Yasuda et al.
Journal of Physiological Anthropology (2023) 42:23
https://doi.org/10.1186/s40101-023-00340-5

Journal of
Physiological Anthropology

ORIGINAL ARTICLE

Open Access

Venous dilation effect of hot towel(moist and dry heat) versus hot packfor peripheral intravenous catheterization:a quasi‑experimental study
Kae Yasuda1 , Inaho Shishido2 , Michito Murayama2 , Sanae Kaga2   and Rika Yano2*   

Abstract
Background Heat application before peripheral intravenous catheterization is recommended for venous dilation.
Hot pack application enlarges the venous diameter in healthy adults; however, hot towels (moist and dry heat) areused often in some medical cases. However, it is unclear whether hot towel application promotes venous dilation
better than hot pack application. This study compared the venous dilation effect of using a hot towel (moist and dryheat) to a hot pack before applying the tourniquet at an access site for peripheral intravenous catheterization.
Methods Eighty-eight healthy females aged 18–29 years were recruited for this quasi-experimental study. They
underwent three types of heat applications (hot pack, moist hot towel, and dry hot towel [moist hot towel wrappedin a dry plastic bag], all of which were warmed to 40 ± 2 °C and performed for 7 min) to their forearm and tourniquet application for 30 s after each heating. Venous diameter and depth were measured using ultrasonography,
and venous palpability and visibility (venous assessment score) was observed as venous dilatation effects. In addition,
the skin temperature, stratum corneum hydration, and subjective evaluation of the warmth were measured.
Results There were no significant differences in venous diameter and assessment scores after intervention
between the dry hot towel and the hot pack groups, and the effect size was negligible (Cohen’s d < 0.20). However, these measurements were significantly lower for the moist hot towel than for the other two heat applications(P < .001). Although there was no significant difference in skin temperature and warmth rating score between the dry
hot towel and the hot pack, these were significantly lower for the moist hot towel than for the other two heat applications (P < .001). The amount of change in stratum corneum hydration of the dry hot towel was not significantly different from that of the hot pack; however, that of the moist hot towel was significantly larger than that of the other twoheat applications (P < . 001.)
Conclusions A method in which a towel warmed in hot water is wrapped in a dry barrier may be an alternative
to a hot pack.
Trial registration This study was registered with University Hospital Medical Information Network in Japan (Registration No.: UMIN000048308. Registered on July 7, 2022).

*Correspondence:
Rika Yanor-yano@med.hokudai.ac.jp
Full list of author information is available at the end of the article© The Author(s) 2023, corrected publication 2024. Open Access This article is licensed under a Creative Commons Attribution 4.0
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Yasuda et al. Journal of Physiological Anthropology (2023) 42:23

Page 2 of 14

Keywords Heating, Hot towel, Hot pack, Venous dilation, Vein, Skin temperature, Peripheral intravenous
catheterization

Background
According to the National Home Infusion Association(2023), the practice of infusion therapy has shifted toin-home care settings in recent years because of costeffectiveness and personal lifestyle considerations [1].
The home infusion therapy market was valued at US$31
billion in 2021 and is expected to increase to US$61.7
billion by 2030 [2]. Insertion of a peripheral intravenous
catheter (PIVC) is a basic medical procedure that is lessinvasive than central venous access. However, complications such as extravasation and occlusion occur in 75%
of home care patients who undergo PIVC insertion, andhalf of them experience multiple insertions because of
failure at the first attempt [3]. Most medical professionals select the insertion site for a PIVC by observing andpalpating the vein. Thin, poorly palpable, or poorly visible veins make PIVC insertion difficult despite the useof a tourniquet [4]. Therefore, it is important to dilate thevein sufficiently to safely insert the PIVC [5].
Before using a tourniquet at the access site for PIVC
insertion, heat application is recommended as a venous
dilation procedure [6]. When thermal energy is transferred to the skin, venodilators such as nitric oxide
are released, and the blood flow in the cutaneous veins
increases [7]. In terms of safety and venous dilation
effects, the surface temperature of heated items applied
to the skin is recommended to be 40 ± 2 °C [5]. Hot packs
have the highest utilization rate for heat applications in
hospitals (65%), but hot towels are also used often not
only in America but also in Japan [8]. Hot towel applications include two methods: direct application of a towel
moistened with hot water (moist heat) and wrapping it ina dry barrier and applying it (dry heat) [8].
Previous studies on the venous dilation effects using a
hot pack (gel sealed in dry plastic) in the forearm cutaneous veins of healthy adults revealed the following: 1)
in a randomized controlled trial, using a tourniquet after
15 min of heat application significantly enhanced venous
cross-sectional area dilation than using tourniquet alone[9], 2) there was no significant difference in the venous
dilation effect of application times between 5 and 15 min[10], and 3) the venous dilation effect persisted for atleast five minutes after the removal of heat in the 15 minapplication [11]. For heat application using hot towels,
the effectiveness of the moist and dry heat methods wascompared in a randomized controlled trial involving 136
hematology outpatients [12]. The results showed that thesuccess rate of the first PIVC insertion was significantly

