SEDATION / ANALGESIA MONITORING in ADULTS

 

S. Kannan

 

 

The word ‘monitor’ is derived from the Latin verb monere – ‘to warn’. The purpose of a monitoring device is to measure a ‘variable’ [usually physiological] and to indicate trends of change, thus enabling appropriate therapeutic action to be taken if necessary. No device can replace human observations of the patient as information from the monitor requires clinical interpretation.

 

Is monitoring useful?

It is difficult to prove that monitoring per se reduces morbidity and mortality. In a study of 20,802 patients, Moller et al [1993, Anesthesiology] randomized patients to be monitored with and without pulse oximetry. Pulse oximetry was 20 times more likely to detect hypoxemia than other methods of monitoring. The trend continued into the recovery phase. However, there was no difference in mortality and cardiovascular, neurologic and infectious complications between the two groups. This does not mean that pulse oximetry is not useful. Since the incidence of directly attributable complications and mortality is so low, a study sufficiently powered to detect a difference will be practically impossible.

The NCEPOD reported in 2000 on deaths during vascular and neurovascular interventional radiology identified 445 deaths from 21000 procedures within 30 days of a procedure. West Midlands had 36 deaths. 30% of the deaths occurred within 72 h of the procedure.  19 patients were not monitored at all, 60 did not have oximetry and 40 did not have BP taken during the procedure. 16 of the dead were monitored by a radiographer, 97 died when being monitored by the operator alone. In half of the patients, death was not expected. Ninety two percent of patients who died were ASA grade 3 or higher and 88% had coexisting medical conditions

 

Are the standards being followed?

A postal survey of British and Irish interventional radiologists was carried out in 1991 in order to assess current practice with respect to sedation and monitoring of patients during angiography and interventional procedures. The response rate was 65%. 49% of patients are fasted prior to angiography and 68% prior to interventional procedures. Radiologists participate in obtaining consent in 60% of cases. Patients are often (50%) sedated for angiography and usually (62-94% depending on the procedure) sedated for interventional procedures. Nurses are present for most procedures, but are given the task of monitoring the patient's vital signs in only 49% of cases. Anaesthetists are present for less than 10% of interventional procedures. Pulse oximetry is used routinely in 20% of departments, and automatic blood pressure monitors in 16%. 28% of radiologists never administer oxygen to patients under sedation, whereas 4% always do. 43% of departments have a staffed recovery area. Most vascular/interventional suites are stocked with emergency drugs and 80% with a defibrillator. 28% of departments report at least one death during or shortly after a procedure during the last 10 years. 18% of interventional radiologists have taken a refresher course in cardiopulmonary resuscitation in the past year. These findings indicate a wide variation in practice and a need to standardize practice at a uniform high level. The situation has changed considerably following the guidance from the Royal college of Radiologists.

 

Who should do the monitoring?

Ideally the patient should be monitored by a healthcare professional, trained to administer sedation who will not have any other role at the time of the procedure. It is difficult for the radiologist performing the procedure to safely monitor the patient unaided. Providing staff to monitor a patient is currently a difficult area for many departments. The overriding consideration must be that patient safety should not be compromised because of staffing or financial constraints. Some non-vascular interventional procedures can cause severe pain and require sedation and analgesia administered by an appropriately trained healthcare professional with the appropriate level of monitoring. There are some procedures that radiologists might consider require general anaesthetic, because they are particularly painful or because of the individual needs of a particular patient. If such anaesthetic support is not available then it might be inappropriate to perform that procedure.

 

When to monitor?

•         All patients receiving any form of sedation

•         During and after the procedure

•         Baseline values

•         High risk patients

–        ASA IV or worse

–        Multiple co morbidities

•         DM, HT, COAD, Obesity, heart failure, IHD, Elderly, Renal Failure

•         Complicated / Prolonged procedure

 

Which Monitors to use?

The NCEPOD recommended that the gold standard for monitoring should be ECG, NIBP and Oximetry. However, monitoring oxygenation by pulse oximetry is not a substitute for monitoring ventilatory function. Deeply sedated patients can hypoventilate and become significantly hypercapnic without becoming hypoxic if they are given supplemental oxygen. Other parameters to monitor should include Consciousness, pain relief, respiratory rate and pattern, skin colour, perfusion, urine output, hydration and side effects of drugs. Vital signs (blood pressure, pulse, respiratory rate), should be recorded before and immediately after any drug administration and should be monitored and recorded at 5-minute intervals until the patient has reached a stable level of sedation. Throughout the procedure and in the immediate recovery period, vital signs should be recorded every 15 minutes. Electrocardiographic monitoring should be used for all patients undergoing deep sedation. It should also be used during moderate sedation for patients with significant cardiovascular disease Patients must be continuously monitored to assess the depth of sedation and to recognize complications of oversedation, including respiratory depression, airway compromise, and cardiovascular instability. The level of monitoring chosen will depend upon the patient and the procedure. If the patient has poor systemic reserve, is considered ASA III or worse, then all the parameters should be monitored. If the patient is fit and well, young and is undergoing a short procedure, then pulse oximetry may suffice. Due to the increasing complexity of many radiological procedures, including those in the young and very elderly, a greater need for anaesthetic assistance and sessions in radiology departments should be anticipated.

