P&S Journal: Spring 1996, Vol.16, No.2
Nitric Oxide Saves Lives of Some Newborns
By Lynne Christensen
For babies born with meconium aspiration syndrome, the first few days of life are critical. These babies are full-term, but because of stress they pass meconium (the first fecal discharge of a newborn) into the amniotic sac, which gets into the lung, causing pulmonary hypertension. "Some babies start to recover in the first few days after birth and tend to do well; otherwise, this is life-threatening," says Dr. Arthur Smerling, assistant professor of anesthesiology and of pediatrics.
This potentially deadly condition can now be treated easily and inexpensively with nitric oxide gas. In the 1980s a chemical was found in normal arteries that caused them to dilate; this was later identified as nitric oxide. After animal studies showed that administration of nitric oxide could dilate pulmonary arteries, it was tested in humans.
Administration of nitric oxide has now been shown in clinical trials to relieve pulmonary hypertension and respiratory distress syndrome. In the past two years researchers at P&S have treated 150 patients with nitric oxide for pulmonary hypertension. Sixty of those patients were babies, 25 of whom had meconium aspiration syndrome.
Approximately 20 percent of newborn babies are meconium-stained-that is, some meconium has passed into the amniotic sac. In 10 percent to 20 percent of these babies the thick meconium passes into the lung and the infants require treatment in the intensive care unit. Some of these babies get better on their own, while some quickly deteriorate. Treatment options have been limited to use of special ventilators and, as a last resort, extracorporeal membrane oxygenation (ECMO), in which blood is temporarily diverted outside the body to an artificial lung.
Clinical trials conducted at P&S have shown that infants with persistent pulmonary hypertension can be treated effectively with nitric oxide gas, which is administered through the inspiratory limb of a standard ventilator. The gas causes the pulmonary arteries to relax, which restores normal blood flow to the lungs. "You see the baby turn from blue to pink before your eyes," says Dr. Smerling. After a few days of treatment, the breathing tube can be removed.
In one clinical trial, Dr. Smerling treated 15 babies who had meconium aspiration syndrome. Fourteen were treated with only nitric oxide and survived. The other baby was put on a special ventilator together with nitric oxide and recovered. None needed ECMO. In fact, Dr. Smerling reports that of all the babies treated at CPMC with nitric oxide-for all causes of pulmonary hypertension-few required ECMO.
In addition to meconium aspiration syndrome, persistent pulmonary hypertension in newborns can be brought on by diaphragmatic hernia, sepsis, and surgery for heart disease. Dr. Smerling and his colleagues have successfully treated babies with all of these conditions. However, he notes that the most dramatic results are seen in cases of meconium aspiration syndrome and heart surgery. Pulmonary hypertension can develop either before or after heart surgery, and in both cases administration of nitric oxide was shown to be very helpful.
Diaphragmatic hernia is associated with hypoplastic lungs, a physiologic condition that cannot be reversed, and sepsis causes organ damage that also cannot be reversed completely. In these cases, the effect of nitric oxide is limited by the underlying pathological condition of the lungs.
Dr. Smerling also has used nitric oxide therapy to improve pulmonary function in adolescent and adult heart transplant candidates being maintained by left ventricular assist devices.
In addition to its clinical benefit, treatment with nitric oxide should prove cost-effective: It costs hundreds of dollars compared with thousands of dollars for ECMO.