Fig. 10.1
ECG and pulse oximetry waveforms after induction of general anesthesia
10.1.3 Isn’t That a Little Too Much Propofol?
The usual induction dose for adults is 1.5–2.5 mg/kg body weight. Small children and newborns need higher doses of propofol and other hypnotic agents. Among other things, this is due to significantly larger volume of distribution.
>> Until now William had been quiet, but now with the propofol injection he began to cry and hiccup a little. “It is such a shame that we can’t give the guy a little lidocaine,” Dr. Clare said to Patricia. The hiccups remained, even after William had gone to sleep.
Dr. Clare tried to ventilate him carefully, but without success. The S p O 2 value was now 99 % and the heart rate was 170 beats/min. The sliding door to the OR opened. Anesthesiologist-in-charge Dr. Eldridge glanced at William and Dr. Clare’s attempts and announced: “The most common cause of difficult mask ventilation is lack of sufficient anesthesia depth.” According to Dr. Clare’s orders, CRNA Patricia administered another 20 mg of propofol, followed by 10 μg fentanyl. The hiccups disappeared, but the ventilation still was difficult.
10.1.4 What Are the Causes for Difficult Mask Ventilation When the Anesthesia Is Deep Enough?
The mask ventilation of a newborn and infants is difficult for the inexperienced. The most common mistakes are obstruction of the airway:
Due to overextension of the neck – mask ventilation is only possible in the neutral position
Due to strong pressure of the mask on the nose, causing obstruction of the nasal passages
By pressure on the floor of the mouth, causing closure of the choana by the tongue
>> Dr. Clare heard the oxygen saturation of the pulse tone dropping, and she started to get nervous.
“We’ll be fine,” whispered Patricia calmly. “Don’t extend the neck quite so much, and don’t press on the floor of the mouth.”
Dr. Clare was thankful for the advice, as William then allowed himself to be effortlessly ventilated with the mask. The saturation increased all at once to 99 %. “Now we can intubate,” she said to Patricia.
10.1.5 Wasn’t Something Forgotten Here?
Intubating without muscle relaxants is controversial. Not only does it make the intubation more difficult, but it is also associated with an increased incidence of hoarseness, throat pain, and laryngeal damage [3]. Despite this, muscle relaxants are often avoided in pediatric anesthesia [13]. The main reasons are the presence of a contraindication for muscle relaxants and an anticipated short duration of surgery.
In newborns and especially former preterm babies, there is a further issue: due to their increased volume of distribution in comparison to adults, relatively larger doses of muscle relaxants are needed. The hepatic and renal elimination occurs more slowly, and the duration of action cannot be accurately estimated. A possible residual relaxation increases the danger of postoperative hypoxemia.
Newborns have less muscular tone than older children and adults so that intubation without muscle relaxants is more easily performed. There is the danger, however, that the depth of anesthesia is misinterpreted as being deep enough, when in fact it is not.
>> Dr. Clare laid the mask to the side and CRNA Patricia gave her an endotracheal tube with an internal diameter of 3.5 mm. She guided the tube first into the right, then into the left nasal passage, but each time, she felt resistance. This had never happened to her before. The oxygen saturation tone of the monitor was already deeper. Dr. Clare aborted the intubation attempt and ventilated William again by mask.
“Please give me a smaller tube,” she requested. CRNA Patricia responded, “It will probably leak. Perhaps you should perform an oral intubation.” Thankful again for the advice, Dr. Clare was able to promptly intubate the trachea. The tube was secured and William was turned on his side. To maintain sufficient depth of anesthesia, Dr. Clare turned on the sevoflurane vaporizer.
After turning the child prone, she prepped the sacral region. CRNA Patricia had already prepared ropivacaine 0.2 % as the local anesthetic and had set up the caudal tray.
10.1.6 How Much of the Local Anesthetic Would You Use for William’s Caudal Anesthesia?
The dose is calculated according to height, weight, and the planned procedure. Usually the Armitage formula is used (see Table 10.1). Interestingly, the Armitage formula is not based on any scientific tests, but from a “Letter to the Editor” that Armitage wrote in 1979 [1]. Since then, the formula has been cited as evidence-based knowledge.
Dose [ml/kg] | Dermatome affected |
|---|---|
0.5 | Lumbar 1 |
0.75 | Thoracic 12 |
1 | Thoracic 10 |
1.25 | Thoracic 6–8 |
With a body weight of 4 kg and a planned inguinal hernia operation, 4 ml of local anesthetic should be injected. To increase the duration of action, 1–2 μg/ml of clonidine can be added [11]. In newborns, however, clonidine should not be given due to possible post-op respiratory depression [2].
>> Dr. Clare’s placement of the caudal catheter was unremarkable. As no cerebrospinal fluid and no blood returned, she injected 4 ml of ropivacaine 0.2 %, removed the needle, and taped a sterile dressing over the injection site. Suddenly an alarm sounded from the ventilator; “decreased end-expiratory CO 2 ” was blinking on the screen. “I hope the endotracheal tube didn’t come out,” she said to Patricia. Together they rolled William supine, and Dr. Clare changed the ventilator to manual ventilation, increased the inspiratory oxygen to 100 %, and checked the placement of the endotracheal tube. “The tube is properly placed.” Dr. Clare announced, as the next alarm went off – this time for bradycardia. Pulse was now only 110 beats/min.
10.1.7 What Would You Do Now?
A decrease in heart rate is life-threatening in infants and toddlers; cardiopulmonary insufficiency and a functional circulatory arrest occur with a heart rate under 100 beats/min.
The most common cause is hypoxemia, which was already ruled out by Dr. Clare in this case. The goal of therapy now must be to increase the heart rate as fast as possible.
>> Dr. Clare was now very nervous and hectically squeezed the bag. “Give me 0.1 mg atropine,” she said to Patricia, “and call for help!” Anesthesiologist-in-charge Dr. Eldridge was in the PACU with another baby. He dropped everything (except the baby) when the call for help reached him.
10.1.8 How Do You Interpret Fig. 10.2 and What Action Would You Now Take?
Compared to Fig. 10.1, wide ECG complexes are visible with a rate of about 100 beats/min. The pulse oximetry curve is flat. Taking into consideration the decreased end-tidal CO2, the baby is in cardiopulmonary arrest and CPR must begin immediately and advanced cardiac life support begun immediately [5, 7].
>> Dr. Eldridge checked placement of the endotracheal tube once more. William now appeared cyanotic. Dr. Eldridge encircled William’s torso with his fingers and placed his two thumbs side by side over the lower third of the sternum. Then he began chest compressions, compressing the sternum to approximately one-third of the anterior–posterior diameter. William quickly became rosy again. The monitor showed the following (see Fig. 10.3).