higher under dry heat than under moist heat. However,the venous palpability and visibility after heating were
not significantly different. A PIVC insertion is associatedwith the promotion of venous dilatation and improvement venous palpability and visibility [4, 13]. Therefore, it
is unclear whether the dilated veins increased the successrate of PIVC insertion in the context of dry heat. Because
no study involved a control group that underwent thestandard procedure (only tourniquet application), it is also
unclear how many veins dilate when using the hot towel.
Heat transfer to the skin seems to be affected not only
by temperature but also by the material of the item andmoist and dry heat stimulation. However, it is unclear
how extensively veins dilate when using hot towels andwhether hot packs or hot towels are more effective heatapplication methods for venous dilation. As these methods are mixed in medical practice, it is necessary to show
evidence of a more effective method that leads to secure
PIVC insertion.
This study compared the venous dilation effect of using
a hot towel (moist and dry heat) to a hot pack before
applying the tourniquet at an access site for PIVC insertion. This study provides basic evidence that heat application methods should be selected for PIVC insertion
to promote greater venous dilatation. In addition, if hot
towels provide the same venous dilation effect as hot
packs, using hot towels instead of hot packs may be recommended in resource-limited situations, such as homenursing and disaster situations.

Methods
Study design

This quasi-experimental study followed the Transparent
Reporting of Evaluations with Nonrandomized Designs
guidelines (see Additional file 1). After each of the threeheat applications (hot pack: using a hot pack, moist hot
towel: using a face towel warmed with hot water, dry
hot towel: using a moist hot towel wrapped in a plastic bag), a tourniquet was applied to each participant’s
forearm. Allocations of heat applications were assigned
using computer-generated random numbers assignedby an independent study associate. Experiments were
performed on three consecutive days whenever possible. The washout period for the heat applications was
24 h. Each heat application was performed at the sametime between 10:00 a.m. and 4:00 p.m. to minimize its
influence on the autonomic nervous system [14]. It wasYasuda et al. Journal of Physiological Anthropology (2023) 42:23

impossible to blind the participants to the intervention
because it involved thermal intervention. The evaluator
was not blinded because they were the same person as
the interventionist.
Participants

Ninety healthy female students aged 18–29 years who
visited a Japanese national university between July 2022
and November 2022 were recruited as a conveniencesample. This study aimed to control for differences invenous degeneration and reactivity caused by aging andhormonal balance between sexes [15, 16]. Females havesmaller vessel diameters than males [17, 18] and it ismore challenging to insert PIVCs in females [19]. The
exclusion criteria were as follows: 1) a history of cardiovascular disease; and 2) receiving any treatment on theforearm skin because of severe skin diseases, injuries,
or eczema. Participants were instructed to refrain fromalcohol consumption within eight hours and from eating, consuming caffeine or stimulants, and engaging instrenuous exercise or showering within an hour before
the experiment initiation.
Sample size

Based on the difference in venous diameter between heatapplications in an unpublished pilot study, 88 participants were required in this study [dry hot towel vs. hot
pack: two-sided significance of 0.05, power of 80%, andeffect size of 0.50, Student’s t-test]. We enrolled 90 participants after considering the dropout rate. The sample
size was determined using the G Power software version
3.1.9 (G*Power, Heinrich Heine University, Düsseldorf,
Germany).
Target vein

The cephalic, median, or basilic veins of the non-dominant arm were selected, which were ≤ 30 mm distal fromthe antecubital fossa, ≤ 120 mm proximal to the radialstyloid, and as large as possible. In addition, the vein
was straight ≥ 2.5 mm, lying ≤ 10 mm deep, and with adiameter ≥ 0.9 mm [20–24]. This criterion assumes a
22-gauge thick and 25 mm long catheter insertion (BDInsyte Autoguard™ BC Shielded IV Catheter with BloodControl Technology, Nippon BD Co., Tokyo, Japan). The
measurement sites were marked with surgical tape andphotographed whenever possible to ensure that the same
position could be measured.
Measurement environment

This study was conducted in a measurement room at auniversity in Japan. The measurement environment was astandard hospital room. The temperature was 22–24 °C,
the humidity was 45–60%, and illuminance was set toPage 3 of 14

185–215 lx in this room based on Japanese industrial
standards [25].
Procedure

The intervention methods were based on previous studies of heat application before PIVC insertion [9, 12]. One
researcher conducted all the interventions in a unified
manner.
Heat application ‑1: Hot pack1) A hot pack (gel sealed in plastic: ­3MTM, Cold/Hot
Pack, 10 cm × 25 cm, 290 g, 3M Health Care, Tokyo,
Japan) was heated at 40 ± 2°C in a thermostatic chamber
filled with hot water (46℃) and patted with a dry towel.
2) It was applied to the participant’s forearm for sevenminutes. 3) After discontinuing heating, the participants
were instructed to rest for 4 min and 30 s. 4) A tourniquet(TTQ‐100‐1, TAIYO Instruments INC, Osaka, Japan)
was placed 10 cm proximal to the measurement site [26]and a constant pressure of approximately 75 mmHg wasapplied for 30 s [27].
Heat application ‑2: Moist hot towel

