Fisiología respiratoria hipoxemia / Hypoxemia

La hipoxemia ocurre producto de una inadecuada captación de oxígeno a nivel pulmonar y se manifiesta como presión arterial de oxígeno menor a 60 mmHg o saturación arterial de oxígeno menor de 90%. Los mecanismos fisiopatológicos por los cuales se puede producir hipoxemia son hipoventilación, alteración del equilibrio ventilación perfusión, shunt cardiaco, alteración de la difusión y disminución de la presión inspirada de oxígeno. La comprensión de estos mecanismos es fundamental para entender su presentación clínica en distintas enfermedades.

Hypoxemia is the name given to inadequate uptake in the lung and is defined as an arterial oxygen pressure less than 60 mmHg or arterial oxygen saturation less than 90%. The pathophysiological mechanisms that can produce hypoxemia are: hypoventilation, ventilation perfusion mismatch, cardiac shunt, diffusion impairment and decreased inspired oxygen pressure. Full comprehension of these mechanism facilitates the understanding of hypoxemia among different diseases.

Trastorno de hipoventilación central del sueño en pediatría: causas poco frecuentes / Central hypoventilation disorders sleep-related in pediatrics: unusual causes

Congenital central hypoventilation syndrome (CCHS) and rapid-onset obesity syndrome with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation (ROHHAD) are rare causes of hypoventilation during sleep in the pediatric population. This group of disorders are characterized by the absence or decrease in the automatic control of ventilation, decreased sensitivity of chemoreceptors to CO2, causing hypoventilation during sleep and even in wakefulness, in the most severe cases. For these reasons it is important to diagnose and treat them promptly. The objective of this review is to provide current and complete literature, to be able to identify, treat and refer this group of children early, and thus reduce the complications and/or associated comorbidities in the short and long term, improving their quality of life.

El síndrome de hipoventilación central congénita (CCHS) y síndrome de obesidad de inicio rápido con disfunción hipotalámica, hipoventilación y desregulación autonómica (ROHHAD), son causas poco comunes de hipoventilación durante el sueño en la población pediátrica. Este grupo de trastornos se caracterizan por ausencia o disminución en el control automático de la ventilación, sensibilidad disminuida de los quimioreceptores al CO2, provocando hipoventilación durante el sueño e incluso en vigilia, en los casos más severos. Por estas razones es importante diagnosticarlos y tratarlos oportunamente. El objetivo de esta revisión es proporcionar literatura actual y completa, para poder identificar, tratar y referir a éste grupo de niños tempranamente, y así disminuir las complicaciones y/o comorbilidades asociadas a corto y largo plazo, mejorando su calidad de vida.

Congenital central hypoventilation syndrome associated with Hirschsprung's Disease: case report and literature review / Síndrome de hipoventilação central congênita associada à doença de Hirschsprung: relato de caso e revisão de literatura

Abstract Objective: To report the case of a newborn with recurrent episodes of apnea, diagnosed with Congenital Central hypoventilation syndrome (CCHS) associated with Hirschsprung's disease (HD), configuring Haddad syndrome. Case description: Third child born at full-term to a non-consanguineous couple through normal delivery without complications, with appropriate weight and length for gestational age. Soon after birth he started to show bradypnea, bradycardia and cyanosis, being submitted to tracheal intubation and started empiric antibiotic therapy for suspected early neonatal sepsis. During hospitalization in the NICU, he showed difficulty to undergo extubation due to episodes of desaturation during sleep and wakefulness. He had recurrent episodes of hypoglycemia, hyperglycemia, metabolic acidosis, abdominal distension, leukocytosis, increase in C-reactive protein levels, with negative blood cultures and suspected inborn error of metabolism. At 2 months of age he was diagnosed with long-segment Hirschsprung's disease and was submitted to segment resection and colostomy through Hartmann's procedure. A genetic research was performed by polymerase chain reaction for CCHS screening, which showed the mutated allele of PHOX2B gene, confirming the diagnosis. Comments: This is a rare genetic, autosomal dominant disease, caused by mutation in PHOX2B gene, located in chromosome band 4p12, which results in autonomic nervous system dysfunction. CCHS can also occur with Hirschsprung's disease and tumors derived from the neural crest. There is a correlation between phenotype and genotype, as well as high intrafamilial phenotypic variability. In the neonatal period it can simulate cases of sepsis and inborn errors of metabolism.

