# Weight formula validation

Further validation of the UK-derived Luscombe weight formula has been made in the Australian setting. The nice simple formula for estimating the weight of a child based on age is:

Weight (kg) = 3 x age(years) + 7

It was compared with other formulae including the Best Guess formula, which is a bit more difficult to apply as the formula varies according to age range. This is reported in a previous post.
The authors provide the following cautionary advice:
“Whereas age-based formulae are, in the main, easy to calculate, the evidence suggests that ethnicity and body habitus pose serious challenges to their accuracy. In comparative studies, age-based formulae were found to be less accurate than the Broselow tape and parental estimate, with parental estimate being the most accurate weight estimation method. In light of this evidence, age-based formulae should only be used when these more accurate methods are not available.”

OBJECTIVE: Several paediatric weight estimation methods have been described for use when direct weight measurement is not possible. A new age-based weight estimation method has recently been proposed. The Luscombe formula, applicable to children aged 1-10 years, is calculated as (3 × age in years) + 7. Our objective was to externally validate this formula using an existing database.
METHOD: Secondary analysis of a prospective observational cohort study. Data collected included height, age, ethnicity and measured weight. The outcome of interest was agreement between estimated weight using the Luscombe formula and measured weight. Secondary outcome was comparison with performance of Argall, APLS and Best Guess formulae. Accuracy of weight estimation methods was compared using mean difference (bias), 95% limits of agreement, root mean square error and proportion with agreement within 10%.
RESULTS: Four hundred and ten children were studied. Median age was 4 years; 54.4% were boys. Mean body mass index was 17 kg/m(2) and mean measured weight was 21.2 kg. The Luscombe formula had a mean difference of 0.66 kg (95% limits of agreement -9.9 to +11.3 kg; root mean square error of 5.44 kg). 45.4% of estimates were within 10% of measured weight. The Best Guess and Luscombe formulae performed better than Argall or APLS formulae.
CONCLUSION: The Luscombe formula is among the more accurate age-based weight estimation formulae. When more accurate methods (e.g. parental estimation or the Broselow tape) are not available, it is an acceptable option for estimating children’s weight.

Validation of the Luscombe weight formula for estimating children’s weight
Emerg Med Australas 2011 Feb;23(1):59-62

# In V.Fib and talking to you!

Some patients with severe refractory heart failure are kept alive thanks to implantable pumps such as the left ventricular assist device (LVAD). Many emergency physicians are likely to be unfamiliar with these but could encounter patients who have them. One particular peculiarity is that latter generation devices maintain non-pulsatile flow and provide or assist cardiac output independent of cardiac rhythm. In extreme situations patients can have life-sustaining cardiac outputs without palpable pulses or even audible heart sounds.

A great example of how weird this can get is provided by a case of a 66 year male with an LVAD (HeartMate II (Thoratec Corporation)) who presented due to spontaneous discharge of his internal cardioverter-defibrillator (ICD). He was alert but had no pulses, and no detectable blood pressure using both a manual sphygmomanometer and an automated non-invasive blood pressure device. His 12 lead showed ventricular fibrillation. An invasive blood pressure showed a mean arterial pressure (mAP) of 80 mmHg. Several hours later his VF was successfully terminated and his mAP remained 80 mmHg
Some interesting points made by the authors include:

• CPR was unnecessary in this guy but in cases of severe RV dysfunction it might need to be done to provide flow into the LV.
• A danger of CPR in patients with an LVAD is the risk of damage to the device or ventricular rupture

LVAD use is significantly increasing so we can expect to encounter more episodes of previously impossible presentations to our emergency departments.

ABSTRACT
Optimal medical treatment, cardiac resynchronization, and the use of an implantable cardioverter defibrillator are established therapies of severe congestive heart failure. In refractory cases, left ventricular assist devices are more and more used not only as bridging to cardiac transplantation but also as destination therapy. Ventricular arrhythmias may represent a life-threatening condition and often result in clinical deterioration in patients with congestive heart failure. We report a case of asymptomatic sustained ventricular fibrillation with preserved hemodynamics caused by a nonpulsatile left ventricular assist device. Consecutive adequate but unsuccessful discharges of the implantable cardioverter defibrillator were the only sign of the usually fatal arrhythmia, prompting the patient to consult emergency services. Electrolyte supplementation and initiation of therapy with amiodarone followed by external defibrillation resulted in successful restoration of a stable cardiac rhythm after 3.5 hours.

