10.14639/0392-100X-N1956
Objective. Early recognition of free flap vascular impairment is essential for flap salvage attempts. Several methods for surveillance of post-operative flaps are available. Among these, we have extensively used Laser-Doppler Perfusion Flowmetry (LDF) monitoring. We report our experience on this topic and illustrate the advantages and weak points. Methods. Over seven years, 110 consecutive free flaps for head and neck reconstruction were monitored using the Periflux System 5000® (Perimed AB, Järfälla, Sweden). In addition to maximum and minimum peaks, a pattern called vasomotion can be detected. Monitoring time lasted from 3 to 7 days, 24/24 h. Results. Six of 110 (5.5%) cases of vascular problems were detected and clinically confirmed. In 5 cases, venous thrombosis was present: 4 patients were successfully treated. In 1 case, both arterial and venous thrombosis occurred. Flowmetry data always showed a more or less sudden disappearance of vasomotion. Conclusions. LDF is a highly sensible, specific and reliable method. It is easy to use and interpret at low cost. Remote monitoring could also be developed.
text/xml
1827-675X
1956
en
Andrea Zani
http://creativecommons.org/licenses/by-nc-nd/4.0
ACTA Otorhinolaryngologica Italica
Laser-Doppler Flowmetry
Free flaps monitoring by Laser-Doppler Flowmetry in head and neck surgery
Text.Serial.Journal
https://www.actaitalica.it/
42
Head and neck
2022-11-23
2021-12-05
2022-12-13
2022-12-13
427-433
1
Andrea Zani
2022/11/23
10.14639/0392-100X-N1956
427
Department of Otorhinolaryngology, Portogruaro Hospital (VE), Italy
1827-675X
Laser-Doppler Flowmetry
en
433
Free flaps monitoring by Laser-Doppler Flowmetry in head and neck surgery
https://www.actaitalica.it/article/download/1956/868
42
ACTA OTORHINOLARYNGOLOGICA ITALICA 2022;42:427-433; doi: 10.14639/0392-100X-N1956




Head and neck


Free flaps monitoring by Laser-Doppler Flowmetry
in head and neck surgery
Monitoraggio dei lembi liberi mediante flussometria Laser-Doppler nella chirurgia
della testa e del collo
Pietro Salvatori 1, Stefano Paradisi 2, Andrea Zani3
1
 Head & Neck Surgeon (Ret.), Milan, Italy; 2 Department of Otorhinolaryngology, Vimercate Hospital (MB), Italy, 3 Department of
Otorhinolaryngology, Portogruaro Hospital (VE), Italy


SUMMARY
Objective. Early recognition of free flap vascular impairment is essential for flap salvage
attempts. Several methods for surveillance of post-operative flaps are available. Among
these, we have extensively used Laser-Doppler Perfusion Flowmetry (LDF) monitoring. We
report our experience on this topic and illustrate the advantages and weak points.
Methods. Over seven years, 110 consecutive free flaps for head and neck reconstruction
were monitored using the Periflux System 5000® (Perimed AB, Järfälla, Sweden). In addi-
tion to maximum and minimum peaks, a pattern called vasomotion can be detected. Moni-
toring time lasted from 3 to 7 days, 24/24 h.
Results. Six of 110 (5.5%) cases of vascular problems were detected and clinically con-
firmed. In 5 cases, venous thrombosis was present: 4 patients were successfully treated. In 1
case, both arterial and venous thrombosis occurred. Flowmetry data always showed a more
or less sudden disappearance of vasomotion.
Conclusions. LDF is a highly sensible, specific and reliable method. It is easy to use and
interpret at low cost. Remote monitoring could also be developed.
KEY WORDS: free flap, monitoring, thrombosis, salvage, Laser-Doppler Flowmetry

