Capnography Monitoring During Intravenous Conscious Sedation Sedation With Midazolam for Oral Surgery

Background Intravenous sedation allows procedures to be performed in dentistry, and other areas of medicine beyond the operating room. Its application in each area is tailored to the requirements of the relevant procedure, the setting and the levels of operator training and expertise. The Academy of Medical Royal Colleges emphasises that each speciality must produce its own form of guidance in the use of sedative techniques. The following definition for conscious sedation in dentistry is accepted by the General Dental Council and the Dental Sedation Teachers Group: "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". The Standing Dental Advisory Committee Guidance 2003, which remains the standard of guidance in the UK, further states: "Any technique resulting in the loss of consciousness is defined as general anaesthesia and in the UKm 'deep sedation' is considered within this category". To summarise; dental sedation lies within the range of minimal to moderate sedation on the sedation continuum i.e. conscious sedation. Deep sedation is to be avoided in this setting.

Dentists who have completed a recognised postgraduate course can practice conscious sedation independently. For intravenous sedation, dentists use a "standard" conscious sedation technique, defined as "intravenous sedation", using midazolam alone. The drug is titrated to an end-point; it is rapid in onset and possesses a short duration of action, which means that midazolam is very useful in the field of dental sedation.

The current standard of monitoring for patients is clinical monitoring, which must be supplemented by pulse oximetry and blood pressure readings. The most important side effect of midazolam is respiratory depression.

Although it is generally considered a safe practice, conscious sedation is not entirely risk-free.Ventilation (breathing) and oxygenation are related but seperate physiological processes. During the process of sedation, clinicians rely on pulse oximetry as a surrogate measure of ventilation. Capnography, a staple gold standard in general anaesthesia, is becoming an increasingly important area of interest for procedural sedation, with studies from other settings suggesting, capnography to be an effective ventilatory monitor for sedated patients.

One significant limitation of pulse oximetry is the lag time; this means that the partial pressure of oxygen may decrease significantly before the pulse oximeter signals the fall.

Reviewing the literature Previous studies on capnography for sedation are difficult to summarise. A review of the available literature has shown a relative paucity of randomised trials and no trials in the dental setting. Three trials from other settings are summarised here. Beitz et al (2012): A total of 760 patients were enrolled. Patients received 2L/min of supplemental oxygen. The intention-to-treat analysis revealed a significant reduction in the incidence of oxygen desaturation in the capnography arm in comparison with the conventional arm (38.9% vs. 53.2%). The study conclusion was that additional capnography monitoring reduces the incidence of oxygen desaturation and hypoxemia during propofol sedation for colonoscopy. Deitch et al (2010): A total of 132 patients in an emergency room setting. Hypoxia was defined as an SpO2 < 93%. The incidence of oxygen desaturation in the capnography arm in comparison with the conventional arm was 25% vs. 42%. All patients received supplemental oxygen (3L/minute). Conclusion: The addition of capnography to standard monitoring reduced the incidence of hypoxia and provided advanced warning for all hypoxic events. Qadeer et al (2009):This trial showed a significantly reduced rate of hypoxia (46% vs 69%), defined as an oximetry reading < 90% for 15 sec. There was a relatively large cohort of ASA 3 patients in the study. 147 patients received supplemental oxygen. The study conclusion was that capnography monitoring of respiratory activity improves patient safety during procedural sedation for elective endoscopy.

Waugh et al (2010) conducted a meta - analysis, the main finding being that during procedural sedation , cases of respiratory depression were 17.6 times more likely to be detected if monitored by capnography than cases not monitored by capnography ( 95% CI, 2.5-122.1).

The results from the three randomised trials and the meta-analysis cannot be generalised and extrapolated to the standard dental sedation technique because of:

1. Different patient populations The reviewed studies contain many elderly patients who are known to be more sensitive to sedative drugs and more likely to have co - morbidities. For standard dental sedation the age is less than 65 years.
2. Supplemental Oxygen In standard dental technique patients breath room air. In the reviewed studies supplemental oxygen was often administered.
3. Drugs Different drugs were used to achieve sedation in the reviewed studies e.g. Propofol and Ketamine.
4. Analgesia Local anaesthetic is employed for analgesia in dentistry. In the reviewed studies, analgesia was often achieved with the use of intravenous agents such as opioids. The synergistic effect of drugs used in combination are likely to have resulted in increased respiratory depression.
5. Desaturation (SpO2) For the standard dental sedation technique an SpO2< 95% is regarded as the threshold for early desaturation.This is a reasonable threshold in this setting where sedation is administered by a non-anaesthetist outside of the operating room. In the reviewed studies the thresholds varied. Deitch et al used a threshold < 93% and Qadeer et al. <90%.
6. Depth of sedation Varied between the studies and in some cases was beyond conscious sedation.

