Regional variations in pain to controlled mechanical skin traumas from automatic needle insertions and relations to ultrasonography

Multi-modal transducer-waveguide construct coupled to a medical needle

Annually, more than 16 × 109 medical needles are consumed worldwide. However, the functions of the medical needle are still limited mainly to cutting and delivering material to or from a target site. Ultrasound combined with a hypodermic needle could add value to many medical applications, for example, by reducing the penetration force needed during the intervention, adding precision by limiting the needle deflection upon insertion into soft tissues, and even improving tissue collection in fine-needle biopsy applications. In this study, we develop a waveguide construct able to operate a longitudinal-flexural conversion of a wave when transmitted from a Langevin transducer to a conventional medical needle, while maintaining high electric-to-acoustic power efficiency. The optimization of the waveguide structure was realized in silico using the finite element method followed by prototyping the construct and characterizing it experimentally. The experiments conducted at low electrical power consumption (under 5 W) show a 30 kHz flexural needle tip displacement up to 200 μm and 73% electric-to-acoustic power efficiency. This, associated with a small sized transducer, could facilitate the design of ultrasonic medical needles, enabling portability, batterization, and improved electrical safety, for applications such as biopsy, drug and gene delivery, and minimally invasive interventions.

Injectability as a function of viscosity and dosing materials for subcutaneous administration

Injectability is a term related to the ease of parenteral administration of a dosing solution, and includes dose preparation, dose administration, ergonomics related to these procedures, pain of injection, and other adverse events at the injection site. This article focuses on force measurements related to injectability, namely: force to expel syringe contents (expulsion force - a mimic for in vivo injection force), needle-penetration force, and needle-bending force, and these results are supplemented by expulsion time measurements with 18 participants, as well as injections in a porcine model. Based on the expulsion time measurements, where 80 N injection force was found to be difficult for most people, we consider the maximum acceptable injection force to be 40 N, and recommend targeting no more than 20 N, especially if the configuration may be used in an autoinjector or similar device. The injectability of antisense oligonucleotide solutions was assessed to determine optimal dosing materials (among those evaluated) for a variety of solution viscosities. Dosing materials varied in syringe inner diameter, needle inner diameter, needle length, and needle wall thickness: standard-wall vs. thin-wall. In general, short (6-8 mm) thin-wall needles are recommended as a way to improve patient perception and comfort during subcutaneous dose administration.

A Delphi-Based Consensus Statement on the Management of Anticoagulated Patients With Botulinum Toxin for Limb Spasticity

OBJECTIVE

To create a consensus statement on the considerations for treatment of anticoagulated patients with botulinum toxin A (BoNTA) intramuscular injections for limb spasticity.

DESIGN

We used the Delphi method.

SETTING

A multiquestion electronic survey.

PARTICIPANTS

Canadian physicians (N=39) who use BoNTA injections for spasticity management in their practice.

INTERVENTIONS

After the survey was sent, there were e-mail discussions to facilitate an understanding of the issues underlying the responses. Consensus for each question was reached when agreement level was ≥75%.

MAIN OUTCOME MEASURES

Not applicable.

RESULTS

When injecting BoNTA in anticoagulated patients: (1) BoNTA injections should not be withheld regardless of muscles injected; (2) a 25G or smaller size needle should be used when injecting into the deep leg compartment muscles; (3) international normalized ratio (INR) level should be ≤3.5 when injecting the deep leg compartment muscles; (4) if there are clinical concerns such as history of a fluctuating INR, recent bleeding, excessive or new bruising, then an INR value on the day of injection with point-of-care testing or within the preceding 2-3 days should be taken into consideration when injecting deep compartment muscles; (5) the concern regarding bleeding when using direct oral anticoagulants (DOACs) should be the same as with warfarin (when INR is in the therapeutic range); (6) the dose and scheduling of DOACs should not be altered for the purpose of minimizing the risk of bleeding prior to BoNTA injections.

CONCLUSIONS

These consensus statements provide a framework for physicians to consider when injecting BoNTA for spasticity in anticoagulated patients. These consensus statements are not strict guidelines or decision-making steps, but rather an effort to generate common understanding in the absence of evidence in the literature.

Evaluation of Pain and Specimen Quality by Use of a Novel 25-Gauge Blood Collection Set With Ultra-Thin Wall Cannula and 5-Bevel Tip Design

BACKGROUND

Phlebotomy has significant impact on overall patient satisfaction. Smaller gauge needles, such as a 25 gauge, may lessen patient discomfort but increase hemolysis and tube-filling times. Our studies evaluated the effect of a 5-bevel, 25-gauge blood collection set (BCS) with ultra-thin wall cannula [BD Vacutainer® UltraTouch™ Push Button BCS (UltraTouch)] on patient pain and anxiety compared with two 3-bevel, thin-wall, 23-gauge BCSs [BD Vacutainer® Safety-Lok™ (Safety-Lok) and Greiner Bio-One Vacuette® (Vacuette)]. Our studies also evaluated the 25-gauge UltraTouch for sample quality and tube filling compared with the 3-bevel, thin-wall, 23-gauge BD Vacutainer Push Button BCS.

