The Changing Role of Monitored Anesthesia Care in the Ambulatory Setting

Conscious analgesia/sedation with remifentanil and propofol versus total intravenous anesthesia with fentanyl, midazolam, and propofol for outpatient colonoscopy

BACKGROUND

This study tested the hypothesis that, for colonoscopy, analgesia/sedation with remifentanil and propofol might be more effective compared with anesthesia by intravenous administration of midazolam, fentanyl, and propofol.

METHODS

In a prospective, randomized trial, 100 adult patients received either conscious analgesia/sedation (Sedation group) or total intravenous anesthesia (TIVA group). Analgesia/sedation was achieved by infusion of remifentanil (0.20 to 0.25 microg/kg/min) and propofol in titrated doses. TIVA was induced by intravenous administration of fentanyl (2 microg/kg), midazolam (0.05 mg/kg) and propofol (dosage titrated). Cardiorespiratory parameters and bispectral index were monitored and recorded. The quality of the analgesia was assessed with a Numerical Pain Rating Scale (NRS); recovery level and return of psychomotor efficiency were evaluated with, respectively, the Aldrete scale and a Modified Post Anesthesia Discharge Scoring (MPADS) system.

RESULTS

Both groups of 50 patients were comparable with respect to demographic data, initial parameters, and duration of colonoscopy. All patients in the TIVA group found the colonoscopy painless (NRS score 0). In the Sedation group, the average pain intensity score was 0.4 (0.8). There was a marked difference between the Sedation and TIVA groups with respect to the time from the end of the procedure until the maximum MPADS score was reached: respectively, -6.9 (4.0) versus 25.7 (8.4) minutes (p < 0.001). In the TIVA group, changes in mean arterial pressure and heart rate and signs of respiratory depression were significant (p < 0.05).

CONCLUSIONS

Combined administration of remifentanil and propofol for colonoscopy provides sufficient analgesia, satisfactory hemodynamic stability, minor respiratory depression, and rapid recovery, and allows patients to be discharged approximately 15 minutes after the procedure.

Low-dose propofol infusion for sedation during local anesthesia

The safety and efficacy of lose-dose propofol for sedation were investigated on 90 consenting patients who had undergone surgical procedures with local anesthesia. After being premedicated with intravenous midazolam 0.05 mg.kg(-1), all patients were randomly divided into two groups and received intravenously either a loading dose of propofol 0.8 mg.kg(-1) followed by a continuous infusion of propofol 30 microg.kg(-1)min(-1) (propofol group) or an equivalent volume of saline (placebo group) during operation. Study groups were compared with respect to the level of sedation, hemodynamic variables, oxygen saturation, and the incidence of intraoperative side effects. In addition, the discharge time and the satisfaction of both patients and surgeons with this sedative technique were assessed. Propofol reduced patients' discomfort and lowered their arterial pressure and heart rate during the infiltration of local anesthetics. It also promoted an adequate level of sedation without clinically significant oxygen desaturation in the intraoperative period. Surgeons and patients in the propofol group showed a higher level of satisfaction than those in the placebo group. There was no significant difference between the two groups with regard to the incidence of adverse effects and the discharge time. In conclusion, it was found that the use of low-dose propofol infusion was a safe and effective sedative technique for local anesthesia.

Fast-tracking after ambulatory surgery

The fast-tracking recovery concept examines different paradigms for streamlining the postoperative recovery process. Fast-tracking anesthetic techniques allow suitable outpatients to be discharged earlier after ambulatory surgery. Outpatients are normally transferred from the OR to the PACU, followed by transfer to the Phase II step-down (day-surgery unit) before discharge home. With conventional fast-tracking, it is possible to bypass the PACU and take patients directly from the OR to the step-down unit if they meet specific criteria before leaving the OR. Alternatively, if the step-down unit is already functioning at maximum capacity, the PACU can be restructured to include a fast-track area, where appropriate patients are treated as if they had been admitted directly to the step-down unit. For these PACU fast-track patients, less monitoring is performed, a family member is permitted to be with the patient, and the patient is allowed to ambulate, change into street clothes, and be discharged home directly from the PACU without any time restrictions. Preliminary studies have shown that outpatients who are fast-tracked can be discharged home earlier without any increase in complications or side effects. Importantly, fast-tracking after ambulatory surgery does not seem to compromise patient satisfaction with the surgical experience.

