Laryngeal masks

Re: Laryngeal masks

Mike Martin — Sat, 29 May 2010 12:38:41 GMT

Thanks. A word of warning on the above mentioned idea. And I'll not mention any names here except to say it occurred along time ago, in fact the last century.

In a really difficult bronchoscopy in a cat, which kept going cyanotic quicker than normal, it was decided to give O2 via the channel. That worked well in preventing the cyanosis. However on deeper bronchoscopy, and (in hindsight) as a result of the bronchoscope occluding a bronchus, the O2 thro the channel had no way to escape, that associated section of lung inflated, resulting in a pneumothorax and by the time people realised (or worked out) what had gone wrong, the cat was irrecoverable.

I appreciate your concerns and warnings about aspiration. My intention was not to replace an ET with a mask for the whole GA, but only when (or if) extubating for the bronchoscopy (and the cat would not be moved during that procedure). Re-intubate when bronchoscopy would be complete.

Re: Laryngeal masks

Ian Battersby — Fri, 28 May 2010 17:59:59 GMT

HI mike,

I had chatte to louise clarke our anaesthetist about them about a month ago. SO i asked her to draft her thoughts. Which are below. Certainly alot more comphrensive and detailed a reply than i could have done

All the best and hope this of interest

Ian

Hi, ian

My preference is for oxygenation by “mass flow” with a urinary catheter alongside the scope – or via the scope channel if possible………this won`t control CO2 but high O2 flows tend to keep them well enough oxygenated.

If you get adequate pre-oxygenation – either by having them ventilated on O2 prior to extubation (fills the FRC with oxygen), or if you are avoiding intubation from the outset with 5 minutes mask/ flow-by pre-oxygenation ( no data on this just a lot of personal experience) and then use the catheter technique, I normally find that we can “get away” with it…. We sometimes use appropriate pre-op bronchodilation and the drug choice for anaesthesia can improve bronchodilation and hence oxygenation in the really bad asthmatics (ketamine is a really effective bronchodilator in these cases)

I personally have tried and do not get on with laryngeal masks…..my experience is that they displace easily if/when the patient is moved especially in cats. They do not adequately protect the airway from reflux (they are contra-indicated in procedures in people where reflux is a potential problem), although I appreciate that this isn’t an issue with bronchoscopy. The following is also of interest………..

Vet Anaesth Analg. 2009 Nov;36(6):547-54.

Gastro-oesophageal reflux during anaesthesia in the kitten: comparison between use of a laryngeal mask airway or an endotracheal tube.

Sideri AI, Galatos AD, Kazakos GM, Gouletsou PG.

Clinic of Surgery, Faculty of Veterinary Medicine, University of Thessaly, Karditsa, Greece. ksideri@vet.uth.gr

Abstract

OBJECTIVE: To compare the incidence of gastro-oesophageal reflux (GOR) during anaesthesia in the kitten when using a laryngeal mask airway (LMA) or an endotracheal tube (ET). STUDY DESIGN: Prospective randomized cross-over experimental study. ANIMALS: Forty Domestic Short Hair laboratory cats, 19 females and 21 males, aged 12-15 weeks and weighing 0.57-1.73 kg (mean 1.13 +/- SD 0.26). METHODS: Kittens were anaesthetized twice, once using the LMA and once the ET. Following induction of anaesthesia with isoflurane in an anaesthetic chamber and intubation of the trachea with the ET or placement of the LMA, a pH-electrode was introduced into the lower oesophagus. Monitoring of the oesophageal pH was performed for 45 minutes while anaesthesia was maintained with isoflurane. At the end of the experiment, gastric pH was measured. Kittens that had GOR during the experiment were treated with sucralfate, cisapride and ranitidine for 15 days. Results Oesophageal pH was 6.51 +/- 0.76 and gastric pH was 1.54 +/- 0.59. GOR was observed in nine kittens when the ET was used, and in 20 kittens when the LMA was used, the difference being significant (p = 0.013). The refluxate nearly always was acidic, being alkaline in only one kitten. Most of the GOR episodes occurred shortly after induction of anaesthesia and the oesophageal pH remained below 4.0 until the end of the experiment. No regurgitation was observed. CONCLUSIONS AND CLINICAL RELEVANCE: The use of the LMA is associated with an increased incidence of GOR during anaesthesia in the kitten, which is not detected by observation. That this may have occurred should be considered if the kitten demonstrates signs of oesophagitis in the postoperative period.

PMID: 19845926 [PubMed - indexed for MEDLINE]

Re: Laryngeal masks

james hunt — Fri, 28 May 2010 15:09:57 GMT

Is it possible to direct an oxygen flow through the sampling port on the endoscope?

Re: Laryngeal masks

Mike Martin — Fri, 28 May 2010 11:36:42 GMT

Ian,

Currently we perform bronchoscopy thro the ET tube, but in very small things like cats, this can restrict airflow. Sometimes we have to extubate to perform bronchoscopy. In both cases, cats in particular occasionally go a tad blue, limiting time for bronchoscopy, which then has to be performed in repeated short steps, alternating with re-oxygenation. So I hence the thought of using a mask to maintain oxygenation.

So what technique do you use that keeps you happy?

Re: Laryngeal masks

Ian Battersby — Thu, 27 May 2010 12:24:42 GMT

HI Mike,

we discussed the masks here from time to time. We went thorugh a variety of diffeent scenarios and couldn't really come up with a reason to use them over current techniques.

we were not really sure there was much advantage for bronchoscopy - as currently we are happy with our techniques.

Are anaesthetists main concern about them is that there is no data to support that they give any airway protection during regurgitation etc. Infact in humans they are contraindicated in any surgery were this is more likely to occur e.g. GI surgery

Ian