EFFECT OF AMINOPHYLLINE ON RESPIRATORY MUSCLE STRENGTH AFTER UPPER ABDOMINAL-SURGERY - A DOUBLE-BLIND-STUDY

Background-The effect of aminophylline on maximum respiratory muscle s trength in patients undergoing upper abdominal surgery was investigate d. Methods-An open pilot study was performed in which aminophylline wa s administered continuously for 48 hours after surgery (protocol I). I n a second group of subjects aminophylline was given for 24 hours afte r cholecystectomy in a double blind placebo controlled trial (protocol II). Twelve patients participated in the pilot study (group A) and 25 in protocol II of which 14 received aminophylline (group B) and 11 pl acebo (control, group C). Respiratory muscle strength was assessed by measuring mouth pressures during maximum static inspiratory and expira tory efforts. Forced expiratory volume in one second (FEV1), forced vi tal capacity (FVC), vital capacity (VC), inspiratory maximum pressures (PImax), expiratory maximum pressures (PEmax) were measured 24 hours preoperatively, PImax and serum theophylline 24 hours postoperatively, and FEV1, FVC, VC, PImax, PEmax, and serum theophylline 48 hours afte r surgery. Results-FEV1, FVC, and VC decreased in all groups of patien ts at +48 hours. Pimax fell at +24 hours and +48 hours but this decrea se was significantly smaller in the two groups who received aminophyll ine than in the control group. PEmax showed a decrease at +48 hours bu t this reduction was similar in all three groups studied, independent of the treatment given. These data suggest that either aminophylline h ad a protective effect only on the inspiratory muscles or, most probab ly, that the effect of aminophylline was central, reducing the phrenic nerve inhibition induced by cholecystectomy and thus improving diaphr agmatic function. Conclusions-Upper abdominal surgery decreases inspir atory and expiratory muscle strength and aminophylline has a protectiv e effect only on inspiratory muscle function. This may have important clinical applications in minimising pulmonary complications after chol ecystectomy.