High pressure ( resistance to injection ) can be the only indicator of an intramural injection. Ban Tsui has developed and validated a simple method of pressure monitoring.
1 - draw up an extra column of air in the local anesthetic syringe
2- hold the syringe vertically so that the local is dependent and the column of air is siting on top between the local anesthetic and the syringe plunger
3- The column of trapped air acts like a cushion. If you have to push with force and the air is compressed by 50% or more, stop injecting because that pressure ( about 1 atm) is way too high and associated with injurious intramural injection.