RESPIRATORY EFFECTS OF PROLONGED TRENDELENBURG POSITION

Transcription

1 Brit. J. Anaesth. (1968), 40, 103 RESPIRATORY EFFECTS OF PROLONGED TRENDELENBURG POSITION BY D. B. SCOTT AND K. B. SLAWSON SUMMARY Twenty-six patients undergoing major gynaecological surgery were given epidural analgesia and light general anaesthesia, and operated upon either in the horizontal, head-down or lithotomy position. Minute volumes were recorded during the operations, and capillary blood-gas data obtained before, during and after the procedures. No significant effect of posture on respiration was detected. The Trendelenburg position has been severely criticized (Inglis and Brooke, 1956; Swain, 1960) but is still popular for pelvic surgery. One of the main complaints about this position is that it reduces ventilation as a result of pressure by the abdoal contents upon the diaphragm. This, of course, applies only to patients breaching spontaneously, because, if artificial ventilation is used, there should be little difficulty in perforg the small amount of extra work entailed. During epidural blockade, spontaneous respiration continues, and this form of analgesia is widely used for pelvic surgery. A study carried out to measure the effects of steep head-down tilt upon the blood gases showed that no significant hypoventilation occurred under nitrous oxide/oxygen/halothane anaesthesia (Scott, Lees and Taylor, 1966), but the duration of the tilt used in these experiments was short (10 utes). The following study was carried out to exae the effects of more prolonged tilting during epidural analgesia combined with general anaesthesia. METHODS Patients. Three groups of patients were studied, all of whom were undergoing major gynaecological surgery. Epidural block was performed on them all, and this was followed by the adistration of light general anaesthesia. The first two groups had pelvic operations carried out through the abdomen, one group in the horizontal position and one group with a 30 head-down tilt. The third group had major vaginal operations per- E formed in the lithotomy position. Details are shown in table I. Anaesthesia. All patients were premedicated with papaveretum 20 mg and atropine 0.6 mg. Lumbar epidural block was performed in each case using 400 mg (20 ml) of prilocaine 2 per cent (plain). It was felt that the block would eliate any respiratory stimulation from the surgery. Epidural analgesia itself has little or no effect upon respiration (Moir, 1963). Following the epidural injection, thiopentone 0.4 g was injected, and a mixture of nitrous oxide (3 l./) and oxygen (1 l./) was adistered using a semiclosed circuit on a BOC Mark II absorber system. Endotracheal intubation was not performed, gases being given by facepiece, and great care was taken to ensure a perfectly clear airway and an airtight fit. Spontaneous respiration was maintained throughout, patients being in the chosen position for the entire procedure. The durations of operations in the horizontal position averaged 52.5 (range ), in the Trendelenburg position 57 (45-75 ) and in the lithotomy position 59 (50-70 ). Blood-gas study. Capillary blood samples were used in this study and measurements made with a Radiometer micro-electrode system using the Astrup technique. Standard bicarbonate values were detered from the Siggaard-Andersen nomogram.

2 104 BRITISH JOURNAL OF ANAESTHESIA Measurements of ph and Paooi were made before premeditation, just before induction of anaesthesia, and at 10-ute intervals throughout operation. Postoperative values were obtained 2 and 4 hours after the end of the anaesthesia. While patients were conscious, a hand was wrapped in a warm wet towel for some utes before taking the capillary sample, to ensure arterialization of the blood. During anaesthesia this was not done, capillary blood gas tensions being very close to those of arterial blood under these circumstances (Raison, 1963). The limitations imposed by not estimating oxygen tensions were appreciated but facilities for making these measurements on a capillary sample were not then available; it was thought that any significant Group Horizontal Trendelenburg Lithotomy TABLE I Age, weight and duration of anaesthesia in the three groups of patients. Mean values are shown with the range in parentheses. No. of cases Age () 29.8 (19-47) 39.5 (33-53) 48.1 (37-56) Weight (kg) 64.5 ( ) 67.2 ( ) 72.9 ( ) Duration of anaesthesia () 52.5 (35-90) 57 (45-75) 59 (50-70) PREMED ANAESTHESIA POST-OP MINUTE VOLUME 7. (l./) f TRENOELENBURG HORIZONTAL LITHOTOMY PH -TT., - so Paco 4* (mm Hg) 4O J- 34- STANDARD BICARB 33- (m.equlv/l.) 3O- Minutes lio 34b FIG. 1 Mean values of ute volume,, ph and standard bicarbonate of patients before, during and after light general anaesthesia combined with epidural blockade for gynaecological surgery. Two standard deviations are shown for each of the mean values in the Trendelenburg position.