End-tidal CO₂ monitoring allows visual monitoring of the respiratory rate and may detect respiratory depression sooner than pulse oximetry. Although CO₂ monitoring requires specialized monitoring equipment, it can be performed on patients wearing an oxygen mask. Patients receiving anxiolysis or moderate sedation are at low risk of respiratory depression, but monitoring of exhaled CO₂ should be considered for all patients receiving deep sedation.

The confusion arises from terminology traditionally used in textbooks and journals [Table 1]

Table 1 Definition of General Anaesthesia and Levels of Sedation/Analgesia

Responsiveness Airway Spontaneous Ventilation Cardiovascular Function Minimal sedation (anxiolysis) Normal response to verbal stimulation Unaffected Unaffected Unaffected Moderate sedation/analgesia ("conscious sedation") Purposeful response to verbal or tactile stimulation No intervention required Adequate Usually maintained Deep sedation/analgesia Purposeful response after repeated or painful stimulation Intervention may be required May be inadequate Usually maintained General anaesthesia Unarousable even with painful stimulus Intervention often required Frequently inadequate May be impaired Note.—Adapted from Practice guidelines for sedation and analgesia by non-anesthesiologists. Anesthesiology 2002; 96:1004–1017.

 ‘Heavy’, ‘conscious’ or ‘deep’ sedation are unsatisfactory and misleading terms and should not be used in adult practice. In paediatrics a deeper level of sedation is acceptable, is strictly defined, and should be administered only by an anaesthetist or other appropriately trained healthcare professional. If an adult patient is sedated to a point where they are Unarousable to verbal or painless physical stimuli, then that patient is anaesthetised, not sedated, with all the inherent risks attached.

Depending upon the patient, a given dose of 3 mg of midazolam may cause only anxiolysis in a ASA I young patient and cause deep sedation in an 80 year old patient. Hence it is important to always titrate the dosage of medications rather than assume a fixed dose based on body weight. The ultimate aim is to achieve adequate sedation so that the whole experience becomes bearable for the patient. Although it may considered ideal for all such patients to be given deep sedation, many of them undergo interventional procedures since they are high risk candidates for a general anaesthetic or surgery. A sedation continuum has been suggested to be a guide to the sequence of events during a procedure [table 2].

Table 2 The Sedation Continuum

Alert-anxious     Alert-calm (anxiolysis)         Drowsy but clear mentation (sedation)             Eyes open, speech slurred                 Eyes closed but answers questions appropriately                     Opens eyes to voice, is confused                         Oxygen desaturation on room air                             Opens eyes to pain, responds purposefully                                 Eyes closed, moans and withdraws from pain                                     Moans to pain, non-specific motor response to pain                                         CO2 retention                                             Oxygen desaturation on 2 L O2                                                 No response to pain                                                     Bradypnea, poor gag reflex                                                         Apnoea, hypotension                                                             Death

 

 

Again a patient may progress rapidly from moaning to pain to losing the gag reflex. The rate and degree of progression cannot be accurately predicted in any given patient and hence the need for titration. What can be said though is that if a patient is alert and calm, then without further medication, he is unlikely to slip into unconsciousness.

A different sedation score has been proposed [Table 3]. This scoring system is slightly more convenient as it has less number of variables. It can be used to decide on suitability of transfer to the ward.

 

 Table 3. Sedation Scale (Ramsey Scale)

Score Description 0 None, patient maintains wakefulness 1 Mild, occasionally drowsy 2 Moderate, frequently drowsy, easy to arouse 3 Severe, somnolent, difficult to arouse S Sleeping

 

 

 

Problems and pitfalls of monitoring

 

ECG – Poor electrode contact and electrical interference can be problematic.

 

Pulse oximetry – Most pulse oximeters have a lag by default and hence desaturation is picked up slightly later than onset. Moreover, due to the nature of oxygen dissociation curve, it does not take long for a patient to desaturate from 90% to 70%. Hence, corrective action should be taken when the saturation reads 90% rather than wait for it to fall. Pulse oximetry is also affected by finger movement, nail varnish, cold extremities, methaemoglobinemia, hypotension and blood pressure cuff inflation in the same arm.

