2 P H Y S I O T H E R A P Y DECEMBER. 1 9 7 3 Artificial Increase of Dead Space for the Improvement of Post-Operative Ventilation — A R eview A rn o ld E. D . van de V ijver M .D . (U trecht) Senior L ec­ turer, D epartm ent o f Anaesthesia, University o f S tel­ lenbosch, Senior Anaesthetist, K a rl B rem er H ospital, Bellville. A reduction in post-operative pulm onary ventilation is alm ost invariably present am ongst patients undergoing upper abdom inal surgery*1- 2). It is very com m on amongst those having low er abdom inal surgery and very ra re following orthopaedic operations*1). N ichols and H ow ell (1 9 7 0 /l> analysing th e ir results conclude th at there is no significant difference in venti­ latory capacity changes between patients receiving the classical pre- and post-operative physiotherapy and between those patients w ho did n o t receive this tre a t­ ment. However, they excluded from this trial patients w ith pre-existing acute o r chronic obstructive lung- disease because, fo r this type o f patient, there is general agreem ent about the therapeutic value o f classical physiotherapeutic procedures. F ro m their trial it is evident th at a post-operative decrease of pulm onary ventilation is not correlated w ith an obstructive p attern o f respiration. It is, however, clearly correlated w ith a restrictive p attern of ventilation i.e. shallow breathing, as a result o f diaphragm atic inhibition. F u rth er evidence to their conclusions is prom ulgated by the w ork of FinerV'* who studied the variability in expiratory efforts before and after cholecystectomy. T his a u th o r stresses the im portance of encouragem ent — “ the elicitation of the latent encouragem ent potential,” in order to over­ come diaphragm atic inhibition and to im prove p u l­ m onary ventilation. However, he also stresses the clinical value of post-operative pain relief, which he effects by different and m utually com pared kinds of nerve blocks (intercostal, epidural and splanchnic). C ontrolled measurem ents of vital capacity (V.C.), forced expira­ tory volume (F.E.V.) and peak expiratory flow showed th a t the best results were obtained by a com bination o f encouragem ent and intercostal block. A som atic and visceral pain block com bination did not' appear to be superior to a som atic pain block alone. T h e a u th o r’s opinion is th at the relief o f som atic pain by analgesic therapy, following cholecystectomy, is the m ore im ­ p o rtan t factor in th e im provem ent o f post-operative expiratory efforts. D iaphragm atic inhibition causes a consequent reduc­ tion of lung volume. T his reduced lung volum e is a con­ tributory cause o f segmental and massive lung collapse, of raised diaphragm an d o f pleural effusion. In the early stages of their developm ent these com plications frequently cannot yet be diagnosed by clinical sym p­ toms and have to be detected by radiological changes. I t is thus clear that, in order to prevent the clinical complications of reduced lung volum e, diaphragm atic inhibition m ust a t all costs be overcom e. Because of the inadequacy of classical physiotherapeutic measures fo r the im provem ent of post-operative pulm onary ventilation, a new therapeutic ap proach is needed, by which at will an increase of ventilation, especially after abdom inal surgery, can be obtained. T he next problem posed is the m ethod o f choice, because different m ethods have been proposed and evaluated. A recent com parison h as been m ade by Jones (1968)*3) in a clinical study o f the rath er small n um ber o f 15 patients w ho h ad recently undergon thoracotom y o r laparotom y operations. H e compared five com m only em ployed m ethods fo r enhancing ventila tion, using them sequentially in each p atien t fo r two to five days post-operatively and estim ating their effective­ ness tow ards the increase of th e V t . A ll these methods were applied w ithout the adm inistration o f narcotics for fo u r hours previous to th e study. In six o f the patients involved pre-operative as w ell as post-operative studies were done. F ro m this study it is apparent, as it is from th e a b a ' literature, th a t follow ing abdom inal o r thoracic surgl there is a dim inished ventilatory ability, the post-opera­ tive b reathing values averaging 60% of