Pulmonary volume recruitment manoeuvre restores pulmonary compliance and resistance after apnoea in anaesthetized lambs

BACKGROUND: We studied the effects of an episode of induced apnoea on the dynamic compliance (Crs) and resistance (Rrs) of the respiratory system in anaesthetized lambs and investigated the mechanisms underlying the effectiveness of a timed reexpansion inspiratory manoeuvre (TRIM). METHODS: Following 2 min of apnoea, three manoeuvres were randomly performed: (i) control: reventilated without TRIM using initial settings and gas composition of 30% oxygen in 70% nitrous oxide; (b) T1: TRIM with 30% oxygen in 70% nitrous oxide, followed by reventilation with the initial settings; and (c) T2: preoxygenate with 100% oxygen, apnoea, then TRIM with 100% oxygen, then reventilation with 100% oxygen at the initial settings. The percentage change in Crs and Rrs was calculated at first breath, second breath, 10, 20, 40, 60, 90, 120 and 180 s postapnoea. RESULTS: Mean control decreased 15% and did not return to baseline during the study period. TRIM increased mean Crs in T1 and T2 by 8% and 9%, respectively, at first breath and returned to baseline and did not deteriorate for the remainder of the study period. Mean Rrs in the control group increased 20% and did not return to baseline during the study period. Mean Rrs in T1 and T2 initially increased 17% and 27%, respectively, at first breath and returned to baseline within 40 s. CONCLUSIONS: These results demonstrate that significant deterioration occurs in Crs and Rrs following 2 min of apnoea in anaesthetized lambs, which is not corrected with normal ventilation but is rapidly and completely reversed with a TRIM. This supports our hypothesis that volume recruitment of alveoli is an effective manoeuvre in restoring lung function. The practice of preoxygenation is also reinforced as the lambs maintained maximal oxygen saturation if they were ventilated with 100% oxygen prior to the 2 min of apnoea.     

Computerized tomography of the lungs and arterial oxygen tension studies during apnoea in anaesthetized young lambs

Computerized tomography (CT) of the lungs and arterial oxygen tension studies were performed during general anaesthesia in an animal model to understand changes in pulmonary atelectasis associated with anaesthesia in children during a 2 min apnoeic period. Six anaesthetized lambs were subjected to three periods of apnoea lasting 2 min each. A series of 10 mm CT transaxial views were taken at three levels of the chest and arterial blood gases were analysed at the start of the apnoeic period (baseline) and again every 30 s during the apnoeic period. The areas of atelectasis were measured using the extended Hounsfield scale. The results confirmed that significant background atelectasis was associated with general anaesthesia as found in adult human studies, but failed to demonstrate any increase in atelectasis during the period of induced apnoea. The decline in arterial oxygen tension in this study could be explained due to simple utilization of oxygen in keeping with physiological principles.     

Effects of an alveolar recruitment manoeuvre guided by lung ultrasound on anaesthesia‐induced atelectasis in infants: a randomised,controlled trial

Atelectasis occurs in the majority of children undergoing general anaesthesia. Lung ultrasound has shown reliable sensitivity and specificity for diagnosing anaesthesia‐induced atelectasis. We assessed the effects of a recruitment manoeuvre on atelectasis using lung ultrasound in infants undergoing general anaesthesia. Forty infants, randomly allocated to either a recruitment manoeuvre group or a control group, received volume‐controlled ventilation with 5 cmH₂O positive end‐expiratory pressure. Lung ultrasound examination was performed twice in each patient, the first a minute after starting mechanical ventilation of the lungs and the second at the end of surgery. Patients in the recruitment manoeuvre group received ultrasound‐guided recruitment manoeuvres after each lung ultrasound examination. The incidence of significant anaesthesia‐induced atelectasis at the second lung ultrasound examination was less in the recruitment manoeuvre group compared with the control group (25% vs. 80%; p = 0.001; odds ratio (OR ) 0.083; 95% confidence interval (CI ): 0.019–0.370). The median (IQR [range]) lung ultrasound scores for consolidation and B‐lines on the second examination were lower in the recruitment manoeuvre group compared with the control group; 6.0 (3.0–9.3 [0.0–14.0]) vs. 13.5 (11.0–16.5 [8.0–23.0]); p < 0.001 and 6.5 (3.0–12.0 [0.0–28.0]) vs. 15.0 (10.8–20.5 [7.0–28.0]); p < 0.001, respectively. The lung ultrasound scores for consolidation on the first and second examinations showed a negative correlation with age (r = ?0.340, p = 0.008; r = ?0.380, p = 0.003). We conclude that ultrasound‐guided recruitment manoeuvres with positive end‐expiratory pressure proved useful in reducing the incidence of anaesthesia‐induced atelectasis in infants, although 5 cmH₂O positive end‐expiratory pressure alone was not sufficient to eliminate it. In addition, the younger the patient, the more susceptible they were to atelectasis.     

