Most detailed image of night sky unveiled

From New Scientist

18:30 11 January 2011 by David Shiga, Seattle

It would take 500,000 high-definition TVs to view it in its full glory. Astronomers have released the largest digital image of the night sky ever made, to be mined for future discoveries.

It is actually a collection of millions of images taken since 1998 with a 2.5-metre telescope at Apache Point Observatory in New Mexico. The project, called the Sloan Digital Sky Survey, is now in its third phase, called SDSS-III.

Images of the northern and southern hemispheres of our galaxy (bottom) reveal "walls" of galaxies that are the largest known structures in the universe. Zooming in on a patch of sky in the southern hemisphere reveals the spiral galaxy M33 (top left). Zooming in further (top centre) reveals a region of intense star formation known as NGC 604 (green swirls, top right)

Altogether, the images in the newly released collection contain more than a trillion pixels of data, covering a third of the sky in great detail.

“This is one of the biggest bounties in the history of science,” says SDSS team member Mike Blanton of New York University in New York City. “This data will be a legacy for the ages.”

via Most detailed image of night sky unveiled – space – 11 January 2011 – New Scientist – READ MORE…

Hypothermia and hypokalaemia

We all like to treat selected post cardiac arrest patients with hypothermia now, but isn’t hypothermia associated with a drop in potassium, which of course can precipitate pesky ventricular dysrhythmias in patients who would really rather not arrest again. Maybe the hypothermia itself is protective against the dysrhythmias?

A study from the Mayo Clinic updates our knowledge of this area:

METHODS: We retrospectively analyzed potassium variability with Therapeutic Hypothermia (TH) and performed correlative analysis of QT intervals and the incidence of ventricular arrhythmia.

RESULTS: We enrolled 94 sequential patients with OHCA, and serum potassium was followed intensively. The average initial potassium value was 3.9±0.7 mmol/l and decreased to a nadir of 3.2±0.7 mmol/l at 10 h after initiation of cooling (p<0.001). Eleven patients developed sustained polymorphic ventricular tachycardia (PVT) with eight of these occurring during the cooling phase. The corrected QT interval prolonged in relation to the development of hypothermia (p<0.001). Hypokalemia was significantly associated with the development of PVT (p=0.002), with this arrhythmia being most likely to develop in patients with serum potassium values of less than 2.5 mmol/l (p=0.002). Rebound hyperkalemia did not reach concerning levels (maximum 4.26±0.8 mmol/l at 40 h) and was not associated with the occurrence of ventricular arrhythmia. Furthermore, repletion of serum potassium did not correlate with the development of ventricular arrhythmia.

CONCLUSIONS: Therapeutic hypothermia is associated with a significant decline in serum potassium during cooling. Hypothermic core temperatures do not appear to protect against ventricular arrhythmia in the context of severe hypokalemia and cautious supplementation to maintain potassium at 3.0 mmol/l appears to be both safe and effective.

Hypokalemia during the cooling phase of therapeutic hypothermia and its impact on arrhythmogenesis
Resuscitation. 2010 Dec;81(12):1632-6

Pre-hospital iv and increased mortality

The US media seem to be making a big thing of a recent article published ahead of print which demonstrates an association between increased mortality from trauma and the insertion of an intravenous line with or without the administration of fluid.

This was a retrospective cohort study of over 770 000 patients from the National Trauma Data Bank. Approximately half (49.3%) received ‘prehospital IV’, which could mean fluids, or could just mean insertion of an intravenous cannula: ‘we could not definitively differentiate IV fluid administration versus IV catheter placement alone‘.

Unadjusted mortality was significantly higher in patients in the prehospital IV group, although the abstract inaccurately reports this to be ‘in patients receiving prehospital IV fluids‘ (4.8% vs. 4.5%, P < 0.001).

Multivariable logistic regression was used to examine the relationship between prehospital IV and mortality in the 311,071 patients with complete data. After adjustment, prehospital IV patients had significantly higher mortality than those without a prehospital IV. The odds ratio of death associated with prehospital IV placement was 1.11 (95% CI 1.06–1.17). When Dead-On-Arival patients were excluded from the group as a whole, the association persisted (OR 1.17, 95% CI 1.11–1.23).

