One hundred and twentypatients who had SpO2≤ 94% were studied and randomized into the 2 oxygen therapy groups (A and B) on arrival at the recovery room, with 60 patients in each group.
Prior to the commencement of oxygen therapy in the recovery room, the mean oxygen saturation was 93.2± 7.0% in group A and 93.3± 2.6% in group B (p = 0.461).
Fig 1: shows the pattern of recruitment of patients with SpO2 ≤ 94% for Oxygen therapy.
It showed that de-saturation occurred within 30mins of arrival in the recovery room .
39
The total number of cases done under general anaesthesia within the period of this study was six hundred and sixty-four. One hundred and twenty patients with SpO2 ≤ 94% were studied, giving an incidence of 18.1%.There wasno incidence of hypoxaemia recorded during theatre–recovery room transit period.Also,there was no incidence of hypoxaemia while the patients were on oxygen therapy with either of the devices.
Table I: displays the demographic data and clinical characteristics of each group. There was no statistically significant difference between the two groups with age, weight, BMI, and preoperative Hb concentration .The age range for the study population was 18-80 yr with a mean age 41.2 ± 14.2 yrs in group A which was similar to a mean age 42.7±17.9 yrs in group B (P=0.61).
Both groups showed female preponderance (24:36 in Group A; 14:46 in Group B)
Fig 2: Compares the distribution of the surgical procedures performed for the patients in the 2 groups studied. Majority of the cases were myomectomyin both groups; 21 patients ( 35% ) in group A and 19 patients ( 32% ) in group B . Similarly, the least number of cases presented for thyroidectomy;two patients( 3% ) in group A and three patients ( 5% ) in group B.
Fig 3: shows the oxygen saturation trends during theatre/recovery room transit period. The patients’ oxygen saturation was observed to be highest (99-100%) at the immediate post-extubation period following 3minonsupplemental oxygen (Time 0). Thereafter, saturation declined steadily during transportation .
Table Il and Fig 4 shows the comparative performance of the two oxygen therapy devices during oxygen therapy in the recovery room. The mean Oxygen saturation dropped in both groups (93.2 ± 7.0%) in group A versus ( 93.3 ± 2.6% ) in group B) prior to the administration of oxygen (Pre Oxygen therapy); the difference was not statisticallysignificant ( p = 0.461 ). However, the patients in group B ( Nasal Prong ) responded faster ( 0.63 ± 1.42 min ) to oxygen therapy,
40
compared with group A (1.78 ± 1.10 ) min, with P value of 0.001. Significantly higher SpO2values(97.4 ± 2.5%) was achieved in the group B compared to group A(96.0 ± 3.5%) at 5minutes duration of oxygen therapy( p= 0.002 ) .Thereafter, the mean SpO2achieved with the 2 oxygen devices did not differ significantly throughout the rest of the study periods.There was no incidence of hypoxaemiaor de-saturation while patients were on oxygen therapy with either of the devices, throughout the study period.
Tables III and IV: Showsthe changes in BP and HR during oxygen therapy.The mean heart rate was significantly higher in Group A than in Group B ; at 5min (109.5 ± 10.6 beats/min) versus (102.1 ±16.2 beats/min), p=0.004,and 10minutes; Group A ( 108.6 ± 10.5min ) versus group B (100.1 ±16.5), p= 0.002). At 45min; Group A (88.6 ±7.8) versus Group B (85.2 ±7.8), p=0.005,andat60min; Group A (86.1± 6.9) versus Group B (82.6 ± 7.1 ), p=0.02. At other time intervals, the heart rate was still higher in Group A than in Group B; however the difference was not statisticallysignificant( Fig 5 ).
Patients in group A had higher systolic blood pressure 130.2 ± 16.6mmHg when compared with 123.3 ± 15.2mmHg in group B at 5min of study period; this was statistically significant p
= 0.02, (Table IIIb).
Table IV shows the trend in mean arterial blood pressure. There was agradual drop in MAPduring the study period. Though patients in group A exhibited higher mean values, this was not statistically significant until 30minsinto the study when MAP was 70.4 ±16.5mmHg in group A compared to 57.9 ± 16.2mmHg in group B (p = 0.01).
Table V shows the comparison of the mean respiratory rate during oxygen therapy. Patients in group A maintained higher mean respiratory rate compared to patients in group B. There
41
were statistically significant differences at 5minutes (p = 0.017), 25minutes (p = 0.01), 30minutes (p = 0.03), 45minutes(p = 0.01) and 60minutes (p = 0.03).
