B. S. Skjonsby

The optimal length of insertion of central venous catheters for pediatric patients.

Incorrect positioning of central venous catheters (CVC) in infants and children may lead to serious complications such as perforation of the heart or great vessels. CVC position is not usually assessed until the first postoperative chest radiograph, potentially leaving malposition undetected for several hours. We studied a series of 452 right internal jugular and subclavian catheter placements in infants and children undergoing surgery for congenital heart disease, and measured the distance from the skin insertion site to the radiographic junction of the superior vena cava and right atrium (RA). Based on these data, the following formulae predict that a CVC will be positioned above the RA 97% of the time: correct length of insertion (cm) = (height in cm/10) − 1 for patients ≤100 cm in height, and (height in cm/10) − 2 for patients >100 cm in height. Weight-based recommendations were also developed which predict placement of CVC above the RA 98% of the time.

Positive pressure ventilation with the laryngeal mask airway in children.

We studied the safety of positive pressure ventilation (PPV) when using the size 2 laryngeal mask airway (LMA) in 46 ASA physical status I or II children (aged 38 +/-21 mo) undergoing elective surgery. The LMA cuff was inflated in incremental steps to achieve a cuff leak pressure >or=to 15 cm H2 O. Abdominal circumference was measured before and after PPV in study patients, as well as in a control group managed with tracheal intubation. Cuff leak pressure was 17 +/- 4 cm H2 O (range 12-34 cm H2 O). Forty-five patients successfully underwent PPV. Gas leak around the LMA cuff prevented PPV in one infant. The only respiratory variable that changed significantly was end-tidal CO2, which decreased from 40 +/- 6 to 34 +/- 5 mm Hg. Abdominal circumference increased in 28 patients but was not associated with any complications. Change in abdominal circumference in the study group was not significantly different from that observed in the control group. However, abdominal circumference increased 8 cm in one study patient, prompting insertion of an orogastric tube. The size 2 LMA provides an effective airway for PPV. Mild gastric distention often occurs. The risk of clinically significant gastric distention appears to be small, but it warrants close monitoring. We conclude that with certain precautions described in the text, the size 2 LMA provides a relatively safe airway for PPV in children. (Anesth Analg 1996;82:33-8)

POST-CAESAREAN SECTION ANALGESIA : A COMPARISON OF EPIDURAL BUTORPHANOL AND MORPHINE

Epidural butorphanol 1, 2 and 4 mg were compared with morphine, 5 mg, for postoperative analgesia in 92 consenting, healthy, term parturients who had undergone Caesarean section under epidural lidocaine anaesthesia in a randomized double-blind study. Postoperative pain was assessed using a visual analogue scale and recorded with heart rate, blood pressure and respiratory rate. The demographic characteristics, and the incidences of primary and repeat Caesarean sections, were not different among the four treatment groups. At 15, 30, 45 and 60 min after treatment the median pain scores following butorphanol were similar and lower than those following morphine (P < 0.05). Calculated median percentage pain relief values for butorphanol were higher than morphine at each of these times (P < 0.05). At 90 min and 2 hr the pain scores and pain relief values were similar. Beyond 45 min the number of patients requesting supplemental medication and dropping out of the study increased progressively in both the butorphanol and morphine treated patients. The attrition profiles for butorphanol were different from morphine (P < 0.01). The median time in the study was > 24 hr for morphine, and 3, 2.5 and 4 hr for butorphanol, 1, 2 or 4 mg, respectively. No patient developed a clinically important change in heart rate or blood pressure, and none experienced a decrease in respiratory rate below 12 breaths · min−1. One of 69 patients (1.4 per cent) who received butorphanol developed pruritus compared with ten (43 per cent) of 23 patients who received morphine. The global assessments of the adequacy of analgesia were indistinguishable between morphine and butorphanol. Epidural butorphanol provides safe, effective postoperative analgesia, has a prompt onset, and a limited duration.RésuméDans une étude à double insu lors de césarienne chez 92 parturientes à terme, nous avons comparé l’efficacité de 1, 2 et 4 mg de butorphanol à celle de 5 mg de morphine injectés dans le cathéter employé pour l’anesthésie épidurale à la lidocaïne. Nous jaugions la douleur postopératoire sur une échelle visuelle analogue et mesurions le pouls, la tension artérielle et la fréquence respiratoire. Les variables démographiques et la proportion de césariennes itératives étaient semblables dans les quatre groupes. Les valeurs médianes d’intensité douloureuse 15, 30, 45 et 60 min après l’injection de butorphanol étaient les mêmes pour les trois doses et étaient inférieures à celle de la morphine (P < 0,05); en même temps, les pourcentages médians de soulagement étaient plus grands avec le butorphanol qu’avec la morphine (P < 0,05). Toutefois, à 90 min et 2 h post injection, ces variables étaient les mêmes pour les deux morphiniques. A partir de la 45ième minute, de plus en plus de patientes traitées à la morphine ou au butorphanol nécessitaient d’autres analgésiques, mettant ainsi un terme à leur participation à l’étude mais à une fréquence différente selon le morphinique (P < 0,01). La durée médiane de participation à l’étude était de plus de 24 h pour la morphine et de 3, 2,5 et 4 h pour les doses de 1, 2 et 4 mg de butorphanol respectivement. Il n’y eut pas de modification clinique du pouls ou de la tension artérielle non plus que de bradypnée à moins de 12 min−1. Une seule des 69 patientes (1,4 pour cent) ayant reçu du butorphanol se plaint de prurit mais 10 des 23 patientes (43 pour cent) du groupe morphine firent de même. L’évaluation globale de l’efficacité analgésique était la même pour la morphine et le butorphanol. Le butorphanol épidural offre une analgésie postopératoire sûre et efficace; il agit rapidement et pendant une période limitée.

