Fig. 1.1
The Shadwell laryngoscope
He noted that the epiglottis in the neonate was proportionally longer than in the adult and that with each breath, the larynx tended to move anteriorly and out of the field of vision; deepening the anesthetic to further relax the child tended to induce signs of impending cardiorespiratory failure. He stressed the need for gentleness and warned that any use of force might cause complications varying from a croupy cough to acute edema of the larynx. In his own reported series of 70 infants under the age of 2 years, he had remarkably few complications, especially in view of his statement that the largest possible tube should be passed. He was concerned not to narrow the airway, as all his patients were breathing spontaneously. However, he did stress the need to attempt to pass the tube “gently.”
The use of endotracheal intubation in infants was not without problems however, and cases of postoperative laryngeal edema and, more rarely, subglottic stenosis were reported. The need to use a tube, which passed easily through the glottis and subglottic space and allowed a slight leak on pressurization of the anesthesia circuit, was, in time, recognized by anesthesiologists. A classic paper by Eckenhoff [22] in 1951 described the anatomy and dimensions of the infant larynx and stressed the need to avoid injury to the mucosa in the region of the cricoid ring. The problems that sometimes followed intubation and the fear that these might adversely affect outcomes led many surgeons, particularly in USA, to oppose this practice in their patients. Anesthesia providers were directed to manage neonates for complex repairs, e.g., tracheoesophageal fistula or coarctation of the aorta, using mask anesthesia. However, the pioneers of pediatric anesthesia persisted, perfected safer methods, and thus facilitated acceptance of the need for endotracheal intubation, essential if progress in neonatal surgery was to continue.
Red rubber tubes were largely abandoned in favor of plastic tubes in the 1950s. However, early plastic tubes were also not without problems. Irritant chemical substances (Organo-tins) within the plastic material were found to be capable of stimulating local tissue reactions that could lead to fibrosis [23]. The establishment of routines for implantation testing of plastic material led to improvements in endotracheal tube composition and manufacture and a subsequent decrease in complications.
In 1945 Cole described a new endotracheal tube for infants. This tube had a wider proximal portion and a narrower distal segment to pass through the glottis, the rationale being that the wider portion would decrease the resistance to airflow. In addition, it was claimed that the shoulder of the tube would decrease the likelihood of the tube passing too far and entering a bronchus. In fact, the resistance of the Cole tube was found to be greater than that of a similar internal diameter parallel-sided tube [24]. This was attributed to turbulent flow within the Cole tube. More seriously, the shoulder on the tube was shown to cause laryngeal damage if advanced into the glottis [25]. The Cole tube was generally abandoned for use during anesthesia but remained in use for neonatal resuscitation in some centers, the claim being that it was easier for the less expert practitioner to insert.
The concept of prolonged endotracheal intubation as an alternative to tracheostomy was presented by Bernard Brandstater at the First European Congress of Anesthesiology in 1962 [26]. He reported his experience with seven patients ranging in age from the neonate to 4 years. Until that time it had been customary to perform a tracheostomy if infants required ventilator assistance [27]. The tracheostomy tubes in general use were uncuffed and the variable leak that occurred via the glottis made a constant level of ventilation difficult to attain—especially in patients with reduced pulmonary compliance. Fortunately the ventilators in common use in North America at this time were pressure cycled (the “Bird” mark VIII) and this reduced the problem to some extent. In the middle 1960s, the use of intermittent positive pressure ventilation (IPPV) in the therapy of newborn respiratory distress syndrome was becoming established as was the need to treat respiratory insufficiency in the postoperative cardiac patient [28]. In 1965 Reid and Tunstall reported a case of respiratory distress syndrome in a 1,800 g preterm infant successfully treated by IPPV via a 2.5 mm ID nasotracheal tube [29]. In the same year, McDonald and Stocks from the Royal Children’s Hospital in Melbourne Australia reported a larger series of infants treated with prolonged nasotracheal intubation [30]. They described the complications, including post-intubation subglottic stenosis, and offered suggestions to minimize the incidence of this serious outcome. By the end of the 1960s, prolonged endotracheal intubation had superseded tracheostomy as the management of choice for infants requiring ventilatory assistance.
