Clinical Hypotension & Anaesthesia of the High-Risk Patient Flashcards
MAP depends on
CO & systemic vascular resistance
MAP =
CO x SVR
MAP is often monitored during GA to provide info on…
CO (major determinant of tissue perfusion)
B/c MAP depends on vascular tone, itis possible for a p w/ normal or high arterial BP to have low…
CO, but high peripheral resistance –> tissue blood flow may be impaired despite reasonable BP
You can have a high MAP w/ poor
CO
BP readings should not be viewed in…
isolation
A rough eval of vascular tone may be made by…
assessing mm colour & CRT
During GA, the BP should be maintained at:
SAP > 90 mmHg (kidney perfusion)
MAP >60-70 mmHg (brain perfusion)
DAP > 40 mmHg (myocardial perfusion)
Explain these equations:
MAP = CO x SVR, CO = HR x SV
- BP increases when HR increases, stroke volume increases
- SV depends on cardiac filling (preload), contractility of the heart
- Preload depends on venous return & HR and rhythm
- systemic vascular resistance increases w/ vasoconstriction
How do you treat hypotension?
- find & treat underlying cause
- decrease depth of anaesthesia
- provide analgesia to decrease reqmt of maintenance agents
- if bradycardia, increase HR (atropine, glycopyrrolate)
- if cardiac arrhythmias present, treat them, can cause hypotension
- give a fluid bolus (crystalloid &/or colloid)
- if mechanically ventilated, decrease peak airway pressure - mechanical ventialtion; decrease TV, increase RR but ensure I:E remains 1:2-1:3
- start positive inotrope: dobutamine, dopamine
- if severe vasodilation: start vasopressor (noradrenaline, ephedrine, dopamine
Common situations that cause hypotension
- hypoxaemia
- reduction of cardiac contractility
- cardiac arrhythmias
- massive vasodilation (anaphylaxis, inflammatory mediator release)
- massive blood loss
- tension pneumothx (pressure buildup, vasoconstriction, impacts heart)
- closed breathing system exhaust valve
- Sx/physical disruption of venous return
- pulmonary thromboembolism
- electrolyte/pH imbalances
Txt of hypotension
- decrease depth of anaesthesia
- increase HR? treate arrhythmias
- consider fluid boluses
- start positive inotrope OR increase systemic vascular resistance (vasopressor)?
How do you decrease the depth of anaesthesia?
- decrease vaporiser/ increase fgf
- if you cant decrease b/c p will wake up, use MAC-sparing drugs for analgesia to reduce iso dosing
- if not super painful but plane of anesthesia is low, infuse dexmedetomidine/medetomidine,etc.
How do you increase heart rate or treat arrhythmias?
- Bradycardia: atropine, glycopyrrolate
- No atipamezole (reversal of alpha-2) - worsens vasodilation & hypotension
- All cardiac arrhythmias (both brady/tachy) must be txt’d if they negatively affect CO or BP, vagal induced 2nd deg AV block –> treat if P’s BP is affected
How do you choose fluid boluses?
- Crystalloids: 5-10 ml/kg bolus (over 10-20 mins)
- Colloids: 2-5 ml/kg bolus (over 10-20 mins)
