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SCHOLARLY PAPER

Effects of Chest Physiotherapy for Children in Intensive Care after Surgery Juliette Hussey

Key Words Chest physiotherapy, paediatric intensive care.

Summary Due to differences in developing respiratory anatomy and physiology, children may be more at risk of post-operative pulmonary complications than adults. While the aims of chest physiotherapy for children are similar to those for adults, clinical practice may differ somewhat. Positioning, percussion and vibrations, manual hyperinftation and suctioning are described in relation to infants and children.

Introduction After cardiac surgery, major abdominal surgery, neurosurgery and other major surgery, infants and children often need to be nursed in intensive care (fig 1). Where possible, children and parents should be seen pre-operatively, to build up a relationship, assess the children’s respiratory status and teach deep breathing exercises and coughing.

The aims of chest physiotherapy after surgery are similar in adults and children, ie to maintain alveolar expansion, prevent respiratory complications and achieve optimum ventilatiodperfusion matching. However, children are more pre-disposed to respiratory failure owing to their respiratory physiology (James, 1991) and, because of the many anatomical and physiological differences between adults and children, their specific treatment requirements differ (Webber, 1988).

Some Anatomical and Physiological Differences between Adults and Children Various anatomical and physiological factors contribute to the vulnerability of infants and children. Some of the most important for physiotherapy are: 1. In children under two years of age the ribs are horizontal and lack the bucket handle movement. The intercostal muscles are poorly developed and therefore the young child relies almost completely on the diaphragm for respiration (Webber, 1988). As the diaphragm is so important for infant ventilation, anything which impairs its function (eg phrenic nerve palsy after cardiac surgery) may cause respiratory deficiency (James, 1991).

2. Young children have a compliant chest wall but less compliant lungs (Mackenzie, 1989). The floppy chest wall of infants does not counteract the elastic recoil of the lungs, resulting in a low functional residual capacity (FRC). Factors which further reduce the FRC, such as anaesthesia, will therefore cause an increase in the work of breathing (Craig, 1981). 3. Hatch and Sumner (1986) reported that the resistance of the diaphragm to fatigue depends on the amount of high oxidative type I muscle fibres (strength and endurance fibres) and that whereas an adult diaphragm has 55% of these fibres, the diaphragm of a term baby has 25% and that of a premature baby of less than 30 weeks gestation has only 10%. This explains why children are less well able to withstand respiratory distress.

Fig 1: Baby after cardlac surgery in intensive care

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4. Collateral ventilation is not well established in infancy and therefore atelectasis is more likely to occur with respiratory infections. The cilia are immature, especially in pre-term babies, so secretions may accumulate (Kendall, 1987). Ciliary function is further reduced by anaesthesia, intubation and certain drugs (Gamsu et al, 1976).

5. Infants have a higher metabolic rate for oxygen consumption than adults and, therefore, may develop hypoxaemia more rapidly (Kendall, 1987).

6. Children have the reverse of the gravitational distribution of ventilation seen in adults due to differences in lung mechanics and diaphragmatic function (Davies et al, 1985). It has been shown that children with unilateral lung pathology have a higher arterial oxygen tension when their unaffected (‘good’) lung is uppermost and therefore should be nursed with their affected lung dependent to achieve optimum ventilatiodperfusion matching (Davies et al, 1985). The effect of gravity on perfusion is similar in children and adults and this ‘imbalance’ in children may have clinical importance (Bhuyan et al, 1989).

Post-operative Lung Changes Pulmonary complications can significantly contribute to the morbidity and mortality of paediatric surgical operations (Rowe et al, 1973). Respiratory insufficiency may develop post-operatively because of increased metabolic demands and reduced lung function (Fairshter and Williams, 1989). Lung and chest wall compliance diminish and the net effect is a reduction in FRC. When the FRC is reduced, small airways which need transmitted positive transmural pressure to keep them open (as they lack cartilaginous support) become narrow or closed, leading to low ventilatiodperfusion relationships thus causing hypoxaemia (Craig, 1981). Craig (1981) also reported that failure of an airway to re-open will lead to total collapse of the lung unit served by that airway. Under normal circumstances, phagocytosis, ciliary activity and coughing provide adequate airway clearance. However, these defence mechanisms may become impaired by anaesthetic drugs, intubation, hyperoxic mixtures and dry anaesthetic gases. Impairment of mucus transport is considered significant to the development of post-operative atelectasis. Post-operative immobilisation, lack of deep breathing and coughing and narcotic analgesia all insult the lungs’ clearance mechanism (Gamsu et al, 1987).

