Category Archives: PHARM

Prehospital and Retrieval Medicine

All Updates, Kids, PHARM, Resus

Ketamine update

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Anaesthetist Dr Jan Persson from Stockholm has published an updated review of recent ketamine literature. The following interesting facts about our favourite drug are extracted from Dr Persson’s paper:

  • Action on multiple receptors earns it the nickname: ‘the nightmare of the pharmacologist’
  • Recently ketamine has also been shown to inhibit tumor necrosis factor-alpha (TNF- alpha) and interleukin 6 (IL-6) gene expressions in lipopolysaccharide (LPS)-activated macrophages. It has been speculated that these antiproinflammatory effects may be responsible for antihyperalgesic effects of ketamine
  • Ketamine can exist in two forms, or enantiomers; S-ketamine and R-ketamine. The physical properties of the enantiomers are identical, but their interactions with complex molecules, underlying PK/PD parameters, might differ. It has been well established that the elimination clearance of S-ketamine is larger than that of R-ketamine. The S-form has been commercially available for several years, probably based on the perception that it would have a better effect to side-effect ratio. The recent literature calls into question the proposed advantages of the S-enantiomer.

  • Ketamine has been shown to induce neuroapoptosis, or neuronal cell death, in newborn animals. This is obviously a concern in paediatrics, where ketamine plays an important role, both in anaesthesia and for sedation/analgesia during painful procedures. The relevance in humans of these effects, however, is unclear, and as pointed out by Green and Cote it does seem unlikely, for various reasons, that such an effect would be of major importance. It does not seem likely, though possible, that a clinically relevant effect would have passed unnoticed.
  • Another, somewhat unexpected, side effect that has emerged in recent years is bladder dysfunction. In some cases the bladder effects progress to ulcerative cystitis. Although the reported cases have mainly concerned recreational drug users, they are relevant for long-term analgesic use as well. The mechanisms involved are unknown. This side effect might turn out to be the most serious limitation to long-term analgesic treatment with ketamine.

Wherefore ketamine?
Curr Opin Anaesthesiol. 2010 Aug;23(4):455-60

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Swimming the Channelopathy

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Drowning is one of the leading causes of accidental death in children. Some apparent drownings may be related to sudden cardiac death, in particular to unidentified channelopathies, which are known to precipitate fatal arrhythmias during swimming-related events.
The majority of cases of sudden cardiac death in children and adolescents are secondary to either hypertrophic or right ventricular cardiomyopathy with coronary artery abnormalities also prevalent, and reports have demonstrated these cardiac abnormalities on autopsy following sudden swimming-related deaths.
However, the majority of autopsies in swimming-related sudden deaths are normal suggesting causation at molecular level, in particular ion channel defects such as type 1 long-QT syndrome (LQT1) and catecholaminergic polymorphic ventricular tachycardia (CPVT).

The gene deletion in LQT1 (KCNQ1) leads to a reduction in the repolarising potassium current (IKs) and prolongation of repolarisation. This lengthens the QT interval (which may be lengthened further by facial immersion in cold water). A premature ventricular contraction (PVC) again which may be initiated by swimming occurring during the vulnerable part of repolarisation leads to establishment of polymorphic ventricular tachycardia (torsades de pointes).

The ryanodine receptor gene mutation (RyR2) in catecholaminergic polymorphic ventricular tachycardia leads to defective closure of the receptor on the surface of the sarcoplasmic reticulum during diastole. This leads to increased calcium (Ca2+) leakage from the sarcoplasmic reticulum and increased potential for delayed afterdepolarisations and subsequent ventricular tachycardia.

Some recommendations are made in an article in Archives of Disease in Childhood:
Proposed implementations to improve detection and appropriate management of apparent drownings secondary to cardiac channelopathies

  1. Improving awareness in the coronial service of the possibility of a cardiac cause for poorly explained drownings.
  2. Education of lifeguards and provision of automated defibrillators in swimming pools.
  3. Molecular autopsy for non-survivors to look for potential channelopathies.
  4. Screening for survivors and family members of non-survivors to identify those with a channelopathy.
  5. Proper counselling for those identified to have a channelopathy on family screening.

Drowning and sudden cardiac death
Arch Dis Child 2011;96:5-8

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HEMS transport may be predictor of survival

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Helicopters are controversial in EMS circles, particularly in the United States, which seems to have a high number of Helicopter Emergency Medical Services (HEMS) crashes. Although this may in part be a reflection of a large increase in HEMS missions, and the factors contributing to crash fatalities have been studied, it makes sense to limit HEMS missions to those that are likely to make a difference to the patient. Advantages of HEMS services may include the ability to deliver a patient more rapidly to the most appropriate facility, as well as being able to convey a highly skilled team more rapidly to the scene.
Analysis of patients from the National Trauma Databank identified 258,387 subjects transported by either helicopter (HT) (16%) or ground ambulance (GT) (84%). HT subjects were younger (36 years ± 19 years vs. 42 years ± 22 years; p < 0.01), more likely to be male (70% vs. 65%; < 0.01), and more likely to have a blunt mechanism (93% vs. 88%; < 0.01) when compared with GT subjects.