1) A face towel (48 × 66 cm, 81 g, dry), folded into a sizeof 11 × 24 cm was soaked in a thermostatic chamber
filled with hot water (46℃), and wrung out to 290 ± 5 g(the surface temperature of the towel was 40 ± 2°C). 2) It
was applied to the participants’ forearm for seven minutes. The following interventions were the same as in 3)
and 4) for heat application: 1.
Heat application ‑3: Dry hot towel

1) The moist hot towel was wrapped in a dry plastic bag(size, 25 × 35 cm; thickness, 0.02mm, hereafter referred
to as the “Dry-hot towel”). The surface temperature of
the dry hot towel was also 40 ± 2°C. 2) It was applied tothe participants’ forearm for seven minutes. The following interventions were the same as in 3) and 4) for heatapplication: 1.
The heating method applied to each item in this study
was validated to maintain a consistent temperature of
40 ± 2°C using thermography (R300, Nippon Avionics
Co., Ltd., Yokohama, Japan). This validation was accomplished through a preliminary process conducted 20
times for each item (Mean [SD], Hot pack: 41.4 [0.4] °C,
Dry hot towel: 41.1 [0.6] °C, Moist hot towel: 41.0 [0.6]°C). Therefore, the surface temperatures of the three
items were comparable. To ensure temperature stability,
no measurements were taken during each intervention,
mitigating any potential decrease in surface temperature
after preparation of the items. Applying 40 ± 2°C to theskin increases blood flow in the cutaneous veins [7]; thistemperature is also lower than 44°C, which can lead toYasuda et al. Journal of Physiological Anthropology (2023) 42:23

skin burns [28]. The resting time between heat application and tourniquet application was considered the timerequired to remove the heat applied during the actual
PIVC insertion [29–31]. The participants were instructed
to refrain from forearm movements, such as clenching afist, which affects venous dilation.
Data collection (Fig. 1)
Venous diameter and depth

The primary outcome measure was the venous diameter,a success factor for PIVC insertion [4]. Venous depth wasmeasured as a secondary outcome. These were measured using portable ultrasonography (Vscan Air, 11-3L

Page 4 of 14

probe, GE Healthcare, Little Chalfont, UK) before theintervention (baseline, T1), after the removal of heat
(after heating, T2), and at 30 s of tourniquet application(after applying the tourniquet, T3). The venous diameter (mm) was calculated as the average of the shortest
diameter (from the upper end to the lower end of thevein) and the longest diameter (perpendicular to theshortest diameter) (= [shortest diameter + longest diameter] / 2). Venous depth (mm) was measured as the vertical distance between the skin surface and the upper
end of the vein (Fig. 2). One researcher with experiencein measuring cutaneous vein size in previous studies [24,32] performed the measurements in this study under
the guidance of a study associate who was a registeredFig. 1 Protocol of the data collection. Measurements performed at each time point are shown in parentheses "●". Participants’ characteristics were
measured before heating on the first day. SCH, stratum corneum hydration; T1, baseline; T2, after heating; T3, after applying the tourniquet; T4,
at the end of each measurement day

Fig. 2 Measuring the venous diameter and the venous depth. The venous diameter (mm) was calculated as the average of the shortest diameter(from the upper end to the lower end of the vein) and the longest diameter (perpendicular to the shortest diameter) (= [shortest diameter + longest
diameter] / 2). Venous depth (mm) was measured as the vertical distance between the skin surface and the upper end of the vein

Yasuda et al. Journal of Physiological Anthropology (2023) 42:23

medical sonographer in cardiology and gastroenterology
with more than eight years of experience. The high reliability of the measurements was confirmed before thisstudy (ICC [2.1]; venous diameter, 0.975; venous depth,
0.929). Portable ultrasonography was performed after
confirming the reliability and validity of the measurements using previously used stationary ultrasonography(Aplio XG SSA-790A, PLT-1204AT probe, Canon Medical Systems, Tochigi, Japan). Before the measurement,
the gel was warmed to approximately the temperature of
the participant’s skin surface using a gel warmer.
Venous assessment score

The venous assessment score, which evaluates the palpability and visibility of veins on a 5-point scale [33], wasused at baseline (T1) and after applying the tourniquet(T3). This score was evaluated in a previous study thatcompared moist and dry hot towels [12]. The evaluation
degrees were as follows:1) veins are neither visible nor
palpable; 2) veins are visible but not palpable; 3) veins arebarely visible and palpable; 4) veins are visible and palpable; and 5) veins are clearly visible and easily palpable.
One researcher who was a licensed nurse with at least
three years of clinical experience standardized the evaluation. The researcher practiced for several days following prior instructions from an expert nurse and midwife
with at least five years of clinical experience [34]. Given
the remarkable agreement rate of 0.998 (weighted kappa
coefficient) between the assessments by the researcher
and their collaborator on the 26 data points, we concluded that there was no problem with the researcher’s
assessment skill.
Skin temperature on the heat application site

A skin surface thermometer (Hardware N543, NIKKISOTHERM CO. LTD., Tokyo, Japan) was used at the intervention site to measure the changes in skin temperature
at the heat application site over time (T1–T3). The measurement probe was placed at a location that did not overlap the venous measurement site within the range of thethermal item.
Stratum corneum hydration

Stratum corneum hydration (SCH) was performed using
a Corneometer® CM825 (Courage + Khazaka, Cologne,
Germany) at baseline (T1), after heating (T2), and after
applying the tourniquet (T3) to identify changes in watercontent in the stratum corneum of the forearms. The
measurements were repeated five times, and the mean of
the three values obtained was calculated, excluding the
maximum and minimum values.