During the 1960s and 1970s, it was a very common, almost standard, practice to intubate the trachea while the infant was awake, before induction of anesthesia. This minimized the danger of regurgitation and aspiration and facilitated the rapid induction of anesthesia [31]. In addition, if tracheal intubation failed, there was little danger as the infant would usually maintain the airway and ventilation. Awake intubation of the neonate continued to be widely practiced until toward the end of the twentieth century when concerns that the physiological stress that might be imposed on the infant prompted further consideration [32]. In addition, it was demonstrated that intubation is much more likely to be successful with fewer attempts at and less time for successful intubation if performed in the anesthetized infant [33].
Having intubated the airway in the neonate, the scene was set to control ventilation during anesthesia. This would facilitate procedures to correct intrathoracic congenital defects. In addition, it would allow the administration of neuromuscular blocking drugs to provide optimal conditions for abdominal surgery and reduce the need for high concentrations of inhaled anesthetics.
Neuromuscular Blocking Drugs
d-Tubocurarine was introduced into anesthesia practice in the 1940s and succinylcholine became available in the 1950s. Both drugs were used in neonates soon after their introduction, but initially there was a lack of universal enthusiasm for using relaxant drugs in the neonate. In Europe a pioneering neonatal anesthetist, Dr. Jackson Rees, wrote in 1950 “In the newborn, as has already been shown, control of the respiration is easily obtained at light levels of anaesthesia without the use of relaxants: muscle relaxation does not appear to be of major importance in the production of good operating conditions, and the usual untoward effects of endotracheal-tube induction are not seen.(sic) On these grounds it can be said that the use of relaxant drugs in anaesthesia is contraindicated in the newborn patient, and I have abandoned these drugs in such cases [34].”
In the USA, the study of Beecher and Todd published in 1954 [35] demonstrated an increased mortality associated with the use of relaxant drugs—especially in those in the early years of life. Postoperative respiratory difficulties were reported in infants given relaxants [36]. In 1955, Stead reported that the neonate was sensitive to the effects of non-depolarizing neuromuscular blocking drugs but was resistant to the effect of the depolarizing drug succinylcholine [37]. This further supported the impression that residual curarization was a problem in infants. However Rackow and Salanitre in New York reported their experience with relaxant drugs [38] and suggested that postoperative respiratory depression was seen only as a result of drug overdose or with hypothermia; the latter was not uncommon at that time in the smaller infants. Warming from hypothermia had been demonstrated to potentiate any residual block [39]—hence the infant placed in a heated isolette to rewarm after surgery was at risk! This observation encouraged efforts to maintain normothermia during neonatal surgery (see below).
In the 1960s, the use of neuromuscular blocking drugs in the neonate was widely accepted, and the use of heating blankets and overhead warmers to maintain normothermia became routine. Rees wrote “Following intubation the child may be saturated with nitrous oxide as rapidly as possible by intermittent positive pressure ventilation, and the relaxant drug may then be administered. In this way perfect operating conditions are obtainable, and the more potent and, therefore more toxic agents are eliminated from the anesthetic technique” [31]. This was the “Liverpool technique,” which was widely used in Britain and elsewhere. For brief procedures, it was not uncommon to use repeated injections of succinylcholine as a relaxant.
The question of the sensitivity of the neonate to d-tubocurarine (dTc) was finally resolved by Fisher in 1982 [40]. The neonatal neuromuscular junction is indeed sensitive to the effects of dTc, but this is largely compensated by the increased volume of distribution of the drug in this age group [40].
Anesthesia Circuits and Controlled Ventilation
The T-piece system was considered by many to be the anesthesia circuit of choice for the neonate. It is lightweight and simple and has low dead space and resistance, and ventilation could be controlled simply by intermittently occluding the expiratory limb with the finger. Jackson Rees in Liverpool improved on this system by adding an open-ended bag to the end of the expiratory limb [34]. A vulcanite tap was inserted into the open end of the bag and adjusted to maintain the bag inflated but to allow escape of expired and excess gases. Manual controlled ventilation was readily applied with this system. However, a fresh gas flow of 2–2.5 times the minute ventilation was required to prevent rebreathing of expired gases. This was wasteful of anesthetic gases, which were cheap in those days, and potentially caused significant atmospheric pollution (not appreciated to be a problem until the 1970s). A modification to prevent rebreathing with lower fresh gas flows was to use a small-sized Waters soda lime canister on the expiratory limb for CO2 absorption, but this was generally considered less easy to apply to the small infant. Indeed, Leigh and Belton writing in 1950 stated “Use of absorption technic in the first few months of life is impracticable and affords no distinct benefits to patient, surgeon and anesthesiologist” [41].
