**1. Introduction**

The incidence of postoperative sore throat (POST) varies depending on the source from 15 to 60%. POST is mainly caused due to the pressure that the airway device exerts on the respiratory mucosa. This pressure causes a reduction in blood flow through the small capillaries which can cause an anoxic-ischemic local reaction. The pressure and local inflammatory mediators can also activate local c fibers that signal pain. The airway devices are made of silicone and PVC which even when lubricated can adhere to the mucosa due to a normal reduction in local secretion of mucus secondary to the presence of a foreign body and cause trauma when removing the device. In long procedures, the slight movements of the device can cause chafing of the area, and local inflammation. The excessive manipulation of the airway in the presence of a difficult intubation or inadequate laryngeal mask airway (LMA) size causes edema that can further add to the inflammation and pain present in the postoperative period. It has been theorized that the passage of cold anesthetic and medicinal gases in the airway through the devices can also be a cause of airway irritation, similar to the use of supplemental oxygen through nasal tips, but more evidence is necessary to confirm this. It is evident that several factors add to the presence of inflammation and mucosa

lesion which can be reduced by increasing awareness amongst anesthesiologists of its importance. In 2010, a bi-continental survey demonstrated that patient dissatisfaction is often due to postoperative nausea and vomiting (PONV) followed by POST [1]. This highlights the need for our attention to this symptom and maneuvers aimed towards preventing or reducing it.

## **2. Risk factors associated with POST**

Risk factors have been largely identified in both patient specific details, as well as surgical and anesthetic related factors. It is important to identify the patients risk factors to plan accordingly and prevent this undesirable symptom when its presence is looming. Pain is a subjective feeling and therefore can be influenced by the patient's state of mind prior to the procedure. Anxious patients are more likely to refer POST as well as perceive a higher intensity of the pain. Sufficient information about what to expect upon anesthesia emersion is important to help the patient cope with these symptoms as they appear.

#### **2.1 Age**

There have been different results depending on the population studied and have found conflicting results. Some authors have found a higher incidence amongst young patients [2], and others claim the incidence is higher amongst geriatric patients [3]. It is well known that as we age, our nervous fibers become less sensitive to pain stimuli, so it is probable that the risk factor of old age is more associated to difficult airways that are common in geriatric patients, rather than old age itself.

#### **2.2 Sex**

Authors agree that female patients are more likely to report the presence of POST as well as a higher incidence of intense pain [1, 4, 5]. This is explained due to smaller airways in females in comparison to males which can translate to a tighter fit of the device in the airway.

#### **2.3 Airway device**

POST is present in higher proportion of patients in which endotracheal intubation was the airway management of choice compared to LMA [6, 7], and the incidence is even higher when and endobronchial tube is used [2, 8, 9]. POST can be reduced or even prevented in some cases with the use of a video laryngoscope [10], to reduce airway manipulation and number of intubation attempts.

#### **2.4 Difficult airway**

Patients with predicted difficult airways, are more likely to present POST due to the use of intubation stylets, multiple attempts for intubation or vocal cord lesion. This risk is even greater when the difficult airway is not predicted during preoperative evaluation due to an inefficient planning, which may result in even more airway manipulation, and a blood stained ETT is more probable upon extubation.

#### **2.5 Endotracheal tube size**

POST is importantly linked to the use of larger lumen endotracheal tubes (ETT). Many authors have found a lower incidence of POST when reducing the ETT size [2, 3, 5, 6] even by 0.5 mm. Traditionally, larger ETT were selected to reduce airflow resistance and provide better ventilation, but this intervention has little significance when the ventilation is transitory as is in a surgical procedure. The adequate size of ETT has not been determined to avoid adverse events regarding mechanical ventilation, but a simple reduction in 0.5 mm in the size normally selected in healthy patients seems to be a safe choice to reduce incidence of POST.

Nasotracheal intubation is also associated with higher incidence of POST due to manipulation of the airway, ETT size and blood stained ETT upon removal. Until now, the only maneuver that seems to reduce this risk when selecting nasotracheal intubation is the use of fiberscope for its insertion as opposed to manual insertion assisted by laryngoscopy and Magill clamps.

#### **2.6 Cuff pressure**

When using ETT or LMA, guidelines have always recommended the use of a manometer to maintain cuff pressure ETT between 20 and 30 cmH2O and to monitor every 30 minutes, or less if using nitrous oxide. Adequate control of intracuff pressure can help reduce the incidence of POST [11].

