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Hypoxia

Extracted from Myles Textbook for Midwives 15th Edition. Diane M. Fraser, Margaret A. Cooper (Eds). London; Churchill Livingstone: 2009. Courtesy Elsevier.

Literally lack of oxygen, hypoxia in itself is initially the stimulus for the baby to take its firth breath following birth. The majority of babies gasp and establish respiration within 60 seconds of birth. However, if they fail to do so, prompt resuscitation is needed. The length of time that the fetus or neonate is subjected to hypoxia determines the outcome.

Before birth

Oxygenation of the fetus is dependent on oxygenation of the mother, adequate perfusion of the placental site, fetoplacental circulation and adequate fetal haemoglobin. Absence or reduction of any of these factors will result in reduced oxygen supply to the fetus. The fetus responds to hypoxia by accelerating the heart rate in an effort to maintain supplies of oxygen to the brain. If hypoxia persists, cerebral blood vessels will dilate and some brain swelling may occur. As cardiac glycogen reserves are depleted, bradycardia develops, the anal sphincter relaxes and the fetus may pass meconium into the liquor. Gasping breathing movements triggered by hypoxia may result in aspiration of meconium-stained liquor into the lungs. Auscultation of the fetal heart, use of cardiotocography and observation of meconium staining of liquor draining from the vagina should alert the midwife to fetal compromise. Efforts should be made to expedite delivery. [insert figure 39.3]

After birth

In the neonate, the initial response to hypoxia is gasping respirations followed by a period of apnoea lasting 1½ minutes - primary apnoea - which if not resolved by intervention, is followed by a further episode of gasping respirations, which accelerate while diminishing in depth until, approximately 8 minutes after birth, respirations cease completely - secondary (terminal) apnoea. During primary apnoea, circulation and heart rate are maintained, and such babies respond quickly to simple resuscitation measures. In terminal apnoea, the circulation is impaired, heart rate is slow and the baby looks shocked.

The aims of resuscitation are to:

A. Airway - Open airway

B. Breathing - Inflate lungs and breathe for the baby

C. Circulation - Ensure effective circulation with chest compression if necessary

D. Drugs - Consider drugs to achieve this if initially unsuccessful

Do not allow the baby to get cold, and observe and record the sequence of events during resuscitation accurately.

Further reading

American Heart Association (2010) Guidelines for cardiopulmonary resuscitation and emergency cardiovascular care science. Part 15: Neonatal resuscitation. Circulation 2010, 122:S909-S919. Available at: http://circ.ahajournals.org/content/122/18_suppl_3/S909.full

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