3 Position Horizontal Minute (n = 10) volume (l./) ph SHCO, Trendelenburg Minute (n=9) volume (l./) ph SHCO, Lithotomy Minute (n=7) volume (l./) PH SHCO. -60 TABLE II Mean values±one standard deviation of ute volume, Paco,, ph and standard bicarbonate in twenty-six patients having gynaecological operations in various positions. Zero tune is taken as time of thiopentone injection. Postoperatively, zero time is end of operation. The number of observations for each mean value is shown in parentheses. Premed ± " ± ± ± ± ± ± ±2.1 T8) 42.2 ± ± ± ±13.3 ± ± ±6.6 ± ± ± ± ± ± miii 5.57 ± ± ± ± ± ± ± ± ±7.4 ± ± ± ± ±6.3 Anaesthesia ± ±7.7 ± ± ±5.7 ± ± ± O) ± ± ± ± ± ± ± ± ± ± ± ± (2) (1) 22.4 (1) 7.83 ± ± ± ±5.0 " 23.1 Postoperative ± ± ± ± ± CO 42.4 ±

4 106 BRITISH JOURNAL OF ANAESTHESIA respiratory depression would be indicated by changes in Paooj over the long periods of anaesthesia employed. Ventilation study. Minute volume was measured with a Wright respirometer placed between the mask and the yoke of the closed circuit tubing. Measurements were begun 5 utes after the adistration of thiopentone, by which time all patients were considered to be breathing adequately. All gases inspired from this point to the end of anaesthesia were measured, readings being made at 5-ute intervals. RESULTS Results are given in table II and shown graphically in figure 1. Minute volume rose slowly with rime throughout the operation. Arterial ph fell during the 20 utes following induction of anaesthesia and then appeared to remain constant, even 2 hours after the end of the procedures. Paoo 3 rose to a peak of approximately 50 mm Hg 20 utes after induction and thereafter fell back to normal by the end of the operation. Standard bicarbonate fell slowly over the whole period of the study. As can be seen, there was no evidence that the Trendelenburg position caused significant respiratory embarrassment when compared with either the horizontal or the lithotomy position. DISCUSSION The absence of respiratory embarrassment during a short period in a steep Trendelenburg position has been demonstrated previously (Scott, Lees and Taylor, 1966), and these observations now tonfirm that a period of about 1 hour in this position is similarly without ill effects. We believe that the amount of extra work imposed upon the diaphragm in moving the abdoal viscera has been exaggerated. The effective weight of the organs, acting at an angle of 30 from the horizontal upon the diaphragm is probably of the order of 1-2 kg and this is obviously within the capability of the respiratory muscles. One might have expected obesity to render this position more disadvantageous. However, one of our patients, weighing 101 kg, maintained a Pa COa of 50.5 mm Hg and a ute volume of 5.31 l./, in spite of steep head-down tilt. Unfortunately, as we did not measure oxygen tensions, we have no information as to whether the slight falls in lung volume, which may occur in the Trendelenburg position (Altschule and Zamcheck, 1942), caused hypoxaemia analogous to that seen by Nunn and his colleagues (1965). Alveolar collapse can be improved by taking deep breaths (Ravin, 1966) and this can be encouraged postoperatively while the epidural block persists, especially if an epidural catheter is left in place and postoperative analgesia provided by this route. We conclude that the combination of epidural block, light general anaesthesia and the Trendelenburg position does not adversely affect respiration when compared with similar anaesthesia in other positions. The time-course and extent of that imal respiratory depression which was seen was unaffected by posture. ACKNOWLEDGEMENTS We wish to thank Professor R. J. Kellar for allowing us to study his patients, and his staff for their full cooperation. All the biochemical analysis were carried out by Mrs. M. Moodie, to whom we are most grateful. This work was supported in part by a grant from the Scottish Hospitals Endowment Research Trust. REFERENCES Altschule, M. D., and Zamcheck, N. (1942). Significance of changes in subdivisions of the lung volume in the Trendelenburg position. Surg. Gynec. Obstet., 74, Inglis, J. H., and Brooke, B. N. (1956). Trendelenburg tiltan obsolete position. Brit. med. J., 2, 343. Moir, D. D. (1963). Ventilatory function during epidural analgesia. Brit. J. Anaesth., 35, 3. Nunn, J. F., Coleman, A. J., Sachithanandan, T., Bergman, N. A., and Laws, J. W. (1965). Hypoxaemia and atelectasis produced by forced expiration. Brit. J. Anaesth., 37, 3. Raison, J. C. A. (1963). Choice of blood for acid-base studies. Lancet, 2, Ravin, M. B. (1966). Value of deep breaths in reversing postoperative hypoxaemia. N.Y. St. J. Med., 66, 244; cited in Lancet (1966), 2, 209 (leading article). Scott, D. B., Lees, M. M., and Taylor, S. H. (1966). Some respiratory effects of the Trendelenburg position during anaesthesia. Brit. J. Anaesth., 38, 174. Swain, J. (1960). The case for abandoning the Trendelenburg position in pelvic surgery. Med. J. Aust., 2, 536.