Page 5 of 14

Subjective evaluation of the warmth

The participants were instructed to recall and evaluate
the degree of forearm warmth experienced during eachheat application at the beginning, just before the heatremoval, and after the applying the tourniquet. These
were evaluated at the end of each measurement day (T4).
The evaluation degrees of the warmth were as follows:
0 = feeling cold, 1 = feeling cold slightly, 2 = feeling nothing, 3 = feeling a little warmth, and 4 = feeling warmth.
Participants’ characteristics

The participants’ characteristics were measured on thefirst day. The participants were asked to provide information about their age, height, and experience with peripheral venipuncture (blood sampling or PIVC insertion)
failure using a 4-point scale: never, rarely, sometimes, andoften [35]. Body weight, body mass index (BMI), bodyfat percentage, and muscle mass were measured using abody composition analyzer (RD-917; TANITA, Tokyo,
Japan). Blood pressure and pulse were measured using
an electronic sphygmomanometer (ES-H56; TERUMO,Tokyo, Japan), and body temperature was measured
using an electronic thermometer (MC-681; OMRON,
Kyoto, Japan). The change in venous diameter before
and after tourniquet application was measured before
heat application (tourniquet only). The washout period
between the use of a tourniquet alone and heat application was 15 min [24].
Data analysis

For descriptive statistics, the mean (standard deviation[SD]; 95% confidence interval [CI]) and frequency (%) of
categorical variables were used. Least square mean (LSM)
was calculated using the mixed model. In terms of SCH,
changes in heating (T2 – T1) and changes after removed
heating (T3 – T2) were calculated. The skin temperature
was calculated every 30 s from T1 to T3. All data wereanalyzed using the JMP® Pro software, ver.16.1 (SASInstitute Inc., Cary, NC, USA). The significance level was
set at P ≤ 0.05. For comparisons between heat applications, Bonferroni correction was performed, and p-values were considered significant at α = 0.05 / 3 = 0.0167.
First, a one-way repeated ANOVA and Dunnett’s test
(tourniquet only = control, adjusted for baseline values)
using a mixed linear model were used to confirm thedilating effect of each heat application compared withtourniquet only on changes in the venous diameter andvenous depth (= after tourniquet ‒ baseline).
The following comparisons between the heat applications were performed: venous diameter, venous
depth, skin temperature, and subjective evaluation of
the warmth were analyzed using a two-factor repeatedYasuda et al. Journal of Physiological Anthropology (2023) 42:23

measures analysis of variance (ANOVA) with a mixedlinear model. In this model, the dependent variables werethe venous diameter, depth, skin temperature, and subjective evaluation of the warmth. The fixed effects, conditions, times, and interactions were determined. The
participants were statistically assigned to random effects.
One-way repeated ANOVA and Bonferroni correction
were used to compare interventions at each time point.
Comparisons between time points within groups were
performed using one-way repeated ANOVA and Dunnett’s test (baseline = control). The amount of change
in SCH was analyzed using one-way repeated ANOVA
and Bonferroni correction. In this model, the change in
the amount of SCH is the dependent variable. The effectsize (Cohen’s d) of these group comparisons of venous
diameter and depth. Cohen’s d was interpreted as negligible (< 0.2), small (0.2‒0.4), medium (0.5‒0.7), andlarge (≥ 0.8) [36]. Venous assessment scores were compared between heat applications within time points andbetween time points within heat applications (T1 vs. T3)
using the Freeman–Halton extension of Fisher’s exact
test and Bonferroni correction.

Results
Participant characteristics

This study was able to complete the measurements in
89 of the 90 participants. One participant was excluded
because her veins did not meet the measurement criteria

Fig. 3 Diagram of the study flow

Page 6 of 14

and 88 participants were included in the analysis (Fig. 3).
All participants had an average BMI of 20.2 (2.4) kg/m2
and a body fat percentage of 25.3 (4.9) %, which is thestandard for Japanese female in their twenties (Table 1).
Venous sizes before and after the tourniquet are shown in
Table 1. No adverse events such as burns occurred withthe use of these heat applications.
Comparison of the venous dilation effects

