Military guys are great at coming up with practical solutions. Need to infuse fluid in the field but have no pressure bag or drip stand? Putting the bag under the patient’s body can squeeze fluid in, but the best place under the patient wasn’t known. A volunteer military study infusing saline through a 14G cannula compared six under-body locations: heels, buttock cleft, sacrum, interscapular region, cervical spine and occiput.
The buttock cleft was best.
In some circles, ‘wuntwuntwun’ is in danger of becoming the new dogma of trauma fluid replacement (ie. 1 unit of plasma and 1 unit of platelets for every unit of red cells). Since it takes longer to thaw some plasma than it does to throw in some O negative packed red cells, some really sick patients may be dead before they get the plasma, biasing comparisons that show a reduced mortality in patients who were still alive to receive plasma. This ‘survivor bias’ has been suggested as a reason that high plasma:red cell ratios are associated with mortality reduction, although this has been challenged.
The survivor bias explanation receives some new support by the following (small) study from Journal of Trauma: BACKGROUND: In light of recent data, controversy surrounds the apparent 30-day survival benefit of patients achieving a fresh frozen plasma (FFP) to packed red blood cell (PRBC) ratio of at least 1:2 in the face of massive transfusions (MT) (≥10 units of PRBC within 24 hours of admission). We hypothesized that initial studies suffer from survival bias because they do not consider early deaths secondary to uncontrolled exsanguinating hemorrhage. To help resolve this controversy, we evaluated the temporal relationship between blood product administration and mortality in civilian trauma patients receiving MT.
METHODS: Patients requiring MT over a 22-month period were identified from the resuscitation registry of a Level I trauma center. Shock severity at admission and timing of shock-trauma admission, blood product administration, and death were determined. Patients were divided into high- and low-ratio groups (≥1:2 and<1:2 FFP:PRBC, respectively) and compared. Kaplan-Meier analysis and log-rank test was used to examine 24-hour survival. RESULTS: One hundred three patients (63% blunt) were identified (66 high-ratio and 37 low-ratio). Those patients who achieved a high-ratio in 24 hours had improved survival. However, severity of shock was less in the high-group (base excess: -8.0 vs. -11.2, p=0.028; lactate: 6.3 vs. 8.4, p=0.03). Seventy-five patients received MT within 6 hours. Of these, 29 received a high-ratio in 6 hours. Again, severity of shock was less in the high-ratio group (base excess: -7.6 vs. -12.7, p=0.008; lactate: 6.7 vs. 9.4, p=0.02). For these patients, 6-hour mortality was less in the high-group (10% vs. 48%, p<0.002). After accounting for early deaths, groups were similar from 6 hours to 24 hours. CONCLUSIONS: Improved survival was observed in patients receiving a higher plasma ratio over the first 24 hours. However, temporal analysis of mortality using shorter time periods revealed those who achieve early high-ratio are in less shock and less likely to die early from uncontrolled hemorrhage compared with those who never achieve a high-ratio. Thus, the proposed survival advantage of a high-ratio may be because of selection of those not likely to die in the first place; that is, patients die with a low-ratio not because of a low-ratio.
The authors state “The current study underscores the need for well-designed prospective studies to address the important question of which ratio results in improved survival and stresses the importance of timing of blood product administration as this may impact survival.” Improved survival after hemostatic resuscitation: does the emperor have no clothes? J Trauma. 2011 Jan;70(1):97-102
Pre-hospital therapeutic hypothermia might be a good thing, but there may be difficulties in achieving it if the 4 degrees C saline warms up during the infusion. What’s the optimal way of administering it? Czech investigators attempt to answer the question: Background The cooling efficacy of intravenous administration of cold crystalloids can be enhanced by optimisation of the procedure. This study assessed the temperature stability of different application regimens of cold normal saline (NS) in simulated prehospital conditions.
