Shock is an unstable physiological state that occurs following acute failure of the circulation, which results in inadequate tissue perfusion and oxygenation and incomplete removal of harmful metabolic waste products. Shock leads to a decrease in intravascular volume, a disruption to circulating intravascular volume, or impaired cardiovascular function (Waltzman, 2015). Recognising shock can be difficult as the signs and symptoms of shock are not those of the underlying disease/process, but the body's attempts to maintain homeostasis by preserving an effective circulation (Cameron et al, 2019). If shock is not recognised, anaerobic metabolism and tissue acidosis will result; if these changes are not reversed, end organ failure will follow (Crisp and Rainbow, 2007).
Types of shock
In this article, ‘children’ will refer to any child or young person up to 16 years of age. However, although infection is recognised as the leading cause of mortality and morbidity in the newborn (Bedford Russell, 2015), early-onset neonatal infection will not be discussed. Shock is classified in many ways, describing the physiological response to the underlying cause. Waltzman (2015) identified the three classifications for shock as hypovolaemic, distributive and cardiogenic; Cameron et al (2019) added obstructive and dissociative to total five classifications. Although these classifications support an understanding of the underlying cause of shock, an alternative approach is to consider how the child's circulation is compromised. For an effective circulation the child requires three essential components: fluid to transport oxygen and remove metabolic waste (blood), a pump to circulate the fluid (the heart), and vessels (arteries/veins) to contain the fluid.
The common types of shock in children, and therefore the focus of this article, are hypovolaemic and distributive shock (Cockett and Day, 2010). Uncommon causes include cardiogenic shock, leading to an acute state of circulatory failure due to impairment of myocardial contractility and diminished cardiac output (Fuhrman and Zimmerman, 2006; Brissaud et al, 2016). Obstructive shock, caused by an inability to produce adequate cardiac output despite normal myocardial function and circulating volume, such as in tamponade (Badheka et al 2018), and dissociative shock affecting the oxygen-carrying capacity of the blood—for example, carbon monoxide poisoning or profound anaemia (Cameron et al, 2018)—are uncommon in children.
It is important to remember that children can present with more than one classification. For example, a child in a road traffic accident with a head injury may lose the ability to control how vessels constrict and relax, which is distributive shock, and blood loss from an open wound would add hypovolaemic shock.
Sepsis
Sepsis is the systemic inflammatory response to infection, and usually presents with the common classifications of hypovolaemic and distributive shock. The inflammatory response leads to increased permeability in capillary beds, allowing fluid to escape from the circulating volume into the interstitial spaces (Bersten and Soni, 2003). Although Bentley et al (2016) recognised that efforts to improve the management of sepsis in children within 1 hour of diagnosis will lead to a reduction in mortality and morbidity, Plunkett and Tong (2015) have pointed out a key problem in that the initial clinical presentation of sepsis in younger age groups may be non-specific, leading to a potential delay in diagnosis
Table 1 summarises the five classifications of shock and aligns each with its effect on the child's circulation
| Classification | Problem | Cause | Fluid, pump and vessel |
|---|---|---|---|
| Hypovolaemic | A loss of circulating volume | Gastroenteritis, bleeding, vomiting | Lack of fluid, leading to an empty pump and vessels |
| Distributive | Abnormal dilation or constriction of vessels. Dilation is more common | Sepsis, head injury, anaphylaxis | Blood volume and pump are normal, abnormal vessels prevent blood from reaching the peripheries |
| Cardiogenic | Reduction in cardiac contractility | Congenital heart disease, pneumothorax, cardiac tamponade | Blood volume and vessels are normal, heart cannot effectively pump blood through the vessels |
| Obstructive | Abnormal blood flow | Obstructed vessels, tension pneumothorax or cardiac tamponade | Blood volume is normal but cannot reach tissues due to an obstruction in vessels or pump |
| Dissociative | Oxygen-carrying capacity of the blood is too low | Profound anaemia, carbon monoxide poisoning | Fluid (blood) does not work effectively |
Stages of shock
Shock follows three distinct phases and it is imperative the nurse caring for a child recognises the presenting features of each stage. Timely and targeted interventions will reduce the likelihood that a child will reach the final stage where interventions become ineffective and the condition is fatal. The stages are comparable regardless of the classification.
Compensated
In the first stage a series of physiological changes occur to ensure the core essential organs of the brain, heart and lungs are prioritised in terms of oxygenated blood supply (Waltzman, 2015). Peripheral vessels constrict to minimise blood flow to the extremities and the heart increases the rate of blood flow. At this stage, the child can initially compensate for an inadequate circulation (Jevon, 2012) and maintain end-organ perfusion (Crisp and Rainbow, 2007).
The nurse can observe these changes as the child's heart rate and respirations will increase, peripheral capillary time will be delayed and the child's hands and feet will feel cooler to touch, resulting in a clear warm/cool demarcation line. Importantly, at this stage blood pressure may be unchanged.
Uncompensated
When peripheral vasoconstriction and increased cardiac effort fail to compensate for a reduced circulation, this leads to uncompensated shock and inadequate tissue perfusion occurs. Healthy tissues rely on carbohydrates to provide energy; the main source of this energy is glucose (Grosvenor and Smolin, 2006). Glucose metabolised in the presence of oxygen is known as aerobic metabolism. In uncompensated shock, tissues deprived of oxygen rely on anaerobic metabolism. Lactic acid is a by-product of anaerobic respiration and leads to metabolic acidosis and is used as a marker of hypo-perfusion (Friedman and Bone, 2014). The combination of anaerobic metabolism and acidosis disrupts the healthy environment required for normal cell function (Cockett and Day, 2010).