In terms of venous diameter, the amount of change
between baseline (T1) and after tourniquet (T3) application was found to be significantly greater for both hotpack (LSM: 0.59 [0.50–0.68] mm) and the dry hot towel(0.50 [0.42–0.59] mm) was significantly larger (P < .001,
P = .016) than that observed with the tourniquet only
(0.35 [0.26–0.43] mm). Conversely, the moist towel
exhibited a significantly smaller alteration (0.09 [0.00–
0.18] mm) compared to tourniquet only (P < .001).
Upon comparing the various heat application methods,
notable main effects were identified for heat application(F [2, 694.0] = 25.11, P < .001), time (F [2, 694.0] = 78.97,
P < .001), and interaction (F [4, 694.0] = 12.50, P < .001,
Table 2). No significant difference was observed
between using the hot pack and the dry hot towel, andthe effect size was negligible (T2: mean [95% CI] mm ofdifference:0.06 [-0.19–0.07], d = 0.12, P = .448, T3: 0.12[-0.25–0.02], d = 0.17, P = .120). However, the moist
hot towel application was significantly smaller than theYasuda et al. Journal of Physiological Anthropology (2023) 42:23

Page 7 of 14

Table 1 Participant’s characteristics (n = 88)
Characteristic

n

(%)

Mean

(SD)

Right

81

(92.0)

-

Left

7

(8.0)

Age (years)

-

21.7

(2.3)

BMI (kg/m2)

-

20.2

(2.4)

Dominant forearm-

Body fat percentage (%)

-

25.3

(4.9)

Body muscle mass (%)

-

35.7

(4.0)

Body temperature (°C)

-

36.6

(0.2)

Forearm area ­(cm2)

-

170.5

(18.3)

Pulse rate (beats/min)

-

67.4

(11.5)

Systolic BP (mmHg)

-

100.4

(7.5)

Diastolic BP (mmHg)

-

75.7

(18.5)

Venous diameter (mm)Before Tourniquet only

-

3.16

(0.77)

After Tourniquet only

-

3.51

(0.84)

Venous depth (mm)Before tourniquet only

-

4.12

(1.55)

After tourniquet only

-

3.82

(1.45)

Failure of venipuncture
Never

60

(68.2)

Rarely7(8.0)

Sometimes

7

(8.0)

14

(15.9)Often

BMI body mass index, BP blood pressure, SD standard deviation

hot pack at T2 and T3 (T2: P = . 006, T3: P < .001). The
moist hot towel was also significantly smaller than thedry hot towel at T3 (P < .001).
Regarding venous depth, there was also no significant
difference between the tourniquet only and each heatapplication at T3 (LSM [95%CI]; tourniquet only: -0.30[-0.19 – -0.40] mm, hot pack: -0.35 [-0.24 – -0.45] mm,
P = .955; dry hot towel: -0.27 [-0.16 – -0.37] mm, P = .828;
moist hot towel: -0.26 [-0.16 – -0.37] mm, P = .934).
When a comparison was made among the different heatapplications, a significant main effect was observed solely
for time (F [2,693.0] = 35.50, P < .001, Table 3). All threeheat treatments were significantly shallower from T1 to
T3 (P < .01, Table 3).
There was no significant difference in the ratio of
venous assessment scores between using the hot packand dry hot towel, and approximately 90% of the participants had a score of 3 or higher at T3 (hot pack, 95.5%;
dry hot towel, 89.7%). However, the ratio of these scoressignificantly differed between the moist towel and theother two heat applications at T3 (P < .001, Table 4).

Changes in skin temperature and subjective evaluationof the warmth

Skin temperature at the intervention site had significant main effects among heat applications (F [2,6959.0] = 746.88, P < .001), time (F [26, 6959.0] = 3838.08,
P < .001), and interaction (F [52, 6959.0] = 87.97, P < .001).
The dry hot towel from 120 s to T2 was significantly
lower than that of the hot pack (P < . 01, Fig. 4). In contrast, the difference in temperature between the hot
pack and two-towel methods at T2 was approximately
0.4 °C (mean [95% CI] °C of difference, dry hot towel:0.45[0.21–0.69]; moist hot towel:0.43 [0.19–0.67], P < .001 foreach). There was no significant difference between using
the hot pack and the dry hot towel from 450 s to T3, andboth at T3 maintained significantly higher temperatures
than at T1 (mean [95% CI] °C of difference, hot pack:1.70[1.50–1.89], dry hot towel:1.47 [1.34–1.59], P < .001 foreach). On the other hand, the moist hot towel application
showed a significantly higher temperature than the othertwo heat applications at 30–150 s (P < .001), but gradually
decreased after 210 s. The temperature of the moist hot
towel from T2 to T3 was significantly lower than that of
the other two heat applications (P < .001 for all).
Subjective evaluation of the warmth also had statistically significant main effects among the heat applications(F [2, 657.7] = 76.04, P < .001), time (F [2, 271.5] = 353.42,
P < .001), and interaction (F [4, 603.9] = 46.28, P < .001).
The use of the dry hot towel was significantly lower atthe beginning than at the other two heat applications(P < .001 each, Fig. 5). Thereafter, however, the use of the
moist hot towel scored significantly lower than that of theother two heat applications (just before removal: P < .001,
after tourniquet: P < .001).
Changes in SCH after applying and removing heat

There was no significant difference in the amount ofchange between the use of the hot pack and the dry hot
towel. In contrast, the moist hot towel significantly
increased SCH during heating (T2 – T1, P < .001) and significantly decreased SCH after heating (T3 – T2, P < .001)
compared to the hot pack (Table 5).

