Pain perception during colonoscopy in relation to gender and equipment: a clinical study

Introduction

The colonoscopy procedure allows safe and effective examination of the large intestine, enables easy access to tissue biopsies, is considered the gold standard for confirming diagnoses, but can be painful even with light sedation [1], [2], [3]. Pain and discomfort during the procedure is not only a risk factor in prolonging intubation time unnecessarily, it may also deter patients from consenting to the procedure. There is mounting evidence that longer colonoscopy withdrawal time increases the clinical quality of the procedure [4], [5], an additional factor to take into account when considering pain management. There are several studies concerning the variety of factors influencing pain perception during colonoscopy [1], [6], [7] but no studies with gender as the main discriminator have been conducted, albeit an older study concluded that male patients are more likely to complete a colonoscopy without asking for sedation [8]. While the large intestine anatomically is similar between genders, its surroundings are not. It has previously been shown that female gender combined with a variety of factors may predict lower pain tolerability during a colonoscopy procedure [2], [6], [7], [9], and a very extensive study on colonoscopy success-rates by chance found that women reported the procedure to be more painful than men, a finding that was not pursued further at the time[1].

A difference in pain perception between women and men during colonoscopy could be attributed to anatomy, physiology, or a result of biopsychological differences. Catastrophizing thoughts have previously been argued to be in effect when patients prepare for the procedure and can be described as ruminations and feelings of helplessness [10].

In the present study, we aimed to investigate gender-related difference in pain perception during the colonoscopy procedure. Further, to test a pilot intervention by implementing an instructional text tailored by a psychologist to prevent effects of possible patient catastrophizing. Finally, we aimed to compare the present results with data from a previous study where the previous generation endoscopes were utilized.

Materials and methods

Design

A consecutive clinical study (Figure 1) with no interventions was chosen to best characterize the patient population in day to day setting. A pilot study with text-based psychological intervention was completed within the same study period.

Figure 1:

Flowchart of the present study and origin of the data sets presented. The 190 UPD data set is the basis of the present study and represents the consecutively included patients within the study period.

Results

In total, 391 patients were recruited for the main study within the period, 242 females and 149 males. Six patients abstained from either participating or filling out the VAS form. An additional 38 patients were recruited for the pilot study, 18 females and 20 males.

Main study: patients undergoing colonoscopy with the 190 UPD-series endoscopes

There was no difference in VAS reports from male and female patients when using the 190 UPD-series colonoscope (Figure 2A). Male patients reported a median VAS of 1.70, and female patients 1.90, with the 75th percentiles being as low as 3.30 and 4.33, respectively. Use of sedation in the combined male and female population did not reveal any statistical difference. However, when stratifying for gender and sedation, the females reported a significantly lower VAS score when sedation was used (p=0.012) (Table 2 and 3). There was no difference in VAS for neither male nor female when cross-testing for age and/or examination time; demographics shown in Table 4.

Figure 2:

Box-plots with quartiles and min-max whiskers of Visual Analogue Score (VAS) 0–10 on the y-axis. A: The 190 UPD data set stratified for gender and use of sedation. B: The 190 UPD, 180 UPD, and 180 data sets stratified by gender. C: The 180 and 180 UPD data sets stratified for gender and use of sedation (gender divided by dotted vertical line).

Table 1:

Descriptive statistics for both original and imported data sets with comparisons.

Data set	Group	n	Median	Percentile		p-Value
				(25th)	(75th)
190 UPD	All	391	1.80	(0.60)	(3.90)	for comparison
	Female	242	1.90	(0.60)	(4.33)	for comparison
	Male	149	1.70	(0.60)	(3.30)	for comparison
190 UPD PIT	All	38	1.85	(0.75)	(4.30)	p>0.999a
	Female	18	1.60	(0.75)	(2.85)	p>0.999a
	Male	20	2.15	(0.68)	(4.70)	p>0.999a
180 UPDb	All	186	3.40	(1.50)	(6.30)	p=0.009 a
	Female	105	3.80	(1.50)	(6.30)	p=0.009 a
	Male	81	3.30	(1.45)	(6.15)	p=0.009 a
180b	All	141	5.00	(2.00)	(7.35)	p=0.009 a
	Female	88	5.90	(2.80)	(7.40)	p=0.009 a
	Male	53	3.20	(1.35)	(7.10)	p=0.009 a

1. The 190 UPD data set was compared with the other data sets individually.

   Bold font signifies statistical significance.

   190 UPD: The main dataset of the present study with new and original data with patients having undergone the colonoscopy procedure with 190 UPD series endoscopes.

