Pythagoras and Cosines: The skin-dural sac distance and optimal angles in paramedian spinal anesthesia.
The classical recommendation for paramedian approaches is needle insertion 1-2 cm paramedian and an angle of 10°-15° medial-cephalad to the plane of the back, but contact with vertebrae is frequent. A mathematical approach to individualizing punctures is proposed on the basis of skin-dural sac distance (d): Optimal angle ∼ inverse cosine [d/ √(1+d^2) ] and the distance covered by the needle ∼ √(1+d^2) for 1 cm paramedian punctures. The inferred angles were compared to optimal angles leading to the central dorsal part of the dural sac from 1 to 2 cm paramedian, measured by Magnetic Resonance Imaging (MRI) in seven cases and in a short stature volunteer (1.58 m, Body Mass Index (BMI) 23.2), to study supine and fetal positions using both closed MR and ultrasound. The average (d) decreased rostrally [6.8 cm (L4-L5)-4.3 cm (T11-T12)] while the mean optimal incidence angles increased [8.3°-16.5° (L4-L5) to 12.7°-24.1° (T11-T12) at 1-2 cm paramedian, respectively] and coincided with the estimated angles with a correlation coefficient = 0.98. In the volunteer, the optimal lateromedial angles increased from 14.4° to 26.7° (L3-L4) to 17.1°-30.3° (T11-T12) for a (d) = 3.7 cm (L3-L4)-3.1 cm (T11-T12) and increased ≤3.7° and ≤5.1° at 1 and 2 cm paramedian, respectively, in fetal positions in MR. Ultrasound yielded comparable figures. The range of possible angles for dural punctures is wider at 1 cm paramedian in lower approaches in lateral decubitus [from 3.6° at T12L1 (12.2°-15.8°) to 9° at L3L4 (8.8°-18.7°)]. The classically recommended angles of 10°-15° differ from the optimal angles, particularly in small patients, suggesting the need for ultrasound guidance or for inferring angles prior to spinal anesthesia. Clin. Anat. 29:1046-1052, 2016. © 2016 Wiley Periodicals, Inc.
Human Anatomy and Embryology Unit, Faculty of Medicine, University of Barcelona, Barcelona, 08036, Spain. apuigdellivol@ub.edu.|Antón de Borja Primary Care Center, Terrassa Health Consortium, Rubí, 08191, Spain. apuigdellivol@ub.edu.
Anna
A
Puigdellívol-Sánchez
Department of Anesthesiology, Madrid-Montepríncipe University Hospital, and School of Medicine, CEU San Pablo University, Madrid, 28660, Spain.
Miguel A
MA
Reina
Human Anatomy and Embryology Unit, Faculty of Medicine, University of Barcelona, Barcelona, 08036, Spain.|Department of Anesthesiology, Hospital Clínic, Universitat de Barcelona, Barcelona, 08036, Spain.
Xavier
X
Sala-Blanch
Department of Anesthesiology, Hospital Clínic, Universitat de Barcelona, Barcelona, 08036, Spain.
Jaume
J
Pomés-Talló
Human Anatomy and Embryology Unit, Faculty of Medicine, University of Barcelona, Barcelona, 08036, Spain.
Alberto
A
Prats-Galino
D000328:Adult; D000775:Anesthesia, Spinal / Q000379:methods*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D012016:Reference Values; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging*; D014463:Ultrasonography; D055815:Young Adult
adverse effects of needles; magnetic resonance imaging; paramedian spinal anesthesia