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Non-depolarising neuromuscular blockers can be used routinely instead of suxamethonium at induction of general anaesthesia for caesarean section
Internotiunal Journal a/ Obsletric Anesrhesia (1999) 8,26&272 0 1999 Harcourt Publishers Ltd
CONTROVERSIES
Non-depolarising neuromuscular blockers can be used routinely instead of suxamethonium at induction of general anaesthesia for caesarean section Proposer: D. M. Levy University Hospital, Nottingham,
UK
anaesthetised with this technique in Hamer Hodges’ unit.* Although two patients regurgitated small amounts of fluid, which pooled in the pharynx, there were no cases of aspiration pneumonitis. However, in the Confidential Enquiries for 196466 (the period when the use of thiopentone and suxamethonium became widespread), technical difficulties with tracheal intubation were first mentioned, and the percentage of maternal deaths from anaesthesia more than doubled.3
I shall argue that l
l
l
Rapid sequence induction with suxamethonium has had its day Rocuronium is the best available alternative to suxamethonium In the event of difficult or failed tracheal intubation, profound non-depolarising block is preferable to unpredictable recovery from suxamethonium.
SUXAMETHONIUM NEUROMUSCULAR BLOCK IN OBSTETRIC ANAESTHESIA, 1959
- PROBLEMS
AT ONSET
If suxamethonium were presented today as a new drug for approval by the official regulatory bodies, I doubt it would get very far. Based on the incidence of adverse reactions at the time of a survey of UK anaesthetic drug usage in the mid-1980s, Watkins calculated that a serious reaction to suxamethonium might be expected once in every 4000 inductions.4 A French multi-centre enquiry in the early 1990s found that suxamethonium accounted for 5% of the usage of neuromuscular blockers, but 30% of the anaphylactic reactions.5 Suxamethonium was responsible for a maternal death in the 1991-93 triennium,6 and I am aware of a more recent near-fatal proven reaction to suxamethonium at caesarean section in a north Nottinghamshire hospital. ‘Excellent’ intubating conditions mean that the jaw is relaxed with no resistance to the laryngoscope blade, the cords are abducted and motionless, and there is no coughing or limb movement in response to intubation. From two recently published studies,7,8 I have calculated that intubating conditions at 60 s were less than ‘excellent’ in almost one-quarter of nonobstetric patients receiving suxamethonium 1 mglkg at rapid sequence induction. This is not particularly impressive for a drug revered as a gold standard.
The widespread use of neuromuscular blockade in obstetric anaesthesia dates from the publication 40 years ago this year of a landmark paper by Hamer Hodges and colleagues in Portsmouth.’ A thiopentone, suxamethonium, nitrous oxide/oxygen technique was compared with three anaesthetic regimens in which mothers received trichloroethylene, cyclopropane or diethyl ether. Suxamethonium was the ‘relaxant of choice’ because of concerns that the only two alternatives, gallamine and tubocurarine, crossed the placenta. All patients were given pre-operative atropine, but no antacid. Anaesthesia was induced with steep head-up tilt, but without cricoid pressure (not yet described). Those mothers who had minimal anaesthesia facilitated by neuromuscular blockade had a greater percentage of babies in whom regular breathing and active crying were established within 60 s. There was no anaesthetic-related mortality in 2000 obstetric patients
Dr David M. Levy MB ChB FRCA, Consultant Anaesthetist, University Hospital NHS Trust, Queen’s Medical Centre, Nottingham NG7 2UH, UK. 266
Controversies Almost half of patients receiving thiopentone and suxamethonium have increased masseter tone exceeding 50% of baseline.9 This might go some way to explain why suxamethonium does not always work perfectly. In one of 23 cases of failed intubation at caesarean section over 17 years in a Leeds teaching hospital,‘” profoundly increased masseter tone rendered mouth opening impossible. Masseter rigidity with subsequent signs of hypermetabolism points to the ominous diagnosis of malignant hyperthermia, another potentially lethal complication of suxamethonium. The risk of bradyarrhythmias particularly after a second dose of suxamethonium has been recognized for many years, and necessitates use of an anticholinergic agent.” A variety of myopathies contraindicate the use of suxamethonium because of the risk of hyperkalaemia.” Suxamethonium is the only neuromuscular blocker with the potential for precipitating a myotonic crisis. We recently had a patient whose diagnosis of myotonic dystrophy was established only after the condition had been identified antenatally in the fetus. Intragastric pressure increases have been shown to correlate with the intensity of fasciculations.” It is not known whether pregnant women with reflux necessarily have the same simultaneous protective increases in lower oesophageal sphincter tone that have been demonstrated in non-pregnant subjects given suxamethonium.14
SUXAMETHONIUM
- PROBLEMS
AT OFFSET
I argue that the use of a non-depolarising drug with a duration of action of the order of half an hour is quite safe and, indeed, desirable. Prolonged suxamethonium block is a problem only if the drug is given in the expectation that the return of spontaneous respiration will resolve a failed ventilation scenario. Benumof, a guru of difficult airway management, has stressed that suxamethonium cannot be relied upon to enable a patient to breathe spontaneously before critical desaturation occurs.‘5 Metabolism of suxamethonium is dependent upon plasma cholinesterase, and one in 25 of the population is other than homozygous for the normal gene. A heterozygote whose plasma cholinesterase activity is further reduced by pregnancy may well have clinically significant prolongation of block.16 Furthermore, recovery from suxamethonium occurs at different rates in different muscles. At the laryngeal adductors recovery occurs twice as fast as in adductor pollicis.17 Two cases of critical desaturation after failed intubation in obstetrics have been graphically described. Both women had suxamethonium. In one case repeat laryngoscopy revealed a small aperture in the larynx, opening and closing, through which it was impossible to insert an 8,7
267
or 6 mm cuffed endotracheal tube’. It is noteworthy that spontaneous respiration returned at 7 min in this case and 23 min in the other.18 To make matters worse regurgitation and vomiting are very real threats to the lightly anaesthetised patient in whom neuromuscular block is wearing off. Huge increases in intragastric pressure have been measured.19 The partially anaesthetised, partially paralysed patient who is bucking and straining will consume colossal amounts of oxygen. Laryngospasm, airway oedema and reduced chest wall compliance will conspire against effective ventilation. I suggest that suxamethonium can transform a difficult intubation into a failed intubation, and turn ‘can’t intubate can ventilate’ into ‘can’t intubate can’t ventilate’. Lastly, myalgia might never have killed anyone, but 7.5% of caesarean section patients have aches and pains in the back or neck after a 100 mg bolus dose of suxamethonium.20 As Thorburn and Reid commented, ‘it is interesting that, in the present aggressive attack on the control of postoperative pain, we should continue to use a drug known to cause considerable morbidity.?’
ALTERNATIVES VECURONIUM
TO SUXAMETHONIUM
.. .
Vecuronium is an aminosteroidal non-depolarising neuromuscular blocker devoid of the catalogue of potential complications peculiar to suxamethonium. It has been shown that 0.1 mg/kg actual body weight has a more rapid onset in pregnant women at term. This might be attributed to the increased cardiac output or to the fact that skeletal muscles receive a relative overdose in pregnancy, because the drug doesn’t distribute to the extra water, fat, or the fetus.22 However, a standard intubating dose does not allow sufficiently rapid attainment of the requisite block for intubation without a period of mask ventilation to maintain oxygen saturation. There is not time at emergency caesarean section to wait 34 min for a small priming dose to accelerate the onset of the principal dose. A single large bolus dose will speed onset, but only at the cost of unacceptably increased duration of block.23 One study has demonstrated the feasibility of vecuronium for emergency caesarean section. Teviotdale studied 30 patients, all of whom had antacid prophylaxis with sodium citrate. Vecuronium 0.5 mg was given in advance of a fixed principal dose of 8 mg, which was followed at least 20 s later by thiopentone 250 mg. With cricoid pressure applied, the lungs were maskventilated with isoflurane in oxygen for 2 min before intubation, without any discernible regurgitation or aspiration.‘4
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International
ALTERNATIVES ROCURONIUM
Journal of Obstetric Anesthesia TO SUXAMETHONIUM
.. .