RIASSUNTO
Obiettivi. Il riconoscimento precoce della compromissione vascolare del lembo libero è
essenziale per i tentativi di salvataggio del lembo. Sono disponibili molti metodi per la          Received: December 10, 2021
sorveglianza postoperatoria dei lembi. Tra questi, abbiamo ampiamente utilizzato la flus-          Accepted: July 26, 2022
sometria Laser-Doppler (FLD). Lo scopo del presente articolo è di riportare la nostra
esperienza, illustrando vantaggi e punti deboli.                                                   Correspondence
                                                                                                   Pietro Salvatori
Metodi. In un lasso di tempo di sette anni, sono stati monitorati 110 lembi liberi consecu-
                                                                                                   Head & Neck Surgeon (Ret.), via C. Saldini 28,
tivi per la ricostruzione della testa e del collo utilizzando Periflux System 5000® (Perimed       20133 Milan, Italy
AB, Järfälla, Svezia). Oltre ai picchi massimi e minimi, veniva rilevato il pattern chiamato       E-mail: 14carbonio@gmail.com
vasomotricità. Il tempo di monitoraggio è durato da 3 a 7 giorni, 24/24 h.
Risultati. Sono stati rilevati e clinicamente confermati 6/110 (5,5%) casi di disturbi va-
scolari. In 5 casi si è verificata una trombosi venosa: 4 di questi sono stati trattati con suc-     How to cite this article: Salvatori P, Paradisi
cesso. In 1 caso si è verificata sia trombosi arteriosa che venosa. I dati della flussometria        S, Zani A. Free flaps monitoring by Laser-Dop-
                                                                                                     pler Flowmetry in head and neck surgery. Acta
hanno sempre mostrato una più o meno improvvisa scomparsa della vasomotricità.
                                                                                                     Otorhinolaryngol Ital 2022;42:427-433. https://
Conclusioni. FLD è un metodo altamente sensibile e specifico, quindi molto affidabile. È             doi.org/10.14639/0392-100X-N1956
facile da usare e interpretare con un costo contenuto. Potrebbe essere sviluppato il moni-
toraggio in remoto.
                                                                                                   © Società Italiana di Otorinolaringoiatria
PAROLE CHIAVE: lembi liberi, monitoraggio, trombosi, chirurgia di salvataggio,                     e Chirurgia Cervico-Facciale
flussometria Laser-Doppler
                                                                                                                  OPEN ACCESS

                                                                                                   This is an open access article distributed in accordance with
Introduction                                                                                       the CC-BY-NC-ND (Creative Commons Attribution-Non-
                                                                                                   Commercial-NoDerivatives 4.0 International) license. The
Microvascular free tissue transfer is recognised as an important method for the                    article can be used by giving appropriate credit and mentio-
                                                                                                   ning the license, but only for non-commercial purposes and
reconstruction of large and complex defects, owing to its superior functional                      only in the original version. For further information: https://
and aesthetic outcomes, especially for the head and neck region even in older                      creativecommons.org/licenses/by-nc-nd/4.0/deed.en




