Essay: Are Hsp in Critical Illness for Children?



Introduction

Heat shock proteins (Hsps) are detected in all cells, prokaryotic and eukaryotic. In vivo and in vitro studies have shown that various stressors transiently increase production of Hsps as protection against harmful insults.

Hsps are a family of highly conserved proteins with molecular mass ranging from 15-110 kDa.

The Hsp70 group consists at least four distinct proteins as follows: Hsp72, Hsp73, Hsp75, and Hsp78, in which Hsps70, 72, and 73 exist in cytosol, whereas Hsp75 and Hsp78 are localized in mitochondria and endoplasmic reticulum, respectively.

It has been recognized that cytosolic 70-kDa Hsps are present in cells as two different but closely related gene products as follows: the stress-inducible form, Hsp72 (also known as Hsp70) and a constitutively expressed form, Hsp73 (also known as the 70-kDa heat shock cognate protein, Hsp70).

Intracellular HSPs (iHSPs) are high evolutionary conservative proteins that play an important role in regulating host response against infections, thermal injury, oxidative damage, and hypoxia.

Particularly, the major heat shock proteins iHSP70 and iHSP90α confer tolerance to sepsis by maintaining the conformational homeostasis, exerting anti apoptotic effects, and mediating lipopolysaccharide (LPS)-signaling as a part of the LPS receptor cluster.

However, although animal studies have demonstrated a protective effect of iHSP72 in sepsis, human studies are inconclusive showing either protection or relation to mortality and infections.

To add more questions about the extracellular HSPs (eHSPs) function and their role in sepsis, eHSP90α levels were recently shown to decline in controls and remain increased in septic patients, contrasting eHSP72, which increased over time in both groups.

Thus, the involvement of extracellular bound HSPs as signals for activation of the immune system and especially macrophages raises interest about the role of these proteins in sepsis. Apart from septic patients, serum levels of eHSP72 measured early after injury in trauma patients correlated with survival, with significantly higher levels in trauma patients who survived compared to non survivors.

Previously glutamine has been regarded as safe, non-toxic and easy to administer potentially representing an attractive modulator of the heat shock response. Previous meta-analysis of randomize controlled trials of parenteral nutrition (PN) supplemented with glutamine showed an associated decreased length of ICU stay and ventilator days, although there are no such similar reports of the effects of Gln supplementation on outcomes in critically ill children.

Conversely, recent work suggests that glutamine depletion may not always occur in critically ill adults with septic shock, as only 31% of the patients admitted had low glutamine levels in contrast to 15% of patients had supra physiological glutamine levels, which was associated with increased mortality. Rodas et al. have corroborated these finding showing that high plasma glutamine levels (>930 mmmol/l) were associated with an increased mortality.

CRITICAL ILLNESS

One ultimate example of stress is critical illness. The term critically ill child doesn’t refer to any particular disease but it refers to any child who is in a clinical state which may result in respiratory or cardiac arrest or sever neurologic complications if not recognized and treated promptly.

Shortly, critically ill child can be rapidly recognized if suffering from one or more of the following:

 Respiratory emergency :

Airway obstruction "stridor or wheezing" or respiratory distress (tachypnea, retraction and cyanosis)

 Cardiovascular emergency:

Heart failure (tachypnea, tachycardia and enlarged tender liver) or circulatory failure (tachycardia, poor peripheral perfusion and hypotenson) or hypertensive encephalopathy.

 Central nervous system emergency :

Convulsion, disturbed consciousness and increased intracranial pressure (bulging anterior fontanel, sluggish pupillary reaction, headache and vomiting). All these may be due to encephalitis, meningitis or intracranial hemorrhage.

 Metabolic emergency:

Hepothermia, hyperpyrexia, severe dehydration and sever metabolic acidosis.

 Hematological emergency:

Sever acute anaemia due to acute blood loss or acute haemolysis.

 Serious injury:

Include major trauma (falls of traffic road accident), burns, drowning and poisoning.

