Full text of DOI:10.1007/s12009-001-0072-3

A B S T R A C T
In a double-blind study, room-temperature lidocaine was injected
randomly into 1 eyelid of 40 patients during facial anesthesia. The
other eyelid of the same eye received injection of warm lidocaine
(
group 1) or bicarbonate-buffered lidocaine (group 2). Based on a
pain scale, warming or buffering lidocaine did not significantly
reduce the amount of infiltration pain. Buffering lidocaine was
effective in reducing the quality of pain, as judged by the patient’s
report of dominant pain.
O R I G I N A L A R T I C L E
Effect of Warming and Buffering Lidocaine
on Pain During Facial Anesthesia
Haluk Talu, MD, Orhan Elibol, MD, Ates Yanyali,
MD, Levent Karabas, MD, Banu Alp, MD, &
Yusuf Çaglar, MD
mall-incision cataract surgery procedures have
S
provided simpler techniques such as topical intra-
cameral, subconjunctival, and sub-Tenon anesthesia,
but ophthalmologists still use bulbar and facial anes-
thesia in most of their procedures. Although local
anesthetic agents are used for analgesia, they can
cause considerable discomfort, especially on skin
1-3
infiltration. The needle size, the volume of the anes-
thetic agent, and the rate of injection have been
4
shown to cause pain. On the other hand, the chemical
properties of the local anesthetics and their interac-
tion with nerves have been shown to play an impor-
tant role in pain development. Several studies have
explored the relationship between various factors and
pain of injection. The effect of pain reduction of warm-
5
,6
7,8
ing and pH adjustment of local anesthetics has
been investigated by some researchers, but their
9
-11
results are conflicting.
This study was made to assess whether warming
or buffering lidocaine would reduce infiltration pain
in patients receiving facial anesthesia for their
cataract surgeries.
Materials & Methods
Forty patients, who were to undergo cataract extrac-
tions with the use of retrobulbar anesthesia combined
with facial anesthesia, were enrolled into this prospec-
tive, randomized, double-blind study, according to the
study design approved by our institution’s ethics com-
mittee. Informed consent was obtained. Patients were
randomized into 2 groups of 20 each, according to the
anesthetic solutions used for facial anesthesia. In
Reprints:
Haluk Talu, MD, Sarigul Sok. Nigar Ap. 4/3, 81080 Caddebostan, Istanbul, Turkey.
The authors are from the Ophthalmology Department, Kocaeli University School of
Medicine, Kocaeli,Turkey.
ANN OPHTHALMOL. 2001;33(1):43–47
43

group 1 patients, room-temperature lidocaine was
injected into either the inferior or superior eyelid,
selected randomly, of the eye undergoing surgery, and
lidocaine warmed to body temperature was injected
into the other eyelid of the same eye. Patients in group
block of each eyelid, the amount of pain sensation was
asked and recorded as the pain score of the particular
anesthetic solution used. When the injections to both
eyelids were completed, and the pain scores were
recorded, the patient was asked, ignoring the pain
scores given, whether any of the injections had caused
a stronger, long-lasting, or more apparent pain. The
reply was recorded as the preference of dominant pain
sensation. Even in cases when the pain scores of both
solutions were the same, the patient was asked
whether the pain was sharper on 1 of the injections.
In this study, the sensation of pain was evaluated in
2 forms: The quantity of pain felt during skin infiltra-
tion was recorded as the pain score, and the relative
comparison of discomfort felt during the anesthesia
was recorded as the dominant pain. The pain score thus
was quantitative and dominant pain was a qualitative
measurement of the sensation of pain during facial
anesthesia. Linear analogue pain scores were evaluated
with Wilcoxon matched pairs signed rank test. The
2
also randomly received injection of room-tempera-
ture lidocaine in 1 eyelid, but the other eyelid received
injection of buffered lidocaine as the anesthetic solu-
tion during facial anesthesia.
