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Balanced conscious sedation with intravenous induction and inhalational maintenance for patients requiring endoscopic and/or surgical procedures

Lahoud, G. Y.*; Hopkins, P. M.*

European Journal of Anaesthesiology: February 2007 - Volume 24 - Issue 2 - p 116–121
doi: 10.1017/S0265021506001207
Original Article

Background and objective: The use of inhalation sedation with sub-anaesthetic concentrations of sevoflurane and nitrous oxide mixture is expected to reduce amounts of intravenous sedative drugs needed to produce a balanced sedation with the benefits of having reduced side-effects.

Methods: Eighty-two patients requiring endoscopic and/or surgical procedures under conscious sedation and local anaesthesia were recruited for this pilot study. Conscious sedation was induced with a titrated dose of midazolam and propofol given intravenously until the clinical end-point of conscious sedation was achieved. Subsequently, during the procedure, the patient was asked to breathe sevoflurane 0.1–0.3% and a fixed ratio of 40% nitrous oxide in oxygen given through a face mask.

Results: In 78 patients (95.1%), the treatment was completed successfully. Patients were discharged back to the wards within 4–16 min (10.1) without significant side-effects. Treatment was satisfactorily accepted by 38 patients (48.7%) and considered excellent by 40 patients (51.3%).

Conclusions: The use of titrated doses of intravenous sedative drugs for induction of conscious sedation followed by the use of low concentrations (0.1–0.3%) of sevoflurane combined with 40% nitrous oxide for maintenance of conscious sedation in patients requiring endoscopic and/or surgical procedures under local anaesthesia, has the potential advantages of reducing amounts of intravenous sedative drugs, less likelihood of problems from drug side-effects and fast recovery and discharge time. Further investigations to establish the technique are currently in progress.

*University of Leeds, Academic Unit of Anaesthesia, St. James's University Hospital, Leeds, UK

Correspondence to: G. Y. Lahoud, Department of Anaesthesia, Scarborough General Hospital, Woodland Drive, Scarborough, North Yorkshire, YO12 6QL, UK. E-mail:; Tel: +44 1723 342394; Fax: +44 1723 385160

Accepted for publication 26 June 2006

First published online 8 August 2006

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As patient awareness of the risk of general anaesthesia and the availability of sedation has increased, so the popularity of conscious sedation for dentistry, diagnostic and interventional surgery has also increased [1]. Conscious sedation results in an altered state of awareness, a reduction in pain, an alleviation of anxiety and fear and an improvement in patient co-operation during the treatment. It is anticipated that with conscious sedation, the patient continues to breathe spontaneously and remains conscious and responsive to verbal contact throughout the sedation period and during recovery. Intravenous (i.v.) sedation is commonly used as a supplement to local anaesthesia in a wide range of outpatient procedures. i.v. sedation usually means giving increasing doses of the benzodiazepine drug, midazolam or a sedative dose of propofol, or a combination of these drugs with or without the use of opioids such as fentanyl, alfentanil or remifentanil. Patients should be fully monitored by experienced personnel who are trained to carry out advanced life support when needed. Monitoring devices (pulse oximeter, electrocardiogram and a non-invasive blood pressure (BP) measurement) are an essential basic requirement for the technique [2–4].

The pharmacokinetic variability in plasma concentrations and clearance of i.v. sedative drugs create less predictable responses, particularly in young children or elderly patients. This unpredictability can occur even with the use of a single sedative drug and even when the standard dosage is used [5]. Problems encountered with i.v. sedation may include poor co-operation where the patient becomes restless, agitated and combative which can be easily misinterpreted by inexperienced personnel, that the patient is under sedated, when in fact they are over sedated. Also, it may precipitate loss of consciousness, a compromised airway and loss of protective reflexes, cardiovascular and respiratory depression [6–9]. i.v. sedation can be associated with delayed recovery and discharge time that may require an overnight hospital admission for observation, with the added strain on hospital beds and resources.

Recent studies showed that spontaneous inhalation of 0.1–0.3% sevoflurane and a fixed ratio of 40% nitrous oxide in oxygen is safe and a more effective inhalation conscious sedation technique than the use of nitrous oxide alone [10,11]. The technique can be also used as an alternative to i.v. sedation particularly in patients with needle phobia or when the risk of i.v. sedation is considered unacceptable, such as in young children and in frail elderly patients. Conscious sedation with the use of i.v., intramuscular, oral, nasal or rectal sedative drugs [12–18] or tranquilizers combined with nitrous oxide, opioids or ketamine [19–21] has been previously reported. However, drug combinations result in an increased likelihood of complications particularly when used by inexperienced personnel.