th e pre-opera­ tive values. T h e com parison betw een the five different clinical m ethods fo r enhancing ventilation h ad the following results: 1. R ebreathing w ith the A dler re b re a th e r (1967)<‘> was relatively ineffective in increasing depth o f respira­ tion. 2. I.P.P.B. (Interm ittent Positive Pressure Breathing) w ith th e conventionally em ployed inspiratory pres­ sure o f 15 cm H 20 and the in h alatio n of 5% C 0 2 were m ethods o f interm ediate value. T hey were, how ever, infrequently equal o r su p erio r to voluntary efforts in producing significant increases in V t 3. V o lu n tary deep breathing w as frequently quite effective. Increases in V t of 80% o r m ore occurred in tw o-thirds of the subjects, w hile V t as large or larger th a n those produced by any other method were observed in a b o u t 50% of th e patients. 4. I.P.P.B. a t the relatively high in sp irato ry pressure o f 25 cm H 30 was clearly the m ost superior method. W hen V t greater th an those due to voluntary deep breathing were observed, they w ere alm ost always produced by I.P.P.B. o f 25 cm H 20 . H ow ever, the a u th o r stresses the lim itation of study. A com parative evaluation o f these m ethods inv. larger series o f patients, w herein the augm entation of V t is th e only variable, is recom m ended. “T h e v o lu n tary deep breathing” m entioned in 3 can be com pared w ith “ the elicitation o f th e latent en­ couragem ent p o ten tial” o f F in er (1970)(2>. In a departm ent of physiotherapy one needs fo r the average daily hospital practice “efficient” m ethods for the im provem ent o f post-operative ventilation. A t the sam e tim e, the m ethods applied should be as simple as possible, require a m inim um o f routine instrum entation and a m inim um o f p atien t conveyance. In h alatio n o f C 0 2 requires C 0 2 supply, oxygen supply, a gas flow m easuring device and a well-fitting gas ad­ m inistration set. I.P.P.B. requires a ra th e r expensive and com plicated equipm ent fo r artificially assisted respiration. O ne w onders w hether Jones (1968)*3> has paid sufficient atten tio n to the clinical possibilities o f rebreathing m ethods fo r the im provem ent o f post-operative pul­ m o n ary ventilation. In experim ental physiology th e principle of a simple procedure, by which at the sam e tim e p u lm onary ventila- R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) DESEMBER 1973 F I S I O T E R A P I E 3 co u ld be increased an d a n orm al P a C 0 2 could t l 0 I1m a i n t a i n e d , has been described by G ad (1880). H e be m te(j a large tube w ith a d iam eter o f 0,4 cm and con"lume o f ab o u t 108 ml to the trach ea o f a ra b b it thus 3 vnking by this m anoeuvre an increase o f respiratory Pr? me and resp irato ry rate. L iljestrand (1918) nlied tubes w ith a d iam eter of 1,8 cm and a volum e of ^740-1950 ml to hum an beings. H e discovered th a t the CO content o f the in spiratory a ir w ould increase to the same degree, as the am o u n t of C 0 2 p resent in the hvsiological dead space from th e previous expiration. 13 S c o t t and C utler (1928) describe th e addition of dead space in order to p roduce hyperventilation fo r th e prevention of atelectasis. T hey give evidence th a t there is a direct relationship between th e size o f P a C 0 2 and the V t i.e. the P a C O s an d VT -curves closely parallel each other. T he greatest increm ent in “stim ulated T idal Volume” occurred during th e first tw o m inutes: in this time the V t increased fro m a co n tro l value o f 596 to 1178 ml. D uring the th ird m inute there was an o th er significant increase from 1178 to 1334 ml. F ro m the 3rd to the 10th m inute there was little change. Sim i­ larly the greatest rise in P a C 0 2 fro m a control value of 39,44 to 44,17 m m o f H g occurred during th e first two minutes. A second increase fro m 44,17 to 47,20 mm Hg was noted between the 2nd an d th e 5th m inutes. A concomitant decrease o f P a 02 w as also dem onstrated during the first tw o m inutes o f hyperventilation (100,5 mm Hg control value, sharply decreasing to 77,61 mm Hg); over the follow ing 8 m in P a 02 rose steadily and gradually to 88,93 m m Hg. A lthough the low ered P A 0 2 was generally w ell to lerated by the patients, this eventual P a 02 