Etiology and Use of the “Hanging Drop” Technique: A Review

Table 4

Summary of studies on epidural pressure.

Author (year)	Level	𝑛	Epidural pressures	Comments
Galbert and Marx (1974) [7]	Lumbar	12	All positive	Pressures transduced from epidural catheter
Gil et al. (2008) [3]	Thoracic	28	Consistent negative epidural pressures in the sitting position only at T5-6	Pressures measured 120 s after entry into the epidural space
Johnston et al. (1989) [8]	Lumbar	14	All positive	Pressures transduced from epidural catheter
Messih (1981) [9]	Lumbar	21	All positive upon needle entry and after catheter insertion	Pressures measured in parturients
Moon et al. (2010) [4]	Cervical	30	All positive in the prone position, 10/15 negative in the sitting position	Pressures measured 120 s after entry into the epidural space
Okutomi et al. (1993) [6]	Thoracic	13	Initial negative pressure right after puncture, positive in 12/13 patients after 90 s.	Lateral decubitus position at T7-8
Rocco et al. (1997) [10]	Lumbar	25	All positive after needle was stabilized in the epidural space	negative in 4/4 patients where pressure was measured upon entry
Rodiera et al. (1995) [11]	Lumbar	20	All positive	Pressures measured >5 s. after entry into the epidural space
Shah (1981) [12]	Lumbar	43	All positive	Pressures transduced from epidural catheter
Shah (1984) [13]	Lumbar	40	All positive	Pressures transduced from epidural catheter
Takahashi et al. (1995) [14]	Lumbar	10	All positive	Measurements performed with a catheter transducer
Takahashi et al. (1995) [15]	Lumbar	19	All positive	Measurements performed with a catheter transducer
Thomas et al. (1992) [16]	Lumbar	39	All positive	Pressures measured 180 s after entry into the epidural space
Usubiaga et al. (1967) [17]	Lumbar	16	Consistent negative pressures measured at the time of entry into the epidural space, all positive pressure measurements after needle stabilization	Lateral decubitus position
	Thoracic
	Cervical
Usubiaga et al. (1967) [5]	Cervical	405	Consistent negative thoracic/cervical pressures in the sitting position	Pressures measured at the time of entry into the epidural space
	Thoracic		Negative lumbar pressures in 42/48 patients in the sitting position
	Lumbar		Negative lumbar pressures in 202/228 patients in the lateral decubitus position
Visser et al. (2006) [18]	Thoracic	40	Negative pressures in 8/17 patients at T3–T5 and 2/20 at T7–10 (lateral decubitus)	Pressures measured 120 s after entry into the epidural space
Zarzur (1984) [19]	Lumbar	30	Negative pressures in 24/30 patients upon entry into the epidural space

Results are listed as either below (negative), or above (positive) atmospheric pressure.