                                                                                                                                                           427
P. Salvatori et al.




patients 1. Free flap surgery appears to also be rewarding in      Table I. Demographics
terms of long-term outcomes and survival 2. Despite suc-            Characteristics                          Value (%)
cess rates of around 95% or more3, flap failure secondary          Age, years
to vascular impairment remains a demanding complication,             Median                                     58
leading to higher patient morbidity, prolonged hospital stay         Range                                     17-85
and increased healthcare costs.                                    Gender
Although salvage rates of failing free flaps vary with aetiol-       Male                                     79 (71.8)
ogy, flap type and experience, there is large consensus that         Female                                   31 (28.2)
early detection of vascular compromise and swift surgical          Type of free flap
re-exploration significantly increases the likelihood of suc-        Forearm                                  51 (46.3)
cessful free flap salvage 4. Vascular impairment leading to
                                                                     Fibula                                   21 (19.1)
flap failure occurs because of problems in either the flap’s
                                                                     ALT                                       12 (11)
arterial inflow, capillary microcirculation, or venous out-
                                                                     Rectus abdominis                          11 (10)
flow. As a consequence, monitoring methods to aid the ear-
                                                                     Jejunum                                   9 (8.2)
ly recognition of disturbances in flap circulation are critical
                                                                     Dorsalis major                            6 (5.4)
in performing revision, thus maximising the success of free
flap reconstruction. Numerous flap monitoring strategies           Reconstructed site
and technologies exist, which vary in complexity, invasive-          Oral cavity                              78 (70.9)
ness, efficiency and cost 5,6. Properties of the ideal free flap     Larynx-hypopharynx                       18 (16.4)
monitoring technique should be: inexpensive; harmless to             Pharynx                                   8 (7.3)
both patient and flap; produce rapid, reliable, and objec-           Cranio-maxillo-facial                     6 (5.4)
tive results; simple to interpret by relatively inexperienced
personnel; and applicable to all types of free flaps 6. Various    cating how the clusters of minimum/maximum peaks vary
methods have been proposed, including prick test 7, micro-         over time 14. This wave conveys vasomotion (Fig. 1, green
dialysis 8, Doppler (both implantable and external) 9, Near-       line). Vasomotion is the spontaneous oscillation in vascular
Infrared Spectroscopy (NIRS) 10, Single Photon Emission            tone in microcirculation and is believed to be a physiologi-
Computed Tomography (SPECT) 11, thermal scan 12, Mac-              cal mechanism facilitating the transport of blood gases and
rophage Migration Inhibitory Factor 13 and Laser-Doppler           nutrients to and from tissues. Vasomotion can be described
Flowmetry (LDF) 14,15. The latter exploits wavelength vari-        as recurrent organised fluctuations in vessel diameter over
ations of photons hitting blood red cells (BRC) while flow-        time. By frequency analysis, distinct frequency intervals
ing. In other words, it is the known Doppler effect applied        related to physiological aspects can be presented as heart
to the light laser instead of ultrasounds.
                                                                   rate, respiration and myogenic, neurogenic, and endotheli-
We have gained a considerable experience with LDF moni-
                                                                   al-dependent activity 15.
toring and report on the use of this technique for flap moni-
                                                                   According to the Doppler effect, ischaemia or reduced RBC
toring.
                                                                   speed (i.e. venous stasis) cause alterations that are shown as
                                                                   decreasing values in the chart. An arbitrary threshold of RFV
Materials and methods                                              can be set, below which an alarm is triggered. The threshold
We retrospectively studied 110 consecutive free flaps for          value was usually chosen according to prudential behaviour
head and neck reconstruction over seven years, which were          (i.e. better a false alarm than a missed critical event). The
postoperatively monitored with the Laser-Doppler Peri-             probe (reusable) was stitched to the flap at the most suitable
flux System 5000® (Perimed AB, Järfälla, Sweden). De-              position before the end of reconstruction or, whenever possi-
mographics are shown in Table I. The device includes a             ble, before removal of clamps (Fig. 2). We always raised the
suturable probe and the main unit, coupled with specific           flap together with a skin island – even when the main goal
software (Perisoft) in a laptop; continuous recording is           was bone reconstruction – to allow a more reliable signal.
plotted on a chart: the y-axis indicates the Relative Flow         The skin island (or omentum, in the case of the jejunum)
Values (RFV), and the X-axis reports the time. Besides the         was systematically superficialised in the case of buried flaps.
sinusoid indicating the minimum and maximum peaks of               Monitoring time lasted from 3 to 7 days, 24/24 h. In the
RFV (Fig. 1, blue line) – whose frequency is similar to the        beginning, the recording was checked by physicians or in-
cardiac one – a further sinusoid with a frequency of about         structed paramedics on an hourly basis. later, the control was
0.05-0.15 Hz (3-9 cycles per minute) is detectable, indi-          integrated remotely using an app on a dedicated smartphone.



428
                                                                               Free flaps monitoring by Laser-Doppler Flowmetry in head and neck surgery




Figure 1. Relative flow values (RFV) show maximum (sky-blue, added) and minimum peaks (fuchsia, added), with a frequency similar to the cardiac one. Alarm
line (red). A further wave (green, added) is also detectable: vasomotion.