Aim:

The aim of this randomized, controlled study is to determine whether early intervention based upon data from capnographic monitoring reduces the incidence of arterial oxygen desaturation during midazolam sedation for dentistry.

Objectives:

1. Determine if early intervention based on capnography will influence the incidence of arterial oxygen desaturation.
2. Characterise the ETCO2, respiratory rate and SPO2 at baseline pre sedation, during sedation and post sedation.

This will be a prospective, randomised controlled trial on dental patients receiving intravenous conscious sedation with midazolam.

Goal: To determine whether use by the dental team of real - time capnography is associated with a decrease in the incidence of oxygen desaturation (hypoxia) compared with standard monitoring alone during intravenous sedation with midazolam for dentistry.

Setting and selection of participants:

Patients attending the oral surgery department and the dental theatre for sedation procedures at Cork University dentalo school and Hospital and Cork University Hospital will be prospectively invited to take part. Patients will be randomly assigned to the study group (standard monitoring and capnography) or control group (standard monitoring and blinded capnography) . The sedation team will be blinded to the randomisation choice until after enrolment. A member of staff not directly involved in the study will conduct the randomisation. There is evidence for utilising intravenous midazolam in the age group 14 to 16years (post pubertal) for dentistry. Including this age cohort ( with parental consent) will provide additional research data to add to the body of evidence. Patients will have intravenous sedation with midazolam primarily for the relief of anxiety and to help them to accept invasive procedures. The operative procedures will range from simple extractions to minor oral surgery procedures such as the removal of impacted wisdom teeth.

Pre sedation visit:

Patients will be assessed as to their suitability for sedation at a separate pre sedation visit Baseline capnography and pulse oximetry data will be collected at this visit. Patients meeting the inclusion criteria will be given written information about the study. This information will be written in lay language.

Enrolment to the study will take place at the beginning of the subsequent treatment visit for those patients who consent to take part having had time to consider the information provided about the study at the pre assessment visit. Patients will receive pre sedation instructions. Standard electronic monitoring (pulse oximetry, pulse rate and blood pressure) will be available to the clinical staff at all times. Standard dental sedation will be used according to the institutions policy and protocol. A capnostream 20 monitor ( Oridian medical, Needham, MA), using a disposable oral - nasal CO2 cannula capable of delivering oxygen, with an oral sampling port to accommodate mouth breathing will be attached to all patients. The capnostream 20 monitor displays oximetry and CO2 waveform and calculates ETCO2. The capnography monitor will be calibrated every day of the study.

Continuous recording of SpO2, Heart rate, ETCO2 and respiratory rate will be stored on a laptop computer via specialised software for post hoc analysis. In addition, clinical staff will keep paper records of the patients' age, sex, body mass index, ASA status and medical history. All patients will be assigned a code to maintain confidentiality.

Before the study, all clinicians and nursing staff will be trained in the interpretation of capnography in relation to respiratory depression including waveform interpretation. A laminated interpretation card will be attached to the monitor as a reminder. The sedation team will perform conscious sedation according to standard protocol for dental sedation. Intervention for an adverse event will be based on judgement and clinician expertise with or without capnography depending on randomisation arm. In the capnography arm,in addition to standard monitoring, changes in the shape of the capnography waveform, ETCO2 numeric changes will be considered as triggers to take measures to avoid desaturation. In the control group, capnography will be blinded by placing an opaque screen over the capnostream 20 capnographydisplay of ETCO2 values, respiratory rate and waveform. Pulse oximetry will continue to be displayed. Baseline monitoring data will be obtained for at least 2 minutes prior to the first infusion. Midazolam will be titrated at a rate of one mg per minute to an end point. Most patients are discharged 60 minutes after the last increment provided they are fit for discharge. We propose collecting study data until discharge.

All patients will receive written pre and post sedation instructions. the benzodiazepine antagonist , flumazenil will be available in the sedation suite at all times in addition to emergency drugs and equipment.

The Null hypothesis states: The study group is the same or equal to the control group in terms of hypoxemia rates i.e arterial oxygen desaturation.