Abstract
Shock is a complex clinical syndrome caused by an acute failure of circulatory function resulting in inadequate tissue and organ perfusion. Digital infrared thermal imaging is a non-invasive technique that can detect changes in blood perfusion by detecting small changes in the temperature of the skin. In this preliminary study, eight pediatric patients (five boys, three girls), ages ranging from 6 to 14 years (average: 9.8 years), were admitted to the Intensive Care Unit at “Dr. Ignacio Morones Prieto” Central Hospital; here, the patients were examined using digital infrared thermal imaging. Patients in shock showed a significant decrease in distal temperature (at least 7°), compared to critically ill patients without shock. The latter group presented a skin temperature pattern very similar to the one previously reported for healthy children. The results show that infrared thermography can be used as a non-invasive method for monitoring the temperature in pediatric patients in intensive care units in order to detect shock in its early stages.
Keywords: Thermography, infrared imaging, shock, pediatric patients, temperature
Introduction
It has been shown that the temperature of skin in healthy individuals can vary from 32.5°C to 35.5°C in adults and children,1 and the measured temperature is higher in the head and lower in the distal areas.2,3 Blood flow is a major component of skin temperature, that is, inflammation and an increase in blood perfusion will increase the local temperature, while ischemia will result in a decrease in the local temperature. Shock is a complex clinical syndrome caused by an acute failure of circulatory function resulting in inadequate tissue and organ perfusion, which decreases delivery of oxygen and substrates to body tissues as well as the removal of metabolic waste products.4 This critical condition may eventually lead to cell death, whereas in adult patients, vasomotor paralysis represents the predominant cause of mortality; death in pediatric shock is associated with severe hypovolemia and low cardiac output.5 All types of shock can cause deterioration in the function of vital organs such as the brain (decreased consciousness) and kidneys (decreased urine output, ineffective filtration, among others), be it due to an insufficient supply of oxygen to the tissues or an increased oxygen demand from the tissues. The first line of defense of the organism is tachycardia, compensating for a low systolic volume. Tachycardia increases cardiac output in some extent; however, if it is excessive, the filling time is shortened to the extent that the systolic volume cardiac outputs are reduced. Assuming the oxygen content remains constant, the supply of oxygen to the tissues is reduced. When a decrease in cardiac output results in a decreased supply of oxygen to the tissues, the second line of defense of the body is to redirect or divert the blood of non-vital organs to the vital organs. This redistribution occurs through an increase in systemic vascular resistance (vasoconstriction), which preferably sends blood to vital organs while reducing the flow to areas such as the skin, skeletal muscle, intestine, and kidneys. Clinically, the result is a reduction in peripheral perfusion; that is, slow capillary refill, cool extremities, and decreased peripheral pulses. The evolution of seriously ill children can be greatly improved with early recognition and management of shock. If untreated, shock may progress rapidly to cardiopulmonary failure and then heart attack. The sooner the shock is recognized, the better the possibilities of a favorable response to treatment. The initial assessment in children, mainly the seriously ill ones, includes appearance, breathing and circulation. The primary assessment of circulation includes both cardiovascular function assessment and the end organ. Cardiovascular function is evaluated through skin color and temperature, heart rate and rhythm, blood pressure, pulse, and capillary refill; whereas end-organ function was assessed by brain perfusion (consciousness), perfusion skin, and renal perfusion (diuresis). The skin color, the skin temperature, and capillary refill time may all reflect central cardiovascular function as well as peripheral perfusion. When perfusion is impaired, hands and feet are usually affected at first. They can become cold, pale, dark, or blue. For this assessment, the recommendation is to use the back of the hand, sliding it along the limbs to see if at some point the skin changes from cold to hot, as well as to monitor the response to treatment. The line between hot versus cold skin should move distally as the patient improves.4 This type of assessment is subjective and therefore prone to clinical error. Digital infrared thermal imaging is a non-invasive procedure that detects infrared radiation, which produces a temperature pattern of the imaged surface. In the case of imaging the human body, the results correspond with the subject’s skin surface temperature, which resembles the anatomical area under study; this information has been used to evaluate the blood circulation in people who are subjected to extreme temperatures and smoking as well as for investigating the arterial functions in arterial coronary and myocardium.6–8 In this work, the use of Digital infrared thermal imaging is proposed as a clinical and experimental methodology for the detection of shock in pediatric patients in an intensive care unit (ICU).