                                                                               Results
                                                                               In 104/110 (94.5%) cases the post-operative course was
                                                                               uneventful and chart analysis revealed a near-constant in-
                                                                               crease of RFV during the first 3 post-operative days, which
                                                                               then became stable.
                                                                               Conversely, vascular problems were detected and con-
                                                                               firmed in 6 of 110 (5.5%) free flaps. At re-exploration, 5
                                                                               pedicles were affected by venous thrombosis and 1 suf-
                                                                               fered from both arterial and venous occlusion. Analysis of
                                                                               the charts confirmed that – in an otherwise normal find-
                                                                               ing (Fig. 3, top) – the first sign of vascular trouble was
                                                                               the diminution of the vasomotion wave (Fig. 3, middle),
                                                                               until its disappearance, together with complete maximum/
                                                                               minimum peaks fall below the threshold, within minutes
Figure 2. Probe insetting and start monitoring.
                                                                               (Fig. 3, bottom): a slow wave was still appreciable, prob-
                                                                               ably due to the push/pull movements that the still patent
                                                                               major vessels transmitted to the occluded micro-vessels.
Parameters under monitoring were both RFV peak values
                                                                               Both normal signals were again present after successful re-
and vasomotion sinusoid (Fig. 1). Flattening (up to vanish-
                                                                               vision (Fig. 4). The delay between final diagnosis and revi-
ing) of the vasomotion wave was considered the most im-
                                                                               sion ranged from 1 to 3.5 hours.
portant sign of serious trouble affecting flap blood circula-                  Interestingly, sometimes discordance between clinical
tion and monitoring personnel was made aware. However,                         features and chart parameters was detected. Some flaps
when alarmed, the responsible physician invariably pur-                        “looked better” than the flow parameters that were regis-
sued clinical examination including prick test to confirm or                   tered.
discard the suspicion. If the diagnosis was confirmed, sur-                    The salvage protocol allowed 4 of 5 venous thromboses
gical revision took place as soon as possible. The salvage                     to be successfully managed and flaps were completely
protocol included thrombus removal, irrigation, intraarte-                     rescued. On the other hand – in the last case of venous
rial delivered fibrinolytic, a new anastomosis and assess-                     thrombosis and the case of both arterial and venous occlu-
ment of the adequate pedicle setting. The salvaged flap then                   sion – the flap salvage failed. In those cases, the problem
underwent the usual monitoring. Failure to rescue the flap                     was overcome by raising a pectoralis major myocutaneous
was overcome by a pedicled flap whenever possible.                             flap. The salvage success rate was 67%, while the overall
Antithrombotic prophylaxis (lysine acetylsalicylate 1 gr,                      success rate reached 98%.
intravenously) was routinely administered just before mi-                      Minor complications included 3 partial necrosis and 2 fis-
croanastomosis. Anticoagulant prophylaxis was never pre-                       tulas, which were all successfully managed by conservative
scribed for free flap purposes.                                                treatment.



                                                                                                                                                    429
P. Salvatori et al.




Figure 3. Top: normal perfusion. Middle: a few minutes later, the vasomotion wave begins flattening and circulation speed slows down. Bottom: RFV below the
threshold and absence of vasomotion.


The positive predictive value was 100%, whereas the nega-                       tially invalidate the morphologic and functional success of
tive predictive value did not move beyond 0%.                                   the reconstruction, thus leading to higher patient morbidity,
                                                                                prolonged hospital stay and increased healthcare costs 5.
Discussion                                                                      Circulation disturbances leading to flap failure may involve
                                                                                either the flap’s arterial inflow, capillary microcirculation,
Microvascular free tissue transfer has become a popular                         or venous outflow 5. Salvage rates of failing free flaps vary
technique for the reconstruction of challenging defects.                        with aetiology, flap type and experience, but there is large
The results are considered to be superior compared to other                     agreement that early detection of vascular compromise and
methods in terms of both functional and aesthetic outcomes,                     prompt surgical re-exploration significantly increases the
especially for the head and neck region. This is true when                      chances of free flap salvage. Chances of flap salvage are
dealing with bone reconstruction, very large or composite                       significantly linked to the timing of detection. Yang et al. 17
defects, and facial reanimation. On the other hand, free flaps                  showed that the salvage rate at 16 h (62.2%) was much
superiority over pedicled ones almost invariably occurs when                    higher than that at > 16 h (21.4%, p = 0.0039). Accordingly
dealing with speech and swallowing, even if not at a statisti-                  monitoring methods to aid the early recognition of distur-
cally significant level 16. However, despite success rates be-                  bances in flap circulation are critical in deciding on revi-
ing around 95% or more 3, flap failure secondary to vascular                    sion, thus increasing the success of free flap reconstruction.
disturbances remains a major complication that can poten-                       Numerous flap monitoring strategies and technologies exist,



