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Clinical Use
Dosage
The optimal dosage of PFCs is unknown as of yet. Most clinical trials have been using the patient's functional residual capacity (FRC). The initial dose to bring the patient to FRC has been anywhere from 5-20 ml/kg with an average of 16 ml/kg. These amounts were given over a 25-minute period. Other clinical trials have been using ½ of FRC. Neither of the two dosages have shown to be better than the other. Since this liquid evaporates from the lungs, replacement is necessary. The rate of evaporation is determined by the patient's minute ventilation, the physical properties of the liquid, lung function, and the communication with the alveoli. To account for this loss, PFC was given at 3.3 ml per kilogram each hour. The PFC must be warmed prior to administration. Typically it is warmed to 35-37 degrees Celsius.
An adapter is required to infuse the PFC into the endotracheal tube.
Upon administration of PFCs to a patient, debris is removed from the alveoli with each exhalation. The atelectatasis when relieved increases total lung volume (TLV) which increases static compliance. An increase in compliance will decrease the amount of pressure needed to extend the lungs. Conventional ventilation in ARDS can require high pressures to expand the lungs. Too high of pressures can cause volutrauma or barotrauma. PFCs have a high density making their time constants through the lungs slower. Slow time constants mean long inspiratory and expiratory times for the liquid to move from the mainstem bronchi to the alveoli. The respiratory rate is between 4-6 breaths/minute. This slow rate is adequate because PFCs have a high affinity for oxygen and carbon dioxide.
In PLV, ventilator settings will change drastically after administration of PFC. In volume ventilation, the volume will stay the same with a much lower peak pressure. Typical tidal volume settings are 10-15 ml/kg body weight. In pressure ventilation, the volume will increase drastically with the same pressures because of the increase in compliance. PEEP could be decreased because some of the PFCs will stay in the alveoli holding it open and with the increase in PaO2 there is no need to keep the high mean airway pressure. The rate will need to be decreased since the long time constants of the PFCs in the lung. PCO2 will stay within normal range because of the increased affinity that PFCs have toward carbon dioxide. FIO2 can also be decreased because of the increased ventilated areas of the lung and increased carrying capacities. If the normal alveolar-capillary membrane is thickened, then PFCs can not help the oxygen dissolve across the membrane. The only way that PFCs would help in dissolving of oxygen across this membrane is by it's anti-inflammatory properties.
Weaning from the ventilator would follow weaning protocols as normal. PFCs would be discontinued, the liquid will evaporate, and the patient will have to rely on conventional ventilation. The oxygen index would decrease with the decrease in PFCs, when converted from liquid to conventional ventilation. A residual volume of PFC can stay in the lungs up to seven days after discontinuing the dosage. Ventilator settings will have to change in accordance to the change in lung tissue. The lung may be normal or it may have an underlying disease.
Case Study
The following is a mock case study to help show how PFC might be used.
A 50 year-old 70 kilogram quadriplegic man was brought into the ER with signs of ARDS. The ARDS was found to be secondary to an over dose of his pain medication. The patients arterial blood gas was as followed: pH 7.30, PCO2 56, PaO2 49, SaO2 75% with a Qt/Qs of 70 %. The ventilator settings were in volume control with an FIO2 at 1.0; PEEP at 15 cm H2O; tidal volume of 425 ml; rate of 20 breaths per minute. Peak airway pressures were being measured at 45 cmH2O. PLV was started to help support the patient until the medication could be eliminated from the body.
PLV was given to the level of FRC over a 30 minute period. To account for the loss of PFC from evaporation, a maintenance drip was administered at 3.3 ml per kilogram each hour. The CXR after administration of the PFC showed complete opacification of the center of the lung. With each day that perflubron was given, there was a growth in the amount of opacification. The increase in opacification meant that there was more lung tissue being ventilated. With the increased lung ventilation, ventilator settings had to be adjusted as the patient improved. An increased dosing of perflubron had to be given to account for the increase in lung volume. On the 5th day of administration, the lung fields were completely opacified by the PFC. The pain medication was completely excreted from the body on this day so the doctors decided to withdraw the PFC. The administration of the PFC was stopped and the patient was weaned from the ventilator. An investigation is pending on how he received that amount of pain medication. He went back to live his former life.