Both innate and acquired immunity are involved in the response to acute severe illness. The innate immune response is characterized by an initial local inflammatory reaction at the site of infection or injury, which involves activation of macrophages and monocytes, the alternate complement pathway, and the blood coagulation system. The local inflammatory reaction is amplified through the release of pro-inflammatory mediators (e.g., tumor necrosis factor, interleukin-1, prostaglandins,

leukotrienes, thromboxanes) that in turn leads to the systemic inflammatory response syndrome (SIRS). The initial phase of the SIRS response is felt to be an adaptive process that facilitates resolution of the acute inciting process. However, a maladaptive response secondary to overwhelming or prolonged systemic inflammation (e.g., ‘‘excessive SIRS’’) may ensue as the result of factors such as the type of infecting organism, genetic predisposition to overexpression of inflammatory cytokines, patient age, and comorbidities.

Clinical syndromes associated with excessive SIRS include the following: the acute respiratory distress syndrome (ARDS), septic shock, disseminated intravascular coagulation, and the multiple organ dysfunction syndrome. The mechanism for organ dysfunction in the setting of systemic

inflammation appears to involve extensive mitochondrial damage resulting from overproduction of nitric oxide and its metabolite peroxynitrite.

The adaptive immune response develops several days after the initial innate response and involves the interaction between antigen-presenting cells (e.g., macrophages, dendritic cells) and lymphocytes that are responsible for cell-mediated immunity and antibody production. A transient downregulation of adaptive immunity is commonly seen in patients with acute critical illness that is termed the ‘‘compensatory anti-inflammatory response syndrome’’ (CARS).

The components of the CARS include both cellular/molecular

elements (e.g., lymphocyte dysfunction and apoptosis, monocyte/ macrophage deactivation, increased production of interleukin-10) and clinical elements (e.g., cutaneous anergy, hypothermia, and leukopenia).

 

ASSESSMENT OF CRITICALLY ILL CHILD

To evaluate the degree of critical illness in the child, we should do:

1) Physical examination and investigation (invasive and noninvasive).

2) Prognostic scoring system.

a) Physical examination:

(A) Examination: One immediate priority is to exclude and treat the acute medical emergencies, it is also always necessary to remember that diagnosis not to be missed, so thorough medical examination is of extreme importance in identifying the cause of critical illness.

►Vital sign:

 Temperature: It should be measured before starting the physical examination. Rectal temperature is the most reliable. Hypothermia is seen in shock states, while fever may be noted in children with brain injury particularly cerebral haemorrhage or tumours or unable to sweat because of poisoning especially atropine.

 Pulse: Rate, rhythm, volume, equality and special characters should be noted.

 Respiratory rate: Accurate respiratory rate is obtained during sleep, however, children with rapid respiratory rate usually have respiratory distress or severe infection.

 Blood pressure: It is preferable obtained before examination when child is relaxed not crying.

►Anthropometric measures: Height, weight, head, chest circumference and mid-arm circumference.

► General appearance: In acutely ill child, general appearance can determine the system involved and the degree of distress. For example, earthy look in acute renal failure on top of chronic, cyanotic face in hypercyanotic spells as in Fallot tetralogy, delirium and coma may indicate toxicity due to drugs or contaminated food. High pitched cry may indicate that the child has increased intracranial pressure. Low pitched cry may indicate that the child is very sick or seriously ill.

► Head and neck examination:

Eye:

 Color of the sclera, jaundice and pallor.

 Signs of lateralization, unequal pupil or squint in intracranial insult-trauma and haemorrhage.

 Subconjunctival haemorrhage may be an extension of intracranial hemorrhage.

 Nystagmus which may be due to vestibular, ocular or neurological insult.

Ear:

 Ear discharge may be of extreme importance in chronic suppurative otitis media leading to brain abscess.

 Blood from the ear may be due to fracture base of the skull and intracranial haemorrhage.

 Nose:

 CSF rhinorrhea due to fracture base of skull with affection of cribrifom plate of ethmoid bone.

 Epistaxis (hypertensive encephalopathy).

Mouth:

 Excessive salivation in organophosphorus poisoning.

 Odor is acetone odor in diabetic ketoacidosis.

► Chest and heart examination:

 Inspection: for shape, symmetry, expansion, intercostal retraction, type of breathing, pericardial bulge, cardiac pulsation and tracheal position.

 Palpation: for masses, tenderness, tracheal position, cardiac pulsation and thrill and TVF.

 Percussion: for dullness, hyperresonance over the lungs, bare area of the heart and cardiac borders.

 Auscultation: of breath and heart sounds if there are adventiious sounds or heart murmur.

► Neurological examination:

 First, we should determine the level of consciousness which may be lethargy, stupor, delirium, semicoma or deep coma.

