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Noninvasive Positive Pressure Ventilation in burns
Burns 28 (2002) 795–801
Noninvasive Positive Pressure Ventilation in burns S.T. Smailes St. Andrew’s Centre for Plastic Surgery and Burns, Broomfield Hospital, Broomfield, Chelmsford CM1 7ET, UK Accepted 2 August 2002
Abstract Objective: Acute respiratory failure is a common complication of the severely burn-injured patient. Endotracheal intubation and mechanical ventilation is associated with a high rate of complications. Noninvasive Positive Pressure Ventilation (NIPPV) has been shown to be as effective as conventional ventilation in improving gas exchange and is associated with fewer complications with patients in acute hypercapnic and hypoxaemic respiratory failure. We report our experience with NIPPV in 30 burn patients. Method: The records of all burn patients from 1998 to 2000, where NIPPV was used as part of their management at the St. Andrew’s Centre for Plastic Surgery and Burns, were reviewed. Results: Mean age was 47.56 years (range 12–81). Nine patients were female. Mean burn size was 24.4% total body surface area (TBSA) (range 3–54). Inhalation injury was confirmed in eight cases. A positive diagnosis of pneumonia was made in 29 patients. The mean PaO2 /FiO2 ratio prior to institution of NIPPV was 28.98 Kpa (range 8.75–52). Intermittent Positive Pressure Breathing (IPPB) was the most common ventilatory mode employed (25 patients) and the face mask was the most used interface (18 cases). Twenty-two patients (74%) avoided endotracheal intubation and their respiratory function continued to improve after NIPPV was discontinued. One patient (3%) died and seven patients (23%) were reintubated. Three out of the seven were electively reintubated for burns surgery. Conclusion: In burn-injured patients with acute respiratory failure, NIPPV appears to be effective in supporting respiratory function such that endotracheal intubation can be avoided in most cases. © 2002 Elsevier Science Ltd and ISBI. All rights reserved. Keywords: Acute respiratory failure; Burns; Endotracheal intubation; Complications; Noninvasive Positive Pressure Ventilation
1. Introduction Pulmonary dysfunction is common following a burn injury and the aetiology is multi-faceted. Respiratory complications may result from smoke inhalation, direct airway burn from superheated smoke particles, the effect of the systemic inflammatory response to a burn or a combination of these factors. Airway obstruction is produced by the presence of mucosal casts, oedema and tenacious secretions. Ventilatory restriction and an increased work of breathing may result from the associated pain and wound tightness of the cutaneous chest burn. Furthermore, the patient may present with inflammatory changes within the lung parenchyma resembling the Acute Respiratory Distress Syndrome (ARDS). This results in capillary leak, widespread atelectasis, consolidation and ventilator dependence. Further respiratory complications arise from the onset of pneumonia, immobility and anaesthesia-induced atelectasis [1–5]. Endotracheal intubation and positive pressure ventilation are commonly used to prevent or treat hypoxia and to secure a patent airway in the burn-injured patient [2,4]. However, the presence of the endotracheal tube introduces
problems by bypassing the protective mechanisms of the upper airway, increasing the incidence of nosocomial pneumonia, damage to the airway resulting in tracheal stenosis [6,7] and secondary complications associated with invasive monitoring and sedation [8]. Noninvasive Positive Pressure Ventilation (NIPPV) refers to techniques of augmenting alveolar ventilation without an endotracheal airway [9]. NIPPV has been used with success in the treatment of chronic respiratory failure in patients with neuromuscular diseases and chest wall disorders [10,11]. There is also a large body of literature including five randomised studies that support the efficacy and advantages of NIPPV with patients in hypercapnic acute respiratory failure and hypoxaemic acute respiratory failure [12–16]. However, the outcome of NIPPV with burn patients is less well documented. The purpose of this article is to report on our initial experience with NIPPV in a series of burn-injured patients. NIPPV was used in patients who showed signs of deteriorating respiratory function in an attempt to avoid endotracheal intubation or reintubation. To our knowledge, this is the first report of the use of NIPPV with this group of patients.
