Complications of Anaesthesia

If you'd like to support us, check out our awesome products:


There are two main types of anaesthesia administered to patients to perform surgery:

Complications of anaesthesia mostly depend on the type of anaesthesia the patient has received.

This article will focus on the complications of general anaesthesia, with a short section on the complications of regional anaesthesia.

Want discounted access to all Geeky Medics products, including our medicine flashcard collection? Check out our bundles to save money and supercharge your learning πŸ”₯

Respiratory system


Injury to lips, tongue, gum, dentition and other oral soft tissue structures can occur during airway instrumentation. In patients with loose teeth, there is a risk of dislodgement and subsequent tooth aspiration.

Injury to structures of the glottis

Glottic structures, including the epiglottis, vocal cords and cartilage, can be injured during endotracheal intubation as the endotracheal tube passes through the glottis. Injury to glottic structures may result in transient changes in voice, stridor and laryngospasm. This is especially problematic in patients with difficult airways.

Sore throat

A sore throat, dryness and pain on swallowing are common but transient symptoms following a general anaesthetic. They occur due to inflammation caused by irritation following instrumentation of the airway.


Bronchospasm and laryngospasm are more common in patients with hyper-responsive airways (e.g. asthma, recent respiratory tract infection). It can also occur following aspiration of gastric contents during anaesthesia. Patients may present with hypoxia, increased CO2 and reduced ventilation.

Bronchospasm causes a classical wheeze, whereas laryngospasm is associated with high-pitched stridor.

Aspiration of gastric contents

Aspiration of gastric contents is a rare but life-threatening complication. It typically occurs in non-fasted patients with increased intra-abdominal pressure, impaired lower oesophageal sphincter competence or obtunded airway reflexes.

Pregnant patients, obese individuals, patients with hiatus hernias, patients with impaired laryngeal reflexes and patients with reduced GCS are at increased risk of aspiration.

Clinical features include bronchospasm, laryngospasm, hypoxia, increased airway pressures. Furthermore, this may collapse a lung lobe secondary to bronchial obstruction. Aspiration of gastric contents may result in pneumonia.

Injury to the trachea, bronchial structures or alveoli

This may present with subcutaneous emphysema or pneumothorax following an episode of anaesthesia. These are rare complications associated with additional airway instrumentation or complex ventilation procedures (e.g. Bougie-assisted intubations and one-lung ventilation).

Pneumothorax may also result from the rupture of pre-existing bullae.

Pulmonary oedema

Pulmonary oedema may occur in patients following laryngospasm or airway obstruction, especially during the recovery phase from anaesthesia. Inspiratory effort against the closed glottis leads toΒ excessive negative pressureΒ within the alveoli resulting in pulmonary oedema.

Pulmonary oedema should be suspected in hypoxic patients following laryngospasm. On examination, there may be audible fine bi-basal crepitations. Treatment of pulmonary oedema includes diuretics and CPAP. For more information, see the Geeky Medics guide to the acute management of pulmonary oedema.Β 

Pharyngeal obstruction

Pharyngeal obstruction is common due to sedation following anaesthesia, especially when using long-acting sedative agents. This may be worsened by obstructive sleep apnoea (OSA). Pharyngeal obstruction can be identified by snoring.

Initial management includes basic airway manoeuvres or placing the patient in the lateral position. When the cause is more deeply seated (such as in OSA), overnight CPAP may be required following a general anaesthetic.


Hypoxia is common among patients immediately following GA and is multifactorial. Hypoventilation secondary to anaesthetic agents and opioid analgesia, along with atelectasis, leads to hypoxia. This may not be apparent as most patients receive supplemental oxygen.

Patients with pre-existing respiratory disease, obese individuals and patients following upper abdominal or thoracic surgeries are more prone to hypoxia.

Pulmonary embolism

Though not a direct complication of anaesthesia, the conditions in the postoperative setting predispose to developing venous thromboembolism. Reduced mobility following surgery and increased prothrombotic factors enhance thrombus formation in deep veins. Patient-related factors such as dehydration and malignancy also contribute.

Identifying high-risk patients and using mechanical and pharmacological prophylaxis alongside general measures (e.g. good hydration and early mobilisation) is important in reducing the risk of venous thromboembolism.

Cardiovascular complications


Hypotension following anaesthesia can occur for many reasons. Anaesthetic agents can reduce the contractility of the heart and slow the heart rate. However, the effects of most of these agents are short-lived, and other causes of hypotension should be considered.