Aims of Chest Physiotherapy and its Indications in Children after Surgery The indications for chest physiotherapy in the post- operative period are similar in adults and children - lobar collapse and retention of secretions (Kiriloff et al, 1985) Chest physiotherapy in the immediate post- operative period has four independent aims: 1. To prevent and treat atelectasis. 2. To improve oxygenation. 3. To assist the removal of excess secretions. 4. To facilitate early extubation.

Atelectasis becomes clinically important when there is a large alveolar-arterial oxygen gradient. If arterial oxygenation cannot be maintained by increasing the inspired oxygen concentration, the work of breathing is increased, with the risk of precipating cardiorespiratory failure (Gale et al, 1979). Cochrane et a1 (1977) showed that removal of bronchial secretions reduces airflow obstruction. Changes in total lung and thorax compliance after chest physiotherapy suggest that the improvement in intrapulmonary shunt is a result of clearance of secretions from smaller airways (Lyle et al, 1979). Early extubation has many advantages, including making it easier to move patients. If radiographs show loss of lung volume, this should be treated promptly, as atelectatic areas may become infected before they are re-inflated, and pneumonia may result (Bartlett et al, 1973).

General Ventilatory Management of Children The anatomical and physiological respirahry differences between adults and children influence approach to general management of their respiratory state. In children the peripheral airways are small and offer high resistance. The lack of connective tissue support for the smaller airways may lead to a closing volume exceeding FRC which predisposes to atelectasis and ventilatiodpervasion mismatch. For this reason, the use of continuous positive airway pressure (CPAP) or positive end expiratory pressure (PEEP) is indicated in all children under six years who are intubated (James, 1991). CPAP and PEEP cause an increase in transpulmonary pressure, preventing airway closure by maintaining alveolar distension at the end of expiration, which results in an increase in FRC (Anderson et al, 1979). As the basal metabolic rate is higher in children than adults, minute volume is higher and ventilator rates of 20-40 are used (James, 1991). Small tidal volumes must be delivered at fast rates without generating high airway pressures. After extubation it is often useful in children under six months to provide CPAP for about 24 hours. This can be achieved by attaching to the ventilator a nasotracheal tube cut to 3 cm to 5 cm long, thus providing nasopharyngeal CPAP (James, 1991). The narrowest part of an infant’s airway is the subglottic area. Non-cuffed tracheal tubes which allow a leak around the tube are used, in order to reduce the risk of pressure-induced subglottic stenosis.

Chest Physiotherapy in Children after Surgery Chest physiotherapy in children after surgery may involve positioning, percussion and vibrations, manual hyperinflation (bag squeezing), suctioning, deep breathing and encouragement in coughing and mobilisation.

Positioning Body position directly effects ventilatiodperfusion matching and arterial oxygen levels (Dean, 1985). Atelectasis and mucus pooling tend to occur in the posterior lung bases when the patient adopts a supine posture for long periods of time. Turning patients regularly ensures that no lung region remains

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dependent for long periods and the uppermost lung is periodically stretched and drained.

Positioning children is therefore frequently part of physiotherapy. As already stated, young children ventilate their uppermost lung preferentially but physiotherapists may wish to place the ‘bad’ lung higher in order to drain secretions and to open up atelectatic areas. This may cause oxygen saturation to drop unless an increased fraction of inspired oxygen is given. However, in order to optimise gas exchange young children with uni-lateral lung disease should be nursed with their ‘good’ lung uppermost (Davies et al, 1985).