 Glasgow Coma Score (GCS) by which we can determine the level of consciousness.

 Cranial nerve examination.

 Muscles for tone, power, passive and active movement.

 Sensations: intact, lost and distribution of sensory loss.

 Reflexes: Normal, exaggerated or depressed and if there is positive Babinski, ankle clonus or not. If they are present search for pathological reflexes.

MONITORING THE CRITICALLY ILL CHILD

A) Respiratory Monitoring:

The lungs are highly unique in that they are internal organs, yet at the same time they are constantly exposed to the external environment. For example, with each breath, the lungs are exposed to pollens, viruses, bacteria, smoke and other pollutants and all of the other substances in the environment. At the same time, at any one point in time the lungs receive approximately half of the cardiac output and all of the potential internal toxins (proinflammatory cytokines, drugs, etc.). Many studies stated that acute respiratory failure and the need for respiratory support are one of the most common reasons of children admission to the PICU.

► Monitoring Oxygenation

 Arterial Blood Gas analysis: It is invasive method for monitoring the systemic arterial oxygen saturation (SaO2). The primary purpose of monitoring SaO2 is to assure adequate oxygen delivery.

 Pulse Oximetry: the most common non-invasive method for monitoring SaO2.

► Monitoring Ventilation

 Arterial Blood Gas analysis: The partial pressure of carbon dioxide (CO2) in the arterial blood is inversely proportional to alveolar minute ventilation. The efficiency of ventilation, i.e. the efficiency of CO2 elimination, can therefore be measured directly using arterial blood gas analysis.

 End-Tidal CO2 Monitoring: CO2 can be measured in expiratory gases via the concentration of CO2 reached at the end of expiration (partial pressure of CO2 at end-tidal; PetCO2 or EtCO2).

 Transcutaneous CO2 (TcCO2) Measurements: Whereas transcutaneous O2 monitors correlate poorly with PaO2 (and with pulse oximetry, these monitors are probably not necessary anyway), transcutaneous CO2 (TcCO2) monitors can reasonably approximate PaCO2, particularly in certain settings. TcCO2 measurements can provide noninvasive monitoring of PaCO2.

B) Hemodynamic Monitoring:

► Vascular Pressure Measurement

 Maintaining an adequate perfusion pressure is a vital adjunct to ensuring adequate oxygen delivery. The two common invasive pressure measurements undertaken in the ICU are arterial and central venous pressures.

► Cardiac Output

 Cardiac output is the volume of blood ejected by the heart per minute. It is usually expressed relative to body surface area, which means that the normal range of 3.5–5.5 L/min/m2 is applicable throughout the entire pediatric age range. Common techniques for measurement of cardiac output can be categorized as utilizing indicator dilution, the Fick principle, Doppler ultrasound, impedance, pulse contour analysis, and other miscellaneous methods. In addition, these modalities can also be categorized as intermittent versus continuous, as well as invasive versus non- (or minimally) invasive.

► Regional Perfusion

 Delivery and consumption abnormalities can occur at the regional level. Unfortunately measures of regional perfusion at the bedside are lacking.

 Capillary Refill: Capillary refill figures prominently in the major resuscitation manuals and has been shown to be a marker of hypovolemia in the emergency room setting. The significance of this variable in the ICU is less clear, perhaps due to the coexistence of confounding factors such as fever, hypothermia, and vasoactive medication use.

C) Neurological Monitoring:

► Intracranial Pressure (ICP) Monitoring

 Measurement and management of abnormal increases in intracranial pressure has been a mainstay of medical care of children and adults for decades. Measurement of ICP can be accomplished using monitors in a variety of locations. Currently, ICP monitors are placed either in the brain parenchyma or in the ventricular space.

► Evaluation of cerebral spinal fluid

 A lumbar puncture provides valuable information regarding both the state of the cerebrospinal fluid (CSF) and intracranial pressure transmitted down the spinal column. Bleeding disorders including thrombocytopenia (platelets less than 50 K/uL) or prolonged International Normalized Ratio (INR) (greater than 1.4) may predispose a patient to the development of a spinal epidural hematoma. If bacterial meningitis or herpes simplex encephalitis is suspected in a patient who has an absolute contraindication for CSF removal, the lumbar puncture should be deferred, blood cultures should be obtained and the child should be treated presumptively with antibiotics and/or antivirals.