Demographic data are listed in Tables 1 and 2 for
group 1 and group 2, respectively. Group 1 was com-
posed of 12 men and 8 women, with a mean age of 66.5
years (SD, 8.5). Group 2 had 10 men and 10 women,
with a mean age of 69.8 years (SD, 10.22).
Lidocaine (2-mL Jetocaine ampoules consisting of
2
0 mg/mL lidocaine hydrochloride and 0.0125 mg/mL
adrenaline) was used as the local anesthetic agent. In
this study, lidocaine solutions referred to as room-tem-
perature lidocaine were stock lidocaine ampoules,
which a pilot study showed were at 19°C to 20°C when
kept at room temperature. The same pilot study
showed that warming stock lidocaine ampoules in a
baby bottle warmer (Avent) up to 48°C was found to
provide lidocaine at 36.5°C to 38.0°C for 2 minutes
when 2.5 mL was drawn up into a 5-mL disposable
syringe. This method of warming was used to warm
lidocaine to body temperature in this study.
2
dominant pain preferences were evaluated with the χ
test. A significance level of P<.05 was assigned.
Results
Table 1 shows the pain scores and the dominant pain
preferences of group 1, in which injection of room-tem-
perature vs body-temperature lidocaine was compared.
In group 1, pain scores of room-temperature lidocaine
injection varied between 2 and 7, with a mean of 4.50
(SD, 1.46), and pain scores of body-temperature lido-
caine injection ranged between 2 and 7, with a mean of
3.90 (SD, 1.61). No statistically significant difference
was found between the pain scores of room-tempera-
ture and body-temperature lidocaine injections.
In group 1, 10 patients (50%) had dominant pain
during the injection of room-temperature lidocaine, 4
patients (20%) had dominant pain during the injection
of body-temperature lidocaine, and 6 patients (30%)
had no preference of dominant pain. There was no sta-
tistically significant difference in dominant pain sen-
sation of the injection of either anesthetic solution.
Table 2 shows the pain scores and the dominant
pain preferences of group 2, in which injection of
stock (room-temperature) and buffered (neutralized)
lidocaine was compared. In group 2, pain scores of
stock lidocaine injection varied between 2 and 8, with
a mean of 4.75 (SD, 1.78). Pain scores of buffered lido-
caine injection varied between 2 and 6, with a mean of
3.20 (SD, 1.19). No statistically significant difference
was found between the pain scores of room-tempera-
ture and body-temperature lidocaine injections.
In group 2, although 13 patients (65%) had domi-
nant pain during the injection of stock lidocaine and 7
patients (35%) had no preference of dominant pain,
injection of buffered lidocaine did not cause dominant
pain in any of the patients.
In another pilot study, stock lidocaine ampoules
were measured to have a pH of 5.98. The addition of 1
unit of sodium bicarbonate (NaHCO ) into 10 units of
3
stock lidocaine was found to neutralize lidocaine, with
a resultant pH of 7.16. This group of lidocaine solu-
tions was referred to as buffered lidocaine. Two sepa-
rate 5-mL injectors were prepared for the facial
anesthesia. One of the injectors was filled with 2.5 mL
of stock (room-temperature) lidocaine, and the other
with 2.5 mL of warm (body-temperature) lidocaine or
2.5 mL of neutralized (buffered) lidocaine according to
the study group. The injectors were prepared and
marked secretly by 1 investigator (H.T.). Another
investigator (O.E.) injected the lidocaine for facial
anesthesia in all patients using a standardized, modi-
fied Van Lint technique. Upper and lower eyelid injec-
tions were made separately using 2 different syringes
that had already been prepared. The first injection
was made at one third distal of the eyebrow; 1.5 mL of
the anesthetic solution from the randomly chosen
syringe was injected medially. The remaining 1.0 mL
was injected laterally. The estimated injection time
was 5 seconds: 3 seconds for the medial injection and
2
seconds for the lateral. A parallel injection was made
with the other anesthetic solution in the same quanti-
ty as for the lower eyelid, using the same technique
and injecting the solution at the same speed.
