Effect on noradrenaline on tissue oxygen delivery

Some persist in thinking and teaching that the ‘vasopressor’ noradrenaline (norepinephrine) increases mean arterial pressure (MAP) simply by increasing systemic vascular resistance, leading to concerns that it may increase blood pressure at the expense of tissue perfusion. This assertion is contested by many, who now have further support from this study.

In 16 patients with septic shock, various measures of peripheral perfusion were recorded while the dose of noradrenaline was increased to achieve target MAPs. The use of noradrenaline to achieve incremental targets for MAP was associated with increases in global oxygen delivery, cutaneous microvascular flow, and tissue oxygenation in patients with established septic shock; there were no associated changes in the preexisting abnormalities of sublingual microvascular flow. The authors state that these findings suggest that in patients with septic shock, improvements in global hemodynamics and tissue oxygen delivery can be achieved with noradrenaline, without exacerbating microcirculatory flow abnormalities.

The effect of increasing doses of norepinephrine on tissue oxygenation and microvascular flow in patients with septic shock
Crit Care Med. 2009 Jun;37(6):1961-6

Cuffed tracheal tubes for children

In a prospective randomised controlled multi-centre trial, cuffed tracheal tubes were compared with uncuffed tubes in 2246 children aged from birth to five years undergoing general anaesthesia. There was no significant difference in post-extubation stridor but the need for tube exchange was 2.1% in the cuffed and 30.8% in the uncuffed groups (P<0.0001).

From the resuscitation point of view, there remain few if any arguments for using an uncuffed tube.

Prospective randomized controlled multi-centre trial of cuffed or uncuffed endotracheal tubes in small children

Br J Anaesth. 2009 Dec;103(6):867-73

First Aid for Burns

A review of burn first aid treatments highlights the paucity of evidence on which to make firm recommendations. The authors recommend using cold running tap water (between 2 and 15 degrees C) and to avoid ice or alternative therapies. The optimum duration of first aid application and the delay after the injury for which first aid can still be effective are two areas of research which need further exploration.

A review of first aid treatments for burn injuries
Burns. 2009 Sep;35(6):768-75

Physicians didn’t improve outcome from nontraumatic cardiac arrest

A Norwegian study retrospectively compared outcomes from non-traumatic cardiac arrest between ambulances staffed by physicians (PMA) and non-physician ambulances (non-PMA). There were no differences in any of the clinical outcome measures used in this study of 977 patients, in which 13% (PMA) and 11% (non-PMA) survived to hospital discharge.

Out-of hospital advanced life support with or without a physician: Effects on quality of CPR and outcome
Resuscitation. 2009 Nov;80(11):1248-52

Fluids for cooling post cardiac arrest

Large volume cold fluid resuscitation after return of spontaneous circulation can contribute to effective cooling but does it impair cardiac or respiratory function? A retrospective review of 52 resuscitated cardiac arrest patients suggests that the infusion of large volumes of cold fluid does not cause a further significant reduction in respiratory function beyond that normally seen after cardiac arrest despite significantly reduced LV function.

Effects of large volume, ice-cold intravenous fluid infusion on respiratory function in cardiac arrest survivors
Resuscitation. 2009 Nov;80(11):1223-8

In the same issue of Resuscitation, a prospective study of cardiac arrest survivors in positive fluid balance from cold fluid cooling showed frequent evidence of hypovolaemia as determined by serial ultrasound assessment.

An accompanying editorial suggests this may be due to the systemic inflammatory response syndrome that follows successful cardiac arrest resuscitation; large volumes are tolerated well and myocardial dysfunction should not lead to restriction of fluids after cardiac arrest.

Assessment of intravascular volume by transthoracic echocardiography during therapeutic hypothermia and rewarming in cardiac arrest survivors
Resuscitation. 2009 Nov;80(11):1234-9

Pre-hospital intubation for head injury: ?no benefit

A systematic review of pre-hospital intubation for head injured patients failed to show evidence of benefit of tracheal intubation or invasive ventilation. The authors acknowledge the lack of methodological quality in the studies reviewed and the predominance of US paramedic-delivered intubations without the use of anaesthetic drugs.

