Received: December 8, 2009;
Initial review: February 2, 2010;
Accepted: May 25, 2010.
Published online. 2010 November 30.

Brain cooling initiated within 6 hours and maintained for 72 hours after an asphyxial insult has been shown to reduce mortality and morbidity among newborn survivors of perinatal asphyxia [1-7]. Meta-analyses, including the Cochrane systematic review on cooling for hypoxic ischemic encephalopathy conclude that there is evidence that therapeutic hypothermia is beneficial to term newborns with hypoxic ischemic encephalopathy [8-10]. Cooling reduced mortality without increasing major disability among survivors. However, most studies have been done in developed countries using expensive equipment.

The present trial was conducted to evaluate whether whole body cooling (WBC) could be achieved in a low-resource setting using simple and easily available cooling materials.

The study was conducted in the neonatal unit of the Christian Medical College, Vellore between October 2007 to September 2008 after approval from the Institutional Review Board. Term and near-term babies (gestational age ≥35 weeks) were recruited, and included both inborn and outborn babies with perinatal asphyxia.

Inborn babies were included in the study if the following criteria were satisfied: umbilical cord or a postnatal (in the first hour of life) arterial blood gas pH of < 7.0 or base deficit ≥12 along with any two of the following: (a) Apgar score ≤5 at 5 minutes; (b) Ventilation initiated at birth and continued for at least 10 minutes; and, (c) Perinatal predisposition to perinatal asphyxia (any one) - intrapartum fetal distress, cord prolapse, placental abruption, maternal respiratory arrest, and uterine rupture/dehiscence.

The criteria for outborn babies was a history of not having cried/breathed immediately after birth with evidence of encephalopathy at admission and any or all of the following features: (a) not breathing normally at five minutes of birth; (b) given assistance for breathing soon after birth; (c) flaccid since birth; (d) poor feeding; and, (e) Apgar score of 5 or less at 5 minutes.

Babies were excluded from the study if they were small for gestational age, had chromosomal or major congenital anomaly, refusal of consent, or inability to start cooling by 5 hours of age. As per the unit protocol, severely asphyxiated babies (no spontaneous respiration by 30 minutes of life) were not ventilated.

After obtaining informed consent from the parents of eligible babies, a neurological examination was performed using a standardized neurological examination that was based on the modified Sarnat criteria and used in the NICHD study [6,11]. The infant warmer was turned off and cooling achieved by placing 3-5 cloth-covered cooling ice packs over the back, head, abdomen and the axillae of the baby. These packs were plastic containers filled with cooling gel used in vaccine carriers and were stored in the freezer of the refrigerator. These packs were reused after adequate cleaning.

A rectal probe (Philips-ref no 21090 A or Drager-ref no 4329848-08) to monitor core temperature was inserted 5 cm within the rectum and connected to a multi-parameter monitor (Philips Intellivue MP20 or Drager vista XL). The desired rectal temperature was 33±0.5°C. The temperature was continuously monitored and recorded every 15 minutes for 4 hours and then subsequently every hour for 80 hours. The skin temperature was measured simultaneously. During the cooling process, if the infant’s rectal temperature approached 33.5°C, more cloth-covered cooling-gel packs were placed on the body, and these were removed one by one when the rectal temperature dropped to 33°C. After 72 hours of hypothermia, re-warming was achieved by removing the packs, turning on the warmer and raising the temperature of the baby by not more than 0.5°C per hour. The environmental temperature of the nursery was also recorded during the study period. The nurse to patient ratio was 1:3. All infants had a central venous line and arterial access. Continuous monitoring of vital parameters was done. All treatment including medications (antibiotics, anticonvulsants, inotropes and sedatives), ventilation, and use of blood products were as per existing treatment protocols. Neurological examination was repeated at 24 and 72 hours. Serum electrolytes, blood urea, serum creatinine, prothrombin time (PT), activated partial thromboplastin time (aPTT), liver enzymes and blood counts were monitored at 0, 24, 48 and 72 hours. Blood gas was done at 0, 2, 8, 12, 24, 48 and 72 hours. An ECG was obtained if the heart rate was less than 80/min.

An external data and safety monitoring committee was notified within 48 hours if any of the following adverse events occurred: cardiac arrhythmia requiring medical treatment; persistent hypoxemia (transcutaneous oxygen saturation of 85% or a paO₂ <50 mm Hg in spite of a FiO₂ of 1 on mechanical ventilation); hypotension despite adequate inotropic support (dopamine at 10 µg/kg/min and dobutamine at 20 µg/kg/min); skin changes (sclerema, aposteatonecrosis); thrombocytopenia (<100×10³/µL); life-threatening coagulopathy; arterial thrombosis; hepatic and renal failure; electrolyte disturbances; and, death.

Statistical analysis: The sample size was calculated using the design of Gehan (1961). With a 10% precision and a 20% desired effectiveness, the sample size was calculated as 20. The analysis of the data was done using the SPSS 16.0 software. Mean, median, mode, standard deviation and frequency were calculated. Tests for significance used were Pearson’s coefficient and Mann-Whitney U test.

Twenty infants were recruited in the study, of whom 11 (55%) were outborn, and 12 (60%) were female. Maternal and neonatal details are provided in Tables I and II. Most mothers were primigravid (90%), had no complications of pregnancy, and went into spontaneous labour. Fetal heart deceleration was seen in the majority of inborn babies and 45% were born normally. Cooling was started at a mean of 3.4 ± 1.2 hours after birth. Majority of the infants recruited developed moderate encephalopathy.