The effect of nitrous oxide diffusion on laryngeal mask airway cuff inflation in children

We studied the effect of nitrous oxide (N2O) diffusion on size 2 LMA cuff inflation in 52 children, 38±21 months of age. LMA cuffs were inflated with air (Group A) or 65% N2O, oxygen and halothane (Group B). Cuffs were inflated in a stepwise manner, achieving a cuff leak pressure of 17±4 cm H2O for all patients. Cuff volume and intracuff pressure increased in Group A (8.5±1.0 ml to 10.8±1.4 ml and 101±36 mmHg to 152±42 mmHg, respectively) and decreased in Group B (8.9±1.0 ml to 6.6±1.5 ml and 90±30 mmHg to 53±37 mmHg, respectively). Cuff leak pressure did not change significantly in either group. We conclude that cuff inflation with a mixture of N2O/oxygen prevents N2O diffusion into the cuff, avoiding cuff overinflation without compromising LMA function.

Comparison of NAD 6000 and servo 900C ventilators in an infant lung model.

UNLABELLED We compared the ability of the NAD 6000 (North American Dräger, Telford, PA) and the Servo 900C (Siemens-Elema AB, Solna, Sweden) anesthesia ventilators to maintain precise delivery of small tidal volumes (V(t)) and positive end-expiratory pressure using an infant test lung model. A variety of ventilator and lung model settings were selected to test clinical conditions simulating normal and extremely compromised lung function. Differences in ventilator output were analyzed by using an independent t-test with P <0.05 considered significant. With the ventilators set to deliver a V(t) of 30 mL, the actual delivered V(t) was significantly better for the NAD 6000 (25 +/- 2 mL) compared with the Servo 900C (18 +/- 3 mL), P <0.001. When the ventilators were set to deliver 100 mL V(t), their delivered V(t) were not significantly different, NAD 6000 (66 +/- 19 mL) and Servo 900C (60 +/- 12 mL), P = 0.09. The exhaled V(t) read by the anesthesia machines was significantly closer to the delivered V(t) for the NAD 6000 (11 +/- 9 mL) compared with the Servo 900C (37 +/- 11 mL), P < 0.001. Both ventilators maintained the end expiratory pressure delivered to the test lung within 2 cm H(2)O of the set positive end-expiratory pressure on average. As the conditions changed requiring the ventilator to develop a higher peak inflating pressure, both ventilators showed a decrease in V(t) delivered, which was proportionate to the tubing compression volume loss. IMPLICATIONS The NAD 6000 (North American Dräger, Telford, PA) and Servo 900C (Siemens-Elema AB, Solna, Sweden) are able to precisely deliver small Tidal Volumes. They both decreased in performance when tested under extreme conditions. Earlier studies of traditional anesthesia ventilators suggest that the NAD 6000 and Servo 900C are superior pediatric ventilators.

Neuromuscular effects of rocuronium in children during halothane anaesthesia

Rocuronium bromide, a nondepolarizing muscle relaxant has been shown to have a short onset and intermediate duration of action in adults and young children. We evaluated onset time, intubating conditions, as well as duration of action of rocuronium in children ages four to 12 years during nitrous oxide‐halothane anaesthesia. Following a stable recording of train‐of‐four (TOF) impulses at the ulnar nerve, patients were given rocuronium 600 μg˙kg−1 intravenously. We found that the time to 90% and 100% neuromuscular (N‐M) block of the (TOF) was 51 ± 18 s and 66 ± 32 s respectively. Intubation was achieved at 94 ± 31 s and rated as good or excellent in all cases. Time to recovery of N‐M transmission to 25%, 75% and 90% of control was 29 ± 8 min, 42 ± 14 min and 46 ± 16 min respectively. Heart rate increased ∼12 BPM after drug injection, while the blood pressure remained unchanged. From our data we conclude that, as in other age groups, rocuronium has a rapid onset, intermediate duration of action in children 4–12 years of age, and appears devoid of significant side effects.