Postthoracotomy Respiratory Muscle Mechanics During Incentive Spirometry Using Respiratory Inductance Plethysmography

Postthoracotomy Respiratory Muscle Mechanics During Incentive Spirometry Using Respiratory Inductance Plethysmography· Jose A. Melendez, M.D.;t Ramdas Alagesan;* Ruth Reinsel, Ph.D .;§ Charles Weissman, M .D.;II and Michael Burt, M.D ., Ph.D., F.C.C.P.lI

We undertook this study to characterize the postthoracotomy compartmental displacement and respiratory mechanical changes occurring during and after the performance of the incentive spirometry maneuver. We also evaluated the effect of recumbencyangle on compartmental recruitment. Sixteen patients were randomized to perform incentive spirometry either at 30" or 60" recumbencyangle. They were studied using respiratory inductance plethysmography to measure tidal volume, respiratory frequency, inspiratory time, rib cage motion/tidal volume ratio, inspiratory duty cycle, and inspiratory Row. Patients were studied before surgery and on postoperativedays 1 and 3. Statistical analysiswas accomplishedusing multiple measures ANOVA with post-hoc Student's r-tests when appropriate. Preoperative incentive spirometry augmented VT by increasing

both VT/fl and TI. Postoperatively, the incentive recruitment of VT was reduced, a resuit of a decrease in TI and TIffTOT; VT/fl was unchanged. There was postoperative decrease of AB and ABNT during incentive spirometry, greatest in the 60" group. Our results characterize the nature of the respiratory recruitment afforded by incentive spirometry, befOre and after thoracotomy. We also IOund evidence of postthoracotomy diaphragmatic derecruitment during incentive spirometry exacerbated by a high recum(Chest 1992; 101:432-36) bency angle.

FollOwing thoracic surgery, pulmonary changes can lead to hypoxemia, atelectasis, pneumonia, and occasionally, respiratory failure . The causes of abnormalities are multifactorial including atelectasis due to anesthesia, intraoperative manipulation and lung deflation during one-lung anesthesia, pain, and postoperative alterations in breathing patterns. Modifications of compartmental displacement, ie, thoracic-diaphragmatic motion, have been demonstrated to affect regional distribution of ventilation.'> Decreased lung compliance and distal airway sputum retention only serve to compound the respiratory embarrassment.s' These mechanical changes can be reversed in a hysteresis fashion by inhaling a single breath to total lung capacity. This maneuver increases pulmonary compliance and reduces regional ventilation-perfusion inequalities. The sustained respiratory effort also re-

suIts in a decrease in physiologic dead space and a replenishment of surfactant. 5,6 These changes suggest that a crucial factor in prevention and treatment of postoperative respiratory complications is the maintenance of intermittent deep prolonged inspiratory efforts," In this situation, it seems appropriate to use physical therapy or mechanical aids or both methods that increase lung volume to reduce postoperative complications. The most popular mechanical maneuver used in the United States has been incentive spirometry; it is used extensively because it encourages deep breathing, needs minimal supervision, and therefore, less personnel. Initially, incentive spirometry was found to be as effective as, if notsuperior to, other modalities including chest physical therapy. 8.9 However, the value of incentive spirometry in the prevention of postoperative complications has been recently ques-

·From the Departments of Anesthesiology and Critical Care Medicine, and Surgery, Memorial Sloan-Kettering Cancer Center and Cornell University Medical College. and the Departments of Anesthesiology and Medicine, College of Physicians and Surgeons, Columbia University Medical College, New York. This study was supported by a starter grant from the Society of Cardiovascular Anesthesiologists. t Assistant Professor of Anesthesiology. *Research Fellow. §Research Associate. IIAssociate Professor of Anesthesia and Medicine . 'Assistant Professor of Surgery. Manuscript rece ived February 15; revision accepted May 9. Reprint requests : Dr. Melendez . Memorial Sloan-Kettering Cancer Center; 1275 York Avenue. New York 10023

432

AB=abdomen; QDC=quality diagnostic calibration; RC = rib cage; RCNT ri6 cage motionItid8I volume ratio; TI inspiratory time; TJITror inspiratory duty cycle; VTfft inspiratory

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How

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tioned .":" While the benefit of an increase in lung volumes in the postoperative period is appreciated, the mechanism underlying the possibly beneficial effect is poorly understood. To date, studies performed have only examined the role of incentive spirometry in the prevention of postoperative respiratory complications. This study was undertaken to examine the alterations of respiratory muscle mechanics and compartmental displacement during the incentive spirometry maneuPostlhoracotomy Respiratory Muscle Mechanics (Melendez 8/ eI)

Table I-Comparison ofPopulation Parameters by Angle ofIncUnation Incline Angle

Age, yr

Height, em

Weight, kg

%Pred FVC

FEV,IFVC

50· 30·

52.1±12 59.4±9.8

176.3±12.6 , 172± 12.1

74.4±9.6 , 72.1 ± 12.8

113±34 102±12

.72 ± .07 .71 ±.07

ver in patients who have undergone thoracic surgery. The goal was to identify possible mechanical abnormalities that could contribute to postoperative gas exchange impairment.

maximum pain equal to 10 and no pain equal to 0." In the event of a patient appearing uncomfortable to an independent observer or having a pain score greater than 5, the study was postponed until patients met analgesic criteria.