Pre-hospital tracheal intubation in patients with traumatic brain injury: systematic review of current evidence
Br J Anaesth. 2009 Sep;103(3):371-86

Pre-hospital intubation ’success’ at a US centre

Of 203 patients attending a US Level 1 trauma centre who had pre-hospital airway management, 25 (12%) had unrecognised oesophageal intubations.

Patients were treated in the field by fire rescue personnel of various municipalities and with different experience levels. Patients transported by air were significantly more likely to be successfully intubated than those transported by ground, perhaps due to both increased experience and the use by air crews of succinylcholine. The authors in their discussion contrast these results with those of European studies which report higher success rates with pre-hospital systems that employ emergency physicians and anaesthetists.

Prehospital intubations and mortality: a level 1 trauma center perspective
Anesth Analg. 2009 Aug;109(2):489-93

Vehicle Rollover

Vehicle rollover as an indicator of mechanism of injury was investigated in a study examining accident databases and the medical literature. Only 2.4% of crashes involved rollovers but they accounted for one third of occupant deaths.

Some facts on vehicle rollover from the article:

• Rollover is defined as a vehicle overturned by at least one quarter turn (at least onto its side).
• Some rollovers involve many quarter turns and the final resting position may be on the vehicle’s side, roof, or back on its wheels.
• Factors that cause a vehicle to roll over include trajectory (i.e., turning vs. straight), vehicle type, and speed (precrash velocity may be the most predictive factor)

The importance of vehicle rollover as a field triage criterion
J Trauma. 2009 Aug;67(2):350-7

Paramedics apply cervical spine rule successfully

The Canadian C-Spine rule – a decision instrument designed to clinically rule out important cervical spine injuries in alert patients – was successfully and safely applied by Canadian paramedics in a study of 1949 patients. Any misinterpretation erred on the side of safety.
This important work could ultimately result in less stress, discomfort, and wasting of ambulance resources and time for this large subgroup of pre-hospital patients.

The Out-of-Hospital Validation of the Canadian C-Spine Rule by Paramedics
Ann Emerg Med. 2009 Nov;54(5):663-671

emergence with ketamine overstated

A prospective study of 746 children sedated in the emergency department with iv or im ketamine revealed 2.1% may have experienced ‘emergence delirium’ although the authors concede this was difficult to define. In contrast, 291 (38%) reported pleasant altered perceptions. Follow up revealed at least one nightmare in the following weeks in 3.4% of patients, which may be well under the rate reported in the normal unsedated paediatric population.

What is the nature of the emergence phenomenon when using intravenous or intramuscular ketamine for paediatric procedural sedation?
Emerg Med Australas. 2009 Aug;21(4):315-22

Ambulance transport induces stress

Plasma levels of adrenaline and noradrenaline increased signficantly in patients with acute coronary syndrome during ambulance transportation – a finding in keeping with studies on normal volunteers. I wonder how much more of an effect helicopter retrieval might have?

Emergency ambulance transport induces stress in patients with acute coronary syndrome
Emerg Med J. 2009 Jul;26(7):524-8.

Ketamine lowered ICP in brain-injured kids

• Ventilated children between the ages of 1 and 16 with traumatic brain injury and elevated intracranial pressure (ICP) were given ketamine and effect on cerebral perfusion pressure (CPP) and ICP was measured. Ketamine decreased ICP while maintaining blood pressure and CPP. These results refute the notion that ketamine increases ICP. The authors conclude: “Ketamine is a safe and effective drug for patients with traumatic brain injury and intracranial hypertension, and it can possibly be used safely in trauma emergency situations”
  Effectiveness of ketamine in decreasing intracranial pressure in children with intracranial hypertension
  J Neurosurg Pediatr. 2009 Jul;4(1):40-6 (Full text)

Etomidate versus ketamine for rapid sequence intubation

Finally a well designed blinded randomised controlled trial on this subject. 0.3 mg/kg etomidate was compared with 2mg/kg ketamine for RSI in 655 patients requiring emergency intubation in the pre-hospital, emergency department, or intensive care unit environments. No difference was observed in intubation conditions or the primary endpoint of maximum SOFA score in the first three days, although the etomidate group had a higher rate of adrenal insufficiency as defined by response to an ACTH test.

