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Intra-ocular pressure changes associated with intubation with the intubating laryngeal mask airway compared with conventional laryngoscopy.

SUMMARY

This open, prospective randomised study was designed to evaluate the changes in intra-ocular pressure and haemodynamics after tracheal intubation using either the intubating laryngeal mask airway (ILMA) or direct laryngoscopy. Sixty adult patients, ASA physical status 1 or 2 with normal intra-ocular pressure were randomly allocated to one of the two techniques Anaesthesia was induced with propofol followed by rocuronium. Tracheal intubation was performed using either the ILMA or Macintosh laryngoscope Intra-ocular pressure, heart rate and blood pressure were measured immediately before and after tracheal intubation and then minutely for five minutes In the laryngoscopy group there was a significant increase in intra-ocular pressure (from 7.2[+ or -] 1.4 to 16.8[+ or -] 5.3 mmHg P < 0.01), which did not return to pre-intubation levels within five minutes, and also in mean arterial pressure after tracheal intubation, which returned to baseline levels after five minutes In the IL MA group there were no significant changes in intra-ocular pressure (from 7.6[+ or -] 1.8 to 10.4[+ or -] 2.8 mmHg P > 0.05) or mean arterial pressure after tracheal intubation. Time to successful intubation was longer with the ILMA, 56.8[+ or -] 7.8 seconds compared with the laryngoscopy group, 33[+ or -] 3.6 seconds (P < 0.01). Mucosal trauma was more frequent with the IL MA (eight of 30) compared with the laryngoscopy group (three of 30) (P < 0.01). The postoperative complications were comparable In terms of minimising increases in intra-ocular pressure and blood pressure, we conclude that the IL MA has an advantage over direct laryngoscopy for tracheal intubation.

Key Words: equipment, intubating laryngeal mask airway, Macintosh laryngoscope, intubation, tracheal, eye, intra-ocular pressure

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The stress response leading to increases in heart rate, blood pressure, intra-ocular pressure (IOP) and intracranial pressure during laryngoscopy and tracheal intubation has been well documented, 2. Such changes are likely to be harmful to the patients with hypertension and cardiovascular disease, glaucoma, penetrating eye injury or an intracranial space-occupying lesion e. Various techniques have been tried to attenuate this response but none has been completely successful. The laryngeal mask airway offers some advantage over conventional laryngoscopic intubation with less pharyngolaryngeal stimulation' but with limitations'. The intubating laryngeal mask airway (ILMA) was designed to facilitate intubation and have better ventilation characteristics than the standard laryngeal mask airway in normal and difficult airway patients'. Studies comparing the haemodynamic response to ILMA guided tracheal intubation with conventional laryngoscopic intubation are limited and have shown conflicting results(6, 7). The IOP changes following ILMA-guided tracheal intubation have not been reported so far. This prospective, randomised study was designed to compare the changes in IOP, heart rate and blood pressure following ILMA-guided tracheal intubation with that of direct laryngoscopic tracheal intubation.

METHOD

After obtaining ethics committee approval and written informed consent, 60 adult patients of ASA grade 1 or 2, scheduled to undergo elective spinal surgery were randomly allocated to one of the two groups using a closed envelope technique. Patients with anticipated difficult intubation, history of glaucoma, uncontrolled hypertension, gross obesity, increased intracranial pressure or those receiving any drug likely to have an effect on IOP were excluded. All patients received diazepam 0.1 mg/kg orally the night before the procedure and two hours before surgery. Intraoperative monitoring included electrocardiograph, heart rate, oxygen saturation (Sp[O.sub.2]), endtidal carbon dioxide and noninvasive blood pressure through a multi-channel cardiac monitor (Datex AS3). After preoxygenation for three minutes, anaesthesia was induced with fentanyl 2 [micro]kg/kg followed by propofol 2 to 3 mg/kg until loss of verbal communication. Neuromuscular block was achieved with rocuronium 0.6 mg/kg. The patients' lungs were manually ventilated by facemask with 1% inspired isoflurane and 50% nitrous oxide in oxygen for two minutes.

