Journal of Postgraduate Medicine Medknow Publications and Staff Society of Seth GS Medical College and KEM Hospital, Mumbai, India ISSN: 0022-3859 EISSN: 0972-2823 Vol. 47, Num. 3, 2001, pp. 181-184

Journal of Postgraduate Medicine, Vol. 47, Issue 3, 2001 pp. 181-184

Comparative Evaluation of Intraocular Pressure Changes Subsequent to Insertion of Laryngeal Mask Airway and Endotracheal Tube

Ghai B, Sharma A, Akhtar S

Department of Anaesthesia, Maulana Azad Medical College and associated Lok Nayak Hospital, New Delhi, India.

Abstract

AIMS: To evaluate the intraocular pressure and haemodynamic changes subsequent to insertion of laryngeal mask airway and endotracheal tube. SUBJECTS AND METHODS: The study was conducted in 50 adult patients. A standard general anaesthesia was administered to all the patients. After 3 minutes of induction of anaesthesia baseline measurements of heart rate, non-invasive blood pressure and intraocular pressure were taken following which patients were divided into two groups: laryngeal mask airway was inserted in group 1 and tracheal tube in group 2. These measurements were repeated at 15-30 second, every minute thereafter up to 5 minutes after airway instrumentation. RESULTS: A statistically significant rise in heart rate, systolic blood pressure, diastolic blood pressure and intraocular pressure was seen in both the groups subsequent to insertion of laryngeal mask airway or endodotracheal tube. Mean maximum increase was statistically more after endotracheal intubation than after laryngeal mask airway insertion. The duration of statistically significant pressure responses was also longer after endotracheal intubation. CONCLUSION: Laryngeal mask airway is an acceptable alternative technique for ocular surgeries, offering advantages in terms of intraocular pressure and cardiovascular stability compared to tracheal intubation.

Key Words: Opthalmology; intraocular pressure, Equipment; laryngeal mask airway.

Laryngoscopy and tracheal intubation is a time-tested method to achieve the airway control in anaesthesia practice and resuscitation. However, it is associated with significant cardiovascular response in the form of hypertension and tachycardia because of sympathetic discharge following laryngotracheal stimulation.(1-3) Laryngoscopy and tracheal intubation is also known to be associated with increase in intraocular pressure.(4,5) Attempts have been made by many workers in the past to mitigate or prevent cardiovascular and ocular reactions especially the acute increase in intraocular pressure (IOP) associated with laryngoscopy and endotracheal intubation. Use of Brain laryngeal mask airway (LMA) as an alternative to endotracheal tube has attracted the attention of several workers with regard to haemodynamic and IOP changes, as it obviates the need for laryngoscopy and endotracheal intubation. Previous workers, who compared IOP response to LMA and endotracheal tube insertion, have reported different results.(6-11) In view of the conflicting observations of earlier workers, we had undertaken this study. We hope that the results of this study will assist us to formulate guidelines for anaesthetic management in ophthalmic surgeries and to establish which of the two methods of airway control is superior with respect to margin of safety in patients who are at increased risk of rise in IOP.

Subjects and Methods

After obtaining approval of the ethics committee of the institution and informed consent from the patients, the study was conducted on 50 adult ASA grade I patients aged between 18 to 50 years, taken up for elective non-ocular surgeries. The patients with cardiovascular or pulmonary disease, those with diabetes mellitus or glaucoma and obstetric patients were excluded from the study. The patients with contraindications to the use of LMA i.e. patients with mouth opening less than 1.5 cm, inability to extend the neck, pharyngeal pathology, patients at risk of regurgitation, airway obstruction at or below the larynx were also excluded from the study. All the patients were premedicated with oral diazepam 10 mg 2 hours before surgery; pethidine (1 mg/kg) and promethazine (0.25 mg/kg) intramuscularly 45-60 minutes prior to induction. Monitoring consisted of electrocardiogram, non-invasive blood pressure, end tidal CO2, oxygen saturation and airway pressure. After preoxygenation, all patients were induced with thiopentone 5 mg/kg. Neuromuscular blockade was achieved with vecuronium 0.1 mg/kg and anaesthesia was maintained at normocapnia with 0.5% halothane and 60% nitrous oxide in oxygen using facemask. Throughout the study, every patient was in supine position and any pressure on eyes was avoided. Lignocaine 1% and fluorescein were instilled in both eyes and all intraocular pressures were measured by hand- held aplanation tonometer by one investigator.

Baseline measurements of heart rate, non-invasive blood pressure and IOP were taken 3 minutes after the induction following which, patients were randomly allocated to either of the following two groups. Group 1, (n=25) in which LMA of appropriate size was inserted blindly as described by Brain. Men received size 4 LMA, women received size 3 LMA and cuff inflated according to manufacturer’s instructions. In group 2, (n=25) laryngoscopy was done and airway was secured with endotracheal tube of appropriate size after which cuff was inflated avoiding leak. Air entry was checked by auscultation of chest to confirm proper positioning of endotracheal tube. The above-mentioned parameters viz. heart rate, non-invasive blood pressure and IOP were measured serially at 15-30 second, 1 minute and every minute thereafter up to 5 minutes in both the groups. Pre-insertion values were compared with post insertion values.

Results

The two airway groups were comparable in respect of weight, age, sex and surgical procedures. The patient characteristics and operations performed are summarised in Table 1. Mean baseline readings of heart rate, systolic blood pressure, diastolic blood pressure and intraocular pressure of right and left eyes were comparable in both groups.

