Non-invasive measurement of cardiac output during induction of anaesthesia and tracheal intubation: thiopentone and propofol compared

Causes of arterial hypotension during anesthetic induction with propofol investigated with perfusion index and ClearSightTM in young and elderly patients

BACKGROUND

Mechanism underlying the hypotension during anesthetic induction in elderly patients is inferred to differ from that in younger patients due to structural changes in arteries. The aim of the study was to determine if a decrease in cardiac output (CO) or systemic vascular resistance (SVR) is the main mechanism of the hypotension.

METHODS

Fifty-six patients comprising 28 healthy elderly patients aged 75-90 years (group E) and 28 healthy younger patients aged 20-40 years (group Y) were enrolled. General anesthesia was induced with propofol (1.2 mg/kg, group E; 2 mg/kg, group Y), remifentanil (0.15 µg/kg/min, group E; 0.3 µg/kg/min, group Y) and rocuronium. Primary outcome was to compare serial changes in PI of Radical-7^TM, SVR, CO and stroke volume variations (SVV) of ClearSight^TM (Edwards Lifesciences Corp., Irvine, CA, USA) during the five-minute period from propofol administration until intubation.

RESULTS

The degree of increase in PI and reduction in SVR in group Y were significantly greater than those in group E (P<0.01 with repeated measure ANOVA). The degree of reduction in CO and increase in SVV were significantly larger in group E (P<0.01). All values of mean arterial blood pressure measured during the five-minute correlated negatively with PI in group Y (r=0.44, P<0.01) and positively with CO in group E (r=0.4, P<0.01).

CONCLUSIONS

The main mechanisms of hypotension during anesthetic induction contribute to the decrease in CO in elderly and reduction of SVR in younger. PI only shows the vascular tone of a finger but can be a surrogate for SVR.

Comparison of the Haemodynamic Effects of Three Different Methods at the Induction of Anaesthesia

OBJECTIVE

Haemodynamic variations are inevitable during induction of anaesthetic drugs. The present study investigates the haemodynamic variations of three different drugs (thiopental, propofol, and etomidate) used for induction of general anaesthesia together with fentanyl.

METHODS

In a randomized, double-blind study, 45 patients were assigned to one of three groups (n=15 each). Fentanyl 1 μg kg(-1) was injected over 60 sec followed by propofol 2 mg kg(-1) (Group P), thiopentone 6 mg kg(-1) (Group T), or etomidate 0.3 mg kg(-1) (Group E). Noninvasive measurements of systolic arterial pressure (SAP), diastolic arterial pressure (DAP), mean arterial pressure (MAP), and heart rate (HR) was performed on admittance, immediately before the induction of anaesthesia, and 1, 3, and 5 min thereafter. Cardiac output (CO) values were recorded before induction, immediately after the injection of the drug, and at 1 min after the intubation.

RESULTS

In all groups, during the study period, SAP, DAP, MAP, and CO values decreased with respect to time before induction. Following the administration of the induction dose of propofol (Group P), a significantly greater decrease of systolic and diastolic blood pressure was observed with etomidate (Group E) or thiopentone (Group T). Decrease in CO was also more marked with propofol (Group P) than with etomidate (Group E) or thiopentone (Group T).

CONCLUSION

It's concluded that, in this study, the combination of fentanyl-etomidate is safer than both the groups of fentanyl-propofol and fentanyl-thiopental in terms of providing haemodynamic stability.

No evidence for decreased incidence of aspiration after rapid sequence induction

PURPOSE

The purpose of this structured, evidence-based, clinical update was to determine if rapid sequence induction is a safe or effective technique to decrease the risk of aspiration or other complications of airway management.

SOURCE

In June 2006 a structured search of MEDLINE from 1966 to present using OVID software was undertaken with the assistance of a reference librarian. Medical subject headings and text words describing rapid sequence induction or intubation (RSI), crash induction or intubation, cricoid pressure and emergency airway intubation were employed. OVID's therapy (sensitivity) algorithm was used to maximize the detection of randomized trials while excluding non-randomized research. The bibliographies of eligible publications were hand-searched to identify trials not identified in the electronic search.

PRINCIPAL FINDINGS

A total of 184 clinical trials were identified of which 163 were randomized controlled trials (RCTs). Of these clinical trials, 126 evaluated different drug regimens with 114 being RCTs. Only 21 clinical trials evaluated non-pharmacologic aspects of the RSI with 18 RCTs identified. A parallel search found 52 trials evaluating cricoid pressure (outside of the context of an RSI technique) with 44 classified as RCTs. Definitive outcomes such as prevention of aspiration and mortality benefit could not be evaluated from the trials. Likewise, the impact on adverse outcomes of the different components of RSI could not be ascertained.

