanism of action of noradrenaline ?
- Catecholamine. Powerful alpha-1 agonist with much weaker beta effects (most pronounced at low dose).
- As such it is used as a vasopressor rather than an inotrope to increase SVR.
Why is noradrenaline the most commonly used in ICU of all the vasopressors/inotropes?
Because the most common problem in adult sepsis is reduced SVR
What is the mechanism of action of metaraminol ?
Similar in action to naradrenaline, but with weaker activity
What is the drug of choice in theatre to increase SVR & blood pressure & why?
- Metaraminol - because it can be given peripherally
- Note - Can also be given by infusion if no central access available for noradrenaline
What is the mechanism of action of ephedrine ?
Acts on both alpha-1 and beta-1 receptors to increases both SVR and heart rate.
How is ephedrine given and what way cannot it be given?
Given peripherally and therefore used in theatre in bolus form (not given in infusion because quickly becomes ineffective by a process called tachyphylaxis).
What is the mechanism of action of paracetamol ?
Inhibits prostaglandin synthesis in the CNS
What is the standard doseage of paracetamol?
1 gram 6 hourly - Remember to reduce dose if weight <50kg
What is the mechanism of action of NSAID’s?
Inhibit the enzyme cyclooxygenase [cox]
What are the contraindications to NSAID use ?
- Gastrointestinal bleeding [old or new] or active peptic ulceration
- Coagulopathy
- Renal impairment
- Aspirin/NSAID allergy
What are the cautions to NSAID use ?
- Elderly
- Dehydration
- Asthmatics [ask about sensitivity to NSAIDS]
- Certain types of surgery, e.g. - plastic or eye surgery, some orthopaedic surgery
- Cardiac failure
- Pregnancy
- Concurrent medication e.g. anticoagulant
What is the mechanism of action of opioids ?
Act through μ - opioid receptor
Give the main examples of strong and weak opioids
Strong opioids:
- Morphine, Diamorphine, Oxycodone, Fentanyl, Methadone
Weak opioids:
- Codeine, Tramadol
What are the main features of oxycodone ?
Fast onset and short time to steady state
What is the additional points to the mechanism of action of tramadol (an opioid)?
Centrally acting synthetic analgesic: mu opioid receptor activity + inhibits the uptake of noradrenaline and serotonin
What are the advantages of tramadol?
- Absence of tolerance
- Lower abuse potential
- Less respiratory depression
- Less constipation although nausea, vomiting and sedation may still occur
Who should tramadol not be givne to ?
Epileptics
What should you be aware of coedine in ?
‘co-’ drug preparations
What does the analgesic action of coedine depend on ?
On the metabolism to morphine - 9% of caucasians lack enzyme responsible for this
What is patient controlled analgesia (PCA)?
Analgesia prescribed by doctor and administered by patient
When is PCA used ?
Used in the control of postoperative pain and also for those with severe non operative pain e.g. pancreatitis, fractured ribs.
What is the standard prescription of PCA ?
A 1 mg bolus of morphine with a 5 minute lockout i.e. the patient can receive up to 12 mgs morphine per hour
List the advantages of PCA
- Enables individual titration of analgesia to keep plasma opioid levels within the analgesic corridor
- Patients feel in control of their analgesia, they can titrate the dose of drug according to the intensity of their pain and to minimise side effects
- No delay waiting for nurses to be available
What are the contraindications to PCA ?
- Patient inability to comprehend the technique e.g. extremes of age
- Patients inability to press the button e.g. severe rheumatoi
- Patient rejection
- Ward staff must be trained appropriately
What are the advantages of epidural analgesia ?
- Excellent analgesia
- Less stress response to surgery
- Lower incidence of DVT and thus Pulmonary Embolus
- Earlier mobilisation
- Earlier recovery of GIT function
What are the disadvantages of epidural analgesia?
- Special staff training required
- Blocks may not be perfect
- Hypotension may occur-need to keep patients well hydrated
- Can not insert if patient on anticoagulants
- Major complications can occur e.g. spinal haematoma or abscess