Hey you're killing me here!

On subgroup analyses, the association between IV placement and excess mortality was maintained in nearly all patient subsets; the effect was more exaggerated in penetrating trauma victims.

Media speculation as to the reason for this association abounds, like USA Today‘s ‘those who are given pre-hospital IV fluids are actually 11% more likely to die than those who aren’t, not only because of transport delays but also in part because of the increased risk for bleeding that can accompany a fluid-induced increase in blood pressure‘. However the study did not record any pre-hospital times and could not tell which patients received fluid, let alone what the effect of fluid on blood pressure was.

The authors are open about this and other limitations: ‘The NTDB did not report prehospital transport times or differentiate urban versus rural care. Thus, we could not examine whether excess mortality in patients treated with IVs was directly associated with delays in transport to definitive care. We were also not able to control for transport time within the multiple regression model or perform a stratified analysis by urban versus rural patients. Perhaps this analysis would have identified a subset of patients who may benefit from IV placement‘.

No doubt this will be added to the pile of mainly hypothesis-generating literature quoted by the scoop-and-run brigade whose black-and-white worldview includes paramedics who want to delay proper treatment and a homogeneous trauma population whose lives can only be saved by a trauma surgeon in a hospital. Those who have evolved colour vision find this an interesting, but hardly practice-changing study; caution regarding injudicious fluid administration has been the game plan for many civilian and military pre-hospital providers since early last decade, and it is clear that different patients with different injury patterns, different degrees of physiological derangement, and different distances from the right hospital will continue to have different clinical needs specific to their presentation, some of which are likely to be of benefit if provided in the field, through an intravenous line.

Prehospital Intravenous Fluid Administration is Associated With Higher Mortality in Trauma Patients: A National Trauma Data Bank Analysis
Ann Surg. 2010 Dec 20. [Epub ahead of print]

Body position in poisoning

You come across a patient in the community who has taken an overdose of pills. The ambulance is on its way and you have no medical equipment. Is there any first aid that might help? How should you position the patient if they are unconscious?

Authors of a BestBet in the EMJ searched the literature to answer the three-part question:
In [orally poisoned patients] does [a specific body position] result in [a better outcome for the patient]?

The limited evidence they found from just two papers suggests that drug absorption is lowest in patients lying on their left side, so you might want to consider placing an unconscious overdose patient in the left-sided recovery position prior to definitively managing them in hospital. The theoretical increased risk of pulmonary aspiration on the left side should be considered however. The table shows just how limited this evidence base is – but the idea is an interesting one.

Optimal body position in oral poisoning cases
Emerg Med J 2010;27:952-953 Full text from the BestBets site

Bleeding Tracheostomy

Adapted from the UK Intensive Care Society’s ‘Standards for the care of adult patients with a temporary tracheostomy

Bleeding from an established tracheostomy (ie. ‘late bleeding’, as to opposed to peri-operative bleeding that is more common and often benign) may occur because of erosion of blood vessels in and around the stoma site. This is more likely if there has been infection of the stoma site. Such bleeding may settle with conservative management. More worryingly, however, is the prospect of such bleeding being the result of erosion of a major artery in the root of the neck where there has been pressure from the tracheostomy tube itself or the cuff tube. Most commonly, this erosion occurs into the right brachiocephalic artery (also known as the innominate artery), resulting in a tracheo-innominate artery fistula. This situation may be heralded in the preceding hours by a small, apparently insignificant, sentinel bleed. Bleeding from such a fistula will be massive. THIS IS A LIFE-THREATENING EMERGENCY and so decisions need to be rapidly made.

  1. Call for help– senior medical and nursing staff, other health professionals with tracheostomy care skills (e.g. respiratory therapist, physiotherapist).
  2. Clear airway – blood clots may need to be suctioned.
  3. Replace blood products as required
  4. Bleeding may be temporarily reduced or stopped by applying finger pressure to the root of the neck in the sternal notch, or by inflating the tracheostomy tube cuff (if present) with a 50ml syringe of air. This inflation should be done slowly and steadily to inflate the balloon to a maximum volume without bursting it. Depending on the type and size of the tracheostomy tube this may be anywhere between 10 and 35 ml.
  5. Urgent referral for surgical exploration must now be made, if not already done so. In addition to an ENT or maxillofacial surgeon, it may be necessary to get help from a vascular surgeon. Sometimes, the damage can only be repaired utilising cardio-pulmonary bypass, and so a cardiothoracic surgeon may also be needed to help.
  6. Consider palliation – it is well recognised that fatalities occur in this situation, and that this may be the mode of death for some patients with head and neck cancers

Tracheostomy resources

The National Tracheostomy Safety Project at in the UK aims to allow patients with tracheostomies or laryngectomies to be safely cared for in hospitals.

