Instructors and graduates of certain Life Support courses will be familiar with the ‘four stage’ approach to teaching procedural skills (demonstration, deconstruction, formulation, performance):
Silent run through in which teacher performs without commentary;
teacher then performs while commentating;
teacher then performs with commentary from student(s);
finally student performs and commentates.
Two randomised studies published this month showed no improvement in skills performance with this teaching method compared with simpler approaches. One involved needle cricothyroidotomy1 and another laryngeal mask insertion2.
An accompanying editorial3 acknowledges that this might put an end to this educational dogma, but one should consider that the procedures taught in these studies were simple to perform, and the results might not be extendable to more complex procedures. The editorial points out there are some interesting data describing the neurophysiological basis of learning. Observing actions made by others activates the cortical circuits responsible for the planning and execution of those same actions; this visual-motor coupling happens through a neuronal matching network called the Mirror Neuron System (MNS). Listening to a verbal description of a skill can activate the same visual-motor circuit as those activated by the hand or the leg when completing the skill. Even during new motor pattern formation there is significant NMS activation, supporting the concept that the building of motor memories is based on the combination of observation and execution.
The ingredients of the complex mechanism of motor learning are observation, listening and immediate execution. The priority that should be given to each of the individual components of motor skills teaching is difficult to quantify and should be the subject of future research.
The editorialists conclude: The four-stage approach has been used for years with no evidence of better skill acquisition and retention compared with traditional methods. Medical educators need high-quality data to address the knowledge gaps for this topic and the two studies in this issue have set a precedent for future research. In our opinion, we should continue to use the four-stage approach to skill teaching while waiting for more evidence of a superior approach.
I differ slightly in my conclusion: if I have a limited time to teach a skill station (like airway management in the APLS course), I know I’m a little more justified in ditching this time consuming ritual in favour of more hands-on time for the paying delegates.
1. Emergency skill training—A randomized controlled study on the effectiveness of the 4-stage approach compared to traditional clinical teaching Resuscitation. 2010 Dec;81(12):1692-7
2. A randomised trial comparing a 4-stage to 2-stage teaching technique for laryngeal mask insertion Resuscitation. 2010 Dec;81(12):1687-91
3. The four-stage approach to teaching skills: The end of a dogma? Resuscitation. 2010 Dec;81(12):1607-8
Neurologist Vilayanur Ramachandran explains the mirror neuron system in this video from TED.com:
Two dedicated devices for transtracheal oxygen delivery through a cricothyroidotomy needle are available, the ENK Oxygen Flow Modulator (ENK) and the Manujet. Both maintain oxygenation, but the ENK is thought to achieve better ventilation (as previously shown in a pig model) because of a continuous flow that provides CO2 washout between insufflations. Very little is known concerning the lung pressures generated with these 2 devices, so a study using a simulated trachea and artificial lung model sought to determine oxygen flow, tidal volumes, and airway pressures at different occlusion rates and during both simulated partial and complete upper airway obstruction. Manujet
Gas flow and tidal volume were 3 times greater with the Manujet than the ENK (approximately 37 vs 14 L/min and 700 vs 250 mL, respectively) and were not dependent on the respiratory rate. In the absence of ventilation, the ENK delivered a 0.6+/-0.1 L/min constant gas flow. In the totally occluded airway, lung pressures increased to 136 cm H2O after 3 insufflations with the Manujet, whereas the ENK, which has a pressure release vent, generated acceptable pressures at a low respiratory rate (4 breaths/min) (peak pressure at 27.7 +/-0.7 and end-expiratory pressure at 18.8+/- 3.8 cm H2O). When used at a respiratory rate of 12 breaths/min, the ENK generated higher pressures (peak pressure at 95.9 +/- 21.2 and end-expiratory pressure at 51.4+/- 21.4 cm H2O). In the partially occluded airway, lung pressures were significantly greater with the Manujet compared with the ENK, and pressures increased with the respiratory rate with both devices. Finally, the gas flow and tidal volume generated by the Manujet varied proportionally with the driving pressure.
The authors asset that this study confirms:
the absolute necessity of allowing gas exhalation between 2 insufflations and
maintaining low respiratory rates during transtracheal oxygenation.