The patient was asked to quantify the sensation of
infiltration pain (disregarding the pain of needle pen-
etration), by using a visual linear analogue scale. This
linear scale was a 10-unit ruler, from 0 to 10, with 0
indicating no pain and 10 indicating the greatest
imaginable pain. When the surgeon completed the
When the pain scores of both groups were com-
pared, no statistically significant difference was
found. When the preferences of dominant pain sensa-
tion of both groups were compared, buffered lidocaine
44
ANN OPHTHALMOL. 2001;33(1)

T A B L E 1
Group 1 Demographic Data, Pain Scores, and Dominant Pain Preferences
Pain Score
Patient
No.
Room-Temperature
Lidocaine
Body-Temperature
Lidocaine
Dominant
Pain
Age (y)/Sex
1
2
3
4
5
6
7
8
9
88/M
4 (I)
6 (S)
4 (S)
6 (I)
4 (I)
4 (I)
4 (S)
2 (S)
4 (S)
5 (S)
6 (S)
4 (I)
6 (S)
4 (I)
2 (S)
6 (I)
4(S)
6 (I)
7 (S)
2 (I)
4 (S)
6 (I)
4 (I)
4 (S)
2 (S)
2 (S)
6 (I)
2 (I)
6 (I)
7 (I)
2 (I)
4 (S)
4 (I)
2 (S)
2 (I)
4 (S)
3 (I)
6 (S)
4 (I)
4 (S)
I
—
S
I
69/F
57/F
65/M
61/M
57/M
76/M
56/M
55/M
80/F
57/F
67/F
52/M
62/M
60/M
70/F
59/F
57/M
69/M
62/F
I
—
I
—
—
I
1
1
1
1
1
1
1
1
1
1
2
0
1
2
3
4
5
6
7
8
9
0
S
S
S
I
—
I
S
—
S
S
I indicates inferior eyelid; S, superior eyelid; and —, no preference.
injection was found to cause significantly less domi-
nant pain sensation compared with stock and warm
lidocaine injections (P<.05).
Discussion
Local anesthesia is the most commonly used type of
1
1,12
anesthesia in ophthalmology.
Modern surgical pro-
None of the patients had any complication or side
effect of the local anesthetic solutions used in this study.
cedures have enabled faster surgeries with shorter
recovery time, leaving the application of local anes-
ANN OPHTHALMOL. 2001;33(1)
45

T A B L E 2
Group 2 Demographic Data, Pain Scores, and Dominant Pain Preferences
Pain Score
Patient
No.
Room-Temperature
Lidocaine
Body-Temperature
Lidocaine
Dominant
Pain
Age (y)/Sex
1
2
3
4
5
6
7
8
9
70/F
4 (I)
6 (S)
4 (I)
4 (I)
6 (I)
6 (I)
6 (S)
6 (I)
2 (S)
4 (S)
4 (S)
4 (I)
6 (S)
2 (S)
4 (I)
5 (S)
4 (S)
4 (S)
6 (I)
8 (S)
4 (S)
4 (I)
4 (S)
4 (S)
2 (S)
2 (S)
4 (I)
2 (S)
2 (I)
4 (I)
4(I)
—
S
—
—
I
80/F
57/F
66/M
75/M
70/F
72/M
70/F
65/M
63/M
59/M
67/F
74/M
72/M
80/M
78/F
71/F
54/M
66/F
69/F
I
S
I
S
S
—
I
1
1
1
1
1
1
1
1
1
1
2
0
1
2
3
4
5
6
7
8
9
0
2 (S)
2 (I)
2 (I)
2 (S)
6 (I)
4 (I)
4 (I)
2(S)
4 (I)
S
—
I
S
—
—
I
S
I indicates inferior eyelid; S, superior eyelid; and —, no preference.
thetics to be the most unpleasant and painful phase of
the surgery for the patient. Although anterior seg-
ment surgeons have started to convert to using topical
anesthesia, most ophthalmologic surgeries still are
being done using local anesthesia. Hence, much effort
is placed on avoiding the complications and discom-
fort of local anesthesia.