 

► Electrophysiological Monitoring

Electrophysiological monitors have similar strengths and weaknesses. All of the monitors discussed below are non-invasive, can be used effectively at the patient’s bedside and can be used serially to follow interval changes in the child’s condition. However, most of the monitors require relatively advanced training in interpretation and can be adversely affected by the relatively hostile electrical environment within intensive care units. Electrophysiological monitoring includes Bispectral (BIS) Index Monitoring to detect depth of sedation in case of ventilated patients, Electroencephalography (EEG) for tracing brain electrical activity and Evoked Potentials for tracing electrical activity of relevant brain regions after a peripheral stimulus has been applied.

► Assessments of Blood Flow and/or Metabolism

 Because of the brain’s large requirement for oxygen and its dependence on aerobic respiration for optimal neuronal functioning, it has been widely accepted that measures of cerebral blood flow, metabolism and oxygenation are useful indicators of local or global cerebral function. Procedures include Transcranial Doppler Ultrasonography (TCD) and Jugular Venous Oxygen Saturation (SjvO2) which depends on principle that measurement of the oxygen saturation in the blood leaving the brain (SjvO2) is a global, indirect measure of cerebral blood flow that is contingent upon both blood flow and oxygen metabolism.

► Neuroimaging

The ability to diagnose and treat acute CNS disease has been dramatically improved by advances in imaging techniques. Computerized tomography (CT) provides a rapid assessment of intracranial pathology. Magnetic resonance imaging (MRI) offers further delineation of normal and pathologic structures without radiation exposure.

► Serum Markers of Neurological Injuries (Neuromarkers)

Currently, several CNS-specific proteins such as neuron-specific enolase (NSE) from neurons, S100β from astrocytes, myelinbasic protein (MBP) from oligodendrocytes – have been tested in a variety of clinical conditions to detect neurological injuries. The concept underpinning neuromarkers assumes that the detection of these brain-related proteins within the serum (or sometimes urine) necessarily implies the death of brain cells within the CNS and release of these proteins within the systemic circulation.

D) Monitoring Kidney Function:

 Acute kidney injury (AKI), formerly known as acute renal failure, continues to represent a very common and potentially devastating problem in critically ill children and adults. The reported incidence of AKI affects anywhere is between 5 and 50 % of critically ill children and adults.

► Glomerular Filtration Rate (GFR)

 GFR is the best known and most widely used global index of kidney function. GFR may be thought of as the sum of the filtration rates for all of the functioning nephrons in a given patient and is typically measured by calculating the clearance of a filtered marker solute, administered either as a bolus or continuous infusion:

GFR (mL / min) = (Ua ×V) / Pa

Where a represents the filtered marker solute, Ua is the urinary concentration of the filtered marker solute, V is the urine flow rate, and Pa is the serum concentration of the marker solute.

Ideally, the marker solute used to calculate GFR should be water-soluble with minimal protein binding, freely filtered at the glomerulus, and excreted unchanged in the urine (i.e. the marker solute is not secreted, reabsorbed, or metabolized). The marker solute should be stable (not synthesized in the body), non-toxic, and easily measured using inexpensive and widely available assays. Commonly used solute markers for measurement of GFR in the clinical setting include inulin, iohexol. The measurement of even these commonly used marker solutes can be technically challenging, expensive, and infeasible in the everyday clinical setting.

► Serum Creatinine

Creatinine is an amino acid compound derived from the metabolism of creatine, a protein found in skeletal muscle, as well as dietary protein intake. It is freely filtered by the glomerulus and is not reabsorbed or metabolized by the kidney. Therefore, creatinine clearance is frequently used to estimate the GFR in the clinical setting. There is an inverse relationship between serum creatinine and GFR, such that a reduction in GFR produces an increase in serum creatinine.

► Serum Urea

Urea is a water-soluble, low molecular weight byproduct of normal protein metabolism that is produced by the liver and excreted by the kidney. Azotemia is defined as an increase in the serum concentration of nitrogenous compounds, such as urea – classically, azotemia is classified by the underlying pathophysiology as pre-renal, intrinsic, or post-renal. Similar to creatinine, there is a nonlinear and inverse relationship between serum urea (commonly measured as “blood urea nitrogen” or BUN) and GFR.