decrease could be prevented by directing a flow of oxygen into th e distal end o f th e dead space tube. A dead space o f 1 000 m l gave a m ore th a n 100% in ­ crease o f V t in 14 patients during th e first three post- jerative days w ithout any significant alteratio n o f R piratory rate. The sam e study w as repeated, b u t this tim e a flow of 3 4 litres of oxygen p e r m inute was introduced in to the distal end o f the rebreathing tube. In the three patients involved th e P a O z was m aintained above the control value o f 100,5 m m Hg. T h e average increases in VT and P A C 0 2 w ere sim ilar to th e changes noted in 15 patients breathing room air. T his clearly indicates that while subjects reb reath e thro u g h the 1 000 ml dead space tube, the elevation of P a C 0 2 is the critical factor th a t effects th e increase o f V T Schw artz-D ale-Rahn (1957)(‘> evaluated th e ir clinical experience in over 1 000 p atien ts w ith a dead space rebreathing tube as a post-operative routine. T h e tube was used fo r a period o f five m inutes a t tw o hourly intervals. Its use caused an a p p a re n t decrease in the incidence of post-operative atelectasis and was thus established as an effective th erap y in th e treatm en t of atelectasis. N o difficulties due to hypoxia w ere observed, although the occasional p atien t h ad to receive additional oxygen through the distal end o f the tube. Giebel (1968)(s> investigated five groups totalling 52 patients in ranges o f norm al, subnorm al an d abnorm al ven tilatio n /p erfu sio n -ratio s. Tw elve of the patients re ­ viewed w ere im m ediate post-operative cases. A com ­ plete radiological docum entation o f six o f th e patients, w ith severe form s o f atelectasis and p u lm o n ary col­ lapse, was presented both before an d a fte r th e treatm en t by m eans of artificial dead-space-increased ventilation. F rom his investigations th e follow ing conclusions emerge: . 1. T h e addition o f artificial dead space induces an increase of R .M .V . in all patients. T h e increase o f R .M .V . is pro p o rtio n al to th e volum e o f dead space added. A s long as alveolar ventilation does n ot decrease, resp irato ry ra te does n o t increase sig­ nificantly. H ow ever, as soon as resp irato ry ra te in adults increases to m ore th an 20-24 p e r m inute, dead space ventilation increases and alveolar v en ­ tilation decreases, leading to consequent hyper- capnia. 2. In all groups of patients th ere is a decrease of A a D 0 2 (alveoloarterial oxygen difference) during respiration w ith artificial increase of dead space. T his m ay only be explained as an overall im prove­ m en t an d norm alisation of th e pre-existing v en tila­ tion/perfusion disturbances. T h e increase o f V t in­ duced by the addition o f dead space th erefo re n o t only im proves the p u lm onary ventilation, bu t also th e to ta l pulm onary perfusion. 3. T h e decrease o f A a D 0 2 parallels closely the in ­ crease in P a 0 2. 4. T h e P a C 0 2 rem ains within no rm al lim its during th e efficient addition of volum e to th e artificial dead space. T h e increase in p u lm o n ary ventilation as a result o f the increased P C 0 2 in the inspired air is autoregulated in such a way th a t th e P a C 0 2 rem ains w ithin n o rm al limits. 5. D uring respiration w ith artificial increase o f dead space th ere is n eith er increase o f th e blood pressure n o r o f the pulse rate. 6 . T h e best criterion f o r testing w hether th e volum e added to th e dead space is correct is th e behaviour o f th e resp irato ry rate. In ad u lt patients the resp irato ry ra te should n o t surpass 20-24 p e r m inute. 