The prone position (fig 2) has been shown to increase tidal volume and minute volume with a 25% increase in arterial oxygen tension in babies turned from supine into the prone position (Mackenzie et al, 1989). It may be difficult to place children in prone immediately after surgery because of cardiovascular instability, pain, lines and drains but, if indicated, it should be attempted as soon as possible.

drainage and percussion, whereas there was no change in arterial oxygen tension following postural drainage alone. This led to a belief that the ‘narrow airways of premature infants may not allow secretions to drain without the assistance of percussion and vibrations’ (Finer and Boyd, 1978). Therefore, based on limited research, it appears that percussion (fig 3) and vibration (fig 4) are effective in mobilising retained secretions and enhancing peripheral airway clearance, particularly in paediatric patients with acute lung pathology.

Fig 3: Percussion

Fig 2: Child in prone position

Percussion and Vibrations Percussion and vibrations are thought to facilitate both large and small airway clearance by creating an energy wave which advances secretions centrally so that they can be expectorated or removed by suction (Mackenzie et al, 1989). In infants, acute lung collapse unresponsive to other methods of treatment has been reported to repond to chest percussion by re-inflation (Mellins, 1974). Percussion and vibration in neonates have been shown to lead to increased secretion removal and may improve oxygenation (Etches and Scott, 1978; Finer and Boyd, 1978).

Clinically these techniques are rarely used as a treatment in themselves but as adjuncts to postural drainage, positioning, breathing exercises, coughing and suctioning. This has also been the case in most clinical research, making it difficult to assess the efficacy of each treatment component separately. Fbwe et al (1973) found an improved clearance of dye radiologically in piglets who received mechanical vibration. Finer and Boyd (1978) in a study on neonates recovering from respiratory distress found that there was an increase in arterial oxygen tension following postural

Fig 4: Vibration

Manual Hyperinflation It is believed that manual hyperinflation or ‘bag squeezing’ expands the lungs fully and loosens secretions in ventilated patients (Mackenzie et al, 1989). The deep inflation recruits alveoli by expanding those unused during the tidal ventilation of IPPV, and so helps to prevent and reverse atelectasis. The fast expiratory flow rate generated can be enhanced by vibration causing secretions to loosen and move toward the main airways (Cash, 1987). Theoretically, bag squeezing may cause a decrease in venous return secondary to the increase in intrathoracic pressure. Gormenzano and Branthwaite (1972) found in adults with unstable cardiovascular states that an increase in intrathoracic pressure caused a decrease in arterial oxygen tension and theorised that this was due to a decrease in cardiac output.

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In neonates or young infants, manual hyperinflation should be carried out only with extreme care. Peak inspiratory pressures should be measured using a pressure manometer, because their delicate lung tissue can easily be damaged. Due to the possible changes in cardiac output with deep inflations, it is physiotherapy practice in The Hospital for Sick Children, Great Ormond Street, to alternate one hyperinflation of 20% above the ventilator inspiratory pressure with three or four tidal volume breaths. Neonates or young children may already be receiving maximum end inspiratory pressure through a ventilator and any increase in pressure may result in barotrauma to delicate lung tissue, possibly leading to pneumo- thorax.

Suctioning Suctioning ventilated patients is necessary to maintain a patent airway, but is often accompanied by undesired physiological effects - it can cause mucosal trauma, hypoxia, bradycardia and atelectasis (Young, 1984a). Mucosal trauma occurs from the suction catheter adhering to the tracheal mucosa during continuous negative pressure. If the resulting trauma causes even a small amount of oedema the diameter of the trachea is narrowed and there may be a significant increase in the work of breathing. When mucosal tissue repairs, it does so by formation of granulation and fibrous tissue. Hypoxia has been documented as an adverse effect of airway suction in a multitude of studies (Young, 1984a, b; Crummer-Feaster et al, 1985; Fox et al, 1978; Simbruner et al, 1981; Pierce and Piazza, 1987; Fell and Cheney, 1971; Kerem et al, 1990; Durand et al, 1989). Removing a patient from the oxygen source and using too large a catheter are probably the most significant contributing factors. The catheter size should not be greater than half the size of the airway and a negative pressure of less than 120 mm Hg should be used (Young, 1984). Suctioning patients on mechanical ventilation should be kept below 30 seconds (15 sec for neonates) and adequate time must be allowed between suction passes for patients to re-oxygenate (Fell and Cheney, 1971). Bradycardia may occur in a child with suctioning and is thought to be secondary to hypoxia or vagal stimulation. Oxygen desaturation and bradycardia are potentially detrimental in patients with poor cardiac output.

