Intrathecal morphine plus general anesthesia in cardiac surgery: effects on pulmonary function, postoperative analgesia, and plasma morphine concentration.
OBJECTIVE
To evaluate the effects of intrathecal morphine on pulmonary function, analgesia, and morphine plasma concentrations after cardiac surgery.


BACKGROUND
Lung dysfunction increases morbidity and mortality after cardiac surgery. Regional analgesia may improve pulmonary outcomes by reducing pain, but the occurrence of this benefit remains controversial.


METHODS
Forty-two patients were randomized for general anesthesia (control group n=22) or 400 microg of intrathecal morphine followed by general anesthesia (morphine group n=20). Postoperative analgesia was accomplished with an intravenous, patient-controlled morphine pump. Blood gas measurements, forced vital capacity (FVC), forced expiratory volume (FEV), and FVC/FEV ratio were obtained preoperatively, as well as on the first and second postoperative days. Pain at rest, profound inspiration, amount of coughing, morphine solicitation, consumption, and plasma morphine concentration were evaluated for 36 hours postoperatively. Statistical analyses were performed using the repeated measures ANOVA or Mann-Whiney tests (*p<0.05).


RESULTS
Both groups experienced reduced FVC postoperatively (3.24 L to 1.38 L in control group; 2.72 L to 1.18 L in morphine group), with no significant decreases observed between groups. The two groups also exhibited similar results for FEV1 (p=0.085), FEV1/FVC (p=0.68) and PaO2/FiO2 ratio (p=0.08). The morphine group reported less pain intensity (evaluated using a visual numeric scale), especially when coughing (18 hours postoperatively: control group= 4.73 and morphine group= 1.80, p=0.001). Cumulative morphine consumption was reduced after 18 hours in the morphine group (control group= 20.14 and morphine group= 14.20 mg, p=0.037). The plasma morphine concentration was also reduced in the morphine group 24 hours after surgery (control group= 15.87 ng.mL-1 and morphine group= 4.08 ng.mL-1, p=0.029).


CONCLUSIONS
Intrathecal morphine administration did not significantly alter pulmonary function; however, it improved patient analgesia and reduced morphine consumption and morphine plasma concentration.
dos Santos
Luciana Moraes
LM
Department of Anesthesia, Heart Institute, Faculdade de Medicina, Universidade de São Paulo, São Paulo, SP, Brazil. lumoraesrj@yahoo.com.br
Santos
Verônica Cavani Jorge
VC
Santos
Silvia Regina Cavani Jorge
SR
Malbouisson
Luiz Marcelo Sá
LM
Carmona
Maria José Carvalho
MJ
D000701:Analgesics, Opioid / Q000097:blood / Q000494:pharmacology*; D000704:Analysis of Variance; D000768:Anesthesia, General; D001784:Blood Gas Analysis; D001026:Coronary Artery Bypass; D005260:Female; D005541:Forced Expiratory Volume / Q000187:drug effects; D006801:Humans; D007278:Injections, Spinal; D008168:Lung / Q000187:drug effects*; D008297:Male; D008875:Middle Aged; D009020:Morphine / Q000097:blood / Q000494:pharmacology*; D010147:Pain Measurement / Q000187:drug effects; D010149:Postoperative Pain / Q000188:drug therapy; D013147:Spirometry; D018709:Statistics, Nonparametric; D014797:Vital Capacity / Q000187:drug effects
D000701:Analgesics, Opioid; D009020:Morphine