98
Journal o f T o n g j i Medical University 14 ( 2 ) :
98-104, 1994
S h i f t w o r k and Heat Stress in an Intensive Care Unit
LIU L i - wang ( ~b]~ ~ ) Institute of Occupational Medicine, Tongji Medical University, Wuhan
Costa G, Schallenberg G. , Trinco R. Institute of Occupational Medicine, University of Verona,
Policlinic Hospital, 37134 Verona, Italy
Summary : This paper reported the results of investigation on shiftwork and heat stress in an intensive care unit. The aim of this study was to analyse the physiological strain of nurses during the three shifts (Morning, Afternoon, Night) in relation to the specific microclimatic conditions and job activities. 8 professional nurses (6 female and 2 male ), aged between 21 and 38 years (mean 29.8:1: 5. fi years), having from 3 to 18 years service, were monitored throughout a complete working cycle of 4 days. They worked on a three shift system at fast rotation. Their working environment was an independent unit for intensive care and expert surgical treatment which was entirely air conditioned. The observation indexes included: twenty-five blood parameters; ten urine parameters, net cardiac cost and relation cardiac cost, etc. The results of the investigation have not envideneed serious alterations of the psycho-physical conditions of the nurses, but do pointed out some problems pertaining both to the environmental and physiological conditions. Key words: shiftwork, heat stress, nurse
It is of prime importance in hospital to achieve t h e r m o - h y g r o m e t r i c conditions fit to guarantee m a x i m u m comfort for patients. H o w e v e r , a standard thermal environment suitable for the whole hospital is unachievable; on the c o n t r a r y , many climatic conditions exist a n d / o r are required for the patients in different zones, i. e. isolation boxes, operating r o o m s , intensive care units, etc. It is moreover vital to ensure thermal comfort for the sanitary staff devoted to such engaging and responsible tasks. In fact, the peculiar thermal needs of patients are often interlinked but at times counteract that of the staff according to different tasks and environmental c o n t e x t s , w h i c h are influenced by space, architectural l a y - o u t , type and a m o u n t of equipment and number of persons present tl-4~. T h e r m a l l y comfortable environment is also conducive for optimal mental activity, and exposure ' to temperatures above the
comfort zone is an environmental stress which tends to impair performance efficiency ES~, taking also into account that thermoregulating responses to thermal stimh|i fluctuate around the clock, being worse in the early morning and better in the afternoon [~ Shift and night work is nowadays generally recognized as a further stress factor for working people by disrupting circadian r h y t h m s and impairing psycho-social conditions [8~, also in addition to other specific working situations, e. g. exposure to noise, heat and chemical substances. U p to now, there are a few articles reporting the combined effects of heat and shiftwork on human adaptation [9'1~ With particular reference to a 'r Burns C e n t e r " , object of this s t u d y , nurses working on rotating shifts were obliged to operate under unfavorable microclimatic conditions, due to the therapeutic necessity of
"Journal o f Tongji Medical University 14 (2): 98-104, 1994 99 high environmental temperatures, required for keeping uncovered the burns in order to facilitate tissue repair. Nurses complained of remarkable thermal discomfort, overtiredness, heavy-headiness and ankle oedema; moreover, episodes of faintness were also reported among non-acclimatized persons (student nurses, new personnel). Therefore, the aim of this study was to analyse the physiological strain of nurses during the three shifts (Morning, Afternoon, Night) in relation to the specific microclimatic conditions and job activities. SUBJECTS AND METHODS Subjects 8 professional nurses (6 females and 2 m a l e s ) , aged between 21 and 38 years (mean 29.8-t-5.6 year s ) , having form 3 to 18 years service, were monitored throughout a complete working cycle of 4 days. All they were acclimatized and wore light cotton clothes, consisti'ng of a short-sleeved Tshirt and light trousers (0. 6 Clo). Shiftwork Schedule They worked on a three shift system at fast rotation " 1-1-2": Morning (07-13) Afternoon (13-21) - Night (21-07) - Night (21-07), followed by 2 days off. This 6-day cycle was repeated for 6 weeks, followed by a month without night shifts. Work e n v i r o n m e n t The "Burns Center", an independent unit for intensive care and expert surgical treatment, was entirely air conditioned. It was divided into two adjacent areas: a) the " confinement" area, provided with 6 boxes for patients, isolated by glass walls ; b) the " service" area, including an operating room, a bath-tub, a store room, a small kitchen and a toilet. Methods ( 1 ) The environmental microclimatic conditions were monitored continuously for 3 weeks, by means of a computerized recorder ( T e c o r a , Milano, I t a l y ) p r o v i d e d by globe, dry and wet-bulb thermometers and thermocouple anemometer. On the whole 292 readings were recorded concerning air temperature, relative humidity and ventilation.
