Intraoperative events encompass all physiological changes, complications, and unexpected situations that arise during surgery — that is, from anaesthesia induction through to the end of the procedure. Throughout this period, the anaesthesiologist does not merely keep the patient asleep; they continuously monitor, interpret, and intervene in response to constantly shifting physiological conditions. The intraoperative period represents the most dynamic and decision-intensive component of anaesthetic practice.
Cardiovascular Events
Hypotension The most frequently encountered cardiovascular event during surgery. It can develop as a result of the vasodilatory effects of anaesthetic agents, inadequate fluid replacement, bleeding, or a fall in cardiac output. Mild hypotension is corrected with a fluid bolus and positional changes, while resistant cases require vasopressors such as ephedrine, phenylephrine, or noradrenaline.
Hypertension Can arise from inadequate depth of anaesthesia, a response to painful stimulation, hypercapnia, or pre-existing hypertension. It is managed by deepening anaesthesia, adding opioids, or administering antihypertensive agents.
Tachycardia and Bradycardia Tachycardia may develop due to light anaesthesia, hypovolaemia, pain, or drug interactions. Bradycardia is seen with vagal reflex activation — particularly in ocular, abdominal, and neck surgery — as well as with drug effects and hypercapnia. Both are treated according to their underlying cause.
Arrhythmias Electrolyte imbalances, hypercapnia, myocardial ischaemia, drug interactions, and surgical stimulation can all provoke various rhythm disturbances. Continuous ECG monitoring is therefore maintained throughout the intraoperative period.
Myocardial Ischaemia In patients with coronary artery disease or high cardiovascular risk, the stress of surgery can trigger myocardial ischaemia. ECG changes and haemodynamic fluctuations may herald this condition.
Respiratory Events
Bronchospasm A bronchial constriction triggered by airway manipulation, a history of asthma, smoking, or allergen exposure. It manifests as rising peak airway pressure and expiratory wheeze. It is treated with bronchodilators, deepened anaesthesia, and corticosteroids.
Laryngospasm A reflex response in which sudden spasm of the vocal cords partially or completely closes the airway. It can occur when secretions, blood, or a foreign body contacts the vocal cords, or during a light plane of anaesthesia. It is managed with positive pressure ventilation and, where necessary, a low dose of suxamethonium.
Hypercapnia and Hypocapnia Carbon dioxide accumulation (hypercapnia) results from inadequate ventilation or increased metabolic activity, while excessive ventilation leads to hypocapnia. Both adversely affect cerebral blood flow, cardiac rhythm, and acid-base balance, and are corrected through ventilator adjustments.
Hypoxaemia A fall in arterial oxygen saturation. It can arise from atelectasis, bronchospasm, pulmonary embolism, pneumothorax, or endobronchial intubation. Management involves increasing the inspired oxygen concentration, applying PEEP, and treating the underlying cause.
Pneumothorax Can develop particularly during upper thoracic or neck surgery, central venous catheter insertion, or as a consequence of mechanical ventilation causing lung injury. It presents with sudden haemodynamic deterioration and a drop in oxygen saturation, and may require emergency tube thoracostomy.
Neurological Events
Anaesthesia Awareness A state in which the patient partially regains consciousness during surgery and becomes aware of their surroundings or experiences pain. In modern anaesthetic practice, this risk has been substantially reduced through BIS (bispectral index) monitoring. Inadequate depth of anaesthesia is the primary cause.
Intraoperative Seizures Can occur in patients with a history of epilepsy or during cranial surgery. They are treated with benzodiazepines and propofol.
Cerebral Ischaemia Brain perfusion can be compromised in situations such as prolonged hypotension, embolism, or cardiac arrest. Specialised neuromonitoring techniques are employed in neurosurgical and cardiac surgery cases.
Metabolic and Biochemical Events
Malignant Hyperthermia A rare but life-threatening pharmacogenetic disorder. Exposure to triggering agents such as suxamethonium or volatile anaesthetics initiates uncontrolled hypermetabolism in skeletal muscle. It manifests as a rapidly rising body temperature, muscle rigidity, acidosis, and hypercapnia. Dantrolene sodium is the specific antidote; prompt administration is life-saving.
Hypoglycaemia and Hyperglycaemia In diabetic patients and those receiving intensive insulin therapy, blood glucose fluctuations are an important parameter to monitor throughout surgery. Both hypoglycaemia and significant hyperglycaemia adversely affect wound healing, infection risk, and neurological outcomes.
Electrolyte Imbalances Hypokalaemia, hyperkalaemia, and hypocalcaemia can predispose to cardiac arrhythmias. Large-volume fluid replacement, massive transfusion, and renal dysfunction are the main causes of these imbalances.
Acid-Base Disturbances Metabolic or respiratory acidosis and alkalosis impair drug efficacy, cardiac function, and clotting mechanisms during surgery.
Haematological Events
Massive Haemorrhage Life-threatening bleeding can occur in trauma, vascular surgery, or major organ resections. Massive transfusion protocols are activated, combining packed red blood cells, fresh frozen plasma, platelets, and cryoprecipitate.
Coagulopathy Disseminated intravascular coagulation (DIC), dilutional coagulopathy, and hypothermia-induced coagulopathy are serious complications of massive haemorrhage. Coagulation status can be monitored in real time using thromboelastography (TEG/ROTEM).
Anaphylaxis A severe allergic reaction to agents such as latex, antibiotics, muscle relaxants, and contrast media. It presents with hypotension, bronchospasm, and urticaria. Epinephrine is the primary treatment.
Thermoregulatory Disturbances
Hypothermia Intraoperative hypothermia can develop rapidly from the combination of a cold operating theatre environment, open body cavities, and large volumes of unwarmed fluid infusion. It leads to coagulopathy, cardiac arrhythmias, wound infection, and prolonged recovery. It is prevented with forced-air warming systems and warmed intravenous fluids.
Malignant Hyperthermia Discussed in detail above; an acute, life-threatening hyperthermia triggered by a pharmacogenetic susceptibility.
Position-Related Complications
Different surgical positions carry their own specific risks. The lithotomy position is associated with compartment syndrome and lower extremity nerve injury; the prone position with raised intraocular pressure, retinal ischaemia, and brachial plexus injury; and the sitting position with venous air embolism. The anaesthesiologist assesses position-specific risks in advance and takes the necessary precautions.
Venous Air Embolism
Occurs when air enters the surgical field under negative pressure. The risk is highest in neurosurgical cases performed in the sitting position and in certain orthopaedic procedures. Early diagnosis can be made using capnography and transoesophageal echocardiography.
Intraoperative Monitoring
Early recognition and management of all these events depends on comprehensive monitoring. Standard monitoring includes ECG, non-invasive blood pressure (NIBP), pulse oximetry (SpO₂), capnography (EtCO₂), and body temperature. In high-risk cases, additional monitoring may include invasive arterial blood pressure, central venous pressure, transoesophageal echocardiography, BIS monitoring, and neuromuscular transmission monitoring.
Conclusion
The intraoperative period is the most critical and intervention-intensive phase of anaesthetic practice. The vast majority of events that can arise during this time are recognised early and successfully managed by an experienced anaesthesiologist. Thorough preoperative assessment, careful drug selection, and uninterrupted monitoring significantly reduce both the frequency and severity of intraoperative complications.
This content has been prepared for general informational purposes only. Please consult a specialist for your individual health situation.