The effect of noise on the bispectral index during propofol sedation

Because noise in the operating room has been alleged to interfere with the ability to sedate patients before surgery, we evaluated the effect of noise on the Bispectral index (BIS) value during propofol sedation. Thirty unpremedicated patients were studied before the start of surgery while receiving propofol sedation on two separate occasions according to a randomized, crossover protocol design. After achieving a stable baseline BIS value of either 75 or 80 with a target-controlled infusion of propofol, an external sound source administered noise at 50, 80, 110, and 120 dB. The changes in the BIS value were recorded over a 1-min interval at each noise level. In the BIS 75 group, increasing levels of noise did not significantly alter the BIS value. However, in the BIS 80 group, the BIS values at 80, 110, and 120 dB were significantly higher compared to the value at 50 dB. In conclusion, experimental noise increases the BIS and appears to have a greater effect on the BIS value at "lighter" levels of propofol sedation.

IMPLICATIONS

Experimental noise levels can increase the Bispectral index (BIS) values during propofol sedation in the operating room. However, the magnitude of the BIS response is influenced by the depth of sedation.

The Effects of Small-Dose Ketamine on Propofol Sedation: Respiration, Postoperative Mood, Perception, Cognition, and Pain

We compared the effects of coadministration of propofol and small-dose ketamine to propofol alone on respiration during monitored anesthesia care. In addition, mood, perception, and cognition in the recovery room, and pain after discharge were evaluated. In the Propofol group (n = 20), patients received propofol 38 +/- 24 microg x kg(-1) x min(-1). The Coadministration group (n = 19) received propofol 33 +/- 13 microg x kg(-1) x min(-1) and ketamine 3.7 +/- 1.5 microg x kg(-1) x min(-1). Respiration was assessed by using end-expiratory PCO(2) measurements at nasal prongs. After surgeries, mood, perception, and thought were assessed by using visual analog scales, and cognition was assessed by Mini-Mental State Examination (MMSE). Pain after discharge was assessed by a five-point rating scale in the evening for 5 days. End-expiratory PCO(2) was lower in the Coadministration group (P < 0.0001). Mood and MMSE scores were higher in the Coadministration group (P < 0.004 and P = 0.001, respectively). Pain scores and analgesic consumption after discharge were less in the Coadministration group (P = 0.0004 and P < 0.0001, respectively). We conclude that coadministration of small-dose ketamine attenuates propofol-induced hypoventilation, produces positive mood effects without perceptual changes after surgery, and may provide earlier recovery of cognition.

Clinical and economic factors important to anaesthetic choice for day-case surgery