Rocuronium is similar to vecuronium but less potent. Thus a greater mass of drug is required for the same effect, resulting in a significantly faster onset time. Rocuronium does not release histamine,25 and anaphylaxis appears to be exceedingly rare. Abouleish and colleagues demonstrated that rocuronium is a genuine alternative to suxamethonium for rapid sequence induction of anaesthesia for caesarean section. After pre-oxygenation, 4 or 6 mg/kg of thiopentone was followed by a bolus of rocuronium 0.6 mg/kg. Intubating conditions were ‘excellent’ or ‘good’ when two twitches of a train of four at adductor pollicis had disappeared, at a mean time of 84 s. The duration of block was ideal for caesarean section, and there were no untoward neonatal effects.26 Interestingly, in a study with ketamine 1.5 mg/kg, intubating conditions were ‘excellent’ or ‘good’ in every patient when the block at adductor pollicis, measured by electromyography, was only 50%. This was at a mean of only 42 s.~’ Enhancement of cardiac output or depression of laryngeal reflexes by ketamine might explain this remarkable halving of the time to successful intubation. Although contraindicated in hypertensive disorders of pregnancy, ketaminerocuronium would seem to be an ideal combination in the hypovolaemic obstetric patient.
ALTERNATIVES TO SUXAMETHONIUM ORG 9487 (RAPACURONIUM)
...
Org 9487 is the newest aminosteroidal non-depolarising neuromuscular blocker. Even less potent than rocuronium, its onset time is, predictably, further shortened. At 1 min intubating conditions were deemed poor in one of 18 patients given Org 9487 compared with two of 20 who had suxamethonium (NS).28 After 40 years, surely the fate of suxamethonium will now be sealed?
CONSEQUENCES BLOCK
OF NON-DEPOLARISING
The fact that non-depolarising neuromuscular block commits the anaesthetist to maintaining oxygenation by positive pressure ventilation is not necessarily a disadvantage. When the original failed intubation drill was conceived in the early 1970s general anaesthesia for caesarean section was predominant. In the failed intubation drill, the place of regional anaesthesia was
as an alternative to letting the patient wake up, emptying the stomach, and undertaking inhalational anaesthesia with spontaneous ventilation.29 In 1999, there is minimal use of general anaesthesia, even for emergency caesarean section. 30*3’ General anaesthesia is most often used because a regional technique is contraindicated or has failed. If a regional technique is out of the question and the history or evaluation of the airway is suggestive of difficult tracheal intubation, awake direct laryngoscopy or fibre-optic intubation are then considered. Non-depolarising neuromuscular block rules out the option of maintaining inhalational anaesthesia with spontaneous respiration after failed intubation. However, as Harmer has argued, ‘conversion of this crisis state into a smooth, safe mask anaesthetic, of sufficient depth to allow surgery, calls for a high degree of skill and experience’32 - which is undoubtedly rare today. I do not believe that suxamethonium makes airway management any safer. Trust placed in rapid recovery from suxamethonium is trust misplaced.
THE UNANTICIPATED
DIFFICULT
AIRWAY
Profound non-depolarising neuromuscular block may be safer than block with suxamethonium because sustained optimal conditions maximize the chances of intubation or alternative successful tracheal approaches to airway management. A McCoy laryngoscope can convert a Cormack and Lehane grade 3 view to a grade 2. 33A gum-elastic bougie has been recommended for every grade 3 laryngoscopy.1° This advice might now include grade 2b as defined by Yentis and Lee.34 The guaranteed absence of movement at the larynx can only make things easier. It has been suggested that teaching anaesthetists to implement a failed intubation drill without delay in the event of difficulty might contribute to the increased incidence of failed intubation in obstetrics.35 The use of non-depolarising neuromuscular blockers means it is no longer essential to intubate swiftly or give up early. Instead, a calm, sequential approach to airway management can be adopted. As Sellick stated in his original paper, cricoid pressure should prevent gastric distension during positive pressure ventilation of the lungs.36 It has been emphasized that cricoid pressure not speed - is the main safety factor of rapid sequence induction.” Looking back at Hamer Hodges’ series2 and the absence of aspiration in over 600 at-risk patients reported by Snow and Nunn,‘* I wonder whether the head-up position should be revisited. If the oesophagus runs uphill from the stomach, it should be extremely difficult for gastric contents to get
Controversies anywhere near the pharynx of a fully paralysed patient unable to vomit. In the absence of iatrogenic glottic trauma and presence of profound neuromuscular blockade ‘can’t intubate, can’t ventilate’ must be vanishingly rare. Obstructed ventilation can result from difficulty in displacing the tongue, epiglottis, or larynx from the posterior pharyngeal wall. Brimacombe and Berry have stated that ‘the laryngeal mask airway would appear to be the airway of choice in the obstetric patient who can be neither intubated nor mask-ventilated.‘j’ I am sure that everyone who uses the laryngeal mask routinely in non-obstetric practice would agree that the chances of successful placement are greatly heightened when pharyngeal and laryngeal reflexes are obtunded. Similarly, deliberate oesophageal intubation with a tracheal tube40 or the more sophisticated Combitube will be more likely to meet with success if the pharyngeal and laryngeal musculature is profoundly relaxed. Laryngeal obstruction is surely less likely to challenge any of us in the course of a career than anaphylaxis to suxamethonium. The best chance of successful cricothyrotomy will be in a fully paralysed patient. The procedure will be doomed to failure in a venocongested moving target. CONCLUSION If tubocurarine, gallamine, suxamethonium and rocuronium had all been available in 1959, which would have been the relaxant of choice for caesarean section? Rapid recovery from suxamethonium was never originally perceived as an advantage. I question the continued allegiance to suxamethonium, founded on ndive faith in its unpredictable offset. Bruce Scott, who died last November, wrote this of the introduction of neuromuscular block to obstetric practice. ‘If we had been honest, the attraction of the new method was the speed and ease with which we could present the intubated paralyzed patient to the obstetrician. We did not advertise the increased incidence of death due to Mendelson’s syndrome and failed intubation resulting from suxamethonium and crash induction.‘4’ Over 20 years ago, Green investigated two cases of Mendelson’s syndrome and was moved to abandon suxamethonium in favour of alcuronium or tubocurarine, with mask ventilation and the patient 30” head-up. 42 In 1999, we have rocuronium, a clean, safe drug with an onset time to rival that of suxamethonium. Waiting in the wings is Org 9487. We have at our disposal revolutionary devices to help manage the difficult airway. Suxamethonium has reigned unchallenged for 40 years. The time has come for a coup.
