ECG machines may give a printed report saying ***ACUTE MI***. In a retrospective study, patients on the ICU whose 12 lead ECGs contained this electronic interpretation did not have an elevated troponin 85% of the time. Even in the minority of patients whose electronic ECG diagnosis of MI was agreed with by a cardiologist, only one third developed an elevated troponin.
The authors state ‘In contrast to nonintensive care unit patients who present with chest pain, the electrocardiographic ST-segment elevation myocardial infarction diagnosis seems to be a nonspecific finding in the intensive care unit that is frequently the result of a variety of nonischaemic processes. The vast majority of such patients do not have frank ST-segment elevation myocardial infarction.’
Electrocardiographic ST-segment elevation myocardial infarction in critically ill patients: An observational cohort analysis
Crit Care Med. 2010 Dec;38(12):2304-230
Massive haemorrhage guideline
The Association of Anaesthetists of Great Britain and Ireland has published guidelines on the management of massive haemorrhage. Their summary:
- Hospitals must have a major haemorrhage protocol in place and this should include clinical, laboratory and logistic responses.
- Immediate control of obvious bleeding is of paramount importance (pressure, tourniquet, haemostatic dressings).
- The major haemorrhage protocol must be mobilised immediately when a massive haemorrhage situation is declared.
- A fibrinogen < 1 g.l)1 or a prothrombin time (PT) and activated partial thromboplastin time (aPTT) of > 1.5 times normal represents established haemostatic failure and is predictive of microvascular bleeding. Early infusion of fresh frozen plasma (FFP; 15 ml.kg)1) should be used to prevent this occurring if a senior clinician anticipates a massive haemorrhage.
- Established coagulopathy will require more than 15 ml.kg)1 of FFP to correct. The most effective way to achieve fibrinogen replacement rapidly is by giving fibrinogen concentrate or cryoprecipitate if fibrinogen is unavailable.
- 1:1:1 red cell:FFP:platelet regimens, as used by the military, are reserved for the most severely traumatised patients.
- A minimum target platelet count of 75 · 109.l)1 is appropriate in this clinical situation.
- Group-specific blood can be issued without performing an antibody screen because patients will have minimal circulating antibodies. O negative blood should only be used if blood is needed immediately.
- In hospitals where the need to treat massive haemorrhage is frequent, the use of locally developed shock packs may be helpful.
- Standard venous thromboprophylaxis should be commenced as soon as possible after haemostasis has been secured as patients develop a prothrombotic state following massive haemorrhage.
Blood transfusion and the anaesthetist: management of massive haemorrhage – full document
Aorta/IVC ratio and dehydration
Two studies this month report a correlation between ultrasound detected aorta/IVC ratio and dehydration in children presenting with diarrhoea and/or vomiting. In both studies the IVC diameter was measured in expiration and the aortic diameter in systole, using a transverse view in the subxiphoid area. Both used acute and post-discharge weight comparison to ascertain degree of dehydration.
The first study took place in Rwanda and a percent weight change between admission and discharge of greater than 10% was considered the criterion standard for severe dehydration. 52 children were included ranging in age from 1 month to 10 year. Vessel diameter measurements were inner wall to inner wall. The IVC-to-aorta ratio correlated significantly with percent weight change (r = 0.435, p < 0.001). Using the best ROC curve cutoff of 1.22, aorta/IVC ratio had a sensitivity of 93% (95% CI = 81% to 100%), specificity of 59% (95% CI = 44% to 75%), LR+ of 2.3 (95%CI=1.5to3.5), and LR– of 0.11 (95%CI=0.02to 0.76) for detecting severe dehydration. The same study did not find ultrasound assessment of inferior vena cava inspiratory collapse or the World Health Organization scale to be accurate predictors of severe dehydration in this same population of children.
Ultrasound Assessment of Severe Dehydration in Children With Diarrhea and Vomiting
Acad Emerg Med. 2010 Oct;17(10):1035-41
The second study took place in the USA. The subjects were considered to have significant dehydration if the weight loss was at least 5%. 71 were children were included. The area under the curve (AUC) was 0.73 (95% CI = 0.61 to 0.84). An IVC ⁄ aorta cutoff of 0.8 produced a sensitivity of 86% and a specificity of 56% for the diagnosis of significant dehydration. The positive predictive value was 56%, and the negative predictive value was 86%. Note this equates to an aorta/IVC ratio of 1.25, similar to that in the first study.
My rough-and-ready take home message from these two studies appears to be that an aorta/IVC ratio less than about 1.2 makes severe dehydration less likely in children with symptoms of gastroenteritis.
Use of Bedside Ultrasound to Assess Degree of Dehydration in Children With Gastroenteritis
Acad Emerg Med. 2010 Oct;17(10):1042-7
The Heart Point Sign
A case report describes the echo findings of a patient with a traumatic left sided pneumothorax. Although the subcostal view was unremarkable, upon imaging the parasternal region, the sonographer noted a flickering phenomenon where the heart was clearly visualized in late diastole, but would disappear in mid- systole only to reappear in late diastole during the next cardiac cycle. This ‘‘heart point’’ sign occurs because as the heart fills with blood in diastole, it enlarges and displaces the air from the precardiac space, allowing the heart to transiently contact the chest wall and be visualized with US. As the heart contracts during systole, the pneumothorax fills the space between the heart and the anterior chest wall, preventing the transmission of US and causing the heart to momentarily disappear from view.
The Heart Point Sign: Description of a New Ultrasound Finding Suggesting Pneumothorax
Academic Emergency Medicine 2010;17(11):e149–e150
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
Echocardiography videos from Vienna
Folks from the Medical University of Vienna have produced a great resource with free online echocardiography videos at www.123sonography.com
Check out their video on right heart endocarditis:
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.
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