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Hypertension

Created: 13/4/2004

 
Hypertension is defined as: a series of blood pressure measurements revealing pressures greater than 160/100 mmHg

Normal increases in blood pressure are seen with age as the arteries become stiffer

Preoperative causes:

Primary or essential hypertension

Secondary (10%)

(a) renal: chronic pyelonephritis/renal artery stenosis/ polycystic kidneys

(b) endocrine: phaeochromocytoma/Cushing's syndrome/ Conn's disease

(c) pregnancy

(d) coarctation of the aorta

Perioperative causes:

  • Pain
  • Light anaesthesia
  • Hypoxia
  • Hypercarbia
  • Fluid overload
  • Drug interactions/vasopressors given
  • Surgical effects
  • Malignant hyperthermia
  • Measurement error

Postoperative causes

  • Inadequate postoperative analgesia
  • Anxiety
  • Hypothermia
  • Raised intracranial pressure
  • Rebound hypertension after aortic valve replacement or coarctation repair
  • Anaesthetic assessment

  • Aetiology investigated
  • Cancel elective surgery if diastolic pressure >110 mmHg

Minimum investigations

  • Full blood count/urea and electrolytes (renal impairment)
  • Blood sugar (diabetes)
  • ECG (left ventricular hypertrophy or ischaemia)
  • Chest X-ray (enlarged heart or distended upper lobe veins)
  • Look for signs of end-organ damage

Continue medication

?Local blocks, e.g. brachial plexus blocks or ankle blocks

Monitoring and induction

Monitoring depends upon the degree of hypertension

Arterial line and central venous pressure line may be used

Measures to attenuate the pressor response to laryngoscopy and intubation

  • Beta-blockers
  • Short-acting opioids
  • Lidocaine to larynx or IV 1 mg/kg

Induction and maintenance using agents with cardiovascular system stability

Ketamine and pancuronium are contraindicated

Maintenance

  • Balance between light anaesthesia with hypertension and deep anaesthesia with hypotension
  • Avoid hypertension and tachycardia
  • High concentrations of volatile agents can cause hypotension by decreasing the systemic vascular resistance and by depressing the myocardium
  • Nitrous oxide can be safely used
  • Local anaesthetic nerve blocks or infiltration are useful either on their own or to supplement general anaesthesia
  • Adequate fluids; hypotension poorly tolerated

Postoperatively

  • Good analgesia
  • Adequate warming; shivering and tachycardia dangerous
  • Restart regular antihypertensive medication

Drugs used in an emergency

  • Labetalol 10-200mg IV Alpha & beta blocker:1-4 hours
  • Propranolol 1-4mg IV Beta blocker: 1-2 hours
  • Hydralazine 5-20mg IV Vasodilator: 3-6 hours
  • Nifedipine 10mg sublingual or oral Calcium channel blocker: 2-5 hours
  • Diazoxide 30mg boluses IV (max 300mg) Vasodilator: 4-12 hours

ArticleDate:20040413
SiteSection: Article
 
   
    
                                            
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