In the case of total airway obstruction, the ENK may be less deleterious because it has a pressure release vent. Using a Manujet at lower driving pressures may decrease the risk of barotrauma and allow the safe use of higher respiratory rates ENK Oxygen delivery during transtracheal oxygenation: a comparison of two manual devices Anesth Analg. 2010 Oct;111(4):922-4
One infrequently used option for refractory status epilepticus is isoflurane anaesthesia. A report of two cases demonstrates progressive MRI changes suggestive of neurotoxicity, that improved after discontinuation of isoflurane. Impossible to prove cause and effect here, since the both patients had status for weeks and were on multiple anticonvulsant medications, for example lorazepam, fosphenytoin, levetiracetam, valproate, and subsequent infusions of midazolam, pentobarbital, and ketamine. Neither patient recovered beyond a minimally conscious state. This article serves as a reminder that:
Persistent status epilepticus may be associated with a poor neurologic outcome
Some cases are extremely refractory to treatment
Isoflurane is one of many options to try when standard anticonvulsant regimens are failing
Dr WFS Sellers and colleagues describe several cases that demonstrate convincingly a protective effect of intravenous magnesium sulphate against the tachycardia produced by intravenous salbutamol in patients with asthma. This effect was observed both when magnesium was given before and when given after the salbutamol. It was seen in critically ill asthmatic patients and in a volunteer with well-controlled asthma.
Intravenous magnesium sulphate increases atrial contraction time and refractory times. It is used to treat atrial tachyarrhythmias and has a negative chronotropic and dromotropic effect. Intravenous magnesium sulphate prevents intravenous salbutamol tachycardia in asthma Br J Anaesth. 2010 Dec;105(6):869-70
Level 1 evidence is great, but for useful tips that can add options to your resuscitation toolbox there are some great finds in journal letters pages.
Try this one: An apneoic patient requires assisted ventilation in your resuscitation room. Bag-mask ventilation is ineffective. You then notice a mature tracheostomy at the same time that you’re told he had a laryngectomy. How would you ventilate him?
The obvious answer is to intubate the stoma with a size 6.0 tracheal tube or a tracheostomy tube if you have one. However prior to that you could bag-‘mask’ ventilate with a size 2 laryngeal mask airway applied to the stoma, holding the cuff in place with pressure through an index finger.
Such a technique is desribed in the context of an elective anaesthesia case in this month’s Anaesthesia. The LMA cuff provided an effective seal around the stoma, thereby allowing leak-free ventilation.
Stoma ventilation using a paediatric facemask is another option. Tracheostomy ventilation using a laryngeal mask as a ‘bridge to extubation’ Anaesthesia 2010;65(12):1232–1233
A case report of massive obstetric haemorrhage due to placental abruption describes the successful management of haemorrhage associated with a low fibrinogen level with blood products that included fibrinogen concentrate.
Fibrinogen concentrate can be available more quickly than other clotting products as it is rapidly solubilised from an ampoule in 50 ml water and given as a bolus. To raise the plasma fibrinogen concentration by 1 g/l in a 70-kg person, 1000 ml fresh frozen plasma (6 standard UK units), or 260 ml cryoprecipitate (10 standard UK units) will be required. Administration of adequate doses of fresh frozen plasma or cryoprecipitate to treat hypofibrinogenaemia during obstetric haemorrhage will therefore take a substantial amount of time, even with an efficient blood bank and portering system. Fibrinogen concentrate use during major obstetric haemorrhage Anaesthesia 2010;65(12):1229–1230
A previous retrospective study showed its use in a series of surgical and obstetric haemorrhage cases may have been associated with a subsequent decreased need for other blood products. Fibrinogen concentrate substitution therapy in patients with massive haemorrhage and low plasma fibrinogen concentrations Br. J. Anaesth. (2008) 101 (6): 769-773 (Full text)
Made a radiologist go red with rage recently? If not, you could try showing them this paper1 in this month’s Annals of Emergency Medicine that describes accurate emergency physician ultrasound diagnosis of deep vein thrombosis after just ten minutes training!
ED patients with a suspected lower extremity deep venous thrombosis were assessed using a bedside 2-point compression technique by emergency physicians using a portable US machine and all patients subsequently underwent duplex ultrasonography performed by the Department of Radiology.
The emergency physicians had a 10-minute training session before enrolling patients
The techinque involved 2 specific points: the common femoral and popliteal vessels, with subsequent compression of the common femoral and popliteal veins. The study result was considered positive for proximal lower extremity deep venous thrombosis if either vein was incompressible or a thrombus was visualised. Free DVT ultrasound tutorial at Sonoguide.com
A total of 47 physicians performed 199 2-point compression ultrasonographic examinations in the ED.