Clinical and economic factors that are important to consider when selecting anaesthesia for day-case surgery can differ from those for inpatient anaesthesia. Patients undergoing day-case surgery tend to be healthier and have shorter durations of surgery. They expect less anxiety before surgery, amnesia for the surgical experience, a rapid return to normal (normal mentation with minimal pain and nausea) after surgery, and lower expenses. However, the latter 2 expectations can conflict; older generic drugs have lower acquisition costs but often impose longer recovery times. Longer recovery periods can increase costs by prolonging the time to discharge from labour-intensive areas such as the operating suite or the post-anaesthesia recovery unit. The challenge for today's anaesthetist is to use newer drugs judiciously to minimise their expense without compromising the rate or quality of recovery. Several approaches can secure these aims. Most apply the least anaesthetic needed. 'Least anaesthetic' may mean the particular form of anaesthetic (e.g. local infiltration with monitored anaesthesia care versus a general anaesthetic), or may mean the delivery of the smallest effective dose, perhaps guided by anaesthetic monitors such as end-tidal analysers or the bispectral index. For patients requiring general anaesthesia, a combination of several drugs usually secures the closest approach to the ideal. Drug combinations used usually include a short-acting properative anxiolytic (e.g. midazolam), intravenous propofol (a short-acting potent anxiolytic and amnestic agent) for induction of anaesthesia (and sometimes for maintenance) and primary maintenance of anaesthesia with inhaled nitrous oxide combined with a poorly soluble (low solubility produces rapid recovery; the least soluble is desflurane) potent inhaled anaesthetic delivered at a low inflow rate (to minimise cost). Although old, nitrous oxide is inexpensive and has favourable pharmacokinetic and cardiovascular advantages; however, it is limited in its anaesthetic/amnestic potency, and has the capacity to increase nausea. In children, induction of anaesthesia is often accomplished with sevoflurane rather than desflurane; although sevoflurane is modestly more soluble than desflurane, it is non-pungent whereas desflurane is pungent. Moderate- or short-acting opioids (fentanyl is popular) or nonsteroidal anti-inflammatory agents (especially ketorolac), or local anaesthetics are added to secure analgesia during and after surgery. Similarly, when needed, moderate- or short-acting muscle relaxants are selected. Before the end of anaesthesia, an intravenous antiemetic may be given. With this drug combination, patients usually awaken within minutes after anaesthesia and can often move themselves to the vehicle for transport to the recovery unit. These combinations of anaesthetics and techniques minimise use of expensive drugs while expediting recovery (again minimising cost) with minimal or no compromise in the quality of recovery.

The cost-effectiveness of methohexital versus propofol for sedation during monitored anesthesia care

We designed this study to test the hypothesis that methohexital is a cost-effective alternative to propofol for sedation during local anesthesia. Sixty consenting women undergoing breast biopsy procedures under local anesthesia were randomly assigned to receive an infusion of either propofol (50 microg x kg(-1) x min(-1)) or methohexital (40 microg x kg(-1) x min(-1)). The sedative infusion rate was titrated to maintain an observer's assessment of alertness/sedation (OAA/S) score of 3 (with 1 = awake/alert to 5 = asleep). Fentanyl 25 microg i.v. was administered as a "rescue" analgesic during the operation. We assessed the level of sedation (OAA/S score), vital signs, time to achieve an OAA/S score of 3 at the onset and a score of 1 after discontinuing the infusion, discharge times, perioperative side effects, and patient satisfaction. The direct cost of methohexital was lower than that of propofol, based on the milligram dosage infused during the operation. The sedative onset (to achieve an OAA/S score of 3) and the recovery (to return to an OAA/S score of 1) times, as well as discharge times, did not differ between the two groups. Patients receiving methohexital had a significantly lower incidence of pain on initial injection compared with those receiving propofol (10% vs 23%). Because the use of methohexital (29.4 +/- 2.7 microg x kg(-1) x min(-1)) for sedation during breast biopsy procedures has a similar efficacy and recovery profile to that of propofol (36.8 +/- 15.9 microg x kg(-1) x min(-1)) and is less costly based on the amount infused, it seems to be a cost-effective alternative to propofol for sedation during local anesthesia. However, when the cost of the drug infused and drug wasted was calculated, there was no difference in the overall drug cost.

IMPLICATIONS

When administered to maintain a stable level of sedation during local anesthesia, methohexital is an acceptable alternative to propofol. However, the overall drug costs were similar with the two drugs.