CONCLUSION

An absence of evidence from RCTs suggests that the decision to use RSI during management can neither be supported nor discouraged on the basis of quality evidence.

Propofol ensures a more stable A-line ARX index than thiopental during intubation

BACKGROUND

The A-line autoregressive modelling with exogenous input index (AAI) is a new method of assessing depth of anesthesia. We examined the effects of tracheal intubation on the AAI and hemodynamics during induction of anesthesia with propofol compared with thiopental in patients aged over 50 yr.

METHODS

40 patients scheduled for a laminectomy, posterior spinal fusion, vertebroplasty, or total hip replacement, ASA physical status I or II and aged over 50 yr, were randomly divided into two groups. Thiopental 5 mg.kg(-1) iv, fentanyl 2.5 microg.kg(-1) iv, and rocuronium 0.7 mg.kg(-1) iv were used in the thiopental group (n = 20) for anesthetic induction; the same protocol was used in the propofol group (n = 20) except that 2 mg.kg(-1) propofol iv was given instead of thiopental. The AAI, non-invasive blood pressure, and heart rate were measured every minute before induction for three minutes, at 1.5 min post-induction, and then each minute post-intubation for eight minutes.

RESULTS

The AAI increased significantly at one and two minutes after intubation in the thiopental group (to 56.5 +/- 18.6 at 1 min and 44.7 +/- 18.7 at 2 min after intubation vs 19.9 +/- 7.5 at 1.5 min after induction; P < 0.05). Thereafter, AAI values gradually decreased three minutes after intubation. The AAI was inhibited continuously after intubation in the propofol group, and no significant elevation was seen.

CONCLUSION

Our results, using the AAI to monitor anesthetic depth during induction and tracheal intubation, suggest that at equipotent doses propofol provided a more stable level of anesthesia than did thiopental.

Should etomidate be the induction agent of choice for rapid sequence intubation in the emergency department?

The ideal induction agent for emergency airway management should be rapidly acting, permit optimum intubating conditions, and be devoid of significant side effects. This review was performed to ascertain whether etomidate should be the induction agent of choice for rapid sequence intubation (RSI) in the emergency department, specifically examining its pharmacology, haemodynamic profile, and adrenocortical effects. A search of Medline (1966-2002), Embase (1980-2002), the Cochrane controlled trials register, and CINAHL was performed. In addition, the major emergency medicine and anaesthesia journals were hand searched for relevant material. Altogether 144 papers were identified of which 16 were relevant. Most studies were observational studies or retrospective reviews with only one double blind randomised controlled trial and one un-blinded randomised controlled trial. Appraisal of the available evidence suggests that etomidate is an effective induction agent for emergency department RSI; it has a rapid onset of anaesthesia and results in haemodynamic stability, even in hypovolaemic patients or those with limited cardiac reserve. Important questions regarding the medium to long term effects on adrenocortical function (even after a single dose) remain unanswered.

The effect of prophylactic metaraminol on systemic hypotension caused by induction of anaesthesia with propofol in patients over 55 years old

We conducted a double-blind, randomised, placebo-controlled study evaluating the efficacy of prophylactic metaraminol for preventing propofol-induced hypotension. Thirty patients aged 55-75 years undergoing general anaesthesia were randomly allocated to receive either metaraminol 0.5 mg or saline before administration of fentanyl 1 microg.kg(-1) and propofol 2 mg.kg(-1). Induction of anaesthesia was associated with a decrease in mean and systolic arterial pressure in both groups (p = 0.0001). However, there was no significant difference between the two groups. These results show that prophylactic use of metaraminol 0.5 mg does not prevent the decrease in blood pressure following fentanyl and propofol induction in older patients.

Anaesthetic technique for transoesophageal echocardiography in children

OBJECTIVE

To document the safety and efficacy of an anaesthetic technique in paediatric patients undergoing transoesophageal echocardiography (TOE).

METHODS

Prospective descriptive study performed in a children's hospital with all patients undergoing TOE. Topical analgesia of the pharynx was achieved with lidocaine. Anaesthesia was induced with midazolam (25 microg.kg-1), fentanyl (1 microg.kg-1), and propofol (0.5-1 mg.kg-1), followed by a continuous infusion of propofol (5-10 mg.kg-1.h-1).

