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Correspondence |
Valencia, Spain
To the Editor:
I agree with Kuczkowski and Benumof,1 and with others who reviewed the topic,2–4 that saline is the fluid of choice to detect the epidural space (ES) using the loss of resistance (LOR) technique. However, other aspects should be considered. Some of them have been previously discussed,1–4 but others have sparsely been considered. Due to the patient’s position (sitting) during the attempted epidural, in the event of a dural puncture air will migrate into the central nervous system (CNS), producing the symptoms described. Theoretically, lumbar puncture in the lateral decubitus cannot produce a pneumocephalus. On the other hand, although controversial, there is a trend to change from air to saline to determine LOR amongst obstetric anesthesiologists.4 However, if the operator is experienced in the LOR to air, the incidence of pneumocephalus should be low. The volume of air or saline used to detect the ES is, in my opinion, of capital importance with respect to both interference with the effects of local anesthetics,2 and with the adverse CNS effects in the case of a subarachnoid injection. Most of the clinical notes published reported amounts greater than 3 to 4 mL of air injected, both as a single bolus, or as repeated boluses in difficult epidurals. Usually a small volume of 1 to 2 mL of air is sufficient to detect the ES. In some patients, changing from air to saline can be an option for repeated attempts. If a pneumocephalus occurs, nitrous oxide should be avoided when an epidural is combined with a general anesthetic.
References
1 Kuczkowski KM, Benumof JL. Images in Anesthesia: Headache caused by pneumocephalus following inadvertent dural puncture during epidural space identification: is time to abandon the loss of resistance to air technique? Can J Anesth 2003; 50: 159–60.
2 Saberski LR, Kondamuri S, Osinubi OY. Identification of the epidural space: is loss of resistance to air a safe technique? A review of the complications related to the use of air. Reg Anesth 1997; 22: 3–15.[Medline]
3 Shenouda PE, Cunnigham BJ. Assessing the superiority of saline versus air for use in the epidural loss of resistance technique: a literature review. Reg Anesth Pain Med 2003; 28: 48–53.[Medline]
4 Howell TK, Prosser DP, Harmer M. A change in resistance? A survey of epidural practice amongst obstetric anaesthetists. Anaesthesia 1998; 53: 238–43.[Medline]
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