Loss of resistance

paindoc · Oct 23, 2006

Use of air is far more hazardous than saline for loss of resistance techniques. There have been reported cases and series of pneumocephalus, canal compression, nerve root compression, intraventricular air, and several other unnecessary complications due to the use of air. The use of air in several studies has been shown to prevent adequate spread of the anesthetics administered in the epidural space. The use of air in other countries is waning, but not here in the states.

zrmorgan · Oct 24, 2006

used air in school for 2 years in a very busy obstetric practice where all but 2 or 3 providers used air and never saw or heard of a pneumocephalus case.

now using saline with a small air bubble and am liking the feel of it...seems like a more definitive loss when it occurs.

did a research project on it last year in school, seems it was very controversial when it came to safety or success rates. there was one article that suggested that quality of analgesia may be better with saline...the authors discussed possiblity of less patchy block.

good review article: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=15098532&query_hl=1&itool=pubmed_docsum

another article from this year: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=16918122&query_hl=1&itool=pubmed_docsum

I think those that are touting the use of air as dangerous are probably imagining people injecting large volumes of air in the space inadvertently or otherwise. Just a rough estimate, I would inject probably less than 2cc when I was using air for LOR. A volume hardly sufficient to cause a pneumocephalus.

paindoc · Oct 24, 2006

Sorry, but pneumocephalus does not mean filling the entire cranial vault with air. 1cc of air can easily travel subarachnoid during a noted or unrecognized dural puncture, and cause a whopping headache for many days.

Below is part of a monograph I wrote on the subject:

While it is difficult to appreciate the incidence of unintended subarachnoid injection due to a paucity of studies on the subject, there is some evidence the incidence of unrecognized subarachnoid/subdural placement up to 7% (635). The dural puncture rate is as high as 3.6% in the obstetrical population undergoing epidural labor analgesia. (838). One study using epidural access for placement of steroids had a 4% recognized dural puncture rate and a 2% unrecognized dural puncture rate for a total of 6% rate (600).

The other issues regarding inadvertent subarachnoid puncture relates to the injection of undesired substances into the cerebrospinal fluid, and the complications of the dural puncture itself. The loss of resistance technique is the most common method of locating the epidural space when a blind, non-fluoroscopic guided technique is employed. Frequently, air is used as the injectate, although by 2006 in the UK, the percentage of anesthesiologists using air had fallen to 25% (820). In Spain, the use of air loss of resistance in 2005 was 59%. (821). In the US, air loss of resistance remains commonly employed. The use of air instead of liquid for determining the loss of resistance causes a significant increase in dural punctures (647). If air is inadvertently injected subarachnoid or subdural, the results may range from mild side effects to catastrophic. Since interlaminar epidural injections are frequently performed without the benefit of diagnostic fluoroscopy with contrast study, the actual location of any air injection is speculative. However, a strictly epidural injection would be very unlikely to cause a pneumocephalus due to the termination of the epidural space at the foramen magnum. Certainly a subarachnoid injection of air could rapidly ascend to the brain, causing severe headache with radiological evidence of pneumocephalus. This complication has been reported on primary epidural access using the air loss of resistance technique for labor epidural analgesia (822, 836). In the first case, after 4ml air injected, it was noted CSF effluxing from the needle, and there was an immediate onset of a severe occipital headache that required seven days before spontaneous resolution. Pneumocephalus has also been reported with air loss of resistance during an attempted epidural blood patch as a treatment for a post lumbar dural puncture headache. The onset of symptoms was immediate and was associated with a positive brain CT for subarachnoid air. There was no clinical evidence of a new dural puncture during the air loss of resistance location of the epidural space. due to a previous dural puncture. (823). There are other reports of pneumocephalus after attempted epidural access (837). A large study (n=3,730) demonstrated a 7 times higher incidence of post dural puncture headaches when using air for the loss of resistance compared with saline.(839).

Other more severe complications from air injection during air loss of resistance location of the epidural space include generalized convulsions and loss of consciousness associated with pneumocephalus (824), paraplegia due to nerve root displacement from injected peridural space air (825), and in a review by Saberski spinal cord compression, retroperitoneal air, subcutaneous emphysema, and venous air embolism. (826)

Saberski and others (827) have called for the end of air loss of resistance usage with the substitution of saline loss of resistance that is devoid of these complications, yet the former technique inexplicably persists with significant numbers of uses today.

catcolalex · Oct 24, 2006

I trained with saline, and have tried air to see what it feels like, I think that saline gives a much better definitive loss of resistance feel simply because you cannot compress it. you can compress air which, to me, muddies the water, also, paindoc brings up more reasons why i choose saline.

zrmorgan · Oct 25, 2006

paindoc-

an interesting and thorough monograph. if you would please post the references (647) and (839). I am not surprised to see the info about increased risk of dural puncture with air. From personal experience (as well as another post I read by cato) the noncompressible fluid with saline LOR feels a lot more definitive early on, allowing more precision. Furthermore, I believe a small amount of saline in the epidural space may ease the threading of the cathetar.

I believe if we had some sort of study demonstrating an increased risk of pneumocephalus or nerve root compression (or other catastrophic complication) then the issue would be put to rest here in the US, and we could teach students how unsafe it may be. Unfortunately, it is still considered "controversial" where I was taught. I believe this is largely due to the comfort level of our experienced anesthetists. It was hard to raise the debate with anyone with a few case studies. This is why I am interested in the articles you are citing.

paindoc · Oct 25, 2006

647. Valentine SJ, Jarvis AP, Shutt LE. Comparative study of the effects of air or saline to identify the extradural space.Br J Anaesth. 1991 Feb;66(2):224-7.

839. Aida S, Taga K, Yamakura T, Endoh H, Shimoji K. Headache after attempted epidural block: the role of intrathecal airAnesthesiology. 1998 Jan;88(1):76-81.

This section of the monograph is a small part of the entire paper that evaluates accuracy of placement using anatomical surface landmarks (pretty poor...two studies show the correct interspace was identified only 29-30% of the time), subdural injections, effect of the retroligamentous space on false positive LOR, etc.

JessP · Nov 17, 2006

Disclaimer- 1st year SRNA with 70 or so epidurals under my belt.

All with a glass syringe- At first I used only air just because in my head it seems easier and some mentors did it that way.... but after trying saline with some sticky syringes.... it is better. And I believe it makes the catheter easier to pass, and allows a sooner, more confident LOR.

Just my humble opinion