(2) Blood tests: T w ent y five blood parameters were tested at t h e beginning and at the end of each shift, such as: Hct, H b , RBC, WBC, Platelets, Urea nitrogen, Creatinine, Uric acid, Glucose, Cholesterol, Triglycerides, Total protein, Albumin, Sodium, Potassium, Osmolarity, Chloride, Calcium, Phosphorus, Iron, total and conjugated Bilirubin, A S T , ALP and Cortisol. All the analysis were carried out by means of Technicon Automated Multianalyzer (International S y s t e m ) except for Cortisol, which was determined by Fluorimetric Enzyme Immunoassay (Baxter). (3) Twenty-four hours urine samples were collected for evaluation of ten parameters: Volume, Specific gravity, Osmolarit y, Creatinine, Urea nitrogen, Sodium, Potassium, Chloride, determined by multianalyzer, 17-OH, 17-KS determined by colorimetric method. (4) Continuous recording of two ECG tracings by Holter's method (ICR Mod. 7200, N. Y. , USA) was carried out on one or two work shifts, an off-duty period and a night rest for calculation of heart frequency. Two indices of cardiac strain were also derived [:~z,13] -Net Cardiac Cost (NCC) = W o r k heart rate - Rest heart rate -Relative Cardiac Cost (RCC) = NCC / Max heart rate - rest heat rate. " Rest heart rate" was considered the mean heart rate of the night sleep period, and "Max heart rate" was calculated according to Astrand and Rodhal tl<. (5) All the subjects kept a diary for the four days reporting work and off-duty activities, sleeping t i m e s , food and drink intake. (6) Statistical analysis was carried out by means of Student " t" test and two-ways analysis of variance by SPSS. RESULTS A N D DISCUSSION
The microclimatic conditions in the two working areas during the three shifts are summarized in Table 1. T h e relative humidity was constantly maintained at 50% and the air velocity under 0. 4 m / s e e , while the dry-bulb and globe temperatures resulted practically the same; under these conditions
100
the Operative Temperature was equivalent t o the Air Temperature. In both areas, the Operative Temperature resulted always above the comfort zones for light work according to AS HR A E t~sl, being significantly higher (-+-3. 5~ on average, Student " t " = 17.66; P < 0 . 0 0 1 ) in the " confinement" Table 1.
area compared to the " service" area, without noticeable fluctuations during the course of the day, except for a slight reduction in confinement rooms on Morning Shift ( F = 3.48; P < 0 . 05) due to more frequent opening of the doors for service.
Operative temperature ( ~ ; x •
SERVICE
CONFINEMENT
Morning shift
29. 84-0. 9
32.7-I-0.4
Afternoon shift
29.95:0.9
33.65:0.4
Night shift
29.75:0.8
33.45:0.7
Relative humidity ( ~ )
49. 1-4-2.9
47.2+2.8
Air speed (m/see) ..