There were 45 proximal lower extremity deep venous thromboses observed on Department of Radiology evaluation, all correctly identified by ED 2-point compression ultrasonography. The 153 patients without proximal lower extremity deep venous thrombosis all had a negative ED compression ultrasonographic result. One patient with a negative Department of Radiology ultrasonographic result was found to have decreased compression of the popliteal vein on ED compression ultrasonography, giving a single false-positive result, yet repeated ultrasonography by the Department of Radiology 1 week later showed a popliteal deep venous thrombosis. The sensitivity and specificity of ED 2-point compression ultrasonography for deep venous thrombosis were 100% (95% confidence interval 92% to 100%) and 99% (95% confidence interval 96% to 100%), respectively.
These figures may appear to fail the ‘sniff test’, ie. seem too good to be true. Not surprisingly Annals acknowledge this by providing an accompanying editorial2 by emergency ultrasound heavyweight Michael Blaivas, MD, who is healthily skeptical of such a minimal training program but is overwhelmingly supportive of the principle. Dr Blaivas also provides a fantastic summary of the existing evidence base on ED ultrasound for DVT. To me he hits the nail on the head when with a philosophical point on the practice of EM: ‘One common challenge proponents of any new application or procedure face in emergency medicine is overcoming the inertia of comfort with the status quo.’ Spot on, Dr B.
1. Compression Ultrasonography of the Lower Extremity With Portable Vascular Ultrasonography Can Accurately Detect Deep Venous Thrombosis in the Emergency Department Annals of Emergency Medicine 2010;56(6):601-10
2. Point-of-Care Ultrasonographic Deep Venous Thrombosis Evaluation After Just Ten Minutes’ Training: Is This Offer Too Good to Be True? Annals of Emergency Medicine 2010;56(6):611-3
The guys at ‘EM Live’ have a short video on how to do DVT ultrasound:
Can cardiotocography be applied in the pre-hospital setting? French physicians assessed its feasibility in 145 patients enrolled during 119 interhospital transfers and 26 primary prehospital missions.
Their physician-staffed ambulance teams included 19 emergency physicians and one anaesthetist.
Interpretable tracings were obtained for 81% of the patients during the initial examination, but this rate decreased to 66% during handling and transfer procedures. Only ground EMS transportations were included in the study. For 17 patients (12%), the monitoring led to a change in the patient’s management: an acceleration of chronology of prehospital management in 5 cases, a decision to directly admit the patient to the operating room for immediate cesarean section in three cases, a change in hospital admission in three cases, an adaptation or implementation of tocolytic treatment in six cases, and placing the patient in the left lateral decubitus position or oxygen administration in three cases. Fetal monitoring in the prehospital setting J Emerg Med. 2010 Nov;39(5):623-8
Another stab at assessing noninvasive ventilation in cardiogenic pulmonary oedema has been made by Italian researchers who compared CPAP with noninvasive pressure support ventilation (nPSV – similar to BiPAP) in a randomised trial of 80 patients. The primary outcome was endotracheal intubation rates. There was no significant difference between the two modalities. This result is in keeping with the much larger 3CPO trial. Continuous Positive Airway Pressure vs. Pressure Support Ventilation in Acute Cardiogenic Pulmonary Edema: A Randomized Trial J Emerg Med. 2010 Nov;39(5):676-84
Certain chemical burns require a little extra thought than just irrigation and good wound care – which may even be contraindicated. An article in The Journal of Emergency Medicine addresses these, and some of the points are summarised below, with some additional information from Toxbase: Hot tar (bitumen)
Immerse contaminated area in cool water until the bitumen has hardened and cooled.
Adherent material may be left in place to avoid causing further injury by removal attempts, and will spontaneously detach after a few days.
If a finger or limb is completely surrounded, split the bitumen to prevent a tourniquet effect.
To remove bitumen, apply a lipid or polysorbate based agent and a clean non-adherent dressing. Suitable products include melted butter, sunflower oil, liquid paraffin, and petroleum or polysorbate based antibiotic ointments. Solvents such as alcohol, acetone, kerosene, ether or gasoline are not suitable.
Change the dressing frequently, and reapply the product as necessary, until the bitumen is completely removed. This may take up to 72 hours.
Treat as a thermal burn.
Elemental sodium
– utilised in the manufacturing of methamphetamine.
will spontaneously ignite above 115°C
Contact with water releases sodium hydroxide and hydrogen gas. It is the heat released in the reaction with the water in air that then ignites locally produced hydrogen gas.
