119

Correspondence

REFERENCES 1. De Angelis J: Clinical studies involving neostigmine reversal of d-tuhocurarine, gallamine, and pancuronium in man. Anesth & Analg 53: 268-270, 1974 2 . Miller RD, Larson CP Jr, Way WL: Comparative antagonism of d-tubocurariqe, Ballmine, and pancuronium-induced neuromuscular blockade by neostigmine. Anesthesiology 37: 503-509, 1973

3. Epstein RA, Epstein RM: EMG and the mechanical response of directly stimulated muscle in anesthetized man foilowing curarization. Anesthesiology 38: 212-223, 1973

4. Gissen AJ: Standardized technique for transmission studies. Anesthesiology 39: 567560, 1973

*

*

*

To the Editor: Thank you for the opportunity to respond to Dr. Miller's most appropriate letter. I wish to extend my apologies to Dr. Miller in that 1 certainly did misinterpret his article. He did indeed use both higher and lower doses of neuromuscular blocking agents than I used in my studies. Dr. Miller also reversed all patients at 5 per cent recovery. I chose a Block-AidR monitor rather than a Grass stimulator for the same reason that I used mg./kg. rather than mg./sq.m. for drug-dosage determination, in an attempt to utilize methods employed by the anesthesiologist in his daily practice. I have never seen a Grass stimulator used during anesthesia except during a research project. Also, I ' m not aware that anesthesiologists, in general, use mg./sq.m. to determine dosage of neuromuscular blocking agents, even though mg./sq.m. is probably a more accurate method of drug-dose determination. It is my personal belief that the anesthesiologist in clinical practice can relate more to information presented in a manner similar to that which he uses daily. There are obvious pitfalls in my type of reasoning. Dr. Miller could have easily pointed out these pitfalls in his very kind letter, but he did not choose to do so. John De Angelis, M.D. Anesthesiology-South Surgery Hollywood Presbyterian Hospital Los Angeles, California

*

*

*

To the Editor:

I was extremely disappointed when I read the guest discussion by Doctor Morley M. Singer, following the paper by Downs, Block and Vennum, "Intermittent Mandatory Ventilation in the Treatment of Patients with Chronic Obstructive Pulmonary Disease" 53:437-443, 1974. At first I thought it would not be appropriate for me to write to you regarding Dr. Singer's comments, particularly since I have co-authored some of Dr. Downs' work on IMV and therefore, my comments might be construed

120

ASESTH~.SIA ASD ASALCESIA . . . C u r r e n t Researches Vor.. 54. No. 1, ~ A N . - F E 1975 R.,

as having a "sour grapes attitude" or having a vested interest in the technique. After several weeks and several rereadings, however, I think it is important that Dr. Singer's comments be answered for fear your readers will get a warped view of what, at least in the hands of many, has proven to be a valuable adjunct to our respiratory care armamentarium.

As I read Dr. Singer's discussion, I questioned, in his opening paragraph, whether his philosophy was one of reluctance to change and he was more concerned with terminology than with the response of the patient. He states, "I personally deplore the use of the term weaning in reference to mechanical ventilation." While based on his personal prejudices, he may deplore the word "weaning" in reference to mechanical ventilation, it should be apparent that if our patients are to return productively to society, mechanical ventilation needs to be discontinued and the patient needs to be capable of breathing spontaneously. I believe it is accepted terminology to use the term "weaning" to describe this conversion. Dr. Downs and his co-authors did not demonstrate "impatience" with mechanical ventilation nor did they state that mechanical ventilation is inherently noxious, as Dr. Singer suggests. They described three patients with Chronic Obstructive Lung Disease who were treated briefly with a new form of mechanical ventilatory support and were able to spontaneously maintain their own respiratory function soon afterward. Dr. Singer states that "Patients can spend weeks, months, or even years on ventilators without demonstrable adverse effects." I sincerely doubt that Dr. Singer is advocating prolonged ventilatory support far beyond what is necessary for a particular patient. Over the years it has become apparent to most people who are involved in ventilatory care, that in spite of our best efforts by specially trained physicians, nurses and paramedical personnel, accidents do happen to patients on ventilators and complications are all too frequent. Just from a chance standpoint, it would appear that the incidence of complications and/or mechanical accidents would increase with time. If one is willing to accept this clinical impression as being valid, it then seems reasonable to discontinue mechanical ventilation as soon as the patient is able to adequately supply his own ventilation. Unfortunately, there are no precise guidelines applicable to every patient as to when this conversion can take place easily. Furthermore, we all have had experience with some patients in whom we are able to disconnect their ventilator and have them immediately take over and breathe adequately. More commonly, a "weaning period" with intermittent trials of spontaneous ventilation between some type of mechanical support, be it brief periods of controlled or assisted ventilation, is needed. Discoordinated breathing patierns have been described2 9 3 and it is apparent from spirograms presented by

