During the past three decades a number of technological advances in the field of neonatology have improved the survival of critically ill preterm and term infants. Some of those advances include the use of exogenous surfactant, high frequency ventilation, extracorporeal membrane oxygenation (ECMO), and nitric oxide (NO) treatment. Yet another therapy--liquid ventilation--has the potential for meeting the ventilatory needs of those infants who did not fare well with the previously mentioned technologies, either because of physiological immaturity or the nature of the illness and its subsequent deliterious effects. The idea of liquid ventilation is not a new concept; its possibilities for the improvement of minute ventilation have been pondered since the late 1960s. The use of saline lung lavages in the 1920s helped spark some of the current research with liquid ventilation. In 1989, the first three human trials using perfluorocarbons as a liquid ventilation medium were conducted on extremely critical preterm neonates. The results showed an improvement in gas exchange as well as drastic improvement in the physiologic function of the lung itself (Greenspan and others, 1990).
While seemingly an unusual concept, liquid ventilation appears to have two main benefits over other technologies such as surfactant replacement, in that the fluid-filled lung even when surfactant deficient demonstrates increased compliance. Uniformly filling the lung with fluid diminishes surface tension, reducing required inflation pressures and subsequent barotrauma in preterm and sick term neonates. Additional advantages of using liquid ventilation with perfluorocarbons are the increased removal of pulmonary debris such as meconium; distention of lung parenchyma; and its use as a medium or transporter of drugs, such as antibiotics and surfactant, directly into the smaller capillaries of the lung which are usually unreachable (at least uniformly so) in neonatal pulmonary disorders such as respiratory distress syndrome.
Perfluorocarbons (PFCs) are inert liquids derived by replacing all the carbon-bound hydrogen atoms on organic compounds with fluorine. PFCs are clear, odorless, inert, and require no metabolism by the kidneys or liver. Furthermore, oxygen and carbon dioxide are highly soluble in PFCs, which are removed from the body by evaporation. No adverse histologic, biochemical or toxic effects have been identified in these substances, thus making them highly attractive as a medium for liquid ventilation (Cox, Wolfson and Shaffer, 1996).
The two main types of liquid ventilation delivery techniques are total (or tidal) liquid ventilation (TLV) and partial liquid ventilation (PLV), sometimes called perfluorocarbon assisted gas exchange (PAGE). For an in depth explanation of TLV and PLV mechanics refer to the article by Cox, Wolfson and Shaffer, 1996. With PLV, the lungs are filled with perfluorocarbons through the endotracheal tube during the inspiratory phase, which is somewhat slower than regular gas ventilation, with a filling volume equal to functional residual capacity. Gas ventilation is interspersed with PFC insertion until the desired effects are achieved. In TLV oxygenated PFCs are continuously instilled into the lungs with special equipment. Once gas exchange and lung mechanics improve, the neonate is weaned from ventilatory support, often within a matter of hours. In both systems PFCs lost to evaporation are replaced through the mechanical ventilation system to achieve the desired results. Liquid ventilation may be used in conjunction with extracorporeal membrane oxygenation and nitric oxide. PFC fluids are radiopaque and may be used to assess the lungs for ventilation-perfusion function and to view anatomic lung structures.
The nursing care of the infant on liquid ventilation is similiar to the care of any infant on conventional gas ventilation. Special attention to lung sounds and adequacy of therapy by assessment of arterial blood gases is imperative; with TLV actual breath sounds will not be auscultated; fine rales and course ronchi may be auscultated with PLV. Attention is given to the positioning of the neonate, suctioning only when indicated and assessing for complications related to the infant's status or the equipment being used for gas and liquid delivery. Heart tones will be much more distinct with liquid ventilation because sound wave transmission is increased with fluids. The infant is evaluated for signs of a pneumothorax and/or signs of deteriorating pulmonary status. Vital signs are assessed according to the severity of the infant's condition (Cox, Wolfson and Shaffer, 1996). Liquid ventilation has also been shown to be effective in the treatment of persistent pulmonary hypertension, congenital diaphragmatic hernia, meconium aspiration, and pneumonia. Perhaps the most attractive feature of liquid ventilation with the use of PFCs is the relative safety of its use in neonates, even critical preterm, with practically no reported adverse physiologic sequelae such as intraventricular hemorrhage or sepsis. Clinical trials have thus far demonstrated the efficacy of liquid ventilation for respiratory illnesses in the sick term and preterm neonate. There is also evidence that liquid ventilation may be useful in older children with pulmonary insufficiency and in adults with acute respiratory distress syndrome (ARDS) (Dirkes, 1996). As this therapy becomes more available in hospitals it is increasingly important that nurses equip themselves with the knowledge and skills required to care for such patients.
Greenspan JS and others: Liquid ventilation of human preterm neonates, J Pediatr 117 (1 Pt 1):106- 111, 1990.
See Chapter 12 in Nursing Care of Infants and Children, 5th and 6th editions.
See Chapter 9 in Essentials of Pediatric Nursing, 5th edition.
March 15, 2002