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REFERENCES 1. Hamer Hodges RJ, Bennett JR, Tunstall ME, Knight RF. General anaesthesia for operative obstetrics. Br J Anaesth 1959; 31: 152-163. ME. The choice of anaesthesia 2. Hamer Hodges RJ, Tunstall and its influence on perinatal mortality in caesarean section. Br J Anaesth 1961; 33: 572-588. 3. Morgan M. Anaesthetic contribution to maternal mortality. Br J Anaesth 1987; 59: 8422855. 4. Watkins J. Anaesthetic reactions. In Watkins J, Levy CJ, eds. Guide to immediate anaesthetic reactions. London: Butterworths, 1988: p 27. 5. Bevan DR. Editorial. Neuromuscular relaxants ~ 1997. Can J Anaesth 1997;44: 113551137. 6. Department of Health et al. Report on confidential enquiries into maternal deaths in the United Kingdom 1991-1993. London: HMSO, 1996: p 95. KC, Salmela L, Mirakhur RK et al. Comparison of 7. McCourt rocuronium and suxamethonium for use during rapid sequence induction of anaesthesia. Anaesthesia 1998; 53: 8677871. 8. Andrews JI, Kumar N, van den Brom RHG, Olkkola KT, Roest GJ, Wright PMC. A large simple randomized trial of rocuronium versus succinylcholine in rapid-sequence induction of anaesthesia along with propofol. Acta Anaesthesiol Stand 1999; 43: 4-8. 9. Ummenhofer WC, Kindler C, Tschak? G, Hampl KF, Drewe J. Urwyler A. Propofol reduces succinylcholine induced increase of masseter muscle tone. Can J Anaesth 1998; 45: 417423. 10. Hawthorne L, Wilson R. Lyons G, Dresner M. Failed intubation revisited: 17-yr experience in a teaching maternity unit. Br J Anaesth 1996: 76: 680-684. 11. Lupprian KG, Churchill-Davidson HC. Effect of suxamethonium on cardiac rhythm. Br Med J 1960; 2: 1774-1777. 12. Crochetiere C. Myopathies. In Gambling DR, Douglas JM, Eds. Obstetric Anaesthesia and Uncommon Disorders. Philadelphia: Saunders, 1998: pp 171-182. 13. Miller RD, Way WL. Inhibition of succinylchohne-induced increased intragastric pressure by nondepolarizing muscle relaxants and lidocaine. Anesthesiology 1971; 34: 1855188. 14. Cotton BR, Smith G. The lower oesophageal sphincter and anaesthesia. Br J Anaesth 1984; 56: 3746. 15. Benumof JL, Dagg R, Benumof R. Critical hemoglobin desaturation will occur before return to an unparalyzed state following 1 mg/kg intravenous succinylchoiine. Anesthesiology 1997; 87: 979-982. 16. Davis L, Britten JJ, Morgan M. Cholinesterase. Its significance in anaesthetic practice. Anaesthesia 1997; 52: 244260. 17. Wright PMC. Caldwell JE, Miller RD. Onset and duration of rocuronium and succinylcholine at the adductor pollicis and laryngeal adductor muscles in anesthetized humans. Anesthesiology 1994; 81: 1110~1115. 18. French GWG, McBrien ME, Sellers WFS. Failed intubation in obstetrics a time for review. Today’s Anaesthetist 1994; 9: 60-64. 19. Spence AA, Moir DD, Finlay WEI. Observations on intragastric pressure. Anaesthesia 1967; 22: 2499256. 20. Thind GS, Bryson THL. Single dose suxamethonium and muscle pain in pregnancy. Br J Anaesth 1983; 55: 743-745. 21. Thorburn J, Reid JA. Editorial. Suxamethonium (succinylcholine) in obstetric anaesthesia. International Journal of Obstetric Anesthesia 1992; 1: 1855186. 22. Baraka A, Jabbour S, Tabboush 2, Sibai A, Bijjani A, Karam K. Onset of vecuronium neuromuscular block is more rapid in patients undergoing Caesarean section. Can J Anaesth 1992; 39: 1355138. 23. Hawkins JL, Johnson D, Kubicek MA, Skjonsby BS, Morrow DH, Joyce TH. Vecuronium for rapid-sequence intubation for cesarean section. Anesth Analg 1990; 71: 1855190.
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24. Teviotdale BM. Vecuronium-thiopentone induction for emergency caesarean section under general anaesthesia. Anaesth Intens Care 1993; 21: 288-291. 25. Levy JH, Davis GK, Duggan J, Szlam F. Determination of the hemodynamics and histamine release of rocuronium (Org 9426) when administered in increased doses under N,O/O,-sufentanil anesthesia. Anesth Analg 1994; 78: 318-321. 26. Abouleish E, Abboud T, Lechevalier T, Zhu J, Chalian A, Alford K. Rocuronium (Org 9426) for Caesarean section. Br J Anaesth 1994; 73: 336-341. 27. Baraka AS, Sayyid SS, Assaf BA. Thiopental-rocuronium versus ketamine-rocuronium for rapid-sequence intubation in parturients undergoing Cesarean section. Anesth Analg 1997; 84: 1104-l 107. 28. Abboud TK, Bikhazi G, Mroz Let al. Org 9487 vs. succinylcholine in rapid sequence induction for cesarean section patients: maternal and neonatal effects. Anesthesiology 1997; 87: A906. 29. Tunstall ME, Sheikh A. Failed intubation protocol: Oxygenation without aspiration. Clin Anaesth 1986; 4: 171-187. 30. Brown GW, Russell IF. A survey of anaesthesia for caesarean section. International Journal of Obstetric Anesthesia 1995; 4: 214-218. 31. Tsen LC, Pitner R, Camann WR. General anesthesia for cesarean section at a tertiary care hospital 1990-1995: indications and implications. International Journal of Obstetric Anesthesia 1998; 7: 1477152.
32. Harmer M. Only maternal, not fetal, survival should persuade the anaesthetist to proceed with general anaesthesia for caesarean section after failed intubation. International Journal of Obstetric Anesthesia 1993; 2: lO&lOl. 33. Chisholm DG, Calder I. Experience with the McCoy laryngoscope in difficult laryngoscopy. Anaesthesia 1997; 52: 906-908. 34. Yentis SM, Lee DJH. Evaluation of an improved scoring system for the grading of direct laryngoscopy. Anaesthesia 1998; 53: 1041l1044. 35. Lyons G, Macdonald R. Difficult intubation in obstetrics. Anaesthesia 1985; 40: 1016. 36. Sellick BA. Cricoid pressure to control regurgitation of stomach contents during induction of anaesthesia. Lancet 1961; 2: 404406. 37. Pilkington S, Carli F, Dakin MJ et al. Increase in Mallampati score during pregnancy. Br J Anaesth 1995; 74: 638-642. 38. Snow RG, Nunn JF. Induction of anaesthesia in the footdown position for patients with a full stomach. Br J Anaesth 1959; 31: 493497. 39. Brimacombe J, Berry A. The laryngeal mask airway for obstetric anaesthesia and neonatal resuscitation. International Journal of Obstetric Anesthesia 1994; 3: 211-218. 40. Boys JE. Failed intubation in obstetric anaesthesia. A case report. Br J Anaesth 1983; 55: 187-188. 41. Scott DB. Awareness during Caesarean section. Anaesthesia 1991; 46: 693-694. 42. Green RA. Anaesthesia for Caesarian Section. Anaesthesia 1978; 33: 70.