Etomidate versus ketamine for rapid sequence intubation in acutely ill patients: a multicentre randomised controlled trial.
Lancet. 2009 Jul 25;374(9686):293-300

Clinical Update July 2009 CME Questions

Answer True or False to the following questions. Answers at the bottom of the July 2009 Update.

1) In refractory septic shock there is no clear evidence that steroids reduce mortality.

2) Noradrenaline (norepinephrine) may cause cerebral vasodilation by reducing minute ventilation

3) Intravenous morphine provides more effective analgesia to children than nebulised fentanyl

4) Paediatric non-femoral central venous catheter tips should be sited at the level of the carina

5) Following fibrinolysis for ST-elevation myocardial infarction, transferring the patient for urgent percutaneous coronary intervention (PCI) within six hours may improve outcome compared with delayed cardiac catheterisation.

July 2009

A Systematic Review of Corticosteroids in the Treatment of Severe Sepsis and Septic Shock in Adults

This thorough review confirms that steroids have no clear benefit on mortality in severe sepsis / septic shock. Looking at prolonged courses of low dose steroids, there may be a beneficial effect but this did not reach statistical significance.

JAMA. 2009 Jun 10;301(22):2362-75

http://www.ncbi.nlm.nih.gov/pubmed/19509383

Evaluation of emergency medicine trainees’ ability to use transport equipment

47 senior emergency medicine trainees from three Australian hospitals were tested three pieces of transport equipment from their own EDs: portable ventilator, infusion pump, and monitor-defibrillator. They didn’t do as well as you’d want....how would you fare?

Emerg Med Australas. 2009 Jun;21(3):170-7

http://www.ncbi.nlm.nih.gov/pubmed/19527275

Investigating pressure bandaging for snakebite in a simulated setting: Bandage type, training and the effect of transport

Previous work showed that systemic spread of venom from a snakebite to the limb could be prevented or delayed by complete immobilisation of the limb in combination with a pressure bandage of 55-70 mmHg or 40-70 mmHg in the lower and upper limbs, respectively. An assessment of the public’s and health care professionals’ ability to apply this ‘Aussie wrap’ revealed elasticised bandages to be far more likely than crepe bandages to achieve appropriate pressures, even after training, and a 30 minute ambulance ride further rendered the pressures achieved by crepe bandages inadequate.

Emerg Med Australas. 2009 Jun;21(3):184-90

http://www.ncbi.nlm.nih.gov/pubmed/19527277

Is cerebral oxygenation negatively affected by infusion of norepinephrine in healthy subjects?

An interesting study on nine healthy volunteers demonstrated noradrenaline infusions to increase MAP without increasing cardiac output (by increasing systemic vascular resistance). Measures of cerebral (frontal lobe) oxygenation, jugular venous saturation, and mean flow velocity in the middle cerebral artery all reduced with increasing doses of noradrenaline. The authors conclude that doses greater than 0.1 mcg/kg/min may reduce cerebral oxygenation. However increases in noradrenaline lowered paCO2 (through increases pulmonary ventilation) and it is unknown whether this was the major contributor to reduced oxygenation. It is also hard to ascertain the relevance to patients receiving noradrenaline, who unlike the healthy volunteers are not driven to supranormal blood pressures. In the meantime we will continue to attempt to optimise cerebral perfusion pressure using vasoactive drugs, but should be mindful that gross estimates of CPP may not tell us what we’re doing to cerebral oxygenation.

Br J Anaesth. 2009 Jun;102(6):800-5

http://www.ncbi.nlm.nih.gov/pubmed/19376788

Measuring the performance of an inter-hospital transport service

“There is currently no consensus on how the performance of an interhospital transport service can be measured” say the busy Children’s Acute Transport Service (CATS) in London, who classify their indicators under headings of safety, speed, efficiency, and satisfaction. They include a number of useful outcome measurements (such as unplanned subsequent transfers, and need for urgent intensive care interventions at the receiving hospital) that should stimulate other retrieval services - adult and paediatric - to look out how they measure their own performance. Nice paper, proving once again that paediatricians are not just little doctors.

