4 Jwnai

Vol. 6 No. I January 1991

of Pain and SymptomManagement

Evaluation of Patient-Controlled Analgesia (PCA) versus PCA Plus Continuous Infusion in Postoperative Cancer Patients Lea Ann Hansen, PharmD, MargaretA. Noyes, PharmD, and Mark E. Lehman, PharmD

qf two dosing mcl.hLs, patient-co&-off& analgesia (PCA) uul/~ morphine $ alone and PCA plus continuous infusion of mo#ine su@e (PCA C Cl) &a@ eva&u& itadlrandomized, single-blinded study of 30 atlull abdomiual pie&. L&es we adjusted based on pain and sedation ratitJg.s. ~~~i~, pulse, blood pTcsst(re, pain and sedation ratings wcra assessed. Subject3 The rated their pain huice dai@using a visual analog scale for 72 hr postoperati&y No statistically, sign$tIcant su&jects reported pain re!ief with both dosing regk~. d#r~~ccs between the g~#ups wcrt found in pai?8 and s&rion ratings, or kugth of time using the &ice, wirh tlu, excepion a hi&r amount of MS used on postopvuti~ a@ two by the in$sion group (p C 0.003). t thk~ PCA + Ci grorc)r to harrc, ~?ES fluctuation in sedation Mseemstobea ntrol (as ~rno~~t~t~ by wvbal aud visual analog pain day. %t=&ka/ sigu$-ane~ wav not found, howevtv, us iNfksio?~ fM%may k a knry%ial tz/s@mtd~ lo the managemtnt n in s&&d @kv& studks to iden@ the.~ patients need to lip i991;Q:+&.

of

of

inc, narcotics, analgesics,

Individual variations in the perception of pain and response to narcotic analgesicsconstitute major okacles to the successful treatment of pin. Traditional intramuscularinjectionsof narcotic anal ic3 given “as needed” (pn) frequently fail to pxluce optimal pin relief.‘” ta:LeaAnn Hansen,PharmD, 3, Richmend.VA 23298. : June 25.1990. U.S.clnm F%in Rdicf Cammime. 1991 Ptddihd by Else&r. New York, New York

intruvenous

infmious

Time delay in administration, variation in narcotic needs, unpredictable intramuscular absorption, fluctuations in analgesic levels beyond the therapeutic range, and inadequate dose titration are often implicated in the many over and undermedicated patients seen in postoperative nursing wards.‘M-‘~ The result is excessive sedation or uncontrolled pain. Several dosing strategies and innovations have been employed to maximize patient comfort and overcome these barriers. Innovative dosing techniques such as patient-controlledanOE’R5-3924/91/53.50

Vol. 6 No. 1 Janwq

1991

PC.4 in Postopemlit~eCart

algesia (PCA) and continuous

morphine infusions (CI) have been used as alternatives to intermittent injections of narcotic analgesics .s~9~‘-” Both the PCA dosing method and continuous infusion provide a higher degree of patient comfort and minimize anxiety compared with intermittent intramuscular injections of narcotic agents.‘2,‘“,‘H-‘” PCA enables patients to titrate t,heir analgesic medication to maintain a balance between adequate pain relief and sedation. Potential advantages of the PCA dosing method include mini~l ~UctuationS in ailalgesic serum conccntrations, analgesia without excessive sedation, increased ambulation, and less ini~l)pr~~l~rii~t nursing Screening for itlXllgC?SicIllediW ion. There ttre several cIevic=es ~~~entl~ ilv~tilit~~lein the United States that operate cmthe basic principle of administ!&on of a designated doss t :! drug U~OII requcat, with it set lockout period,

5

ment using the combined approach cover PCA after hysterectomy, but not after cholecystectomy.“” Patients in the combined group all received 1 mg/hr infusion, regardless of weight, which started shortly after surgery. Data were collected for only 24 hr. Oxymorphone was used in a similar study design for patients after cesarean delivery.“’ During the 24 hr postoperatively. ~o~~tit~~~c~~~s infusion plus PCA was more effective than PCA alone, although nauSea WilS ill!40 I~MWe prevalent in tile former group. 0~~9 antI coiie~gu~ alSo studied the tW0 ttcfministritlir~n iiietli(~is for 24 hr afler ab* dominal surgery and found that they were ecl~illy ellcctivc, but 1he iV:A -t (11 group used more morphitir illlcl IliWlIt% llillISC3,2H In our Sittdy, ill) ii)f~lsi~~ild0Se hitSed 011 weight WI& USWI; @I1 iilK Se~i~~ii~~i~ raukitigs, ~1~~~0~11~~of i~~lilllgt!SiC IlWrl, ill14 oawlll I)illiC’llt impressictns Of tllC dosing I~Wlhods were ~AV~lllliitCXi for 72