7. If correctly applied, the m ethod o f artificial in ­ crease o f dead space provided an efficient treatm ent o f subacute an d chronic atelectasis. E delist and O rkin (1967)(1“> produced, w ith dead space increase o f 750 ml an d an oxygen flow of 300 m l p e r m inute in to th e rebreathing tube, an increase of the inspiratory P C 0 2, which was sufficient to increase p u l­ m onary ventilation at least 2 | times. T h e au th o rs’ as­ sum ption was, th a t by th e significantly increased p u l­ m onary ventilation areas o f m iliary atelectasis w ould be opened and thus venous adm ixture w ould decrease. T hey could, how ever, n o t su p p o rt these assum ptions with th eir results. In only tw o o f the eight patients was the post rebreathing Pa 0 2 elevated in com parison w ith pre-rebreathing P a 02. In th e rem ainder, th ere was no change, o r an actual decrease of P a 0 2. T his seems illogical, but it m ust be rem em bered th a t their patients were n o t suffering from any know n cardio­ p u lm onary disease. V enous adm ixture, w ith th e ex­ clusion o f actual anatom ical shunts from the right to the left h eart, m ay be caused by tw o pulm o n ary m echanism s: 1. A telectasis: In this case th e atelectatic areas o f the lungs a re perfused, b u t n o t ventilated. 2. M aldistribution: D ifferent areas o f th e lungs have different ventilation/perfusion ratios. It is clear th a t no n e of these conditions are present in patients not suffering from cardio-pulm onary disease. T his m eans th a t, as ventilation/perfusion ratios are R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) 4 P H Y S I O T H E R A P Y DECEMBER, 1973 norm al, increases o f p u lm o n a ry ventilation do n o t im ply changes o f P a 0 2, a t least if th e 0 2 co n cen tratio n o f the inspired gas m ixture rem ains unchanged. E delist and O rkin (1967(1"> should first hav e selected p atien ts in tw o g roups: a gro u p w ith a n d a group w ith o u t pulm onary ventilation/perfusion disturbances. T h ey should then have tested th eir assum ption on th e first group in o rd er to m ake sure th a t th e P a 0 2 w ould h av e increased, p ro ­ p o rtio n ately to th e decrease of venous adm ixture, by th e im provem ent o f ven tilatio n in eith er th e atelectatic areas o r in th e areas o f m aldistribution. H a ld and Johanson (1970)*11) exposed 23 p atien ts to in h alatio n o f 2% C 0 2 in ro o m a ir fo r 20 m inutes afte r the com pletion o f surgery. D u rin g this ad m in istratio n period an increase in P a 0 2 a n d p u lm o n ary ventilation was observed, w hereas th e P a C 0 2 rem ained constant. T h e increasing P a 0 2 contrasts w ith th e d a ta of E delist a n d O rkin, b u t once again I sho u ld like to refer to ' th e im p o rtan ce o f p a tie n t selection. In p o st­ an aesthetic p atien ts especially th e re is a know n high ra tio o f m icro-atelectatic changes a n d consequent arteriovenous p u lm o n ary shunting. T h is co rrelates well w ith th e fav o u rab le effect of p u lm o n ary hyperventilation on th e P a 0 2 in these cases. Summary F ro m th e literatu re review ed, as regards the value of m ethods used fo r im provem ent o f p u lm o n ary ventilation, several concepts have em erged. 1. P ost-operative v en tilato ry disturbances a re prevalent especially in thoracic an d ab d o m in al (b o th h igher a n d low er) surgery. 2. In patients w ith o u t pre-existing cardio-pulm onary disease these v entilatory disturbances a re never o f the obstructive type, b u t alw ays o f the restrictive type. 3. C lassical p h y sio th erap y procedures are o f great value fo r th e prev en tio n an d treatm en t o f p u l­ m o n ary com plications in the p a tie n t suffering from o bstructive lung disease. H ow ever, th e value of these procedures as regards restrictive ventilatory disturbances is questionable. 4. I t is o f prim e im portance th a t post-operative ven­ tilato ry disturbances b e treated in o rd e r to prevent incipient atelectasis, b ro n ch o p n eu m o n ia an d massive lung-collapse. 5. A m ong the m eth o d s described fo r th e treatm en t of p ost-operative v en tilato ry disturbances a n d th eir com plications, different grades o f com plexity an d efficiency m ay b e distinguished. 6. I t is generally acceptable th a t the best m eth o d o f treatm en t should be an id eal co m b in atio n o f efficiency an d sim plicity cap ab le o f covering the w idest possible clinical field. I t seem s th a t th e d ata derived fro m the literatu re review ed indicates th a t th e m eth o d o f choice is th e artificial increase o f dead space; subject to certain conditions. T hese condi­ tions are: (a) T h e m eth o d should be applied fo r a m axim um tim e o f five m inutes. (b) I t should be repeated tw o hourly. (c) T h e a d d itio n al d ead space volum e should be guided b y th e resp irato ry rate. A resp irato ry ra te of 20-24 p e r m inute should n o t b e exceeded in the case of adults. F o r a s ta rt an o p tio n al d ead space increase o f 500-1 000 m l fo r ad u lts an d o f 250-500 m l f o r children should be selected. 