A timed reexpansion inspiratory manoeuvre (TRIM) for treating oxyhaemoglobin desaturation in children following a period of apnoea—studies in an animal model

Our clinical experience has shown that the use of a constant distending airway pressure of 30 cm water for 10 s, termed a timed reexpansion inspiratory manoeuvre (TRIM), is often successful in correcting oxyhaemoglobin desaturation in anaesthetized children. The aim of this study was to assess the efficacy of TRIM in lambs. Following a standard relaxant anaesthetic, ventilation was stopped and oxyhaemoglobin saturation allowed to fall to 70% and the time taken to return to baseline was compared between three groups. The median time was 42.5 s when ventilation was restarted with 33% oxygen in nitrous oxide (33% group), 30 s when ventilation was restarted with 100% oxygen (100% group) and 22.5 s with a TRIM before restarting ventilation with 33% oxygen in nitrous oxide (TRIM group). The correction of desaturation was more rapid in the TRIM group compared with the 33% group ( P <0.004) and the 100% group ( P <0.003). Oxyhaemoglobin desaturation due to apnoea in anaesthetized lambs is more effectively treated with a TRIM than by increasing the inspired oxygen fraction.     

Lung protective ventilation during pulmonary resection in children: a prospective,single-centre,randomised controlled trial

Background

Perioperative ventilatory strategies for lung protection in children are underexplored. This study evaluated the effects of lung protective ventilation (LPV) on postoperative clinical outcomes in children requiring one-lung ventilation (OLV) for pulmonary resection.

The influence of body position and differential ventilation on lung dimensions and atelectasis formation in anaesthetized man

The effects of body position and anaesthesia with mechanical ventilation on thoracic dimensions and atelectasis formation were studied by means of computerized tomography in 14 patients. Induction of anaesthesia in the supine position reduced the cross-sectional area for both lungs and caused atelectasis formation in dependent lung regions in 4/5 patients. Conventional ventilation with positive end-expiratory pressure (PEEP) increased thoracic dimensions and reduced, but did not eliminate, the atelectatic areas. The vertical diameters of both lungs were smaller in the lateral position as compared to the supine position (16.7 vs 10.4 cm in the left lung and 17.3 vs 12.8 cm in the right lung). The lateral positioning also caused a large reduction of the atelectatic area in the non-dependent lung. Differential ventilation with selective PEEP to the dependent lung eliminated (3/8 patients) or reduced (5/8 patients) dependent lung atelectasis. It can be concluded that lung geometry is altered in the lateral position: the shape of the lung makes the vertical diameter of each lung less in the lateral position, compared to the supine position. The atelectatic areas are mainly located in the dependent lung in the lateral position, and these atelectatic areas could be further reduced by selective PEEP to this lung.     

Atelectasis and pulmonary shunting during induction of general anaesthesia - can they be avoided?