Patients in the laryngoscopy group were intubated with a size 7.5 or 8 cuffed polyvinylchloride tube, using a size 3 or 4 Macintosh laryngoscope. In the ILMA group, a size 3 or 4 intubating laryngeal mask airway (3 for female, 4 for male) was inserted keeping the head in neutral position and the cuff inflated with air (size 3: 20 ml, size 4: 30 ml). The ILMA was then attached to the anaesthesia breathing system and adequate ventilation was judged by chest wall movement and capnography. If ventilation was unobstructed, a size 7.0 or 7.5, well-lubricated, reinforced, straight, cuffed, silicone tracheal tube was passed through the metal tube of the intubating laryngeal mask until it reached the 15 cm depth marker and then advanced gently into the trachea without applying undue force. If no resistance was felt after the tube was advanced a further 8 cm, the cuff of the tracheal tube was inflated and the circuit reconnected. Correct tube placement was confirmed by auscultation of bilateral breath sounds and capnography. In the absence of expired carbon dioxide, oesophageal placement was diagnosed and the tube was removed immediately to re-establish ventilation through the ILMA. If it was difficult to insert the tube, adjusting manipulations, such as up-down manoeuvring of the ILMA, raising the mask upwards, partial withdrawal and rotating the tube bevel or exchanging the mask for either a smaller or larger size, were used to optimise the airway(5). After successful tracheal intubation the ILMA device was removed using a 25 cm stabilising rod, to maintain the tube in place and prevent accidental extubation. The patients' lungs were ventilated using a closed circuit and Ohmeda ventilator to maintain the endtidal carbon dioxide at 32 to 35 mmHg. Anaesthesia was maintained with isoflurane and 66% nitrous oxide in oxygen. Tracheal intubation time was defined as the time from removal of the facemask to the time ventilation was established through the tracheal tube with C[O.sub.2] confirmation.

The IOP was measured using applanation tonometry just before and after tracheal intubation and then at every minute for the next five minutes in both eyes. The mean of three readings was recorded at every measurement. The heart rate, mean arterial pressure and oxygen saturation were recorded at the same time and then at five minute intervals until the end of surgery. Any episode of hypoxaemia (SP[O.sub.2]<90%) and mucosal or dental trauma during intubation was recorded. Patients were assessed for a 48 hour postoperative period for sore throat and hoarseness of voice.

Statistical evaluation

The data has been presented as mean [+ or -] SD. Student's t-test was used to compare demographic data and intra-ocular pressure and haemodynamic parameters at each point of time. The trends of heart rate, blood pressure and IOP within the group were analysed using two-way analysis of variance with post-hoc analysis. Postoperative adverse effects were compared using the chi square test. P <0.05 was considered significant.

RESULTS

There were no significant differences between the two groups in respect of demographics (Table 1).

All the patients in the laryngoscopy group were intubated at first attempt, as compared to 26 of 30 patients in the ILMA group. Three of the remaining four were intubated at the second attempt after manipulation of the ILMA. One patient required changing the size of the ILMA for successful intubation. The time to successful intubation was longer in the ILMA group (56.8[+ or -]7.8 s) as compared to the laryngoscopy group (33[+ or -]3.6 s) (P <0.01).

[FIGURE 1 OMITTED]

The changes in IOP in both the groups are shown in Figure 1. In the laryngoscopy group there was a significant increase in IOP from baseline values after tracheal intubation, from 7.2[+ or -]1.4 to 16.8[+ or -]5.3 mmHg (P <0.01) which did not return to pre-intubation levels within five minutes. In the ILMA group there was no significant increase in IOP (from 7.6[+ or -]1.8 to 10.4[+ or -]2.8 mmHg, P >0.05) after tracheal intubation.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The heart rate increased significantly (P <0.05) after tracheal intubation in both groups. The changes in heart rate were comparable between the groups (Figure 2).

There was a significant rise in mean arterial pressure after tracheal intubation in the laryngoscopy group (from 73.08[+ or -]9.4 to 78.06[+ or -]12.1, P <0.05) which returned to baseline after five minutes. In the ILMA group the post-intubation rise in mean arterial pressure was statistically insignificant (72.4[+ or -]7.4, 73.6[+ or -]13.1, P >0.05) (Figure 3).

The maximum changes in IOP and mean arterial pressure after tracheal intubation were significantly (P <0.05) greater in the laryngoscopy group compared to the ILMA group.

No episode of hypoxaemia was observed during tracheal intubation in either group. Mucosal trauma occurred more frequently in the ILMA group as compared with the laryngoscopy group (P <0.01). The incidence of postoperative sore throat and hoarseness of voice was comparable in both groups (Table 2).