► Urine Output

Urine output is one of the more commonly measured parameters of kidney function measured in hospitalized patients. Decreased urine output, or oliguria, is generally defined as urine output less than 400 mL in 24 h in adults, or urine output less than 1 mL/kg/h in children. The differential diagnosis of oliguria is broad in scope and is relatively non-specific for AKI. Oliguria is typically classified according to pre-renal, renal (intrinsic), or post-renal (primarily obstructive) causes.

► Urinalysis and Microscopy

Critical illness is frequently associated with endothelial dysfunction with increased capillary leak. Increased capillary leak in the kidney results in proteinuria, a frequent finding in critically ill patients. For example, the presence of microalbuminuria appears to correlate with severity of illness, as well as increased morbidity and mortality in critically ill patients with trauma, acute lung injury, sepsis, multiple organ dysfunction syndrome (MODS), and in children following surgery.

► Renal biomarkers

The ideal biomarker would be non-invasive, inexpensive, accurate, and rapidly measurable (ideally at the bedside), be sensitive to subclinical disease, and would correlate with disease severity, allowing prognostic information. Optimally, biomarkers should also allow differentiation of AKI etiologies or subtypes (such as ischemic or toxic) and allow monitoring of the course of injury and response to therapy. The most promising of these are neutrophil gelatinase-associated lipocalin (NGAL), cystatin C, interleukin-18 (IL-18), liver fatty acid binding protein (L-FABP), and kidney injury molecure-1 (KIM-1).

 

MANAGEMENT OF CRITICALLY ILL CHILDREN

Stabilization should proceed in a systematic manner adhering to the “ABCDs” as outlined in the Pediatric Advanced Life Support approach. Following an expanded ABCD format can aid in stabilization and early initiation of life-saving therapies in the infant presenting in extremis.

A) Airway:

The head of a pediatric patient is larger relative to body size, with a prominent occiput. This predisposes to airway obstruction in asleep children, because the neck is in flexed when they lie on a flat surface. A folded towel is often required as a shoulder roll to achieve a neutral position of the neck and open up the airway. This is demonstrated visually in Figure 1. The larger occiput combined with a shorter neck makes laryngoscopy relatively more difficult by providing obstacles to the alignment of the oral, laryngeal, and tracheal axes.

B) Breathing

It is essential to assess the adequacy of ventilation. The rate, depth, work of breathing and oxyhemoglobin saturation should be quickly noted. An arterial blood gas should be obtained if there is any question of inadequate gas exchange. If there is evidence of hypoxemia or severe respiratory acidosis, bag mask ventilation with 100% oxygen should be initiated while preparing for endotracheal intubation. If there is coexisting hemodynamic compromise, volume expansion prior to the institution of positive pressure ventilation may be necessary to prevent hypotension.

C) Circulation

Pulse rate, rhythm, quality of distal perfusion, mental status and urine output should be assessed. If necessary, begin volume resuscitation with 20 mL/kg boluses of normal saline. A rapid (>220 bpm), regular, narrow complex tachycardia is suggestive of supraventricular tachycardia. P waves may be, inverted, retrograde or absent. In infants who are hemodynamically stable (pulses with adequate perfusion), vagal maneuvers (i.e. ice water in a plastic bag forcefully applied to face without obstructing ventilation) may be attempted. Alternately, adenosine may be administered once IV access is established. In hemodynamically unstable infants (pulses but poor perfusion), rapid administration of adenosine (0.1mg/kg) or synchronized cardioversion (0.5–1 J/kg) is indicated.

D) 3 Ds:

 Disability: Infants with suspected meningitis, intracranial injury, or certain metabolic disorders may have progressive increased intracranial pressure. A rapid neurologic assessment should be performed looking for signs of raised intracranial pressure (altered mental status, hypertension, bradycardia, bulging fontanel). Raised intracranial pressure should be treated with maintenance of oxygenation and mean arterial pressure, elevation of the head of bed, and mannitol 0.5–1 g/kg.

Dextrose: Without exception, every critically ill infant should have a rapid glucose determination performed within minutes of arrival.

Stress-induced hyperglycemia has been well described in the literature in the acutely ill patient population owing to insulin resistance and increase gluconeogenesis. Studies in children also suggest that special consideration should be given to the safety of the youngest patients given their higher risk of hypoglycemia if an investigation of tight glycemic control is performed.

 Drugs: It is important to inquire about medications given to the infant, and those taken by a breastfeeding mother. Also, consider specific medications needed for further stabilization (i.e. antibiotics, intubation medications, prostaglandin, inotropes and/or pressors).

