Difficult airway is defined as difficult ventilation and/or intubation resulting from anatomic or pathologic problems or a situation in which optimal positioning of the patient may be unsafe .
Airway regional blocks have been commonly used for years in patients with anticipated difficult intubation because of the ability to maintain spontaneous ventilation, airway patency and cooperation of the patient .
The simplicity of these techniques is one of the advantages of airway blocks  but complications such as elimination of highly effective airway protective reflexes, bleeding, nerve damage and intravascular injection are the disadvantages of airway blocks .
Besides the complications mentioned above, the absence of enough access to airway landmarks needed for regional airway blocks in oropharyngeal, laryngeal and neck tumors and obesity, are other encouraging reasons to search for alternative methods to regional airway blocks. Laryngopharyngeal lesions are among the common causes of predicted difficult intubation and the airway is very difficult to handle  and therefore airway regional blocks are commonly used in these cases to keep the airway secure during laryngoscopy and intubation. Airway manipulation without sedation is terribly annoying and the anesthesiologist is obliged to use a kind of sedation.
In laryngeal tumors Direct Laryngoscopic Biopsy (DLB) performs through rigid bronchoscope and this kind of surgery requires general anesthesia, and tracheal intubation is necessary in order to prevent aspiration of blood and tumor particles. General anesthesia is induced after awake tracheal intubation
Laryngeal tumors (supraglotic, glotic, subglotic) produce partial mild to severe obstruction of the airway at the glotic or subglotic region (predicted difficult airway) and sometimes localization and/or the bulk of the tumor make the intubation impossible. Therefore we have to keep the patient awake during the laryngoscopy and intubation in order to maintain a secure airway.
In this study "subcutaneous Dissociative Conscious Sedation" was evaluated as a non invasive method for awake laryngoscopic procedures to provide enough sedation and a peaceful situation for the patient by preparing a cooperative, conscious and deeply sedated patient for the anesthesiologist during the laryngoscopy and intubation.
The most important advantage of this method is the ability to maintain spontaneous ventilation in a deeply sedated patient while the patient is cooperative enough to obey.
Conscious sedation as a method to safeguard the patients with compromised airway is a confusing term because we need a fully sedated, calm patient with no respiratory depression and no disturbing effect on the cooperation. A variety of methods have been used to provide enough analgesia and sedation during the manipulation of airway in an awake patient [5–16].
Dissociative conscious sedation was designed and used for the first time in 2004 by the author for laparoscopic implantation of peritoneal dialysis catheter in patients who had very poor physical condition because of their end stage chronic renal failure and related complications (vascular access problems for hemodialysis, severe cardiovascular diseases, volume overload, severe fluid and electrolyte imbalances,...) and were not suitable for general anesthesia . Dissociative conscious sedation or in other words dissociative conscious anesthesia is defined as using an intravenous or subcutaneous injection of "low dose ketamine' in conjunction with narcotics to achieve an acceptable level of sedation, pain relief and amnesia . Then this method was reported as an alternative method for regional airway blocks in "The 1st International Congress of Airway Management/and Anesthesia in Head and Neck Surgery" [18, 19]. In the two previous studies a very low dose of midazolam (0.015 mg/kg) was used in order to achieve a desirable level of sedation and amnesia [17, 18]. Although using midazolam has been reported in order to improve patient's comfort , it can be life threatening in the case of difficult airway because it causes an unintended deep sedation, hypoxemia, desaturation  and upper airway obstruction which is irreversible with flumazenil [21, 22], also midazolam interferes with the patient's cooperation considerably. Using midazolam in conjunction with other drugs can be dangerous and life threatening in the case of compromised airway and it should be avoided.
Regarding the unique ability of ketamine to provide simultaneous anxiolysis, analgesia and amnesia and maintaining airway and breathing reflexes  this study was conducted without using midazolam and patient's comfort and amnesia were provided by using a low dose of ketamine. The study showed that "low dose ketamine" can be an appropriate substitute for midazolam. The dose of ketamine for inducing dissociative conscious sedation can be variable in different procedures (o.5 mg/kg -1 mg/kg).
Ketamine has been used for decades as an analgesic and anesthetic drug. Ketamine is used by oral, intranasal, rectal and subcutaneous routes .
In the recent decade, sub anesthetic doses of ketamine have been used as an adjuvant to increase the duration of action and the analgesic effect of narcotics in palliative care, in the control of chronic pain  and postoperative pain . Sub-anesthetic dose of ketamine as an adjuvant to narcotics has a dramatic pain relief and opioid dose sparing effect . Ketamine is a small lipophilic molecule with rapid onset and relatively short duration of action (about 15 minutes), in intravenous administration and it requires continuous infusion for maintenance of clinical effects .
In this study the subcutaneous route of injection was chosen, because the gradual absorption of the drug decreases the adverse effects because of the low plasma concentration, and increases the duration of the analgesic effect of narcotics considerably. It has been shown that psychomimetic side effects can be prevented by keeping the plasma concentration at or below 150 ng/ml  and psychomimetic side effects have not been reported after rectal administration, which is known to result in low plasma levels . A subcutaneous infusion might therefore provide analgesia without hallucinations or other psychotomimetic effects [30, 31].
Avoiding midazolam increases the safety of dissociative conscious sedation considerably.
By avoiding midazolam, narcotic related respiratory depression is easily reversible by asking the patient to breathe.
Comparison of subcutaneous and intravenous Dissociative Conscious Sedation  showed the superiority of subcutaneous DCS.
The results of this study confirmed that subcutaneous DCS provides an appropriate situation for a safe and successful manipulation of the airway and tracheal intubation, with the ability to maintain a patent airway, spontaneous ventilation, and a deeply sedated, cooperative and obedient patient during the procedure.
Limitations of the study
This study as an interventional initiative study had some limitations. Because of the ethical limitations for using a new interventional method, I had to include only ASA class I and II patients and choose the patients who had no accessibility to the landmarks needed for airway regional blocks and therefore airway regional blocks were impossible or contraindicated. Cases in this category of difficult airway are not common. Given the limitations mentioned above and as a preliminary study, the small sample size of the study may be excusable.
On the other hand small sample size and high incidence of laryngeal tumors in men (much more common in men) resulted in another limitation and the study included only male patients.
Regarding the limitations mentioned above obviously we need complementary studies in the future. This method should be evaluated in comparison to other pre-existing methods of awake intubation as well.