Nociception-directed Erector Muscle Spinae Plane Block in Open Heart Surgery

DETAILED DESCRIPTION OF STUDY

A. Ethics

Local Ethics Committee approval and Informed Consent from patient or next-of-kin are obtained prior to study enrolment.

B. Study enrolment

Eighty adult patients scheduled for elective open cardiac surgery under general anaesthesia (GA) are randomly allocated to receive either GA plus ESP block (ESP group, n = 40) or GA alone (control group, n = 40).

C. Methods - Preinduction

1. Premedication with intramuscular morphine 0.1mg/kg 30 minutes before induction.
2. 16-G peripheral intravenous cannula and radial artery catheter.
3. Five-lead ECG, pulse oximetry, non-invasive and invasive blood pressure monitoring.
4. Analgesia monitor - the NoL index (PMD200TM, Medasense) finger probe will be connected to the index finger of the non-cannulated hand.
5. Surgical antibiotic prophylaxis (Cefuroxime 1.5g)
6. Stress ulcer prophylaxis (omeprazole 40 mg)

D. Methods - ESP block (intervention group only)

Before induction, patients in the intervention group are placed in sitting position under the close supervision of the attending nurse anaesthetist. After skin asepsis with chlorhexidine 2%, a high-frequency linear ultrasound probe is positioned parasagittally, 2-3 cm from midline, bilaterally, at the level of the T5 transverse process. A 25-G echogenic block needle is inserted at 20⁰-30⁰ in a caudal-to-cephalad direction until the tip of the needle reaches the interfascial plane between the erector spinae muscle and the inter-transverse ligaments. Correct hydrodissection at T5 level is first certified using normal saline. Subsequently, ropivacaine 0.5% with dexamethasone 8mg/20ml is used and maximum spread is attained by slowly advancing the needle as the interfascial plane splits up ahead. A maximum dose of 3mg/kg ropivacaine is used, corresponding to 1.5 mg/kg per side (e.g., 20 ml ropivacaine 0.5% / side for a 70kg adult). Supine position is resumed after completion of block.

E. Methods - General anaesthesia

1. End tidal CO2 (ETCO2).
2. Bispectral index (BIS) monitoring of hypnotic depth (target 40-60).
3. The nociception monitor (PMD200TM, Medasense) is started after induction of general anaesthesia; a calibration period of 1-2 minutes is usually required.
4. CVP insertion into the right internal jugular vein under ultrasound guidance. Any other hemodynamic monitor deemed useful is left at the discretion of the treating anaesthetist.
5. Urinary catheter, rectal temperature probe placement.

6. Intubating conditions

   6.1. Propofol 1-1.5 mg/kg or Etomidate 0.2-0.3 mg/kg.

   6.2. Fentanyl 5 mcg/kg.

   6.3. Atracurium 0.5 mg/kg.

7. Maintenance of anaesthesia

7.1. Sevoflurane in O2 during periods of preserved pulmonary blood flow and mechanical ventilation according to BIS (see target above).

7.2. Propofol infusion according to BIS (see target above) during periods of extracorporeal support.

7.3. Atracurium 0.2-0.3 mg/kg/h for adequate neuromuscular blockade.

7.4. Management of analgesia divides in:

7.4.1. Analgesia support

7.4.1.1. ESP block in the intervention group only:

• Theoretical duration of ESP block with surgical intensity is 4-6 hours.

7.4.1.2. Fentanyl (both study groups):

• Analgesia monitoring (see below) provides feedback to its administration.

• Administration follows a combination of continuous infusion and bolus dosing according to our local protocol:

  • Fentanyl 1.5 mg/50ml (30 mcg/ml).
  • Bolus dose (ml): Weight/20, which is equivalent to 1.5 mcg/kg.
  • Infusion rate (ml/hour): Weight/10, which is equivalent to 3 mcg/kg/h.
  • Last infusion rate before large vessel cannulation is maintained throughout the bypass period.

7.4.1.3. Paracetamol (both study groups):

• Administration of 2 grams following induction of general anaesthesia.

7.4.2. Analgesia monitoring

7.4.2.1. NoL index provides a multiderivative assessment of nociception before large vessel cannulation; depending on the spontaneous cardiac rhythm, it may be expected to continue reflecting nociception even after completion of extracorporeal circulation.

• Optimal analgesia is defined as a NoL index of 10-25.
• Allow periods of fluctuation of less than 1 minute.
• After sternotomy, allow a maximum fluctuation interval of 3 minutes before vital data are gathered.
• In the ESP group, if NOL target is attained, stop fentanyl administration.

7.4.2.2. Ancillaries such as mean arterial blood pressure (MAP) and heart rate (HR) provide complementary decision loops: targets are within ± 20% of preoperative baseline.

• During CBP they provide the only feedback on adequacy of analgesia, although highly unspecific.
• May be used at any time to complement the NoL index.

F. Methods - Postoperatively

1. Criteria to be met before extubation:

   1.1. Normothermia (T◦ ≥ 36◦C).

   1.2. No clinical bleeding.

   1.3. Wakefulness and RASS [-1;1].

   1.4. Hemodynamic stability with minimal vasoactive support (dobutamine \< 5 µg/kg/min and norepinephrine \< 100 ng/kg/min):

   1.4.1. MAP ≥ 60 mmHg

   1.4.2. Lactate ≤ 2 mmol/L

   1.4.3. Preserved flow (CI ≥ 2.2L/min/m2) assessed by:

   1.4.3.1. TTE any time after ICU admission

   1.4.3.2. TOE only before extubation, regardless of patient location

   1.5. Respiratory:

   1.5.1. Adequate gas exchange:

   1.5.1.1. Normocarbia.

   1.5.1.2. PaO2/FiO2 ≥ 250.

   1.5.2. Adequate effort:

   1.5.2.1. Tidal volume ≥ 5 ml/kg.

   1.5.2.2. Negative inspiratory force ≤ -20 cmH2O.

   1.5.3. Adequate airway reflex to handle secretions.

2. Management of analgesia divides in:

2.1. Analgesia support:

2.1.1. Paracetamol 1g iv 6 hourly is standard in both groups.

2.1.2. Morphine bolus doses of 0.03 mg/kg in combination with continuous iv morphine 0.03 mg/kg/h as elicited by nociception monitoring (see below).

2.2. Analgesia monitoring

2.2.1. The visual analogue scale (VAS) is used to provide feedback on adequacy of analgesia.

2.2.2. If VAS > 3, then provision of a combination of paracetamol and morphine is warranted (see above).