E) Initial Investigations

During stabilization, initial data gathering should occur. A rapid beside glucose determination is essential and should be performed as soon as possible. Blood and urine cultures, a complete blood cell count with differential, electrolytes, liver function tests, a coagulation profile and urinalysis should be obtained in all critically ill-appearing infants. Arterial blood gas determination will aid in the assessment of gas exchange and acid– base status. A methemoglobin and carboxyhemoglobin level should be obtained in infants with unexplained cyanosis.

A lumbar puncture is best deferred until the infant is stable. The lack of cerebrospinal fluid for analysis does not preclude early initiation of antibiotics. Imaging studies including chest/abdominal radiographs, head computerized axial tomography, skeletal survey, and echocardiogram should be obtained as clinical suspicion dictates.

 

SCORING SYSTEMS IN PICU

Mortality reduction is an important aim of a pediatric intensive care unit (PICU). Risk-adjustment tools that predict death in PICUs are a rational and objective way to quantify severity and have become established in the past 20 years. Diverse scoring systems have been developed for all age groups including pediatric.

► Categories of PICU scoring system:

I. Anatomic injury scores:

1. Injury Severity Scale (ISS).

2. Abbreviated Injury Scale (AIS).

3. A Severity Characteristic of Trauma (ASCOT).

II. Therapeutic intervention scores:

1. Therapeutic Intervention Severity Score (TISS).

2. Pediatric-Therapeutic intervention Severity Score (PTiSS),

III. Physiologic stability scores:

1. Physiologic Stability Index (PSI).

2. Simplified Acute Physiology Score (SAPS).

3. Pediatric Risk of Mortality score (PRISM).

4. Pediatric Risk of Mortality III score (PRISM III).

5. Pediatric Index of Mortality score (PIM).

6. Pediatric Index of Mortality 2 score (PIM-2).

IV. Disease specific scores:

1. Meningococcemia score.

2. Pediatric Trauma score (PTS).

3. Oncologic-Pediatric Risk of Mortality score (O- PRISM).

V. Disease and organ failure markers:

1. Lactate for shock severity.

2. Multiple Organ Dysfunction Score (MODS).

3. Organ Dysfunction and/or Infection score (ODIN).

4. Pediatric Logistic Organ Dysfunction (PELOD).

VI. Subjective:

1. Individual experience.

2. Institutional experience.

3. Glasgow Coma Scale (GCS).

a) The Pediatric Risk of Mortality (PRISM) score:

 PRISM scores should be used in critically ill neonates, infants,

children, or adolescents, not in premature infants or in adults. Three

versions were published. The first was named the physiologic stability index, and it contained 24 variables. Daily (dynamic) assessment of the Physiologic Stability Index score was reported in 1986.

IT was published an improved version of the score that was named the Pediatric Risk of Mortality (PRISM) score (it is named PRISM II score by some intensivists). The PRISM score contained 14 variables; its daily assessment was published in 1991. The PRISM score was again improved in 1996 to PRISM III.

► Variables included in PRISM III:

 The PRISM III score contains 17 variables or signs of cardiovascular, neurologic, or vital functions (systolic blood pressure, heart rate, Glasgow coma score, Pupillary reflex and temperature), acid base status (pH, CO2, PaCO2 and PaO2), chemistry tests (glucose, potassium, creatinine and blood urea nitrogen), hematology tests (white blood cell count, platelet count, prothrombin time and partial thromboplastin time), and other factors like operative status and some types of diseases.

► Timing of PRISM III data collection:

 Data incorporated into the PRISM III score can be collected during first 8 hours (PRISM III-8), during the first 12 hours (PRISM III-12), or during the first 24 hours after entry into PICU (PRISM III-24). The most abnormal values are retained and used to calculate that score.

► Validation of PRISM III score:

 Strengths of the PRISM III score are significant. It was very well validated with large sample size involving many different PICUs. It is used frequently for quality assurance and quality assessment. It is also frequently used to describe the severity of cases at baseline in the different arms of randomized clinical trials performed with critically ill children: a good balance between the severity of illness at baseline must be found if the randomization process worked correctly; if this is not the case, some adjustment is required while doing the statistical analysis.