and a 4-hr maximum infusion volume aS an additional safety feature. Continuous narcotic infusions are an etfectire means of providing analgesia. Protocols for the proper use of morphine infusions have been previously described?“~‘X’l’i-L’T, There is cc9nsiderable di~culty in predicting an initiai dose that may delay optimization of pain control, After the initial titration to the desired response, hourly monitoring of vital signs (especially respiration) is advocated to avoid potent~l adverse effects. Although it is a viable option for pain

hr. A tievice that allows continuous adciiti(~il to P(IA dosing writ used.

control, Cl may not he a practic;tl alternative in many patient care settings due to fear of adverse effects, in§u~icient personnel to inonit~~r the pittient, and it~stitutionill protocols restricting their

ized, single-blincied clinicxil trii1l of Iwo dosing methods. P(:A or P(:A 9 (3 using morphine as (he at~ttlgesicagent, Placebo was not used. All patients admitted to the Surgical Oncologv service were evaluated as potential study candidates by one of the investigators. Subjects were eligible br entry into the study if they confortned 10 the itl~iusi(~n criteria listed in Table I, Written informecl cr9rrSent was obtained, which included the possibility of receiving a continuous infusion of analgesic. These patients were also instructed preo~ratively in se!f-administration of parenteral ;,ralgesics with the PCA device, Subjects were reevalualed to ensure that they met eligibility criteria postope~dtively Ijeft9re actuat enrollnle~tt and rat~dotni~~ition into the p(IA or PCA + (11 group. s~it~i~~ts began PCA when they were alert lX9doperaLively and had been transferred to tire nursing unit. If the subject was admitted to the intensive care unit postol~ei~tively, the start of study was

use. The object of this investigation wa!; IO utempt to combine the advat~~~s of both str~ltegi~s: a continuous infusion to p~9vid~ a co~lsti~nt dose of pain medication in order to prevent Huctuations in analgesia (especially after a period of sleep when no analgesic is administered), plus the elf-tit~tion of pain medication using the PCA approach. This was compared to standard PCA therapy. We observed that llatients using PCA at this institution had fragmented sleep due to the short du~tion of small doses of analgesic. We hypothesized that a contit~uous dose of analgesic in addition to self-administration by the PCA method may result in smoothet pain control without excessive sedation. Vickers

and coIl~gues

have shown a small improve-

infusion

in

Thirty suljects who had ab(i(~i~litl~~lsurgery under general anesthesia. which utilized C lb pg/kg of fentanyl, participated in this study, which was approved by the Committee on Con-

duct of Hum;llt &!SC!it!XTll itt the ~lecIic~91 College of Virginia. The stucly design was a random-

Table I

IncIusion Criteria Admitted to Surgical Oncohqgy service for abdominal surgery

Age >18 NO other psychoactive, hypnotic, analgesic, or antiemetic agents No history of p~]chiitric or neurological disorder, alcohol or drug abuse No historyof morphine allergy NO active serious metabolic or hepatic d~fun~~n, ~lnut~~n, active signs of

sepsis, or hemodynamicinstabilily Able m understand and sign the consent form Able to operate the device Begin PCA within 48 hr ~to~~tively Received < 13 pglkg fentanyt as anesthesia

