The Effectiveness of Lidocaine Spray in Reducing Pain During Intramuscular Injection: A Randomized Controlled Trial

Introduction

Intramuscular (IM) injection is a standard nursing procedure widely used in clinical practice for administering medications. However, improper administration can lead to various complications, including pain, muscle tightness, sterile abscess formation, tissue necrosis, granuloma, nerve injuries, intravascular injection, and hemorrhage (Aydin & Avşar, 2019). Despite the therapeutic benefits of IM injections, they are often associated with significant discomfort and pain, which can affect patient compliance and satisfaction.

Injections are one of the most frequently performed medical procedures globally, with approximately 16 billion injections administered annually in developing and transitioning countries (Jin et al., 2015). Effective administration of IM injections requires technical proficiency and careful decision-making regarding the appropriate tools and techniques. Pain during IM injection primarily results from mechanical trauma caused by needle penetration and the rapid pressure exerted during drug administration (Sedat et al., 2019).

IM injections involve the delivery of medication deep into selected muscles, which have rich vascularization, enabling rapid absorption into systemic circulation while bypassing first-pass metabolism. These injections are commonly used for both preventive (e.g., vaccinations) and therapeutic purposes, with over 95% of IM injections administered for treatment (Gutierrez & Munakomi, 2023).

In recent years, advancements in pain management have significantly influenced nursing practice, emphasizing the importance of minimizing patient discomfort. Nurses play a crucial role in pain relief, as they are directly involved in patient care. Effective pain management depends on nurses’ knowledge, competencies, and approach to painful procedures. Therefore, it is their responsibility to administer injections carefully and provide pain relief to improve patient outcomes (Aydin & Güven, 2020).

To reduce injection-related pain, both pharmacological and non-pharmacological interventions are utilized. Among the pharmacological approaches, topical anesthetics such as prilocaine, piroxicam creams, and lidocaine spray are commonly used (Kaplan et al., 2023). Lidocaine, a widely used local anesthetic, is frequently administered as a spray in clinical settings due to its moderate effectiveness in numbing the skin and mucous membranes (Marvi et al., 2023).

Lidocaine spray functions as a topical anesthetic, blocking nerve signals in the body to provide short-term pain relief. It is commonly used for medical procedures such as injections, minor surgeries, dental treatments, and insect bites. Additionally, it offers relief for conditions like sunburn and minor burns (Jamalinik et al., 2023; Hoseini et al., 2022). The 10% lidocaine spray formulation is particularly advantageous due to its rapid onset of action, painless application, easy availability, cost-effectiveness, and pleasant odor (Kulkarni et al., 2023).

The mechanism of pain alleviation with lidocaine is based on its ability to block sodium channels, thereby preventing nerve transmission and reducing pain perception. Its rapid onset and moderate efficacy make it a preferred choice for local anesthesia and pain relief in various medical applications (Marvi et al., 2023).

Aim of the Study

This study aims to evaluate the effectiveness of lidocaine spray in reducing pain levels associated with intramuscular injections. By comparing pain perception between patients receiving lidocaine spray and those in a control group, the study seeks to determine whether this intervention can serve as an effective and practical pain management strategy in clinical settings.

Materials and Methods

Study Design

This study was designed as a single-blind, randomized controlled trial to assess the effectiveness of lidocaine spray in reducing pain severity during intramuscular (IM) injections.

Blinding

A single-blind approach was employed, where the researcher was aware of the treatment allocation, but the participants were blinded to their assigned group. This blinding method ensured that participants' knowledge of treatment assignment did not influence their pain perception, thereby minimizing potential bias.

Study Setting

The study was conducted at Imam Al-Sadiq General Hospital in Babylon, Iraq, over a period spanning December 28, 2023, to February 14, 2024.

Sample and Sampling Procedure

The sample size was determined using power analysis, with a 95% confidence level and a 5% margin of error, leading to a calculated sample size of 100 participants. The study population consisted of adult patients admitted to the emergency department who required an intramuscular injection of diclofenac sodium.

Participants were randomly assigned to either the lidocaine spray group (n = 50) or the control group (n = 50) through a simple randomization process. This involved drawing a sealed envelope containing a color-coded assignment (yellow for the lidocaine spray group and green for the control group).

Eligible participants were briefed on the study objectives, and those who provided informed consent completed a baseline questionnaire before receiving the IM injection. Pain levels were evaluated using the Visual Analog Scale (VAS) one minute after the injection.

Intervention

Experimental Group (Lidocaine Spray Group)

1. The injection site was disinfected using an alcohol swab and allowed to dry (Bilgiç, 2021; Chung & Wong, 2002; Derya et al., 2015).
2. Two puffs of lidocaine spray (20 mg) were applied from a distance of 5 cm.
3. The lidocaine spray was left to act for 1 to 5 minutes, followed by a 2-minute waiting period before drug injection (Khosravi Pour et al., 2023).
4. The intramuscular injection was then administered into the ventrogluteal region at a 90-degree angle.