► Problems faced with PRISM III:

However, a few problems must be underlined:

1) Early treatment bias is the main problem. The shorter the scoring period, the more the score reflects the patient's condition rather than the therapeutic response. All scores of the PRISM series include data from the first 12 or 24 hrs in the ICU, not only at entry into the ICU; therefore, better early treatment given in the PICU before the first data of the PRISM score are observed can improve the most abnormal values collected during the first day in the ICU. For example, better mechanical ventilation should improve PaO2, PCO2, and pH if these variables are measured on a blood sample taken a few hours after entry in the PICU. This means that the average PRISM score will be lower in this ICU than it would be for similar patients in a less efficient ICU. If data collected after beginning of treatment in these less efficient ICU and compared to data collected just after admission in better ICU, the result could be that the risk of death can look worse in better ICUs. It has been suggested that the prolonged period of time required to collect the variables for PRISM mortality prediction model obscures poor quality of care.

2) A second bias is possible. All PRISM scores include data collected up to death. A significant proportion of critically ill children who die do so during the first day of their stay in the ICU (> 40% in Australia), and this should inflate the capacity of PRISM scores to predict death. In other words, there is a danger that the score is really diagnosing death rather than predicting it.

3) A third problem is that the equation required to estimate the predicted mortality with the PRISM III score is not in the public domain: It is patented, and users have to pay to get this equation. This is not well received in many countries, and it probably explains why the PRISM III score is not used in many PICUs outside North America. Despite this, the PRISM III score is used extensively in North American PICUs. However, a considerable fee is charged for using it routinely, which has limited its use, even in developed countries.

b) Pediatric Logistic Organ Dysfunction (PELOD):

The creation and development of the PELOD score is reported in detail in an article published in 1999. The development study of the PELOD score included 594 consecutive patients and 51 deaths. Thereafter, a validation study was undertaken in Canada, France, and Switzerland.

Six systems contributed to the PELOD score, and 12 variables were retained. It is clear that the most important organ dysfunctions "were neurologic and cardiovascular. Accordingly, a greater number of points (maximum of 1, 10, or 20) were attributed to the more significant systems.

The limitations of the PELOD score are: First, treatment bias may be a problem because the PELOD score includes data that can be modulated by the care provided during PICU stay. Second, the PELOD score has not been tested in countries other than Canada, France, and Switzerland; its applicability to other countries needs to be studied. Third, the PELOD score is not validated to predict post-IC.U morbidity and mortality; further studies are required before the PELOD score can be used as a surrogate outcome of post-ICU morbidity and mortality.

GLUTAMINE

Glutamine (GLN) is the most abundant nonessential free amino acid and has traditionally been classified as a nonessential amino acid able to be synthesized de novo in states of health. Glutamine is now commonly described as a conditionally essential amino acid, particularly in catabolic and stress states. In catabolic states, large amounts of GLN are released from muscle tissue as part of the body’s conserved evolutionary response to stress. Previous explanations for the release of GLN in periods of stress include use as a fuel source for rapidly dividing cells, a precursor for synthesis of nucleic acids, and a role in renal acid buffering. Recent data has revealed that following illness and injury, GLN plays a vital role in inducing cellular protection pathways, modulation of the inflammatory response, and prevention of organ injury.

► Glutamine structure:

Glutamine is one of the conditionally essential amino acids, with the standard amino acid backbone and a 3-carbon side-chain with a ketone group on the furthest carbon from the amine group and culminating with nitrogen on the end of the side-chain Figure (2). Glutamine is not highly soluble in an aqueous environment, and thus when used in intravenous infusion it tends to be bound to the amino acid Alanine as Alanyl-glutamine.

   

► Sources and synthesis:

Glutamine is present in high amounts in most meat and animal products and any dairy product or by-product such as Whey Protein or Casein Protein. Average dietary intake of glutamine is around 6.85+/-2.19g glutamine daily. It should be noted that the above percentages are depending on total protein content, and not total caloric content nor weight. If assessed by weight, beef protein has 1.23g of glutamine per 100g product whereas skim milk has 0.28g glutamine per 100g product. Interestingly, some plant sources have higher glutamine amount on a percentage basis, but they are not the best sources of dietary glutamine due to the low overall amount of protein from plant sources relative to meat and dairy sources.