The target plasma concentration of propofol required to place laryngeal mask versus cuffed oropharyngeal airway

To determine the target plasma concentration of propofol required to place either a laryngeal mask airway (LMA) or a cuffed oropharyngeal airway (COPA), we started a continuous target-controlled infusion of propofol in 60 ASA physical status I or II unpremedicated patients scheduled for minor orthopedic surgery with peripheral nerve block. The target plasma concentration of propofol was initially set at 2 microg/mL. When the effect-site calculated concentration of propofol was equal to the plasma concentration according to the computer simulation, the target plasma concentration was increased by 0.5-microg/mL steps until successful placement of either the LMA (n = 30) or the COPA (n = 30). The mean target plasma concentration of propofol required to place a LMA was 4.3 +/- 0.8 microg/mL compared with 3.2 +/- 0.6 microg/mL to place a COPA (P < 0.001). To successfully place the airways in 95% of patients, the target plasma concentration of propofol had to be increased up to 4 microg/mL for the COPA and 6 microg/mL for the LMA. We conclude that placing a LMA in healthy, unpremedicated patients requires target plasma concentrations of propofol higher than those required for placing a COPA.

IMPLICATIONS

We evaluated the use of target-controlled infusion of propofol to place extratracheal airways in this prospective, randomized study and demonstrated that the target plasma concentration of propofol required to successfully place a laryngeal mask in >95% of healthy, unpremedicated patients is 6 microg/mL, compared with 4 microg/mL to place a cuffed oropharyngeal airway.

Remifentanil administration during monitored anesthesia care: are intermittent boluses an effective alternative to a continuous infusion?

This randomized, double-blind study was designed to evaluate the analgesic effectiveness and respiratory stability of remifentanil when administered as intermittent bolus injections, a variable-rate infusion, or a combination of a constant basal infusion supplemented with intermittent boluses during monitored anesthesia care (MAC). Forty-five patients undergoing extracorporeal shock wave lithotripsy (ESWL) procedures were randomly assigned to one of the three modes of remifentanil administration. All patients received midazolam 2 mg i.v., followed by a propofol infusion at 50 microg x kg(-1) x min(-1). Two minutes before administering a series of test shock waves: Group I received a remifentanil infusion of 0.1 microg x kg(-1) x min(-1), and a saline bolus (5 mL); Group II received a saline infusion and a remifentanil bolus (25 microg in 5 mL); and Group III received a remifentanil infusion of 0.05 microg x kg(-1) x min(-1), and a remifentanil bolus (12.5 microg in 5 mL). The average pain intensity was scored on an 11-point scale, with 0 = no pain to 10 = severe pain. During the ESWL procedure, pain was treated by increasing the study drug infusion rate by 25%-50% and administering 5-mL bolus injections of the study medication in Groups I (saline) and II (remifentanil 25 microg). In Group III, intermittent 5-mL boluses (remifentanil 12.5 microg) were administered as needed. Patients in Groups II and III reported lower pain scores in response to the test shocks. Significantly more remifentanil was administered in Group I (379 +/- 207 microg) than in Group II (201 +/- 136 microg). However, more interventions were required for the treatment of intraoperative pain in the intermittent bolus group (Group II). When remifentanil is administered as the analgesic component of a MAC technique, these data support the use of intermittent bolus doses (12.5-25 microg) alone or in combination with a basal infusion (0.05 microg x kg(-1) x min(-1)) as alternatives to a variable-rate continuous infusion.

IMPLICATIONS

In this study, three different modes of remifentanil administration were used during monitored anesthesia care for extracorporeal shock wave lithotripsy procedures. These results suggest that using intermittent bolus injections of remifentanil (25 microg) or a continuous infusion (0.05 microg x kg(-1) x min(-1)) supplemented with intermittent bolus (12.5 microg) injections may be more effective than a variable-rate infusion of remifentanil during propofol sedation.

Clinical assessment of target-controlled infusion of propofol during monitored anesthesia care

PURPOSE

To determine the plasma concentrations of propofol required to achieve different levels of sedation during monitored anesthesia care.