Opposer: G. Cooper Birmingham Women’s Hospital, Edgbaston, Birmingham, UK
The absolute need for continued use of suxamethonium as the routine neuromuscular blocker to achieve intubation during general anaesthesia for caesarean section is best appreciated using the analogy of a car race! Today in the final of the Caesarean Section Grand Prix, we have only two cars, but they each represent the best in their class. Firstly, we have the sleek new model of Rocky (Rocuronium) that has only recently come on to the market but is already proving popular. Rocky had years of development invested in it, resulting in a car which is ultra smooth, has terrific control and can easily be set up to run on cruise control (infusion). The car does not harm the environment, having no nasty emissions and comes up to every known European Union standard of exhaust quality. Since its recent launch its superior qualities and particularly its cleanliness have been widely advertised. In contrast, the second contestant in the Caesarean Section Grand Prix is a veteran model, which being well over 50 years old attracts unsolicited junk mail from SAGA. This car, with the abbreviated name of
Griselda Cooper, Birmingham Women’s Hospital, Edgbaston, Birmingham B 15 2TG, UK.
Sux, unlike Rocky, is known to be rather a jerky starter (fasciculations). However, despite this rather inelegant departure, it accelerates well getting it off to a quick start (rapid onset of action). For longer journeys Sux requires intermittent refuelling and there have been problems designing a cruise control because of unpredictability of performance. Automobile Association membership is advised for drivers of this car because of the high likelihood of spontaneous breakdown. Special refrigerated garaging is required to keep the car in tip-top condition. Sux also sends out nasty emissions in the form of histamine and potassium. These can be serious enough to cause significant breathing difficulties (anaphylaxis) and stress the driver. Another temperamental feature of this car is unpredictable overheating (malignant hyperthermia). Unlike Rocky, this car is really dirty. Looking at the two cars on the starting line, we can admire the smooth profile of Rocky and speculate about the outcome of this prestigious race which is such an important event. It is usually such a safe race that many of the spectators are in family groups. Other relatives, betting on the outcome, are in constant telephonic communication (hospital switchboard jammed). But, what is going on with Rocky? Right at the beginning of the race, a mechanic has
Controversies come out and is undertaking last minute adjustments. I am informed by the company that this is a special procedure known as priming. Priming is necessary to get Rocky off to a fast enough start to be able to negotiate the first corner (to make it work fast enough to achieve intubation before hypoxia supervenes). Without priming Rocky would not be able to establish an early lead. For the first time as tension mounts in the spectators, doubts are creeping in as to whether this car lives up to its promises. The television cameras in the Steward’s helicopter enable a bird’s eye view of the track. Over in the distance the gaily-coloured banners of the Caesarean Section Grand Prix can be seen. Sponsorship as always, is by Airways Management without whom this race would never have existed. These benefactors also provide generous travelling grants for drivers with disabilities. The flag is down, the race is underway and our two contestants are coming up the long straight just to the left of our screen. From their position on the long straight at full throttle, they are expecting a clear run. There is no way they can see the disaster ahead ~ a press car touring the circuit has broken down on a blind corner. Will it move out of the way in time? Will there be a pile up? Will the race lose its enviable safety record? At this point consider another facet of these two contestants-their braking distances. The two cars are going at the same speed. The drivers today are both world class and there isn’t a hair between them in their thinking distances. The brakes are slammed on. Look how quickly Sux stops. In comparison Rocky cruises on agonisingly after putting the stops on. How will this translate into the potential disaster ahead? The press car has stalled and is stranded right in the middle of the track. Everyone can see the inevitable is going to happen. Rocky’s brakes are just not up to it and poor Rocky collides into the press car. Everyone’s life is in danger. Fortunately, Sux pulls up with seconds to spare away from the melee. What is happening at the crash scene? The emergency bells are going and all possible helpers are summoned from the grandstand. The second on-call mechanic (consultant) is watching the race from the comfort of his armchair at home and is on his way as quickly as he can. Unfortunately, he is 8 miles away and the roads around the area are packed with sightseers and daytrippers. The race circuit paramedics arrive, and all the emergency equipment is brought out of the back of the vehicle. Despite their best efforts it’s too late to save the life of the driver. Emergency measures are now required to evacuate the baby who was travelling in the back seat of Rocky. This is a really bad day for racing. A popular driver killed and a baby with brain damage.
27 1
At the Steward’s enquiry, the safety of Rocky was castigated. How could one race a car with such defective brakes? In response to the defence of Rocky’s design, the enquiry re-examined the problems associated with Sux to decide whether they were a real issue or not. At the public enquiry (morbidity and mortality meeting) the Steward represented these risks as a balance. On the negative side he established that the likelihood of overheating (Malignant Hyperpyrexia) is 1 in 100 000, but taking into account the fact that an effective treatment is available in the form of dantrolene, malignant hyperpyrexia should not be a reason for abandoning Sux. The Steward found it more difficult to establish with accuracy the incidence of anaphylaxis to Sux but agreed that estimates of 1 in 5000 are not likely to be exceeded. Furthermore, the rules of the British Driving Association insist that treatment protocols for anaphylaxis are in the driver’s pocket of every car (attached to every anaesthetic machine) and that the kit required to fix it is immediately available. This leaves suxamethonium apnoea as the remaining problem. The Steward agreed that this in itself is not likely to be life-threatening but could lead to the same problems that Rocky exhibits if combined with an unexpectedly difficult intubation. The likelihood however, of this happening is approximately 1 in a million. No cases exist in the literature to date (pregnant or not). The Steward found that unexpected problems with the track, both at this race meeting and others world wide had a remarkably constant incidence of one in 280. He discounted weak evidence that there were increases in (crash) barrier pressure and the occurrence of muscle pains after racing because these did not relate to the race in question, namely the Caesarean Section Grand Prix. Anyway, barrier pressure could be countered by making a stronger seal (cricoid pressure). Thus, the weight of evidence was firmly in favour of Sux since although it had problems, each had a solution. However, the Steward was far-sighted and wanted further evidence - he wanted to know whether these obstacles that appeared on the racing track could be foreseen. Could better management of the race track avoid such crashes? Looking back through the archives he found that on numerous occasions races had been cancelled, diverted to another track, or other vehicles used (regional block, awake intubation). Searching through the back copies of the British Journal of Autosport (apologies to the BJA) he found the information he needed. Oates’ (great nephew of the noble explorer) compared two ways of preparing the race track. The Mallampati method simply takes a careful look at the track before the race. In contrast, the Wilson index, takes five factors into account, even including the weight of the driver. Both
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methods show low sensitivity (proportion of difficult laryngoscopies that were predicted) only moderate specificity (proportion of straightforward laryngoscopies predicted to be easy) and have a low positive predictive value (proportion of patients predicted to be difficult who proved to be difficult). Using the Mallampati method only 4.4% of difficult intubations would be predicted which is only improved to 8.9% detection using the Wilson method. Like most things in life, risk can be quantified and minimised but never reduced to zero. The unexpected does happen and we should be ready for it. The outcome of the Steward’s Enquiry (Confidential Enquiry into Maternal Deaths) was not published until years after the crash, It concluded, despite the length of time taken in the development of Rocky and its extremely clean profile that it failed in basic design. Drivers and promoters ignored basic safety. Not one of the expert advisers consulted would use a car without good brakes. The current enviable safety record that had taken years to achieve should not be put in jeopardy. Therefore, the report concluded that there was no indication to depart from the safe practices of decades. REFERENCE
1. Oates J D L, Macleod A D, Oates P D, Pearsall F J, Howie J C, Murray G D. Comparison of two methods for predicting difficult intubation. British Journal of Anaesthesia 1991; 66:305-309.
go80 70 3
60
1
g B 50 5 40 ~_ 1 5 30 P 20
78.1
I
34.2
10 0 for
against
abstain
Voting in the motion: Non-depolarising neuromuscular blockers can be used routinely instead of suxamethonium at induction of general anaesthesia for caesarean section. Voting by Brlhler ICS UK Ltd.