► Pharmacology:

a) Absorption and bioavailability:

The amount of glutamine devoted to intestinal and hepatic tissue (splanchnic extraction) does not differ between food-bound sources and supplemental dosages. Glutamine is able to 'blunt' glucose of the blood spikes in response to dietary carbohydrate, attenuating rises and values of blood glucose and insulin in response to dietary carbohydrate ingestion.

b) Serum:

In some instances, supplementation of glutamine has been found to increase plasma glutamine concentration, however, in most cases glutamine supplementation is stored in muscles. Plasma levels in healthy humans are typically 500-750umol/L after a morning fast. Muscle concentrations are typically regulated at 20umol/kg and release 50umol/L into plasma per hour in a fed state. This is due to muscle being a prime location for glutamine synthesis via the enzyme glutamine synthetase. These plasma levels are typically reduced in periods of critical illness due to increased usage of glutamine as substrate in various metabolic processes.

c) Tissues:

Glutamine is synthesized by the enzyme glutamine synthetase from glutamate and ammonia. The most relevant glutamine-producing tissue is the muscle mass, accounting for about 90% of all glutamine synthesized. Glutamine is also released, in small amounts, by the lung and the brain. Although the liver is capable of relevant glutamine synthesis, its role in glutamine metabolism is more regulatory than producing, since the liver takes up large amounts of glutamine derived from the gut. The most eager consumers of glutamine are the cells of intestines, the kidney cells for the acid-base balance, activated immune cells, and many cancer cells.

► Biological functions:

Glutamine is a semi-conditional amino acid, with its biological need being increased in certain states such as disease or cachexia. It is the most abundant amino acid in human tissue (mostly muscle tissue) and plasma. It has various biological roles including acting as a nitrogen transport between tissues alongside Alanine, acting as a precursor for the antioxidant glutathione, acting as a precursor for nucleotides, regulating acid/base metabolism and being involved as a substrate in gluconeogenesis. It can also stimulate production of L-citrulline and L-glycine via acting as substrate.

Glutamine is a very effective intestinal and immune system health compound, as these cells use glutamine as the preferred fuel source rather than glucose. It is generally touted as a Muscle Builder, but has not been proven to enhance muscle building in healthy individuals; only those suffering from physical trauma such as burns or muscular wounds (knife wounds) or in disease states in which muscle wasting occurs, such as AIDS.

► Medical use of Glutamine in children

In children, the use of glutamine remains largely undefined with paucity of data regarding the benefits of glutamine as a pharmacological agent in paediatric critical illness. Conflicting results with respect to the benefits of glutamine supplementation was found in pre-term infants, infants with gastrointestinal disease and surgery, burns and malnutrition. Reasons for the lack of consistent results, following glutamine supplementation in children may be as a result of the different individual study designs, heterogeneity of the populations studied, route of enteral administration chosen e.g. enteral or IV, dosage g/kg given and duration of glutamine supplementation.

However, beneficial effects of glutamine have been reported in children which include, decreased duration of acute diarrhoea, reduced severity of mucositis post bone marrow transplant, decreased muscle catabolism in Duchene muscular dystrophy and improved growth in sickle cell anaemia.

The use of glutamine in pre-term infants has received considerable attention, with some results showing benefit with respect to infectious complications and time to full enteral feeds, with other studies showing no difference. However there are inherent difficulties with trying to interpret the data from these studies as outlined below.

 Heterogeneous groups e.g. sick versus relatively well versus surgical neonates.

 L-glutamine – most of the studies used L-glutamine, which rapidly degrades to the unusable pyroglutamate. Adult studies have used the stable alanyl-dipeptide of glutamine with much better effects relative to morbidity and mortality at 6 months.

 Isonitrogenous – many of the pre-term studies compared the use of total parental nutrition enriched with glutamine to isonitrogenous control, the issue with this is that it potentially leads to suboptimal delivery of other essential amino acids, especially tyrosine and phenyl alanine.

 Time taken to get to goal rate – due to the delivery method some of the studies took up to ten days to reach the goal rate of delivery e.g. 0.3g/kg.

► Safety and toxicity:

 The Observed Safety Limit of glutamine supplementation, of which is the highest amount one can take and be assured of no side effects, has been suggested as being 14g/d in supplemental form (above food intake).

Higher levels than this have been tested and well tolerated, but there is not enough evidence to suggest that higher doses are completely free from harm over a lifetime of supplementation nor enough evidence to assume harm exists, 50-60g for a period of a few weeks is not associated with significant adverse effects.