O. I+0. 05
<0. 05
I t is to be taken into account that the time spent by the staff in the two areas varied on the three shifts in relation to the specific work organization. On Morning Shift, about 80% of total work time was spent in the patients boxes since m o s t of the nursing care (as change of linen, medication, hygiene of the patient ) and doctor's rounds are carried out. On the contrary, the time spent in this hotter area was remarkably reduced on Night shift (about 3 0 ~ of the tot a l ) , being limited only to drug administration, emergency procedures or urgent requests of the patients. Similarly, the work load allocated to the staff varied on each shift, since it entailed moments of light work and sedentary jobs ( 1 . 5 - 2 . 5 M E T ) , e. g. completion of charts and forms, preparation of drugs, transport of materials, and bouts of heavier work (3-5 M E T according to Vaichere et al EI6]), namely lifting of patients, making of beds and removal of equipment; the latter were carried out mainly on morning shift. T h e task of medication, which is not excessively heavy in itself, may well become so considering the postures the nurse are compelled to maintain, causing prevalently static weight on the vertebral column and limbs. On duty the nurses wore light cotton clothes, consisting of a short-sleeved, T-
shirt, light trousers, representing a global thermic resistance comparable to 0. 6 Clo. Nevertheless, the hot environment appeared quite uncomfortable particularly in relation to the specific activities carried out. In fact, he Heat Stress Index of Belding and Hatch Cln indicated a moderate-severe heat strain (ranging from 30 to 60) when the staff operated in the " service" area, thus becoming very high (ranging from 60 to 90) in the " confinement rooms". All the 25 blood parameters resulted within normal range and no statistically significant difference was detected between the beginning and the end of each shift, and also among the three shifts, except for cortisol (Table 2). Cortisol levels (Table 3) resulted remarkably lower at the end of the two dayshifts (Morning: " t" paired = - 3 . 0 1 , P < 0. 01; Afternoon: " t" paired = -4. 97, P < 0. 001), while noticeably higher at the end of both night shifts (1st Night: " t" paired = 2. 10, P < 0 . 0 5 ; 2nd Night:" t" p a i r e d = 2. 11, P < 0. 05). These variations appear to reflect the normal circadian rhythm of this hormone tlsl , which has its acrophase in early morning hours and declines gradually towards evening. It did not result to be altered by two consecutive night shifts. As concerns the other parameters, it is worth m~ntioning that haematocrit presented a constant decrease at the end of each
Journal o f Tongji Medical University 14 (2) 9 98-104, 1994
101
c r e a s e at t h e b e g i n n i n g an d at t h e end o f t h e a f t e r n o o n s h i f t in c o n n e c t i o n w i t h t h e p o s t l u n c h and p o s t - d i n n e r p h a s e s r e s p e c t i v e l y . Also regarding the 1 0 urinary indices ( T a b l e 4 ) , no s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e s w e r e o b s e r v e d d u r i n g t h e f o u r d a y s of s h i f t w o r k in a n y of t h e p a r a m e t e r s .
shift ( f r o m -0. 75 t o - 1 . 0 7 on a v e r a g e ) , probably indicating a slight haemodilution due to t h e liquid i n t a k e ( v a r y i n g f r o m 600 to 1800 ml p e r w o r k s h i f t ) to c o m p e n s a t e the e x c e s s i v e s w e a t i n g . H o w e v e r , n o d i f f e r ences w e r e d e t e c t e d f o r e l e c t r o l y t e s a n d o s m o l a r i t y . O n l y g l u c o s e s h o w e d a s l i g h t in-
Table 2. Mean values of 25 haemato-ehemieal parameters, determined before and after each work shift (International System Units)
Morning before
Afternoon
after
before
1st Night
after
before
2nd Night
after
before
after
Hct
41.5
40. 5
41.5
40. 4
40. 9
40.6
41.1
40. 3
Hb
14.4
14.1
14. 2
13.8
13.9
13.7
14.1
13.6
RBCs
4.9
4.8
4.8
4.6
4.9
4,6
4.6
4.6
WBCs
7.5
8.1
6.8
7.7
7; 1
7.3
7. 2
7.5
Platelets
190
213
195
202
201
202
193
205
Urea nitrogen
6.0
5.5
5.5
6.2
6.3
5.4
5.1
5.3
Creatinine
102
92
86
91
106
89
77
82
Uric acid
0, 3
0. 3
0. 3
0. 3
0. 3
0.3
0. 2
0. 3
~tucose
4.8
4.9
5.3
5.2
4. 5
4. ?
