Aspiration for blood (if it enters the vein) or CSF (if the dura mater is punctured ) with caudal access is more important than with intervertebral, because the position of the patient’s body, posture in vivo (with a pillow under the pelvis) or knee-pectoral position , does not contribute to the independent flow of blood or cerebrospinal fluid even through a thick needle. Unfortunately, blood and cerebrospinal fluid are not always collected through a thin needle into a syringe, even when a vein or dural sac is punctured (this is why
long puncture with a thicker needle — not only easier, but safer). The more important is the introduction of the test dose .
A test dose of local anesthetic mixed with adrenaline (1: 200.000) is administered according to the same principles as for intervertebral access. And the volume may be sufficient for low spinal anesthesia, the local anesthetic solution must contain epinephrine, and we must wait for the effect for 5 minutes, checking blood pressure, pulse and the presence of anesthesia or unusual sensations in the patient.
But here it can also be used to further confirm the needle’s stay in the sacral canal. To do this, it is introduced quickly (watching if the skin does not “inflate” over the sacrum), and then quickly remove the finger from the syringe piston. If the needle is dorsal (on the back) of the sacrum (under the skin or in a bundle), the piston will move back slightly with a light stroke, and from 0.5 ml to 1 ml of solution will return to the syringe. If the needle is in the sacral canal, no more than 0.2 ml will return or nothing will return.
The main dose is administered slowly, if you do not want an unexpectedly high (and also uneven) anesthesia. In addition, with the rapid introduction of a significant amount, transient arterial hypertension is possible (see below). Complaints of bursting and even pain in the thighs and lower legs when the main dose is injected show only the correct position of the needle. When the needle is ejected, you can add a little more local anesthetic (up to 5 ml) for additional anesthesia of the punctured (and with repeated attempts — well-pricked) tissues.
The time of onset of the effect (if reliable surgical anesthesia is needed) is at least 20 minutes. With labor anesthesia, the third contraction after performing caudal analgesia can be less painful.
Repeated doses (if a short cannula or a long catheter remains) are administered only after the test dose.