The pattern of ventilation chosen by the Liverpool group for infants is interesting. Dr. Jackson Rees always encouraged the use of rapid shallow ventilation for the neonate. He admitted that this often led to hyperventilation and hypocapnia but did not consider this to be a significant problem [34]. In later years, he would add small concentrations of carbon dioxide to the inspired gases when indicated to prevent hypocapnia (Rees GJ, Personal communication). The pattern of ventilation used, however, did tend to limit the duration of expiration and maintain a constant positive pressure—both of which acted to reverse the reduction in lung volumes that occurs during anesthesia and muscle paralysis and thus improve gas exchange. Dr. Rees was quite gratified to read much later of the clinical studies that defined adverse changes in pulmonary function which accompanied infant anesthesia, changes which his technique had tended to moderate.
As neonatal surgery became more complex and longer procedures were performed, the need to provide for mechanical ventilation during surgery was apparent. Fortunately by this time, progress in ventilator design made this possible. Quite simply, the Bird mark VIII ventilator or the Ohio Ventimeter Ventilator could be adjusted so that they would periodically serve to occlude the expired limb of a T-piece system.
As an alternative to the T-piece system, which required a fresh gas flow 2–3 times the minute ventilation to prevent rebreathing, some anesthesiologists preferred to use non-rebreathing valves. These required only a gas flow equal to the minute ventilation. Ronald Stephen and Harry Slater described their non-rebreathing valve in 1948. It incorporated 2 rubber valves and was described as having very low resistance to breathing and negligible dead space. Controlled ventilation could be delivered by compressing the exhalation valve with a finger while compressing the reservoir bag, and the authors claimed to have used this method in infants of 3 weeks for up to 90 min [42]. In 1948, Digby Leigh independently described a valve of very similar design, which could be used in infants [43]. George Lewis modified the Leigh valve to permit controlled ventilation without the need to digitally compress the exhalation valve. The Lewis/Leigh valve incorporated a flap that would close the exhalation port if the reservoir bag were compressed [44].
A problem with the T-Piece system and with non-rebreathing valves was that they delivered very dry gases to the airway. In the USA, this concern led to the development of circle systems modified for the neonate. The Bloomquist infant circle was marketed by the Foregger company and incorporated a soda lime canister. However, a laboratory study of the humidity output of this circuit concluded that it offered no advantage over a humidified T-piece system and was more cumbersome to use [45]. The Columbia Valve was developed to allow a modified adult circuit to be used for infants; the valve had low resistance and a very low dead space of 0.5 ml [46]. This valve was used in a circuit in which the fresh gases were passed through the soda lime canister together with the expired gases in an effort to maximize the level of humification (Rackow H, Personal communication). The T-piece and its variants were almost always used for the neonate in Britain and Canada; non-rebreathing valves and various circle absorber systems were more commonly used in the USA.
In later years, pediatric anesthesiologists adapted various neonatal ventilators for operating room use. Progressive improvements in anesthesia machine design eventually allowed small infants to be successfully managed simply by changing to a smaller diameter set of circuit tubing.
Monitoring
As has been stated previously, monitoring in the early days consisted of watching the chest movements, examining the color, and perhaps feeling the pulse. Indeed this situation persisted well into the twentieth century. Writing on anesthesia for neonatal chest surgery in 1965, Bell stated “A guide to the general clinical condition I find useful is this:
baby pink and pulses palpable-condition good;
baby pale, pulses palpable or baby pink, pulses not palpable-condition satisfactory, but check ventilation and blood balance;
baby pale, pulses not palpable—condition serious.