METHODS

Sixty ASA I-II, 18-65 yr-old patients, received a target-controlled continuous iv infusion of propofol. The target plasma concentration of propofol (Cpt) was initially set at 0.4 microg x ml(-1). Two minutes after calculated equilibrium between plasma and effect-site concentrations, the Cpt of propofol was increased by 0.2 microg x ml(-1) steps until the patient showed no reaction to squeezing the trapezius. The level of sedation was assessed immediately before each increase in propofol Cpt using the Observer's Assessment of Alertness/Sedation (OAA/S) scale.

RESULTS

The Cpt of propofol required to induce lethargic response to name was 1.3 microg x ml(-1) (5 degrees and 95 degrees percentiles: 1.0 - 1.8 microg x ml(-1)), to obtain response after loud and repeated calling name was 1.7 microg x ml(-1) (1.2 - 2.2 microg x ml(-1)), to obtain response after prodding or shaking was 2.0 microg x ml(-1) (1.6 - 2.6 microg x ml(-1)), to obtain response after squeezing the trapezius was 2.4 microg x ml(-1) (1.8 - 3.0 microg x ml(-1)). Patients showed no response after squeezing the trapezius at 2.8 microg x ml(-1) (2.0 - 3.6 microg x ml(-1)). Correlation between Cpt propofol and sedation scores were r = 0.76, P < 0.0001.

CONCLUSIONS

Target-controlled infusion of propofol provided easy and safe management of intraoperative sedation, allowing fast and predictable deepening in the level of sedation, while minimizing systemic side effects of intravenous sedation due to the minimal risk of overdosing the drug.

Physiological dead space/tidal volume ratio during face mask, laryngeal mask, and cuffed oropharyngeal airway spontaneous ventilation

OBJECTIVE

To compare the physiological dead space/tidal volume ratio and arterial to end-tidal carbon dioxide tension (ETCO2) difference during spontaneous ventilation through a face mask, a laryngeal mask (LMA), or a cuffed oropharyngeal airway.

DESIGN

Prospective, randomized, cross-over study.

SETTING

Inpatient anesthesia at a university department of orthopedic surgery.

PATIENTS

20 ASA physical status I and II patients, without respiratory disease, who underwent ankle and foot surgery.

INTERVENTIONS

After a peripheral nerve block was performed, propofol anesthesia was induced and then maintained with a continuous intravenous (i.v.) infusion (4 to 6 mg/kg/h). A face mask, a cuffed oropharyngeal airway, or an LMA were placed in each patient in a random sequence. After 15 minutes of spontaneous breathing through each of the airways, ventilatory variables, as well as arterial, end-tidal, and mixed expired CO2 partial pressure, were measured, and physiological dead space/tidal volume ratio was calculated.

MEASUREMENTS AND MAIN RESULTS

Expired minute volume and respiratory rate (RR) were lower with LMA (5.6 +/- 1.2 L/min and 18 +/- 3 breaths/min) and the cuffed oropharyngeal airway (5.7 +/- 1 L/min and 18 +/- 3 breaths/min) than the face mask (7.1 +/- 0.9 L/min and 21 +/- 3 breaths/min) (p = 0.0002 and p = 0.013, respectively). Physiological dead space/tidal volume ratio and arterial to end tidal CO2 tension difference were similar with the cuffed oropharyngeal airway (3 +/- 0.4 mmHg and 4.4 +/- 1.4 mmHg) and LMA (3 +/- 0.6 mmHg and 3.7 +/- 1 mmHg) and lower than with the face mask (4 +/- 0.5 mmHg and 6.7 +/- 2 mmHg) (p = 0.0001 and p = 0.001, respectively).

CONCLUSION

Because of the increased dead space/tidal volume ratio, breathing through a face mask required higher RR and expired minute volume than either the cuffed oropharyngeal airway or LMA, which, in contrast, showed similar effects on the quality of ventilation in spontaneously breathing anesthetized patients.