   190 UPD PIT: A pilot study dataset with new pilot instructional text.

   180 UPD: A previously published data set with patients having undergone the colonoscopy procedure with 180 UPD series endoscopes.

   180: A previously published data set with patients having undergone the colonoscopy procedure with 180 non-UPD series endoscopes.

   UPD: Endoscope Position Detecting Unit.

   PIT: Pilot instructional text.

   ^aBonferroni corrected.

   ^bData imported with permission [1].

Table 2:

Descriptive statistics stratified for use of light sedation in the 190 UPD data set.

190 UPD	Group	n	Median	Percentile
				(25th)	(75th)
Sedation	All	305	1.70	(0.50)	(3.70)
	Female	206	1.55	(0.50)	(3.95)
	Male	99	1.70	(0.60)	(3.20)
No sedation	All	86	2.40	(0.78)	(4.83)
	Female	36	3.45	(1.50)	(6.38)
	Male	50	1.60	(0.60)	(3.35)

1. 190 UPD: The main dataset of the present study with new and original data with patients having undergone the colonoscopy procedure with 190 UPD series endoscopes. Stratified for use of light sedation.

   UPD: Endoscope Position Detecting Unit.

Table 3:

The impact of sedation on VAS stratified for gender in the 190 UPD data set.

VAS Comparisons	p-Value
Female, sedation versus no sedation	p=0.012 a
Male, sedation versus no sedation	p>0.999a
Sedation, female versus male	p>0.999a
No sedation, female versus male	p=0.052a

1. Bold signifies statistical significance.

   ^aBonferroni corrected.

Table 4:

Patient and procedure demographics in 190 UPD Data set.

			Male			Female
n	149			242
ASA Score	≤2			≤2

	Median	Percentile		Median	Percentile
		(25th)	(75th)		(25th)	(75th)
Agea	61.0	(47.0)	(71.5)	59.0	(47.0)	(70.0)
Intubation time (min)a	8.0	(5.0)	(13.0)	8.0	(5.0)	(13.0)
Withdrawal time (min)a	7.0	(7.0)	(7.0)	7.0	(7.0)	(7.0)
VAS	1.7	(0.6)	(3.3)	1.9	(0.6)	(4.3)

1. ASA: ASA Physical Status Classification System (Grade 1–6).

   VAS: Visual Analogue Scale (0–10).

   ^aParameter was not affected by or did not affect use of sedation.

Comparing datasets from the 190 UPD-series, 180 UPD-series, and 180-series endoscope datasets

Compared with the patients from the previous study having undergone the colonoscopy procedure with the 180 UPD-series endoscopes, the group from the present study reported a significantly lower VAS score (p<0.009) regardless of gender (Table 1), use of sedation (Table 2 and 3), or physician (data not shown). As seen in Figure 2B and Table 1, women reported a higher VAS score when no UPD was used with the 180-series endoscopes, whereas no difference were seen with men when not taking strata for sedation into account. However, when stratifying for sedation, men appear to benefit more from sedation than the addition of UPD to the 180-series endoscopes, and no additive effect was observed (Figures 2C and 3).

Figure 3:

A heatmap of gender-specific reduction in median VAS-scores when using different equipment and sedation. The 180-series endoscopes without UPD and without sedation is set to base-level 1.00. The baselines are not equal for male and female and cannot be compared vertically. Lower is better and a lighter hue of blue signifies a lower ratio.