I do not think that cardiac stethoscopes (the heart action can be seen in thoracic operations), sphygmomanometers, pulse monitors or E.C.G. tracings contribute enough additional information about a baby’s condition to merit their use; they may be distracting” [47].
I cannot say that this was the general attitude to monitoring in those years but it is a recorded opinion.
Accounts of neonatal anesthesia prior to 1960 make little or no mention of monitoring [31, 34, 36]. In fact the technology to satisfactorily monitor blood pressure in the neonate was not generally available until the late 1950s. Palpation or auscultation distal to a blood pressure cuff was noted to be very difficult in small infants. Oscillometry had been used but was not uniformly reliable. Hence, it was not common practice to monitor the blood pressure even in larger infants. Anesthesia records from this era commonly displayed only a heart rate. In an article on anesthesia for major surgery in 1950, CR Stephen displayed an anesthesia record for pyloromyotomy on which the only vital signs recorded were the heart rate and respiratory rate [48].
The optimal width of the blood pressure cuff (one inch) that was required for accurate measurement in the neonate was determined in 1939 by direct comparison with an intra-arterial needle [49]. However, as noted above, it was uncommonly used in anesthesia practice. Detection of pulsation distal to the cuff most often depended upon oscillometry. To detect the very small deflection of the oscillometer needle was frequently highly dependent upon “the eye of faith.” This could be very worrying during thoracic surgery or indeed any other major procedure; this I remember well.
In 1969, the use of the Doppler flow meter to monitor flow in the radial artery distal to a blood pressure cuff and reliably measure intraoperative blood pressure in infants was reported [50]. The battery-operated “Parks Doppler Flowmeter” became widely available and took much of the worry out of neonatal anesthesia. It could be used to measure blood pressure and also served as a continuous audible monitor of the pulse volume, serving as an early warning of adverse changes.
Direct measurement of intra-arterial pressure in the neonate was initially performed via the umbilical artery; however this resulted in a relatively high incidence of serious complications (e.g., bowel infarction) and was only applicable in the immediate neonatal period. Percutaneous cannulation of the radial artery in neonates was described in 1975 as a safer alternative [51, 52]. The use of the temporal artery for monitoring was also suggested [53] but was later generally abandoned when it became known that retrograde cerebral embolism was associated with this technique [54]. Femoral artery lines were also used on occasion but, in the neonatal age group, the incidence of ischemic complications exceeded that with radial lines [55].
Monitoring the oxygen saturation of blood during anesthesia was described by a group from Montreal in 1950 [56]. They used an earpiece which had been developed during World War II for the purpose of studying pilots flying at various altitudes. The equipment they used was delicate however and required a dedicated technician to operate it. Continuous monitoring of transcutaneous oxygen tension (TcpO2) in neonates was described in 1972 [57], but this was not introduced as a routine into the neonatal nursery for several years. Though TcpO2 was capable of indicating trends, individual readings lacked precise accuracy especially with decreased skin blood flow [58]. Electrodes required frequent attention and had to be moved periodically to prevent burns. During anesthesia it was found that inhaled agents further interfered with the performance of the electrode and decreased accuracy, though not to a significant degree [59].
Pulse oximetry became available for clinical use in 1983 [60] and was rapidly adopted as a routine monitor during the surgery and acute care of neonates; it was far easier to apply than the TcpO2 electrode. It was now possible to continuously display the level of oxygenation throughout the perioperative period and immediately respond to any adverse changes. It was also quite possible to apply two probes: one in the preductal area and one in the postductal area. The question now arose as to the safe level of preductal oxygen saturation to maintain in the preterm infant at risk for retinopathy of prematurity (ROP). Surveys performed in recent years indicate that many units aim to maintain SpO2 in the 85–93 % range [61] and that this does indeed decrease the incidence of serious ROP changes [62].
Monitoring of end-tidal carbon dioxide as a routine procedure in anesthesia care became commonplace during the 1980s. When applied to the neonate, it became apparent that both methods for CO2 analysis, mainstream and sidestream, are problematic [63]. The increase in dead space with mainstream analysis may lead to rebreathing in small infants. During sidestream analysis the site of sampling, flow rate, and length of the sampling tube are critical factors in obtaining valid results.