430
                                                                                  Free flaps monitoring by Laser-Doppler Flowmetry in head and neck surgery




Figure 4. Charts recorded on 1st (top) and 4th (bottom) day after salvage re-exploration: high RFV and presence of vasomotion are evident.


which vary in complexity, invasiveness, efficiency and cost.                      the absence of any bleeding is considered a sign of arte-
Furthermore, their intrinsic value might be affected accord-                      rial flow block. Direct puncture appears to be quite reliable,
ing to the flap setting: buried or non-buried. Properties of the                  but needs substantial human resources and is somewhat
ideal free flap monitoring technique should be: inexpensive;                      operator-dependent. Moreover, the results are sometimes
harmless to both patient and flap; produce rapid, reliable, and                   ambiguous and may lead to a dangerous delay in flap re-
objective results; simple to interpret by relatively inexperi-                    exploration. Nevertheless, some authors consider the prick
enced personnel; and applicable to all types of free flaps 6.                     test the gold standard for free flap monitoring 7.
Clinical evaluation is based on parameters such as the col-                       Transcutaneous Doppler suffers from similar limitations to
our of the skin flap, presence or absence of oedema, pres-                        the prick test, in addition to the cost of the device.
ence of capillary refill (rapid or delayed) and quality of                        Implantable Doppler is more reliable and needs fewer hu-
bleeding with prick test. The prick test consists of a direct                     man resources, but is limited by the high cost of disposable
puncture of the flap. Parameters to be considered are la-                         materials. Moreover, in rare instances, removal of the probe
tency of bleeding and blood colour. Normal latency lasts                          leads to pedicle damage, requiring salvage surgery 9.
2-5 seconds. The immediate flowing of deep-bluish blood,                          Microdialysis measures glucose, lactate, and lactate/pyru-
together with a lack of spontaneous haemostasis, is consid-                       vate ratios8 abnormally produced in the poorly perfused tis-
ered highly suspicious of venous impairment. Quite often                          sue. It is believed to be highly reliable, but local trauma and
the site of puncture bears ecchymosis (Fig. 5). In contrast,                      high costs hinder its widespread use.



                                                                                                                                                      431
P. Salvatori et al.




                                                                                 Austrian scientist Johan Christian Doppler 14. The device
                                                                                 exploits wavelength variations of photons hitting blood red
                                                                                 cells while flowing. In other words, the Doppler effect is
                                                                                 applied to the light Laser instead of ultrasound.
                                                                                 In our series, cases with an uneventful course showed a
                                                                                 constant RFV increase during the first 3 post-operative
                                                                                 days. This can probably be interpreted as hyperaemia, an
                                                                                 initial step of the progressive settling towards the steady
                                                                                 state of the flap perfusion. By contrast, careful analysis of
                                                                                 charts related to free flaps suffering vascular disturbances
                                                                                 revealed that the first sign of impairment was the diminu-
                                                                                 tion of sinusoid expressing vasomotion. Vasomotion is a
                                                                                 phenomenon characteristically seen under normal perfu-
                                                                                 sion conditions. It is accentuated in connection with reac-
                                                                                 tive hyperaemia such as in a reperfused flap and may repre-
                                                                                 sent a vasoregulatory mechanism in response to increased
                                                                                 metabolic demand. As the free flap is denervated, it has
                                                                                 been concluded that this mechanism should be under local
                                                                                 control 15. Vasomotion analysis potentially offers measures
                                                                                 that are more directly related to physiological mechanisms
                                                                                 than the measurement of microvascular perfusion alone,
                                                                                 and have been utilised to investigate microvascular dys-
                                                                                 function in various disease states 15.
                                                                                 Therefore, we strongly recall attention to this sign as a very
                                                                                 early indicator of vascular trouble, even if clinical appear-
                                                                                 ance and prick test are negative.
                                                                                 Another important finding is the possible rapid evolution
                                                                                 of the vascular disturbance: in some cases, the complete
                                                                                 arrest of the flap perfusion may occur within a few minutes
                                                                                 (Fig. 3).
Figure 5. Top: ecchymosis around the puncture sites in a case of venous
thrombosis. Bottom: the resolution of bruising after 15 days from the success-   To reduce the diagnostic delay and unnecessary surgical
ful salvage procedure. Still appreciable the typical homogeneous greyish col-    intervention, we adopted an expedient. A smartphone was
our of the skin affected by the previous ecchymosis.                             installed to capture the screen of LDF monitoring, and –
                                                                                 in case of alarm – paramedics were instructed to send the
Near-infrared spectroscopy (NIRS) relies on recording                            responsible surgeon a clip including at least 10 minutes
photons at 700-950 nm that have traveled through a tissue.                       of recording before the alert rang. In cases in which the
Oxygenated haemoglobin (HbO2) and non-oxygenated                                 diagnosis of serious vascular disturbance was evident, the
haemoglobin (Hb) absorb photons differently at different                         surgeon had the possibility of immediately activating the
wavelengths: this allows for the calculation of the oxygen                       surgical team. In dubious cases, the surgeon had the possi-
saturation of the tissue (StO2). Unit and disposable costs                       bility of remotely monitoring the evolution of the suspected
appear to limit the use of this efficient monitoring meth-                       vascular disturbance. Today, this has been implemented
od 5,10. Thermal scan 12 and Macrophage Migration Inhibi-                        with a streaming app. Indeed, in 2017, Yuen 18 highlighted
tory Factor 13 are still under evaluation.                                       this possibility in telemedicine. Advisable implementation
LDF is a non-invasive method enabling the monitoring of mi-                      of the instrument should allow the possibility of directly
crovascular blood flow 14,15. Even though LDF measures are                       transmitting data from the recording device to the operator.
non-absolute, the enormous interest in microvascular perfu-                      The delay between diagnosis and actual revision is also
sion has led to many clinical investigations. Indeed, it can                     conditioned by the immediate availability of all the required
be used in many areas and on many organs, such as the skin,                      resources (i.e.: emergency team, emergency theatre, etc.).
brain, kidney, liver and intestines 14.                                          Our findings confirm considerations about the importance
The Laser-Doppler perfusion monitoring and imaging                               of the vasomotion wave 15,19.
techniques rely on the Doppler effect, first described by the                    At present, our policy is to promptly re-explore free flaps



