The mean (SD) sedation time was 26.6 (12.19) min [range 10–70]. The median dose of midazolam was 3.0 mg (range 0.5–3 mg). The median dose of propofol was 30 mg (range 5–30 mg). The median end-tidal concentration of sevoflurane was 0.25% (inspired and end-tidal concentrations of sevoflurane were between 0.1% and 0.3% for all patients).
Spearman's rank correlation coefficient showed a significant correlation between the given doses of midazolam and propofol (0.730, P < 0.0001) and between the dose of propofol and the median end-tidal (Et) sevoflurane concentrations (0.310, P = 0.008) in 72 patients who successfully completed their treatment under conscious sedation. The remaining six patients were omitted from this analysis due to lack of accurate recording of either midazolam or propofol doses. No significant correlation is illustrated between the midazolam doses given to patients and the median end-tidal (Et) concentrations of sevoflurane.
Seventy of the 78 patients (89.7%) who satisfactorily completed the treatment under sedation were within the desired target Levels 3–4 of the sedation score and managed to satisfactorily complete the treatment under sedation. Of the eight patients whose sedation level was outside the target range, two (2.6%) scored 2 (awake not anxious), five (6.4%) scored 5 (eyes closed, responds to mild physical stimulation) and one (1.3%) scored 6 (unresponsive to mild physical stimulation) as shown in Table 4.
During the sedation, 38 patients were given 20 mg of ketorolac and 10 patients felt uncomfortable with pain due to inadequate effect of the local anaesthetic and each patient received fentanyl up to 100 μg i.v. for pain relief.
During sedation and recovery, the lowest observed oxygen saturation was greater than 93% in all patients. HR and BP recording were all within ±15% of baseline readings.
The conscious level [22,23] of the patients on arrival in the recovery room as assessed by the recovery nurse is shown in Table 4.
The VAS as recorded by patients prior to their discharge from the recovery room, showed that 61 of the 78 patients (78.2%) who completed the treatment under sedation scored 0–10 (no pain), another 11 patients (14.1%) scored 20–50 (mild to moderate pain) and the remaining six (7.7%) patients scored greater than 50 (moderate to severe pain).
No serious adverse incidents were encountered during sedation and in the recovery room. Five of 78 (6.4%) patients who completed the treatment under sedation did complain of mild postoperative nausea and vomiting (PONV) but did not require antiemetics.
Of the 78 patients who completed the treatment under sedation, 12 patients (15.4%) had full recall of events during their procedures but did not feel anxious. Thirty-two patients (41.0%) had partial recall of events and the remaining 34 patients (43.6%) had no recall.
The mean (SD) time to discharge back to the wards was 10.2 (4.41) min [range 3–16].
Forty-eight patients (61.5%) regarded the overall management as excellent and the remaining 30 patients (38.5%) as satisfactory.
The authors believe that the sequential use of i.v. midazolam and propofol for induction of conscious sedation followed by inhalation of low-concentration (0.1–0.3%) sevoflurane and 40% nitrous oxide mixture for maintenance of conscious sedation for patients requiring endoscopic and/or interventional surgical procedures has not been investigated or published before. Numerous problems may be encountered with the use of total i.v. sedation which may include deep sedation with or without an unprotected airway, loss of consciousness, poor patient co-operation, loss of protective reflexes, respiratory depression, hypoxaemia and cardiovascular collapse. These risks can be unpredictable particularly when potent or combined i.v. sedative drugs are used in children or sick elderly patients . Other patients who are at risk of developing complications related to sedation include those with severe systemic diseases such as cardiac, pulmonary, hepatic or central nervous system diseases, morbid obesity with sleep apnoea and drug or ethanol abusers. This unpredictability is considered unacceptable and does not comply with the second part of the definition of conscious sedation adopted by the General Dental Council and the Department of Health [24,25]: ‘A technique in which the use of a drug or drugs produces a state of depression of the central nervous system enabling treatment to be carried out, but during which verbal contact with the patient is maintained throughout the period of sedation. The drugs and techniques used to provide conscious sedation for dental treatment should carry a margin of safety wide enough to render loss of consciousness unlikely.’