Discussion
This study compared the venous dilation effect of using
a hot towel (moist and dry heat) with a hot pack before
applying the tourniquet for PIVC insertion. Our results
showed that the moist hot towel was significantly inferior
to the hot pack and the dry hot towel in terms of venous
dilation under identical conditions. However, there wasno significant difference between the dry hot towel andthe hot pack. Therefore, dry hot towels and hot packs are

.816
-0.04
-1.32
.188

Pc

MD [95%CI]

t, d

Pc

0.02
0.53

MD [95%CI]

.658

t, d

-0.77

t, d

Pc

,0.04

[-0.10–0.02],0.06[-0.05–0.09],0.08[-0.09–0.05](0.76)

-0.02

3.17

(0.76)(0.81)

3.15
3.13

MD [95%CI]

Mean (SD)

Baseline

.056

1.93

0.11

.006

-3.01

-0.17

.448

-1.09

-0.06

3.23

3.34

3.39

A mixed-linear model for two-way repeated-measures ANOVA

One-way repeated-measures ANOVA and Dunnett’s test (T1 = control; * P < .01)

One-way repeated-measures ANOVA and Bonferroni correction (P < .0167)

a

b

c

,0.14

[-0.00–0.23],0.32[-0.30–0.05],0.12[-0.19–0.07](0.74)(0.84) *(0.77) *After heating< .0015.90

0.38< .001

-7.89

-0.49

.120

-1.84

-0.12

3.26

3.63

3.75

,0.46

[0.25–0.51],0.84[-0.63–0.35],0.17[-0.25–0.02](0.86)(0.84) *(0.85) *After tourniquet

T3

25.11 (2,694.0)

F(df)Condition

T2

b

T1

Main effectTime

CI conference interval, df degree of freedom, MD mean difference, SD standard deviation

Dry hot towel vs. Moist hot towel

Hot pack vs. Moist hot towel

Hot pack vs. Dry hot towel

Moist hot towel

Dry hot towel

Hot pack

Venous diameter (mm)Table 2 The venous diameter of hot towel (moist and dry heat) versus hot pack (n = 88)< .001Pa78.97 (2,694.0)

F(df)

Time

< .001Pa

12.50 (4,694.0)

F(df)< .001Pa

Interaction
Condition × Time

Yasuda et al. Journal of Physiological Anthropology (2023) 42:23
Page 8 of 14

0.02
.999
-0.01
0.02
.989
-0.01
0.15
.188

t, d

Pc

MD [95%CI]

t, d

Pc

MD [95%CI]

t, d

Pc

,0.01

[-0.11–0.13],0.01[-0.14–0.13],0.00[-0.14–0.14](1.47)(1.55)(1.58)

A mixed-linear model for two-way repeated-measures ANOVA

One-way repeated-measures ANOVA and Dunnett’s test (T1 = control; * P < .01)

One-way repeated-measures ANOVA and Bonferroni correction (P < .0167)

a

b

c

CI conference interval, df degree of freedom, MD mean difference, SD standard deviation

Dry hot towel vs. Moist hot towel

Hot pack vs. Moist hot towel

0.00

MD [95%CI]

4.18

Hot pack vs. Dry hot towel

Moist hot towel

4.19

Baseline

4.19

Mean (SD)

T3

.463

1.19

0.07

.345

0.12

0.01

.989

1.26

0.08

4.04

4.15

4.04

,0.12

[-0.07–0.22],0.01[-0.13–0.15],0.13[-0.06–0.21](1.52)(1.64)(1.51)

After heating

.882

1.19

0.07

.418

1.14

0.08

.389

1.19

0.08

3.91

3.92

3.84

,0.05

[-0.04–0.19],0.12[-0.08–0.23],0.13[-0.07–0.23](1.44) *(1.52) *(1.48) *After tourniquet
1.08(2,693.0)

F(df)Condition

T2

b

T1

Main effectTime

Dry hot towel

Hot pack

Venous depth (mm)Table 3 The venous depth of hot towel (moist and dry heat) versus hot pack (n = 88)

.340

P

a

35.50
(2,693.0)

F(df)

Time

< .001Pa

0.49(4,693.0)

F(df)

.741

Pa

Interaction
Condition × Time

Yasuda et al. Journal of Physiological Anthropology (2023) 42:23
Page 9 of 14

a

19
11

4: visible and palpable

5: clearly visible and easily palpable< .00154

3: barely visible and palpable0

5: clearly visible and easily palpable1

10

4: visible and palpable

2: visible but not palpable38

3: barely visible and palpable3

9

2: visible but not palpable

1: neither visible nor palpable31

1: neither visible nor palpable

N (%)

Hot pack(12.5)(21.6)(61.4)

(1.1)

(3.4)

(0.0)

(11.4)(43.2)(10.2)(35.2)< .001

9

17

53

3

6

0

12

31

10

35

(10.2)(19.3)(60.2)

