Impaired Microvascular Perfusion Improves With Increased Incubator Temperature in Preterm Infants

Abstract

ABSTRACT:The optimal thermal environment for sick preterm infants is unknown. Incubator temperature can be regulated to an abdominal wall temperature of 36.5°C [neutral temperature (NT)] or to a minimal temperature difference (Ͻ2°C) between abdominal wall and extremities [comfort temperature (CT)]. This could affect the microcirculation, particularly in infants with impaired perfusion. We assessed the microvascular perfusion with near-infrared photoplethysmography (NIRP) at these two target temperatures between d 1 and 4 of life in preterm infants with normal (NL group) or impaired (RED group) microcirculation as determined by a clinical score. Signal strength variables such as area under the curve (AUC) and the first derivate of the amplitude (FLUX) were calculated. Starting temperature was randomized to NT or to CT and then followed by the other temperature. A significant increase of FLUX and AUC in the RED group was found with NT as starting temperature (FLUX: 282 Ϯ 76 at NT versus 627 Ϯ 211 at CT; p ϭ 0.025; AUC: 73 Ϯ 47 at NT versus 234 Ϯ 112 at CT; p ϭ 0.009), but not with CT. In NL infants, both parameters did not change significantly. Increasing the incubator temperature to CT changes thermoregulatory flow to the extremities in preterm infants with impaired microvascular perfusion and might improve tissue flow. T he optimal thermal environment for nursing sick preterm infants is not known. Neutral thermal zone is traditionally defined as a range of environmental temperatures within which the metabolic rate is minimal and thermoregulation is achieved by nonevaporative means (1,2). NT corresponds to a body surface temperature of about 37°C above the liver, in accordance with a core temperature of approximately 36.5°C regardless of the temperature of the extremities (3,4). CT is defined as a minimal temperature difference between the abdominal wall and the extremities (Ͻ2°C) (3). CT corresponds to an approximate core temperature of 37°C and higher and is close to an intrauterine temperature of 38°C (2,4).Changes in body temperature of about 1°C are primarily associated with changes in total peripheral skin blood flow (5). In term infants with NL exposed to phototherapy an increase of 224% in skin blood flow has been observed using electrocapacitance plethysmography (6). The effect of incubator temperature on circulation and microcirculation of preterm infants with signs of an impaired peripheral microcirculation (e.g. mottled skin) has not yet been reported. In the present study, we compared the effect of different incubator temperatures (NT and CT) on indices of peripheral blood flow in preterm infants matched for gestational age either with infants showing clinical signs of an impaired microcirculation or those without such signs. Microcirculation was assessed noninvasively with NIRP (7).Photoplethysmography was first described by Hertzman and Spealman in 1937 (8). It is a noninvasive technique consisting of a red/infrared light-emitting diode and a photosensitive detector (9). The emitted light is eithe...

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“…The neutral thermal environment is the one in which the metabolic rate is at a minimum as has been redefi ned by Sauer et al [19] as the ambient temperature at which the core temperature of the infant at rest is between 36.7 ° C and 37.3 ° C and the core and mean skin temperatures are Brought to you by | University of Iowa Libraries Authenticated Download Date | 6/3/15 8:29 PM changing < 0.2 and 0.3 ° C/h, respectively. Some authors have established an increase in thermal gradient > 1 ° C to consider the presence of thermal stress [15] , whereas keeping a thermal gradient < 2 ° C contributed to improve microvascular perfusion in preterm infants with microcirculation compromise [5] .…”

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“…Therefore, the change in microcirculation is unlikely to be caused by lower incubator temperature. In the past, we have shown, that under the condition of "comfort temperature" (a minimal temperature difference between the abdominal wall and the extremities smaller than 2°C) preterm infants with signs of a compromised microcirculation have higher skin blood flow than under "neutral temperature" (body surface temperature at the liver of ϳ37°C regardless of temperature of the extremities) (19). There are major differences between the studies, which make comparisons very difficult.…”

Functional Vessel Density in the First Month of Life in Preterm Neonates

“…It is less likely that the lower incubator temperatures lead to constriction of vessels to reduce heat loss, since incubator temperatures were closely regulated to keep body temperature constant at 37°C. With NIRP we have found previously, that raising incubator temperature to "comfort temperature" with a temperature difference of less than 2°C between abdominal wall and extremities significantly changes skin blood flow in the extremities of premature infants with clinical signs of compromised microcirculation, but not in infants without such signs (32). NIRP primarily assesses the nutritive flow in the deeper layers of the skin.…”