Clinical Anaesthesia

Bradycardias During Anaesthesia

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Bradycardia is defined as a heart rate below 60bpm and occurs commonly under anaesthesia. Although most bradycardias are benign, they have the potential to cause haemodynamic compromise and progress to asystole/cardiac arrest. Being able to predict when a bradycardia may occur, as well as understanding the underlying cause, is pivotal to early and successful treatment.

 

 

 

 

 

 

 

 

 

 

 

 

General approach to the management of bradycardias

 

SAFETY

  • Confirm reading
  • Call for help (depending on severity / seniority)
  • Scan patient / surgical field / anaesthetic / monitors (check oximeter and capnography to rule out hypoxaemia; assess ECG for 2nd or 3rd degree blocks)
  • Stop surgery / remove stimulus (eg, pneumoperitoneum, pressure on globe, squint surgery, spermatic cord manipulation)

 

TEMPORISATION / INITIAL MANAGEMENT

  • Administer IV atropine 300-600mcg boluses to a maximum of 3mg (IV glycopyrrolate 200-400mcg boluses may also be considered depending if less severe bradycardia)
  • Consider IV ephedrine 3-12mg boluses if hypotension and bradycardia present despite administration of anticholinergic
  • IV fluids and legs up / Trendelenburg position to optimise preload and venous return to heart (underfilled heart may cause a Bezold Jarisch reflex causing bradycardia)

 

  • IF ABOVE FAILS
  • Administer 100% oxygen and ensure airway is safe/managed with basic to advanced techniques.
  • Early preparation of transcutaneous pacing, especially if 2nd or 3rd degree block present on rhythm strip
  • IV adrenaline at 10-100mcg boluses (while awaiting pacing) If responsive, consider adrenaline infusion at 0.05-0.10 mcg/kg/min

 

  • IF ASYSTOLE/ARRREST
  • Commence CPR with advanced life support algorithm

 

DIAGNOSIS

  • Probability gambit – See below for common causes of bradycardias during anaesthesia (surgical / anaesthetic causes)
  • 4 H’s and 4 T’s
  • Underlying cardiac pathology – 12 lead ECG, ECHO, bloods, and cardiology consult.

 

Common causes of bradycardia during anaesthesia

 

Bezold-Jarisch reflex

  • Common cause – Following spinal anaesthesia or as a complication of an interscalene brachial plexus block, pneumoperitoneum.
  • Trigger – Ventricular chemoreceptors and mechanoreceptors are stimulated by reduced ventricular filling, chemical substances, or drugs.
  • Response – Increased renin and vasopressin release, sympathetic nervous system (SNS) inhibition and parasympathetic nervous system (PNS) activation.
  • Initial treatment –
    • Cease trigger (deflate pneumoperitoneum)
    • Administer atropine (300-600mcg) and
    • increase preload (IV fluid / Trendelenburg / legs up).
    • Other medications may be required (ephedrine, adrenaline)
    • If severe bradycardia or asystole – commence ALS measures

 

Oculocardiac reflex

  • Common cause – Facial or ocular surgery, where the trigeminal nerve may be involved.
  • Trigger – Direct pressure placed on the extraocular muscles, globe, or conjunctiva mediates reflex through connections between the ophthalmic branch of the trigeminal nerve and the vagus nerve.
  • Response – PNS activation.
  • Initial treatment –
    • Remove pressure from area.
    • Administer atropine (300-600mcg) or glycopyrrolate (200-400mcg).

 

Bradycardia due to pneumoperitoneum

  • Common cause – Laparoscopic surgery.
  • Trigger – Peritoneal stretch due to CO2 insufflation of the peritoneum during laparoscopic surgery.
  • Response – SNS inhibition and PNS activation.
  • Initial treatment –
    • Pneumoperitoneum deflation and stop surgery.
    • Administer atropine (300-600mcg) or glycopyrrolate (200-400mcg).
    • Other medications may be required (ephedrine, adrenaline)
    • If severe bradycardia or asystole – commence ALS measures

 

 

Bradycardia due to spermatic cord traction

  • Common cause – Orchidectomy or inguinal hernia repair where there is manipulation of the spermatic cord.
  • Trigger – Manipulation/traction on spermatic cord results in vagal reflex.
  • Response – SNS inhibition and PNS activation.
  • Initial treatment –
    • Release traction on spermatic cord.
    • Administer atropine (300-600mcg) or glycopyrrolate (200-400mcg).

 

Bradycardia due to endotracheal suctioning

  • Common cause – Endotracheal suctioning in mechanically ventilated patients.
  • Trigger – Vagus nerve stimulation.
  • Response – PNS activation.
  • Initial treatment –
    • Stop suctioning,
    • 100% O2. Atropine (300-600mcg) or glycopyrrolate (200-400mcg).

 

Bradycardia due to suxamethonium

  • Common cause – Administration of suxamethonium in a young patient, particularly when a second dose is given.
  • Trigger – Activation of nicotinic receptors causes muscarinic stimulation resulting in bradycardia.
  • Response – Increased vagal tone.
  • Initial treatment –
    • Administer atropine (300-600mcg)
    • Anticholinergics may be considered as pre-treatment in patients of higher risk (eg, paediatric patients).

 

Bradycardia due to metaraminol

  • Common cause – Administration of metaraminol.
  • Trigger – Increased arterial pressure in response to vasoconstriction is detected by baroreceptors (baroreceptor mediated reflex).
  • Response – SNS inhibition and PNS activation.
  • Initial treatment –
    • Often no treatment required, but may exacerbate other causes of bradycardia
      • Eg giving metaraminol for a low BP, as pneumoperitoneum is being commenced.
    • Administer atropine (300-600mcg) or glycopyrrolate (200-400mcg).
    • Other medications may be required (ephedrine, adrenaline)
    • If severe bradycardia or asystole – commence ALS measures

 

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