Applied anatomy, physiology and pharmacology Flashcards
Define sedation
A continuum which extends from normal alert consciousness to complete unresponsiveness
Minimal sedation responsiveness, airway, ventilation and cardiovascular effects?
Responsiveness - Normal response to verbal commands
Airway - Unaffected
Ventilation - Unaffected
Cardiovascular - Unaffected
Moderate sedation responsiveness, airway, ventilation and cardiovascular effects?
Responsiveness - Purposeful response to verbal or tactile stimulation
Airway - Maintained without intervention
Ventilation - Adequate
Cardiovascular - Usually maintained
Deep sedation responsiveness, airway, ventilation and cardiovascular effects?
Responsiveness - Purposeful response following repeated or painful stimulation
Airway - Intervention may be required
Ventilation - May be inadequate
Cardiovascular - Usually maintained
GA responsiveness, airway, ventilation and cardiovascular effects?
Responsiveness - Unrousable even with painful stimulation
Airway - Intervention often required
Ventilation - Frequently inadequate
Cardiovascular - May be impaired
Steps to respiration?
- Ventilation – moving of gas into and out of the lungs
- Diffusion – transfer of gases from the lungs into the blood
- Transport – the transport of oxygen by the blood to the cells and the transport away of carbon dioxide
- Diffusion – transfer of gases from the blood to the cells
- Oxidation – the use of oxygen to produce energy within the cell and the production of carbon dioxide
Inspiration features?
Active process Initiated by diaphragm Supported by intercostals Accessory muscles for more vigorous inhalation Normal rate 10-18 per minute
Expiration features?
Passive process
Elastic recoil of lung
Forced expiration involves abdominal and intercostals
Where does pulmonary gas exchange occur?
Alveoli
Alveoli features?
Wall single layer thick
0.2 micrometers
Adjacent to pulmonary capillary wall
Gas diffuses down concentration gradients
How does delivery of O2 occur?
O2 binds to haemoglobin Each molecule can carry 4 O2 molecules Carried within RBC CaO2= 1.34 x Hb x SpO2 Delivery = CaO2 x Cardiac Output Properties of haemoglobin means it releases O2 when it gets to the tissues
Hb - Lungs - Resp centre - Tissues
What does O2 delivery equal?
CaO2 x Cardiac Output
What makes up the Autonomic Nervous System?
Brainstem, medulla, pons
How to monitor the pt whilst sedated?
Resp rate 10-18 per minute
Depth of breathing
Pattern of breathing
Cyanosis
Advanced - pulse oximetry (mandatory), carbon dioxide monitoring (optional)
Venous blood O2 and CO2 levels compared to air? How does this impact diffusion?
Venous blood has less O2 compared to air - diffuses out alveoli
Venous blood has more CO2 compared to air - diffuses into alveoli
Cellular respiration?
Mitochondria uses O2 for metabolism
CV system basic function?
Deliver oxygenated blood to body organs and tissues for metabolism
“tissue perfusion”
What happens with inadequate perfusion?
Organs, tissues fail
Cardiac ischaemia - angina - myocardial infarct
Cerebral ischaemia - fain, collapse - stroke
Lung - hypoxia
What is the main determinant of organ perfusion?
Blood pressure
- Systolic, diastolic and mean (MAP) 12060 (80)
How to calculate MAP?
Diastolic + 1/3 (systolic - diastolic)
What is the normal MAP?
80mmHg
What determines BP?
Cardiac output
Systemic vascular resistance
What is cardiac output?
Amount of blood ejected by the heart per minute - average 5 litres/min
Determined by HR and stroke volume
HR between 50-180 have little effect
How to reduce stroke volume?
Dehydration/blood loss
Ischaemic heart disease/heart failure
- Anaesthetic drugs
Systemic vascular resistance?
Resistance produced by the vascular system to the flow of blood
Predominantly small arterioles throughout the body
Constriction increases SVR and BP
Dilation decreases SVR and BP
How to decrease systemic vascular resistance?
Sedative drugs
Anaphylaxis
Sepsis/infec
Acute control of BP?
Baroreceptors in aortic arch and internal carotids
Send signals to brainstem
Autonomic nervous system alters rate and strength of heart contraction and constriction of blood vessels
Chronic control of BP?
Renin-angiotensin system
Aldosterone
Chronic regulation of blood sodium concentration and body fluid retention
Drugs for moderate sedation?
Benzodiazepines - Midazolam
Opiates - fentanyl, remifentanil
Others - propofol, ketamine, dexomethomedine
Midazolam mode of action?
–
Midazolam features?
Benzodiazepine Given IV for moderate sedation Onset 1-3 mins Peak 5-7 mins Duration 20-30 mins Titrate dose to desired end point e.g. slurred speech
Midazolam dosing? Cautions?
Initial dose 2.5mg given over 2 mins
Wait 2 mins for effect
Subsequent doses of 1mg
Usually no more than 5mg
Cautions - decrease initial dose to 1.5mg in the elderly
If used with a pre-med then reduce dose by 1/3
Midazolam advantages?
Quick onset
Short action of duration
Minimal CV effects
Midazolam disadvantages?
Resp depression
Airway obstruction
Flumazentil features?
Reverse benzodiazepine effects quickly
Dose of 200mcg every 1-2 mins as required
Onset within 1-2 minutes, peak effect within 6-10 minutes
Fentanyl features?
Opiate Provides analgesia and sedation Onset 1-2 mins Peak 10-15 mins Duration 30-60 mins
Dosing 25mcg (0.5ml) bolus up to 200mcg max
Fentanyl advantages?
Provides analgesia as well as sedation
Fast onset
Short duration of action
Fentanyl adverse effects?
Hypotension and bradycardia
Respiratory depression
Nausea and vomiting
Remifentanil features?
Ultra short acting opiate
V potent analgesic effect
Has to be administered by continuous infusion via syringe driver
Remifentanil advantages?
Excellent analgesic properties
Extremely short duration of action (8 mins)
Adverse effects of Remifentanil?
Hypotension
Bradycardia
Respiratory depression and apnoea
Propofol features?
Intravenous anaesthetic induction agent
Onset: 30 seconds
Duration: 10 - 15 minutes
Dosage:
10 - 20mg (1 -2 mls) every 5 minutes
Or
By continuous infusion
Propofol advantages?
Very potent sedative
Rapid onset
Propofol adverse effects?
Only for use by trained sedationist or anaesthetic staff
Can rapidly progress to general anaesthesia
Significant cardiovascular and respiratory depression
Tips for sedation?
Use single drug if possible - avoid ‘polypharmacy’
Give small incremental boluses to titrate effect in individual patient
Easier to give a bit more than to deal with effects of giving too much
Knowledge of time to onset and peak effect of the drug you are using
Polypharmacy positives?
Use of more than one drug
Can have advantages
Different drugs give different effects
e.g. Opiate + Benzodiazepine gives both sedation and analgesia
Giving a second drug means you can use less of the first drug and so potentially reducing side effects
Polypharmacy negatives?
Opens the door for greater risk of overdosing and over-sedating patients
Drugs with the same side effects will have synergistic action and make those side effects even more likely
Must be aware of time to peak effect of the drugs you are using…..
Midazolam 5 - 7 minutes
Fentanyl 10 - 15 minutes
Propofol 1 minute
Not waiting for full effect of first drug may lead to dosing of second drug peaking with first drug
Leads to significant over-sedation and side effects