delayed until the patient had been transferred

to the nuking unit. The study design was such that both groups of subjects were eligible to begin PCA postoperatively on the day of surgery (provided the subject was not in the intensive care unit). The infusion was delayed until the day after surgery in the PCA + CI group to allow complete recovery from anesthesia and to avoid potential problems when staffing is low (night shift). All subjects were initially dosed at 0.015 mg/k~ body weight of morphine per injection, with an inactivation period (lockout) of 6 min imposed following each dose. A maximum 49hr limit of 0.3 mgkg For subjects under age 60 and 0.2 mg/kg For subjects over age 80 was ~nit~~Iyset. An optimal dose per injection was defined as that which produced acceptable analgesia without significant R. IF after two consecutive stint the d~t~~i~ that the sub&t had marked sedation or maximal pain rankings, the investigators were notified. IF a subject did not obtain adequate analgesia with the initial dose, the PCA dose was increased by 50%. Similarly, if a subject complained of drowsiness or sedation scores were indicative of excessive somnolence, the doseper injection was decreased by At 300 a,m. on the First ~to~rative day (P0D-I), an infusion of morphine sulfate was be@m in tht: PCA + CI group in a singleMinded manner (the subjects were unaware OF the settings on the PCA device). Visible indicators on the device prevented blinding of the obdelvers. A standard morphine dose of 0.015 mglkg;lhr was administered to each subject ini-

dally. This infusion dose was chosen based on previous studies that used I-1.5 mg/hr when combined with PCA26*28and those that used continuous infusions of 0.01-0.05 mg/kg/hr alone.5*‘s*‘8 Subjects were allowed to selfadminister additional morphine using the PCA mode while the infusion was being administered. The Stratofuse PCA device (Strata Medical Corporation, Beverly, MA) was used. Microbore tubing (Strato Medical Corporation, everly, MA) connected the device to the intravenous catheter. Morphine sulfate injection and syringes (1 mglmL, 50 mL total vofume) were prepared by the Department of Pharmacy Services. Morphine sulfate F&Jr injection 15 mgl mt (Elkins-Sinn, Cherry Hill, YJ) was diluted with Sterile Water for Injection (Travenol Laboratories, Deerfield, IL), and prepared in 50mL syringes (Becton-Dickenson, Rutherford, NJ). Syringes were changed and appropriate narcotic administ~tion records mainlined by the nursing and pharmacy stafr”saccording to standard institutional procedures for PCA administration. Respiration, sedation, and pain were evaluated hourly for the first 4 hr that a subject used the device, after each dosage change, and once every 4 hr thereafter. Hourly evaluations were again performed For the first 4 hr OFthe infusion. Blood pressure and heart rate were monitored every 8 hr while he subject received PCA. Sedation was evaluated by the nursing staff according to a five-point scale, presented in Table 2. Documentation of other side effects T&e 2 sedation Rating Scale

-

0 Nose:(wide awake) 1 MILD(subject lethargic, aroused by verbal stimuli, completely oriented when awakened) 2

MoDERA’rE (subject aroused only by physical stimuli, completely oriented when awakened)

3

MARKED(subject aroused only by physical stimuli, disoriented when awakened)

4

SEVERE (subject unarousable)

Vol. 6 No, I January 1991

PCP. in Postoperative Care

was performed by musing personnel as they recorded respirations and pain/sedation rankings. Pain rankings were assessed by two different methods, Nurses used a verbal five point scale to assess pain. Subjects were asked to describe their pain on a scale of zero to four, with zero being no pain and four being the worst pain imaginable. The study investigators assessed pain rankings twice daily using a visual analog scale, adapted from that of Price and colleagues. 2B The scale consisted of a 15O-mm line with the distance from the “no pain” endpoint recorded. To maintain consistency between investigator, a standardized phrase was used: “We are interested in measuring how intense your pain is. 0ne end of the line is no pain, the other is the most pain im~lginable. Please mark where your pain lies on the line.” Subjects were studied for 72 hr postoperatively for the purposes of collecting efficacy data, although the toxicity data reported reflect the total time that subjects were using the device. Subjects were allowed to continue using the PCA device until taking oral analgesics. No other centrally acting medications or analgesics were allowed while the study was in progress, with the exception of a designated antiemetic agent (intramuscular prochlorperazine, 10 mg) given every 3-4 hr as needed. Use of the antiemetic was documented to assess possible effect on sedation rankings. Any untoward effect possibly attributable to the analgesic therapy (for example, marked sedation or confusion) was documented and was designated as grounds for removal of the device and conversiot~ to intramu~ular injections at the discretion of the subject’s physician. Subjects were asked to complete a questionnaire ~ga~ing their experience upon compietion of the study. Inquiries were made regarding pain control, interruption of sleep due to pain, ease of use, comparison to previous surgeries, and their favorite and least favorite aspects of the device. Nursing personnel were also questioned about their experience with the device and the dosing methods (safety mechanisms, ease of use, observed patient satisfaction).