Asymptomatic Sustained Ventricular Fibrillation in a Patient With Left Ventricular Assist Device
Ann Emerg Med. 2011 Jan;57(1):25-8.

# 2J or 4J/kg in Paediatric Defibrillation?

Should we shock with 2J/kg or 4J/kg in Paediatric Defibrillation? The answer seems to be ‘we still don’t know’. Don’t worry – just follow the guidelines (reproduced for you at the bottom)
OBJECTIVE To examine the effectiveness of initial defibrillation attempts. We hypothesized that (1) an initial shock dose of 2 ± 10 J/kg would be less effective for terminating fibrillation than suggested in published historical data and (2) a 4 J/kg shock dose would be more effective.
PATIENTS AND METHODS This was a National Registry of Cardiopulmonary Resuscitation prospective, multisite, observational study of in-hospital pediatric (aged 18 years) ventricular fibrillation or pulseless ventricular tachycardia cardiac arrests from 2000–2008. Termination of ventricular fibrillation or pulseless ventricular tachycardia and event survival after initial shocks of 2 J/kg were compared with historic controls and a 4 J/kg shock dose.

RESULTS Of 266 children with 285 events, 173 of 285 (61%) survived the event and 61 of 266 (23%) survived to discharge. Termination of fibrillation after initial shock was achieved for 152 of 285 (53%) events. Termination of fibrillation with 2 ± 10 J/kg was much less frequent than that seen among historic control subjects (56% vs 91%; P < .001), but not different than 4 J/kg. Compared with 2 J/kg, an initial shock dose of 4 J/kg was associated with lower rates of return of spontaneous circulation (odds ratio: 0.41 [95% confidence interval: 0.21–0.81]) and event survival (odds ratio: 0.42 [95% confidence interval: 0.18–0.98]).
CONCLUSIONS The currently recommended 2 J/kg initial shock dose for in-hospital cardiac arrest was substantially less effective than previously published. A higher initial shock dose (4 J/kg) was not associated with superior termination of ventricular fibrillation or pulseless ventricular tachycardia or improved survival rates. The optimal pediatric defibrillation dose remains unknown.
Effect of defibrillation energy dose during in-hospital pediatric cardiac arrest
Pediatrics. 2011 Jan;127(1):e16-23
Here’s what the guidelines say:
Many AEDs have high specificity in recognizing pediatric shockable rhythms, and some are equipped to decrease (or attenuate) the delivered energy to make them suitable for infants and children <8 years of age. For infants a manual defibrillator is preferred when a shockable rhythm is identified by a trained healthcare provider (Class IIb, LOE C). The recommended first energy dose for defibrillation is 2 J/kg. If a second dose is required, it should be doubled to 4 J/kg. If a manual defibrillator is not available, an AED equipped with a pediatric attenuator is preferred for infants. An AED with a pediatric attenuator is also preferred for children <8 year of age. If neither is available, an AED without a dose attenuator may be used (Class IIb, LOE C). AEDs that deliver relatively high energy doses have been successfully used in infants with minimal myocardial damage and good neurological outcomes
Pediatric Basic Life Support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care
Full text document

# Plasma:red cell ratios

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

# Estimating child weight in Hong Kong

We know that the ‘APLS formula’ is inaccurate as a tool for estimating weight in Western children, and British and Australian researchers have devised more fitting formulae for their local populations as described here.

The emergency medicine team at the Accident and Emergency Medicine Academic Unit, Chinese University of Hong Kong have now provided a solution for Chinese children:

weight (kg) = (3 x age) + 5.

This was most accurate and precise in children <7 years old.
Age-based formulae to estimate children’s weight in the emergency department
Emerg Med J. 2010 Oct 13. [Epub ahead of print]

# Compression-only CPR vs standard CPR

Two studies comparing compression-only CPR with conventional CPR:

BACKGROUND: The role of rescue breathing in cardiopulmonary resuscitation (CPR) performed by a layperson is uncertain. We hypothesized that the dispatcher instructions to bystanders to provide chest compression alone would result in improved survival as compared with instructions to provide chest compression plus rescue breathing.
METHODS: We conducted a multicenter, randomized trial of dispatcher instructions to bystanders for performing CPR. The patients were persons 18 years of age or older with out-of-hospital cardiac arrest for whom dispatchers initiated CPR instruction to bystanders. Patients were randomly assigned to receive chest compression alone or chest compression plus rescue breathing. The primary outcome was survival to hospital discharge. Secondary outcomes included a favorable neurologic outcome at discharge.
RESULTS: Of the 1941 patients who met the inclusion criteria, 981 were randomly assigned to receive chest compression alone and 960 to receive chest compression plus rescue breathing. We observed no significant difference between the two groups in the proportion of patients who survived to hospital discharge (12.5% with chest compression alone and 11.0% with chest compression plus rescue breathing, P=0.31) or in the proportion who survived with a favorable neurologic outcome in the two sites that assessed this secondary outcome (14.4% and 11.5%, respectively; P=0.13). Prespecified subgroup analyses showed a trend toward a higher proportion of patients surviving to hospital discharge with chest compression alone as compared with chest compression plus rescue breathing for patients with a cardiac cause of arrest (15.5% vs. 12.3%, P=0.09) and for those with shockable rhythms (31.9% vs. 25.7%, P=0.09).
CONCLUSIONS: Dispatcher instruction consisting of chest compression alone did not increase the survival rate overall, although there was a trend toward better outcomes in key clinical subgroups. The results support a strategy for CPR performed by laypersons that emphasizes chest compression and minimizes the role of rescue breathing. (Funded in part by the Laerdal Foundation for Acute Medicine and the Medic One Foundation; ClinicalTrials.gov number, NCT00219687.)

CPR with chest compression alone or with rescue breathing
N Engl J Med. 2010 Jul 29;363(5):423-3

BACKGROUND: Emergency medical dispatchers give instructions on how to perform cardiopulmonary resuscitation (CPR) over the telephone to callers requesting help for a patient with suspected cardiac arrest, before the arrival of emergency medical services (EMS) personnel. A previous study indicated that instructions to perform CPR consisting of only chest compression result in a treatment efficacy that is similar or even superior to that associated with instructions given to perform standard CPR, which consists of both compression and ventilation. That study, however, was not powered to assess a possible difference in survival. The aim of this prospective, randomized study was to evaluate the possible superiority of compression-only CPR over standard CPR with respect to survival.
METHODS: Patients with suspected, witnessed, out-of-hospital cardiac arrest were randomly assigned to undergo either compression-only CPR or standard CPR. The primary end point was 30-day survival.
RESULTS: Data for the primary analysis were collected from February 2005 through January 2009 for a total of 1276 patients. Of these, 620 patients had been assigned to receive compression-only CPR and 656 patients had been assigned to receive standard CPR. The rate of 30-day survival was similar in the two groups: 8.7% (54 of 620 patients) in the group receiving compression-only CPR and 7.0% (46 of 656 patients) in the group receiving standard CPR (absolute difference for compression-only vs. standard CPR, 1.7 percentage points; 95% confidence interval, -1.2 to 4.6; P=0.29).
CONCLUSIONS: This prospective, randomized study showed no significant difference with respect to survival at 30 days between instructions given by an emergency medical dispatcher, before the arrival of EMS personnel, for compression-only CPR and instructions for standard CPR in patients with suspected, witnessed, out-of-hospital cardiac arrest. (Funded by the Swedish Heart–Lung Foundation and others; Karolinska Clinical Trial Registration number, CT20080012.)

Compression-Only CPR or Standard CPR in Out-of-Hospital Cardiac Arrest
N Engl J Med. 2010 Jul 29;363(5):434-42

# Weight formula for kids

The traditional ‘APLS formula’ for weight estimation in children based on age (wt in kg = [age+4] x 2) is recognised as underestimating weight in ‘developed’ countries, with the degree of underestimation increasing with increasing age.
Several authors have attempted to derive a more accurate formula.
In the UK, the measured weights of over 93 000 children aged 1-16 who attended a paediatric emergency department were used to compare a previously derived formula (wt=3[age]+7) with the APLS formula.
The formula ‘Weight=2(age+4)’ underestimated children’s weights by a mean of 33.4% (95% CI 33.2% to 33.6%) over the age range 1–16 years whereas the formula ‘Weight=3(age)+7’ provided a mean underestimate of 6.9% (95% CI 6.8% to 7.1%); this latter formula remained applicable from 1 to 13 years inclusive.
The authors state: ‘The APLS formula has clearly become a victim of better nourished children. With a mean underestimate of more than 20% (nearly 40% at age 10 years), its place as a weight estimation tool is questionable…. To continue with an inaccurate formula with no evidence base cannot be considered good medical practice.’
Weight estimation in paediatrics: a comparison of the APLS formula and the formula ‘Weight=3(age)+7’
Emerg Med J. 2010 Jul 20. [Epub ahead of print]
A previous retrospective Australian study on over 70 000 paediatric ED attendances derived formulae for three different age ranges:

• For Infants < 12 months: Weight (kg) = (age in months + 9)/2
• For Children aged 1-5 years: Weight (kg) = 2 x (age in years + 5)
• For Children aged 5-14 years: Weight (kg) = 4 x age in years.

Make your Best Guess: An updated method for paediatric weight estimation in emergencies
Emerg Med Australas. 2007 Dec;19(6):528-34

# LMA for newborn resuscitation

An observational study of near term infants (34 weeks gestation to 36 weeks and 6 days) born in an Italian centre over a 5 year period showed that nearly 10% of near-term infants needed positive pressure ventilation at birth, confirming that this group of patients is more vulnerable than term infants. Most were able to be managed with either bag-mask ventilation (BMV) or with a size 1 laryngeal mask airway (LMA). Of the 86 infants requiring PPV, 36 (41.8%) were managed by LMA, 34 (39.5%) by BMV and 16 (18.6%) by tracheal intubation. Why not slap a tiny LMA on your neonatal resuscitation cart – it could come in handy!

Delivery room resuscitation of near-term infants: role of the laryngeal mask airway
Resuscitation. 2010 Mar;81(3):327-30

# Cardiocerebral resuscitation

An emergency medical service introduced a cardiocerebral resuscitation protocol and compared outcomes with a standard ACLS protocol.
Cardiocerebral resuscitation (CCR) was defined as:

1. initiation of 200 immediate, uninterrupted chest compressions at a rate of 100 compressions ⁄ min
2. analyzing the rhythm and delivering a single defibrillator shock, if indicated
3. 200 more chest compressions before the first pulse check or rhythm reanalysis
4. epinephrine (1 mg intravenous or intraosseous) as soon as possible or with each 200 compression cycle
5. endotracheal intubation delayed until after three cycles of chest compressions

Data was analysed from a registry including data on 3515 patients from 62 EMS agencies, some of which instituted CCR (in a total of 1024 patients). Outcome predictors were identified using logistic regression analysis and
Individuals who received CCR had better outcomes across age groups. The increase in survival for the subgroup with a witnessed Vfib was most prominent on those <40 years of age (3.7% for standard ALS patients vs. 19% for CCR patients, odds ratio [OR] = 5.94, 95% confidence interval [CI] = 1.82 to 19.26). Neurologic outcomes were also better in the patients who received CCR (OR = 6.64, 95% CI = 1.31 to 32.8). Within the subgroup that received CCR, the factors most predictive of improved survival included witnessed arrest, initial rhythm of Vfib⁄Vtach, agonal respirations upon arrival, EMS response time, and age. Neurologic outcome was not adversely affected by age.
Cardiocerebral Resuscitation Is Associated With Improved Survival and Neurologic Outcome from Out-of-hospital Cardiac Arrest in Elders
Academic Emergency Medicine 2010;17(3):269 – 275

# Neonatal Emergencies

‘THE MISFITS’ is a popular mnemonic to assist in identifying the cause of critical illness in the neonatal period.
T = Trauma (Accidental and Non Accidental)
H = Heart Disease, Hypovolemia, Hypoxia
E = Endocrine (Congenital Adrenal Hyperplasia, Thyrotoxicosis)
M = Metabolic (Electrolyte Imbalance)
I = Inborn Errors of Metabolism
S = Sepsis (Meningitis, Pneumonia, UTI)
F = Formula Mishaps (Under or Over dilution)
I = Intestinal Catastrophes (Intussusception, Volvulus, Necrotizing Enterocolitis)
T = Toxins / Poisons
S = Seizures
From: Tonia J. Brousseau, Ghazala Q. Sharieff Neonatal Emergencies
http://cme.medscape.com/viewarticle/557824 accessed 29/12/09