Intraoperative Temperature Control
As more prolonged surgery was being performed in neonates, the problem of intraoperative hypothermia became recognized [64] and identified as a cause of increased morbidity and mortality [38, 65–67]. Two of five postoperative deaths in a series of twelve neonates were attributed to hypothermia [65]. In another series of 67 infants, 12 patients died; seven of these were judged due to postoperative hypothermia [67]. It was noted that the decrease in body temperature was directly related to the duration of surgery and that smaller infants suffered a greater decrease. The vulnerability of the small infant to heat loss as a result of the large body surface area to weight ratio was suggested [68]. At this time in the 1950s, little was done to keep the neonate normothermic during surgery and indeed intraoperative hypothermia was considered by some to be beneficial.
An improved understanding of the adverse physiological effects of hypothermia came in the early 1960s. It also became recognized that it was much easier to keep the patient warm during surgery than to resort to rewarming postoperatively. The adverse effects of cooling on oxygen consumption [69], catecholamine levels [70], and acid/base status [71] were identified. Oxygen consumption in the neonate was shown to correlate most closely with the skin to environment temperature gradient, hence the significance of the “neutral thermal environment.” With this new understanding, efforts were made to maintain normothermia intraoperatively. Hot water bottles alongside the infant were recommended, but unfortunately this sometimes led to burns. Heating pads for the operating room table were described by Leigh and Belton in the second edition of their book on pediatric anesthesia published in 1960 [72]. Wrapping the limbs in cotton wadding and placing the infant on a warming blanket set at 40 °C was advocated by Smith in 1968. It was also found that heating blankets were more effective in maintaining normothermia in smaller infants—a beneficial effect of the large surface area to body mass ratio [73]. The addition of overhead radiant heaters during preparation for surgery and humidification of anesthetic gases provided for what was considered optimal patient management in the late 1960s and 1970s [74]. In the 1990s forced air warmers became generally available and proved very effective in maintaining normothermia [75].
Neonatal Anesthesia: Some Landmark Procedures and Their Development
Repair of Esophageal Atresia and Tracheoesophageal Fistula
The first operation for esophageal atresia was performed in London, England, by Charles Steele in 1888 [76]. The diagnosis was made when the infant became livid and had difficulty breathing “after the first nourishment”; a sound could not be passed by mouth for further than five inches. Surgery was performed the next day after “the infant took chloroform well.” The stomach was opened via an abdominal incision and an unsuccessful attempt was made to pass a gum elastic catheter retrograde up the esophagus, in the hope that a simple membrane could be perforated. The surgery was abandoned and the infant died 24 h later. At autopsy, the upper and lower esophagus ended blindly one and one half inches apart. There is no mention of an associated fistula.
The first successful ligation of a tracheoesophageal fistula with anastomosis of the associated esophageal atresia was reported by Haight in 1943 [77]. Local analgesia was used for the first part of the operation; open ether was added during the esophageal anastomosis in order to obtain optimal surgical conditions. Spontaneous ventilation was maintained throughout. In Britain, Franklin described two successful repairs of TEF with esophageal anastomosis in 1947 [78]; both of these procedures were performed using infiltration of local anesthetic (1 % procaine) to the chest wall incision line and no other anesthesia. During the operation “the infant was secured prone over a rubber hot water bottle.”
As has been previously stated, in early days, many surgeons opposed the use of endotracheal intubation for their patients. Swenson, a much respected pioneer pediatric surgeon, reported his experiences with TEF in 1943 and advocated the administration of cyclopropane via a tightly applied face mask [79]. Kennedy and Stoelting reported a series of 86 cases of TEF operated upon at Indiana University Hospital from 1940 until 1956 [80]. Before 1948, 17 cases were managed without intubation using a combination of local analgesia and open ether; the mortality rate was 88 %; two patients died during surgery. After 1948, all 69 neonates underwent tracheal intubation, none died during surgery, and the overall mortality rate was 42 %. Many factors were considered responsible for these improved results, but the role of endotracheal intubation and tracheobronchial toilet was considered to be very significant. General anesthesia methods reported by Zindler and Deming in 1953 [81] employed awake endotracheal intubation to administer cyclopropane via a non-rebreathing valve and controlled ventilation. They also stressed the need for frequent suctioning of the trachea.