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2. Materials and methods The medical records of all patients treated with NIPPV as part of their burns management at the St. Andrew’s Centre between 1 April 1998 and 30 April 2000 were reviewed. In each case the patient’s age, sex, total body surface area (TBSA) burn size and whether burns surgery was performed were recorded. Inhalation injury was documented based on history, physical findings and serial fibre-optic bronchoscopy in all cases. The requirement for endotracheal intubation and ventilation as part of the burns management and the ratio of the PaO2 to the FiO2 (PaO2 /FiO2 ) for each patient immediately prior to the institution of NIPPV was noted. The cause of respiratory failure, NIPPV interface, ventilator mode and pressures and whether intubation/reintubation was avoided was also recorded. The diagnosis of pneumonia was made on the basis of the presence of hyperthermia (>38.2 ◦ C), leukocytosis (WCC >15×109 /l), positive sputum cultures and radiographic identification of infiltrates [17]. NIPPV was delivered using three different ventilators. The Drager CF800 ventilator (Drager Medical, Drager Limited) was used to provide Continuous Positive Airways Pressure (CPAP). CPAP prevents or helps to reopen collapsed alveoli and atelectatic lung zones and it is often used to facilitate weaning from mechanical ventilation [18]. The Bilevel Positive Airways Pressure (BiPAP) Vision ventilator (Respironics) was used to deliver CPAP and Bilevel Positive Airways Pressure ventilation. The spontaneous/timed mode on the BiPAP Vision ventilator provides two ventilatory pressures: the Inspiratory Positive Airways Pressure (IPAP) and the Expiratory Positive Airways Pressure (EPAP). The IPAP minus the EPAP corresponds to pressure support ventilation and the EPAP is equal to Positive End Expiratory Pressure (PEEP) on a mechanical ventilator. Pressure support ventilation has been shown to improve tidal volume, gas exchange, respiratory rate and diaphragmatic activity in proportion to the amount of pressure supplied [19]. The Bird 7A Respirator was used to deliver Intermittent Positive Pressure Breathing (IPPB). IPPB is the maintenance of a positive airway pressure throughout inspiration, with airway pressure returning to atmospheric during expiration. This mode of ventilation provides pressure support to the spontaneously breathing patient and is a useful adjunct to chest physiotherapy treatment. Its effects are as those for pressure support and it is administered intermittently to the patient [20].
bronchial secretions. Patients with extensive and deep burns to the face or facial trauma were excluded for mask ventilation. Evidence of acute respiratory failure had to be exhibited by the patient and this was defined as acute hypoxaemia where the PaO2 /FiO2 ratio was ≤40 Kpa. A PaO2 /FiO2 of ≤40 Kpa forms part of the definition for an acute lung injury (ALI) [21]. NIPPV was used “prophylactically” in four patients (PaO2 /FiO2 >40 Kpa) in an attempt to prevent further respiratory deterioration and endotracheal intubation. Three of these patients showed restrictive ventilatory problems due to the pain caused by abdominal and chest wounds, donor sites and autografts. One patient received NIPPV because he was identified as being at risk of developing respiratory complications after sustaining fractured ribs, a haemopneumothorax and lung contusions. The PaO2 /FiO2 ratio at which mechanical ventilation is indicated is 27.5 Kpa (PaO2 below 11 Kpa on FiO2 0.4) [22]. NIPPV was instituted in all patients fulfilling the selection criteria in an attempt to avoid endotracheal intubation or reintubation. Eight patients, who received NIPPV, had sustained inhalation injuries. In these cases endotracheal intubation was not necessary to protect the airway, i.e. airway oedema had resolved and NIPPV was used to prevent reintubation, or there was little or no evidence of oedema post-injury. Six patients had burns to the face, in these cases mask ventilation could not be used unless the wounds were largely healed. This was because of the ineffective seal produced by applying the mask over dressings and the discomfort for the patient as a firm fitting is essential for ventilation. A mouthpiece was used where mask ventilation was contraindicated. The complications with using NIPPV include skin pressure lesions, facial pain, dry nose, eye irritation, discomfort, poor sleep, mask leakage and gastric distension. The risk of many of these problems occurring was minimised by using the correct mask size, silicone gel masks and by paying close attention to the fitting of the headgear. Significant mask leakage was tolerated by the BiPAP Vision ventilator which continued to deliver ventilation even in patients who did not achieve an optimal mask fit. All patients had a small pressure dressing applied to the bridge of the nose to reduce the risk of pressure sores. Gastric distension was successfully avoided by the placement of nasogastric tubes prior to the institution of NIPPV and by regular decompression of the stomach. Nosocomial pneumonia, thromboembolic disorders and gastrointestinal disorders also occur in patients treated with NIPPV but with a lower incidence than that with invasive ventilation [23].