Both groups were associated with significant haemodynamic and intraocular pressor responses after airway instrumentation, in the form of increase in heart rate, blood pressure (table 2) and IOP (table 3); however the mean maximum increase was significantly higher in group 2 after tracheal intubation compared to group 1 (table 4). The duration of these responses was also significantly longer after endotracheal intubation (table 4). The statistically significant increase in IOP of both eyes lasted only for 15-30 seconds in LMA group, while in tracheal tube group, increase in IOP of right eye lasted for 3 min and increase of left eye IOP lasted for 2 minutes. Haemodynamic parameters subsequently decreased below baseline values in both the groups and IOP decreased subsequently below baseline values only in LMA group. There was a close relation between haemodynamic and IOP response.

Laryngoscopy and tracheal intubation, to achieve airway control in anaesthesia practice, have been consistently bothering anaesthesiologists with regard to regular occurrence of the pressor responses associated with it. The haemodynamic responses, manifesting as increase in heart rate and blood pressure, are due to reflex sympatho-adrenal discharge provoked by epilaryngeal and laryngotracheal stimulation subsequent to laryngoscopy and tracheal intubation.(1-3) The stress response to tracheal intubation and extubation is also associated with increase in IOP.(4,5,12-14) The mechanism of IOP rise is secondary to increased sympathetic activity. Adrenergic stimulation causes vaso and venoconstriction, and an increase in central venous pressure, which has a close relationship with IOP.(11) In addition adrenergic stimulation can also produce an acute increase in IOP, by increasing the resistance to the outflow of aqueous humour in trabecular meshwork between anterior chamber and Schlemn’s canal.(15) This explains the close relationship between haemodynamic and IOP response as also seen in our study.

The acute increase in IOP may be dangerous for patients with impending perforation of eye, perforating eye injuries, glaucoma etc. This problem has drawn the attention of many workers to study the attenuation of these responses with some pre-treatment or by some alternative to laryngoscopy and tracheal intubation viz. LMA. Lignocaine pre-treatment either intravenous or nebulised, has been used to attenuate ocular and systemic responses to laryngoscopy and tracheal intubation.(4,12,13) Intranasal nitroglycerine has also been evaluated to prevent increase in IOP associated with tracheal intubation.(14) LMA, as an alternative to endotracheal tube has attracted the attention of many workers with regards to IOP changes, as it obviates the need for laryngoscopy and tracheal intubation. Holden et al(6) were the first one to compare the IOP changes using LMA and endotracheal tube and their observations as well as those of Lamb et al.(7) revealed a significantly smaller increase in IOP using LMA both on placement and removal as compared to endotracheal intubation. Similar results were reported by Whitford et al(8) and Duman et al.(9)

In our study we found that both groups were associated with significant haemodynamic and intraocular pressor responses after airway instrumentation, in the form of increase in heart rate, blood pressure and IOP, however the mean maximum increase was significantly higher in the tracheal tube group compared to LMA group. The duration of these responses was significantly longer in tracheal tube group. Our results are in accordance with Holden et al.(6), Lamb et al.(7), Whitfold et al(8) and Duman et al.(9) But Akhtar et al.(10), using intravenous propofol anaesthesia noticed no significant changes in intraocular pressure subsequent to LMA insertion or tracheal intubation. However, they noticed fewer complications immediately following surgery in LMA group. The attenuated increase in IOP in their study was possibly due to the use of propofol. Intravenous propofol anaesthesia has been shown to cause a 30 % decrease in IOP from baseline and while the stimulus of tracheal intubation increased IOP, this remained below baseline level.(16) Kilickan et al(11) using alfentanil and propofol for total intravenous anaesthesia reported neither tracheal tube or LMA insertion being associated with increase in IOP. However endotracheal extubation was associated with significant increase in IOP compared to LMA removal.

Haemodynamic parameters subsequently decreased below baseline values in both the groups and IOP decreased subsequently below baseline values only in LMA group. This was possibly due to the use of halothane and vecuronium both of which are known to cause fall in heart rate, blood pressure and IOP.(17,18)

The technique of insertion of LMA is absolutely different from that of inserting an endotracheal tube. It involves no use of laryngoscopy as vocal cords do not need to be visualized and LMA does not enter trachea but instead sits on the hypo pharynx when positioned correctly. So, considering these, the pressor responses to LMA insertion were expected to be different from that of laryngoscopy and tracheal intubation. We believe that not performing laryngoscopy during insertion of LMA is one major reason for the observed attenuated pressor responses to LMA, apart from other reason like no direct laryngeal stimulation. The mechanical stimulation by pressure of laryngoscope on the soft tissue is the major factor in producing stress response to laryngoscopy and tracheal intubation.(1) Laryngoscopy produces the major contribution to the sympatho-adrenal response and tracheal intubation per se-contributed little additional effect.(3)

The LMA offers additional advantages during emergence from anaesthesia; removal does not increase IOP and it is not accompanied by complication like coughing.(7,11) Tracheal extubation, however, causes a marked increase in IOP, coughing and breath holding.(19)

We conclude that the use of LMA is advantageous where marked rise in intraocular pressure due to laryngoscopy and endotracheal intubation could be deleterious in patients with impending perforation of the eye, perforating injury, glaucoma etc. LMA may be recommended as an alternative to tracheal intubation for ocular surgeries. LMA also offers advantage in hypertensives, patients, with coronary artery disease and patients with cerebro-vascular disease because of attenuated cardiovascular response.

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