Changes in mechanics of respiration and efficacy of mechanical ventilation during perioperative period in patients undergoing valve replacement / 中华麻醉学杂志

ABSTRACT

Objective To examine the changes in respiratory mechanics and efficacy of mechanical ventilation during perioperative period in patients undergoing valve replacement and determine the possible causes Methods Twenty ASA Ⅱ Ⅵ patients (8 male, 12 female), aged 24 65 years , undergoing valve replacement were studied The patients were premedicated with intramuscular phenobarbital 0.1g, pethidine 50mg and scopolamine 0 3mg Anesthesia was induced with midazolam, fentanyl and vecuronium and maintained with inhalation of low concentration of desflurane and intermittent intravenous boluses of fentanyl, midazolam and vecuronium Valve replacement was performed with moderate hypothermic cardiopulmonary bypass (CPB), The patients were mechanically ventilated with pure oxygen Tidal volume was maintained at 8 10ml/kg, frequency 12 15 bpm and I∶E ratio 1∶1 5 2 During CPB airway pressure was maintained below 5 cmH 2O After operation the patients were transferred to ICU and mechanically ventilated using Siemens 900C ECG, SpO 2, BP, CVP, left auricle pressure and urine output were routinely monitored Respiratory mechanics was measured with Novametrix 8100 multifunction respiratory monitor Mean airway pressure, peak airway pressure, airway resistance, chest lung compliance and respiratory work were measured 20 min after induction of anesthesia, 10 min before CPB, 10 min after termination of CPB, at the end of operation and 2, 6 and 18h after operation Results Work of breathing and airway resistance increased gradually after induction and reached the maximum at 6h after operation Dynamic compliance decreased significantly before CPB but increased slightly after CPB, then decreased again and to the minimum at 6h after operation Mean airway pressure and peak inspiratory pressure went up significantly after operation All parameters mentioned above returned to the preoperative levels before the patients were weaned from respiratory support in ICU Couclusions Thoracotomy and CPB are the main causes of changes in respiratory mechanics in patients undergoing valve replacement The effects reached the peak at 6 h after operation Therefore mechanical respiratory support is essential for the patients until respiratory function recovers and should be maintained for more than 6h after operation