CONTROVERSIES
Non-depolarising neuromuscular blockers can be used routinely instead of suxamethonium at induction of general anaesthesia for caesarean section Proposer: D. M. Levy University Hospital, Nottingham,
UK
anaesthetised with this technique in Hamer Hodges’ unit.* Although two patients regurgitated small amounts of fluid, which pooled in the pharynx, there were no cases of aspiration pneumonitis. However, in the Confidential Enquiries for 196466 (the period when the use of thiopentone and suxamethonium became widespread), technical difficulties with tracheal intubation were first mentioned, and the percentage of maternal deaths from anaesthesia more than doubled.3
I shall argue that l
l
l
Rapid sequence induction with suxamethonium has had its day Rocuronium is the best available alternative to suxamethonium In the event of difficult or failed tracheal intubation, profound non-depolarising block is preferable to unpredictable recovery from suxamethonium.
SUXAMETHONIUM NEUROMUSCULAR BLOCK IN OBSTETRIC ANAESTHESIA, 1959
- PROBLEMS
AT ONSET
If suxamethonium were presented today as a new drug for approval by the official regulatory bodies, I doubt it would get very far. Based on the incidence of adverse reactions at the time of a survey of UK anaesthetic drug usage in the mid-1980s, Watkins calculated that a serious reaction to suxamethonium might be expected once in every 4000 inductions.4 A French multi-centre enquiry in the early 1990s found that suxamethonium accounted for 5% of the usage of neuromuscular blockers, but 30% of the anaphylactic reactions.5 Suxamethonium was responsible for a maternal death in the 1991-93 triennium,6 and I am aware of a more recent near-fatal proven reaction to suxamethonium at caesarean section in a north Nottinghamshire hospital. ‘Excellent’ intubating conditions mean that the jaw is relaxed with no resistance to the laryngoscope blade, the cords are abducted and motionless, and there is no coughing or limb movement in response to intubation. From two recently published studies,7,8 I have calculated that intubating conditions at 60 s were less than ‘excellent’ in almost one-quarter of nonobstetric patients receiving suxamethonium 1 mglkg at rapid sequence induction. This is not particularly impressive for a drug revered as a gold standard.
The widespread use of neuromuscular blockade in obstetric anaesthesia dates from the publication 40 years ago this year of a landmark paper by Hamer Hodges and colleagues in Portsmouth.’ A thiopentone, suxamethonium, nitrous oxide/oxygen technique was compared with three anaesthetic regimens in which mothers received trichloroethylene, cyclopropane or diethyl ether. Suxamethonium was the ‘relaxant of choice’ because of concerns that the only two alternatives, gallamine and tubocurarine, crossed the placenta. All patients were given pre-operative atropine, but no antacid. Anaesthesia was induced with steep head-up tilt, but without cricoid pressure (not yet described). Those mothers who had minimal anaesthesia facilitated by neuromuscular blockade had a greater percentage of babies in whom regular breathing and active crying were established within 60 s. There was no anaesthetic-related mortality in 2000 obstetric patients
Dr David M. Levy MB ChB FRCA, Consultant Anaesthetist, University Hospital NHS Trust, Queen’s Medical Centre, Nottingham NG7 2UH, UK. 266
Controversies Almost half of patients receiving thiopentone and suxamethonium have increased masseter tone exceeding 50% of baseline.9 This might go some way to explain why suxamethonium does not always work perfectly. In one of 23 cases of failed intubation at caesarean section over 17 years in a Leeds teaching hospital,‘” profoundly increased masseter tone rendered mouth opening impossible. Masseter rigidity with subsequent signs of hypermetabolism points to the ominous diagnosis of malignant hyperthermia, another potentially lethal complication of suxamethonium. The risk of bradyarrhythmias particularly after a second dose of suxamethonium has been recognized for many years, and necessitates use of an anticholinergic agent.” A variety of myopathies contraindicate the use of suxamethonium because of the risk of hyperkalaemia.” Suxamethonium is the only neuromuscular blocker with the potential for precipitating a myotonic crisis. We recently had a patient whose diagnosis of myotonic dystrophy was established only after the condition had been identified antenatally in the fetus. Intragastric pressure increases have been shown to correlate with the intensity of fasciculations.” It is not known whether pregnant women with reflux necessarily have the same simultaneous protective increases in lower oesophageal sphincter tone that have been demonstrated in non-pregnant subjects given suxamethonium.14
SUXAMETHONIUM
- PROBLEMS
AT OFFSET
I argue that the use of a non-depolarising drug with a duration of action of the order of half an hour is quite safe and, indeed, desirable. Prolonged suxamethonium block is a problem only if the drug is given in the expectation that the return of spontaneous respiration will resolve a failed ventilation scenario. Benumof, a guru of difficult airway management, has stressed that suxamethonium cannot be relied upon to enable a patient to breathe spontaneously before critical desaturation occurs.‘5 Metabolism of suxamethonium is dependent upon plasma cholinesterase, and one in 25 of the population is other than homozygous for the normal gene. A heterozygote whose plasma cholinesterase activity is further reduced by pregnancy may well have clinically significant prolongation of block.16 Furthermore, recovery from suxamethonium occurs at different rates in different muscles. At the laryngeal adductors recovery occurs twice as fast as in adductor pollicis.17 Two cases of critical desaturation after failed intubation in obstetrics have been graphically described. Both women had suxamethonium. In one case repeat laryngoscopy revealed a small aperture in the larynx, opening and closing, through which it was impossible to insert an 8,7
267
or 6 mm cuffed endotracheal tube’. It is noteworthy that spontaneous respiration returned at 7 min in this case and 23 min in the other.18 To make matters worse regurgitation and vomiting are very real threats to the lightly anaesthetised patient in whom neuromuscular block is wearing off. Huge increases in intragastric pressure have been measured.19 The partially anaesthetised, partially paralysed patient who is bucking and straining will consume colossal amounts of oxygen. Laryngospasm, airway oedema and reduced chest wall compliance will conspire against effective ventilation. I suggest that suxamethonium can transform a difficult intubation into a failed intubation, and turn ‘can’t intubate can ventilate’ into ‘can’t intubate can’t ventilate’. Lastly, myalgia might never have killed anyone, but 7.5% of caesarean section patients have aches and pains in the back or neck after a 100 mg bolus dose of suxamethonium.20 As Thorburn and Reid commented, ‘it is interesting that, in the present aggressive attack on the control of postoperative pain, we should continue to use a drug known to cause considerable morbidity.?’
ALTERNATIVES VECURONIUM
TO SUXAMETHONIUM
.. .
Vecuronium is an aminosteroidal non-depolarising neuromuscular blocker devoid of the catalogue of potential complications peculiar to suxamethonium. It has been shown that 0.1 mg/kg actual body weight has a more rapid onset in pregnant women at term. This might be attributed to the increased cardiac output or to the fact that skeletal muscles receive a relative overdose in pregnancy, because the drug doesn’t distribute to the extra water, fat, or the fetus.22 However, a standard intubating dose does not allow sufficiently rapid attainment of the requisite block for intubation without a period of mask ventilation to maintain oxygen saturation. There is not time at emergency caesarean section to wait 34 min for a small priming dose to accelerate the onset of the principal dose. A single large bolus dose will speed onset, but only at the cost of unacceptably increased duration of block.23 One study has demonstrated the feasibility of vecuronium for emergency caesarean section. Teviotdale studied 30 patients, all of whom had antacid prophylaxis with sodium citrate. Vecuronium 0.5 mg was given in advance of a fixed principal dose of 8 mg, which was followed at least 20 s later by thiopentone 250 mg. With cricoid pressure applied, the lungs were maskventilated with isoflurane in oxygen for 2 min before intubation, without any discernible regurgitation or aspiration.‘4
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ALTERNATIVES ROCURONIUM
Journal of Obstetric Anesthesia TO SUXAMETHONIUM
.. .
