The spinal needle test effectively measures abdominal wall thickness before cannula placement at laparoscopy

Study Objective. To demonstrate the usefulness of the spinal needle test at laparoscopy to correlate abdominal wall thickness at initial entry sites with body mass index (BMI). Design. Prospective cohort study (Canadian Task Force classification). Setting. University-affiliated hospital. Patients. One hundred thirty-eight women. Intervention. Diagnostic laparoscopy. Measurements and Main Results. After CO₂ insufflation, the spinal needle test was performed by inserting a spinal needle attached to a partially filled syringe and advancing it perpendicular to the skin until the gas pocket was reached. To improve precision, the distance was measured 3 times at two sites, the umbilicus and Palmer's point (left upper quadrant). Patients' mean BMI was 25.8 kg/m² (range 17.2-60.0 kg/m²), with 24 (17%) considered clinically obese (BMI ≥ 30 kg/m²). A significant correlation was noted between BMI and abdominal wall thickness at the umbilicus (R = 0.69) and left upper quadrant (R = 0.81). Excellent correlation was also noted between body weight and thickness at the two points (R = 0.72 and R = 0.78, respectively). The mean thickness at the umbilicus differed significantly between obese (3.0 ± 1.2 cm) and nonobese women (1.7 ± 0.7 cm, p < 0.001); as did mean thickness at the left upper quadrant (4.4 ± 1.0 vs 2.0 ± 0.7 cm, p < 0.001). Conclusion. Thickness of the abdominal wall at umbilical and left upper quadrant entry sites correlates well with weight and BMI. Even among obese women, the distance to the pocket of gas after insufflation at either entry site is remarkably small.