Cardiovascular surgery patients' respiratory responses to morphine before extubation

Analgesia is commonly withheld from cardiovascular surgery patients who are soon to be withdrawn from mechanical ventilation to prevent respiratory depression that can postpone extubation. The effects of analgesia on respiration have not been studied adequately. In this study, weaning parameter measurements were obtained to determine the respiratory impact of a low dose of intravenous morphine administered to cardiovascular surgery patients who were ready to be weaned from the ventilator. A pretest-posttest, quasi-experimental, repeated measures design was used. Eleven alert patients who experienced postoperative pain and met two of five weaning parameter criteria received 1 mg to 5 mg of morphine. Weaning parameters were measured before the intervention and at 15 and 30 minutes afterward. As hypothesized, the administration of low-dose morphine did not have a negative effect on weaning parameters. Mean weaning parameter values either increased or remained the same after the administration of morphine. Despite the small sample size, the results of dependent t tests revealed statistically significant improvements, using an alpha level of 0.05, in the mean tidal volume and negative inspiratory force values at the 30-minute measurement, and in the vital capacity value at the 15-minute measurement. The findings from this study help to refute the notion that a low dose of intravenous morphine will cause respiratory depression, and further suggest that the administration of morphine may enhance patients' respiratory function. If additional research supports this study's findings, both the goals of weaning postoperative patients from the ventilator and controlling pain may be achieved simultaneously.