Rocuronium is similar to vecuronium but less potent. Thus a greater mass of drug is required for the same effect, resulting in a significantly faster onset time. Rocuronium does not release histamine,25 and anaphylaxis appears to be exceedingly rare. Abouleish and colleagues demonstrated that rocuronium is a genuine alternative to suxamethonium for rapid sequence induction of anaesthesia for caesarean section. After pre-oxygenation, 4 or 6 mg/kg of thiopentone was followed by a bolus of rocuronium 0.6 mg/kg. Intubating conditions were ‘excellent’ or ‘good’ when two twitches of a train of four at adductor pollicis had disappeared, at a mean time of 84 s. The duration of block was ideal for caesarean section, and there were no untoward neonatal effects.26 Interestingly, in a study with ketamine 1.5 mg/kg, intubating conditions were ‘excellent’ or ‘good’ in every patient when the block at adductor pollicis, measured by electromyography, was only 50%. This was at a mean of only 42 s.~’ Enhancement of cardiac output or depression of laryngeal reflexes by ketamine might explain this remarkable halving of the time to successful intubation. Although contraindicated in hypertensive disorders of pregnancy, ketaminerocuronium would seem to be an ideal combination in the hypovolaemic obstetric patient.
ALTERNATIVES TO SUXAMETHONIUM ORG 9487 (RAPACURONIUM)
...
Org 9487 is the newest aminosteroidal non-depolarising neuromuscular blocker. Even less potent than rocuronium, its onset time is, predictably, further shortened. At 1 min intubating conditions were deemed poor in one of 18 patients given Org 9487 compared with two of 20 who had suxamethonium (NS).28 After 40 years, surely the fate of suxamethonium will now be sealed?
CONSEQUENCES BLOCK
OF NON-DEPOLARISING
The fact that non-depolarising neuromuscular block commits the anaesthetist to maintaining oxygenation by positive pressure ventilation is not necessarily a disadvantage. When the original failed intubation drill was conceived in the early 1970s general anaesthesia for caesarean section was predominant. In the failed intubation drill, the place of regional anaesthesia was
as an alternative to letting the patient wake up, emptying the stomach, and undertaking inhalational anaesthesia with spontaneous ventilation.29 In 1999, there is minimal use of general anaesthesia, even for emergency caesarean section. 30*3’ General anaesthesia is most often used because a regional technique is contraindicated or has failed. If a regional technique is out of the question and the history or evaluation of the airway is suggestive of difficult tracheal intubation, awake direct laryngoscopy or fibre-optic intubation are then considered. Non-depolarising neuromuscular block rules out the option of maintaining inhalational anaesthesia with spontaneous respiration after failed intubation. However, as Harmer has argued, ‘conversion of this crisis state into a smooth, safe mask anaesthetic, of sufficient depth to allow surgery, calls for a high degree of skill and experience’32 - which is undoubtedly rare today. I do not believe that suxamethonium makes airway management any safer. Trust placed in rapid recovery from suxamethonium is trust misplaced.
THE UNANTICIPATED
DIFFICULT
AIRWAY
Profound non-depolarising neuromuscular block may be safer than block with suxamethonium because sustained optimal conditions maximize the chances of intubation or alternative successful tracheal approaches to airway management. A McCoy laryngoscope can convert a Cormack and Lehane grade 3 view to a grade 2. 33A gum-elastic bougie has been recommended for every grade 3 laryngoscopy.1° This advice might now include grade 2b as defined by Yentis and Lee.34 The guaranteed absence of movement at the larynx can only make things easier. It has been suggested that teaching anaesthetists to implement a failed intubation drill without delay in the event of difficulty might contribute to the increased incidence of failed intubation in obstetrics.35 The use of non-depolarising neuromuscular blockers means it is no longer essential to intubate swiftly or give up early. Instead, a calm, sequential approach to airway management can be adopted. As Sellick stated in his original paper, cricoid pressure should prevent gastric distension during positive pressure ventilation of the lungs.36 It has been emphasized that cricoid pressure not speed - is the main safety factor of rapid sequence induction.” Looking back at Hamer Hodges’ series2 and the absence of aspiration in over 600 at-risk patients reported by Snow and Nunn,‘* I wonder whether the head-up position should be revisited. If the oesophagus runs uphill from the stomach, it should be extremely difficult for gastric contents to get
Controversies anywhere near the pharynx of a fully paralysed patient unable to vomit. In the absence of iatrogenic glottic trauma and presence of profound neuromuscular blockade ‘can’t intubate, can’t ventilate’ must be vanishingly rare. Obstructed ventilation can result from difficulty in displacing the tongue, epiglottis, or larynx from the posterior pharyngeal wall. Brimacombe and Berry have stated that ‘the laryngeal mask airway would appear to be the airway of choice in the obstetric patient who can be neither intubated nor mask-ventilated.‘j’ I am sure that everyone who uses the laryngeal mask routinely in non-obstetric practice would agree that the chances of successful placement are greatly heightened when pharyngeal and laryngeal reflexes are obtunded. Similarly, deliberate oesophageal intubation with a tracheal tube40 or the more sophisticated Combitube will be more likely to meet with success if the pharyngeal and laryngeal musculature is profoundly relaxed. Laryngeal obstruction is surely less likely to challenge any of us in the course of a career than anaphylaxis to suxamethonium. The best chance of successful cricothyrotomy will be in a fully paralysed patient. The procedure will be doomed to failure in a venocongested moving target. CONCLUSION If tubocurarine, gallamine, suxamethonium and rocuronium had all been available in 1959, which would have been the relaxant of choice for caesarean section? Rapid recovery from suxamethonium was never originally perceived as an advantage. I question the continued allegiance to suxamethonium, founded on ndive faith in its unpredictable offset. Bruce Scott, who died last November, wrote this of the introduction of neuromuscular block to obstetric practice. ‘If we had been honest, the attraction of the new method was the speed and ease with which we could present the intubated paralyzed patient to the obstetrician. We did not advertise the increased incidence of death due to Mendelson’s syndrome and failed intubation resulting from suxamethonium and crash induction.‘4’ Over 20 years ago, Green investigated two cases of Mendelson’s syndrome and was moved to abandon suxamethonium in favour of alcuronium or tubocurarine, with mask ventilation and the patient 30” head-up. 42 In 1999, we have rocuronium, a clean, safe drug with an onset time to rival that of suxamethonium. Waiting in the wings is Org 9487. We have at our disposal revolutionary devices to help manage the difficult airway. Suxamethonium has reigned unchallenged for 40 years. The time has come for a coup.