In search of an acceptable alternative technique to total i.v. sedation that may further improve the safety whilst maintaining the effectiveness of conscious sedation, the authors investigated the use of low concentrations (0.1–0.3%) sevoflurane in conjunction with a fixed ratio of 40% nitrous oxide (which proved a safe and effective inhalation conscious sedation technique [10,11]) for the maintenance of conscious sedation. The use of inhalation sevoflurane/nitrous oxide mixture as an alternative to the use of i.v. drugs for maintenance of conscious sedation, may result in reduced amounts of i.v. sedative drugs used during the treatment, with less likelihood of problems with cardiorespiratory depression and delay in recovery and discharge time.
The use of inhalation conscious sedation with sevoflurane/nitrous oxide mixture fulfils the definition of conscious sedation [24,25]. During treatment the level of consciousness and co-operation was observed and recorded every 5 min guided by the six-point scoring scale (19–20). The records showed that 72 of the 78 patients (92.3%) who completed the treatment under sedation were conscious and responsive to verbal contact and remained within the desired target Levels 3–4 during sedation. Five patients (6.4%) scored 5 (eyes closed, responds to mild physical stimulation) on at least one occasion during the procedure. One patient (1.3%) scored 6 (unresponsive to mild physical stimulation) on one occasion during the course of sedation but did not require airway intervention. These six patients continued to breathe spontaneously without airway support and maintained their oxygen saturation over 93%. Each of these six patients was instantly reverted to a lighter level of sedation (Levels 3–4) simply by reducing the sevoflurane concentration to 0.1% or by removing the mask for 10–20 s (Table 4). After surgery, all patients received oxygen for a few minutes whilst assessed by the recovery nurse. This technique relies on a careful titration of sevoflurane to improve patient co-operation. The precise concentration required is tailored to each patient's needs. As we have not used sevoflurane in concentrations higher than 0.3%, we suggest that the concentration of sevoflurane should not exceed 0.3% given in 40% nitrous oxide and oxygen [10,11]. During sedation, there is always a risk that the patient may drift into a deeper level of sedation. This risk is more likely to happen with the use of i.v. sedation rather than with the use of inhalation sedation [9,10]. Therefore, continuous monitoring of oxygen saturation, HR, inspired and end-tidal sevoflurane and the use of a sedation scale [22,23] are recommended for use with any sedation technique. Because of the use of 60% inspired oxygen concentration, reduced oxygen saturation is unlikely with this technique. This was demonstrated in our study.
The 82 patients included five undergoing laparoscopic sterilization and four having diagnostic laparoscopies. Four of the five patients undergoing laparoscopic sterilization did not co-operate with the surgeon and required conversion to general anaesthesia. From these results we suggest that the technique is unsuitable for use for laparoscopic sterilization.
More than 78% of the patients experienced no pain during the procedure and 8% recorded moderate to severe pain. Despite this incidence of moderate to severe pain, patient satisfaction was very acceptable with over 60% rating the overall management as excellent and the rest regarding it as satisfactory. This finding could be due to the amnesic effects of the sedative drugs.
The study showed that 78 of the 82 patients (95.1%) successfully completed the scheduled diagnostic and/or surgical treatment without serious side-effects. This pilot study has indicated that the technique is effective and well accepted and tolerated by both the patients and the surgeons. The use of titrated doses of i.v. sedative drugs for induction of sedation and inhalation agents for maintenance, which are rapidly eliminated, allows more rapid discharge from the recovery area. Also, the technique offers wide clinical applications (Table 3) particularly in the field of ambulatory surgery, orthopaedic, general or vascular surgery and in gynaecology. It could also be used in conjunction with regional anaesthesia and nerve blocks or during insertion of invasive lines in conscious patients. Currently, the technique is in use by one of the authors for adult patients having chair dental treatment outside the hospital setting. It is recommended that the technique is only used by a qualified anaesthetist with continuous monitoring and a high standard of vigilance. Table 5 summarizes the basic requirement needed for the use of any conscious sedation technique. Further clinical studies are needed in order to fully evaluate our technique.
The author would like to thank consultant surgeons and theatre staff at Scarborough General and Bridlington District Hospitals for their valuable participation in this study. Some of the data in this paper were presented at a meeting of the European Society of Regional Anaesthesia, May 2002 and an ad hoc National Anaesthesia Research Meeting, June 2004. G.Y.L. was involved in all parts of the study and will be the guarantor of the data. P.M.H. was involved in the analysis of data and writing of the paper.
1. Coulthard P, Craig D. Conscious sedation. Dent Update
2. The Association of Anaesthetists of Great Britain and Ireland; Recommendation for standards of monitoring during anaesthesia and recovery. The Association of Anaesthetists of Great Britain and Ireland
, 3rd edn, Revised, December 2000.
