Venous gas in COPD exacerbation

Prolific emergency medicine researcher Anne-Maree Kelly and colleague Dr Lim from Tan Tock Seng Hospital in Singapore have published a systematic review of articles assessing the utility of peripheral venous blood gases (pVBG) in exacerbations of COPD1. Their conclusion:

Available evidence suggests that there is good agreement for pH and HCO3 values between arterial and pVBG results in patients with COPD, but not for pO2 or pCO2. Widespread clinical use is limited because of the lack of validation studies on clinical outcomes

pVBG may however be useful as a screening test for significant arterial hypercarbia; Kelly et al. previously reported2 a cutoff value of 45 mmHg (5.9 kPa).

1. A meta-analysis on the utility of peripheral venous blood gas analyses in exacerbations of chronic obstructive pulmonary disease in the emergency department
Eur J Emerg Med. 2010 Oct;17(5):246-8

2. Kelly AM, Kerr D, Middleton P. Validation of venous pCO2 to screen for arterial hypercarbia in patients with chronic obstructive airways disease.
J Emerg Med 2005; 28:377–379

Propofol for kids in the ED

A systematic review of the use of propofol for paediatric procedural sedation (PPS) identified sixty studies and 17 066 published paediatric propofol sedations performed outside the operating theatre setting. The incidence of complications were: desaturation 9.3%, apnoea 1.9%, assisted ventilation 1.4%, hypotension 15.4%, unplanned intubation 0.02%, emesis post procedure 0.14%, laryngospasm 0.1% and bradycardia 0.1%. There are many confounding variables that influence the likelihood of these events: adjunct opiates, propofol dosing strategies and supplemental oxygen. These rates of minor adverse events are similar to that published for ED sedation with other sedation agents

There were no reported incidents of aspiration or emesis during sedation and there were no deaths associated with procedural propofol sedation. The authors conclude: “the published adverse event data for paediatric propofol sedation support its ongoing use in the ED for appropriately selected paediatric patients by experienced physicians who are able to provide advanced cardiorespiratory support.

Review article: Safety profile of propofol for paediatric procedural sedation in the emergency department
Emerg Med Australas. 2010 Aug;22(4):265-86

Left molar approach

The left molar approach is a technique to improve the view at laryngoscopy using a standard macintosh laryngoscope. It was described by Yamamoto1 as follows:

  • insert the blade from the left corner of the mouth at a point above the left molars;
  • the tip of the blade is directed posteromedially along the groove between the tongue and the tonsil until the epiglottis and glottis come into sight;
  • before elevating the epiglottis, the tip of the blade is kept in the midline of the vallecula and the blade is kept above the left molars;
  • the view provided is framed by the flange, the lingual surface of the blade, and the tongue bulged to right of the blade.


The success of this approach in comparison with alternatives has been reproduced by others2. However although Yamamoto and others demonstrated that this improved the laryngoscopic view, actual intubation may still be difficult because of the limited access to the cords, in part caused by the bulging of the tongue.

Physicians from Turkey described a case3 of an unpredicted difficult airway to demonstrate that the use of the gum elastic bougie can facilitate intubation which had otherwise not been successful via the left molar approach.

The take home message for me is that if I have a grade IV view despite my usual first-pass success optimisation manoeuvres such as positioning, reducing or releasing cricoid pressure, and providing external laryngeal manipulation, it is worth trying the left molar approach in combination with a bougie to gain a view of the glottis and to pass the tube.

1. Left-molar Approach Improves the Laryngeal View in Patients with Difficult Laryngoscopy
Anesthesiology. 2000 Jan;92(1):70-4 Full Text

2. Comparative Study Of Molar Approaches Of Laryngoscopy Using Macintosh Versus Flexitip Blade
The Internet Journal of Anesthesiology 2007 : Volume 12 Number 1

3. The use of the left-molar approach for direct laryngoscopy combined with a gum-elastic bougie
European Journal of Emergency Medicine December 2010 ;17(6):355-356

LMA not always successful; needle crike fails often

A meta-analysis of pre-hospital airway control techniques evaluated alternative techniques to tracheal intubation. The outcome was placement success; there were no data on effectiveness of ventilation or other clinical outcomes. Although limited by poor quality studies, there are some interesting findings.

The pooled placement success rates for Combitube and LMA, were similar but unimpressive, with nonphysician placement success rates of 83.0% and 82.7%, respectively. The authors point out that while these devices might offer potential advantages over conventional tracheal intubation in terms of reduced training requirements, or perhaps fewer or less severe complications, they should not be expected to provide higher airway management success rates than conventional tracheal intubation.

Low success rates for this 'rescue procedure'. Just get your scalpel...

They identified only four studies reporting the success rates of needle cricothyroidotomy (NC). Regardless of patient circumstances or clinician credentials, the NC success rate was ubiquitously low, ranging from 25.0% to 76.9%. The pooled results for the 18 surgical cricothyroidotomy (SC) studies produced substantially higher success rates, although the success rate for all nonphysician clinicians was still only 90.4%. The authors state: “EMS systems that choose to incorporate a percutaneous airway procedure into their airway management protocols should recognize that the success rate of SC far exceeds that of NC”.