The objective in the case of LMA is to not exceed 60 cmH2O. On occasion, following the manufacturer's recommended fill volumes, pressures above 60 cmH2O can be obtained [12].

#### **2.7 Muscle relaxants**

The use of succinylcholine has been associated with the presence of POST [2] probable secondary to muscle fasciculations and intense potassium release that can add to the known POST risk factors.

In emergency settings, some medical professionals may choose to avoid muscle relaxants which can cause vocal cord lesions and elevate the risk for POST.

#### **2.8 Anesthetic related factors**

POST is usually present when the airway manipulation has been excessive. This can be associated with difficult airway, use of intubation stylets and use of direct laryngoscopy. Some authors have proposed that the expertise of the person who performs the laryngoscopy could be a factor leading to presence of POST, but there are conflicting results. What has been demonstrated is that a low time to secure the airway can drastically reduce the incidence of POST [5]. Blood stained ETT upon extubation has been linked to POST [9] which is expected since it is evidence of excessive airway manipulation or use of a large ETT.

#### **2.9 Surgical related factors**

Long procedures resulting in endotracheal intubation for 3 hours or more was highly associated to POST [3]. Gynecologic surgery has also been linked to higher incidence of POST that can probably be explained by the extreme Trendelenburg

position required for many laparoscopic gynecologic procedures which elevate the pressure in the airway secondary to blood pooling in the upper body [9]. Head and neck surgery has also been linked to higher incidence of POST, particularly otorhinolaryngologic surgery.

### **3. Interventions for reducing incidence and intensity of POST**

Interventions to reduce the incidence and/or severity of POST have been largely studied varying from nebulized corticosteroids or magnesium, licorice, or ketamine gargles, intracuff saline or lidocaine, and lidocaine or benzydamine spray on the outside of the airway device. Non-pharmacological interventions consist in avoiding large ETT and high-pressure cuffs as well as the use of a manometer to control the cuff pressure during the procedure. The use of video laryngoscopy can reduce the incidence of POST in difficult airways as it reduces the number of attempts to intubation and reduces airway manipulation, but the use of stylets has been associated with a higher incidence of POST and several video laryngoscopes need a specific stylet for the curvature of each device.

#### **3.1 Lidocaine spray**

Lidocaine spray has proved NOT to decrease the intensity or presence of POST and can even be linked to worse outcomes [13]. The lidocaine's vehicle creates a film over the mucosa and prevents normal secretion. This film then adheres to the mucosa and can cause lesion and irritation when the device is removed.

#### **3.2 Intracuff lidocaine**

Lidocaine can permeate through the cuff towards the area of contact due to the cuff's semipermeable nature. The lidocaine tends to diffuse towards the area with a lower concentration and attempts to achieve pH balance. Studies have shown that the diffusion is consequently facilitated if the lidocaine is alkalinized. Authors agree that a relation of 2% lidocaine 9 ml: sodium bicarbonate 7.5% 1 ml is an adequate solution for optimal diffusion [4]. Intracuff alkalinized lidocaine can reduce the incidence and severity of POST up to 50% [14, 15].

#### **3.3 Benzydamine spray**

Benzydamine spray on the outside of the device has been widely used with much better results that lidocaine spray, reducing the incidence of POST in comparison to placebo but has not been effective in concomitant use with intracuff lidocaine [4, 16].

#### **3.4 NDMA antagonists**

Magnesium has been shown to be more effective than ketamine to reduce the incidence and severity of POST [13, 17] but has little clinical use due to the difficulty for preoperative nebulization as well as the added costs in both public and private settings since the equipment for nebulization is not generally necessary in a healthy patient undergoing surgery.

#### **3.5 Multimodal analgesia**

With the advent of the opioid crisis across the globe, multimodal analgesia has become much more appreciated. Current recommendations include the use of opioids as rescue analgesics in the post-anesthesia care unit (PACU). Conventional analgesia generally includes a non-steroidal anti-inflammatory (NSAID) drug, paracetamol/ acetaminophen, and a short life steroid. POST has been compared in patients who have received multimodal analgesia vs. single drug analgesia and have found a superiority of dexamethasone in combination with other analgesic drugs for the reduction in incidence and severity of POST [18, 19]. Opioid sparing anesthesia has also proven beneficial to reduce the incidence of POST, mainly secondary to the use of intravenous lidocaine, magnesium and/or dexmedetomidine in perfusion [19].