METHODS

We conducted 2 studies with 214 subjects to compare pain and anxiety regarding future phlebotomy with the 3 aforementioned devices. Another study with 52 subjects assessed hemolysis in specimens collected with the UltraTouch and Push Button BCS; bench testing evaluated tube-filling times with these devices. A questionnaire captured pain upon needle insertion, overall pain, and anxiety regarding future phlebotomy. Hemolysis was evaluated visually, by Hemolysis Index and hemolysis-sensitive indicators potassium (K) and lactate dehydrogenase (LDH).

RESULTS

A statistically significant decrease was noted for overall pain with UltraTouch compared with Vacuette and with insertion pain compared with Safety-Lok. There was no significant difference in anxiety regarding future phlebotomy. No increase was observed in Hemolysis Index, K or LDH. Tube-filling times were comparable for each device.

CONCLUSIONS

The 25-gauge UltraTouch provided less overall pain compared with the 23-gauge Vacuette, less pain upon needle insertion than the 23-gauge Safety-Lok, and no compromise in specimen quality or flow rate.

The Effect of Microneedle Thickness on Pain During Minimally Invasive Facial Procedures: A Clinical Study

BACKGROUND

Minimally invasive procedures are becoming increasingly popular because they require minimal downtime and are effective for achieving a more youthful appearance. The choice of needle for minimally invasive procedures can be a major factor in the patient's comfort level, which in turn affects the physician's comfort level.

OBJECTIVES

In this comparative study, the authors assessed levels of pain and bruising after participants were injected with 30-gauge or 33-gauge (G) microneedles, which are commonly used for minimally invasive injection procedures.

METHODS

Twenty healthy volunteers were recruited for this prospective study. Eight injection points (4 on each side of the face) were determined for each patient. All participants received injections of saline with both microneedles in a randomized, blinded fashion. Levels of pain and bruising were assessed and analyzed for significance.

RESULTS

The highest level of pain was in the malar region, and the lowest level was in the glabella. Although all pain scores were lower for the 33-G microneedle, the difference was significant only for the forehead. Because most minimally invasive procedures require multiple injections during the same sitting, the overall procedure was evaluated as well. Assessment of the multiple-injection process demonstrated a significant difference in pain level, favoring the 33-G needle. Although the difference in bruising was not statistically significant between the 2 needles, the degree of bruising was lower with the 33-G needle.

CONCLUSIONS

For procedures that involve multiple injections to the face (such as mesotherapy and injection of botulinum toxin A), thinner needles result in less pain, making the overall experience more comfortable for the patient and the physician.

LEVEL OF EVIDENCE

3.

The role of comfort and discomfort in insulin therapy

Despite the recognized importance of optimal insulin therapy, patient adherence to insulin therapy is an ongoing clinical care challenge. Insulin omission continues to be frequent and underestimated and has been correlated with poorer glycemic control and increased rates of diabetes-related complications. Insulin users consistently identify multiple factors that contribute to insulin injection-related anxiety and to non-adherence. Injection-related discomfort continues to bear a significant contribution. Over the last decade, with advances in needle manufacturing technology, shorter and narrower needles have been associated with progressively improving patient self-rating of injection discomfort. Consequently, patient surveys of insulin users show discomfort to rank in the bottom third of significant contributors by prevalence. However, healthcare providers (HCP) and family member care providers continue to demonstrate a high level of anticipated and perceived pain for the patient. HCP anxiety and pain anticipation are each associated with patient anxiety and may therefore play a significant contributing role in patient non-adherence.

Effect of microneedle design on pain in human volunteers

OBJECTIVES

To design microneedles that minimize pain, this study tested the hypothesis that microneedles cause significantly less pain than a 26-gauge hypodermic needle, and that decreasing microneedle length and the number of microneedles reduces pain in normal human volunteers.

METHODS

Single microneedles with lengths ranging from 480 to 1450 microm, widths from 160 to 465 microm, thicknesses from 30 to 100 microm, and tip angles from 20 to 90 degrees; and arrays containing 5 or 50 microneedles were inserted into the volar forearms of 10 healthy, human volunteers in a double-blinded, randomized study. Visual analog scale pain scores were recorded and compared with each other and to the pain from a 26-gauge hypodermic needle.