The aim of the present study was to assess the feasibility and patient acceptability of the use of i.v. sedative drugs for the induction of conscious sedation followed by maintenance of conscious sedation using sevoflurane and nitrous oxide.

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Ethical approval was obtained from Scarborough and North East Yorkshire Local Research Ethics Committee. Eighty-two ASA I–III adult patients aged 18 yr and over were recruited for the study. Each patient was interviewed and clinically assessed prior to the treatment. Patients who were identified as suitable for i.v. or inhalation conscious sedation (with or without the use of local anaesthesia) were given a full verbal and written explanation of the project and written consent was obtained. Patients were excluded if there was a family history of malignant hyperthermia or known hypersensitivity to sevoflurane, midazolam, propofol or local anaesthetic drugs. Patients with a history of psychiatric illness, or who were mentally or physically handicapped were also excluded.

All patients had fasted for a minimum of 2 h for clear fluids and 6 h for solids and dairy products prior to the procedure. A pulse oximeter, electrocardiogram and a non-invasive BP monitor were attached to the patient and a baseline reading was recorded prior to initiating conscious sedation. An indwelling venous cannula was inserted into the patient's hand. The anaesthetist then gave midazolam 0.5 mg increments to a maximum of 3 mg at 1 min intervals to achieve Level 2 of the sedation scoring scale (awake not anxious – see Table 1 [22,23]). Propofol was then given in 5 mg increments to a maximum of 30 mg at 10 s intervals to achieve Level 4 of the sedation scoring scale (eyes closed, responds to speech). For some patients it was clear during propofol administration that Level 4 would not be achieved even using all of the 30 mg. In these cases additional 0.5 mg increments of midazolam (up to a total 3 mg) were given. Once a satisfactory conscious sedation level was achieved (Level 4), no further i.v. sedative drugs were used and conscious sedation was maintained by asking the patient to breathe low concentrations of 0.1–0.3% of sevoflurane (delivered by a Drager vapour 2000 vaporizer which has a minimum dial setting of 0.2 volume concentration) in conjunction with a fixed ratio of 40% of nitrous oxide in oxygen at a gas flow of 6L min−1 delivered by continuous flow through a Bain circuit or McKesson model B scavenging nasal inhaler circuit for patients requiring oral surgery. The face or nasal mask was adapted to incorporate a probe to measure inspired and end-tidal oxygen, nitrous oxide and sevoflurane using a Datex Ohmeda AS/3 anaesthesia monitor. During treatment the level of consciousness and co-operation was observed and recorded (by one of the authors) every 5 min guided by the six-point scoring scale. Patients were maintained ideally between Levels 3 and 4 (Table 1) [22,23].

Table 1

Table 1

Prior to the planned surgery, the surgical site was infiltrated with a local anaesthetic drug such as plain lignocaine 1% by the surgeon who then proceeded with the surgery. Patients were given ketorolac 20 mg i.v. unless contraindicated. If the patient complained of pain despite the local anaesthesia, fentanyl 25 μg repeated as necessary was given to maximum of 100 μg.

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When treatment was completed, all gases were withdrawn and 100% oxygen was given through a face mask for 2 min. The patient was then observed and monitored during recovery by a nurse who recorded the following information:

  1. Time of the patient's arrival in the recovery room.
  2. Oxygen saturation.
  3. Heart rate (HR) and BP.
  4. Patient's conscious level using the six-point scoring system.
  5. Visual analogue pain scale (VAS) as recorded by the patient (0 = no pain, 100 = severe pain).
  6. The presence of vomiting or the patient complaining of nausea.
  7. The patient's opinion of the overall management and experience during treatment (1 = poor, 2 = satisfactory, 3 = excellent) was asked prior to being discharged back to the ward.
  8. Time to discharge back to the ward when the patient was considered fully alert, oriented to time and place and pain free.
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The characteristics of the patients are shown in Table 2. The planned procedures were successfully completed under sedation in 78 of the 82 patients (95.1%). The remaining four patients who were scheduled for laparoscopic sterilization failed to co-operate during sedation and local anaesthetic. Of these four patients, two were restless and moving excessively and the remaining two patients felt pain and discomfort despite receiving ketorolac and fentanyl. All four patients required general anaesthesia in order to complete their procedures. Table 3 shows the type of diagnostic and/or surgical procedures carried out.

Table 2

Table 2

Table 3

Table 3

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.

Table 4

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.

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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 [5]. 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.

Table 5

Table 5

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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.

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