Background: Gas exchange is regularly impaired during general anaesthesia with mechanical ventilation. A major cause of this disorder appears to be atelectasis and consequently pulmonary shunt. After re-expansion, atelectasis reappears very slowly if 30% oxygen in nitrogen is used, but much faster if 100% oxygen is used. The aim of the present study-was to evaluate if early formation of atelectasis and pulmonary shunt may be avoided if the lungs are ventilated with 30% oxygen in nitrogen instead of 100% oxygen during the induction of general anaesthesia.
Methods: Twenty-four adult patients with healthy lungs scheduled for elective surgery were investigated. During induction of anaesthesia, the lungs were manually ventilated via a face mask, using either 30% oxygen in nitrogen (group 1, n=12) or 100% oxygen (group 2, n=12). Atelectasis was estimated by computed x-ray tomography and ventilation-per-fusion distribution with the multiple inert gas elimination technique, both awake and during general anaesthesia with mechanical ventilation.
Results: No atelectasis was present in the awake subjects. After induction of anaesthesia, the mean amount of atelectasis was minor (0.2±0.4 cm²) in group 1 and considerably greater (8.0±8.2 cm²) in group 2 ( P <0.001). The pulmonary shunt was 0.3±0.7% of cardiac output in the awake subjects. This value increased to 2.1±3.8% in group 1 and to 6.5±5.2% in group 2 ( P <0.05). The indices of V_A/Q mismatch showed no difference between the two groups.
Conclusion: During induction of general intravenous anaesthesia in patients with healthy lungs, gas composition plays an important role for atelectasis formation and the establishment of pulmonary shunt. By using a mixture containing 30% oxygen in nitrogen, the early formation of atelectasis and pulmonary shunt may, at least in part, be avoided.     

Carbon dioxide elimination in anaesthetized children

Carbon dioxide elimination (VCO2) was measured in 186 anaesthetized, spontaneously breathing infants and children with body weights ranging from 2.8 to 26.5 kg. They all underwent minor paediatric surgical procedures. The influence on VCO2 of age, operation, premedication, caudal anaesthesia, and different volatile anaesthetic agents was investigated. The volume of exhaled gas, during three- to five-minute collection periods, was measured and the fraction of exhaled CO2 was determined by a CO2 meter. Under basal anaesthetic conditions, the average output before operation followed the equation: VCO2 (ml.min-1) = -1.25X + 13.0X2, in which X = lne (body weight, kg). Expressed on a weight basis, the youngest infants (weighing less than 5 kg) had the lowest VCO2. Higher values were measured up to a body weight of 10 kg above which a negative correlation occurred between VCO2 (ml.min-1.kg-1) and body weight. The use of premedication resulted in a more variable VCO2 during operations than when opioid premedication was not used. The combination of a general anaesthetic and caudal anaesthesia stabilized VCO2. Also, children anaesthetized with halothane had a higher VCO2 than those who were anaesthetized with enflurane or isoflurane (P less than 0.05). The variable VCO2 emphasizes the need for increased monitoring of VCO2 during routine anaesthesia and operation in infants and children.     

Pulmonary ventilation and gas exchange in children anaesthetized with halothane, enflurane and isoflurane

The effects of similar anaesthetic levels of halothane (1.3 MAC), enflurane (1.2 MAC) and isoflurane (1.1 MAC) on pulmonary ventilation and gas exchange were investigated in 24 children subjected to minor and intermediate paediatric surgical procedures. Eight children were anaesthetized with each agent, pneumotachography and capnography were used, and airway as well as oesophageal pressures were measured. Minute ventilation (VE) was lower with enflurane than with halothane (P less than 0.001) and isoflurane (ns). Tidal volumes were, however, similar and variations in VE were thus caused by lower respiratory rates with enflurane than with the two other agents. Alveolar ventilation (VABohr) and carbon dioxide elimination (VCO2) were smaller and end-tidal CO2 tension higher with enflurane. Ventilatory efficiency was, however, somewhat better with enflurane as indicated by lower VDBohr/VT (ns) and VE/VCO2 (P less than 0.05) ratios compared with the two other agents. The effects of all three agents on dynamic compliance were similar, while total pulmonary resistance was less with isoflurane than with halothane and enflurane. It is concluded that although minute ventilation was smaller with enflurane than with halothane and isoflurane, ventilatory efficiency was similar due to a smaller dead space ventilation as a result of the lower respiratory rates in children anaesthetized with enflurane.     

