The contribution of the right phrenic nerve to ventilation.

A 64-year-old man was scheduled for a right anterior thoracotomy and biopsy of an asymptomatic mediastinal mass under general anesthesia. He was a nonsmoker, had no dyspnea, and could lie flat comfortably. Preoperative arterial blood gases were pH 7.39; PCO, 35 mm Hg, and PO, 60 mm Hg while breathing room air. A chest radiograph showed a mediastinal mass, normal lung parenchyma, and normal excursion of both hemidiaphragms (Fig 1). Pulmonary function studies including flow-volume loops were normal (Table 1). After placing an electrocardiogram, pulse oximeter, precordial stethoscope, and right radial arterial catheter, anesthesia was induced with thiopental, fentanyl, and atracurium. The trachea was intubated and the lungs were mechanically ventilated. Anesthesia was maintained with 50% nitrous oxide, isoflurane, and fentanyl. The blood pressure ranged intraoperatively from 120 to lOO/SO to 70 mm Hg, with a heart rate from 60 to 70 beats/min. The patient underwent a right anterior thoracotomy and excisional biopsy of the mediastinal mass. The mass was adherent to the pericardium, but it was entirely removed. Hemostasis was maintained with approximately 200 mL of blood loss. The final pathology showed the mass to be a lymphoma. The oxygen saturation was 98% to 99% during the course of the procedure while being ventilated with 50% oxygen. Transient arterial desaturation to 95% due to right middle lobe collapse responded quickly to pack removal and sustained positive pressure with 100% oxygen. Before removal of the packs, the arterial blood gas was pH 7.46, PCO, 39 mm Hg and PO, 65 mm Hg. At the conclusion of surgery, the lungs were expanded, two right-sided chest tubes were inserted, and T,-T, intercostal nerve blocks were performed from within the pleural cavity. The incision was closed and reversal of neuromuscular blockade was confirmed with a nerve stimulator showing sustained tetanus and a normal train of four. The trachea was extubated when the patient was awake and responsive, with a minute ventilation of 6 L/min and oxygen saturation of 98% with an F,O, of 1. Immediately after extubation, the chest was noted to expand asymmetrically, the right side lagging behind the left. Oxygen saturation on the pulse oximeter decreased rapidly to 88%. The patient complained of shortness of breath, and premature ventricular contractions were noted. Using a nasal airway and a tight-fitting face mask, 100% oxygen was given. The patient’s respiratory pattern improved, and the oxygen saturation increased to 92%. Blood gas analysis results from a sample drawn during the episode were pH 7.32, PCO, 52 mm Hg, and PO, 87 mm Hg. The chest tubea were functioning, breath sounds were diminished, and diffuse rhonchi were heard on the right side. A chest x-ray film taken in the operating room showed an elevated right hemidiaphragm (Fig 2). It was concluded that the right phrenic nerve had been transected during mediastinal dissection. The patient was placed in the sitting position while 50% oxygen was administered by face mask. Oxygen saturation remained stable at 92%, and he was transported to the recovery room. The patient did not require reintubation and was discharged 1 week later. Pulmonary function studies were repeated 12 weeks later. Compared with the preoperative pulmonary function tests, the forced vital capacity (FVC), forced expiratory volume in 1 second (FEV,), and forced inspiratory vital capacity (FIVC) decreased. His FEV,/FVC remained the same. Postoperative PO, was unchanged at 60 mm Hg, but the PCO, increased from 35 mm Hg to 44 mm Hg, resulting in a respiratory acidosis with a compensatory metabolic alkalosis. His postoperative flow-volume loops showed a moderately reduced FVC and proportionate air flow slowing, consistent with mild restrictive impairment and a slight obstructive component (Fig 3). Postoperatively, the inspiratory capacity was 1.83 L (predicted, 2.78 L), functional residual capacity (FRC) was 2.57 L (predicted, 3.33 L), vital capacity was 2.63 L (predicted, 4.2 L), and total lung capacity was 4.4 L (predicted, 6.11 L).