Adrenaline is often used in retrobulbar anesthesia to
counteract the vasodilating effects of the local anesthetics.
It has been shown to slow the absorption of the anesthet-
46
ANN OPHTHALMOL. 2001;33(1)

ic by local vasoconstriction and thus to prolong the dura-
tion of anesthesia, to decrease the amount of anesthetic
needed, and to lessen the danger of systemic toxicity.
the patients reported that they felt dominant pain
with buffered lidocaine injection.
13
In summary, warming or buffering lidocaine was
found to have no significant effect on reducing the
amount of pain of infiltration during facial anesthesia.
However, buffering lidocaine was found to be effective
in reducing the quality of pain.
Factors such as needle size, volume of anesthetic
solution, and the speed of injection may affect the
4
14
pain of injection. Boggia was the first to suggest that
warming local anesthetic solutions may reduce the
pain of their infiltration. His study attracted the
research interest of anesthetists, plastic surgeons, and
dentists, but conflicting results have been presented.
Some authors presented the favorable effect of warm-
References
1
.
.
Wightman MA, Vaughan RW. Comparison of compounds used for
intra-dermal anaesthesia. Anesthesiology. 1976;45:687–690.
Morris RW, Whish DKM. A controlled trial of pain on skin infiltra-
tion with local anaesthetics. Anesth Intensive Care. 1984;12:113–
114.
2
5
,6,15-18
ing local anesthetics on pain reduction.
Nerve
endings have been suggested to be sensitive to cold;
greater nociceptor stimulation may be possible with
solutions colder than the body temperature. Davidson
3.
Morris R, McKee W, Muslin P. Comparison of pain associated with
intra-dermal and subcutaneous infiltration with various local
anesthetic solutions. Anesth Analg. 1987;66:1180–1182.
6
and Bloom suggested that warming lidocaine would
4. Gormly DE. Local anesthesia: pain control with proper injection
technique. J Dermatol Surg Oncol. 1987;13:35–36.
reduce the latent period as a consequence of tempera-
5.
Bainbridge LC. Comparison of room temperature and body tem-
ture-related changes in the pK of lidocaine, resulting
a
perature local anaesthetic solutions. Br J Plast Surg. 1991;44:147–
in a faster onset of neuronal blockade and inhibiting
impulse conduction before the noxious stimulus is
1
48.
6. Davidson JA, Boom SJ. Warming lignocaine to reduce pain asso-
1
9
ciated with injection. Br Med J. 1992;305:617–618.
fully appreciated. Mehta et al, on the other hand, sug-
gested that warming bupivacaine would provide a
faster epidural anesthesia.
7.
Christoph RA, Buchanan L, Kimberly B, Schwartz S. Pain reduc-
tion in local anesthetic administration through pH buffering. Ann
Emerg Med. 1988;17:117–120.
8
.
.
Martin AJ. pH-adjustment and discomfort caused by the intrader-
mal injection of lignocaine. Anaesthesia. 1990;45:975–978.
Krause M, Weindler J, Ruprecht KW. Does warming of anesthetic
solutions improve analgesia and akinesia in retrobulbar anesthe-
sia? Ophthalmology. 1997;3:429–432.
We could not observe a statistically significant effect
of warming lidocaine on reduction of pain during facial
anesthesia. Moreover, the preference of dominant pain
on the area where warm lidocaine was injected in 4
9
1
0. Kaplan PA, Lieberman PE, Vonk BM. Does heating lidocaine
decrease the pain of injection? Am J Radiol. 1987;149:1291.