Postbypass pulmonary artery pressure influences respiratory system compliance after ventricular septal defect closure

It is reported that surgical correction of left-to-right shunt improves respiratory function in paediatric cardiac patients. However, such correction sometimes does not result in an improvement of respiratory compliance. The purpose of this study was to look for factors determining changes in respiratory system compliance (Crs) in patients who underwent closure of ventricular septal defect (VSD closure). In a prospective study, 17 children (< 10 kg) who underwent VSD closure were enrolled. They were divided into two groups, according to postbypass mean pulmonary artery pressure (mPAP). The patients were allocated to Group C if mPAP was < or = 18 mmHg (n=12) and to Group PH if > 18 mmHg (n=5). We compared the ratio of postoperative Crs to preoperative Crs (Cpost/Cpre) between the groups. A multiple occlusion technique was used to measure Crs. The Cpost/Cpre in group C was larger than that in group PH (1.11+/-0.17 vs. 0.81+/-0.12, P<0.01). There was a correlation between postbypass mPAP and Cpost/Cpre (r(s)=0.49, P<0.05), but no correlation was noted between preoperative mPAP, Qp/Qs or Rp/Rs and Cpost/Cpre. We concluded that high postbypass mPAP was associated with a perioperative decrease in Crs after VSD closure.     

Neurogenic pulmonary oedema complicating ventriculoperitoneal shunt revision in a child

The following report emphasizes the potential for neurogenic pulmonary oedema to complicate the postoperative course of a child following ventriculoperitoneal shunt revision. The pathophysiology and therapy of neurogenic pulmonary oedema are reviewed.     

Noninvasive blood pressure measurement in the upper and lower limbs of anaesthetized children

A group of 50 children, aged 5 months to 15 years, and who were undergoing routine surgery under general anaesthesia, were studied to investigate the difference in noninvasive blood pressure readings obtained from inflatable cuffs placed on the upper arm and the lower leg. In contrast to adult data, it was found that the blood pressure measured from the leg in children aged 8 years and under, was significantly lower than that measured from the arm. The leg cuff measurements could not, however, be reliably used to predict arm blood pressure.     

Effect of common airway manoeuvres on upper airway dimensions and clinical signs in anaesthetized, spontaneously breathing children

Chin lift, jaw thrust and these manoeuvres combined with continuouspositive airway pressure (CPAP) can be used to improve the patencyof the upper airway during general anaesthesia. We used videoendoscopy and measurement of stridor to compare the efficacyof these manoeuvres in 24 children (3–10 yr) with adenotonsillarhyperplasia. A bronchofibrescope was passed via the nose whilethe children were breathing spontaneously, to identify (i) theshortest transverse distance between the tonsils during inspirationand during expiration and (ii) the distance from the tip ofthe epiglottis to the posterior pharyngeal wall. Chin lift orjaw thrust lifted the epiglottis and, when combined with CPAP(10 cm H₂O), there was a significant lateral displacement ofthe tonsils. Both chin lift plus CPAP and jaw thrust plus CPAPreduced stridor significantly compared with the unsupportedcondition. In conclusion, in spontaneously breathing childrenwith large tonsils, chin lift plus CPAP is recommended, whereasjaw thrust plus CPAP is no better and may cause post-operativediscomfort. Br J Anaesth 2001; 86: 217–22     

Effects of i.v. metoclopramide, atropine and their combination on gastric insufflation in children anaesthetized with sevoflurane and nitrous oxide

METHODS: To determine effects of i.v. metoclopramide, atropine and their combination on the airway pressures at which gastric insufflation occurs in children, 45 healthy infants and children (ASA I) received an inhalational induction of anaesthesia with sevoflurane, N2O and O2. A blinded observer used a stethoscope to auscultate over the upper abdomen for any air entry. First, proximal airway pressure was slowly increased by closing the pop-off valve of the anaesthesia machine until gas was heard entering the stomach (pop-off point, control measurement). If the peak inspiratory pressure reached 40 cm H2O, the patient was to be excluded from the study. Then, all subjects randomly received i.v. atropine 0.01 mg.kg-1, metoclopramide 0.2 mg.kg-1, or atropine 0.01 mg.kg-1 plus metoclopramide 0.2 mg.kg-1 (n=15 each), and determination of the pop-off point was repeated 5 min later. The stomach was evacuated before each measurement. RESULTS: Atropine significantly decreased the pop-off point [from 21 +/- 3 to 19 +/- 2 cm H2O (mean +/- SD), P < 0.05], while metoclopramide significantly increased the pop-off point (from 20 +/- 3 to 26 +/- 6 cm H2O, P < 0.05). The combination of metoclopramide and atropine did not alter the pop-off point (from 20 +/- 2 to 19 +/- 5 cm H2O). CONCLUSION: Since metoclopramide exerts only mild effect on the pop-off point, cricoid pressure still remains the standard anaesthetic practice to prevent gastric insufflation in children. Prophylactic i.v. metoclopramide may be restricted to, and its clinical usefulness should be determined in, symptomatic patients with gastro-oesophageal reflux.     