Important causes include haemorrhage (resulting in hypovolaemia) and reduced vascular tone. Other causes (e.g. myocardial infarction, pulmonary embolism and pneumothorax) should be excluded if hypotension persists despite initial management.


Anaesthesia can cause both bradycardia and tachycardia. Post-operative pain is a common cause of sinus tachycardia and should be managed appropriately. Other common causes include anxiety, electrolyte imbalances, cardiac surgery, myocardial infarctions/ischaemia, hypoxia/hypercarbia, acid-base imbalances or worsening of pre-existing arrhythmias.

Management involves identifying and treating the cause of the arrhythmia and addressing any haemodynamic compromise.


Hypertension is a common anaesthetic problem, especially in patients with poorly controlled essential hypertension. Other causes include pain, anxiety, bladder distension, fluid overload, hypoxemia, hypercarbia, and hypothermia which activate the sympathetic nervous system producing hypertension.

Significant hypertension can cause bleeding, myocardial infarction, stroke or heart failure and should be treated promptly.

Genitourinary system

Acute kidney injury (AKI)

Acute kidney injury (AKI) is a common complication in the postoperative period, which may present with a reduction in urine output or worsening of metabolic parameters (e.g. acid-base balance and electrolyte imbalance). Causes are broadly divided into pre-renal, intrinsic renal and post-renal.

Hypotension, hypovolaemia, nephrotoxic agents, sepsis or anaemia can contribute towards the development of AKI. Early identification and prompt management may reduce the progression of kidney injury. Recognising patients at high risk of AKI and focusing on correcting precipitating factors is important. Some patients may require renal replacement therapy.

Urinary retention

Urinary retention is an infrequent complication of anaesthesia. Patients at risk include older patients and those with prostatic hyperplasia. The ones who have received a spinal anaesthetic may be at higher risk.

Gastrointestinal complications

Post-operative nausea and vomiting (PONV)

PONV is a direct complication of anaesthetic agents and opioid analgesics. This is predictable, and high-risk patients should be identified so management (pharmacological and non-pharmacological) can be implemented.

Risk factors for PONV include:

  • Female sex
  • Non-smokers
  • Post-operative opioid use
  • Previous history of PONV
  • Type of surgery: laparoscopic surgery, cholecystectomy and gynaecological surgery, middle ear surgeries, squint corrections
  • General anaesthesia
  • Volatile anaesthesia

High-risk patients should be identified during the pre-operative assessment, and the anaesthetic plan should be tailored to avoid precipitants. Prophylactic antiemetic drugs are usually given. The type of antiemetics used depends on the risk assessment and other patient factors.Β  Β 


Post-operative ileus is a common complication of anaesthesia. Risk factors include type of surgery, use of opioids and hypokalaemia. Reversible factors should be managed if identified, and patients should be referred to the surgical team if required.

Post-operative ileus commonly occurs following gastrointestinal surgery, open repair of abdominal aortic aneurysms,Β and other surgical procedures where bowel handling may occur.

Neurological complications

Post-operative cognitive dysfunction

Postoperative cognitive dysfunction (POCD) is a decline in cognition apparent after a patient recovers from the acute impact of surgery and hospital stay. This may present as acute delirium or be more subtle (e.g. memory impairment, difficulty comprehending etc.).

Risk factors for postoperative cognitive dysfunction include:

  • Increasing age
  • Lower educational level
  • Cerebrovascular disease

POCD will become increasingly important as more older patients undergo surgical procedures. Patients and families should be educated on POCD with an appropriate pre-operative assessment undertaken.

Peripheral nerve injuries (positioning-related)

Peripheral nerve injuries can occur due to prolonged durations in certain positions without appropriate preventive strategies.

Table 1. Potential nerve injuries and strategies to prevent them.

Nerve/plexus Position Prevention

Brachial plexus


  • Avoid stretch or direct compression at the neck/axilla
  • Avoid using shoulder braces to support the Trendelenburg position.
  • Minimise shoulder abduction (aim <90 degrees) and avoid external rotation.
  • Avoid rotation and flexion of neck to the opposite side, try to keep head in neutral position throughout.

Common peroneal

Lithotomy and lateral decubitus

Pad lateral aspects of the upper fibula, avoid extreme lithotomy position and avoid lithotomy position for more than 2 hours



Avoid compression of the lateral humerus



Padding at the elbow, forearm supination, avoid elbow extension and extreme flexion.

Other uncommon injuries include sciatic nerve injury in thin patients with prolonged supine positioning, common peroneal nerve injury in the lithotomy position and radial nerve injury in the lateral position being compressed against the humerus. It is important to identify and manage these injuries early.