SWticd

Methods

Demographic characteristics of subjects in the two groups were compared using Student’s t test. Objective data concerning morphine use

7

and millimeter change between ~stope~t~~?e days in visual analog scales were evaluated using a one-way analysis of variance. Mean subjective pain and sedation rankings and change in pain and sedation rankings between postoperative days were evaluated using the Wilcoxon ranksum test. Questionnaire responses regarding the ability to sleep were also analyzed using the Wilcoxon rank-sum test. Results were considered statistically significant at p < 0.05.

Results The 30 subjects f 15 men and 15 women} who met the inclusion criteria postoperatively and were randomized to the study are included in the analysis. All had major a~ominal operations, which are listed in Table 3. Ten patients (5 PCA and 5 PCA + Cl) entered the study at a time > I2 hr after coinpletion of surgery, because they required intensive care unit monitoring. The study was conducted over an 8-mo period. As noted in TabIe 3, the groups were evenly matched in regard to demographic data. There was no statistically significant difference between the groups for age, sex, weight and past surgical history. Only one patient was taking chronic opiates prior to surgery. Total length of time using the device and total milligrams of morphine used were variable, but not apparently different bc?%leen the two groups. The number of PCA attempts was not recorded. Six subjects required a change from the initial analgesic dose, three from each group. Two of the subjects in the PCA group required an increase both in dose and limit (one required two changes in dose), while a third subject’s dose was decreased on postoperative day (POD) 3. Of the three subjects in the PCA + CI group who required dosage adjustment, one had the PCA dose increased, the second required two increases in dose, while the third subject twice required a decrease in dose with subsequent discontinuance of the infusion on POD-3 due to complaints of sedation. Two additional subjects, one from each group, required an increase in the 4-hr maximum dose limit. The mean amounts of morphine used (mg/ kg/day) are presented for each group in Figure 1. There was a statistically significant difference between the two groups in total amount of mot= phine used on the second posto~rative day (POD-Z) v, c O.O03), with more morphine used

Hansen et al.

8

Journal of Pain and SymptomManagement

Table 3

Demographic Characteristics FCA

Range

Mean

25-72 5495.7

52.93 74.15

Hr used Mg MS used Types of surgery(n) Exploratorylaparotomy

Colcctomy Gastrectomy Gastrujejunostomy and exp. lap.

PCA + Cl Group

Group

48-192 29-559.7

109.2 158.42 16 2 1

Mean

Range

53.47 65.66

25-73 47.2-80.5

P NS NS

54512 74.1-1609.8

129.47 294.01 5 2 1

2

Hepatic lobectomy Retroperitonealresection Lowanterior resection Bilroth II reconstruction by the RCA + 61 group (mean 0.720 mglkg vs 0.415 mglkg for the PCA group). There was no statistically significant difference for any of the other values.

PatWMtmhhg Table 4 is a compilation of the mean visual analog scores, in millimeters, for each subject per postoperative day. Mean scores were reported since there was variability in the number of analog scales per subject per postoperative day depending on when RCA was begun and discontinued. Mean millimeter change in visual

Fig.I. Total morphine usage by pmtop etative day.

analog scores between postoperative days was calculated and is presented graphically in Figure 2. While there was considerable intersubject variability in visual analog scales, the mean millimeter change between postoperative days was never > I 1% in either group. The mean of the verbal pain scores was evaluated for each subject by postoperative day. The mean verbal pain scores for the two groups are presented in Table 5. Verbal pain scores tended to decrease with time since surgery, but varied between subjects. There was no apparent clinical difference in verbal pain scores noted between the two groups.

Ta6ie 4

Mean Visual Analog Scores (mm) Postoperative Day

GsW.lp (Pt. No.)