Resumo Objetivo: Relatar caso de neonato com episódios de apneias recorrentes, diagnosticado com síndrome de hipoventilação central congênita (SHCC) associada à doença de Hirschsprung (DH), o que configurou síndrome de Haddad. Descrição do caso: Terceiro filho de casal não consanguíneo, nascido a termo, parto normal sem intercorrências, peso e comprimento adequados para idade gestacional. Logo após o nascimento apresentou bradipneia, bradicardia e cianose, foi submetido à intubação orotraqueal e iniciada antibioticoterapia empírica devido à suspeita de sepse neonatal precoce. Durante internação em UTI neonatal evoluiu com dificuldade de extubação devido a episódios de dessaturação durante sono e vigília. Apresentou quadros recorrentes de hipoglicemia, hiperglicemia, acidose metabólica, distensão abdominal, leucocitose, aumento de proteína C reativa, com hemoculturas negativas e suspeita de erro inato do metabolismo. Aos dois meses foi diagnosticada doença de Hirschsprung de segmento longo, foi submetido à ressecção do segmento e colostomia à Hartmann. Feita pesquisa genética por reação em cadeia da polimerase para pesquisa de SHCC, que evidenciou alelo mutado do gene PHOX2B e confirmou o diagnóstico. Comentários: Trata-se de doença genética rara, de herança autossômica dominante, causada por mutação no gene PHOX2B, localizado na banda cromossômica 4p12, que resulta em disfunção do sistema nervoso autônomo. A SHCC também pode cursar com doença de Hirschsprung e tumores derivados da crista neural. Há correlação entre fenótipo e genótipo, além de grande variabilidade fenotípica intrafamiliar. No período neonatal pode simular quadros de sepse e erros inatos do metabolismo.

Late onset hypoventilation syndrome: is there a spectrum of idiopathic hypoventilation syndromes?

We report a case of late onset central hypoventilation syndrome (LO-CHS) with hypothalamic dysfunction (HD) and ganglioneuroma presenting at the age of ten years. LOCHS-HD is now a well-established syndrome; the key is to investigate each child's history and presentation to expeditiously offer the most accurate diagnosis and optimal management.

Breath holding spells: evaluation of autonomic nervous system function.

This study attempted to determine noninvasively whether a dysregulation of autonomic reflexes exists in children with breath holding spells (BHS).Fifty children between 13 to 47 months of age who had experienced BHS were evaluated at a time when they stopped having spells, for autonomic nervous system (ANS) dysfunction. The results were compared with the test results of control group of 100 normal children (age and sex matched). Breath holding children displayed significantly high resting heart rate and resting diastolic BP significantly abnormal; 30: 15 RR ratio after rising from supine to standing position; showed significant hypersensitivity of pupil on instillation of 0.125 percent pilocarpine into conjunctival sac and positive Orthostatic signs when compared to control group. This study correlates with the hypothesis that a subtle underlying generalized autonomic dysfunction exists in children with BHS.

Trocas gasosas durante ventilaçäo com alta frequência em jatos(VAFJ) em cäes normais / Gas exchange during high frequency jet ventilation in normal dogs

A ventilaçäo de alta freqüência em jatos (VAFJ) é uma técnica de suporte ventilatório recentemente introduzida na prática médica, tendo-se-lhe atribuído vantagens em relaçäo aos sistemas convencionais de ventilaçäo artificial (p. ex., ventilaçäo com pressäo positiva intermitente - VPPI). decidimos, entäo, testar um modelo de ventilador de alta freqüência em jatos nacional (Takaoka M 995) em comparaçäo a um sistema clássico de ventilador ciclado a pressäo (BIRD Mark 7) em 24 cäes pulmöes normais, quanto as trocas gasosas pulmonares. Utilizamos os dois sistemas de ventilaçäo artificial nos animais anestesiados e curarizados, a VPPI com volume corrente entre 10 e 20 ml.kg**-1 e freqüência ventilatória de 16 ipm e a VAFJ em freqüências 250, 450, e 650, jatos. min**-1 (reais de 197, 273, e 374 respectivamente) ajustando-se a ventilaçäo pela PaCO2. Foram analisados em cada período gasometrias arterial e venosa central em ar e O2 a 100%, hematócrito, hemoglobina, temperatura do animal, débito cardíaco (Q), diferença alvéolo-arterial de pressöes parciais de O2 (P(A-a)O2), diferença de conteúdo artério-venoso de O2 (C(a-v)O2) e curto-circuito fisiológico (Qsfis/Q). Os resultados mostraram que as trocas gasosas em VAFJ foram mantidas semelhantes a VPPI até freqüências reais de 273 (equivalentes a 450) jatos. min**-1. Em freqüências superiores ocorreu decréscimo de PaO2, aumento de PaCO2 e desenvolvimento de acidose respiratória, caracterizando-se quadro de hipoventilaçäo alveolar. Tanto a P (A - a)O2 como o Qsfis/Q näo sofreram variaçöes significativas. Assim, os autores concluem que à medida que se aumenta a freqüência no nosso sistema de VAFJ ocorre hipoventilaçäo alveolar e prejuízo das trocas gasosas pulmonares com conseqüênte hipoxemia