RESULTS

All microneedles investigated were significantly less painful than the hypodermic needle with microneedle pain scores varying from 5% to 40% of the hypodermic needle. Microneedle length had the strongest effect on pain, where a 3-fold increase in length increased the pain score by 7-fold. The number of microneedles also affected the pain score, where a 10-fold increase in the number of microneedles increased pain just over 2-fold. Microneedle tip angle, thickness, and width did not significantly influence pain.

DISCUSSION

Microneedles are significantly less painful than a 26-gauge hypodermic needle over the range of dimensions investigated. Decreasing microneedle length and number of microneedles reduces pain.

Does needle size matter?

Hypodermic needles are in widespread use, but patients are unhappy with the pain, anxiety, and difficulty of using them. To increase patient acceptance, smaller needle diameters and lower insertion forces have been shown to reduce the frequency of painful injections. Guided by these observations, fine needles and microneedles have been developed to minimize pain and have found the greatest utility for delivery of vaccines and biopharmaceuticals such as insulin. However, pain reduction must be balanced against limitations of injection depth, volume, and formulations introduced by reduced needle dimensions. In some cases, needle-free delivery methods provide useful alternatives.

Pain following controlled cutaneous insertion of needles with different diameters

BACKGROUND AND AIM

Needle injections are used daily by millions of people around the world for the administration of various drugs (e.g., insulin), venepuncture, and some neurophysiological procedures. The aim of this paper was to study the influence of the outer needle diameter on the pain evoked by controlled needle insertion.

METHODS

An automated needle injection system was used to perform a series of insertions where velocity, angle of insertion, and depth of injection were controlled. The frequency of pain following needle insertions (23G, 27G, 30G, 32G) was recorded together with the pain intensity (measured using the visual analogue scale--VAS) and the occurrence of bleeding.

RESULTS

The outer needle diameter was positively and significantly correlated to the frequency of the insertion pain; for example, 63% of insertions with 23G needles caused pain, 53% of insertions with 27G and 31% of insertions with the thinnest (32G) needle (p < 0.0001) caused pain. The thickest needle caused most insertions associated with bleeding. Bleeding insertions were approximately 1.3 times more painful (as indicated by VAS scores) than insertions without concomitant bleedings (p = 0.004).

CONCLUSION

By decreasing the outer diameter of a needle, the frequency of insertion pain can be reduced and may encourage patients to adhere to demanding injection regimens such as recurrent insulin administration.

Painful and non-painful pressure sensations from human skeletal muscle

Painful and non-painful pressure sensations from muscle are generally accepted to exist but the peripheral neural correlate has not been clarified. The aim of the present human study was to assess the non-painful and painful pressure sensitivity with (1) anaesthetised skin, and (2) anaesthetised skin combined with a block of large diameter muscle afferents. The skin was anaesthetised by a topically applied anaesthetic cream and later lidocaine was administrated subcutaneously. The pressure sensitivity was assessed quantitatively by computer-controlled pressure stimulation on the anterior tibial muscle. Thresholds to detection, pain and pain tolerance were assessed. In the first experiment, computer-controlled needle insertion depths evoking touch and pain sensations were used to assess the efficacy of cutaneous anaesthesia. Touch and pain sensations evoked during needle insertions were found to be superficial in intact skin but when anaesthetised, touch sensation was occasionally evoked at depths related to penetration of the fascia. With the skin completely anaesthetised to brush and von Frey hair pinprick stimulation, skin indentation with the strongest von Frey hair caused a sensation described as a deep touch sensation. Simultaneously, pressure detection and pain thresholds increased but it was still possible to elicit non-painful and painful pressure sensation in all subjects. In a second experiment, a differential nerve block of group I and II afferent fibres was obtained by full-leg ischaemia simultaneously with cutaneous anaesthesia. The efficacy of the tourniquet block was continuously assessed by a battery of somatosensory tests (heat, brush, vibration, electrical and movement detection) applied at the foot simultaneously with pressure stimulation on the anterior tibial muscle. After 20 min of ischaemia, group II afferent fibres mediating the sensations of movement detection, vibration and brush on the foot was blocked but the heat pain threshold was not affected. In this condition (anaesthetised skin and block of group I and II fibres from deep tissue) a pressure sensation was evoked in 70% of subjects although the pressure detection threshold was increased. The pressure pain sensitivity was decreased, which, however, might indicate a partial block of group III and IV muscle afferents. In a third experiment, the tactile sensations elicited by electrical stimulation of the tibialis anterior muscle and skin at the lower leg were significantly decreased after 20 min of ischaemia, validating the blocking effects of group I and II nerve fibres. The present data show a marginal contribution of cutaneous afferents to the pressure pain sensation that, however, is relatively more dependent on contributions from deep tissue group III and IV afferents. Moreover, a pressure sensation can be elicited from deep tissue probably mediated by group III and IV afferents involving low-threshold mechanoreceptors.