0

1

2

s

4

21.5 5.5 17.5 79.5 88

76 PtzA + c:1 9 4 5 9 II 15 17 18 19

97 0 32 51.5 54 27.5 25.5 1IOk5

21 86 25 29 29 85 !17 11 51

f; 24 25

54

27

17

28

Mean sedation rankings for each postoperative day were determined for each group and are graphically presented in Figure 3, The mean of both groups, which were not statistically different, were approximately one on a scale of zero to four for each postoperativeday. The change in mean sedation ratings between con~cutive ~sto~rative days was determjned for each subject. The mean change in sedation ratings between postoperative days for the two groups are graphically presented in Figure 4; no s~t~ti~lIy s~gni~~nt difference was found. Statistical comparison was made of the data collected on PQD=2,presented in Table 6. This day was chosen because not all patients had entered the study by POD- 1. There was no statistically significant difference detected in mean verbal pain and sedation ratings between the two groups. Although the infusion group used

signi~cantly more morphine cfi < ~.~~3), their pain and sedation scores were not determined to be different. AS our objective was to determine whether one method p~vided more reliable relief of pain without excessive sedation, the change in ratings between postoperative days 2 and 3 was examined. There was no statistical difference noted between the two groups in mean change in verbal or visual analog pain scores or sedation ratings. Table 7 is a compilation of this statistiCid Wi3lllittiOt~.

Only tme patient exhibited a respiratory rate of < 16lmin throughout the entire study period. Apl~l~)xitn~~te~y II) hr after the coll~p~etion of surgery and 6 hr following the initiation of PCA (three 0.8~tug dO!XS Id INXll delivwed), it respiratory rate of I Wmin was noted: this resolved without interventiot~ and a rate of 12-20 was observed thereafter, No antiemetics were administered for nausea or vomiting in any patient. Pour subjects, two in the PCA group and two in the PCA + CI group, withdrew before coillpletiug the study period of 72 hr. Of the two PCA subjects, one (no. 2) was discontinued due to lack of pain and removal of IV access; the other (no. 20) requested discontinuance because of her anxiety concerning the alarms from her infusion pumps. Of’the two subjects in the itifusion group who withdrew early, one (no, 19) was disc~~ntir~uedbecause of conversion to oral tlledic~~tion. The fourth subject (no, 27) was ~jthdrawn from the study (by physician request) after experiencing a possible adverse reaction to morphine. On POD-3 54 hr after ~ginnin~ the continuous infusion, subject no. 27 reported shortness of breath “shortly after” activating the PCA button. Her physician described the episode as stridorous respirations without chest pain or tachycardia. Subcutaneous epinephrine (0.1 mg) was given although she was spontaneously rtxoverkg prior to this dose. Her chest radio~aph showed mild right basilar atelectasis with mild effusion; her biood gases were reported as p0, 61, pCO* 3 1, and pH 7.55 on room air. She had no accompanying calf tenderness, negative Homan’s si probability venti~tion-perfusion scan. She was given oxygen and subsequently received intramus&n- meperidine without further incident.

Fig, 8. Chmgc in visual malog Beak by poetopcrativc day,

surprised to learn after the completion of the study that they had been rectiving a continuous morphine infusion. Severalsubjects stated that their anxiety was less than expected during their h~pi~ization. There was no apparent difference between the groups in the responses to the questionnaire regarding pain control. were

All subjectswere satisfied with their pain control and with the concept of patient-controlled anafgesia. Manyof the subjectscomp~in~ that the pmtnct of a nasogastrictube was irritating, causing discomfort that did not respond well to tht PCA morphine. The pain scores reported by the subjects reflect this pain and other types of di~mfo~ indi~t~y related to the (for example, hiccough). One subject flare-up of his gout while on the study and R an attempt to treat his fQgtpain. subj~~ ~~~~ having t~ubie ich they attributed to the stress of being hospitalized and to being awakened by staff. The majorityof subjects did not report t~~~~ sleepi while on the study. Many

Pain is a common sequtla of surgery. Following pelvic and abdominal surgery, severe pain lasting up to 4 days occurs in as many as 55% of patients.‘“-” Mana~ng ~to~~ti~ pain is of conctrn due to the risk of complications attributed to tht patients’ reluctance to breathe deeply and increase their activity. The risk of atelectasis,pneumonia, prolonged ileus, pufmoTable 5

