Chest
Volume 92, Issue 1, July 1987, Pages 66-70
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Clinical Investigations
Continuous Positive Airway Pressure Effect on Functional Residual Capacity, Vital Capacity and Its Subdivisions

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Thirty-four otherwise healthy patients having to undergo elective upper abdominal surgery were randomly assigned to two equal groups. In the treatment group, constant positive airway pressure (CPAP) with an expiratory pressure of 12 cm H2O was applied at one hour following extubation, and at daily intervals for the first five days following surgery for a continuous period of three hours. The control group received no CPAP treatment. All patients were given postoperative physiotherapy. In patients who received postoperative CPAP with an end-expiratory pressure of 12 cm H2O, marked normalization of pulmonary function was noted.

Section snippets

Method

Thirty-four adults having to undergo elective major upper abdominal surgery (cholecystectomy together with bile duct surgery, gastroplasty, or gastric bypass) who were otherwise healthy, consented to partake in the investigation. These patients were randomized into two groups of equal size. Their physical characteristics, the duration of anesthesia, and the type of operation performed are shown in Table 1. Apart from there being 11 women in the control and five in the CPAP group, there were no

Results

Figure 1 shows the vital capacity measurements. The preoperative median vital capacity of the control group was 3,150 ml. This value fell to 990 ml one hour after extubation and gradually rose to 1,880 ml on the fifth postoperative day. We found a similar initial fall in the vital capacity of the CPAP group from 3,560 ml to 870 ml, but a more rapid tendency to return to normal values. Immediately after the first three hours of CPAP application, the vital capacity rose from a median value of 871

Discussion

Extrathoracic factors which restrict diaphragmatic movement, such as surgical trauma to the abdominal wall, pain-induced reflexes, and a rise in intraabdominal pressure, are primarily responsible for the postoperative restriction of pulmonary function.2, 8, 9 The postoperative fall in vital capacity and functional residual capacity found in this study supports previous observations that pulmonary function deteriorates after upper abdominal surgery.10, 11, 12 Immediately following surgery, the

Conclusions

These findings imply that the postoperative prophylactic use of CPAP is, indeed, effective not only in reducing pulmonary complications but in effecting an earlier return to normal pulmonary function. Comparison with previous results indicates that not only should an adequate pressure be applied (>10 cm H2O), but also that the timing of application should be early (ie, during the first postoperative hour), the period of use about three hours per day, and that CPAP treatment should continue for

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  • Cited by (0)

    Manuscript received June 2; revision accepted December 2.

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