Intrathecal morphine for post-sternotomy pain in patients with myasthenia gravis: effects on respiratory function

Thymectomy can induce a remission or at least an improvement in myasthenia gravis (MG) patients. After sternotomy MG patients with compromised muscle strength need an excellent postoperative pain relief. This study was designed to evaluate the efficacy of intrathecal morphine (ITM) on ventilatory function among MG patients undergoing trans-sternal thymectomy, when intravenous morphine served as control.

Twenty consecutive MG patients were randomised to receive either morphine (10 micrograms/kg) intrathecally at induction or intravenous morphine (30 micrograms/kg) with a patient-controlled analgesia (PCA) device. Anaesthesia was standardised. Forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), respiratory rate, oxygen saturation, arterial blood gases, pain intensity and morphine consumption were assessed during 48 hours.

The mean age of the patients was 35 +/- 3.4 years and the mean duration of the disease 1.9 +/- 0.5 years. According to Osserman's classification 70% of the patients belonged to Class IIA and 30% to Class IIB. ITM restored ventilatory function significantly better than iv PCA morphine. FVC recovered to 60% and FEV1 to 57% of the baseline values in the ITM group compared with 32% (P < 0.05) and 37% in the PCA morphine group, respectively. Postpuncture headache occurred in 4/10 patients.

Intrathecal morphine provided effective postoperative analgesia and significantly improved ventilatory function when compared with intravenous morphine.