Tracheal Intubation Using Alfentanil and No Muscle Relaxant

Is the Choice of Hypnotic Important?

Abstract

Administration of alfentanil followed by propofol intravenously (IV) without neuromuscular blockade for induction of anesthesia provides adequate conditions for tracheal intubation.Other hypnotic drugs have not been thoroughly investigated in this regard. Accordingly, 140 ASA physical status I and II premedicated outpatients were randomly assigned to one of seven groups (n = 20/group). Patients in Groups I-VI received alfentanil 40 micro g/kg followed by etomidate 0.3 mg/kg, propofol 2 mg/kg, or thiopental 4 mg/kg. One half of these patients (Groups II, IV, VI) also received lidocaine 1 mg/kg IV prior to the administration of the above drugs. Patients in group VII received d-tubocurarine 3 mg followed by thiopental 4 mg/kg and succinylcholine 1 mg/kg. Ninety seconds after induction, laryngoscopy and endotracheal intubation were attempted and graded. Patients in Group V (alfentanil/thiopental) were significantly (P < 0.05) more likely to have a clinically unacceptable response to intubation (55%) (e.g., vigorous coughing, purposeful movement, or requirement for succinylcholine to complete intubation) compared with patients who received propofol (35%) or etomidate (20%). Alfentanil/etomidate yielded intubation conditions comparable to those achieved with alfentanil/propofol and d-tubocurarine/thiopental/succinylcholine. Lidocaine appeared to improve intubating conditions, although this improvement did not reach statistical significance. The results suggest that healthy, premedicated patients with favorable airway anatomy who have received alfentanil 40 micro g/kg can be reliably tracheally intubated 90 s after administration of propofol 2 mg/kg or etomidate 0.3 mg/kg.

(Anesth Analg 1997;84:1222-6)

Tracheal intubation is commonly facilitated by the administration of a muscle relaxant to supplement other drugs given for induction of general anesthesia. Scheller et al. ^[1] reported that the trachea could be reliably intubated without neuromuscular blockade in most healthy, premedicated patients who received at least 40 micro g/kg alfentanil prior to propofol 2.0 mg/kg. Others have also reported satisfactory conditions at intubation using various combinations of propofol, alfentanil, and lidocaine ^[2-3]. While effective, induction sequences using alfentanil and propofol are associated with reductions in heart rate and arterial blood pressure ^[1-3].

There have been few reports concerning the use of other intravenously (IV) administered hypnotics alone or in combination with alfentanil for tracheal intubation without muscle relaxants. In 1948, Lewis ^[4] reported that the trachea could be intubated using thiopental 500-750 mg alone. More recently, Hovarka et al. ^[5] reported that propofol (2.5 mg/kg) provided no advantage over thiopental (5 mg/kg) for intubation without neuromuscular blockade in patients who had received alfentanil 30 micro g/kg and lidocaine 1.5 mg/kg prior to administration of the hypnotic drug. Etomidate for tracheal intubation without muscle relaxants has not been studied.

In this double-blind, randomized study, we compared intubating conditions and the hemodynamic response to induction and intubation in patients given alfentanil 40 micro g/kg followed by propofol 2 mg/kg, thiopental 4 mg/kg, or etomidate 0.3 mg/kg. The utility of IV lidocaine 1 mg/kg with each of these regimens was also investigated.

Methods

After approval from our institutional review boards, we obtained written, informed consent from 140 ASA physical status I and II outpatients aged 18-60 yr scheduled for elective surgery. All patients enrolled had Mallampati class I or II airway anatomy. Patients with coronary artery disease, hypertension, reactive airway disease, obesity greater than 30% above ideal body weight ^[6], history of drug or alcohol abuse, or gastroesophageal reflux were excluded. Patients taking narcotics or drugs known to interfere with neuromuscular transmission were also excluded.

Midazolam 0.03 mg/kg IV was given approximately 5 min before induction of anesthesia. Approximately 5 mL/kg 0.9% normal saline (NS) or Normosol-R[R] solution (Abbott, N. Chicago, IL) was administered before the induction of anesthesia. Patients were randomly allocated to one of seven groups (n = 20/group) by means of previously prepared envelopes (Table 1).