Data Analysis MATERIALS AND METHODS

Subjects

Sixteen patients, 11 men and 5 women, scheduled for elective thoracotomy were studied. Informed consent was obtained from all subjects according to the guidelines of the Institutional Review Board of Memorial Sloan-Kettering Cancer Center. Patients were excluded from participation in the study if they were concomitantly suffering from a severely debilitating medical or psychiatric illness, weighed under 50 kg or over 100 kg, or found to have a pleural effusion. Patients ranged in age from 30 to 69 years old . All patients except one had pulmonary function tests performed prior to surgery. Eleven of 16 patients were smokers with an average exposure of 45 ± 6 SE pack-years. Nine patients underwent resection for primary lung pathologic condition. The remaining seven patients had metastatic disease. There were five thoracotomies for biopsy, four lobectomies, five wedge resections, one pleurectomy, and one pneumonectomy in the study group. Procedures

Respiratory variables were measured using respiratory inductance plethysmography." Tellon-coated inductance coils of appropriate size were placed around the rib cage and abdomen, with the upper edge of the rib cage band immediately below the axilla and those of the abdominal band at the level of umbilicus. The transducers infer compartmental volume changes from measured changes in the cross sectional area of the chest and abdomen. The system was calibrated using quality diagnostic calibration (QDC).13 The QDC is a two-step procedure wherein the RC and AB electrical gains of the respiratory inductance plethysmography amplifiers are correctly partitioned during tidal breathing and subsequently compared to the output of a spirometer to attain equivalency. The maximum difference accepted between the signals at the beginning of each measurement period was 10 percent. The calibration procedure was performed prior to each measurement period. Preoperatively, the following data were obtained: VT, f, TI, RCI VT, TIII'ToT, and VTIfI. Abdominal motion/tidal volume ratio was computed as l-RCNT. Rib cage contribution to VT was computed as RCNT X VT; abdominal contribution to VT was computed as ABIVT X VT. AVT was calculated as preoperative incentive VT-postoperative incentive VT. All measurements were obtained in the semirecumbent position. Patients were randomly assigned to perform the incentive spirometry maneuver at an incline angle of either 30" (n = 8) or 60" (n = 8). Data were obtained for 10 min prior to , during, and 10 min immediately following coached volumetric incentive spirometry. Patients were trained in its use prior to each study session . Ten consecutive incentive spirometry maneuvers were recorded during each study period. Postsurgical respiratory measurements were performed on the first and third postoperative days. In an effort to study equianalgesic patients, all individuals received intramuscular morphine sulfate, 0.05 to 0.10 mg/kg , 40 to 60 min prior to each study period. To insure adequate pain relief immediately prior to each study period, patients were asked to rate discomfort on a linear analog scale :

All results are expressed as mean±SEM. Statistic comparisons were performed using repeated measures analysis of variance (ANOVA) to assess differences among subjects and between postures. Planned orthogonal contrasts were computed as follow: (1) between the preoperative baseline data and the two postoperative measurement periods; and (2) between the supine and semirecumbent postures. Results were considered statistically significant at p
There were no significant differences between the populations in height, weight, age, percent predicted FVC and FEV/FVC at 30° and 60° angle of inclination (Table 1). The postoperative pain score prior to the study sessions averaged 2.1 ± 0.6 ranging from 1 to 5. There was no significant difference in pain scores on postoperative day 1 and day 3. Total daily doses of morphine sulphate administered was greater on postoperative day 1 than on day 3 (0.42±0.01 mg/kg vs 0.17±0.01 mg/kg, respectively, p
Preoperative

