Tag Archives: investigation

CT cervical spine in obtunded trauma patients

Prolonged collar use and spinal immobilisation in ICU patients can contribute to pressure sores, increased intracranial pressure, venous obstruction, difficulties with airway management, difficulties with central venous access, respiratory complications, and DVT, so a reliable investigation to rule out unstable cervical spine injury is required. Several studies demonstrate the high sensitivity of CT, and now a prospective study from Canada attempts to lend further support to this.

Comparing against their chosen gold standard of dynamic radiography, ie. flexion/extension views (F/E) in 402 patients who received both tests, there was one case of injury detected by F/E but not by CT, leading to quoted sensitivity of 99.75%. However this negative CT turned out to be a reporting error – the scan, which the authors include in their article, was clearly abnormal.

One weakness of this study is that they excluded patients who died on ICU. More worrying are the stats quoted. The authors stat ‘four hundred one patients (99.75%) had normal CT and F-E images facilitating clinical clearance of their C-spine and discontinuation of spinal precautions‘. So in other words, there was only one patient in their series of 402 with an injury (according to the gold standard), and this was missed. The sensitivity is therefore zero percent, not 99.75%. What seems to be a further error is the reporting in a table of 401 patients who had ‘Positive CT and Negative F-E’, which if true, would give a specificty of zero too!

This paper covers an important topic for intensivists but it seems to me to be too flawed to add meaningfully to the existing evidence that necks can be ‘cleared’ by CT in patients without signs of cervical spine injury, in whom it has been said that the risks of prolonged collar use and immobilisation may outweigh the risks of missed cervical injury.

Cervical spine clearance in obtunded blunt trauma patients: a prospective study
J Trauma. 2010 Mar;68(3):576-82

Echo best test for acute LVF in ED

Three diagnostic tests for acute left ventricular heart failure in dyspnoeic patients were compared, with the gold standard being the diagnosis by three independent reviewers (two cardiologists and one respiratory physician) who were blinded to the results of the tests being examined. The tests in question were  NT-proBNP, the Boston criteria, and limited echo performed by emergency physicians.

The primary goal of the echo study was the detection of the following echocardiographic variables, expressed as present or absent: reduced LV ejection fraction (LV ejection fraction <50% on subjective visual estimation of the change in LV size between diastole and systole) and the ‘‘restrictive’’ pattern on pulsed Doppler analysis of mitral inflow (using the apical view).

According to the authors, pulsed Doppler analysis of mitral inflow can be described by three patterns: 1) an ‘‘impaired relaxation’’ pattern, suggesting no increase in LV filling pressures; 2) a ‘‘normal’’ or ‘‘normalized’’ pattern; and 3) a restrictive pattern, suggesting an increase in LV filling pressures.

Trained emergency physicians were able to perform EDecho in a median of 4 minutes, obtaining Doppler data in an average of 80% of patients presenting for acute dyspnea. Considering the 125 patients with both EDecho variables available, reduced LV ejection fraction was less accurate than the restrictive mitral pattern for the diagnosis of aLVHF. The restrictive pattern was more sensitive (82%) and specific (90%) than reduced LV ejection fraction and more specific than the Boston criteria and NT-proBNP for the diagnosis of aLVHF. The accuracy of the restrictive pattern in the overall population was 75%, compared with accuracy of 49% for both NT-proBNP and Boston criteria.

Diagnostic accuracy of emergency Doppler echocardiography for identification of acute left ventricular heart failure in patients with acute dyspnea: comparison with Boston criteria and N-terminal prohormone brain natriuretic peptide.
Acad Emerg Med. 2010 Jan;17(1):18-26

Abnormal head CT in altered mental status

In a study of 674 patients with altered mental status who received a CT scan of the brain, logistic regression analysis identified a series of clinical factors that were associated with an abnormal CT result.

Factors with an adjusted odds ratio between 1 and 2.5 included GCS less than 15, focal weakness, diastolic blood pressure greater than 80mmHg and antiplatelet use.

Four variables were associated with an adjusted odds ratio of 2.5 or above. These included presence of headache, dilated pupils (either unilateral or bilateral), upgoing plantar response and anticoagulant use.

Identifying risk factors for an abnormal computed tomographic scan of the head among patients with altered mental status in the Emergency Department
Eur J Emerg Med. 2009 Sep 21. [Epub ahead of print]

Whole-body CT during trauma resuscitation

German trauma patients are more likely to survive if they have a whole body CT rather than selective scans. Or that’s what this paper would have you believe IF you’re happy with the retrospective comparison, multivariate adjustments, and potential confounders. Still, if it helps you get your radiologists to play ball, the reference is…

Effect of whole-body CT during trauma resuscitation on survival: a retrospective, multicentre study Lancet. 2009 Apr 25;373(9673):1455-61

Imaging for PE in pregnancy

A review article on pulmonary embolism in pregnancy reminds us that the mortality associated with untreated PE far outweighs the potential oncogenic and teratogenic risk incurred by fetal exposure to diagnostic imaging for PE.
The minimum dose of radiation associated with increased risk of teratogenicity in human beings has yet to be firmly established, but on the basis of compiled mouse, rat, and human data, radiation exposure of 0·1 Gy at any time during gestation is regarded as a practical threshold beyond which induction of congenital abnormalities is possible.
An exposure of the conceptus to 0·01 Gy above natural background radiation increases the probability of cancer before the age of 20 years from 0·03% to 0·04%.

Reassuringly, a chest radiograph, ventilation perfusion scan, and conventional pulmonary angiogram combined with CT pulmonary angiogram expose the fetus to a total of 0·004 Gy.

Pulmonary embolism in pregnancy
Lancet. 2010 Feb 6;375(9713):500-12

Can venous blood gases replace arterial gases?

A comprehensive summary of the literature presented by Professor Anne-Maree Kelly in June 2009 at 4ème SYMPOSIUM INTERNATIONAL BLOOD GASES AND CRITICAL CARE TESTING in France can be viewed on her presentation slides at the link below.

She summarises:

  • pH – Close enough agreement for clinical purposes in DKA, isolated metabolic disease; more work needed in shock, mixed disease
  • Bicarbonate – Close enough agreement for clinical purposes in most cases; more work needed in shock, mixed disease, calculated vs measured gap
  • pCO2 – NOT enough agreement for clinical purposes; potential as a screening test
  • Potassium – Insufficient agreement between serum and BG values for clinical purposes
  • Base excess – Insufficient data

Can venous blood gas analysis replace arterial in emergency and critical care?