Mean Verbal Pain Scarea

0

GWP

4

1

2

3

9 2.x6 1.192

14 2.226 0.751

15 1.825 0.682

12 I.798 0.99

11 1.833 0.932

II

i

&an

,416 I.58

14 1.546 1.038

15 1.372 0.957

12 1.267 1.092

11 1.698 1.295

0.098

0.272

0.887

1

~~~~ SD + CI SD P

SO.5

>0.5

Vol. 6 No. I January 1991

PCA in Posto@ratiueCare

!I

24 23 22 2.1 2 1.s *.a a.7 t.a is 1.4 1J 1.2 1.t I as 08 a7 INI

Fig. 9. Scdatian rallkillgs by gtwp ~st~~~tive day.

0

“---~----~

by

0

2

4 *DAY ttRlsIEN

lz6mow

analgesia, causing minimal sedation with little or no respiratory depression.“~‘~~‘7~‘~-2’~9” Based on these considerations, and the conflicting information regarding the benefit of adding an infusion to PCA during the first 24 hr postoperatively,‘fi-2R it was our hypothesis that PCA pius continuous infusion (PCA + CI) may improve pain control without causing excessive sedation or other side effects. As there is trep idation regarding the use of continuous infusions of narcotic analgesics due to the potential for accidental overdosage, the safety of this combination was also assessed. The results of this study indicate that

nary embolism, deep vein thrombosis, and ureteral and bladder hypomotility increases with p~long~ patient irnrnobility~~~*~*s* It is almost universally accepted that intramuscular injections on an intermittent, as needed, schedule is not an ideal method of providing posto~rative analgesia. The optimal postoperative analgesic regimen shoutd be efficacious, safe (avoiding undue cardiovascular and respiratory complications), free from side effects, relatively inexpensive, and convenient for the patient, nurses, and medical staff.‘*‘” Previous studies have shown PCA to be a safe and effective means of providing postoperative

-as a4 a3 a2 a* 0 -08 -52 -a3 -04 -55

-a8 47 -06 -as -1 l-2

Fig. 4. Change in sedation rankings by postoperative day.

2-J

4-L

comparisoa

Table 6 of EMa

fnom FostoPetativeDay2 PCA+ PCA

CI

P

1.75

1.67

NS

1.0

0.857

NS

0.413 Q,ZlI

0.72 0,293

~0,~s

Ye&al pain score

Median Sedation ranking Median ~~~~~ine SD

?CA + Cl is il gafe alternative to PCA alone; ~w~ver~ the infusion ~~i~en did not p~vide ~~ifi~antly better relief of ~t~~mtiv~ pain. Both qimens provided acceptableanalgesia in all patients, The patients in the PCA + CI up used ~gni~~%~tiy more morphine than PCA gtwp consistent with the findings of 0wen,Y” but contrary to Vickers,% who recorded equivalent amounts. It is interesting that despite higher doses used, all measures of outcome were no different, ~a~hall has concluded that continuous infusions induce tolerance,s4 although another explanation may be that PCA doses are used because postoperative pain is p~min%nt~y epi~i~ and the infusion has littIe infIuence on pain of this nature. We s%wno instances of respiratory depression, which ir in agreement with the findings nf Citron,%’ who ~n~iud~ that continuous morphine infusions are %s%feme*hod of analgesic %dministration in patients with chronic cancer pain %nd poor respir%tory st%tus (pay < 50). This is cQntr%ryto the findings of other investiwho have reported instances of respiratory depression with continuous morphine infusions posCoperatively~~‘4~‘6~s~ Dosages cited in these reports varied, but included regimens

PCA+ painscwe Medisn Sedadauixuking

PCA

Cl

P

0.17

-0.23

NS

0

NS

Veti

-0.67 ~~~~~ Mean SD

3.291 17.64

- 16.893 33.826

as conservative as ours. In most studies in which respiratory depression occurred, the continuous infusion began immediately postoperatively in contrast to beginning on POD-l as in our For example, Catley observed study. 5~*o~14~18 > 400 episodes of hy~xemia and > 400 instances of central apnea, almost ail of which occurred while patients were asleep in the first 12 hr after surgery. s3 The potential contribution of anesthesia, therefore, cannot be disregarded. Another concert is that the inherent safety of PCA, in which no drug is administered in the setting of excess sedation, is bypassed with a continuous infusion mode. We demonst~t~ no di~e~n~e in seda~on between the two groups: both had a mean rating of approximately one (mild). This is consistent with that reported with PCA alone .4-12-17-zQ13 Most studies of continuous infusions have only anecdotally reported sedation, and its relative incidence at our conservative dosage is unknown,5~‘s~‘“~‘R~221s” Although we did not observe moderate-severe sedation in any subj~t, the sedation raring scale may not have been sufficiently precise to detect a difference. Nausea and/or vomiting is a common side effect of na~ot~ analgesics and has been reported with varying frequency in previous studies. No antiemetics, however, were administered during our study. In a similarly designed study comparing a continuous morphine infusion to scheduled int~mu~ular mo~hine inj~tions in 42 postoperative gynecologic patients, Briggs reported that five study patients experienced vomiting.’ These subjects received a similar infusion dose to that used in our study and were allowed to receive additional intramuscular injections of 10 mg of morphine as needed, An effat of the large additional doses, with subsequent fluctuations in serum morphine concentrations, on the incidence of nausea and vomiting cannot be excluded. It is not uncommon for patients to experience nausea and/or vomiting after abdominal surgery for numerous reasons, such as ~s~~ion of ~st~int~tinal function or residual effects of anesthesia. While these factors cannot be eliminated as causes of nausea and vomiting in previous studies, they appeared to have had no influence in our study. The presence of a nasogastric tube in many of our

NS

patients may have lessened the incidence of nausea and vomiting.

Vol. 6 No. 1 Jauuff~ 1992

Possible limi~tions of this study that may have contributed to the statistically insignificant results were the small sample size. sensitivity of the measuring jnstrun~ents, and large patient variation in pain ratings, Large variability in pain ratings and amount of analgesic used are typical of many PCA studies in postoperative pain. Although this phenomenon supports individualizing analgesic doses via PCA, it does make the determination of statistical differences more di~cult. Our measurement tools (verbal pain scores, sedation ratings, and visual analog scales) are consistent with those used in the 1ieratut.e l(l.Is,is-)?,~~)~I,ss but it is possible tllat they weri not sensitive enough to detect a difference between groups. Another potential limieaeion of this seudy may be aetrib~~~,ed t.othe fact that the evaluators were not blinded to the subjects’ regimen.

Our hypothesis was that a ~ntinuous infusion of analgesic plus PCA would provide better pain control than PCA without excessive scdation. Based upon the results of this study, we conclude that PCA + CI offers no appreciabte benefit over PCA alone as determined by pain and sedation ratings, and incidence of adverse reactions. Although a trend for improved pain control between the second and third postoperative days in the infusion group was noted, this was not statistically signific~I]t. There was a statistically significant difference between the amount of morphine used by the two groups on POD-2, and the larger dose of morphine used by the PCA + Cl group may account for the difference in pain scores. The variance in individua~ patient needs cannoe be discouneed, alehough randomization should have minimized ehese differen~zs. Initiating the infusion on the morning of POF i appears to be associated with less adverse respiratory effects, compared to continuous infusions started immediately poseoperatively in other studies. Although certain patients may benefit from the combination of PCA plus continuous infusion, such as those with higher morphine requirements, our experience does not support the widespread application of this regimen. Further research is necessary to determine those patients whose postoperative pain control may

I3

be optimized by a coutinuous morphjne infusion plus PCA.

I. Marks. RM, Sachar EJ. Undertreatment of medicat inpatients with narcotic analgesics. Ann Intern Med 19?3;78:173-181. 2. Austin KL, Stapleton JV, Mather LE. Multiple intramuscular i$ections: a major source of variability in analgesic response to meperidine. Pain 1~8~,8:4762. 3, Runcr PC, ~lori~l~y F, Dudiey HAF. Morpl~jn~: controlled l&ii ofdifferent methods of administration for postoperative pilill relief. 13r Med J 1980;280: 1213. 4. Graves DA, Foster 1% Batenhorst tiem-comroiicx1 ikl~~tlgC4il. Ann 1~~83:~)~l: 36~~366,

Rl., et al, Pitlntcrn Mcd

5. Briggs GG. Berman ML, Lange S, et al, Morp phine: continuous intravenous infusion versus intramuscular injections far postoperative pain relief. Gynecoi Oncoi 1~85;22:28~2~. 6. Coleman DL. Control Chest 1987:92:520-528.

of postoperative

pain.

7. Weis OF, Sriwatanakul K, Aiioya JL, et ai, Attitudes of patients, house staff, and nurses toward postoperative analgesic care. Anesth Anaig 1983;G2:7074. 8. Cohen FL. Postsurgical pain rcliefz patients’ status and nurses’ medication choices. Pain 1980:9:2135274. 9, Bullingham

RES. Optimum

management

of post-

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