Progressively improving results from the surgical and anesthesia management of TEF can be followed by examining the Toronto experience. A review of the results from 1959 to 1964 [82] shows an overall mortality rate of 36.5 %, with a rate of 57.5 % for the infants who were under 2,500 g body weight. The predictors of mortality were prematurity, the presence of associated congenital malformations (especially cardiac), and extensive pulmonary disease (i.e., delayed diagnosis). A subsequent review [83] of the years 1964–1968 noted an overall mortality rate of 22 %, and the mortality rate for those under 2,500 g had decreased to 40 %.
The problem of gastric distension due to gases passing through the fistula into the stomach was a concern for the anesthesiologist, especially as this has been reported to cause serious ventilatory embarrassment and cardiac arrest [84]. Some preferred to maintain spontaneous (perhaps gently assisted) ventilation until the fistula was ligated. Other suggestions to prevent this complication included performing a preliminary gastrostomy under local analgesia [85]; this was also favored by some surgeons as part of a two-stage repair, especially in critically ill infants. Passing an endotracheal tube (without a side hole) into the bronchus and withdrawing it until bilateral ventilation could be heard; then positioning the tube with the bevel facing anteriorly was also suggested [86]. This would direct ventilation to the lungs and protect the fistula with the longer side of the bevel. (However the fistula is occasionally at the level of the carina!) Some more complicated methods to position the tube and prevent gastric distension have also been described. If a gastrostomy was present, it was suggested that placing the gastrostomy tube under water in a beaker while advancing the endotracheal tube could indicate when the ETT was below the fistula [87], i.e., no more bubbles! The significance of leaks via the fistula increased as preterm infants with respiratory distress syndrome requiring greater airway pressures presented for surgery. Karl suggested that a balloon catheter should be inserted into the lower esophagus via the gastrostomy to control the leak [88]. Others suggested that a Fogarty or pulmonary artery catheter should be advanced via a bronchoscope directly into the fistula [89]. In many units, it became a routine to perform early ligation of the fistula in preterm infants, thus largely avoiding the problem.
Preoperative endoscopic examination of the fistula was introduced in the 1980s [90] and became routine in some centers [91]. It was suggested that an exact knowledge of the size and site of the fistula would improve results and in addition endoscopy permitted placement of balloon catheters to occlude the lumen. Others preferred to keep things simple and manage the airway without endoscopy [92].
Congenital Diaphragmatic Hernia
Congenital diaphragmatic hernia (CDH) was described in 1757 by a Society of Physicians in London following postmortem examination of an infant who died under 2 h of age in respiratory distress [93]. Early reports of operations for CDH are found in the medical literature of the 1930s [94] and 1940s [95], but it is significant that the neonates were all more than 20 h of age, and some patients were much older, i.e., they had adequate pulmonary function to survive the immediate neonatal period. In 1946, Robert Gross reported seven cases that came to surgery with ages ranging from 22 h to 7 years; he also recorded his preferred anesthesia technique [95]:
“The choice of anesthetic agent and the method of its administration are important considerations, particularly in the cases of patients in whom cyanosis and respiratory embarrassment are pronounced. Ether can be employed, and indeed may be given with an open mask. It is preferable to use a closed system, so that a higher percentage of oxygen can be supplied to the patient and so that collapse of both lungs can be prevented in those rare cases in which there is a free communication between the two pleural cavities. In all cases of the present series, cyclopropane was used and was eminently satisfactory. It is clear, however, that this choice depended on my good fortune in having an anesthetist who is expert in handling babies and who has had enough initiative to devise a homemade apparatus which is suitable for babies of the smallest size. It must be emphasized that cyanosis should not be a deterrent to operation, since the administration of a gas containing a high percentage of oxygen will improve the baby’s color, and the operative removal of the abdominal viscera from the chest will also facilitate the child’s breathing efforts. It is unnecessary to use an intratracheal tube ; indeed, this is apt to be followed by troublesome edema of the larynx in the ensuing twenty-four hours. Only a tightly fitting mask, without an intra-tracheal tube, was used for all of the patients reported on here.” [95]