432
                                                                              Free flaps monitoring by Laser-Doppler Flowmetry in head and neck surgery




whose monitoring shows fading of vasomotion. However,                              cinoma: a retrospective multicentre study. Acta Otorhinolarygol Ital
                                                                                   2014;34:99-104. PMCID: PMC4025181
this is not intended as an automated process, as clinical
                                                                              3
                                                                                   Podrecca S, Salvatori P, Squadrelli Saraceno M, et al. Review of 346
evaluation maintains its value.                                                    patients with free-flap reconstruction following head and neck sur-
Perfusion disturbance (5.5%), type of vascular trouble (ve-                        gery for neoplasm. J Plast Reconstr Aesthet Surg 2006;59:122-129.
nous 5 of 6 cases), salvage rate (67%), and final success                          https://doi.org/10.1016/j.bjps.2005.08.002
rate (98%) are close to those reported in larger series 17. The               4
                                                                                   Moellhoff N, Heidekrueger PI, Frank K, et al. Comparing the time-
case of both venous and arterial disturbance may indicate                          dependent evolution of microcirculation in gracilis vs ALT flaps
                                                                                   using laser-doppler flowmetry and tissue-spectrometry. J Clin Med
that arterial occlusion was secondary to venous thrombosis                         2022;11:2425. https://doi.org/10.3390/jcm11092425
and complete occlusion of micro-vessels. Predictive posi-                     5
                                                                                   Kwasnicki RM, Noakes AJ, Banhidy N, et al. Quantifying the limita-
tive and negative values were reassuring.                                          tions of clinical and technology-based flap monitoring strategies us-
In summary, LDF appears to be a highly reliable technique                          ing a systematic thematic analysis. Plast Reconstr Surg Glob Open
                                                                                   2021;9:e3663. https://doi.org/10.1097/GOX.0000000000003663
with more acceptable costs (the probe is reusable) than oth-                  6
                                                                                   Creech B, Miller S. Evaluation of circulation in skin flaps. In: Grabb
er more sophisticated devices.                                                     WC, Bert Myers M, editors. Skin flaps. Boston, MA: Lippincott Wil-
                                                                                   liams & Wilkins; 1975.
Acknowledgements                                                              7
                                                                                   Frati F, Incorvaia C, Cavaliere C, et al. The skin prick test. J Biol
This paper wishes to pay tribute, commemorate, and                                 Regul Homeost Agents 2018;32(1 Suppl. 1):19-24.
thank our Masters, Prof. Roberto Molinari and Dr. Stefano
                                                                              8
                                                                                   Birkenfeld F, Naujokat H, Helmers AK, et al. Microdialysis in post-
                                                                                   operative monitoring of microvascular free flaps: experiences with
Podrecca, who led our group in pioneering free flaps for                           a decision algorithm. J Craniomaxillofac Surg 2019;47:1306-1309.
head and neck reconstruction at the National Cancer Insti-                         https://doi.org/10.1016/j.jcms.2019.05.006
tute of Milan, Italy in the early 80s.                                        9
                                                                                   Ong AA, Ducic Y, Pipkorn P, et al. Implantable doppler removal after
Much is also due to our collaborative Colleagues and                               free flap monitoring among head and neck microvascular surgeons.
                                                                                   Laryngoscope 2022;132:554-559. https://doi.org/10.1002/lary.29810
enthusiastic nursing team, to whom our warmest thank                          10