Arch Dis Child. 2009 Jun;94(6):414-6

http://www.ncbi.nlm.nih.gov/pubmed/19174393

Nebulized fentanyl versus intravenous morphine in children with suspected limb fractures in the emergency department: a randomized controlled trial

In an nutshell: you can nebulise fentanyl in a dose of 4 mcg/kg for kids of 4 years of age and over and get pain relief equivalent to i.v. morphine 0.1 mg/kg

Emerg Med Australas. 2009 Jun;21(3):203-9

http://www.ncbi.nlm.nih.gov/pubmed/19527280

Practical anatomic landmarks for determining the insertion depth of central venous catheter in paediatric patients

The level of the carina is usually chosen as the target depth for internal jugular vein catheters in children to avoid catheter tip perforation of the right atrium or intrapericardial SVC. This level can now be estimate

d using external landmarks following this study of 90 children under 5 years of age. Ready? Right....

Find the sticky-out bit of the medial head of the right clavicle (point A in diagram) and measure its distance to a point halfway towards the internipple line (B). Add this to the distance between the insertion point of the catheter in the neck (I) and the medial head of the right clavicle (A again) and subtract 0.5. This gives you the catheter tip insertion distance in cm. It doesn’t apply to left sided or subclavian lines, but it seems useful for paediatric RIJV lines.

Br J Anaesth. 2009 Jun;102(6):820-3

http://www.ncbi.nlm.nih.gov/pubmed/19380312

Routine Early Angioplasty after Fibrinolysis for Acute Myocardial Infarction

Oh dear......A randomised controlled trial of 1059 patients who were thrombolysed for STEMI in centres without access to percutaneous coronary intervention (PCI) compared ‘standard’ timing of PCI (median time from randomisation to catheterisation 32 hrs) with urgent transfer and PCI (within 6 hours -actual median time from thrombolysis to ballooon inflation 3.9 hrs). The composite end point of death, reinfarction, heart failure, cardiogenic shock or recurrent ischaemia at 30 days was reduced in the intervention group from 17.2 to 11% (NNT = 16). The authors suggest that previous studies not showing such a benefit pre-dated modern stents and antiplatelet therapies. The study was not powered to detect differences in the individual components of the composite end point. It will be interesting to see if cardiologists consider this a bandwagon to jump upon, in which case let ambulance retrieval services beware!

N Engl J Med. 2009 Jun 25;360(26):2705-18

http://www.ncbi.nlm.nih.gov/pubmed/19553646

Use of a stylet for insertion of a Classic LMA

The most common problem in inserting the LMA classic is difficulty in passing it through the posterior pharynx, a problem made worse by a loss of curvature produced by repeated autoclaving. A stylet can be used to create a bend at two points: near the junction of the mask and the tube, and at the middle of the tube. The mask can then be inserted against the hard palate and swung inward. Care must be taken to avoid protruding the stylet beyond the aperture bar.

Resuscitation. 2009 Aug;80(8):964

http://www.ncbi.nlm.nih.gov/pubmed/19523741

Answers to July CME Questions:

1) T 2) F 3) F 4) T 5) T

Clinical Update June 2009 CME Questions

Answer True or False to the following questions. Answers at the bottom of the June 2009 Update.

1) Intraosseous fluid infusion rates are similar between humeral and tibial insertion sites.

2) Urban populations have a lower threshold for calling an emergency ambulance than rural populations

3) ACLS guidelines for ventilation are easier to achieve with larger self-inflating bags

4) ACLS guidelines for defibrillation are harder to achieve if the team must be formed during the resuscitation

5) The use of a pressure bag halves the rate of intraosseous saline infusion

June 2009

Trauma scissors vs the Rescue Hook, exposing a simulated patient: a pilot study

American military investigators compared traditional trauma scissors with the ‘rescue hook’ (a hooked knife with the cutting edge on the inside of the hook) in rapidly removing the clothes from a simulated casualty. An army desert combat uniform and boots were removed more quickly with the rescue hook, which was favoured by the combat medics employed in the study. We don’t have data on how it would work on denim, leather, or belts, but it looks pretty good. I just want to know if it’ll go through a sternum before I trade in my trauma scissors.

