Comparison of the depth of the subarachnoid space using Stocker’s formula and Ultrasonographic measurements with actual depth of needle insertion in patients receiving subarachnoid block at lumbar level: A prospective observational study

The primary responsibility of the anaesthesiologist as a clinician is to administer safe anaesthesia and minimise the discomfort and complications associated with administering anaesthesia.

In this prospective observational study we studied the correlation between subarachnoid space measured by Stocker’s formula and ultrasonography with the actual depth of subarachnoid space to reduce the complications associated with multiple needle punctures, associated trauma, bleeding and neural damage.

65 patients satisfying inclusion criteria were included in the study. Demographic details of all patients were recorded and subarachnoid space depth was calculated using Stocker’s formula. Standard ASA monitors were attached to the patient. A preoperative lumbar ultrasonographic scan was performed in all individuals and the subarachnoid space measured and the site for puncture marked with a sterile dermographic marker. A blinded anaesthesiologist administered subarachnoid block through the puncture site marked previously and safe anaesthesia was administered with standard intraoperative monitoring and ensured safe recovery.

We found that it is possible to estimate subarachnoid space depth using Stocker’s formula and ultrasonography.

It was also found that Stocker’s formula was more accurate than ultrasonography in estimating SSD.

The average time taken for ultrasonography of the spine significantly increased the time to administer the block with an average of 11.14 mins ± 3.3 minutes.

54 out of 65 patients were administered the block in the first attempt and the first attempt success was found to be 83.1%.

In 92.3% cases no complications were encountered and there were no cases of failed blocks.

Hence, we conclude that

The use of Stocker’s formula is a reliable and easy formula which can be used to estimate the depth of subarachnoid space to reduce the number of complications associated with multiple punctures and trauma.

Ultrasound can also be used to measure the same with additional benefits of real time assessment of the spine and anatomy but with the drawback of time consumption.