In spine surgery postoperative pain can often be severe and difficult to treat.With the use of ultrasound, the performance of plane blocks and other techniques like root blocks, facet infiltration have become possible without the use of either unreliable " pop-techniques" or the use of x-ray.The erector spinae block was recently described as a safe and simple and safe technique for neuropathic pain and acute post surgical pain, with effect on the dorsal rami of the spinal nerves and with promising results. In this observational pilot study we want to test the influence of these to blocks on the postoperative pain and opioid consumption after spine fusion.

In 10-15 patients undergoing back surgery (laminectomy or back surgery with lumbar pedicle screw placement or revision back surgery), will be asked to give informed consent to receive a bilateral lumbar erector spinae block before surgery. In this population it will be clear after 10-15 patients if there is a beneficial effect since these patients normally require a substantial amount of postoperative opioids because of significant postoperative pain.

The blocks will be performed by experts in the field of ultrasound guided locoregional anaesthesia in a separate block room with ultrasound after placement of an iv line and application of standard monitoring (ECG, NIBP, saturation)

Description of block performance according to Chinn et al but at a lumbar level:

The patient will be placed in the lateral or sitting position. With a curve array probe or a high frequency linear probe, depending on the BMI of the patient, will be placed in a longitudinal position 2-3 cm lateral of the vertebral column. The transverse processes of the vertebrae at the (mid) level of surgery, the erector spinae muscle and the psoas muscle are identified. Depending on the depth a 5 or 8 cm 22 G ultrasound needle (pajunk) will be inserted in an in plane technique in a cephalad to caudad direction until bone contact with the top of the transverse process is reached. After slight retraction of the needle, 20 ml of ropivacaine 0,375% will be injected behind the erector spinae muscle. The same procedure will be repeated on the contralateral side.

Sensory loss of the posterior dermatomes and dermatomes of the anterior roots of the spinal nerves (lumbar plexus, upper leg) will be tested Motor function of the legs will be evaluated with a Bromage (0-3) score.

General anaesthesia will then be induced in a standardized way with propofol, sufentanyl and rocuronium. The maintenance of anaesthesia and the procedure will be performed according to protocol.

After surgery analgesia will be provided with nsaid when applicable and 1000 mg paracetamol IV 4 times daily combined with a PCA (patient controlled analgesia) pump depending on the site:

• AZ klina protocol: PCA piritramide/dhbp pump: 0ml/h, 2 mg bolus, 20 minutes lockout
• UZA protocol: Morphine/dhbp pump: 0ml/h 1 mg bolus, 8minutes lock out) and Pain scores (NRS, 0=no pain 10= worst pain ever), will be tested on the post anesthesia care unit every hour and according to hospital postoperative protocol at the ward during the fist 24 hours.

The amount and frequency of the opioid usage of the first 24 hours will be extracted out of the PCA pump. In patients without a block, opioid consumption is mostly expected between 25-40 mg morphine/24h (loading dose excluded) according to weight. We expect to see a substantial decrease (at least 50 %) in opioid consumption.

Inclusion Criteria:

• Patients planned for laminectomy or back surgery with lumbar pedicle screw placement or revision back surgery

Exclusion Criteria:

• patient refusal, bleeding disorder, infection