The authors regret that an error was present in Table 1. The correct table appears below.
Table 1.
Monitoring modalities. BIS, bispectral index; EVD, external ventricular drains; MCAfv, MCA mean flow velocity; PSI, patient state index; rSO2, cerebral regional oxygen saturation; SR, suppression ratio.
| Modality | Main indications | Overview | Advantages | Limitations | Interpretation |
|---|---|---|---|---|---|
| Near infrared spectroscopy (NIRS) | Any procedure at risk of POD, POCD and perioperative stroke (older patients, history of cerebrovascular disease or cognitive decline, major surgery). | Differential absorption of near-infrared light by oxyhaemoglobin and deoxyhaemoglobin (rSO2). | Safe, easy to use, low cost. Provides continuous information on adequacy of cerebral oxygen delivery. | Determines oxygenation under the optodes (i.e. regional). Requires further validation. | A reduction of rSO2 >20% from baseline or an absolute value below 50% may indicate cerebral hypoperfusion. |
| Processed electroenecephalography (pEEG) | Proprietary algorithmic analysis of EEG (e.g. PSI, BIS). A reduction in indices during steady anaesthetic state correlates with critical reduction in CBF. | Safe, easy to use, low cost. Detects patients at risk of oversedation, delayed emergence or intraoperative awareness. | Maps frontal cortical activity. Rapidly evolving technology. Requires further validation. | A reduction of PSI/BIS >30% indicates cerebral hypoperfusion. SR ≥50% indicates close-to-maximum suppression of CMRO2. | |
| Transcranial Doppler (TCD) | Aortic arch and carotid surgery. Patients at risk of intracranial hypertension in whom invasive ICP monitoring is not indicated. | Pulsed Doppler probes assess flow velocities in the circle of Willis. | Allows continuous assessment of cerebral autoregulation, detection of emboli and non-invasive ICP monitoring. | Technically challenging. Normal or high flow velocities do not necessarily indicate adequate perfusion (i.e. vasospasm). No information on oxygen extraction and adequacy of perfusion. | A reduction MCAfv >50% from baseline or a value below 25 cm s−1 indicates high risk of postoperative stroke. Reduced or absent diastolic flow indicates ICP close or exceeding diastolic blood pressure. |
| Intracranial pressure (ICP) | Extracranial surgery in patients at risk of intracranial hypertension (i.e. damage-control or orthopaedic surgery after major trauma). | Intraparenchymal or intraventricular pressure monitoring allows prompt identification of CBF compromise caused by intracranial hypertension. | Well validated in traumatic brain injury. Continuous assessment of CPP. EVDs allow correction of ICP by means of CSF drainage. | Invasive. Potentially significant complications (bleeding, infection). Does not assess adequacy of oxygen delivery. | ICP >20 mmHg indicates a risk of herniation. CPP <50 mmHg indicates risk of cerebral hypoperfusion. |
The author would like to apologise for any inconvenience caused.