For every dead-on-arrival (DOA) subject in the HT group, there were 498 survivors compared with 395 survivors for every DOA subject in the GT group. When comparing indicators of injury severity, patients transported by helicopter were more severely injured (mean ISS and percentage with ISS > 15), were more likely to have a severe head injury, and were more likely to have documented hypotension or abnormal respiratory when compared with those transported by ground ambulance. Furthermore, HT subjects also had longer length of stay, higher rates for ICU admission, and mechanical ventilation, as well as an increased requirement for emergent surgical intervention.
interestingly, this study shows that <15% of HT patients nationally are discharged within 24 hours. This is much lower than the 24.1% reported previously, suggesting that the degree of over-triage may not be as significant on the national level as reported in smaller studies.
Overall survival was lower in HT subjects versus GT subjects on univariate analysis (92.5% vs. 95.6%; < 0.01). Stepwise univariate analysis identified all covariates for inclusion in the regression model. HT became an independent predictor of survival when compared with GT after adjustment for covariates (OR, 1.22; 95% CI, 1.18– 1.27; < 0.01).
Helicopters and the Civilian Trauma System: National Utilization Patterns Demonstrate Improved Outcomes After Traumatic Injury
J Trauma. 2010 Nov;69(5):1030-4
National Transportation Safety Board HEMS data

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Passive leg raising during CPR

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Measuring end-tidal carbon dioxide (ET CO2 ) is a practical non-invasive method for detecting pulmonary blood flow, reflecting cardiac output and thereby the quality of CPR. It has also been shown to rise before clinically detectable return of spontaneous circulation (ROSC).
Passive leg raising (PLR) increases venous return and may therefore augment cardiac output and in a cardiac arrest this may be reflected by an elevation in ETCO2.
A Swedish observational study of 126 patients with out of hospital cardiac arrest due to a likely cardiac aetiology underwent tracheal intubation with standardised ventilation and chest compressions (either manually or using the LUCAS device, as part of larger study of mechanical chest compressions according to a cluster design). Patients were stratified to receive either PLR to 20 degrees or no PLR. ETCO2 was measured during CPR, either for 15min, or until the detection of ROSC.

Hang on I think that's overdoing it a bit

During PLR, an increase in ETCO2 was found in all 44 patients who received PLR within 15s (p=0.003), 45s (p = 0.002) and 75 s (p = 0.0001). Survival to hospital discharge was 7% among patients with PLR and 1% among those without PLR (p = 0.12). Among patients experiencing ROSC (60 of 126), there was a marked increase in ETCO2 1 min before the detection of a palpable pulse.
Passive leg raising during cardiopulmonary resuscitation in out-of-hospital cardiac arrest—Does it improve circulation and outcome?
Resuscitation. 2010 Dec;81(12):1615-20

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UK Military Clinical Guidelines

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In the United Kingdom, The Academic Department of Military Emergency Medicine at the Royal Centre for Defence Medicine produces Clinical Guidelines for Operations on behalf of Surgeon General under the direction of Defence Professor of Emergency Medicine.
These guidelines, last updated in May 2010, are available on line here:

**UPDATE JUNE 2011** I have received correspondence that this document is now out of date. The link is however still active and the document makes for interesting reading.

All Updates, ICU, PHARM, Resus

Needle crike: low rate and allow exhalation

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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

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LMA to stoma ventilation

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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

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Fetal monitoring during EMS transport

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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

All Updates, PHARM, Trauma

Pre-hospital amputation

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British trauma surgeon and pre-hospital pioneer Professor Keith Porter describes how to do a pre-hospital amputation in this months EMJ. Thankfully the procedure is only rarely necessary and often only requires cutting remaining skin bridges with scissors. The indications are:

  • An immediate and real risk to the patient’s life due to a scene safety emergency
  • A deteriorating patient physically trapped by a limb when they will almost certainly die during the time taken to secure extrication
  • A completely mutilated non-survivable limb retaining minimal attachment, which is delaying extrication and evacuation from the scene in a non-immediate life-threatening situation
  • The patient is dead and their limbs are blocking access to potentially live casualties

simple equipment for amputation

The recommended procedure is:

  1. Ketamine anaesthesia
  2. Apply an effective proximal tourniquet
  3. Amputate as distally as possible
  4. Perform a guillotine amputation
  5. Apply haemostats to large blood vessels
  6. Leave the tourniquet in situ
  7. Apply a padded dressing and transport to hospital

Remember: the requirement for prehospital amputation other than cutting minimal soft tissue bridges is rare. However pre-hospital critical care physicians should be trained and equipped to amputate limbs in order to save life. Probably good to have a Gigli saw in your pack and to familiarise yourself with its use, as shown here:

Sydney HEMS doctors training in amputation

Prehospital amputation
Emerg Med J 2010 27: 940-942

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Pelvic splint improved shock

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Splinted any pelvises lately? Karim Brohi’s excellent trauma.org article outlines the strengths and weaknesses of the different devices on the market. One such is the T-POD, which has now been described in a small series in which its application to patients with unstable pelvic injury was associated with improved haemodynamics and decreased symphyseal diastasis.

Here’s a video demonstrating application of the device.

Effect of a new pelvic stabilizer (T-POD1) on reduction of pelvic volume and haemodynamic stability in unstable pelvic fractures
Injury Volume 41, Issue 12, December 2010, Pages 1239-1243 (Full text)