A meta-analysis of prehospital airway control techniques part II: alternative airway devices and cricothyrotomy success rates
Prehosp Emerg Care. 2010 Oct-Dec;14(4):515-30

Ferrofluid

A drop of this fluid containing magnetic nanoparticles is placed in a magnetic field. The peaks and troughs result as the magnet tries to pull the liquid along its field lines.

According to New Scientist, ferrofluids are being used in experimental cancer treatments called magnetic hyperthermia, and are the basis for a new breed of shape-shifting telescope lenses.

Original article from New Scientist

A-a gradient unhelpful in pregnancy

"Man, she's enormous. I can't reach the chest to auscultate!"

Given that thromboembolism is the leading cause of maternal death in the UK according to the latest UK CEMACE report, it would be nice to have reliable non-ionising tests in the ED to rapidly rule out this disease in pregnant women. Unfortunately, the alveolar-arterial oxygen gradient does not do the job.

A recent study compared the A-a gradient with CTPA as the gold standard. Of 102 patients who were pregnant or up to 6 weeks post-partum, there were 13 PEs (2 antepartum and 11 postpartum). The best sensitivity, specificity, and negative and positive predictive values for A-a gradients were 76.9%, 20.2%, 80.0%, and 11.5%, respectively.

Assessment of the alveolar-arterial oxygen gradient as a screening test for pulmonary embolism in pregnancy
Am J Obstet Gynecol. 2010 Oct;203(4):373.e1-4

Etomidate vs midazolam in sepsis

Given that single-dose etomidate can cause measurable adrenal suppression, its use in patients with sepsis is controversial. A prospective, double-blind, randomised study of patients with suspected sepsis who were intubated in the ED randomised patients to receive either etomidate or midazolam before intubation. The primary outcome measure was hospital length of stay, and no difference was demonstrated. The study was not powered to detect a mortality difference.

This study is interesting as a provider of fuel for the ‘etomidate debate’, but still irrelevant to those of us who have abandoned etomidate in favour of ketamine as an induction agent for haemodynamically unstable patients. Personally I remain unconvinced of the existence of patients who can’t be safely intubated using the limited choice of thiopentone or ketamine.

A Comparison of the Effects of Etomidate and Midazolam on Hospital Length of Stay in Patients With Suspected Sepsis: A Prospective, Randomized Study
Annals Emergency Medicine 2010;56(5):481-9

CVCs placed in the ED

Central lines in the ED are more likely to get infected because they’re inserted under less scrupulously aseptic conditions than in ICU, done more urgently, and are more likely to be placed in the mucky old femoral site by clumsy emergency physicians who don’t wash their hands after scratching their arses. Anyway, the intensivists will usually replace them with a ‘more ideal’ line after ICU admission. Right? Well, that’s what’s often taught and assumed to be the case, but a new study from a single centre suggests otherwise. ED-placed central venous catheters (19% of which were femoral) were typically left in for 4 to 5 days. The infection rate was 1.9 per 1,000 catheter-days, similar to that reported for central lines in other ICU case series.

Infection and Natural History of Emergency Department–Placed Central Venous Catheters
Annals of Emergency Medicine 2010;56(5):492-7

GPIIb/IIIa inhibitors

A systematic review on use of GPIIb/IIIa inhibitors in NSTEACS has been updated as part of the Annals of Emergency Medicine‘s Evidence Based Emergency Medicine series. The bottom line:

In patients with non-ST-segment elevation acute coronary syndromes who do not undergo early percutaneous coronary intervention, administration of platelet glycoprotein IIb/IIIa (GPIIb/IIIa) inhibitors, given in addition to aspirin and unfractionated heparin, does not reduce 30-day or 6-month mortality. For the composite endpoint of myocardial infarction or death, there was modest benefit at 30 days and 6 months; however, there was an increased risk of major hemorrhage among those receiving GPIIb/IIIa inhibitors.

Update: Use of Platelet Glycoprotein IIb/IIIa Inhibitors in Patients With Unstable Angina and Non-ST-Segment Elevation Myocardial Infarction
Annals of Emergency Medicine Volume 56, Issue 5 , Pages e1-e2, November 2010

Compare this with the recommendations of the European Resuscitation Council who provide the following summary regarding this class of drug:

Gp IIB/IIIA receptor inhibition is the common final link of platelet aggregation. Eptifibatide and tirofiban lead to reversible inhibition, while abciximab leads to irreversible inhibition of the Gp IIB/IIIA receptor. Older studies from the pre-stent era mostly support the use of this class of drugs. Newer studies mostly document neutral or worsened outcomes. Finally in most supporting, as well as neutral or opposing studies, bleeding occurred in more patients treated with Gp IIB/IIIA receptor blockers. There are insufficient data to support routine pre-treatment with Gp IIB/IIIA inhibitors in patients with STEMI or non-STEMI-ACS. For high-risk patients with non-STEMI-ACS, in-hospital upstream treatment with eptifibatide or tirofiban may be acceptable whereas abciximab may be given only in the context of PCI. Newer alternatives for antiplatelet treatment should be considered because of the increased bleeding risk with Gp IIB/IIIA inhibitors when used with heparins.

European Resuscitation Council Guidelines for Resuscitation 2010 Section 5. Initial management of acute coronary syndromes
Resuscitation 81 (2010) 1353–1363 – full text downloadable