4.9
4. 6
Cholesterol
4. 3
3.9
4.5
4.5
4. 6
4.5
4.6
4. 4
Triglycerides
0. 7
1.1
1.2
1.6
1.3
1.2
1.4
1.1
Total protein
72.3
72.3
72.8
73.6
72.8
72.6
71.6
71.6
Albumin
44.3
44. 6
44.8
45.1
44.6
44.8
44.1
44. 1
Sodium
139
138
139
141
139
139
139
139
Potassium
4.0
3.9
4. 1
5.1
4. 2
4.9
4. 1
3. 7
Chloride
104
104
104
105
104
103
105
104
Calcium
2.4
2.4
2.4
2.4
2.4
2.4
2. 4
2.4
Phosphorus
1.0
1.2
1.1
1.2
1.1
1.2
1.3
1.1
Osmolarity
310
307
314
315
305
308
308
310
Iron
20.6
21.1
21.5
13.7
15. 2
19.0
18. 2
Total bilirubin
10. 2
10. 0
9.8
6. 3
8. 0
9.0
8. 0
8. 6
Conj. billrubin
1.2
1.6
1.5
1.3
1.3
1.5
1.2
1.5
13
13
II
12
12
II
II
12
36
35
34
38
36
36
36
35
AST ALP
18.
102 Table 3. Plasma Cortisol ( n m o l / l ) at the beginning and at the end of each work shift (T-ks) TIME 07 . . . . . . . . . 13. . . . . . . . . 21 . . . . . . . . 07
SHIFT Morning
597•
. . . . . 351•
Afternoon
455•
. . . . . 267•
1st Night
417•
. . . . . . . 634•
2nd Night
365•
. . . . . . . 590+182
Table 4. Total urinary excretion (mg/24 hrs) during the 4 days of shiftwork 1st Day Morning
2nd Day Afternoon
3rd Day Night
4th Day Night
Volume
1250+ 440
1133 + 437
1150-+- 500
1091• 483
Specific gravity
1020+4
1022+4
1019•
1021•
Osmolarity
721 • 170
742 • 136
686 • 130
765 • 152
Creatinine
1170•
1110•
1001•
1060•
Urea nitrogen
8965-+'4235
10973•
9133•
9568•
Sodium
1766•
1423•
1358•
1733•
Potassium
595+239
Chloride
1811•
17-OH
10. 7 •
17-KS
613•
578+856
1478• 3
9.9-t-1.9
516• 153
1415•
1691•
11.3•
9.2+5.7
9.7=t=5.9
10. 4 + 3 . 1
9.4•
9. 3 •
7
Table 5. Mean values of heart rate (beats/min) during work, rest and off-duty periods Work Subject