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REFERENCES 1. Hamer Hodges RJ, Bennett JR, Tunstall ME, Knight RF. General anaesthesia for operative obstetrics. Br J Anaesth 1959; 31: 152-163. ME. The choice of anaesthesia 2. Hamer Hodges RJ, Tunstall and its influence on perinatal mortality in caesarean section. Br J Anaesth 1961; 33: 572-588. 3. Morgan M. Anaesthetic contribution to maternal mortality. Br J Anaesth 1987; 59: 8422855. 4. Watkins J. Anaesthetic reactions. In Watkins J, Levy CJ, eds. Guide to immediate anaesthetic reactions. London: Butterworths, 1988: p 27. 5. Bevan DR. Editorial. Neuromuscular relaxants ~ 1997. Can J Anaesth 1997;44: 113551137. 6. Department of Health et al. Report on confidential enquiries into maternal deaths in the United Kingdom 1991-1993. London: HMSO, 1996: p 95. KC, Salmela L, Mirakhur RK et al. Comparison of 7. McCourt rocuronium and suxamethonium for use during rapid sequence induction of anaesthesia. Anaesthesia 1998; 53: 8677871. 8. Andrews JI, Kumar N, van den Brom RHG, Olkkola KT, Roest GJ, Wright PMC. A large simple randomized trial of rocuronium versus succinylcholine in rapid-sequence induction of anaesthesia along with propofol. Acta Anaesthesiol Stand 1999; 43: 4-8. 9. Ummenhofer WC, Kindler C, Tschak? G, Hampl KF, Drewe J. Urwyler A. Propofol reduces succinylcholine induced increase of masseter muscle tone. Can J Anaesth 1998; 45: 417423. 10. Hawthorne L, Wilson R. Lyons G, Dresner M. Failed intubation revisited: 17-yr experience in a teaching maternity unit. Br J Anaesth 1996: 76: 680-684. 11. Lupprian KG, Churchill-Davidson HC. Effect of suxamethonium on cardiac rhythm. Br Med J 1960; 2: 1774-1777. 12. Crochetiere C. Myopathies. In Gambling DR, Douglas JM, Eds. Obstetric Anaesthesia and Uncommon Disorders. Philadelphia: Saunders, 1998: pp 171-182. 13. Miller RD, Way WL. Inhibition of succinylchohne-induced increased intragastric pressure by nondepolarizing muscle relaxants and lidocaine. Anesthesiology 1971; 34: 1855188. 14. Cotton BR, Smith G. The lower oesophageal sphincter and anaesthesia. Br J Anaesth 1984; 56: 3746. 15. Benumof JL, Dagg R, Benumof R. Critical hemoglobin desaturation will occur before return to an unparalyzed state following 1 mg/kg intravenous succinylchoiine. Anesthesiology 1997; 87: 979-982. 16. Davis L, Britten JJ, Morgan M. Cholinesterase. Its significance in anaesthetic practice. Anaesthesia 1997; 52: 244260. 17. Wright PMC. Caldwell JE, Miller RD. Onset and duration of rocuronium and succinylcholine at the adductor pollicis and laryngeal adductor muscles in anesthetized humans. Anesthesiology 1994; 81: 1110~1115. 18. French GWG, McBrien ME, Sellers WFS. Failed intubation in obstetrics a time for review. Today’s Anaesthetist 1994; 9: 60-64. 19. Spence AA, Moir DD, Finlay WEI. Observations on intragastric pressure. Anaesthesia 1967; 22: 2499256. 20. Thind GS, Bryson THL. Single dose suxamethonium and muscle pain in pregnancy. Br J Anaesth 1983; 55: 743-745. 21. Thorburn J, Reid JA. Editorial. Suxamethonium (succinylcholine) in obstetric anaesthesia. International Journal of Obstetric Anesthesia 1992; 1: 1855186. 22. Baraka A, Jabbour S, Tabboush 2, Sibai A, Bijjani A, Karam K. Onset of vecuronium neuromuscular block is more rapid in patients undergoing Caesarean section. Can J Anaesth 1992; 39: 1355138. 23. Hawkins JL, Johnson D, Kubicek MA, Skjonsby BS, Morrow DH, Joyce TH. Vecuronium for rapid-sequence intubation for cesarean section. Anesth Analg 1990; 71: 1855190.
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24. Teviotdale BM. Vecuronium-thiopentone induction for emergency caesarean section under general anaesthesia. Anaesth Intens Care 1993; 21: 288-291. 25. Levy JH, Davis GK, Duggan J, Szlam F. Determination of the hemodynamics and histamine release of rocuronium (Org 9426) when administered in increased doses under N,O/O,-sufentanil anesthesia. Anesth Analg 1994; 78: 318-321. 26. Abouleish E, Abboud T, Lechevalier T, Zhu J, Chalian A, Alford K. Rocuronium (Org 9426) for Caesarean section. Br J Anaesth 1994; 73: 336-341. 27. Baraka AS, Sayyid SS, Assaf BA. Thiopental-rocuronium versus ketamine-rocuronium for rapid-sequence intubation in parturients undergoing Cesarean section. Anesth Analg 1997; 84: 1104-l 107. 28. Abboud TK, Bikhazi G, Mroz Let al. Org 9487 vs. succinylcholine in rapid sequence induction for cesarean section patients: maternal and neonatal effects. Anesthesiology 1997; 87: A906. 29. Tunstall ME, Sheikh A. Failed intubation protocol: Oxygenation without aspiration. Clin Anaesth 1986; 4: 171-187. 30. Brown GW, Russell IF. A survey of anaesthesia for caesarean section. International Journal of Obstetric Anesthesia 1995; 4: 214-218. 31. Tsen LC, Pitner R, Camann WR. General anesthesia for cesarean section at a tertiary care hospital 1990-1995: indications and implications. International Journal of Obstetric Anesthesia 1998; 7: 1477152.
32. Harmer M. Only maternal, not fetal, survival should persuade the anaesthetist to proceed with general anaesthesia for caesarean section after failed intubation. International Journal of Obstetric Anesthesia 1993; 2: lO&lOl. 33. Chisholm DG, Calder I. Experience with the McCoy laryngoscope in difficult laryngoscopy. Anaesthesia 1997; 52: 906-908. 34. Yentis SM, Lee DJH. Evaluation of an improved scoring system for the grading of direct laryngoscopy. Anaesthesia 1998; 53: 1041l1044. 35. Lyons G, Macdonald R. Difficult intubation in obstetrics. Anaesthesia 1985; 40: 1016. 36. Sellick BA. Cricoid pressure to control regurgitation of stomach contents during induction of anaesthesia. Lancet 1961; 2: 404406. 37. Pilkington S, Carli F, Dakin MJ et al. Increase in Mallampati score during pregnancy. Br J Anaesth 1995; 74: 638-642. 38. Snow RG, Nunn JF. Induction of anaesthesia in the footdown position for patients with a full stomach. Br J Anaesth 1959; 31: 493497. 39. Brimacombe J, Berry A. The laryngeal mask airway for obstetric anaesthesia and neonatal resuscitation. International Journal of Obstetric Anesthesia 1994; 3: 211-218. 40. Boys JE. Failed intubation in obstetric anaesthesia. A case report. Br J Anaesth 1983; 55: 187-188. 41. Scott DB. Awareness during Caesarean section. Anaesthesia 1991; 46: 693-694. 42. Green RA. Anaesthesia for Caesarian Section. Anaesthesia 1978; 33: 70.