Pulmonary gas exchange and ventilation-perfusion relationships during hypocapnia and thoracotomy in anaesthetized dogs

The effects of hypocapnia and thoracotomy, both individually and combined, on pulmonary gas exchange and distribution of ventilationperfusion ratio (V _a /Q) were studied in anesthetized and paralyzed mongrel dogs by the six inert gas elimination technique. Normocapnia (PaCO₂ 35 mmHg) and hypocapnia (PaCO₂ 20 mmHg) were produced sequentially by varying the inspired CO₂ concentration. Thoracotomy was performed at the fourth intercostal space. When ventilation was changed from normocapnia to hypocapnia without thoracotomy, PaO₂ decreased from 160 ± 10 to 147 ± 11 mmHg and Qs/Qt increased from 0.0 ± 0.0 to 0.6 ± 0.7%. However, no change was observed in perfusion distribution following thoracotomy during normocapnia, PaO₂ decreased from 160 ± 10 to 113 ± 15 mmHg together with a shift of perfusion toward the low V _a /Q region. However, no change was observed in Qs/Qt. When ventilation was changed from normocapnia to hypocapnia with thoracotomy, PaO₂ decreased from 113 ± 15 to 98 ± 12 mmHg and Qs/Qt increased from 0.3 ± 0.8 to 3.4 ± 2.0%. After thoracotomy, a shift of perfusion toward the low V _a /Q region was observed, which was probably responsible for the decrease in PaO₂. The decrease in PaO₂ during hypocapnia was due to an increase in the true shunt rather than the developement of low V _a /Q region. Hypocapnia combined with thoracotomy produced a further reduction of PaO₂ and a greater increase in Qs/Qt.     

Differential Ventilation and Selective PEEP During Anaesthesia in the Lateral Decubitus Posture

The potential of differential ventilation (DV) with selective positive end-expiratory pressure (PEEP) has been tested versus conventional ventilation with and without general PEEP. Gas exchange and central haemodynamics were studied in 15 subjects with no clinical or radiological signs of pulmonary disease. The rationale of the method was to ensure ventilation of the well-perfused dependent lung and to counteract airway closure within that lung. The subjects were intubated with a double-lumen catheter prior to scheduled abdominal surgery. During general anaesthesia in the lateral posture, they were given DV. The mean inspired oxygen fraction was 0.32. Fifty per cent ("even" tidal volume (VT) distribution) or 70% ("inverted" VT distribution) of the inspired volume was administered to the dependent lung. Two synchronized ventilators were used. In eight subjects DV was also combined with PEEP applied solely to the dependent lung (selective PEEP). The major findings were that DV with even VT distribution reduced venous admixture by 26% ( P <0.05) and the alveolo-arterial oxygen tension gradient (P(A-a)o2) by 30% ( P <0.05) in comparison with conventional ventilation in the lateral position. The addition of selective PEEP further reduced the P(A-a)o2 by 13%. P(A-a)o2 was consequently 43% lower than during conventional ventilation without PEEP in the lateral posture ( P <0.01). Selective PEEP also had less impact on cardiac output than general PEEP (P<0.05). It is concluded that DV with even distribution of VT and selective PEEP can reduce the P(A-a)o2 in anaesthetized lung-healthy subjects in the lateral position.     

The effect of insufflation pressure on pulmonary mechanics in infants during laparoscopic surgical procedures