Correspondence

121

Doctor Downs a t t h e New York P o s t g r a d u a t e Assembly Meeting l a s t December4, t h a t t h e d i s c o o r d i n a t e d b r e a t h i n g e f f o r t f r e q u e n t l y seen w h i l e weaning p a t i e n t s from c o n t r o l l e d mechanical v e n t i l a t i o n i s n o t as e v i d e n t when t h e IMV t e c h n i q u e i s employed. Doctor S i n g e r a l s o comments on t h e s t a t e m e n t t h a t M I V may have l e s s e f f e c t on venous r e t u r n and c a r d i a c o u t p u t t h a n CMV. H e c o r r e c t l y p o i n t s o u t t h a t i f one i s aware t h a t an adequate i n t r a v a s c u l a r volume i s n e c e s s a r y t o overcome t h e e f f e c t s o f i n c r e a s e d p r e s s u r e w i t h i n t h e c h e s t , t h e d e c r e a s e i n c a r d i a c o u t p u t can b e avoided. Nowhere i n t h i s c a s e r e p o r t i s t h e r e a s t a t e m e n t t o t h e c o n t r a r y .

Dr. S i n g e r r e p o r t s t h a t t h e u s e of IMV t o d e c r e a s e t h e frequency o f hypocarbia i s p u r e l y s p e c u l a t i v e . A t l e a s t two s t u d i e s have been r e p o r t e d 4 , 5 i n which t h e carbon d i o x i d e t e n s i o n w a s s i g n i f i c a n t l y lower d u r i n g CW t h a n d u r i n g IMV. My c o l l eagues and I have had t h e o p p o r t u n i t y t o u s e t h e t e c h n i q u e of IMV i n over 1000 p a t i e n t s i n t h r e e s e p a r a t e medical i n s t i t u t i o n s and our c l i n i c a l impression i s t h a t Dr. Downs' s t a t e m e n t i s correct. Regarding D r . S i n g e r ' s c r i t i c i s m o f t h e i m p l i c a t i o n t h a t m a i n t a i n i n g a normal PaC02 v e r s u s hypocarbia, would p r o v i d e f o r more e f f i c i e n t oxygenation; t h i s h a s been a d e b a t a b l e t o p i c among c l i n i c i a n s f o r some t i m e . However, i f one r e a d s t h e a p p l i c a b l e r e f e r e n c e s c i t e d by Dr. Downs, t h e j u s t i f i c a t i o n f o r t h i s s t a t e m e n t i s a p p a r e n t . How important t h i s i s i n t h e o v e r a l l outcome of t h e p a t i e n t remains t o b e determined. On t h e middle of page 442, D r . S i n g e r c r i t i c i z e s t h e advantages proposed f o r "CMV." I assume t h i s i s a m i s p r i n t , and t h a t he means IMV. If my assumption i s c o r r e c t , t h e f o l l o w i n g a l s o would b e p e r t i n e n t . H e states t h a t c o n t r o l l e d oxygen m i x t u r e s are a requirement of any system of mechanical v e n t i l a t i o n r a t h e r t h a n an advantage. I a g r e e completely. Unfort u n a t e l y , i n many h o s p i t a l s s u f f i c i e n t p r e c i s e oxygen r e g u l a t o r s a r e n o t a v a i l a b l e f o r u s e w i t h b o t h t h e mechanical v e n t i l a t i n g equipment and weaning equipment. Therefore, t h e r e i s a r e l i a n c e on v e n t u r i a p p a r a t u s or some o t h e r r e l a t i v e l y crude d e v i c e t h a t depends upon a i r flows and d i l u t i o n a l e f f e c t s f o r c o n t r o l l i n g Using t h e IMV p r i n c i p l e , a s i n g l e oxygen b l e n d e r o r regu l a t o r i s used b o t h f o r t h e mechanical v e n t i l a t i o n p o r t i o n of t h e c i r c u i t and t h e spontaneously b r e a t h i n g p o r t i o n of t h e c i r c u i t ; t h u s , g i v i n g more i n s u r a n c e t h a t c o n t r o l l e d oxygen m i x t u r e s are maintained. We have found t h e p a t i e n t ' s a b i l i t y t o c o n t r o l h i s own carbon d i o x i d e t e n s i o n t o be a d e f i n i t e advantage of IMV i n o u r e x p e r i e n c e w i t h over 1000 p a t i e n t s . Dr. S i n g e r c o r r e c t l y p o i n t s o u t t h a t r e g a r d l e s s of t h e p a t t e r n o f v e n t i l a t i o n , t h e PaC02 a l s o depends upon t h e v e n t i l a t o r s e t t i n g s and m e t a b o l i c r a t e . H e mentions t h a t PaCO2 a l s o depends on t h e ?/Qabnormality.

