296 Bol med Hosp Infant mex Physiology of nutritive sucking in newborns and infants pediatric theMe Bol Med Hosp Infant Mex 2011;68(4):296-303 Mario Enrique Rendón Macías and Guillermo Jacobo Serrano Meneses Unidad de Investigación en Epidemiología Clínica, Unidad Médica de Alta Especialidad Hospital de Pediatría, Centro Médico Nacional Siglo XXI, Instituto Mexicano del Seguro Social, México D.F., México Correspondence: Dr. Mario Enrique Rendón Macías Unidad de Investigación en Epidemiología Clínica Unidad Médica de Alta Especialidad Hospital de Pediatría, Centro Médico Nacional Siglo XXI Instituto Mexicano del Seguro Social México D.F., México E-mail: mario.rendon@imss.gob.mx Received for publication: 3-7-11 Accepted for publication: 6-14-11 INTRODuCTION From birth throughout the frst 6 months of life, infants will obtain their primary food (milk) through nutritive sucking. During the last months of embryonic development, the fetus acquires refexes and skills required to achieve an independent and effective sucking. This is a physiological process that allows infant to ensure suffcient food intake, which is easy to assimilate, ìsafeî and with low energy requirements. 1-3 To achieve this, a newborn should present no congenital malformations in the mouth or the respiratory or nervous systems and be free of medication effects and lesions that alter normal functions in involved organs and systems (digestive, respiratory, cardiovascular and nervous). 4,5 Healthcare personnel should determine during clinical evaluation of any newborn or infant if feeding is effcient to guarantee an appropriate development. Nutritive sucking should be part of the clinical evaluation; however, this is not always carried out objectively. Here we summarize the current knowledge on normal sucking physiology in newborns and infants. First we describe anatomic characteristics that ease the process and physiological phases involved. We also include data on variations of each phase in order to defne normal limits. Finally, we describe criteria to differentiate normal from abnormal nutritive sucking. Nutritive Sucking Process The process that allows an infant to obtain food, either maternal milk or infant formula, is known as nutritive sucking (NS). 6-8 Although suction can be triggered through oral stimulation (non-nutritive sucking), this has other physiological characteristics and will not be covered in this report. Sucking is a process integrated by three highly correlated phases: a) expression-suction, b) swallow and c) breathing, accompanied by other body stability factors such as cardiovascular and nervous systems. 9 ABSTRACT Nutritive sucking is the process by which infants obtain their feeding, which may be sucking by breastfeeding or through a bottle. This article summarizes the physiological basis of nutritive sucking in order to establish the normal conditions of this process. In this context it is known that the nutritive sucking consists of three phases: expression/suction, swallowing and breathing. Coordination of the frst two phases can provide an adequate supply of food and direct it to the digestive tract without the risk of it passing to the airways. The se- quence in which these phases are given varies with the age of the child. Under normal conditions, nutritive sucking is an aerobic process and is accomplished with jaw and tongue movements, which are capable of generating the necessary pressure from a reservoir for the suction and extraction of milk. Thus, lack of coordination of these phases explains the changes in the rate of suction and the appearance of abnormal clinical signs such as low consumption of food, choking, regurgitation, vomiting or respiratory disorders. The construction of clinical scales has been possible by determining the sequence of the different phases of suction. These scales can detect problems with newborns or infants who do not achieve adequate nutritive sucking either by the identifcation of abnormal clinical signs or because milk consumption is <80% of the recommended volume. Key words: nutritive sucking, infants, physiology.