RESULTS

Thirty patients are reported. The mean age was 11.4 +/- 5.1 years (range 1-22) and weight 40.5 +/- 22.1 kg (range 10-110). All the patients tolerated the procedure well. Two patients experienced brief oxygen desaturations during induction, 10 patients coughed during the procedure, and six patients had significant muscle activity requiring supplemental doses of propofol. None of the patients experienced nausea or vomiting.

CONCLUSION

We conclude that our anaesthetic technique in spontaneously breathing paediatric patients during TOE is effective and appears to be safe in children with heart disease.

Propofol auto-co-induction as an alternative to midazolam co-induction for ambulatory surgery

We propose the use of an intravenous propofol/propofol auto-co-induction technique as an alternative to propofol/midazolam for induction of anaesthesia. We have studied 54 unpremedicated ASA 1 or 2 patients undergoing day-stay anaesthesia for minor orthopaedic surgery. All received 10 micrograms.kg-1 or alfentanil before induction, followed by either midazolam 0.05 mg.kg-1, propofol 0.4 mg.kg-1 or saline, and 2 min later, a propofol infusion at a rate of 50 mg.kg-1.h-1 until loss of eyelash reflex. We compared pre- and postinduction haemodynamic changes, complications at insertion of a laryngeal mask airway and recovery from anaesthesia in the three groups. Both co-induction techniques showed less postinduction hypotension and significant reduction of the total induction dose of propofol when compared to the control group. In the propofol/propofol group there was a decreased incidence of apnoea during induction of anaesthesia. These patients were discharged from hospital 2 h after the end of anaesthesia whereas patients in the midazolam/propofol group were discharged after 2 1/2 h (p < 0.001).

Impedance cardiography. The impact of new technology

The 1990s have witnessed major advances in impedance cardiography technology. Problems existed with the methods used to calculate cardiac output. Excessive lung fluid, as often found in critically ill patients, may also invalidate measurements. The signal processing and measurement techniques used in older systems were deficient. The newer systems, of which there are at least six, incorporate novel and improved signal processing techniques. They also offer analog visual displays, personal computer interfacing, sophisticated analytical software and haemodynamic patient management systems. Evaluation of these systems is difficult because no true 'gold standard' method of cardiac output measurement exists. When compared with thermodilution techniques, limits of agreement of +/- 20-30% seem acceptable. These limits can be achieved in normal subjects but not in critically ill patients. Validation data are available for only half of the new systems. Until recently, the main application for impedance cardiography has been research but improved accuracy should lead to increased clinical usage.

Non-invasive continuous arterial pressure, heart rate and stroke volume measurements during graded head-up tilt in normal man

The haemodynamic effects of head-up tilt (HUT) at different tilt angles were investigated non-invasively in eight normal male subjects. Mean arterial pressure (MAP; by Ohmeda Finapres 2300), stroke volume (SV) and heart rate (HR; by BoMed NCCOM3-R7S) were continuously recorded whilst performing a series of HUTs (55 degrees, 10 degrees, 20 degrees, 30 degrees and 55 degrees) lasting 3 min each. The response to HUT was proportional to the sinc of the tilt angle. The magnitude of the response varied between subjects. HUT to 55 degrees resulted in mean (95% confidence limits) increases in MAP by 16 (+/-16)% and HR by 11 (+/-24)% and a decrease in SV by -25 (+/-22)%. These results were repeatable after 30 min. At small tilt angles, i.e. < or = 20 degrees, MAP did not change and HR decreased by -3 (+/-4)%. A detailed analysis revealed immediate dynamic (0-30 s), late dynamic (30-90 s) and plateau (after 90 s) phases in the response to HUT. In conclusion, HUT produces reproducible haemodynamic effects, although differences exist among subjects. A detailed analysis of these effects can be successfully performed using non-invasive methods.

Cardiac output measurement: lack of agreement between thermodilution and thoracic electric bioimpedance in two clinical settings

STUDY OBJECTIVE

To determine the agreement between thermodilution (TD) and thoracic electric bioimpedance (TEB) techniques in cardiac output (CO) measurements in hyperdynamic kidney recipients and normodynamic patients subjected to radical cystectomy. The main objective was to determine the reliability of TEB in CO measurement.

DESIGN

Open two-group study.

SETTING

University hospital.

PATIENTS

19 kidney recipients and 5 radical cystectomy patients.