While t h i s m i g h t - b e t r u e i n a v e r y s e v e r e s t a t e , it i s my i m p r e s s i o n thaL $/Q a b n o r m a l i t y e x e r t s a profound e f f e c t on a r t e r i a l

oxygen t e n s i o n b u t a r e l a t i v e l y minor e f f e c t on a r t e r i a l carbon d i o x i d e t e n s i o n i n c o x p a r i s o n . He goes on t o mention t h a t cont r o l l e d v e n t i l a t i o n b c a s s e s a D a t i e n t ' s r e s p i r a t o r y d r i v e and t h e r e f o r e p e m i t s t h e physician t o a d j u s t v e n t i l a t i o n t o a given PaCO2. T h i s a l s o i s t r u e , however, how does a p h y s i c i a n know e x a c t l y what PaC02 i s " p h y s i o l o g i c " f o r t h a t p a r t i c u l a r p a t i e n t ? We f r e q u e n t l y a r e f a c e d w i t h t r e a t i n g p a t i e n t s who d i d n o t have a r t e r i a l blood gas t e n s i o n s measured i r n e d i a t e l y p r i o r t o t h e i r a c u t e e p i s o d e which n e c e s s i t a t e d v e n t i l a t o r y i n t e r v e n t i o n . T h e r e f o r e , we are a t t e m p t i n g t o impose what we f e e l i s normal f o r t h e p a t i e n t . Does e v e r y p a t i e n t who e n t e r s t h e I n t e n s i v e Care Unit w i t h a l u n g c o n t u s i o n have e x a c t l y t h e same carbon d i o x i d e t e n s i o n and r e s p i r a t o r y d r i v e immediately p r i o r t o h i s automobile a c c i d e n t ? I doubt t h i s s e r i o u s l y . C e r t a i n l y , i n t h e t y p e of p a t i e n t s r e p o r t e d in D r . Downs' a r t i c l e , t h o s e w i t h Chronic O b s t r u c t i v e Pulmonary D i s e a s e , v e r y few p h y s i c i a n s would want t o v e n t u r e a g u e s s as t o "what i s normal f o r t h a t p a r t i c u l a r p a t i e n t " t h e day b e f o r e h i s a c u t e decompensation. One p o s s i b l e way t o a r r i v e a t a rough e s t i m a t e would b e t o back c a l c u l a t e from h i s b i c a r b o n a t e l e v e l and pH and assume t h a t h e was a d e q u a t e l y compensated immediately b e f o r e t h i s a c u t e e p i s o d e . However, i f t h e p a t i e n t s u f f e r e d s i g n i f i c a n t t i s s u e hypoxia, it i s p o s s i b l e t h a t a m e t a b o l i c a c i d o s i s could b e superimposed t h e r e b y d e c r e a s i n g t h e b i c a r b o n a t e l e v e l from t h e p a t i e n t ' s " n o r n a l . ' : Furthermore, over t h e y e a r s , t o my dismay, I have had t h e o p p o r t u n i t y t o t r e a t p a t i e n t s who have "fought t h e v e n t i l a t o r . " These p a t i e n t s had t o b e s e d a t e d w i t h i n t r a v e n o u s n a r c o t i c s , o r i n a few c a s e s , w e have had t o r e s o r t t o muscle r e l a x a n t s i n o r d e r t o a d j u s t t h e p a t i e n t ' s PaCO2 t o what w e f e l t was normal. The u s e of I".N h a s markedly d e c r e a s e d t h e frequency w i t h which we have t o r e s o r t t c such measures. D r . S i n g e r p o i n t s out t h a t i f t h e p a t i e n t i s u n a b l e t o perform h i s s h a r e of t h e minute v e n t i l a t i o n w i t h 1P.W he w i l l develop h y p e r c a r b i a . There i s no q u e s t i o n t h a t t h i s i s t r u e , b u t a l l t h a t needs t o b e done i s t o i n c r e a s e t h e frequency of mechanical v e n t i l a t i o n . How i s t h i s d i f f e r e n t from t h e p a t i e n t on c o n t r o l l e d v e n t i l a t i o n who develops h y p e r c a r b i a and must have h i s r a t e o r