Postoperative Day 1

Postoperative Day 3

VT,ml f,bpm VE, Umin TI, s TIII'roT Vr/I) , mVs

408±31 16.8± 1.0 6.8±0.6 1.34±0.05 0.38±0.01 318±24

395±23 16.0±0.9 6.3±0.5 1.20±0.05* 0.32±0.01* 346±28

424±31 16.2± 1.0 6.9±0.6 1.22±0.05* 0.34±0.0l* 357±28*

*p
433

Table 3-Respiratory lbrameter8 During Incentive Spirometry

Table 5-Compartmental DUp1acement During Incentive Spirometry

Respiratory Parameter

Preoperative

Postoperative Day 1

Postoperative Day 3

Respiratory Parameter

VT,ml f,bpm VE, Umin TI, s TIII'rOT VTffl, rnl/s

1491± 131 9.3±0.9 13.2± 1.2 2.28±0.24 0.39±0.02 711±74

767 ± 71* 16.3±0.9* 11.8±0.9 1.05±O.06* 0.33±0.02* 684±69

829 ± 68* 15.9± 1.2* 12.7±1.2 1.12 ± 0.06* 0.33 ± 0.00* 747±SO

30" Semirecumbent position VT, ml 1381± 166 51.4±4.1 RCNT, % ABlVT, % 48.6±4.1 RC, ml 695±74 AB, ml 686± 117 60" Semirecumbent position VT, ml 1600±207 RCNT, % 56.3±3.2 ABlVT, % 43.7±3.2 RC, ml 890± 112 AB, ml 711 ± 124

*p
Postoperatively, there was a decrease in the incentive VT, a result of a reduction in TI and TIIIToT with the concomitant preservation of VTlfI. The increase in tidal volume during postoperative incentive spirometry mostly resulted from large recruitment of both RCNT and RC. The increase in RCNT was progressive in nature and by postoperative day 3, it had increased by 23 percent over the preoperative incentive RCNT and by 50 percent over the preoperative RCNT . Conversely, ABNT was reduced during the performance of incentive spirometry; minimal AB recruitment was elicited. Postoperative baseline and incentive f were increased, a reflection of reduced TI. Modification of the angle of inclination revealed differences in incentive compartmental displacement with a greater postoperative ABNT at 30° inclination. Although not reaching statistical significance , the 300aVT tended to be larger than the 600aVT (p=0.1l) and the 30°ABrecruitment was greater than the 60°AB (p = 0.06). The lack of statistical significance was attributed to the high interpatient variability. The 30° angle best resembled preoperative compartmental recruitment patterns. No other significant differences in measured parameters were observed. Resting ventilatory parameters measured prior to incentive spirometry were compared to measurements acquired after the maneuver. There were no differences in all measured parameters exceptfwhich was significantly reduced. Postmaneuver, the angle of inclination did not affect the respiratory parameters prior to and after the performance of the incentive spirometry maneuver. Table 4-Respiratory lbrameter8 After Incentive Spirometry Respiratory Parameter

Preoperative

Postoperative Day 1

Postoperative Day 3

Vrv ml f,bpm VE, Umin TI, s TIffTOT VTffl, ml/s

386±27 16.3±0.9 6.3±0.6 1.32±0.04 0.37±0.01 307±24

388±24 15.3±0.9t 6.0±0.5 1.26±0.06* 0.33±0.01* 322±27

436±36 16.0± Lot 6.8±0.6 1.23±O.05* 0.33±0.01* 369 ± 26*

*p
Preoperative

Postoperative Day 1

Postoperative Day 3

832± III SO.4±5.9 49.6±5.9 447±96 385±54t

877±98 58.3±5.0 41.7±5.0 526±83 353±44t

702±88 67.2±7.0* 32.8±7.0* 468±80 234±55t

781±98 69.2±5.1* 3O.8±5.1* 525±62 255±74t

*p
Respiratory complications remain the most important cause of postoperative morbidity following thoracotomy. Previous investigators have shown that between 10 and 50 percent of patients who have undergone thoracic surgery have evidence of postoperative pulmonary abnormalities.w'" Incentive spirometry is one of the mechanical aids used to increase lung volume and reduce the incidence of such complieations." This study characterizes the global respiratory mechanical changes that occur during the performance of the incentive spirometry maneuver in patients who have undergone thoracic surgery. Sharp et all 7 have shown that during quiet breathing there is an increase in AB and ABNT as the patient moves from the sitting to the supine position. It has also been observed that the RC contribution accounts for most of the increase in tidal volume during deep breathing in normal individuals. 18 This is in agreement with our preoperative measurements which revealed a greater abdominal than rib cage contribution to resting ventilation in the semirecumbent position, with recruitment of the rib cage during incentive spirometry. Along with the higher RCNT and RC during preoperative incentive spirometry, there was an increase in AB despite a decrease in ABNT. The voluntary nature of the maneuver incorporates alterations of inspiratory time and drive described by large increases in TI and VTlfl. The TIIITOT, the transform representing central neural process regulating respiratory cycling, remained unchanged. Although incentive spirometry resulted in patients' taking deeper breaths during the entire study period, the postoperative incentive tidal volume was considerably reduced. The cause of this is unclear; however, contributing causes could include pain reflexes arising from the thoracotomy incision site along with reduced FRC and decreased compliance. The halving of Tt Posllhoracolomy RespIratory Muscle Mechanics (Melendez et aI)