Table VI shows the univariate analysis of the risk factors for the development of post operativehypoxaemia. Gender, site of surgery, volume of infusion and duration of surgery did not show any statistically significant difference. In essence, no risk factor on its own led to the development of hypoxaemia observed in the patients in our study.
Table VII: Compared the level of convenience of the delivery devices. The mean level of convenience using modified VAS pre-oxygen therapywas similar in Group A (0) versus Group B (0). Visual analogue scale ( VAS ) scores of patient’s convenience during the study period.
0-20 on the VAS scale represent most convenient; 21-89 represent inconvenient while, 90 – 100 represents most uncomfortable. In group A, 37 patients ( 61.7% ) found their device most convenient compared to 55 ( 91.7% ) in group B . This was statistically significant, p=0.001.
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TABLE I: DEMOGRAPHIC AND CLINICAL CHARACTERISTICS OF THE PATIENTS
Patients characteristics Group A/ Face mask (n=60)
Mean ± SD
Group B/ nasal prong (n=60)
Mean ± SD
P value
Age (years) 41.2 ± 14.2 42.7 ± 17.9 0.61
Weight (kg)
BMI(kg/m2)
Pre-op Hb(g/dl)
ASA ( I:II ) ratio
69.8 ± 10.7
26.7 ± 5.6
12.0 ± 4.6
34:26
72.9 ± 9.5
27.6 ± 4.8
11.8 ± 4.9
35:25
0.22
0.23
0.81
0.75
29
Gender (M:F) ratio 24:36 14:46
0.06
values represents mean ± SD of demographic and clinical da
30
TABLE II: COMPARISON OF THE EFFICACY OF TWO TYPES OF
OXYGEN THERAPY DEVICES .
Time (min) Group A/ Face mask Mean SpO2(%)
( n = 60)
Group B/ Nasal prong Mean SpO2 (%)
( n = 60 )
P value
Pre - oxygen therapy 93.2 ± 7.0 93.3 ± 2.6 0.461
5 min 96.0 ± 3.5 97.4 ± 2.5 0.002*
10 min 98.0 ± 1.9 97.8 ± 2.8 0.163
15 min 98.6 ± 1.8 99.1 ±1.2 0.211
20 min 99.0 ± 1.4 99.3 ± 1.1 0.657
25 min 99.1 ± 1.5 99.3 ± 1.1 0.810
30 min 99.0 ± 1.6 99.2 ± 1.2 0.317
* statistically significant differences in the oxygen saturation between oxygen therapy devices.
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Table III: Comparison of the Changes in Mean Heart Rate with the two oxygen therapy devices
Time (Min) Group A
(n=60) Mean ± SD
(beat / min)
Group B (n=60) Mean ± SD
(beat/ min)
P Value
Pre – oxygen therapy
103.5 ± 10.5 102.2 ± 15.5 0.276
5min 109.5 ± 10.6 102.1 ± 16.2 0.004*
10 min 108.6 ± 10.5 100.1 ± 16.5 0.002*
15 min 98.5 ± 14.0 94.1 ±10.6 0.792
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20min 95.6 ± 13.1 93.1 ± 8.3 0.445
25min 95.4 ± 8.5 93.9 ± 12.3 0.697
30min
45min
60min
92.8 ± 12.9
88.6± 7.8
86.1± 6.9
91.9 ± 8.0
85.2± 7.8
82.6± 7.1
0.586
0.05*
0.02*
Statistically significant difference .
Table IVa: Comparison of the Systolic Blood Pressure (mmHg) between the two groups.
Time (min) Group A Group B P value
33 (n=60)
Mean ± SD mmHg
(n=60)
Mean ± SD mmHg Pre – oxygen
Therapy
122.2 ± 15.2 120.0 ± 14.5 0.425
5min 130.2 ± 16.6 123.3 ± 15.2 0.020 *
10min 129.0 ± 17.0 123.3 ± 15.2 0.064
15min 127.3 ± 16.7 120.9 ± 15.7 0.247
20min 124.1 ± 15.0 123.5 ± 15.7 0.845
25min 122.3 ± 16.3 121.3 ± 14.1 0.748
30min 122.6 ± 16.7 118.6 ± 13.8 0.215
* Statistically significant difference.