2.1. Institution of NIPPV 2.2. Training of personnel The criteria for selecting patients for NIPPV included a combination of all of the following factors. The patient was haemodynamically stable and their level of consciousness was such that they were alert and cooperative with their treatment. There had to be no need for endotracheal intubation to protect the airway or to remove excessive tracheo-
Before introducing this new technique of ventilatory support to the burns intensive care unit, all nursing and medical staff received a formal 1 h training session in which explanations were given about the use of the ventilators. The initial setting up of ventilation on the patients was done by
S.T. Smailes / Burns 28 (2002) 795–801
the consultant anaesthetist and clinical specialist physiotherapist with the nursing staff on duty in attendance. Informal teaching sessions at the bedside with all intensive care nurses were provided on a daily basis until all staff had been trained.
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Weaning was based on clinical findings and not as part of an established research protocol. On discontinuation of NIPPV, supplemental humidified oxygen was provided and physiotherapy to encourage patient mobilisation and expectoration continued.
2.3. Application of NIPPV The patient was positioned sitting up in bed with the head inclined to approximately 45◦ . A small pressure dressing was applied to the bridge of the nose and the patient was measured so that the correct size mask was selected. The ventilator was switched on, the circuit was attached and the alarms were set and silenced. As the patient was acclimatising to the sounds produced by the ventilator, a full explanation about the modality was given and reassurance was provided. The mask was then offered to the patient and, where possible, the patient assisted with the putting on of the mask to achieve maximum comfort. The pressures set on the ventilator were low initially (CPAP = 2 cm H2 O, pressure support = 5 cm H2 O). When the patient was comfortable with the ventilator the headgear was applied to ensure a firm but not tight fitting, to check this two fingers could be placed beneath the straps. The pressures were titrated upwards according to the patient’s tolerance and arterial blood gas results (the maximum pressures used were CPAP = 10 cm H2 O, pressure support = 20 cm H2 O). A member of staff stayed with the patient all of the time initially. Some patients, once established on NIPPV, could be nursed less intensively (these patients were given a call button). Most patients were able to remove their masks for a few minutes for talking and in some cases to drink small amounts of water. All patients received chest physiotherapy whilst on NIPPV, to assist with expectoration of secretions and reversal of atelectasis, twice daily and on call treatment was required in some cases. IPPB was administered periodically to the patients, in contrast to CPAP and BiPAP ventilation. It was used every 2 h for 15-min periods and also for chest physiotherapy sessions for most patients. A saline nebuliser was included in the circuit and, if prescribed, a bronchodilator was given during these periods. The patients were positioned in the same way as for CPAP and BiPAP ventilation or, if indicated, in a postural drainage position for chest physiotherapy. 2.4. Weaning and discontinuation of NIPPV NIPPV was to be discontinued in those patients who showed signs of haemodynamic instability, poor mask tolerance, persistent poor gas exchange and in those who required endotracheal intubation to remove excessive secretions or protect the airways. Weaning was commenced following improvements in gaseous exchange such that the PaO2 /FiO2 ratio no longer fulfilled the selection criteria for NIPPV. The amount of presssure support was lowered or the patient was allowed “NIPPV free” periods which were gradually lengthened.
