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Editor,—The letter by Gao Lei et al 1 gives an erroneous impression that retrobulbar injection per se produces oculocardiac reflex (OCR). On the contrary, retrobulbar anaesthetic infiltration is a method of prophylaxis to prevent OCR in patients under general anaesthesia.2 In patients operated under retrobulbar anaesthesia, “heart rhythm and rate become stable once the block has taken effect; occasional ectopics or heart rate changes before this seemingly being due to the stimulus of needle prick or the adrenaline in the solution”.3 The author’s experience is the same as described in the last paragraph. Their definition of OCR as at least a 10% decrease in heart rate below relative baseline is arbitrary. In a previous well designed study, Mirakhur et al have taken bradycardia of 70 or less heart beats per minute at any time during surgery and persisting for more than 15 seconds as study criteria and OCR as slowing of heart rate by more than 20% or arrhythmia during traction irrespective of heart rate.4 They felt that smaller decreases in heart rate do not usually require treatment. The findings by Gao et al do not mention the duration of arrhythmias or duration of drop in heart rate. It has been observed that development of inherent endogenous β blockade occurs with increasing age. Therefore isolated heart rate recording without simultaneous recording of blood pressure is erroneous.5The various factors that can increase the risk of OCR reviewed by Scott Lang and van der Val are hypercarbia, hypoxaemia, light anaesthesia, young age due to higher resting vagal tone, pharmacological agents such as potent narcotics (sufentanil, alfentanil), β blockers and calcium channel blockers, and the nature of the provoking stimulus—namely, strength of stimulus, and duration.6 As the patients in the study by Gao et al were all over the age of 60 years and six of 10 patients who had OCR had abnormal preoperative electrocardiograms, the role of pharmacological agents described above must be taken into consideration before implicating steps of cataract surgery in triggering OCR. The adoption of preventive strategies described by Scott Lang and van der Val for avoidance of predisposing factors to the development of OCR (cessation or modulation of surgical stimulus by administering intravenous atropine or glycopyrrolate and by retrobulbar anaesthesia) have reduced the incidence of OCR during ocular surgery.
Sorensen and Gilmore have reported successful resuscitation by external cardiac massage following OCR. This was quoted by Arndt in his reply to Scott Lang and van der Val.7 In his reference Smith mentioned that as death due to OCR which Gao et al have also incorrectly cited.8 The incorrect reference by Gaoet al raises the issue of obligation to reference carefully important points in their manuscript.9
The potential for fatality or cardiac arrest could be chiefly the result of ignoring preventive measures. Cardiac arrest could also be due to cardiac toxicity by inadvertent intravascular injection of local anaesthetic. Considering the above danger associated with retrobulbar block, attention now is focused on a safer peribulbar block. Although peribulbar block is a safe and a superior procedure, its practice is mostly limited to experienced and skilled ophthalmologists in institutes of higher learning. However, retrobulbar block remains a highly popular procedure with many practising ophthalmologists even today. One should be unambiguous when considering the role of retrobulbar anaesthesia in producing OCR, as it is the mainstay of cataract surgery in many countries. Any incorrect information sends the wrong signals to practising ophthalmologists using retrobulbar anaesthesia in cataract surgery in preference to expensive, potentially dangerous, and technically difficult general anaesthesia.
In a control double blind study, Kundra demonstrated that combining peribulbar block with general anaesthesia in children undergoing intraocular surgery completely abolished OCR, reduced the requirement of anaesthetics, and produced early recovery from anaesthesia with satisfactory postoperative analgesia (Kundra Pankaj, Department of Anaesthesia, JIPMER, Pondicherry, personal communication).
Editor,—Dr Seshubabu raised several points with regard to oculocardiac reflex (OCR) and the study we conducted.
Retrobulbar injection is a manoeuvre that begins with needle prick in the region between the lateral rectus muscle and optic nerve. Before the block has taken full effect, the reflex may be induced by stimulus of needle disturbance, retrobulbar bleeding, or even the anaesthetic solution (2.5 ml) which probably has effects on intraorbital pressure within a short time. Ocular compression was found to be the most common triggering event in precipitating the OCR in our study. Five of 30 patients (16.7%), compared with 14 of 20 patients (70.0%) reported by Sun Yuxun (defined as at least a decrease of 10 beats per minute more stringent than ours) were noted to have the OCR during digital pressure of the eyeball. This was highly significant by χ2=14.48, p<0.001. The two groups were similar in demographics. In Sun’s study, however, retrobulbar anaesthesia had not been applied before any manipulation was performed. Therefore, we think that local retrobulbar anaesthesia decreases, not completely abolishes, the OCR.
To our knowledge, there are three main criteria for the OCR, irrespective of blood pressure, cardiac output, and the duration of arrhythmias and bradycardia. Vrabec et al and Eustis et al defined it as a 10% decrease, while Karhunen et al defined it as a 20% decrease in baseline heart. Other reports defined it as at least a decrease of 10 beats per minute. Because of the instability and continuity of electrocardiac activity, we divided the natural standard surgery into six procedures according to their suspected disturbance to the eye and adopted the relative baseline heart rate. We believed that notable changes in electrocardiac activity within a shorter period of time would be more significant in the clinical sense. In our original paper published in Chinese, we suspected that the criteria for the OCR may be too conservative and incomplete, and they may need revision to assure greater clinical significance. It is our desire that more scientific new criteria for OCR would be established by ophthalmologists cooperating with cardiovascular surgeons.
At the beginning of the next century, more than 10% of the total population in China will be over the age of 60. Because of a positive association between cataract and age, patients over 60 years old scheduled for cataract extraction at the practice of one of us (GL) were eligible for our study. They can be recognised as random samples. It is true that various factors may influence the OCR. However, the study that we have conducted was to determine the true incidence of OCR among certain people, regardless of their sex, general health condition, medication, etc.
Owing to a misunderstanding, we incorrectly cited one of our references.