Sex
Age Mean
Max
Off-duty
Rest
NCC
RCC
B. P.
M
31
72
120
73
52
20
14.5
M. P.
M
38
85
112
74
63
22
18.5
N. G.
F
36
80
iii
78
56
24
18.7
B. M.
F
21
98
134
90
70
28
21.7
R. G.
F
30
93
I17
76
56
37
27.6
M. F.
F
25
102
155
Ill
58
44
32.1
G. R.
F
30
105
160
87
64
41
32.5
N. P.
F
27
107
140
89
57
50
36.7
N C C : N e t cardiac cost ( b e a t s / m i n ) ; R C C : R e l a t i v e cardiac c o s t ( ~ ) . A s c o n c e r n s 1 7 - O H and 1 7 - K S in p a r -
t i c u l a r , a s l i g h t b u t n o t s t a t i s t i c a l l y signifi,
Journal o f Tongji Medical University 14 (2) : 98-104, 1994 103
cant decrease of their excretion was recorded on both the days of night shift. The summary of the cardiac recordings are reported in Table 5. Heart rate showed a high interindividual variability among the subjects: in particular three female nurses exceeded 100 beats/rain on average, having peaks above 140 bpm and a net cardiac cost above 35 bpm. The relative cardiac cost resuited "light" (10-19%) for 3 subjects comprising the 2 males, " moderate" (20-29%) for 2 subjects, and " rather heavy" (3039%) for the other three nurses. The cardiac response resulted mainly in relation to the job activities, connected also to environmental and temporal conditions, although it appeared influenced by some individual characteristics. As concerns night shift in particular, the average heart rate varied from 71.6 to 101.3 bpm among the eight subjects resulting on average 8.4 ~ lower in comparison to the day shifts, in connection with the above-mentioned differences in workorganization. Tak;.ng into consideration, for example, the couple B. M. (female) and B. P. (male) on the same night shifts, one may note that the heart rate pattern was quite different. The female nurse B. M. had a constantly higher heart rate compared to the male nurse, both during work and at rest. On work shift, between 9 pm to midnight, they carried out duties which entailed giving care to the patients in the confinement rooms, namely, lifting patients for change of garments, re:making beds and, in addition emptying urine bags and administering drugs. Such duties werecarried out at 6500 beats/h heart rate on average by the female nurse and at 4500 beats/h by the male nurse. For the remaining hours of the shift, the subjects did mostly sedentary jobs in the service area, such as preparing gauze, completion of intake-output charts and making up reports. The female nurse presented a constant difference of about 1500 beats/h compared to the male nurse. In both, the highest heart rate was recorded at 1, 10 a. m. of the first night shift while lifting a patient for change of garments: the female nurse reached 134 beats/min, and the male
nurse 120 beats/min. Also among another couple on night shift, the female nurse showed a Constantly higher cardiac frequency (3-15 bpm of NCC on average) than her male colleague while doing almost the same activities. Regarding another team of 3 female nurses on day shifts (Fig. 3), a similar pattern of cardiac response was noted during the afternoon shift, while they differred significantly on the subsequent Morning shift: one nurse (N. P . ) showed a constantly higher heart rate (109 beats/rain on average with peak at 140 beats/rain) due to a prolonged stay in the confinement area for treatment of a patients in severe conditions, while another (M. F. ) presented a lower frequency (81.2 bpm on average) carrying out mainly ward management. However, this nurse had a peak of 155 bpm while rising a patient for medication and remaking the bed with her colleague G. R . , who reached 160 bpm. CONCLUSIONS The results of the investigation have not evidenced serious alterations of the psycho-physical conditions of the nurses, but do pointed out some problems pertaining both to the" environmental and physiological conditions. Regarding the microclimatic conditions, the temperature recording show how the nurses are compelled to do their duties constantly under conditions of thermal strain, which may become particularly severe when they are in the confinement rooms, where they also have to carry o u t the heaviest tasks. However, the actual thermal range (27.8-34. 5 ~ O T ) , which may justify the complaints of the subjects~ did not cause a significant biochemical imbalance. The cardiac responses, on the other hand, has evidenced that the strain imposed by some physical task may become quite relevant, also in corisideration of the unfavorable microclimatic conditions in which they must be done. As it is impossible to motify the microclimatic conditions because of patients' needs, and the nurses oblige to remain in
104
the unit for sterility p r e c a u t i o n s , s o m e rest pauses have been i n t r o d u c e d , p a r t i c u l a r l y on m o r n i n g and a f t e r n o o n shifts to be s p e n t in the k i t c h e n r o o m of the service a r e a , equipped with a s u p p l e m e n t a r y ceiling fan. H o w e v e r , s h i f t w o r k did n o t s h o w a significant negative effect o n p h y s i o l o g i c a l adaptation. In fact, in relation to the specific w o r k o r g a n i z a t i o n , n i g h t shift a p p e a r e d to be the least u n f a v o u r a b l e b o t h in t e r m s of w o r k load and t h e r m a l s t r a i n , as it entailed l i g h t e r t a s k s and s h o r t e r s t a y in the h o t t e s t areas. M o r e o v e r , the actual a r r a n g e m e n t o n s h o r t r o t a t i o n schedule (" 1 - 1 - 2 " ) helps to reduce its advers~ effects on p s y c h o - p h y s i cal f i t n e s s , w i t h o u t i n t e r f e r r i n g with the r h y t h m i c characteristics of the biological f u n c t i o n s , as p r o v e d b y the s t e a d y n o r m a l circadian rhythm of plasma cortisol t h r o u g h o u t 2 N i g h t Shifts. REFERENCES
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