INTERVENTIONS

Radial artery cannula and pulmonary artery floating catheter were inserted. The eight ECG spot electrodes of the TEB device were situated on the body surface.

MEASUREMENTS AND MAIN RESULTS

Simultaneous CO measurements with TD and TEB were recorded at strategic points during the dynamic state of anesthesia and surgery. The mean difference (bias, TD-TEB) was higher in KRs (1.36 L/min) than radical cystectomy patients (-0.69 L/min). The corresponding 95% confidences of the bias were 1.10 to 1.54 L/min and -0.83 to -0.55 L/min. The precisions (SDs of bias) in kidney recipients and radical cystectomy patients were 1.08 L/min and 0.66 L/min, respectively. The limits of agreement were -0.97 to 3.51 L/min in kidney recipients and -1.99 to 0.61 L/min in radical cystectomy patients. The 95% confidences of the limits of agreement in kidney recipients were -1.09 to -0.49 for the lower limit and 3.21 to 3.81 for the upper limit. The corresponding values in radical cystectomy patients were -2.23 to -1.75 L/min and 0.37 to 0.85 L/min.

CONCLUSIONS

These findings demonstrate lack of agreement between TEB and TD in CO measurements in a hyperdynamic and a normodynamic clinical setting. It is concluded that the TEB device is unreliable in CO measurement and cannot replace or be interchanged with TD.

Nebulized bupivacaine attenuates the heart rate response following tracheal intubation

STUDY OBJECTIVE

To determine whether nebulized bupivacaine attenuates the acute hemodynamic response to laryngoscopy and intubation.

DESIGN

Prospective, randomized, placebo-controlled study.

SETTING

Operating room at a university medical center.

PATIENTS

40 health ASA physical status I and II patients scheduled for minor surgical procedures.

INTERVENTIONS

Patients were randomized to receive 4 ml of a nebulized solution of either saline (n = 20) or 0.75% bupivacaine (n = 20) 15 minutes before induction of anesthesia. On completion of the aerosol treatment, fentanyl 1.5 micrograms/kg was given intravenously (i.v.), and 3 minutes later anesthesia was induced with thiopental sodium 5 mg/kg i.v. and succinylcholine 1.5 mg/kg i.v.. Laryngoscopy was begun 60 seconds after induction, and the trachea was intubated at 90 seconds. Anesthesia was maintained with 50% nitrous oxide in oxygen following intubation, and 1% isoflurane was administered at 180 seconds.

MEASUREMENTS AND MAIN RESULTS

Heart rate (HR) and blood pressure were recorded automatically every 30 seconds for 5 minutes. Bupivacaine significantly attenuated HR (p < 0.05) but not the hypertensive response to laryngoscopy and intubation.

CONCLUSION

Nebulized 0.75% bupivacaine was only partially effective in blunting the hemodynamic response to tracheal intubation.

Thoracic electrical bioimpedance measurement of cardiac output and cardiovascular responses to the induction of anaesthesia and to laryngoscopy and intubation

Noninvasive methods of determining cardiac output (by thoracic electrical bioimpedance) and arterial pressure (by intermittent oscillometry) were used to record minute-by-minute changes in heart rate, mean arterial pressure, stroke volume, cardiac output and systemic vascular resistance following induction of general anaesthesia and laryngoscopy and intubation in 60 healthy female patients who were either unpremedicated, or premedicated with temazepam or papaveretum-hyoscine. Anaesthesia was induced with a sleep dose (3-5 mg.kg-1) of thiopentone and maintained with 70% nitrous oxide in oxygen with 0.5-1% enflurane. Tracheal intubation was facilitated by administration of vecuronium 0.1 mg.kg-1. Mean arterial pressure and cardiac output decreased maximally 5 min after induction in all premedication groups by mean estimates of 21-25% and 14-22% respectively. Heart rate increased initially one minute after induction, but decreased to less than the baseline value 5 min after induction. Systemic vascular resistance was unchanged. The stimulus of laryngoscopy and tracheal intubation was accompanied by a significant pressor response and tachycardia one minute after intubation (with mean increases in mean arterial pressure and heart rate of 29-34% and 22-33% respectively). The increase in mean arterial pressure was secondary to an increase in systemic vascular resistance (36-57%), and was accompanied by a decrease in stroke volume (-25 to -31%). These changes were significant in all three groups. Cardiac output decreased only in unpremedicated patients. There were wide variations in the different haemodynamic indices.(ABSTRACT TRUNCATED AT 250 WORDS)