5 RESPIRATORY EFFECTS OF PROLONGED TRENDELENBURG POSITION 107 EFFETS RESPIRATOIRES DE LA POSITION DE TRENDELENBURG PROLONGEE ZUSAMMHNFASSUNG Sechsundzwanzig Patientinnen, bei denen ein groflerer gynakologischer Eingriff vorgenommen wurde, erhielten eine Epiduralanasthesie und cine leichte Allgemein- narkose. Operiert wurde entweder in der Horizonttl- SOMMAKE Vingt-six patients subissant des interventions chimrgicales gynecologiques majeures re^urent une analgesic epidurale et une legere anesthesie generate, et furent operees soit en position horizontal, soit a tete basse, EINFLUSSE DER TRENDELENBURG'SCHEN LAGE OBER LANGERE ZEIT AUF DIE ATMUNG ou en Uthotornie. Les volun^ute furent enregis- ^^ST^aSSLS^^ jsnsts tres durant l'operation et des donnfes au sujet des gaz Operation aufgezeichnet. Die Blutgaswerte im Bercich sanguins capillaires deterees avant, pendant et der Kapillaren wurden vor, wuhrend und nach dem aprts l'intervention. Aucun effet significatif de la Eingriff festgestellt. Ein signifikanter Einflufi der Lage position sur la respiration ne fut observi. auf die Atmung wurde nicht beobachtet. EUROPEAN SOCIETY FOR MICROCIRCULATION announces its 5th Conference as an International Conference on Microcircolation to be held at the UNIVERSITY OF GOTEBORG, Gothenburg, Sweden, JUNE 24-29, 1968 All individuals interested in the microcirculation are hereby cordially invited to participate. In addition to Free Communications the Organizing Committee is interested in arranging Symposia and Discussions on the following: INTERDISCIPLINARY APPROACH TO MICROCIRCULATION RHEOLOGY AND MICROCIRCULATION COAGULATION, FIBRTNOLYSIS AND MICROCIRCULATION Scientific Exhibits will be accepted and a Workshop will be arranged at which time the Exibitors will be available to discuss their subject. Films will be accepted and shown at Special Sessions. The Organizing Committee also plans to have Demonstrations, Visits to Laboratories and Wards. Forms for Abstracts, Scientific Exhibits, Films, Hotel Reservations and Social Events will be sent out in the near future to Members of the Society. All others who desire to receive application forms, please write to: PROFESSOR LARS-ERIK GELIN, Surgical Department I, Sahlgrenska Sjukhuset, Gothenburg SV, Sweden. Deadline for Abstracts: APRIL 1, The Committee regrets that abstracts received after this deadline cannot be accepted. Please forward this information to your colleagues.