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.
Fluid flow through intravenous cannulae in a clinical model
Anesth Analg. 2009 Apr;108(4):1198-202
In adult patients injured in front impact motor vehicle collisions, the outcomes of obese patients with a Body Mass Index greater than 30 kg/m2 was compared with those less than 30 kg/m2. Obese patients were more likely to suffer a severe head injury from a frontal collision.
J Trauma. 2009 Mar;66(3):727-9
Traumatic Brain Injury After Frontal Crashes: Relationship With Body Mass Index
In 180 intubated trauma patients in the ED, there was little correlation between arterial carbon dioxide tension (PaCO2) and end-tidal carbon dioxide levels (ETCO2) (R2 = 0.277). In fact, in those patients ventilated to the ‘normal range’ of 35-40 mmHg (4.6-5.2 kPa), PaCO2 was over 50 mmHg 30% of the time. Slightly reassuring that in isolated brain injury the correlation was better (r2 = 0.52)
The Utility of Early End-Tidal Capnography in Monitoring Ventilation Status After Severe Injury
J Trauma. 2009 Jan;66(1):26-31
Haemostatic resuscitation of trauma patients, using high ratios of fresh frozen plasma (FFP) to packed red cells (PRBC), is growing in popularity as a result of military experience. Few data support the practice in civilian trauma. It is possible that some of the demonstrated mortality benefit is a result of survival bias: it takes time to obtain FFP, by which time severely injured patients may be dead. Therefore, those that receive large ratios of FFP:PRBC must have survived long enough to receive it. In other words FFP doesn’t lead to survival, but survival leads to FFP. Some evidence in favour of this explanation is provided on a study of 134 patients in the Journal of Trauma. Reanalysing data to correct for survival bias made an apparently significant survival benefit from high FFP:PRBC ratios go away. An interesting paper, although unlikely to dissuade us from paying attention to coagulopathy in trauma. I suspect the debate on optimal blood product resuscitation will be around for a while.
The Relationship of Blood Product Ratio to Mortality: Survival Benefit or Survival Bias?
J Trauma. 2009 Feb;66(2):358-62
Lactate may be an important metabolic substrate for injured brain and sodium lactate may have beneficial effects on cerebral oedema and cerebral blood flow. Sodium lactate was compared with 20% mannitol in severely brain injured patients with cranial hypertension in a randomised controlled trial. Sodium lactate was more likely to lower ICP, and to have a sustained effect on ICP. A nonsignificant improvement in one year outcome was seen with sodium lactate, although the study was not powered for this endpoint. These promising findings should prompt a larger multicentre study.
Sodium lactate versus mannitol in the treatment of intracranial hypertensive episodes in severe traumatic brain-injured patients
Intensive Care Med. 2009 Mar;35(3):471-9
The presence and degree of compartment intrusion (from crash investigation data) was correlated with the likelihood of serious injury in 880 children from age 0-15 years, and odds for presence of serious injury increased for each centimetre of compartment intrusion.
Passenger Compartment Intrusion as a Predictor of Significant Injury for Children in Motor Vehicle Crashes
J Trauma. 2009 Feb;66(2):504-7
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
A comprehensive review of the literature, the findings of which showed ‘compelling’ consistency: digital rectal examination (DRE) as a screening test had sensitivities ranging from 0% to 50%, had consistently high false-positive and false-negative rates, and did not improve the predictive value of the other components of a typical trauma examination.
Based on case reports of five patients, the authors suggest DRE may be of value during trauma evaluation in the following settings: (1) patients with evidence of penetrating trauma in the vicinity of the rectum, (2) cases in which the presence of neurologic injury is neither completely supported nor refuted by the clinical ﬁndings, and (3) before pharmacologic paralysis. A selective approach is therefore recommended. Some good news for your patients if this will persuade you to discard another piece of longstanding dogma perpetuated in basic trauma teaching.
Should the digital rectal examination be a part of the trauma secondary survey?
Ann Emerg Med. 2009 Feb;53(2):208-12
This CT study of 110 trauma patients showed: ‘the standard 4.4-cm angiocatheter is likely to be unsuccessful in 50% (95% conﬁdence interval = 40.7–59.3%) of trauma patients on the basis of body habitus. In light of its low predicted success, the standard method for treatment of tension pneumothorax by prehospital personnel deserves further consideration’. Consistent with several other Ultrasound and CT-based studies published on the same subject then.
Needle thoracostomy for tension pneumothorax: failure predicted by chest computed tomography
Prehosp Emerg Care. 2009 Jan-Mar;13(1):14-7
Blood transfusion in trauma is a risk factor for acute respiratory distress syndrome (ARDS). An analysis of 14070 patients in a trauma database showed that 521 (4.6%) developed ARDS. Logisitc regression analysis demonstrated that, independent of injury type, injury severity, or pneumonia, (1) early PRBCs transfusion of more than 5 units during the ﬁrst 24 h of hospital admission predicted ARDS and (2) each unit of PRBCs transfused early after admission increased the risk of ARDS by 6%.
Early packed red blood cell transfusion and acute respiratory distress syndrome after trauma.
Anesthesiology. 2009 Feb;110(2):351-60