3. The Royal College of Anaesthetists; Report of an Intercollegiate Working Party. Implementing and Ensuring Safe Sedation Practice for Healthcare Procedures in Adults
. November 2001.
4. The National Confidential Enquiry into Patient Outcome and Death. The 2000 Report of the National Confidential Enquiry into Perioperative Deaths
. November 2000.
5. Cote CJ, Karl HW, Notterman DA, Weinberg JA, McCloskey C. Adverse sedation events in pediatrics: analysis of medications used for sedation. Pediatrics
6. Malviya S, Voepel-Lewis T, Prochaska G, Tait AR. Prolonged recovery and delayed side effects of sedation for diagnostic imaging studies in children. Pediatrics
7. Hansen TG. Propofol infusion syndrome in children. Ugeskr Laeger
8. Roback MG, Wathen JE, Bajaj L, Bothner JP. Adverse events associated with procedural sedation and analgesia in a pediatric emergency department: a comparison of common parenteral drugs. Acad Emerg Med
9. Patel S, Vargo JJ, Khandwala F, Lopez R, Trolli P, Dumot JA, Conwell DL, Zuccaro G. Deep sedation occurs frequently during elective endoscopy with meperidine and midazolam. Am J Gastroenterol
10. Lahoud GYG, Averley PA, Hanlon MR. Sevoflurane inhalation conscious sedation for children having dental treatment. Anaesthesia
11. Lahoud GYG, Averley PA. Comparison of sevoflurane and nitrous oxide mixture with nitrous oxide alone for inhalation conscious sedation in children having dental treatment: a randomised controlled trial. Anaesthesia
12. Mason KP, Zurakowski D, Karian VE, Connor L, Fontain PJ, Burrows PE. Sedatives used in paediatric imaging: comparison of IV pentobarbital with IV pentobarbital with midazolam added. AJR Am J Roentgenol
13. Runes J, Strom C. Midazolam intravenous conscious sedation in oral surgery, a retrospective study of 372 cases. Swed Dent J
14. Campbell RL, Ross GA, Campbell JR, Mourino AP. Comparison of oral chloral hydrate with intramuscular ketamine, meperidine, and promethazine for pediatric sedation – preliminary report. Anesth Prog
15. Agostino J, Terndrup TE. Chloral hydrate versus midazolam for sedation of children for neuroimaging: a randomized clinical trial. Pediatr Emerg Care
16. Winn CW, Porter AG, Vincent RN. Oral meperidine, atropine, and pentobarbital for pediatric conscious sedation. Pediatr Nurs
17. Dallman JA, Ignelzi Jr MA, Briskie DM. Comparing the safety, efficacy and recovery of intranasal midazolam vs. oral chloral hydrate and promethazine. Pediatr Dent
18. Manuli MA, Davies L. Rectal methohexital for sedation of children during imaging procedures. Am J Roentgenol
19. Otley CC, Nguyen TH. Conscious sedation of pediatric patients with combination oral benzodiazepines and inhaled nitrous oxide. Dermatol Surg
20. Wilson KE, Welbury RR, Girdler NM. A randomized, controlled, crossover trial of oral midazolam and nitrous oxide for paediatric dental sedation. Anaesthesia
21. Jackson DL, Johnson BS. Inhalational and enteral conscious sedation for the adult patient. Dent Clin North Am
22. Girdler NM, Rynn D, Lyne JP, Wilson KE. Patient controlled propofol sedation in phobic patients. Anaesthesia
23. Cook LB, Lockwood DG, Moore CM, Whitwam JG. True patient controlled sedation. Anaesthesia
24. General Dental Council. Maintaining Standards: Guidance to Dentists on Professional and Personal Conduct
. London: General Dental Council, November 1998 and May 1999.
25. Department of Health. A Conscious Decision. A Review of the Use of General Anaesthesia and Sedation in Primary Dental Care
. London: Department of Health, 2000.
Keywords:© 2007 European Society of Anaesthesiology
CONSCIOUS SEDATION, intravenous, inhalation; ANAESTHETICS INTRAVENOUS, midazolam, propofol; ANAESTHETICS INHALATION, sevoflurane, nitrous oxide; ENDOSCOPICAL PROCEDURES; AMBULATORY SURGICAL PROCEDURES; ANAESTHESIA CONDUCTION