DISCUSSION

To our knowledge changes in IOP after ILMA-aided tracheal intubation have not previously been reported. Most previous studies(1, 3, 9) have shown a marked increase in IOP and blood pressure after conventional laryngoscopic tracheal intubation, with few exceptions(10)[degrees]. The choice of anaesthetic agents may also affect the post-laryngoscopic IOP changes. In a comparative study Mirakhur et al(11) documented that propofol may attenuate the increase in IOP following tracheal intubation. Other studies(12, 11) have shown a significant increase in IOP following tracheal intubation, despite the use of propofol, especially in glaucoma patients". In our study, the intraocular pressure and mean arterial pressure were comparable in both groups after induction of anaesthesia but increased significantly after tracheal intubation in the laryngoscopy group. The mean changes in IOP during airway placement in both groups, although statistically different, are not clinically important in normal patients. The maximum IOP recorded during tracheal intubation was greater than 22 mmHg in six patients in the laryngoscopy group and this may be detrimental to patients with glaucoma(13).

Previous studies have shown conflicting results on the haemodynamic stress response following ILMA guided tracheal intubaation(6, 7). Joo and Rose(6) reported that the haemodynamic response to blind and fibreoptic-guided intubation with the ILMA was less than the response to conventional laryngoscope-guided tracheal intubation whereas Kihara et al(7) observed that blind intubation through an ILMA had no advantage over laryngoscope-guided tracheal intubation in patients with normal airways. In our study post-intubation increase in mean blood pressure was insignificant in the ILMA group as compared to the laryngoscopy group.

It has been suggested that the haemodynamic response to laryngoscopy and tracheal intubation is a reflection of an increase in sympathoadrenal activity due to oropharyngeal and laryngotracheal stimulation". Shribman et all, have shown that the major afferent source of the stimuli responsible for the adrenergic response may be supraglottic structures, distorted by laryngoscopy. Although the mechanisms of IOP response to tracheal intubation is uncertain, it has been suggested that adrenergic stimulation may cause vasoconstriction leading to increase in central venous pressure, which has a closer relationship with IOP than arterial blood pressure. Also, adrenergic stimulation increases the resistance to outflow of aqueous humour between the anterior chamber and Schlemm's canal and thereby can increase IOP(16).

The possible cause for the lesser increase in IOP and blood pressure in ILMA-guided blind intubation may be lesser adrenergic stimulation at supraglottic level, and also at subglottic level due to the soft tip and well-lubricated silicon tube. Our findings of the haemodynamic response to ILMA are similar to those reported by Joo and Rose(6) but differ from the study by Kilara et al(7). These results differ from the study by Kihara et al(7). The inter-study differences may be due to the difference in type of tracheal tube selection and different sequence of adjusting manoeuvres. Kihara et al' did not use the conventional soft tipped silicon tube in their study. Our success rate and intubation time was comparable with previous studies(5-7). Although the intubation time was longer with the ILMA than with the conventional laryngoscope, the ILMA allows ventilation to continue during attempts at intubation decreasing the likelihood of hypoxaemia and hypercarbia during intubation. Although mucosal trauma was more frequent in the ILMA group, postoperative pharyngolaryngeal morbidity was not significantly increased, in accordance with a previous report(7).

We conclude that the ILMA has an advantage over conventional laryngoscopy in minimising the increase in IOP and haemodynamic response to tracheal intubation in patients with normal baseline IOP and blood pressure. The response may be different in glaucomatous and hypertensive patients. Further studies are indicated to find out the response to intubation through ILMA in these susceptible individuals.

Paper presented at 11th Asian Australian Congress of Anaesthesiologists, Kuala Lumpur.

Accepted for publication on February 10, 2008.

REFERENCES

(1.) Watcha MF, Chu FC, Stevens JL, White PE Intraocular pressure and hemodynamic changes following tracheal intubation in children. J Clin Anesth 1991; 3:310-313.

(2.) Fox EJ, Sklar GS, Hill CH, Villanueva R, King BD. Complications related to the pressure response to endotracheal intubation. Anesthesiology 1977; 47:524-525.

(3.) Lamb K, James MFM, Janicki PK The laryngeal mask airway for intraocular surgery: Effects on intraocular pressure and stress responses. Br J Anaesth 1992; 69:143-147.