At the start of cooling, the mean rectal temperature was 36.0±0.8°C and the mean skin temperature was 35.8±0.97°C. The mean time taken to reach target rectal temperature was 52±25 minutes. A Kaplan-Meier survival analysis was done with "time to attain target temperature" as the event. By the end of 15 minutes, 30% had achieved the target temperature; the median time to event was 45 minutes (95% CI 34.3-55.8). At 60 and 90 minutes from commencement of cooling, only 35% and 5% of the newborns, respectively had not achieved the target temperature.

Pearson’s correlation looking at the linear relationship of birth weight and time taken to achieve target temperature showed a positive moderate correlation (r=0.545; P<0.05) suggesting that the larger babies took a longer time to cool. There was no statistical significance between time taken to cool and gestational age, gender, type of labor, place and mode of delivery.

The environmental temperature of the nursery during the study period ranged from 28 to 32^oC.

Clinical and laboratory parameters: The mean heart rate, blood pressure and oxygen saturation during cooling is seen in Fig. 3. The mean heart rate at the start of cooling was 138±15 per minute while the average mean heart rate during the period of cooling was 111±5/min. The mean blood pressure at the start of cooling was 54.7±7.9 mm Hg and the average mean blood pressure during the period of cooling was 55.6 ±1.7 mm Hg. It was noted that many of the babies shivered, especially in the initial few hours.

There was significant acidosis among inborn babies at admission. The acidosis corrected in most instances within 12 hours of the initiation of the procedure, though two babies (10%) had persistent metabolic acidosis requiring sodium bicarbonate infusion. Serum electrolytes and blood urea remained within normal limits. Serum creatinine and blood lactate showed a downward trend as cooling progressed. Two (10%) infants had hypoglycemia, and 3 (15%) had hyperglycemia requiring insulin. Liver enzyme levels were elevated initially but showed a downward trend after 48 hours. The hemoglobin and packed cell volume dropped marginally and the platelet count showed a decreasing trend during cooling.

Serious adverse events: The serious adverse events that occurred during whole body cooling are shown in Table III. There were no cardiac arrhythmias recorded. However, 5 (25%) babies developed transient sinus bradycardia. Bleeding requiring transfusions was seen in 1 (5%) infant. This infant had prolonged bleeding parameters before starting cooling and a subgaleal bleed that worsened with cooling. Cooling was stopped after 27 hours but the baby continued to deteriorate and died. Skin changes (aposteatonecrosis) seen in 3 babies resolved spontaneously. Neurosonogram was done on all infants in the first week. Periventricular white matter changes were seen in 1(5%) baby while the rest were normal.

We have also demonstrated that it is possible to obtain informed consent and initiate treatment within 5 hours of birth in both inborn and outborn infants. The mean time to achieve target temperature in our study was 52±25 minutes. This was similar to the time taken to achieve cooling in previous studies from China and South Africa [4,15]. Although many studies do not indicate the time taken to reach the target temperature, available data suggests that an upper limit of 90 minutes is more realistic [6]. Though only 65% achieved desired temperature in our trial within one hour, using this criterion of 90 minutes, 95% of our newborn infants reached the target rectal temperature.

The results of this feasibility trial are in concordance with other studies that show that hypothermia is not associated with serious adverse events like cardiac arrhythmias, prolonged acidosis, life threatening bleeding or thrombosis. The fall in the heart rate when the rectal temperature was lowered to the target temperature was consistent with other reports. Thrombocytopenia seen in five of the infants could be attributed to cooling. However, there was no significant clinical bleeding in 4 of these babies. One baby, who had deranged coagulation profile before the start of cooling, developed disseminated intravascular coagulation and subsequently died. Hypoglycemia was seen in two infants requiring higher intravenous carbohydrate intake. Hyperglycemia requiring insulin was seen in three babies. This may be attributed to the decrease in insulin secretion during hypothermia [18]. This effect has not been reported in earlier trials involving newborn infants.

We specifically monitored for skin changes as cloth covered ice-gel packs were used in the initiation and maintenance of cooling. At the start of cooling, there was hyperemia in the areas where the ice-gel packs were placed and this required frequent rotation of the packs to different areas of the body. During the maintenance phase, no skin changes were noted. The aposteatonecrosis that was observed in three babies occurred during the start of cooling and subsequently resolved without intervention or residual scarring. These have been well described as an adverse effect of whole body cooling [6,15,19]. Though shivering was not one of the adverse events monitored, we noted that many of the babies shivered especially in the initial few hours. The shivering noted in our study may be related to either under sedation or the method of cooling. Shivering was also noted by Horn, et al. [16], who also reported hypomagnesemia in all the babies who shivered. There is evidence from studies in adult intensive care units to suggest that shivering may be associated with a worse outcome [20]. Other than sedation, clonidine has been used for this shivering, both in neonates who have been cooled and in post operative adult patients [16,21]. A majority of our cooled babies received phenobarbitone, though we did not routinely give analgesia other than if ventilated. Sedation during cooling is recommended and there is animal evidence to show that the neuroprotective effect of hypothermia may be lost if sedation is not used [22].

This feasibility trial in a developing country using low cost techniques with careful monitoring of temperature establishes that this neuro-protective strategy can be achieved safely and at an affordable cost. There are several issues that need to be addressed in terms of further research in a low resource setting [23]. These include the difference in the population in terms of the high incidence of IUGR, unbooked pregnancies, sepsis and meconium aspiration syndrome, the lack of transport facilities, which may preclude cooling in outborn babies and the difference in severity of encephalopathy seen in cooled babies. There is an urgent need to conduct trials looking at the efficacy and safety of cooling in this setting specifically addressing these issues.

Contributors: All the authors were involved in the concept, design, data collection, analysis and drafting of the manuscript.

Funding: CMC, Vellore.

Competing interests: None stated.