Control Group (No Lidocaine Spray Group)

1. The injection site was disinfected using an alcohol swab.
2. The intramuscular injection was administered without the use of lidocaine spray, specifically in the ventrogluteal region.

Data Collection Tools

1. Questionnaire Form

   • The questionnaire consisted of seven questions assessing participants' age, gender, place of residence, educational level, fear of needles, height, and weight.
   • The questionnaire was completed before the injection.

2. Visual Analog Scale (VAS)

   • The VAS is a 10 cm horizontal scale ranging from 0 ("no pain") to 10 ("severe pain") (Karabey, 2021; Aydin & Güven, 2020).
   • After the injection, participants were asked to mark their pain level on the scale.
   • Pain intensity was categorized into four levels:
     • No pain (0 points)
     • Mild pain (1–3 points)
     • Moderate pain (4–6 points)
     • Severe pain (7–10 points) (Karasu et al., 2017).

Reliability and Validity of the Scale

The Visual Analog Scale (VAS) is a widely used and validated tool for pain assessment. Previous studies confirm that VAS is reliable and valid for evaluating pain in adults aged 18 and above (Begum & Hossain, 2019; Joseph & Palappallil, 2017; Mandysová & Kadlečková, 2015).

Ethical Considerations

The study was approved by the Committee of Scientific Research at the College of Nursing, University of Karbala (Approval Code: uok.con.23.019, Decision No: 2023.11.19, Iraq).

As part of an original randomized controlled trial, the trial protocol was registered in the Iranian Registry of Clinical Trials (IRCT) on February 21, 2024. The trial registration details are as follows:

• IRCT Registration Reference: IRCT20240127060820N1
• Trial ID: 75385
• Membership Number: 60820

All participants provided informed consent, and strict confidentiality was maintained throughout the study.

Results

Demographic Characteristics of the Study Sample

The study included 100 participants randomly assigned to two groups: Lidocaine Spray Group (n = 50) and Control Group (n = 50). The participants' demographic and clinical characteristics are summarized in Table 1.

Table 1: Demographic and Clinical Characteristics of the Study Participants

Pain Assessment Results

Pain levels were evaluated using the Visual Analog Scale (VAS), and the distribution of pain intensity across both groups is presented in Table 2.

Table 2: Pain Level Assessment Among Study Groups

Interpretation:

• In the Lidocaine group, most participants (66.0%) reported mild pain, while 24.0% experienced no pain at all.
• In contrast, in the Control group, the majority (56.0%) experienced moderate pain, and 18.0% reported severe pain.
• The mean pain score was significantly lower in the Lidocaine group (1.27 ± 1.340) compared to the Control group (4.46 ± 2.022).

Comparison of Pain Levels Between Groups

A t-test was conducted to compare pain levels between the two groups (Table 3).

Table 3: Effect of Lidocaine Spray on Pain Level

Interpretation:

• The t-value of 7.985 and p-value < 0.001 indicate a highly significant difference in pain levels between the groups.
• The effect size (η² = 0.39) suggests a large practical effect of lidocaine spray in reducing pain intensity.

Predictors of Pain Levels in the Lidocaine and Control Groups

A simple linear regression analysis was performed to examine predictors of pain levels in both groups.

Table 4: Predictors of Pain Levels in the Lidocaine Group

Table 5: Predictors of Pain Levels in the Control Group

Interpretation:

• BMI was a significant predictor of pain levels in both groups.
  • In the Lidocaine group, higher BMI was associated with slightly lower pain levels (β = -0.113, p = 0.028).
  • In the Control group, higher BMI significantly increased pain levels (β = -0.374, p = 0.016).
• Other variables (age, sex, residence, education level, and fear of needles) were not significant predictors in either group.

Summary of Findings:

• Lidocaine spray significantly reduced pain compared to the control group (p < 0.001).
• Most participants in the Lidocaine group experienced mild or no pain, whereas the control group reported moderate to severe pain.
• BMI was a significant predictor of pain intensity, with higher BMI correlating with increased pain in the control group.
• No other demographic factors significantly influenced pain perception.

  Discussion

  This study aimed to assess the effectiveness of lidocaine spray in reducing pain perception during intramuscular (IM) injections and to examine the influence of socio-demographic factors on pain intensity. The findings revealed a significant reduction in pain levels among participants who received lidocaine spray compared to the control group.

  A majority (66%) of participants in the lidocaine group reported mild pain (VAS: 1.27 ± 1.340), while 24% experienced no pain. Conversely, 56% of participants in the control group reported moderate pain, and 18% experienced severe pain, with a significantly higher mean pain score (VAS: 4.46 ± 2.022, p < 0.001).