The site contains a wealth of educational resources of use to the critical care practitioner. For example, have you thought about what do with a laryngectomy patient who presents with dyspnoea, or even apnoea? Remember that although applying oxygen to the face & neck is a default emergency action for all patients with a tracheostomy, these patients cannot be intubated and ventilated through the normal oral route since their tracheostomy is an end stoma – it does not communicate with the mouth:

Compare this with the algorithm for other patients with a tracheostomy, in whom attempts to oxygenate and ventilate, including intubation, can be made in an emergency either from the ‘top end’ (mouth) or via the stoma:

There are also a number of multimedia resources and a link to the UK Intensive Care Society’s Tracheostomy Guidelines

Percutaneous Dilatational Tracheostomy

In ICU, Percutaneous Dilatational Tracheostomy (PDT) is often performed to facilitate weaning from mechanical ventilation, reduce anatomical dead space, avoid laryngeal injury and aid in management of tracheobronchial and pulmonary secretions.

There is still controversy over optimal timing and case selection for PDT. Some organisations have helped to clarify the situation for practicing intensivists.

In 2010 the Australian and New Zealand Intensive Care Society (ANZICS) produced its Percutaneous Dilatational Tracheostomy Consensus Statement, to represent best current practice in Australia and New Zealand.

This can be downloaded from here.

A tracheal tube in the chest

Intercostal catheters can kink, obstruct, or get pulled out. These hazards are greater during transport of the patient. Critical care and retrieval medicine doctors in Queensland, Australia (where many people are having a bad time right now) have invented an elegant alternative: using a cuffed tracheal tube in the pleural space instead. It can be attached to a Heimlich valve.

They even used a bit of science to demonstrate its effectiveness, by creating pneumothoraces and haemothoraces in sheep and comparing the tracheal tube with a standard intercostal catheter (ICC).

The method for insertion is simple:

  1. Breach the pleura
  2. Insert a 14 Fr Cook intubating bougie into the thoracic cavity
  3. Railroad a 7.0 mm internal diameter tracheal tube (ETT) into the chest cavity
  4. Inflate the cuff
  5. Retract the tube until resistance is felt.
  6. Remove the ETT connector
  7. Attach a Heimlich valve

The results of the comparison are convincing: ‘The ETT proved faster to insert for both sheep. This was likely because it did not require suturing. Both the ETT and the ICC were comparable in draining blood. It was noted that neither tube was particularly effective when the haemothorax was positioned ‘side-up’. When turned ‘side-down’, both tubes successfully drained blood. Despite having multiple drainage ports, the ICC required more manipulation and was noted to kink. Conversely, the ETT with a single lumen and a Murphy eye, was stiffer and drained a similar amount of blood without the catheter having to be milked.’

Proposed advantages of this method include:

  • More portable equipment
  • Faster insertion
  • Provides kit redundancy
  • Does not require suturing
  • Avoids operator trauma from any sharp edges such as a fractured rib. (No attempt was made to place a finger into the chest cavity in the ETT group).
  • Allows for a smaller incision
  • Less trauma to the insertion site
  • Might also offer a back up, when conventional equipment has been exhausted.

The authors graciously note that both Portex and Cook have developed ICC kits that now go some way in supporting the original idea behind this study. These include flexible introducers (Portex) and guidewire insertion technique (Cook).

Appraisal of the endotracheal tube as an alternative to the intercostal catheter
Emerg Med Australas. 2010 Dec;22(6):573-4

Cuff pressures and tracheal injury

We all intubate patients with cuffed tubes, but we’re far too busy and important to fart around measuring tracheal tube cuff pressures when we’re saving lives right? Surely something the ICU nurses can sort out between ‘eye care’ and swabbing for MRSA.