Opposer: G. Cooper Birmingham Women’s Hospital, Edgbaston, Birmingham, UK
The absolute need for continued use of suxamethonium as the routine neuromuscular blocker to achieve intubation during general anaesthesia for caesarean section is best appreciated using the analogy of a car race! Today in the final of the Caesarean Section Grand Prix, we have only two cars, but they each represent the best in their class. Firstly, we have the sleek new model of Rocky (Rocuronium) that has only recently come on to the market but is already proving popular. Rocky had years of development invested in it, resulting in a car which is ultra smooth, has terrific control and can easily be set up to run on cruise control (infusion). The car does not harm the environment, having no nasty emissions and comes up to every known European Union standard of exhaust quality. Since its recent launch its superior qualities and particularly its cleanliness have been widely advertised. In contrast, the second contestant in the Caesarean Section Grand Prix is a veteran model, which being well over 50 years old attracts unsolicited junk mail from SAGA. This car, with the abbreviated name of
Griselda Cooper, Birmingham Women’s Hospital, Edgbaston, Birmingham B 15 2TG, UK.
Sux, unlike Rocky, is known to be rather a jerky starter (fasciculations). However, despite this rather inelegant departure, it accelerates well getting it off to a quick start (rapid onset of action). For longer journeys Sux requires intermittent refuelling and there have been problems designing a cruise control because of unpredictability of performance. Automobile Association membership is advised for drivers of this car because of the high likelihood of spontaneous breakdown. Special refrigerated garaging is required to keep the car in tip-top condition. Sux also sends out nasty emissions in the form of histamine and potassium. These can be serious enough to cause significant breathing difficulties (anaphylaxis) and stress the driver. Another temperamental feature of this car is unpredictable overheating (malignant hyperthermia). Unlike Rocky, this car is really dirty. Looking at the two cars on the starting line, we can admire the smooth profile of Rocky and speculate about the outcome of this prestigious race which is such an important event. It is usually such a safe race that many of the spectators are in family groups. Other relatives, betting on the outcome, are in constant telephonic communication (hospital switchboard jammed). But, what is going on with Rocky? Right at the beginning of the race, a mechanic has
Controversies come out and is undertaking last minute adjustments. I am informed by the company that this is a special procedure known as priming. Priming is necessary to get Rocky off to a fast enough start to be able to negotiate the first corner (to make it work fast enough to achieve intubation before hypoxia supervenes). Without priming Rocky would not be able to establish an early lead. For the first time as tension mounts in the spectators, doubts are creeping in as to whether this car lives up to its promises. The television cameras in the Steward’s helicopter enable a bird’s eye view of the track. Over in the distance the gaily-coloured banners of the Caesarean Section Grand Prix can be seen. Sponsorship as always, is by Airways Management without whom this race would never have existed. These benefactors also provide generous travelling grants for drivers with disabilities. The flag is down, the race is underway and our two contestants are coming up the long straight just to the left of our screen. From their position on the long straight at full throttle, they are expecting a clear run. There is no way they can see the disaster ahead ~ a press car touring the circuit has broken down on a blind corner. Will it move out of the way in time? Will there be a pile up? Will the race lose its enviable safety record? At this point consider another facet of these two contestants-their braking distances. The two cars are going at the same speed. The drivers today are both world class and there isn’t a hair between them in their thinking distances. The brakes are slammed on. Look how quickly Sux stops. In comparison Rocky cruises on agonisingly after putting the stops on. How will this translate into the potential disaster ahead? The press car has stalled and is stranded right in the middle of the track. Everyone can see the inevitable is going to happen. Rocky’s brakes are just not up to it and poor Rocky collides into the press car. Everyone’s life is in danger. Fortunately, Sux pulls up with seconds to spare away from the melee. What is happening at the crash scene? The emergency bells are going and all possible helpers are summoned from the grandstand. The second on-call mechanic (consultant) is watching the race from the comfort of his armchair at home and is on his way as quickly as he can. Unfortunately, he is 8 miles away and the roads around the area are packed with sightseers and daytrippers. The race circuit paramedics arrive, and all the emergency equipment is brought out of the back of the vehicle. Despite their best efforts it’s too late to save the life of the driver. Emergency measures are now required to evacuate the baby who was travelling in the back seat of Rocky. This is a really bad day for racing. A popular driver killed and a baby with brain damage.
27 1
At the Steward’s enquiry, the safety of Rocky was castigated. How could one race a car with such defective brakes? In response to the defence of Rocky’s design, the enquiry re-examined the problems associated with Sux to decide whether they were a real issue or not. At the public enquiry (morbidity and mortality meeting) the Steward represented these risks as a balance. On the negative side he established that the likelihood of overheating (Malignant Hyperpyrexia) is 1 in 100 000, but taking into account the fact that an effective treatment is available in the form of dantrolene, malignant hyperpyrexia should not be a reason for abandoning Sux. The Steward found it more difficult to establish with accuracy the incidence of anaphylaxis to Sux but agreed that estimates of 1 in 5000 are not likely to be exceeded. Furthermore, the rules of the British Driving Association insist that treatment protocols for anaphylaxis are in the driver’s pocket of every car (attached to every anaesthetic machine) and that the kit required to fix it is immediately available. This leaves suxamethonium apnoea as the remaining problem. The Steward agreed that this in itself is not likely to be life-threatening but could lead to the same problems that Rocky exhibits if combined with an unexpectedly difficult intubation. The likelihood however, of this happening is approximately 1 in a million. No cases exist in the literature to date (pregnant or not). The Steward found that unexpected problems with the track, both at this race meeting and others world wide had a remarkably constant incidence of one in 280. He discounted weak evidence that there were increases in (crash) barrier pressure and the occurrence of muscle pains after racing because these did not relate to the race in question, namely the Caesarean Section Grand Prix. Anyway, barrier pressure could be countered by making a stronger seal (cricoid pressure). Thus, the weight of evidence was firmly in favour of Sux since although it had problems, each had a solution. However, the Steward was far-sighted and wanted further evidence - he wanted to know whether these obstacles that appeared on the racing track could be foreseen. Could better management of the race track avoid such crashes? Looking back through the archives he found that on numerous occasions races had been cancelled, diverted to another track, or other vehicles used (regional block, awake intubation). Searching through the back copies of the British Journal of Autosport (apologies to the BJA) he found the information he needed. Oates’ (great nephew of the noble explorer) compared two ways of preparing the race track. The Mallampati method simply takes a careful look at the track before the race. In contrast, the Wilson index, takes five factors into account, even including the weight of the driver. Both
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methods show low sensitivity (proportion of difficult laryngoscopies that were predicted) only moderate specificity (proportion of straightforward laryngoscopies predicted to be easy) and have a low positive predictive value (proportion of patients predicted to be difficult who proved to be difficult). Using the Mallampati method only 4.4% of difficult intubations would be predicted which is only improved to 8.9% detection using the Wilson method. Like most things in life, risk can be quantified and minimised but never reduced to zero. The unexpected does happen and we should be ready for it. The outcome of the Steward’s Enquiry (Confidential Enquiry into Maternal Deaths) was not published until years after the crash, It concluded, despite the length of time taken in the development of Rocky and its extremely clean profile that it failed in basic design. Drivers and promoters ignored basic safety. Not one of the expert advisers consulted would use a car without good brakes. The current enviable safety record that had taken years to achieve should not be put in jeopardy. Therefore, the report concluded that there was no indication to depart from the safe practices of decades. REFERENCE
1. Oates J D L, Macleod A D, Oates P D, Pearsall F J, Howie J C, Murray G D. Comparison of two methods for predicting difficult intubation. British Journal of Anaesthesia 1991; 66:305-309.
go80 70 3
60
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g B 50 5 40 ~_ 1 5 30 P 20
78.1
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34.2
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against
abstain
Voting in the motion: Non-depolarising neuromuscular blockers can be used routinely instead of suxamethonium at induction of general anaesthesia for caesarean section. Voting by Brlhler ICS UK Ltd.