 

Blood pressure – Most automatic monitors measure the mean blood pressure and derive the systolic and diastolic pressures. A mean of over 60 mmHg is the minimum acceptable. Some fit and well young patients should be able to tolerate mean up to 45 mmHg if not prolonged. Patients with hypertension and ischaemic heart disease need a higher mean blood pressure. Manual measurements are fraught with inconsistency and inconvenience. An appropriate sized cuff should be used. Smaller cuffs tend to give false higher readings although larger cuffs do not make much of a difference. Avoid putting the cuff in the same arm as the oximeter probe. Avoid putting the NIBP monitor in ‘stat’ mode as it will continuously record BP. There have been cases of inadvertent nerve injury.

 

Analgesia – Some patients require analgesia for the procedure. Most sedatives are not analgesics and hence the use of preoperative paracetamol, NSAIDs or opiates should be considered. Opiates interact with sedatives and potentiate their actions. All sedatives and opiates have the potential of adverse cardiovascular and respiratory depression. It is not wise to give a higher dose of midazolam when the patient needs an analgesic. Analgesia is monitored indirectly using indicators like moaning, heart rate, blood pressure, respiratory rate, movement [all increase with pain]. Use of local anaesthetics will prevent prolonged sedation once the procedure finishes.

 

Alarms – The limits in the equipment should be set to within 20% of expected range rather than so far apart that the monitor never alarms! Avoid silencing all alarms. Even though they may sound as a nuisance, alarms may be the first time an adverse event is picked up especially when they are not expected to happen. The monitor should be in direct view of the main operator. Avoid a tendency to ignore undesirable values especially if the patient has co-existing systemic conditions. If in doubt, repeat the measurement.

 

It is important to anticipate potential problems in patients rather than just observe and treat if something happens. Knowing the patient’s history and cardiovascular reserve and the nature of procedure will help in identifying the common problems and treating them early.

 

HIGH-RISK PATIENTS

Obesity
Sedated obese patients are at increased risk of gastro esophageal reflux, upper airway obstruction, and oversedation. The risk of reflux may be reduced by strict adherence to fasting requirements and preprocedure treatment with an oral H₂ antagonist and metoclopramide. Upper airway obstruction can occur in obese patients at lighter levels of sedation, and therefore patients should be carefully monitored for this complication. Supine positioning of these patients impairs chest muscle wall function, further reducing functional residual capacity and impeding adequate oxygenation. Obese patients are more susceptible to the respiratory depressant effects of sedative agents, and drug doses should be based on an estimated lean body mass not total body mass. Incremental dosing and waiting for effect are crucial.

Chronic Obstructive Pulmonary Disease
Patients with chronic obstructive pulmonary disease are at risk of respiratory adverse events resulting from the administration of sedation and analgesia. Patients with severe chronic obstructive pulmonary disease already have a blunted ventilatory response to CO₂, and excessive sedatives and opiates will further compromise this response, predisposing patients to severe respiratory depression with excessive sedation.

Coronary Artery Disease
Coexistent coronary artery disease is frequently present in patients undergoing IR procedures, particularly for peripheral vascular or renovascular disease. Inadequate sedation can increase the risk of an acute cardiac event in these patients as a result of increased cardiac demand. Similarly, excessive sedation or respiratory suppression can also precipitate cardiac complications by inducing hypotension or hypoxemia.

Chronic Renal Failure
Dialysis-dependent CRF patients should undergo dialysis on the day of the image-guided procedure to correct fluid balance. Because drugs and metabolites are protein bound, hemodialysis is ineffective in removing these substances from the circulation.

Elderly
In addition to being associated with a higher incidence of concomitant illness, increased age is an independent risk factor for adverse effects of sedation and analgesia. In elderly patients, sedatives and analgesics elicit a longer lasting and more pronounced effect because of changes in bioavailability and reduction in drug metabolism. Generally, elderly patients need lower doses on a milligram-per-kilogram basis. Once again, conservative incremental dosing should be used in this patient population, and medication requirements should be minimized with the liberal use of local anesthetics.

 

Summary

Appropriate use of monitoring is vital in interventional radiology as many of the patients are too sick to have a general anaesthetic or surgery. This predisposes them to higher risk of complications. A dedicated person should be in charge of monitoring the patient through out the procedure and during recovery. Basic minimal monitoring should consist of ECG, NIBP and pulse oximeter. Knowledge of patient’s history and the nature of procedure will ensure appropriate choice of monitoring and minimizing the incidence of complications.