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TABLE IVb : Comparison of the Diastolic Blood Pressure ( mmHg ) between the two groups
Time (Min) Group A (n=60)
Mean ± SD ( mmHg )
Group B (n=60)
Mean ± ( mmHg )
P value
0 78.8 ± 9.4 77.9 ± 10.2 0.235
5 78.9 ± 12.0 77.9 ± 8.4 0.983
10 78.1 ± 11.0 78.1 ± 8.7 0.983
15 78.0 ± 11.0 77.4 ± 9.1 0.739
20 77.6 ± 10.9 76.3 ± 8.8 0.503
25 75.8 ± 9.2 74.9 ± 10.1 0.605
30 79.5 ± 7.8 78.3 ± 10.5 0.742
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TableV: Comparison of the Mean Arterial Pressure (MAP) with the Two Devices
Time (Min) Face Mask (n=60) Mean± SD mmHg
Nasal Prong (n=60) Mean ± SD MmHg
P value
Pre – oxygen therapy
74.9± 11.9 71.1± 12.3 0.128
5min 74.2± 12.8 70.0± 12.2 0.188
10min 72.69± 12.7 71.52± 12.7 0.651
15min 71.1± 12.7 70.4± 12.3 0.794
20min 69.8± 13.4 67.8± 14.4 0.469
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25min 70.3± 12.9 65.5± 12.7 0.182
30min
45min
70.4 ± 16.5
69.8± 15.5
57.9± 16.2
61.1± 12.1
0.008*
0.001*
Foot note: *Statistically significant difference in MAP
Table VI: Comparison of Mean Respiratory Rate during Oxygen Therapy
Time (Min) Mask
(n=60) Cycle /per min
Nasal Prong (n=60) Cycle per min
P value
Pre – oxygen therapy 18.3 ± 4.1 18.4 ± 5.2 0.380
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5min 21.0 ± 4.7 18.8 ± 4.2 0.017*
10min 19.3 ± 3.5 18.0 ± 5.1 0.135
15min 18.6 ± 3.7 17.6 ± 4.2 0.180
20min 18.0 ± 3.1 16.6 ± 2.7 0.130
25min 17.7 ± 3.4 16.2 ± 2.5 0.010*
30min
45min
60min
17.6 ± 3.4
15.5± 2.2
14.4± 1.8
15.8 ± 2.2
13.9± 1.8
13.4± 1.30
0.030*
0.001*
0.003*
Foot note
*Statistically significant difference in respiratory rate.
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Table VII: Univariate Analysis of Risk Factors in the Development of Postoperative Hypoxaemia
Prognostic factors
Class Relative risk P value
Gender Male / Female
0.33 0.770
Site of surgery Abdominal / Others 0.58 0.407
Volume of infusion
<2 Litres/>2 Litres 0.22 0.603
Duration of surgery
<2hr / >2hr 0.75 0.507
39 No statistically significant difference
Table VIII: Comparison of Patient Satisfaction with the Two Types of Oxygen Therapy Devices
Visual Analogue Scale
Group A/ Mask n (%)
Group B/ Nasal n (%)
P value
Pre – Oxygen therapy
0 (0) 0 (%) -
0-20 37 (61.7) 55 (91.7) 0.001*
21-89 23 (38.3) 5 (8.3)
90-100 0 (0) 0 (0) -
40 Foot note
*Statistically significant difference in patients satisfaction.
41
Fig 1: Pattern of Recruitment for Oxygen Therapy in the Recovery Room
FIG 2 COMPARISON OF SURGICAL DISTRIBUTION OF PATIENTS
0 5 10 15 20 25 30
5minutes 10minutes 15minutes 20minutes 25minutes 30minutes Time of recruitment in minutes
Face Mask Nasal Prong
No of Patients
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GROUP A VERSUS GROUP B
GROUP A GROUP B
Fig 3: Mean Oxygen Saturation trend during Theatre/Recovery Room Transit Period
3, 5%
13, 21%
19, 32%
12, 20%
13, 22%
Thyroidectomy Mastectomy Myomectomy
Upper Abdomen (Bowel resection and anastomosis) LIMBS (ORIF)
2, 3%
12, 20%
21, 35%
13, 22%
12, 20%
Thyroidectomy Mastectomy Myomectomy
Upper Abdomen (Bowel resection and anastomosis) LIMBS (ORIF)
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Time ( sec ) Foot note
* Time 0 corresponds to oxygen saturation afterextubationand 3min of supplemental 02, post extubation.
Fig 4: Comparison of Oxygen Saturation during Oxygen Therapy with the Two Devices
92 93 94 95 96 97 98 99 100
0 30 60 90 120
Mean SpO2( % )
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Foot note : statistically significant difference at 5min ( p = 0.002 ).
Fig 5: Comparison of Mean Heart Rate with the Two Devices 84
86 88 90 92 94 96 98 100 102
SpO2 %
Duration of Oxygen Therapy
Face Mask
Nasal Prong
*
45 Time/min
*Statistically significant difference