Methods Twelve different application regimens of 4°C cold NS (volumes of 250, 500 and 1000 ml applied at infusion rates of 1000, 2000, 4000 and 6000 ml/h) were investigated for infusion temperature changes during administration to an artificial detention reservoir in simulated prehospital conditions. Results An increase in infusion temperature was observed in all regimens, with an average of 8.163.38C (p<0.001). This was most intense during application of the residual 20% of the initial volume. The lowest rewarming was exhibited in regimens with 250 and 500 ml bags applied at an infusion rate of 6000 ml/h and 250 ml applied at 4000 ml/h. More intense, but clinically acceptable, rewarming presented in regimens with 500 and 1000 ml bags administered at 4000 ml/h, 1000 ml at 6000 ml/h and 250 ml applied at 2000 ml/h. Other regimens were burdened by excessive rewarming. Conclusion Rewarming of cold NS during application in prehospital conditions is a typical occurrence. Considering that the use of 250 ml bags means the infusion must be exchanged too frequently during cooling, the use of 500 or 1000 ml NS bags applied at an infusion rate of $4000 ml/h and termination of the infusion when 80% of the infusion volume has been administered is regarded as optimal. Prehospital cooling by cold infusion: searching for the optimal infusion regimen Emerg Med J. 2010 Aug 23. [Epub ahead of print]
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).
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]
Over a thousand patients in North America with blunt traumatic head injury and coma who did not have hypovolaemic shock were randomised to different fluids pre-hospital. 250 ml Hypertonic (7.5%) saline was compared with normal (0.9%) saline and hypertonic saline dextran (7.5% saline/6% dextran 70). There was no difference in 6-month neurologic outcome or survival.
Using Poiseuille’s law and standardized gauge sizes, an 18-gauge (g) intravenous catheter (IV) should be 2.5 times faster than a 20-g IV, but this is not borne out by observation, in vitro testing, and manufacturer’s data. A nice simple study on normal volunteers compared simultaneous flow rates between a single 18G iv in one arm with two 20G ivs in the other arm. The two smaller ones provided significantly faster flow than the single larger one, although flow rates were slower than manufacturer’s estimates. This is in keeping with this other study on cannula flow rates. Are 2 smaller intravenous catheters as good as 1 larger intravenous catheter? Am J Emerg Med. 2010 Jul;28(6):724-7
A ‘BestBET‘ from the Emergency Medicine Journal examined the evidence for the use of sodium bicarbonate and/or mannitol in the management of rhabdomyolysis.
The clinical bottom line: there is no quality published evidence that alkaline diuresis is a superior treatment to normal saline alone. Rhabdomyolysis and the use of sodium bicarbonate and/or mannitol Emerg Med J. 2010 Apr;27(4):305-8 Full Text at the BestBets site
It is said that when using crystalloids, two to four times more fluid may be required to restore and maintain intravascular fluid volume compared with colloids, although true evidence is scarce. The ratio in the SAFE study comparing albumin with saline resuscitation was 1:1.3, however.
A single-centre, single- blinded, randomized clinical trial was carried out on 24 critically ill sepsis and 24 non-sepsis patients with clinical hypovolaemia, assigned to loading with normal saline, gelatin 4%, hydroxyethyl starch 6% or albumin 5% in a 90-min (delta) central venous pressure (CVP)-guided fluid loading protocol. Haemodynamic monitoring using transpulmonary thermodilution was done each 30 min to measure, among other things, global end-diastolic volume and cardiac indices (GEDVI, CI). The reason sepsis was looked at was because of a suggestion in the SAFE study of benefit from albumin in the pre-defined sepsis subgroup.
Independent of underlying disease, CVP and GEDVI increased more after colloid than saline loading (P = 0.018), so that CI increased by about 2% after saline and 12% after colloid loading (P = 0.029).
Their results agree with the traditional (pre-SAFE) idea of ratios of crystalloid:colloid, since the difference in cardiac output increase multiplied by the difference in volume infused was three for colloids versus saline.
Take home message? Even though an outcome benefit has not yet been conclusively demonstrated, colloids such as albumin increase pre-load and cardiac index more effectively than equivalent volumes of crystalloid in hypovolaemic critically ill patients. Greater cardiac response of colloid than saline fluid loading in septic and non-septic critically ill patients with clinical hypovolaemia Intensive Care Med. 2010 Apr;36(4):697-701
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
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