  These results align with previous studies:

  • Jamalinik et al. (2023) also used the Visual Analog Scale (VAS) to evaluate the effects of lidocaine and cold spray on IM injection pain. Their findings showed a significant reduction in pain levels, with mean VAS scores of 2.63 in the intervention group versus 3.44 in the control group.
  • Hoseini et al. (2022) compared lidocaine spray and acupressure for IM injections and found lower pain levels in the lidocaine spray group (VAS: 1.78) and acupressure group (VAS: 1.83) compared to the control group (VAS: 2.83).

  The pain-reducing effects of lidocaine spray can be attributed to its mechanism of action as a local anesthetic. Lidocaine inhibits voltage-gated sodium channels, preventing neuronal depolarization and reducing pain transmission (Zdybski & Grodzka, 2018).

  Effect of Socio-Demographic Factors on Pain Perception

  1. Body Mass Index (BMI) and Pain Intensity

  This study found a significant relationship between BMI and pain intensity:

  • In the lidocaine group, higher BMI was associated with slightly lower pain levels (β = -0.113, p = 0.028).
  • In the control group, higher BMI significantly increased pain intensity (β = -0.374, p = 0.016).

  These results contrast with Bedel et al. (2022), who studied vapocoolant spray for IM injection pain relief and found no significant association between BMI and pain intensity (p = 0.183). This discrepancy may stem from differences in pain perception, patient experiences, emotional states, and healthcare provider techniques. Further research is needed to explore these inconsistencies.

  2. Age and Sex

  No significant differences in pain levels were observed based on age (p = 0.939) or sex (p = 0.052). These findings are consistent with previous research by Jamalinik et al. (2023), Bedel et al. (2022), and Gürdap & Cengiz (2022), which reported no statistically significant influence of age or sex on pain intensity following IM injections.

  3. Education Level and Pain Perception

  The results showed no significant association between education level and pain intensity in both groups (p = 0.290 in the lidocaine group, p = 0.543 in the control group). This aligns with studies by Abdelkhalek (2019) and Aydin & Avşar (2019), who found that education level does not significantly impact pain perception during medical procedures.

  4. Fear of Needles

  Fear of injections did not significantly correlate with pain perception in either group (p = 0.295 in the lidocaine group, p = 0.741 in the control group). This is consistent with findings from Bilge et al. (2019), who examined the effectiveness of cold spray and shot-blocker in reducing IM injection pain. Their study found that fear of injections did not significantly impact pain levels (p = 0.061).

  5. Residency (Urban vs. Rural)

  The results indicated that place of residence (urban vs. rural) did not significantly affect pain perception (p = 0.726 in the lidocaine group, p = 0.542 in the control group). These findings are in line with previous studies, including Heshmatifar et al. (2022) and Karabey & Karagzolu (2021), which reported similar results.

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  Conclusion and Recommendations

  Conclusion

  This study demonstrated that lidocaine spray is an effective intervention for reducing pain during intramuscular injections. Participants who received lidocaine spray experienced significantly lower pain levels compared to the control group (p < 0.001).

  Among socio-demographic factors, BMI was a significant predictor of pain intensity, whereas age, sex, education level, fear of needles, and place of residence had no significant impact.

  Recommendations

  Based on these findings, the following recommendations are proposed:

  1. Routine Use of Lidocaine Spray: Healthcare providers should consider incorporating lidocaine spray as a standard practice for intramuscular injections to improve patient comfort and compliance.
  2. Further Research: Future studies should investigate the long-term effects of lidocaine spray and its effectiveness in different clinical settings.
  3. Larger Sample Size: Conducting studies with larger and more diverse populations will help validate these findings and explore potential differences across various patient groups.
  4. Comparative Studies: Further research comparing lidocaine spray with other pain-relief techniques (e.g., vapocoolant spray, acupressure, and distraction methods) is recommended.

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  Limitations

  This study has some limitations:

  • The study focused only on patients receiving intramuscular diclofenac sodium, which may limit the generalizability of findings to other medications.
  • Pain perception is subjective and influenced by individual variability, including previous experiences and emotional states.
  • The study was conducted in a single hospital setting, which may not reflect broader population dynamics.

  To address these limitations, future research should explore a wider range of medications, multiple hospital settings, and psychosocial factors influencing pain perception.

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  Acknowledgments

  The author expresses gratitude to all participants who contributed to this study. Special appreciation is extended to:

  • The College of Nursing, University of Kerbala, for academic guidance and ethical approval.
  • Imam Al-Sadiq General Hospital, Babylon, Iraq, for providing the research setting and logistical support.
  • The dedicated nursing staff and healthcare professionals who assisted in the implementation of this study.