Other complications


Inadvertent perioperative hypothermia (IPH), defined as core body temperature <36Β°C, is a common consequence of general and regional anaesthesia.

Patient groups are at higher risk of developing hypothermia include:

  • High ASA grade
  • Combined regional and general surgery
  • Emergency major surgery
  • Low BMI

Adverse effects of IPH include surgical site infection, coagulopathy and increased transfusion requirements, pain, altered drug metabolism and adverse cardiac events.

Prompt pre, intra and post-operative steps will prevent the development of IPH. Keeping patients warm during the pre-operative phase, active warming during the intraoperative phase with fluid warmers and forced air warming blankets and keeping the patient covered during the recovery are all important steps in preventing IPH. Β 

Complications of regional anaesthesia

Different types of regional anaesthesia include central neuraxial blocks and peripheral nerve blocks.

Central neuraxial blocks (CNB) include

  • Subarachnoid block
  • Epidural blocks
  • Combined spinal epidural blocks

A subarachnoid block aims to place local anaesthetic in the subarachnoid space. In contrast, the local anaesthetic (LA) is placed within the epidural space in an epidural block.Β 

Different types of peripheral nerve and plexus blocks exist depending on the anatomy and region requiring anaesthesia/analgesia (e.g. brachial plexus, lumbar plexus or sciatic nerve block).Β 

For more information, see the Geeky Medics guide to regional anaesthesia.Β 

Post-dural puncture headache (PDPH)

A post-dural puncture headacheΒ  (PDPH) occurs following an intentional dural puncture (with a spinal needle) or unintentional dural puncture (with an epidural needle). The leak of CSF through the dural defect causes intracranial hypotension leading to traction on intracranial structures.

Post-dural puncture headache usually occurs 72 hours after the dural puncture. It is usually a frontal or occipital headache worsened by standing or sitting up and relieved by lying down. Patients should be referred to the anaesthetic team whenever PDPH is suspected. It is important to exclude other causes of acute headache.

Management involves bed rest, adequate hydration, avoiding situations which would give rise to an increase in intracranial pressure and simple analgesics. If the headache persists, an epidural blood patch can be performed.

Central neuraxial blocks (CNB)

Though rare, potential major neurological complications following CNB include:1

  • Cord damage: direct injury to the spinal cord or nerve roots caused by a needle or catheter, toxicity caused by local anaesthetic agents
  • Cord ischaemia: anterior spinal artery syndrome
  • Cord compression: haematoma due to needle trauma, vascular anomaly, spinal tumour, coagulation disorder/anticoagulants
  • Abscess: exogenous infections via needle or haematogenous spread
  • Meningitis

Peripheral nerve injuries

Peripheral nerve/plexus injuries may occur in patients undergoing peripheral nerve blocks. These may manifest as sensory or motor deficits along the distribution of the nerve/plexus.

Key points

  • Complications of anaesthesia depend on the type of anaesthesia (general vs regional) and patient factors
  • General anaesthesia is associated with complications involving all the organ systems, especially respiratory and cardiovascular complications
  • Regional anaesthesia/nerve blocks may have more specific complications or risks associated with the procedure
  • Pre anaesthetic assessment should identifying high-risk patients and inform the anaesthetic plan


Dr Chris Jefferies


  1. Miskovic, A., & Lumb, A. B. (2017). Postoperative pulmonary complications.Β BJA: British Journal of Anaesthesia,Β 118(3), 317-334.
  2. Freedman, R., Herbert, L., O’Donnell, A., & Ross, N. (Eds.). (2022).Β Oxford Handbook of Anaesthesia. Oxford University Press.
  3. Webster, K. (2012). Peripheral nerve injuries and positioning for general anaesthesia.Β Anaesthesia Tutorial of the Week,Β 258.
  4. Riley Π‘, A. J. Inadvertent perioperative hypothermia BJA Education, 2018. v. 18 (8).Β P. e227-e233. doi,Β 10.
  5. Mashour, G. A., Woodrum, D. T., & Avidan, M. S. (2015). Neurological complications of surgery and anaesthesia.Β British journal of anaesthesia,Β 114(2), 194-203.
  6. Cook, T. M., Counsell, D., & Wildsmith, J. A. W. (2009). Major complications of central neuraxial block: report on the Third National Audit Project of the Royal College of Anaesthetists.Β British journal of anaesthesia,Β 102(2), 179-190.


Print Friendly, PDF & Email