Waveform characteristics in thoracic paravertebral space: a prospective observational study

Fifty patients scheduled for elective lung surgery (open thoracotomy and video-assisted thoracoscopic surgery) were recruited during 9^th February 2021 to 18^thMay 2021.

Anesthesiology residents or fellows at Ramathibodi Hospital obtained

preoperative information and provided informed consent. The inclusion criteria

were an age of 18 to 80 years and an American Society of Anesthesiologists

(ASA) physical status of I to III. The exclusion criteria were no provision of

informed consent, refusal to receive TPVB, a body mass index of > 35 ²g/m2,

significant thoracic kyphoscoliosis, coagulopathy (platelet count of

<100,000 per mL or international normalized ratio of >1.4), allergies or

contraindications to medications used in the study protocol, and refusal to

participate or withdrawal of consent at any stage of the study.

All enrolled patients were fasted for at least 8 hours before surgery. Standard ASA monitoring was

performed throughout the surgery. Anesthesia was induced using propofol

(2.0–2.5 mg/kg), fentanyl (1–2 mcg/kg), and cisatracurium (0.15–0.2 mg/kg) intravenously.

First, the tip of the needle was identified in the paraspinal muscles. Second, the needle tip was

advanced immediately posterior to the superior costotransverse ligament (SCTL)

and confirmed by a 1.0-mL normal saline injection. Third, the needle tip was located

in the TPVS and confirmed by a 0.5- to 3.0-mL saline injection, which widened

the TPVS and caused anterior displacement of the pleura.

The operator identified the first rib and then counted downward until the fourth rib was

reached. The probe was then moved inward to locate the fourth transverse

process. The ultrasound probe was then dragged downward to locate the fifth

transverse process and identify the location of the TPVS between T4 and T5, labelling

the site with an indelible pen. The ultrasound probe was moved further downward

to locate the sixth and seventh transverse processes and the TPVS was marked

between T6 and T7.

An echogenic needle (SonoTAP; Pajunk GmbH Medizintechnologie, Geisingen, Germany) was connected to a pressure transducer system (TruWave PX260; Edwards Lifesciences, Irvine, CA, USA) via a three-way stopcock (Discofix 3SC; B. Braun, Melsungen, Germany) and a 36-inch

noncompliant pressure tubing (Edwards Lifesciences). The pressure transducer

was connected to a desktop monitor (IntelliVue MP70; Philips, Amsterdam,

Netherlands) and levelled at the spinous process. The needle was then inserted

at the skin approximately 3 cm from the midline and advanced laterally to

medially under in-plane ultrasound visualization. The pressure values and

characteristics of the thoracic paravertebral waveform were recorded along the

needle trajectory in three steps.

The operator then slowly injected 15 mL 0.33% bupivacaine into each desired TPVS. The collected

waveforms were classified into three patterns (A, B, and C) according to our

pilot study and based on previous trials. The “A” waveform was defined as a

smooth and regular sine wave resembling the respiratory pattern with a mean

value of ≤ 25 mmHg; the “B” waveform was defined as an irregular coarse, wavy

line with a mean value of ≤ 40 mmHg; and the “C” waveform was defined as a

tense, straight line with a mean value of > 40 mmHg.