Effects of Chest Physiotherapy on Oxygenation While chest physiotherapy is indicated in acutely ill patients with large amounts of secretions and/or lobar atelectasis, it may be associated with hypoxaemia (Kiriloff et ul, 1985). Several theories that may explain the association between hypoxaemia and chest physiotherapy: 1. An increase in intrathoracic pressure causing a decrease in cardiac output. 2. An increase in shunt effect. 3. An increase in oxygen consumption. 4. Suctioning.

An increase in intrathoracic pressure can be caused by manual hyperinflation which frequently forms part of a chest physiotherapy treatment. Laws and McIntyre (1969) and Gormenzano and Branthwaite (1972) found that large increases in intrathoracic pressure could cause a decrease in cardiac output and therefore a decrease in arterial tension.

Positioning forms an integral part of chest physiotherapy and it is difficult to separate out its effect. Because children ventilate their uppermost lung preferentially, some positions of drainage may cause a decrease in arterial oxygen tension. If chest physiotherapy clears secretions from the airways and opens up previously non- communicating or closed alveoli, it would be reasonable to expect some improvement in expiratory flow rates and lungkhorax compliance (Tyler, 1982). Mackenzie et a1 (1978) verified this in their study on critically ill post- trauma patients. However, incomplete clearance of secretions that have moved centrally to larger airways during chest physiotherapy could lead to a decrease in lungkhorax compliance and a decrease in arterial oxygen tension.

As treatment involves turning, handling and coughing, it is probable that it causes some increase in oxygen consumption (Tyler, 1982). This has been supported by Klein et a1 (1988) who found increases in oxygen consumption and carbon dioxide production during chest physiotherapy in adults after surgery. Neonates when handled or stressed may respond by increasing their energy expenditure, often a t the cost of adequate oxygenation (Langer, 1990). Handling in itself, therefore, can cause a fall in arterial oxygen tension and clustering of care may be followed by a prolonged period of hypoxia. This is very important for physiotherapists. Rather than attempting to reposition patients, manual techniques and suction should be carried out sequentially, as they may need time to recover from position changes alone.

Hypoxia is well recognised as a complication of suctioning. Kerem et a1 (1990) found in their study on paediatric intensive care patients that suctioning alone caused a fall in oxygen saturation of 4.4% and hypoxic levels were seen in some patients. These falls were prevented by pre-suction oxygenation of 100% oxygen through the ventilator for one minute before suctioning and hyperinflation with 100% oxygen performed between suction passes. Much research has been done into different ways of preventing the hypoxaemia associated with suctioning, and Riegal and Forshee (1985) state that some method of pre-oxygenation is necessary.

It must be remembered that excessive handling, especially of low-birth-weight infants, can cause hypoxaemia. Unnecessary handling is costly in terms of oxygen consumption and work of breathing and these cause arterial oxygen tension to fall. Chest physio- therapy should be scheduled around other procedures SO that clustering of care is avoided (Gardner Cole et al, 1990). Sick, unstable infants are unable to tolerate lengthy, vigorous physiotherapy sessions, so short and perhaps frequent treatments may be necessary. As with adult post-operative patients, it is essential that children have adequate analgesia before chest physio- therapy.

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Conclusion Physiotherapy for chi ldren in intensive care must always be preceded by a thorough assessment and should never be routine. Close communication with medical a n d nurs ing staff w i l l he lp t o avoid unnecessary handling. Chi ldren should be closely observed during chest physiotherapy for any change in vital signs or indications o f resp i ra to ry distress. C a r e f u l assessment a n d management wi l l ensure t h a t chest physiotherapy is beneficial and effective ra ther t h a n hazardous.

Author

Juliette M Hussey MSc MCSP is a senior physiotherapist in the cardiothoracic unit, Hospital for Sick Children, Great Ormond Street, London.

Address for Correspondence

Miss J M Hussey MSc MCSP, Physiotherapy Department, Hospital for Sick Children, Great Ormond Street, London WClN 3JH.

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