Table 1: Patient Data

The induction sequence was conducted using four prepared syringes in all patients. Syringe 1 contained alfentanil 40 micro g/kg (Groups I-VI) or d-tubocurarine 3 mg (Group VII). NS was added to Syringe 1 to create a total volume of 9 mL. Syringe 2 contained lidocaine 1 mg/kg (Groups II, IV, VI) or NS (Groups I, III, V, VII). NS was added to Syringe 2 to achieve a total volume of 10 mL. Syringe 3 contained etomidate (Groups I-II), propofol (Groups III-IV), or thiopental (Groups V-VII). Opaque tape was applied to Syringe 3 to disguise the color of the hypnotic drug. Syringe 4 contained 5 mL NS (Groups I-VI) or succinylcholine 1 mg/kg diluted to 5 mL (Group VII).

After a 2-min period of breathing oxygen, Syringe 1 (alfentanil or d-tubocurarine) was administered over 90 s (1 mL every 10 s). Immediately thereafter, Syringe 2 (lidocaine or NS) was rapidly injected (5 s). This was immediately followed by rapid injection of Syringe 3 (hypnotic agent) and Syringe 4 (succinylcholine or NS). Injection of all syringes was performed by an assistant behind a drape so that the intubating anesthesiologist (one of three of the authors) was blinded to the color and volume of the IV drugs.

Once the patient became unconscious, ease of ventilation via a mask was scored (Table 2). Use of an oral airway was at the discretion of the anesthesiologist. Forty-five seconds after completion of drug administration, postinduction vital signs were recorded. Ninety seconds after completion of drug administration, laryngoscopy and intubation was attempted using a Macintosh 3 laryngoscope blade and a 7.0- or 8.0-mm endotracheal tube (for women and men, respectively). The intubating anesthesiologist assessed each patient on four variables: jaw relaxation, exposure of the vocal cords, vocal cord position, and patient response to intubation and slow (5-s) inflation of the endotracheal tube cuff (Table 2). The assessment of response to intubation continued for 1 min after completion of intubation; anesthesia was maintained with N₂ O in O₂ at flows of 2:1 L immediately after intubation. Patients who could not be intubated on the first attempt were given succinylcholine 1 mg/kg, and intubation was completed. Once the trachea was intubated and the cuff was inflated, postintubation vital signs were recorded. The presence of possible myoclonus or fasciculations was noted (Table 1).

Table 2: Scoring Criteria at Induction and Tracheal Intubation

Mean arterial pressure (MAP) and heart rate (HR) data were analyzed for differences among preinduction, postinduction, and postintubation values using one-way analysis of variance (Table 3). Differences among groups were evaluated using Student-Newman-Keuls multiple comparison tests. Kruskal-Wallis analyses were used to compare groups on nonparametric data.

Table 3: Mean Heart Rate (HR) and Arterial Blood Pressure (MAP) Responses to Anesthesic Induction and Endotracheal Intubation

Results

There were no demographic differences between groups (Table 1). MAP decreased significantly (P < 0.05) after induction of anesthesia in all patients who received alfentanil. HR decreased significantly (P < 0.05) from the preinduction level in Groups I-IV (etomidate, propofol), while it was not significantly changed in those who received thiopental (Groups V-VI).

Among groups, postinduction MAP was significantly (P < 0.05) lower in both propofol groups compared with those who received etomidate. Patients who received alfentanil/thiopental (Groups V-VI) had a significantly higher MAP after induction compared with those in Group IV (propofol/lidocaine). Group VII patients (d-tubocurarine/thiopental/succinylcholine) had significantly (P < 0.05) higher HR and MAP compared with all other groups postinduction and postintubation.

No patient was felt to have significant opioid-induced chest wall rigidity. Movements consistent with myoclonus or fasciculations were noted in nine patients (Table 1). Four of these patients had received etomidate and five had received d-tubocurarine/thiopental/succinylcholine for their induction sequence. No patient complained of pain upon administration of any hypnotic agent after alfentanil.

All patients could be adequately ventilated via a face mask after induction. Although the jaw was at least partly mobile in all patients, the jaw was significantly less likely (P < 0.05) to be fully mobile in the those who received thiopental without lidocaine (Group V) compared with all other groups. At least partial exposure of the vocal cords was accomplished in all patients. Vocal cord position was significantly more likely to be midline or closed in patients in Group V (alfentanil/thiopental) compared with those in Groups II and VII (Table 4). Further, patients in Group V were significantly (P < 0.05) more likely to have an unacceptable response (persistent coughing, purposeful movement, requirement for succinylcholine) to intubation and slow inflation of the cuff compared with patients in Groups I-IV and VII (Figure 1).

