How long does incisional pain last: early life vulnerability could make it last a lifetime.

1189 June 2015 T he existence of critical periods of development is an established concept. The vulnerability to potentially adverse effects from “exposure” to certain drugs and stresses at specific times during development is concerning. Recent effort has focused on the impact of exposure to anesthetics during critical periods of development and the detrimental effects on the nervous system.1 however, this month in Anesthesiology, two research articles, Walker et al.2 and schwaller et al.,3 highlight changes in the nervous system from incisional surgery at a critical or vulnerable period of development. These effects are independent of the anesthetic exposure and highlight the reemerging concept of surgery and pain as an “exposure” that results in long-term changes in the developing nervous system, and returns us to the role anesthesia and analgesia play in modulating and minimizing the long-term impact of surgery and inflammation. The authors have focused on two components of noxious input early in life, the potential impact on the neuroinflammatory responses induced by glia in the central nervous system, and alterations in descending spinal cord input. Both studies confirm that incoming nociceptive input from the periphery is the key driver, affecting both the spinal cord and also higher centers, in this case the rostroventral medulla (RVM), which provides important descending input for modulation of sensory neurotransmission in the spinal cord. This is demonstrated by the fact that peripheral nerve blockade reduces or eliminates changes in these parts of the nervous system after incisional surgery. This may have implications for treatment regimens that are effective given age-specific goals and concerns. nerve blockade also confirms that the changes are independent of systemic stress responses or maternal separation and directly related to neuronal input. in addition, the finding that altered responses to nociceptive input later in life are not somatotopically restricted to the previously injured location suggests a more generalized response to previous injury. The simplest interpretation of these two studies taken together is that early surgery alters future responses by changing the balance of descending input from the RVM and increasing the central neuroinflammatory response to future injury. More complex, however, are the implications of these alterations, especially neural immune interactions in higher-order brain regions and associated processes when surgery occurs at critical periods. Changes in the RVM suggest that early nociceptive input may affect development beyond the spinal cord and brainstem, because the RVM connects to more rostral centers, and nociceptive inputs from the spinal cord have connections to higher cortical and subcortical areas as well. Balanced neuronal excitatory and inhibitory input to the nervous system is required for normal maturation of nociceptive circuits in the spinal cord and connections in the brain; synaptic winnowing and synaptic strengthening occur simultaneously and in response to increases and decreases in activity.4 These studies support the concerning possibility that peripheral nociceptive inputs at critical periods may enhance synaptic strengthening inappropriately or winnow connections that help develop integrated forebrain circuits. This may in turn impact pain processing and environmental interactions later in life and result in altered development of higher-order brain circuits and their function. Thus, the possibility exists for potential long-term and evolving behavioral effects as a direct result of inadequate anesthesia and analgesia in the young. How Long Does Incisional Pain Last