                                                                                   Ouyang SY, Cai ZG, Shan XF, et al. Prospective trial of near-infrared
goes.                                                                              spectroscopy for continuous noninvasive monitoring of free fibu-
The authors are grateful to Mr. Achille Moneta for his                             lar flaps. Ann Plast Surg 2021;87:e29-e36. https://doi.org/10.1097/
constant technical support and patience. Finally, we wish                          SAP.0000000000002915
to thank Dr. Giada Beltramini for reviewing the manu-                         11
                                                                                   Tabrizi R, Okhovatpour MA, Hassani M, et al. Comparison of Single
                                                                                   Photon Emission Computed Tomography (SPECT) and implantable
script.                                                                            Doppler in the monitoring of a vascularised fibular free flap for re-
                                                                                   construction of the mandible. Br J Oral Maxillofac Surg 2021;59:661-
Conflict of interest statement                                                     664. https://doi.org/10.1016/j.bjoms.2020.08.018
The authors declare no conflict of interest.                                  12
                                                                                   Rabbani MJ, Bhatti AZ, Shahzad A. Flap monitoring using thermal
                                                                                   imaging camera: a contactless method. J Coll Physicians Surg Pak
                                                                                   2021;30:703-706. https://doi.org/10.29271/jcpsp.2021.06.703
Funding                                                                       13
                                                                                   Megas IF, Simons D, Kim BS, et al. Macrophage migration inhibi-
This research did not receive any specific grant from                              tory factor-an innovative indicator for free flap ischemia after micro-
funding agencies in the public, commercial, or not-for-                            surgical reconstruction. Healthcare (Basel) 2021;9:616. https://doi.
profit sectors.                                                                    org/10.3390/healthcare9060616
                                                                              14
                                                                                   Humeau A, Steenbergen W, Nilsson H, et al. Doppler perfusion
                                                                                   monitoring and imaging: novel approaches. Med Bio Eng Comput
Author contributions                                                               2007;45:421-435. https://doi.org/10.1007/s11517-007-0170-5
PS did conceptualization, performed the clinical work,                        15
                                                                                   Söderström T, Svensson H, Koop T, et al. Processing of laser-doppler
wrote and revised the manuscript. SP and AZ did the clini-                         signals from free flaps. Technol Health Care 1999;7:219-223. https://
cal work and revised the manuscript.                                               doi.org/10.3233/THC-1999-72-312
                                                                              16
                                                                                   Mahieu R, Colletti G, Bonomo P, et al. Head and neck reconstruction
                                                                                   with pedicled flaps in the free flap era. Acta Otorhinolaryngol Ital
Ethical consideration                                                              2016;36:459-468. https://doi.org/10.14639/0392-100X-1153
Not applicable.                                                               17
                                                                                   Yang Q, Ren ZH, Chickooree D, et al. The effect of early detection of
                                                                                   anterolateral thigh free flap crisis on the salvage success rate, based
                                                                                   on 10 years of experience and 1072 flaps. Int J Oral Maxillofac Surg
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