(3.4)

(6.8)

(0.0)

(13.6)(35.2)(11.4)(39.8)

Dry hot towel

.194

2

15

39

8

24

0

11

28

13

36

(2.3)

(17.1)(44.3)(9.1)(27.3)(0.0)(12.5)(31.8)(14.8)(40.9)

Moist hot towel

Freeman–Halton extension of Fisher’s exact test and Bonferroni correction (P < .0167); bFreeman–Halton extension of Fisher’s exact test

Pb

T3
After tourniquet

T1
Baseline

Venous assessment score

Table 4 Comparison of changes in venous assessment score (n = 88)

.714

.761

P

< .001.669

Moist hot towel

Dry hot towela

Hot pack vs

Hot pack vs< .001.945

Moist hot towel

Dry hot towel vs

Yasuda et al. Journal of Physiological Anthropology (2023) 42:23
Page 10 of 14

Yasuda et al. Journal of Physiological Anthropology (2023) 42:23

Page 11 of 14

Fig. 4 Changes in the skin temperature on the heat application site (n = 88). A mixed linear model for two-way repeated-measures ANOVA;
One-way repeated-measures ANOVA and Dunnett’s test (T1 = control; * P < .001); One-way repeated-measures ANOVA and Bonferroni correction(†P < .0167, ‡ P < .001, a: moist hot towel > hot pack b: moist hot towel > dry hot towel, c: hot pack > dry hot towel, d: hot pack > moist hot towel, e:
hot pack and dry hot pack > moist hot towel). T1, baseline; T2, at the removal of heat; T3, after applying the tourniquetsuggested as effective venous dilation strategies for heatapplication before PIVC insertion.
Although dry hot towels (cotton and water) and hot
packs (gel sealed in dry plastic) are made of different
materials, the effect sizes of the differences in venous
diameter between the two methods were negligible, andapproximately 90% of the participants improved to a palpable dilated state after tourniquet use. The skin temperature after tourniquet (in other words five minutes after
the heat removal) was not significantly different between
these methods and remained significantly higher thanthat before (mean [95% CI] of difference, hot pack: 1.70
[1.50–1.89] °C, dry hot towel: 1.47 [1.34–1.59] °C). Therefore, both methods could apply heat to the skin temperature that could continuously promote venous dilation
for seven minutes. Consistent with previous studies thatused a hot pack [9, 11], the hot pack and the dry hot
towel significantly increased venous diameters before
and after the intervention compared to tourniquet onlyin this study. Thus, it can be inferred that dry hot towels

also effectively promote venous dilation before applying a
tourniquet.
On the other hand, there were two reasons why thevenous dilatation effect of using the moist hot towel before
PIVC insertion was inferior to that of the other two heatapplications. First, the heat of the moist hot towel dissipated to the skin and outside air in a short time, resulting inless thermal stimulation of the skin by the moist hot towel
at the end of heat application than by the hot pack. This is
supported by the results that the moist hot towel had thefastest peak out of skin temperature during heating, andsubjective evaluation of the warmth just before removal
was also significantly lower than that of the hot pack. The
second reason is probably because the heat of vaporization [37] occurring from the use of the moist hot towel was
greater than that of the hot pack from removal heating totourniquet application. The moist hot towel increased the
SCH during heat application more than the other two heatapplications and evaporated significantly after heating.
This was supported by the result that the skin temperature

Yasuda et al. Journal of Physiological Anthropology (2023) 42:23

Page 12 of 14

Fig. 5 Changes in subjective evaluation of the warmth. Subjective evaluation scores of the warmth: 0 = feeling cold, 1 = feeling cold slightly,
2 = feeling nothing, 3 = feeling a little warm, 4 = feeling warm. A mixed-linear model for two-way repeated-measures ANOVA; One-way
repeated-measures ANOVA and Dunnett’s test (at the beginning = control; all interventions were * P < .001): One-way repeated-measures ANOVA
and Bonferroni correction (†P < .001, a: hot pack and moist hot towel > dry hot towel, b and c: hot pack and dry hot towel > moist hot towel)

Table 5 Comparison of changes in stratum corneum hydration (n = 88)
SCH (A.U.)

Hot pack

Change in heating = T2 – T1
(After heating – Baseline)

Mean (SD)Dry hot towel
Moist hot towel
Hot pack vs. Dry hot towel

Hot pack vs. Moist hot towel

Dry hot towel vs. Moist hot towel

MD [95%CI]

Change after
removed = T3
– T2
(After tourniquet– After heating)12.2 (8.4)-5.3 (6.4)

10.2 (8.3)-5.1 (6.0)

35.1 (18.8)-28.4 (14.8)

2.00 [-2.48–6.59]

0.19 [-3.45–3.83]t, d

1.00, 0.24

0.12, 0.05

Pa

.319

.907

MD [95%CI]

22.87 [18.91–26.84]

23.30 [19.69–26.92]t, d

11.39, 1.42

14.24, 1.81

Pa

< .001< .001

MD [95%CI]

24.88 [20.43–29.33]