CDH was considered a surgical emergency [96] and immediate operation was recommended once the diagnosis had been made—especially if respiratory distress was present. A case report from 1950 [97] demonstrated the extent to which improvisation was employed to facilitate urgent surgery. The child was five days old and in considerable respiratory distress and required oxygen at all times—a decision was made to perform immediate surgery. “Ether was the anesthetic agent of choice. The equipment at hand was a small open mask, an infant-sized metal oral pharyngeal airway, a rubber infant-sized mask from a Kreiselman resuscitator, a socket elbow, a short corrugated tube section, a Peterson ether drop cup, and for a breathing bag a toy red rubber balloon.” During the procedure the two red rubber balloons that were available both disintegrated due to contact with liquid ether and were replaced by rubber condoms! To the credit of the team, the infant survived.3
In the 1950s, the association between pulmonary hypoplasia and CDH was reported [98]. At this time and into the 1960s, improvements in the care and transportation [99] of critically ill neonates resulted in more infants with CDH presenting for emergency surgery. Many of these who would have died without surgery now died postoperatively secondary to their pulmonary disease. The high mortality rates associated with repair CDH stimulated many investigators and clinicians and attention turned to means to optimize pulmonary function postoperatively. These means included various patterns of controlled ventilation and measures to reduce pulmonary vascular resistance (PVR) [100]. The thought developed that the cause of death in some cases was not simple hypoplasia but potentially reversible changes in PVR [100]. The standard approach to anesthesia for CDH at this time, no bag and mask ventilation, endotracheal intubation, avoidance of N2O, and care to avoid large positive pressures, was augmented by steps to control PVR if required.
One problem that had complicated the management of the infant with CDH was that some experienced very few problems postoperatively while others were desperately ill. Hence, there was great interest in identifying those prognostic factors that determine which infants would require aggressive invasive measures. Raphaely and Downs in Philadelphia developed a scoring system based on the preoperative and postreduction alveolar/arterial oxygen tension gradient [101]. Desmond Bohn and his colleagues in Toronto suggested a system to predict the extent of pulmonary hypoplasia based on the preoperative arterial CO2 tension and a ventilatory index (mean airway pressure x ventilatory rate) [102]. Bohn et al. also suggested that consideration should be given to an initial nonsurgical approach to CDH in the expectation that impaired pulmonary function not due to hypoplasia might improve [102]. In the same year, 1987, another study from Toronto had shown that surgical repair of CDH impaired rather than improved respiratory mechanics [103]. Thus CDH management evolved from a surgical emergency into a potential complex management problem for the neonatal intensivist, sometimes involving preoperative ECMO therapy. Surgery was now performed only when the respiratory status was improved.
Abdominal Wall Defects
Reports of exomphalos (omphalocele) are found in medical writings from the middle ages onwards, but the infants generally soon died—usually of peritonitis. There are a few instances where conservative treatment using antiseptic preparations applied to the lesion resulted in granulation tissue formation and epithelialization with survival. Operative treatment before the 1940s was usually fatal [104]. Successful surgical treatment was reported in 1948 [105], and in 1949 a further successful case was reported in which the anesthetic used “was sugar and whisky administered on a small gauze nipple” [106]. The postoperative course was complicated by peritonitis; however the patient recovered and was discharged on the 75th postoperative day. Much credit for the recovery was given to the use of prolonged intravenous fluid therapy. At this time, it was recognized that omphalocele was often associated with other significant congenital malformations. It was also noted that the immediate prognosis depended on whether the membrane covering the viscera was intact or ruptured; in the latter case, a fatal result was certain [107]. In 1953, a successful case is recorded in which open ether was administered for anesthesia: “The bowels were returned to the abdominal cavity with difficulty, and the wound was closed in a single layer. The anaesthesia must be sufficiently deep to relax the abdominal muscles. This requires the services of a skilled anaesthetist” [107]. It was suggested that a stomach tube should be in place to aspirate secretions as the bowel was reduced into the abdomen—obviously a serious concern when an open technique was used.
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