1. Dalton AM, Sharma A, Redwood M, Wadsworth J, Touquet R. Does
the warming of the local anesthetic reduce the pain of its injec-
tion? Arch Emerg Med. 1989;6:247–250.
(20%) of 20 patients has increased our doubt of the
favorable effect of warming anesthetic solutions.
Local anesthetics have been shown to be more sol-
uble and stable at an acidic pH. However raising the
pH by the addition of sodium bicarbonate has been
suggested to result in enhanced efficacy when the
1
12. Knapp H. On cocaine and its use in ophthalmic and general
surgery. Arch Ophthalmol. 1884;13:402–448.
1
3. Krohn J, Hovdig G, Seland H, Aasved H. Retrobulbar anaesthesia
with and without adrenaline in extracapsular cataract surgery.
Acta Ophthalmol. 1995;73:56–60.
2
0-22
anesthetic is used for regional blockade.
Two mech-
anisms have been proposed to explain the decrease in
pain on infiltration with buffered anesthetic solutions.
The first proposed mechanism is that the infiltration
of an anesthetic solution at physiologic pH levels of
1
1
1
4. Boggia R. Heating local anaesthetic cartridges. Br Dent J. 1967;
1
22:287.
5. Finkel LI, Berg DJ. Heating lidocaine appears to prevent painful
injection. AJR. 1987;148:651.
6. Cragg AH, Berbaum K, Smith TP. A prospective blinded trial of
warm and cold lidocaine for intra-dermal injection. AJR. 1988;148:
7.0 to 7.4 would cause less tissue irritation compared
with a more acidic solution. The second hypothesis is
that neutralizing anesthetic solutions would increase
their uncharged basic form; thus, the diffusion of the
anesthetic solution through interstitial tissues is
increased. This would result in a higher concentration
of the drug in the nerve axoplasm and a more rapid
block of the sensory fibers. As a more rapid block
develops, the pain on skin infiltration is believed to be
6
51.
17. Bloom LH, Scheie HG, Yanoff M. The warming of local anesthetic
agents to decrease discomfort. Ophthalmic Surg. 1984;15:603.
1
8. Bell RWD, Butt ZA Warming lignocaine reduces the pain of injec-
tion during peri-bulbar local anaesthesia for cataract surgery. Br J
Ophthalmol. 1995;79:1015–1017.
19. Mehta PM, Theriot E, Mehrotra D, Patel K, Kimball BG. A simple
technique to make bupivacaine a rapid acting epidural anaesthet-
ic. Reg Anaesth. 1987;12:135–137.
0. Difazio CA, Carron H, Grosslight KR, Moscicky JC, Bolding WR,
Johns RA. Comparison of pH-adjusted lidocaine solutions for
epidural anesthesia. Anesth Analg. 1986;65:760–764.
1. Moorland GH, Douglas MJ, Jeffrey WK, et al. Effect of pH adjust-
ed bupivacaine on onset and duration of epidural analgesia in par-
turients. Can Anaesth Soc J.1986;33:537–541.
22. Tackley RM Coe AJ. Alkalised bupivacaine and adrenaline for
epidural Caesarean section: a comparison with 0.5% bupivacaine.
Anaesthesia. 1988;43:1019–1021.
3. McKay W, Morris R, Mushlin P. Sodium bicarbonate attenuates
pain on skin infiltration with lidocaine, with and without epi-
nephrine. Anesth Analg. 1987;66:572.
2
5
,8,23
blocked before it has even been sensed.
Some authors have presented their results showing
that buffering lidocaine might improve its effect and
reduce the pain on skin infiltration, but, as far as we
know, no contrary result has been presented. Our
results, in fact, did not show a statistically significant
effect of buffering lidocaine on quantitative pain
scores compared with stock and warm lidocaine. On
the other hand, buffered lidocaine was found to cause
significantly less dominant pain in our study. None of
2
2
ANN OPHTHALMOL. 2001;33(1)
47