The nurse can observe these changes as a reduction in compensation leads to reduced blood flow and impaired organ function, a reduction in blood flow presents as:
Irreversible
Irreversible shock is the final stage where despite correcting the underlying cause and restoring an effective circulation, tissue recovery is not possible and tissues continue to die. Despite continued resuscitation and restoration of circulation, this stage is often irreversible and fatal.
Physiological response to shock
Compensation increases systemic vascular resistance (SVR), this restricts blood flow to the extremities and improves venous return to the heart, increasing the volume of blood ejected in each contraction. Reduced peripheral blood flow leaves the child feeling cold to touch with cool extremities and demarcation lines (Friedman and Bone, 2014). Vasoconstriction and poor perfusion lead to prolonged capillary refill time (CRT). CRT is measured by applying pressure to the child's nail bed, leaving a pale area of poor perfusion, and measuring the length of time it takes for blood flow and perfusion to appear. A peripheral CRT of less than 2 seconds is considered normal, with more than 4 seconds abnormal. Mottling is often considered a sign of poor perfusion; however, it is not a valid observation as infants can have mottled skin due to an immaturity of controlling blood vessels, a condition known as cutis marmoratum (Cameron et al, 2019).
Cool extremities are more common in children as shock is the result of fluid loss, this may also be referred to as cold shock. However, presentation of distributive shock involving anaphylaxis, neurogenic and some forms of sepsis cause peripheral vasodilation and an increase in blood flow to the extremities. In these children, they feel warm to touch and Crisp and Rainbow (2007) referred to this as warm shock.
Children maintain an adequate blood pressure through compensation and it is not true to say a child with a normal blood pressure is not shocked, as compensatory responses maintain homeostasis and an effective blood pressure (Jevon, 2012). Although children can maintain normal blood pressures through compensation, this is limited in warm shock where vasodilation is seen.
Heart rate increases as a compensatory measure and is more reliable than blood pressure. Nurses must also palpate the child's pulse as this gives a subjective indication of circulating volume, it also allows an assessment of peripheral vasodilation when comparing peripheral and central pulses.
The compensatory measures of cool peripheries, warm/cool demarcation line and prolonged CRT alongside a potentially normal blood pressure, are central to the UK Resuscitation Council (2015) systematic approach to recognising the early signs of shock in the deteriorating child. As children maintain homeostasis and compensate for inadequate circulatory function (Cameron et al, 2019) it is important therefore that nurses recognise the clinical signs of a child compensating for shock.
Treatment
Fluid
Hypovolaemic and distributive shock are most common in children and for these fluid replacement is essential to limit further deterioration. Limited evidence supports the optimal type, rate and volume of fluid to be administered (Dellinger et al, 2008). However, the preferred fluid for resuscitation, despite limited evidence, is isotonic saline (0.9% sodium chloride). Alternatively, despite no associations with improved outcomes compared with 0.9% sodium chloride, Weiss et al (2017) suggested balanced crystalloid solutions that closely resemble serum electrolyte concentrations, containing electrolytes such as potassium chloride and magnesium chloride alongside sodium chloride, may be considered as alternative intravenous fluids.
Colloids, such as human albumin 5%, may appear to be ideal as the larger molecules may remain in the intravascular space longer. However, despite no large-scale studies in children comparing isotonic 0.9% saline with colloid, no significant differences in mortality were found in the SAFE or CRISTAL trials in adults (Finfer et al, 2004; Annane et al, 2013). However, the UK Resuscitation Council (2015) continues to advocate that an initial fluid bolus of 20 ml/kg should be given as soon as possible. Friedman and Bone (2014) took a similar view, suggesting active fluid resuscitation in the first hour reduces mortality. A decrease in heart rate following fluid is a valuable indicator that the child is responding (Waltzman, 2015).
Unlike hypovolaemic and distributive shock, the definitive treatment for obstructive shock is removal of the obstruction—for example, in cardiac tamponade, where cardiac function is compromised by an accumulation of fluid or gas around the heart (Fuhrman and Zimmerman, 2006).
Inotropes
Fluid replacement is essential for children presenting with hypovolaemia, however, for other types of shock inotropes may be useful for children who have received fluid replacement up to 40 ml/kg but do not respond (McVea and Turner, 2019). Waltzman (2015) cautioned that if given without adequate fluid, inotropes can accelerate tissue death, and so fluid remains the first line of treatment. If inotropic support is required the choice of inotropes depends on the child's clinical presentation (vasoconstriction, vasodilation, increased heart rate or stronger contraction). Although fluid replacement is essential in managing cardiogenic shock, use of active drugs including inotropes is essential to restore myocardial contractility and cardiac output to restore and maintain blood flow (Fuhrman and Zimmerman, 2006).
Table 2 summarises the common inotropes used and their effect.
| Inotrope | Effect | Impact |
|---|---|---|
| Dopamine | Low doses stimulate the heart to improve its function |
Improves cardiac output |
| Adrenaline | Stimulates the heart to improve function in children who do not respond to dopamine | Improves cardiac output |
| Noradrenaline | Stimulates the heart but also causes peripheral vasoconstriction | Improves cardiac output and blood pressure |
| Dobutamine | Increases heart contractility and rate. Causes peripheral vasodilation and increases blood flow to the extremities | Improves cardiac output and blood pressure |
Summary
Understanding the five classifications of shock and their effect on the child's circulation supports nurses in playing a vital role in identifying the child in shock. Accurate assessment and physiological monitoring allows the nurse to recognise the underlying cause and initiate an appropriate intervention.