J Emerg Med. 2009 Apr;36(3):232-5

http://www.ncbi.nlm.nih.gov/pubmed/18155382

Prehospital airway management on rescue helicopters in the United Kingdom

26 of 27 identified UK rescue helicopter bases responded to a questionnaire sent by German anaesthesiologists on the airway equipment they carried. The take home message is that there were some important gaps: not all carried equipment for establishing a surgical airway and not all had a means of capnometry. Pull your socks up guys the Germans are watching.

Anaesthesia. 2009 Jun;64(6):625-31

http://www.ncbi.nlm.nih.gov/pubmed/19453316

An observational, prospective study comparing tibial and humeral intraosseous access using the EZ-IO

Emergency physicians at Singapore General Hospital found flow rates to be similar when comparing the tibia with the humerus as sites for adult IO access. The EZ-IO had a very high insertion success rate. It took about 12 minutes to infuse a litre of saline, which drops to about 6 minutes if a pressure bag is used.

Am J Emerg Med. 2009 Jan;27(1):8-15

http://www.ncbi.nlm.nih.gov/pubmed/19041528

Use of non-invasive ventilation to wean critically ill adults off invasive ventilation: meta-analysis and systematic review

The growing evidence base in support of liberating patients from invasive mechanical ventilation by means of non-invasive weaning is summarised in this systematic review of 12 randomised trials. Non-invasive weaning was associated with decreased mortality, ventilator associated pneumonia, length of stay in intensive care and hospital, total duration of mechanical ventilation, and duration of invasive ventilation. It should be noted that most of the trials exclusively enrolled patients with exacerbation of chronic obstructive pulmonary disease; benefits in other types of ventilated patients remain to be firmly proven.

BMJ. 2009 May 21;338:b157

http://www.ncbi.nlm.nih.gov/pubmed/19460803

Aeromedical retrieval for critical clinical conditions: 12 years of experience with the Royal Flying Doctor Service, Queensland, Australia

Over twelve years in Queensland the RFDS undertook over 72000 fixed wing retrievals, including

over 4000 critically ill patients. Trauma was the commonest diagnostic category. There were only 90 primary retrievals, from locations without healthcare facilities - less than one per month on average. This fascinating service covers vast distances, low population density, and a high number of indigenous people.

J Emerg Med. 2009 May;36(4):363-8

http://www.ncbi.nlm.nih.gov/pubmed/18814993

Does ambulance use differ between geographic areas? A survey of ambulance use in sparsely and densely populated areas

A lower use of emergency department health care services by rural residents as compared with urban residents has previously been described. This Swedish study examined the use of ambulance services in relation to geography, showing that patients from sparsely populated areas were sicker. required more treatment, and were assessed as not needing prehospital care less than half as often as their urban counterparts (16% vs 39%). Take home message is that population density is related to inappropriate use of ambulance services.

Am J Emerg Med. 2009 Feb;27(2):202-11

http://www.ncbi.nlm.nih.gov/pubmed/19371529

Hands-on time during cardiopulmonary resuscitation is affected by the process of teambuilding: a prospective randomised simulator-based trial

During simulated cardiac arrest resuscitations, a comparision was made between those run by teams that had had time to form before the arrest, and those that had to be assembled ad hoc after the arrest occurred. 99 teams of three doctors, including GPs and hospital physicians were studied. ACLS algorithms were less closely followed in the ad hoc formed teams, with more delays to therapies such as defibrillation. Analysis of voice recordings revealed the ad hoc teams to make fewer leadership utterances (eg. ‘we should defibrillate’ or ‘the next countershock will be 360J’) and more reflective utterances (eg. ‘what should we do next?’). The authors suggest that team building is therefore to be regarded as an additional task imposed on teams formed ad hoc during CPR that may substantially impact on outcome. No surprise to those of us who banned ‘cardiac arrest teams’ from our emergency department resuscitation rooms many years ago!

BMC Emerg Med. 2009 Feb 14;9:3

http://www.ncbi.nlm.nih.gov/pubmed/19216796

Full text at http://www.biomedcentral.com/1471-227X/9/3

Is the prevalence of deliberate penetrating trauma increasing in London? Experiences of an urban pre-hospital trauma service

The physician-led pre-hospital service London HEMS examined its penetrating trauma caseload between 1991 and 2006. Overall, stabbings rose annually by 23.2% and shootings by 11.0%.