Discussion

In the present study, we aimed to investigate gender differences in VAS scoring, the impact of equipment, impact of an instructional text expertly tailored by a psychologist, and possible causes for a previously observed difference in pain reaction between men and women. In our previous study, we investigated equipment impact on success-rate, determining the effects of adding an endoscope position detecting unit (UPD) to the 180-series gold standard from Olympus at the time. The results from the present study reject our main gender-related hypothesis and show that women do not report higher VAS scores than men in relation to the colonoscopy procedure. However, when the present data are stratified, some differences are revealed. The proportion of men who abstained from light sedation was higher than for women. This might have some psychological basis that should be considered when interpreting the analysis showing that – unlike men – women are more likely to report a higher VAS score when abstaining from light sedation. This fits well with another study reporting that the male gender is a positive predictive factor for a successful colonoscopy without sedation [8]. In relation to our previous study in which women generally reported a higher VAS score than men, one theory could be that women reach a certain threshold for more pronounced pain-sensations earlier. It has been shown that women may have a lower threshold for perceiving pressure-induced pain, whereas cold and ischemic pain appears to be similarly perceived between genders [10]. Air-inflation induced discomfort during colonoscopy is a well-known factor [3], [12]. It is very plausible that the current 190 UPD-series endoscopes with its slenderer dimensions and enhanced flexibility, made it possible to keep discomfort below such a threshold level and wash out the gender differences previously observed. The reduced thickness of 11.5 versus 12.8 mm scope results in its cylinder shape having a 20% reduced scope tip surface area total insertion volume (full working length of the scope) than the previous generation. While the field of view and angulation properties are the same for the two generations of scopes, the enhanced flexibility of the newer scope allows for both an improved passive bending in the curvatures, and better force transmission along the scope axis. In effect, instead of advancing around a flexure using the resistance created by stretching a colon curvature, the scope passively bends at certain points along its axis while retaining more rigidity in the distal end, allowing the tip of the scope to progress more seamlessly. This ultimately results in less length of scope inserted and reduced stretching of tissue. Moreover, there is evidence that the enhanced flexibility reduces intubation time and patient discomfort [13], [14], [15]; passive bending may be one of the deciding physical factors in the improved VAS scores. The difference observed when women abstain from light sedation suggests that only a combination of the current top-line endoscopes and sedation can bring the discomfort below the hypothesized threshold discussed earlier. A more generalized pain management argument is that men are more likely to report a deflated VAS score [16]. Conceivably, a parabolic effect in VAS difference might be found if a hypothesized threshold for both genders were present, washing out the gender differences in the extreme low and high ends of the VAS-scale. In light of the present results adding on previous observations, we find the threshold theory likely to be in effect. Women gradually report lower VAS with an additive effect of UPD, newer equipment with slenderer dimensions, and sedation, whereas men appear to benefit greatly from sedation or UPD separately – the combination of the two does not further improve scores.

A key factor for improving the clinical quality of the colonoscopy procedure is considering insertion and withdrawal time [4], [17]. In relation to pain management, prolonged or longer intubation time is often regarded as an issue. The sedation regime described in this study has a peak effect shortly after administration, in the minutes during insertion and cecal intubation [11].

In the additional pilot study also described here, we aimed to address a hypothesized psychological effect of catastrophizing. Catastrophizing can be described as a tendency to ruminate about the imminent procedure and a feeling of helplessness in coping with a projected and magnified threat of painful stimuli but should not necessarily be gender-specific [10]. Additionally, it has been argued that compared with men, women’s experience of perceived pain is more influenced by interpersonal transactions and type of these transactions [18]. There was no difference in VAS between male and female patients in relation to the gender of the physician (data not shown). The data from the pilot study with a modified instructional text is limited in power by number of participants. More importantly, a study scope beyond pilot data should include catastrophizing scoring and evaluation of the intervention impact on patient satisfaction, and not only VAS scoring [19]. Nonetheless, the data indicate that an expertly tailored instructional text makes no difference for VAS. Further studies on reducing catastrophizing would be of interest, but for a clinical setting, our present main study results show that the general VAS level is very acceptable.

The present main study is not without limitations. A prospective inclusion period with no interventions was chosen to follow as many random patients as possible within a long time frame in a day to day clinical setting. The drawbacks include no control over male to female ratio, nor choice of sedation versus non-sedation. In consequence, there is no randomization of sedation to reduce bias against patients who are mindful of their pain management limitations, nor to increase statistical power and more equal groups.

Gender-stereotypical expectations on how men and women cope with pain have been explored in the literature and have been hypothesized to influence actual coping mechanisms [20]. In relation to our ongoing investigations, we conducted a vox populi and asked 50 random men and 50 random women: For whom they thought a medical procedure like a colonoscopy would be most unpleasant regarding pain – men or women? All participants unequivocally answered men. It appears expectations and the reality of this study do not meet.

While solid conclusions are difficult to determine on the question of gender-differences, the overall data importantly show that the top-line equipment results in acceptable pain management with no overall difference between men and women. Further, pain was significantly reduced for both men and women compared with using previous generation equipment. Women might benefit from added light sedation. We believe the present results are very useful data where and when general anesthesia is seldomly used (e. g., in Denmark) or is undesirable for the patient.

Conclusions

Men and women find the colonoscopy procedure tolerable with no overall difference in pain perception when using the current high-end 190 UPD-series Olympus endoscopes. Additional pilot data indicates there is no improvement to be gained from a psychological approach tailoring pre-procedure instructions for the patients, but this might be due to overall very low VAS scores. Even for expert senior consultant physicians, access to up-to-date endoscopic equipment can reduce procedure-related discomfort for the patients considerably.