23.30 [20.11–26.50]

t, d

12.48, 1.56

14.41, 1.83

Pa

< .001< .001

A.U. arbitrary units, CI conference interval, MD mean difference, SCH stratum corneum hydration, SD standard deviationa

A mixed-linear model for one-way repeated-measures ANOVA and Bonferroni correction (P < .0167)

of the moist hot towel after heating was significantly lower
than that of the other two heat applications. Our resultsof the venous diameter and venous assessment score areconsistent with the results of Fink et al. (2009) that the success rate of PIVC insertion for moist heat stimulation wasinferior to that of dry heat stimulation [12]. In addition, thevenous dilation effect resulting from the application of the

moist hot towel was inferior to that of the only tourniquet.
This result could be attributed to the tendency of the veinsaffected by the moist hot towel to contract before tourniquet application due to the vaporization heat generated
after heating. Therefore, the moist hot towel application
would not be recommended.

Yasuda et al. Journal of Physiological Anthropology (2023) 42:23

Our results, which clarified that dry hot towels promote venous dilation as well as hot packs, are a new finding in medical practice where heat application methods
are varied. In the future, it could be recommended to use
hot packs or dry hot towels to promote venous dilation
before PIVC insertion. The dry hot towel in this study
was a cotton face towel available in ordinary households
that could be easily prepared by simply warming a face
towel in hot water, wringing it out, and wrapping it in aplastic bag. Therefore, dry hot towels could be an alternative to hot packs for in-home nursing care and disaster situations where hot packs cannot be prepared.
Conversely, the venous dilation effect induced by moist
hot towels is not only inferior to that of dry hot towels,
attributed to the influence of vaporization heat, but also
falls short of the results achieved by employing a tourniquet alone. Thus, when using a hot towel, the pivotal
step of enclosing it in a plastic bag is essential. It is necessary to examine the difference in the success rates of
PIVC insertion between dry hot towels and hot packs forpatients in the future.
This study had some limitations. First, the study population was limited to female students aged 18–29 years.
Second, while there was a notable level of agreement invenous assessment score between the researcher and theexpert nurse, the evaluator of this study was limited to asole researcher.

Conclusions
This study showed that a dry hot towel application for anaccess site for PIVC insertion promotes venous dilation
as well as using a hot pack. Considering the conditions ofpractice in hospitals and the home environment, a method
in which a towel warmed in hot water is wrapped in a dry
barrier and applied may be an alternative to a hot pack.
Abbreviations
ANOVA	Analysis of variance
A.U.	Arbitrary units
BMI	Body mass index
BP	Blood pressure
CI	Confidence intervals
df	Degree of freedom
LSM	Least square mean
MD	Mean difference
PR	Pulse rate
SD	Standard deviation
SCH	Stratum corneum hydration
PIVC	Peripheral intravenous catheter

Supplementary Information
The online version contains supplementary material available at https://​doi.​
org/​10.​1186/​s40101-​023-​00340-5.
Additional file 1.

Page 13 of 14

Acknowledgements
We would like to thank all those who participated in this study.
Authors’ contributions
KY designed and coordinated this study, carried out the data collection, andanalysis and interpretation of the data, and drafted and revised the manuscript. IS and RY contributed to the design of this study, interpretation of thestudy findings, and critically reviewed the manuscript. MM and SK contributed
interpretation of the study findings, and critically reviewed the manuscript. All
the authors approved the final version of the manuscript.
Authors’ information
KY (R.N., M.S.N.) is a PhD student in the Graduate School of Health Sciences,
Hokkaido University, Hokkaido, Japan. IS (R.N., PhD) and MM (M.T., R.M.S., PhD)
are assistant professors in the Faculty of Health Sciences, Hokkaido University,
Hokkaido, Japan. SK (M.T., R.M.S., PhD) is an associate professor in the Facultyof Health Sciences, Hokkaido University, Hokkaido, Japan. RY (R.N., PhD) is a
professor in the Faculty of Health Sciences, Hokkaido University, Hokkaido,
Japan.
Funding
This study was supported by JST SPRING, Grant Number JPMJSP2119.
Availability of data and materials
The datasets during and/or analyzed in the current study are available fromthe corresponding author upon reasonable request.

Declarations
Ethics approval and consent to participate
This study was approved by the ethics committee of the Hokkaido University
Faculty of Health Sciences (approval number: 22–22). Informed consent was
obtained from all participants prior to participating in the study. All methods
were performed in accordance with the relevant guidelines and regulations(e.g., Helsinki guidelines).
Consent for publication
We obtained consent for publication from our participants by oral explanation and documentation. Informed consent to participate in the study was
included in this process.
Competing interests
The authors declare that they have no competing interests.
Author details
1
Graduate School of Health Sciences, Hokkaido University, N12, W5, Kita‑Ku,
Sapporo, Hokkaido 060‑0812, Japan. 2 Faculty of Health Sciences, Hokkaido
University, N12, W5, Kita‑Ku, Sapporo, Hokkaido 060‑0812, Japan.
Received: 25 June 2023 Accepted: 22 September 2023
Published: 19 October 2023

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