volume i n c r e a s e d ? D r . S i n g e r c r i t i c i z e s t h e s t a t e m e n t t h a t mechanical v e n t i l a t i o n t i m e i s d e c r e a s e d w i t h IMV. Other s t u d i e s have been co ducted i n randomly s e l e c t e d p a t i e n t s t h a t document Dr. S i n g e r a l s o s t a t e s , "one would a n t i c i p a t e t h i s finding'95. t h a t when t r e a t i n g l a r g e groups of p a t i e n t s w i t h IMV, e l e v a t i o n s of PaCO2 would m a n i f e s t as a consequence of d e c r e a s e d v e n t i l a t o r y f u n c t i o n from i n c r e a s e d pulmonary s e c r e t i o n s , a t e l e c t a s i s , deThe p r e v i o u s l y mentioned s t u d i e s 4 35 creased cardiac output, e t c have shown no d e c r e a s e i n FRC o r i n c r e a s e d shunt when compared t o CbW. I do not know what D r . S i n g e r would c o n s i d e r a l a r g e group of p a t i e n t s , however, we now u s e IMV r o u t i n e l y i n p a t i e n t s

."

Correspondence

123

requiring mechanical ventilatory support. In some of them, we do have to increase the rate of mechanical ventilation so that their respiration is controlled, in others M I V has been used throughout. To our knowledge these patients have not deteriorated as a result of this type of management. We would hope that this series would be sufficiently large to answer his question.