BACKGROUND: Few studies have reported objective measurements of pulmonary changes under controlled conditions in infants undergoing laparoscopic procedures. We objectively measured the pulmonary effects of laparoscopically-induced pneumoperitoneum in infants less than 1 year of age undergoing surgical procedures under general anaesthesia. METHODS: Nineteen ASA I-II patients less than 1 year of age were enrolled in this direct observational study. Anaesthetic technique included inhalation induction using sevoflurane/O2/air and neuromuscular blockade. Infants were ventilated using 10-15 ml.kg-1 tidal volume at a respiratory rate sufficient to achieve normocarbia [PECO2 4.6-5.8 kPa (35-45 mmHg)]. Opioids and regional anaesthesia techniques were used when appropriate. Peak inspiratory pressure (PIP), expiratory tidal volume (Vt), endtidal carbon dioxide concentration (PECO2) and dynamic compliance (COMPdyn) were recorded at baseline, 5, 10 mmHg and maximal insufflation pressure (Pmax). Pmax was limited to 12 mmHg for infants <5 kg, 15 mmHg for infants >5 kg. At steady state Pmax, ventilator changes were implemented to restore Vt and PECO2 to within 10% of baseline. Each patient served as his own control. RESULTS: At Pmax, average PIP increased 18%, average Vt decreased 33%, average PECO2 concentration increased 13%, average COMPdyn decreased 48%; O2 saturation fell in 41% of patients. Twenty ventilator adjustments were required; one patient experienced no changes in measured pulmonary mechanics, requiring no ventilator changes. CONCLUSIONS: Pulmonary mechanics in infants change significantly during laparoscopic CO2 pneumoperitoneum; the magnitude of change correlates directly with intraperitoneal pressure. Greater than 90% of infants required at least one ventilatory intervention to restore baseline Vt and PECO2.     

Drive and timing components of respiration in young children following induction of anaesthesia with halo-thane or ketamine

Timing and drive components of respiration were studied in 18 young children following induction of anaesthesia with ketamine and were compared with results from ten children following induction of anaesthesia with halothane. During one minute of quiet breathing, signals from a pneumotachograph attached to the anaesthetic mask were analysed for tidal volume (Vt), respiratory frequency (f), minute volume (Ve), inspiratory and expiratory times (Ti, Te) and flow pattern. Following induction of anaesthesia with ketamine, children breathed more slowly and deeply than children receiving halothane, but there was no significant difference in Ve or in Vt/Ti, suggesting that respiratory drive was similar in the two groups of children. In the children receiving ketamine, Ti was more than twice as long, and thus the ratio Ti/Te was significantly increased, in comparison with the group receiving halothane. In addition to the prolonged Ti in the children induced with ketamine, there was a more rapid increase in volume in early inspiration than in late inspiration, which is an apneustic breathing pattern. There was a slower decrease in volume in early expiration, with occasional early expiratory breath holding lasting up to three seconds, in the ketamine-induced children. The unique breathing pattern demonstrated with ketamine, consisting of large Vt, increased Ti/Te ratio, apneustic inspiratory pattern, and expiratory braking, contributed to an increased mean lung volume above functional residual capacity, of 2.40 ml.kg-1 body weight, in comparison to 1.27 ml.kg-1 in the children receiving halothane.     

Effect of thoracic epidural anaesthesia on ventilation= perfusion distribution and intrathoracic blood volume before and after induction of general anaesthesia

Background: Gas exchange is impaired during general anaesthesia due to development of shunt and ventilation-perfusion mismatching. Thoracic epidural anaesthesia (TEA) may affect the mechanics of the respiratory system, intrathoracic blood volume and possibly ventilation-perfusion (V_A/Q) distribution during general anaesthesia.
Methods: V_A/Q relationships were analyzed in 24 patients undergoing major abdominal surgery. Intrapulmonary shunt (Qs/ Q_T), perfusion of "low" V_A/Q areas, ventilation of "high V_A/ regions, dead space ventilation and mean distribution of ventilation and perfusion were calculated from the retention/excretion data of six inert gases. Intrathoracic blood volume (ITBV) and pulmonary blood volume (PBV) were determined with a double indicator technique. Recordings were made before and after administration of 8.5±1.5 ml bupivacaine 0.5% (n=12) or 8.3±1.8 ml placebo (n=12) into a thoracic epidural catheter and after induction of general anaesthesia.
Results: Before TEA, QS/QT was normal in the bupivacaine group (222%) and the placebo group (23%). TEA covering the dermatomal segments T 12 to T 4 had no effect on V_A/Q relationships, ITBV and PBV. After induction of general anaesthesia S/T increased to 84% (bupivacaine group, P < 0.05) and to 72% (placebo group, P < 0.05). ITBV and PBV decreased significantly to the same extent in the bupivacaine group and the placebo group.
Conclusions: TEA has no effect on V_A/Q distribution, gas exchange and intrathoracic blood volume in the awake state and does not influence development of S/T and V_A/Q inequality after induction of general anaesthesia.