The modern ‘high volume low pressure’ cuff has certainly led us to worry less about cuff pressures, and in frontline critical care specialties like emergency medicine and pre-hospital and retrieval medicine it’s the last thing on our minds. However we should consider the accumulating pool of evidence that tells us:

  1. Physicians are hopelessly poor at estimating cuff pressures based on palpating the pilot balloon
  2. Cuff pressures are frequently very high
  3. Tracheal mucosal injury can occur even after short term intubation (a few hours)
  4. When the pressure in the cuff exceeds 22 mm Hg, blood flow in the tracheal mucosa begins decreasing
  5. Tracheal mucosal blood flow reduces markedly when the pressure reaches 30 mm Hg
  6. When the pressure in the cuff reaches 50 mm Hg for 15 minutes, ischemic injury to the tracheal mucosa can occur

Patchy hemorrhagic ulceration in tracheal mucosa

A study from China tested the hypothesis that an appropriate tracheal tube cuff (ETTc) pressure even in short procedures would reduce endotracheal intubation–related morbidity. They compared bronchoscopic appearance of tracheal mucosa, and patient symptoms of tracheal injury, in two groups of elective surgical patients anaesthetised and intubated between 120 and 180 minutes: a control group without measuring ETTc pressure, and a study group with ETTc pressure measured and adjusted to a range 15-25 mmHg. The endoscopist was blinded to the study group allocation.

The mean ETTc pressure measured after estimation by palpation of the pilot balloon of the study group was 43 +/- 23.3 mm Hg before adjustment (the highest was 210 mm Hg), and 20+/- 3.1 mm Hg after adjustment (p< 0.001). The incidence of postprocedural sore throat, hoarseness, and blood-streaked expectoration in the control group was significantly higher than in the study group. As the duration of endotracheal intubation increased, the incidence of sore throat and blood-streaked expectoration in the control group increased. The incidence of sore throat in the study group also increased with increasing duration of endotracheal intubation. Fiberoptic bronchoscopy showed that the tracheal mucosa was injured in varying degrees in both groups, but the injury was more severe in the control group than in the study group.

So..time to get a cuff manometer for your ED or helicopter? Perhaps you already have one. What do you think?

Correlations Between Controlled Endotracheal Tube Cuff Pressure and Postprocedural Complications: A Multicenter Study
Anesth Analg. 2010 Nov;111(5):1133-7

Related posts:

Cuff pressure in flight

Paediatric cuff pressures

Better outcome with paediatric retrieval teams

Data from the England and Wales Paediatric Intensive Care Audit Network on children (aged 16 years or younger) admitted to 29 regional paediatric intensive care units (PICUs) between 1 January 2005 and 31 December 2008 were analysed in a retrospective cohort study to assess the effectiveness of the specialist retrieval teams.

The type of transferring team (specialist or non-specialist) was known for 16 875 cases and was specialist in 13 729 (81%). Compared with children transferred to PICUs from within the same hospital, children transferred from other hospitals were younger (median age 10 months vs 18 months), more acutely ill (mortality risk 6% vs 4% using the Paediatric Index of Mortality), needed more resources (such as invasive ventilation, vasoactive drugs, renal replacement therapy, extracorporeal membrane oxygenation and/or multiple-organ support), had longer stays in the PICU (median 75 h vs 43 h) and had a higher crude mortality (8% vs 6%). On multivariable analysis after adjustment for case mix and organisational factors, the risk of death among interhospital transfers was significantly (35%) lower than among intrahospital transfers. With similar analysis, the times spent in PICU did not differ significantly between these two groups. When the type of transferring team was considered, crude mortality was similar with specialist and non-specialist teams, although the children transferred by the specialist teams were more severely ill. On multivariable analysis, the risk of death was 42% lower with specialist team transfer.

These findings appear to confirm the value of specialist retrieval teams. Why children transferred from other hospitals did better than children transferred to the PICU in the same hospital is not explained.

Effect of specialist retrieval teams on outcomes in children admitted to paediatric intensive care units in England and Wales: a retrospective cohort study
Lancet. 2010 Aug 28;376(9742):698-704