I am sure that Dr. Downs did not imply that IMV obviates the need for continuous clinical and laboratory monitoring of the patient with respiratory failure, nor does it replace the physician or nurse at the bedside. It does, however, provide for a smoother transition between the period of time that the patient requires extensive mechanical ventilatory support and the time when he can breathe spontaneously. Since it is not necessary to remove the patient from the ventilator for brief trials of spontaneous ventilation during weaning, some of the hazards such as discoordinated ventilation, increased work of breathing, acute hypoxia and PaCO2 retention, etc., that might occur during ineffective spontaneous ventilation, might be averted. It also is not necessary for someone to remain at the patient's bedside continuously during these weaning attempts to treat these possible complications. I, too, would be concerned about the possibility of overdistension and/or rupture of the lung resulting from a volume-cycled ventilator, cycling coincident with the end inspiratory effort of a patient's spontaneous respiration as is Dr. Singer. However, in our series of patients we have not recognized this to be a problerr,. Furthermore, our patients adapt readily to IMV and seem to anticipate the next breath of the ventilator so that over ventilation and over distension is rarely seen. If one were truely concerned, a popoff valve can be inserted into the system. Finally, Dr. Singer correctly points out that in patients with discoordinated breathing efforts, due to ineffective I V can be advantageous. Indeed respiratory muscle activity, M this advantage is pointed out in reference 3 of Dr. Downs' paper which is the original paper describing the technique in detail. I do not believe it was the purpose of this case report to be an all inclusive review article. I personally feel the authors are to be commended for having referenced their brief discussion as diligently as they did. It is unfortunate that Dr. Singer did not see fit to reference any of his criticism Could it be that he is reporting his own personal prejudices and bias against something new. If indeed he has used this technique extensively and can support his criticism based on sound scientific data, either from his own experience or from reports in the literature by others, this would have greatly strengthened his discussion. As it stands, however, it appears to me to be one man's opinion who has little or no experience with the technique and might be resistant to possible change. I would not want your readers to get the impression that I

ANESTHESIA AND ANALGESIA . . . Current Researches VOL.54, No. 1, JAN.-FEB., 1975

I24

consider IMV to be a panacea and that it should replace all other types of ventilation. It is but one method available in our armamentarium for treating patients with ventilatory insufficiency. Each patient must be evaluated individually and the proper method of ventilation to provide the optimum response should be employed. We have found IMV to be very helpful in this regard. Perhaps some of your readers might have a similar experience. Thank you for the opportunity to respond to Dr. Singer's discussion. Jerome H. Modell, M.D. Department of Anesthesiology University of Florida College of Medicine Gainesville, Florida REFERENCES 1. Browne AGR, Pontoppidan H, Chiang H, et al: Physiological criteria for weaning patients from prolonged artificial ventilation. ASA Abstracts of Scientific Papers, pp 1972

69-70,

2. Chiang H, Pontoppidan H, Wilson RS, et al: Respiratory muscle discoordination folloving prolonged mechanical ventilation. ASA Abstracts of Scientific Papers, pp 211-212, 1973

3. Downs JF3, Klein EF J r , Desautels D, et al: Intermittent mandatory ventilation: approach to weaning patients from mechanical ventilators. Chest 64: 331-335, 1973

a new

4. Downs JB: Intermittent mandatory ventilation: A prospective evaluation. Presented at the Postgraduate Assembly of the New York State Society of Anesthesiologists, New York City, December LO, 1973 (Arch Surg. In Press) 5. bypass.

Downs JB, Mitchell LA: Intermittent mandatory ventilation following cardiopulmonary C r i t Care Med 2:39, 1974 (Abstract)

*

*

*

To the Editor: The length, if not the content, of D r . Modell's letter is impressive and is a strong testimonial to his personal belief, which I am sure is sincere, in the benefits of IMV. Presumably it is the strength of these personal convictions which prompt his repeated suggestions that 'personal prejudices', 'philosophy of reluctance to change' and 'little or no experience' contribute to my critique of INV. I am reluctant to descend to this form of debate. I will concede, however, that over a ten year period in the Intensive Care Unit, my observations from personal attendance in the day to day, hour to hour bedside management of over 2,000 patients in respiratory failure, coupled with objective measurements of ventilatory function, has generated sone personal opinions and prejudices.

...

I cannot resist commenting on one of Dr. Modell's more surprising and inaccurate statements - that it is his "impression" that $/6, abnormality exerts a relatively minor effect on PaC02. I can only suggest that he read the work of West, consult any basic

Letter: "Intermittent mandatory ventilation in the treatment of patients with chronic obstructive pulmonary disease.".

119 Correspondence REFERENCES 1. De Angelis J: Clinical studies involving neostigmine reversal of d-tuhocurarine, gallamine, and pancuronium in man...
441KB Sizes 0 Downloads 0 Views