(4.) Benumof JL. Laryngeal mask airway and ASA difficult airway algorithm. Anesthesiology 1996; 84:686-699.

(5.) Agro F, Bramicombe J, Carassiti M, Marchionni L, Morelli A, Cataldo R. The intubating laryngeal mask: clinical appraisal of ventilation and blind tracheal intubation in 110 patients. Anaesthesia 1998; 53:1084-1090.

(6.) Joo HS,Rose DK. The intubating laryngeal mask airway with and without fiber optic guidance. Anesth Analg 1999; 88:662-666.

(7.) Kihara S, Watanabe S, Taguchi N, Suga A, Brimacombe JR. Tracheal intubation with the Macintosh laryngoscope versus intubating laryngeal mask airway in adults with normal airways. Anaesth Intensive Care 2000; 28:281-286.

(8.) Brimacombe JR, Brain AIJ, Berry AM. Future directions. In: The laryngeal mask airway: a review and practical guide. Philadelphia: WB Saunders, 1997, p. 227-247.

(9.) Holden R, Morsman CDG, Butler J, Clark GS, Hughes DS, Bacon PJ. Intra-ocular pressure changes using the laryngeal mask airway and tracheal tube. Anaesthesia 1991; 46:922-924.

(10.) Akhtar TM, McMurray P, Kerr WJ, Kenny GN. A comparison of laryngeal mask airway with tracheal tube for intra-ocular ophthalmic surgery. Anaesthesia 1992; 47:668-671.

(11.) Mirakhur RK, Shepherd WF, Elliott P Intraocular pressure changes during rapid sequence induction of anaesthesia. Comparison of propofol and thiopentone in combination with vecuronium. Br J Anaesth 1988; 60:379-383.

(12.) Whitford AM, Hone SW, O'Hare B, Magner J, Eustase P Intraocular pressure changes following laryngeal mask airway insertion: A comparative study. Anaesthesia 1997; 52:794-796.

(13.) Barclay K, Wall T, Warcham K, Asai T Intraocular pressure changes in patients with glaucoma: comparison between the laryngeal mask airway and tracheal tube. Anaesthesia 1994; 49:159-162.

(14.) Derbyshire DR, Chmielewski A, Fell D, Vater M, Achola K, Smith G. Plasma catecholamine response to tracheal intubation. Br J Anaesth 1983; 55:855-860.

(15.) Shribman AJ, Smith G, Achola KJ. Cardiovascular and catecholamine responses to laryngoscopy with or without tracheal intubation. Br J Anaesth 1987; 59:295-299.

(16.) Murphy DE Anesthesia and intraocular pressure. Anesth Analg 1985; 64:520-530.

N. BHARTI *, B. MOHANTY *, P. K. BITHAL ([dagger]), M. DASH ([double dagger]), H. H. DASH ([section])

Department of Neuroanaesthesia, All India Institute of Medical Sciences Ansari Nagar, New Delhi, India

* M.D., Assistant Professor.

([dagger]) M.D., Additional Professor.

([double dagger]) M.D., Senior Resident.

([section]) M.D., Professor and Head.

Address for reprints: Dr N. Bharti, Department of Anaesthesia and Intensive Care, Post Graduate Institute of Medical Education and Research, Chandigarh-160012, India.
TABLE 1

Demographic data, presented as mean (SD)

Variables Laryngoscope Intubating laryngeal mask
 (n=30) (n=30)

Age (years) 39.7 (11.2) 42.2 (15.7)
Weight (kg) 59.4 (13.4) 58.1 (10.3)
Gender ratio (M: F) 21:9 18:12
ASA status (1:2) 27:3 24:6

* P <0.05 (significant).

TABLE 2
Frequency of complications, presented as number of patients
Variables Laryngoscope Intubating laryngeal mask
 (n=30) (n=30)

Mucosal trauma 3 8 *
Dental trauma 0 0
Hypoxaemia 0 0
Sore throat 6 8
Hoarseness of voice 2 3

* P <0.05 (significant).
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Author:Bharti, N.; Mohanty, B.; Bithal, P.K.; Dash, M.; Dash, H.H.
Publication:Anaesthesia and Intensive Care
Geographic Code:9INDI
Date:May 1, 2008
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