Injury. 2009 May;40(5):560-3

http://www.ncbi.nlm.nih.gov/pubmed/19232594

Prehospital management of severe traumatic brain injury

A review of current practice and evidence base of this important topic can be found at

BMJ. 2009 May 19;338:b1683

http://www.ncbi.nlm.nih.gov/pubmed/19454738

Full text http://www.bmj.com/cgi/content/full/338/may19_1/b1683

Smaller self-inflating bags produce greater guideline consistent ventilation in simulated cardiopulmonary resuscitation

A comparison between two sizes of self-inflating resuscitation bags revealed improved adherence to resuscitation guidelines with the smaller bag. Student paramedics were more likely to produce suboptimal tidal volumes and ventilation rates with a 1500ml bag than a 1000ml bag during simulated ventilation of an artificial lung model.

BMC Emerg Med. 2009 Feb 20;9:4

http://www.ncbi.nlm.nih.gov/pubmed/19228432

Full text at http://www.biomedcentral.com/1471-227X/9/4

Answers to June CME Questions:

1) T 2) T 3) F 4) T 5) F

May 2009 Clinical Update CME Questions

Answer True or False to the following:

1. Ketamine when used as an induction agent for rapid sequence induction lowers ICP

2. Firm broad inguinal compression in an infant increases the diameter of the femoral vein for catheterisation

3. Doubling the radius of an intravenous cannula in a vein increases the flow rate by a factor of sixteen

4. Obesity is an independent risk factor for impossible bag-mask ventilation

5. Movement of a tracheal tube from the centre to the corner of the mouth at the same fixed insertion length risks endobronchial migration of the tube tip

May 2009

A comparison of three cervical immobilization devices

A novel, rigid cervical collar was compared with more commonly used one and two piece devices. It permitted less neck movement in normal volunteers in the seated and supine positions, although there was still some movement without manual immobilisation. The authors conclude: ‘the XCollar may provide an acceptable alternative to manual cervical stabilization in situations where the number of patients exceeds the number of EMS providers available to provide care'.

Now if only we had some evidence that collars improved outcome anyway...

Prehosp Emerg Care. 2009 Apr-Jun;13(2):256-60

http://www.ncbi.nlm.nih.gov/pubmed/19291567

Anaesthesia in haemodynamically compromised emergency patients: does ketamine represent the best choice of induction agent?

Yes! And this article does a great job of attempting to convince those that still don’t believe it. An excerpt:Despite widespread avoidance of ketamine by clinicians following (actual or potential) brain injury, this stance does not withstand scrutiny and we would argue that ketamine is a rational choice for use in patients with brain injury, especially where haemodynamic compromise (e.g. polytrauma) is present or likely. C’mon everybody else, catch up here - you know it makes sense.

Anaesthesia. 2009 May;64(5):532-9

http://www.ncbi.nlm.nih.gov/pubmed/19413824

Analysis of the retrieval times of a centralised transport service, New South Wales, Australia

A key first step in quality improvement is knowing what you’re doing now. Newborn and Paediatric retrieval times for over 17000 missions were broken down into components such as initial response, stabilisation, and handover times. These data might provide a benchmark for other services.

Arch Dis Child. 2009 Apr;94(4):282-6

http://www.ncbi.nlm.nih.gov/pubmed/18927147

Does a Higher Positive End Expiratory Pressure Decrease Mortality in Acute Respiratory Distress Syndrome?

This systematic review and meta-analysis makes the following points: (1) while most benefit is likely to be produced when it is used as part of a protective ventilation strategy (including low tidal volumes and limited plateau pressure) high PEEP may have an independent beneficial effect; (2) studies of ALI/ARDS are dogged by the heterogeneous nature of the disease and the spectrum of severity included; (3) the nonsignificant trend towards a greater incidence of barotrauma in high-PEEP patients is outweighed by the benefits, although evidence is limited by the lack of a standard definition for barotrauma.

Take home message: the sicker the patient (in terms of oxygenation), the more likely high PEEP (as defined by >10 cmH₂O or 1-2 cmH₂O above the lower inflection point) will be beneficial, through the prevention of atelectasis, recruitment of already collapsed alveolar units, and avoiding the cyclical opening/collapse of alveoli.