7. P ain is a n im p o rta n t c o n trib u to ry fa c to r to p o st­ o p erativ e ven tilato ry im p airm en t. I t results directly in d iaphragm atic inhibition. Sufficient atten tio n an d skill sho u ld b e spent in providing ad eq u ate p o st­ o perative analgesia, th e degree o f success o f w hich should b e evident fro m a fav o u rab le relationship betw een the degree o f analgesia an d th e am o u n t of resp irato ry depression. 8 . T h e sim ultaneous com bination o f a n artificial in­ crease o f d ead space an d ad eq u ate analgesia merits fu rth e r study. A com parison should th erefore be m ad e betw een th e effects o f reb reath in g methods u n d er painless, p re-operative conditions an d the effects o f reb reath in g m ethods u n d e r painful, post­ operative conditions. T h e re a fte r analgesia should be adm inistered a n d p u lm o n ary ventilation w ith re­ b reath in g m ethods retested. 9. T his study could b e com pleted b y aiding rebreath­ ing w ith an increase o f artificial dead space and ad eq u ate analgesia-therapy w ith th e psycho-therapy o f encouragem ent (F iner: “ th e elicitation o f the laten t encouragem ent p o te n tia l!”). V o lu n tary deep, painless b reath in g supported by the stim ulation o f th e resp irato ry centre by a n artificially increased dead space w ould th en b e th e sum total of therapeutic achievem ent tow ards the difficult task of overcom ing p ost-operative p u lm o n ary ventilation dis­ turbances. T his achievem ent w ould thus have been ob tain ed w ith a m inim um o f costs an d w ithout 1T need fo r sophisticated equipm ent. K*" Conclusion T h e artificial increase o f d ead space is a m o st promis­ ing, b u t an as y et incom pletely evaluated m ethod for the im provem ent of p ost-operative pulm o n ary ventila­ tion. T h e m ajo rity o f the available experim ental studies re p o rt fav o u rab le results. Som e o f the conflicting points regarding this method could possibly be b e tte r u n d ersto o d an d im proved sig­ nificantly if m ore a tten tio n co u ld be paid simultaneously b o th to th e relief o f post-operative som atic pain and to the p erso n al encouragem ent o f th e patient. References 1 N ichols, J. R . and H ow ell, B. (1970) “R outine pre- and p ost-operative p h ysiotherapy” . R heum atol, and Phys. M ed. X , 7, 321. 2 F iner B . (1970) “ Studies o f the variability in ex­ p ira to ry efforts b efo re an d a fte r cholecystectomy”. A cta A naestesiologica Scandinavica Suppl. 38. 3 Jones, F. L . (1968) “ Increasing post-operative ventila­ tion: a com parison o f five m ethods” . Anaesthesiology 29, 1212. 1 A d ler, R . A . (1967) “A re b re a th e r fo r prophylaxis an d treatm en t o f p ost-operative resp irato ry compli­ cations” . D is. C hest 52, 670. 5 S cott, W . J. M . and C utler, E. C. (1928) “Post-opera­ tive m assive atelectasis: T h e effect o f hyperventilate j w ith carb o n dioxide” . J.A .M .A . 90, 1759. 0 D uom acio, J. an d D ia z-R o m ero , C. (1937) “La pro­ lo n g a tio n de espacio m u e rto resp irato rio com o medio p ractico de h y p erv en tilatio n p u lm o n ar.” Arch. Urug. m ed. 10, 599. 7 Schw artz, S. I. an d D ale, W . A . (1955) “Addition o f dead space to produce h yperventilation for pro­ phylaxis of atelectasis” . Surgical F o ru m 6 , 282. 8 Schw artz, S. /., D ale, W. A . and R a h n , H. (1957) “ D ead space re-b reath in g tu b e fo r prevention of atelectasis” . J.A .M .A . 163, 1248. 9 G iebel, O. (1968) “ U b e r das V erh alten von Ventila­ tion, G asaustausch u n d K reislau f by Patienten mit n o rm alen und gestorten G asaustausch unter kiinst- licher T o trau m -V erg ro sseru n g ” . Anaesthesilogie u n d W iederbelebung N o . 41. 10 E delist, G. an d O rkin, L . R . (1967) “Evaluation of a reb reath in g tu b e f o r preventing atelectasis”. Aneste- hesiology 28, 21 1 . 11 H ald, T. and Johansen, S. H . (1970) “C arbon dioxide ad m in istratio n fo r correction o f post-operative hy- poxaem ia” . A cta A naesth. Scandin. 14, 53. R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. )