Burns involving the metallic forms of sodium, potassium, and lithium (alkali metals) produce both thermal and chemical injury to the tissue. The thermal tissue damage is due to the extreme exothermic reaction that metallic sodium undergoes when exposed to water.
At times, water, when mixed with either elemental sodium or potassium, undergoes an explosive reaction.
Avoid water irrigation; if metal is still present in the tissues, the added water could ignite it.
All clothing should first be removed from the victim. If retained metal exists, the affected area should be covered in mineral oil. Removal of embedded sodium should then be undertaken with forceps.
Mineral oil is a practical, and potentially safer, alternative to isopropyl alcohol for the storage of elemental sodium.
Chromic acid
– a corrosive, oxidizing acid. After skin has been exposed to chromium, burns covering as little as 10% of body surface area (BSA) have proven fatal.
Burns involving as little as 1% of total BSA have resulted in acute renal failure.
Wash thoroughly with copious amounts of water and treat as a thermal burn.
Application of 10% ascorbic acid solution at least three times per day may improve the rate of healing
Prompt excision of burned, contaminated areas is recommended to prevent absorption of the chemical.
White phosphorus
– will ignite spontaneously in 30°C air temperature; typically stored in water.
burns of > 10% can have associated mortality.
Three stages of systemic toxicity exist: (1) gastrointestinal symptoms (nausea, vomiting and “smoking stool”). Symptoms of headache, seizures, and coma, as well as the potential for cardiovascular collapse, may occur in the initial phase. Decreasing serum calcium concentrations; (2) symptom-free period; (3) (4 to 8 days post-exposure) neurological toxicity, bleeding diathesis, hepatic failure, renal failure, and shock.
Continuous coverage with water will protect both the patient and staff from ignition and fumes that result from white phosphorus’s contact with air.
Brushing particulate not incorporated in wounds can accomplish a significant amount of decontamination. This brushing should be followed by continuous irrigation until all particles are removed. Those debriding and decontaminating an exposed patient should have a safe method of disposing of particles: a container of cold water would suffice.
A way to identify phosphorous particles for removal is the use of a Wood’s lamp, which will cause the white phosphorous to fluoresce.
Excision may be necessary to remove the chemical if deeply entrenched in fascia.
Phenol
– a corrosive aromatic hydrocarbon that can be absorbed at toxic levels through all routes of absorption
causes extensive denaturisation of tissue proteins, producing an eschar with shallow ulcers
Rescue personnel should use butyl rubber gloves and aprons, and conduct decontamination in a well-ventilated area.
wipe exposed areas immediately with low-molecular-weight polytheylene glycol (PEG 300 or 400)
however Toxbase states: “The use of solvents (such as glycerol, polyethylene glycol and isopropanol) has been suggested. One (animal) study (Hunter et al, 1992) indicated that isopropanol was more effective than water, but there is no evidence in humans that solvents are more effective than washing with copious amounts of water.”
if the burn covers a large skin area, high pressure shower irrigation before PEG application is preferable
Any water applied must be applied in high pressure, as small amounts might dilute the phenol present on the skin and thus expand not only the involved area but also the amount of phenol absorbed.
Hydrofluoric acid
HF is highly corrosive and causes damage by two mechanisms. It produces a corrosive burn from the high concentration of hydrogen ions. It also penetrates tissues due to the lipophilic nature of fluoride, and causes liquefactive necrosis.
Tissue penetration leads to systemic reactions with effects on the cardiac, respiratory, nervous, and gastrointestinal systems. The fluoride ion precipitates calcium, leading to hypocalcemia, and may interfere with enzyme systems by binding magnesium and manganese, as well as important nerve conduction functions that depend on calcium.
Copious irrigation of HF-burned skin with water should begin immediately. Most HF burns will respond well to this.
Pain that persists after irrigation is a marker that the fluoride ion needs detoxification. This can be accomplished through superficial topical treatment, infiltrative treatment, or intra-arterial treatment.
The preferred topical agent is calcium gluconate gel.
The editorial points out there are some interesting data describing the neurophysiological basis of learning. Observing actions made by others activates the cortical circuits responsible for the planning and execution of those same actions; this visual-motor coupling happens through a neuronal matching network called the Mirror Neuron System (MNS). Listening to a verbal description of a skill can activate the same visual-motor circuit as those activated by the hand or the leg when completing the skill. Even during new motor pattern formation there is significant NMS activation, supporting the concept that the building of motor memories is based on the combination of observation and execution.