Anesthesiology. 2009 May;110(5):1098-105

http://www.ncbi.nlm.nih.gov/pubmed/19352160

Effects of reverse Trendelenburg position and inguinal compression on femoral vein cross-sectional area in infants and young children

Ultrasound demonstrated an increase in femoral vein diameter in infants and children when a head up-leg down position was adopted. This was increased further when inguinal compression was performed by applying compression 1–2 cm above the inguinal ligament with three fingers as firmly and as broadly as possible at the point of arterial pulsation. A top tip for optimising success in paediatric femoral vein catheterisation.

Anaesthesia. 2009 Apr;64(4):399-402

http://www.ncbi.nlm.nih.gov/pubmed/19317705

Fluid Flow Through Intravenous Cannulae in a Clinical Model

Published flow rates for cannulae are derived from a test in which fluid runs through a perfectly straight cannula into an open receptacle. Laminar flow is expected in such a model in which the Hagen-Poisseuille formula tells us that flow is proportional to the fourth power of the radius. In this study manufacturers’ published flow rates were compared with an artifical vein model. Hartmann’s flowed faster than Gelofusine. For all cannulas flow was less than the manufacturers’ published rates. Although the radius was the biggest determinant of flow rate, the fourth power could not be used, suggesting a mixture of laminar and turbulent flow. The addition of pressurised infusions increased the flow rate with increasing pressure. Although the vein model used has limitations, and many other factors may influence flow rate in the clinical setting, the authors’ conclusions are helpful:

While the effect of radius is less than commonly believed, it is still important. However, clinicians should be aware of the limitations of increasing radius and use other strategies to increase flow when needed. These could include use of pressure, choice of fluid to be infused, and using multiple cannulae in parallel.

Anesth Analg. 2009 Apr;108(4):1198-202

http://www.ncbi.nlm.nih.gov/pubmed/19299786

Prediction and Outcomes of Impossible Mask Ventilation - A Review of 50,000 Anesthetics

Of 53,041 attempts at mask ventilation, 77 cases of impossible mask ventilation (0.15%) were observed. Neck radiation changes, male sex, sleep apnea, Mallampati III or IV, and presence of beard were identified as independent predictors. Nineteen impossible mask ventilation patients (25%) also demonstrated difficult intubation, with 15 being intubated successfully. Impossible mask ventilation is an infrequent airway event that is associated with difficult intubation. Neck radiation changes represented the most significant clinical predictor of impossible mask ventilation. Risk factors for impossible mask ventilation have not previously been described and you read it here first!

Anesthesiology. 2009 Apr;110(4):891-7

http://www.ncbi.nlm.nih.gov/pubmed/19293691

Focused emergency echocardiography: lifesaving tool for a 14-year-old girl suffering out-of-hospital pulseless electrical activity arrest because of cardiac tamponade

A post-operative pericardial effusion following VSD repair caused a PEA cardiac arrest, during which a pre-hospital physician identified tamponade on portable ultrasound and successfully performed pericardiocentesis. The patient made a full recovery.

Eur J Emerg Med. 2009 Apr;16(2):103-5

http://www.ncbi.nlm.nih.gov/pubmed/19218856

Tracheal tube fixation: the effect on depth of insertion of midline fixation compared to the angle of the mouth

This elegant study from India showed that movement of a tracheal tube from the middle to the corner of the mouth while fixed at the same insertion length results in migration of the tube tip towards the carina, an average of 1.34 cm in females and 1.36 cm in males. This is because the lip is lower at the angle of the mouth, and the tracheal tube slipped off the tongue into the paraglossal area on lateral movement, thereby taking a shorter course. This resulted in a significant risk of endobronchial intubation, particular in females. The authors recommend that the depth of insertion when fixing the tube at the angle of the mouth should be adjusted, and should not be the same as those recommended for midline fixation. When securing the tracheal tube at the angle of the mouth, the depth of insertion should be reduced by an average of 1.35 cm. It is recommended that the tube should be moved to its final position of fixation while the laryngoscope is still in place and the distal insertion mark still in view and the depth of insertion noted.

Anaesthesia. 2009 Apr;64(4):383-6

http://www.ncbi.nlm.nih.gov/pubmed/19317702

Answers to May CME Questions:

1) F 2) T 3) F 4) F 5)T