Table 4: Vocal Cord Position at Laryngoscopy

Figure 1: Patient response to laryngoscopy and intubation. *Significantly (P < 0.05) different compared with all other groups except Group VI. ETOM = etomidate, PROP = propofol, LIDO = lidocaine, STP = thiopental, dTc = d-tubocurarine, Sux = succinylcholine.

All patients enrolled in the investigation were eventually tracheally intubated; there were no dropouts. Of the 120 patients in the various alfentanil groups, 17 required succinylcholine to complete intubation. Thirty-five percent of patients (7 of 20) in Group V (alfentanil/thiopental) required succinylcholine to complete intubation compared with 15%, 10%, 10%, 0%, 15% in Groups I-IV and VI, respectively. These differences reached statistical significance (P < 0.01) only when comparing Group V with Group IV (propofol/lidocaine). No patient in Group VII (d-tubocurarine/thiopental/succinycholine) required additional muscle relaxant for completion of intubation.

Discussion

Our results suggest that etomidate 0.3 mg/kg or propofol 2 mg/kg administered after alfentanil 40 micro g/kg often provides adequate conditions for endotracheal intubation in healthy, premedicated patients with favorable airway anatomy. Thiopental 4 mg/kg appears less likely to lead to a satisfactory intubation in this setting. Although all induction sequences involving alfentanil lead to a decrease in MAP immediately after induction, MAP was more stable in patients who received etomidate compared with those who received propofol.

Scheller et al. ^[1] reported that tracheal intubation can be reliably performed in premedicated outpatients with normal airway anatomy who had received alfentanil 40 micro g/kg followed by propofol 2.0 mg/kg. In addition, they reported a significant decrease in MAP and HR with this technique. Our results confirm Scheller et al.'s data in regard to both intubating conditions and hemodynamic effects. Hovarka et al. ^[5] reported that propofol 2.5 mg/kg provided no advantage over thiopental 5 mg/kg for tracheal intubation in patients who had received 30 micro g/kg alfentanil and 1.5 mg/kg lidocaine prior to the hypnotic agent. Our data suggest that although thiopental with lidocaine provides acceptable intubating conditions in many patients, thiopental without lidocaine results in inferior intubation conditions compared with either propofol or etomidate. It should be noted that Hovarka et al. ^[5] used a larger dose of lidocaine and thiopental and a smaller dose of alfentanil than the present investigation.

We are aware of no previous study evaluating etomidate for tracheal intubation with alfentanil and no muscle relaxant. Our results suggest that etomidate 0.3 mg/kg preceded by alfentanil 40 micro g/kg reliably provides clinically acceptable conditions at intubation in healthy, premedicated patients with less decrease in MAP than in similar patients who receive alfentanil/propofol. Inductions with etomidate after alfentanil were smooth, with no complaints of pain on injection and only four patients having visible myoclonus. This low incidence of myoclonus with etomidate administered after alfentanil has been previously reported ^[7-8].

Although there are few contraindications to the use of neuromuscular blocking drugs for tracheal intubation, some patients have side effects (e.g., histamine release, cardiovascular changes, myalgias, prolonged neuromuscular block) from the use or misuse of muscle relaxants. Further, antagonism of neuromuscular block may result in unwanted changes in HR and MAP or may increase the incidence of postoperative nausea and vomiting ^[9-11]. Nonetheless, attempts at tracheal intubation with inadequate conditions (e.g., poor jaw relaxation, closed vocal cords) may result in airway trauma and inadequate ventilation and should be avoided. If conditions at laryngoscopy appear inadequate for intubation, additional anesthetic or muscle relaxant is indicated before proceeding with tracheal intubation.

In summary, our results suggest that propofol 2 mg/kg or etomidate 0.3 mg/kg is likely to provide adequate tracheal intubating conditions without neuromuscular blockade when administered after alfentanil 40 micro g/kg. This technique may be useful for appropriately selected patients who do not require neuromuscular blockade for the planned surgical procedure.