Material and methods
Eight pediatric patients (five boys and three girls), ages ranging from 6 to 14 years (average age: 9.8 years) admitted to the ICU of “Dr. Ignacio Morones Prieto” Central Hospital were examined using a FLIR T400 infrared camera (FLIR Systems, Wilsonville, OR, USA) which has a 320 × 240 focal plane array of uncooled micro-bolometers with a spectral detection range of 7.5–13 µm and a thermal sensitivity of 50 mK at 30°C. These measurements were taken between November 2010 and June 2011. The characteristics of patients are shown in Table 1. All of them were in pediatric ICU under mechanical ventilation and needed hemodynamic, ventilator, and neurologic intensive support and/or monitoring. The critically ill children in the ICU who needed mechanical ventilation and/or neurological monitoring, but were hemodynamically stable, were considered the “control group.” In the other group, critically ill children with current clinical diagnosis of shock were included. The thermographic analysis was performed using FLIR Quick-Report v1.2 (FLIR Systems, Wilsonville, OR, USA). The measurements were performed at a constant emissivity of 0.97.9 The thermograms were taken from distal areas (hands and feet) following the protocol of Glamorgan10 in three zones: wrist, back of the hand, and the back of the foot. We analyzed the mean differences with a two-tailed Student’s t-test using six degrees of freedom assuming a normal distribution; previously, a Kolmogorov–Smirnov and Shapiro–Wilk for the normal distribution and a F-Snedecor for the equality of variances was obtained and considered statistically significant a p value of <0.05. The ICU room has a controlled temperature that ranges from 22°C to 24°C. This study was approved by the Hospitals’ Ethics Committee, and a written informed consent statement was signed by all the patients’ parents.
Table 1.
Characteristics of the patients participating in the project.
| Age (years) | Diagnosis | Kind of shock | Reason for admission in pediatric ICU | |
|---|---|---|---|---|
| Critically ill children with shock | ||||
| 1 | 8 | Drowning | Cardiogenic | Mechanical ventilatory support, amines |
| 2 | 14 | Heart failure by third-degree AV block | Cardiogenic | Mechanical ventilatory support, amines |
| 3 | 6 | Pneumonia | Septic | Mechanical ventilatory support, amines |
| Critically ill children without shock | ||||
| 4 | 9 | Head trauma, cerebral edema | – | Mechanical ventilatory support, sedation induced by analgesia |
| 5 | 14 | Head trauma, temporal parenchymal hemorrhage | – | Mechanical ventilatory support, sedation induced by analgesia |
| 6 | 8 | Pneumonia | – | Mechanical ventilatory support |
| 7 | 6 | Pneumonia | – | Mechanical ventilatory support |
| 8 | 13 | Epilepsy | – | Mechanical ventilatory support, sedation |
AV: atrioventricular; ICU: intensive care unit.
Results
Thermal imaging results show that patients in shock (three patients) presented decreased temperature in different sites of the body (dorsum of the hand, dorsum of the foot, and wrist), while patients without shock (five patients) presented a normal temperature, very similar to the temperature distribution in the skin of healthy children.3 In the dorsum of the hand of patients with shock, we found a temperature average of 25.98°C with a standard deviation (SD) = 1.38°C, whereas in the same site in patients without shock, we found a temperature average of 33.72°C with a SD = 0.94°C. We found a t-value of −7.74, statistically significant (p < 0.005) (Figure 1). In the dorsum of the foot, in patients with shock, an average temperature of 27.57°C, SD = 2.63°C was found, and in the same site in patients without shock, an average temperature of 33.11°C and SD = 0.92°C was also found, with a t-value of −4.99, statistically significant (p < 0.005). In the wrist, in patients with shock, an average temperature of 26.08°C and SD = 1.54 was found, and in the same site in patients without shock, an average temperature of 33.58°C with a SD = 2.37°C was also found, with a t-value of −5.13, statistically significant (p < 0.005). Figure 2 shows the comparative temperature average and SD of the different sites for patients with and without shock.
Figure 1.
(a) Thermography of the back of the hand of a critically ill child without shock and (b) thermography of the back of the hand of a child in shock.
Figure 2.
Temperature average with SD of three sites for patients with shock and without shock.
Discussion
In this study, it was found that patients in shock showed a significant decrease in distal temperature (at least 7 degrees) compared to critically ill children without shock which presented a temperature pattern very similar to the one reported for healthy children.3 Therefore, infrared thermography is suggested as a non-invasive method for monitoring the skin temperature in patients in pediatric intensive care as an indirect reflection of distal perfusion and shock in its early stages. Further work is taking place in order to overcome the limitations of this study such as the fact that only eight patients were considered, the ones in shock (three) had decompensated cold shock, and it was not possible to compare the distal temperature with other hemodynamic parameters. It is worth noting that due to the small sample size, the results should be interpreted with caution due to the possibility of an inflated effect. A more detailed study with a larger sample size is currently underway in order to verify the results obtained in this work. Neither the air humidity nor the radiation of external sources that might affect the skin temperature could be determined in this study; however, they will be monitored in future studies. The measurement bias was controlled by conducting the study with all patients in the same room with identical environments. A larger study considering these facts will be conducted. This is the first time, to our knowledge, that the distal temperature in children with cold shock is determined quantitatively using infrared thermography, a measurement technique whose main advantages are its non-invasiveness, its precise measurements and ease of data storage for subsequent obtaining of dependent variables. The main disadvantage is the relatively high cost of this type of equipment compared with traditional skin temperature probes.
Footnotes
Declaration of conflicting interests: The authors declare that they have no competing interests.
Funding: All authors report no funding for support of this work.
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