A comparison of non-invasive versus invasive methods of haemoglobin estimation in patients undergoing intracranial surgery

Background: Until recently, invasive monitoring techniques were the only ones available for the estimation of haemoglobin (Hb) in the blood. However, following the introduction of a new non-invasive monitor, Hb concentration could be non-invasively and continuously monitored. It allows immediate and ongoing Hb changes to be displayed during surgery, which may aid in the rapid detection of clinically significant blood loss. To test the accuracy of this non-invasive monitor, we compared Hb levels obtained using standard invasive techniques (laboratory and arterial blood gas machine analysis) with those derived from a non-invasive monitor.Method: Thirty patients undergoing various intracranial surgeries were enrolled in the study. Blood samples were withdrawn for Hb estimation from the laboratory [total haemoglobin mass (tHb)] and arterial blood gas (ABG) machine (aHb), using automated Hb analyser techniques randomly at any point during the surgery. At the same time, the Hb values displayed on the non-invasive monitor [Radical-7® Pulse Co-oximeter (SpHb®)], together with the perfusion index (PI), were also noted.Results: The perfusion index (PI) was less than 1.4 in eight patients. The obtained Hb values were unreliable, as per the manufacturer’s recommendations. Statistical analysis showed poor correlation between the invasive and non invasive techniques of Hb estimation in the remaining 22 patients.Conclusion: Non-invasive Hb monitoring (SpHb®) may not have sufficient accuracy to minimise the need for invasive Hb monitoring. However, it may allow continuous monitoring of Hb and could guide clinicians as to the need for invasive monitoring.Keywords: comparison, haemoglobin estimation, intracranial, invasive, monitoring, non-invasive, surger

Transcranial Doppler

Transcranial Doppler (TCD) is a bedside, non-invasive, reproducible, non-expensive neuromonitoring device which can be used in many clinical scenarios. Based on the principle of the Doppler shift, blood flow velocity (FV) in the cerebral vessels can be measured. It should be noted that TCD measures blood FV and not the cerebral blood flow (CBF). However, in a given condition, FV can be used as a surrogate marker for vessel diameter or CBF. Indirectly, it can also measure the CBF and the intracranial pressure. This review describes briefly the method of using the equipment and the various indices that can be measured. The applications of TCD are varied. The review also gives an account of the various clinical situations where TCD can be used. An inter-operator variability is an important limiting factor with the use of the TCD. However, in many of clinical scenario, the TCD can still be used to guide for decision-making