and the moderate reduction of TuTTOT during the performance of the postoperative incentive spirometry maneuver, likely reflect the restriction of deep breathing due to altered chest wall mechanics. TheVr/Tt, a reflection of respiratory drive, remains unaltered throughout the study period, suggesting that the alterations in the postoperative period are not due to a central chemoreceptor effect , ie, narcotic respiratory depression. Even though irrelevant because of the voluntary nature of incentive spirometry, the higher postoperative incentive f shows that patients attempt to compensate for the reduction in incentive VT, TI and TI!fToT by increasing respiratory rate despite good coaching and supervision. Diaphragmatic function is a principal element in the determination of compartmental displacement (especially abdominal motion) during resting tidal ventilation.w" Gilbert et al 20 demonstrated that changes in abdominal motion measured by respiratory inductance plethysmography correlated with diaphragmatic contribution to VTas depicted by the ratio of change in gastric pressure to change in transdiaphragmatic pressure. The preoperative incentive spirometry maneuver caused a moderate increase in abdominal tidal volume. Postoperatively, however, compartmental displacement was markedly altered with the increase in incentive VT associated with the magnification of the RC recruitment. It is of interest that this 'p henomenon occurred in the presence of a restrictive respiratory pattern and chest wall pain reflexes associated with thoracotomy incision. The inability to recruit diaphragmatic displacement during incentive spirometry has been previously observed in patients after cholecystectomy.w'" Chuter and associates" attributed the inadequacy of the incentive spirometry recruitment pattern to diaphragmatic dysfunction. Similar evidence for diaphragmatic dysfunction during extreme diaphragmatic maneuvers, but not resting ventilation, was presented by Maeda et al. 27 Pleural pressure gradients can be modified by varying compartmental displacement. I Thus, fluctuations in diaphragmatic motion should lead to alterations in air flow patterns." Since dependent lung portions are known to be most prone to atelectatic changes, poor diaphragmatic contraction should only add to a decrease in ventilation in dependent regions. In addition, it has been shown that the effect of interdependence in promoting more homogeneous gas flow to atelectatic segments may be insignificant in the presence of a dysfunctional diaphragm .s" Heneghan et alJO have shown that decreases in movement of the diaphragm may produce serious deterioration in gas exchange. In order to better understand the alterations in compartmental recruitment observed during incen-

tive spirometry, we evaluated the role of recumbency angle . The incentive RCNT and ABNT were not only affected by time of measurement, but also by the recumbency angle (30°, 6()O). This is in agreement with prior investigations that have shown a progressive increase in ABNT as a subject goes from the sitting to the supine position. This is thought to result from an improved diaphragmatic length-tension relationship and a shift in the compartmental compliance as the subject reclines. 17.31 Consequently, postoperative incentive spirometry provided a better AB recruitment in the 30° posture in combination with a possibly larger VT. It is thus likely that the concept of improvement of diaphragmatic displacement resulting from increased abdominal compliance in the supine posture is applicable to the postoperative diaphragm. Our data support the premise that incentive spirometry performed at a low angle of inclination may be of greater benefit than the standard upright maneuver in ameliorating regional ventilation abnormalities. Some studies suggest that there is a mechanical interaction between the diaphragm and the rib cage . Goldman et al32 have shown that diaphragmatic contraction can lead to rib cage expansion. The interpretation of our results could certainly be affected if we postulate the occurrence of a change in the diaphragmatic-rib cage interaction with the operation and/or the modification of the inclination angle . We have not found any evidence for this phenomenon in the literature. However, we believe our observations would remain valid in view of data by Maeda and associates." Comparing preincentive and postincentive spirometry respiratory measurements, we observed minimal differences. Only VE andfwere significantly reduced, probably in response to hyperventilation and relative hypocapnia after performing the incentive spirometry maneuver. Incentive spirometry failed to cause changes in basal respiratory patterns and compartmental displacement both prior to and after thoracotomy. In conclusion, preoperative incentive spirometry provided increases in VT, TI and VTffI. The decrease in postoperative incentive VT was a function of a reduction in both TI and TuTToT; VTffI was spared. In addition, postoperative incentive spirometry elicited diaphragmatic dysfunction as evidenced by reduced diaphragmatic motion, and possibly failed to provide expansion of dependent lung segments. Evidence of improvement in diaphragmatic function was observed with a reduction in the angle of inclination from 60° to 30°. There were no major differences in resting respiratory patterns brought about by the performance of the incentive spirometry maneuver. Given these findings, we believe further study of the effects of posture on incentive spirometry is CHEST / 101 /2/ FEBRUARY, 1992

435

warranted. It would also be of importance to characterize the effect of postoperative compartmental displacement alterations on ventilation-perfusion inequalities and regional ventilation in humans. REFERENCES

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Post1horacotomy Respiratory Muscle Mechanics (Melendez et aI)