Pulse oximetry in methemoglobinemia

Article Abstract:

Pulse oximetry is a method for measuring the saturation of oxygen in the blood that is rapid, easy to perform and painless. Pulse oximetry does not require a blood sample, instead, it uses light absorption to estimate the amount of hemoglobin, the oxygen-carrying protein in red blood cells. Although pulse oximetry is a major advance in monitoring blood oxygen saturation, it does not produce accurate results if the saturation of oxygen is below 65 percent, if two or more different types of hemoglobin are present or if dyes are present in the blood. Methemoglobin is a type of hemoglobin that cannot carry oxygen. Since methemoglobin does not contribute to oxygen saturation, its measurement during pulse oximetry gives an inaccurate assessment of oxygen saturation. Two cases illustrate this potential problem. A 12-month-old, male infant was brought to the hospital after accidentally ingesting the drug pyridium, (a medication used to relieve the pain and discomfort associated with urinary tract infection). Pyridium is known to increase methemoglobin levels. The patient became cyanotic (blue), indicating decreased blood oxygen saturation. She had an elevated level of methemoglobin in her blood, or methemoglobinemia. A three-week-old infant girl was brought to the hospital because of diarrhea, vomiting and irritability. She was experiencing difficulty breathing and appeared to be dehydrated. Blood analysis revealed methemoglobinemia. Despite exhaustive efforts to treat her, the patient died 16 days later. In both cases the infants were given methylene blue, a drug used to treat cyanide poisoning and methemoglobinemia. Although these infants were rapidly diagnosed, it should be noted that there was a difference between oxygen saturation levels as determined by oximetry and direct, invasive methods of estimating oxygen saturation (using arterial blood samples). The oxygen saturation results obtained by pulse oximetry inaccurately estimated the true oxygen saturation in these two patients. A disparity between oximetry and a direct method of measuring oxygen saturation is suggestive of methemoglobinemia. Treatment of methemoglobinemia should be guided by direct measurements of oxyhemoglobin (oxygen bound to hemoglobin) and methemoglobin, and not by pulse oximetry. (Consumer Summary produced by Reliance Medical Information, Inc.)

Case studies, Diagnosis, Measurement, Physiological aspects, Oxygen, Oxygen in the body

---

Home oxygen administration and retinopathy of prematurity: survey of 1988 practices

Article Abstract:

Premature infants receiving oxygen therapy are monitored closely in order to avoid blindness from retinopathy of prematurity (ROP) induced by excessive oxygen. The degree of risk of blindness from severe ROP seems to be proportional to the level of immaturity of the retina. It is felt that the risk for ROP continues until the retina is fully developed; this development may not always coincide with the infant's gestational age. There is much information available about routine use of high levels of oxygen for up to a four-week period for newborns. A few infants who have chronic lung disease may require oxygen administration for a more extended period of time, and oxygen may be given at home. There is very little research regarding safe levels of oxygen during this extended time. This lack of data prompted a survey of current practice regarding discharging infants who still require oxygen. Hospitals having either special or intensive care nurseries were surveyed, and out of 417 responding, 84 percent (349) said that at least occasionally infants were discharged while they still needed oxygen therapy. Eye examination was performed before discharge by 96 percent of these hospitals, although 56 percent stated that the eye examination results would not delay discharge. The infants were monitored at home by either paramedical personnel (39 percent), or parents (19 percent) based on arterial oxygenation; an additional 10 percent were monitored based on presence or lack of cyanosis, blueness. Most of the hospitals that used pulse oximetry saturation to monitor the infant at follow-up examinations sought to keep the rate at 90 to 95 percent, although the range was from 85 percent to no upper limit. At present, there is no established safe upper limit of oxygenation for the avoidance of ROP, and no consensus for the lower limit needed for chronic lung disease. (Consumer Summary produced by Reliance Medical Information, Inc.)

Care and treatment, Prevention, Complications and side effects, Risk factors, Oxygen therapy, Retinal diseases, Retrolental fibroplasia, Retinopathy of prematurity

---

Acquired methemoglobinemia: the relationship of cause to course of illness

Article Abstract:

Acquired methemoglobinemia is a blood disorder in which the iron in hemoglobin, the oxygen-carrying pigment of the blood, is converted to the ferric state, making it less able to bind and carry oxygen. This may result from illness such as gastroenteritis, the inflammation of the stomach and intestines, or from overdose with a drug that converts the iron in hemoglobin to the ferric state. The associations between symptoms, severity of illness, and outcome and the underlying cause of methemoglobinemia were assessed in 17 children admitted to the hospital within a 10-year period for methemoglobinemia. The subjects were classified into an endogenous group, which included the patients with methemoglobinemia associated with illness, and an exogenous group, which consisted of patients with methemoglobinemia related to drug exposure. All children had similar levels of methemoglobin, the ferric state of hemoglobin. However, children in the endogenous group had more acidosis, or increased acidity of their body fluids, as compared with children of the exogenous group. The length of hospital stay averaged one day for children in the exogenous group and 19 days for children in the endogenous group. Children with methemoglobinemia associated with drug exposure had a less severe illness of shorter duration than children with methemoglobinemia due to illness. These findings show that the absolute levels of methemoglobinemia may not be as important as the underlying cause in influencing the development and severity of methemoglobinemia. (Consumer Summary produced by Reliance Medical Information, Inc.)

Causes of, Prognosis, Blood diseases, Hematologic diseases

Similar abstracts:

• Abstracts: Protein-calorie malnutrition in squirrel monkeys: adaptive response to calorie deficiency
• Abstracts: The impact of the acquired immunodeficiency syndrome epidemic on the philosophy of childbirth. Factors predicting severe perineal trauma during childbirth: Role of forceps delivery routinely combined with mediolateral episiotomy
• Abstracts: Changes in physician practice for the prevention of cardiovascular disease
• Abstracts: Postingestional effects of a high-protein diet on the regulation of food intake in monkeys. Effect of breakfast cereals on short-term food intake
• Abstracts: Biology of cancer and aging. Rural-urban differences in stage at diagnosis: possible relationship to cancer screening

This website is not affiliated with document authors or copyright owners. This page is provided for informational purposes only. Unintentional errors are possible.