3. Results Between 1 April 1998 and 30 April 2000, 30 patients were treated with NIPPV as part of their burn management at the St. Andrew’s Centre for Plastic Surgery and Burns. They all received routine burn management according to the unit’s protocols prior to the institution of NIPPV. Table 1 shows the baseline characteristics of the patients. There was a wide age range (12–81 years) and also a large variation in the TBSA burn size (%). The aetiologies of the injuries were thermal (scalds, flames), electrical and frictional in nature; four of the cases were self-inflicted. Inhalation injury, diagnosed at fibre-optic bronchoscopy, was present in eight patients and six patients sustained burns to the face. Most of the group (24 patients) underwent early excision of deep partial thickness and full thickness burns. Wound closure was achieved either temporarily with human cryopreserved cadaveric allograft or permanently with split thickness autografts. Twenty-one of the patients required endotracheal intubation and mechanical ventilation prior to NIPPV use as part of their burn management for a period of between 1 and 22 days. Table 2 shows the pre-morbid conditions of the patients. Three patients were known to local psychiatric services before their burn injury. Two patients who had been diagnosed with chronic obstructive pulmonary disease were receiving ongoing inhaled medication and the two patients who had been treated for asthma did not require regular inhalers. The additional injuries sustained by the patients at the time of the burn injury are shown in Table 3. Treatment for these injuries was on site at Broomfield Hospital. As Table 4 illustrates, the diagnosis of pneumonia was made in 29 cases, this being the most common cause of Table 1 Demographics and clinical course before NIPPV institution Variable
Data
Number of episodes Age (mean year) Female/male Extent of burn (mean %TBSA) Facial burns Inhalation injury Burns surgery Conservative wound therapy Intubated and ventilateda Ventilation days (mean)
30 47.56 (range 12–81) 9/21 24.4 (range 3–54) 6 8 24 6 21 5.6 (range 1–22)
a
Not including elective intubation for surgical procedures.
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Table 2 Pre-morbid conditions of the patients
Table 4 The cause of acute respiratory failure
Medical condition/surgery
Patients
Cause
Patients
Angina Asthma Carcinoma of the prostate Chronic obstructive pulmonary disease Confusion CVA Dementia Epilepsy Glaucoma Hypertension Kyphoscoliosis Left-ventricular failure Meningitis Nocturia Schizophrenia Oophorectomy
2 2 1 2 1 1 1 1 1 3 1 1 1 1 2 1
Upper airway oedema Pneumonia Bronchospasm Pulmonary contusions Pulmonary abscesses
1 29 4 1 1
Table 3 Additional injuries sustained by the group Nature of injury
Patients
Cervical spine injury Head injury Haemopneumothorax Rib fractures Extensor tendon rupture Limb fractures
1 1 1 1 1 1
respiratory deterioration. In some cases, although pneumonia was the primary diagnosis, another respiratory pathology was deemed to be contributing to the acute respiratory failure exhibited by the patient.
The PaO2 /FiO2 ratio of the patients immediately prior to NIPPV institution can be seen in Fig. 1. The mean PaO2 / FiO2 ratio was 28.98 Kpa (range 8.75–52 Kpa). Twenty-six patients had a PaO2 /FiO2 ≤40 Kpa which satisfied part of our selection criteria for NIPPV use and forms part of the definition for an acute lung injury. Table 5 indicates that IPPB was the most commonly used mode of ventilation (25 patients). IPPB was used every 2 h and the patients were always supervised during their treatment. This may have enhanced the patients’ acceptance of ventilation because the nursing staff were present to offer reassurance and to increase motivation. IPPB was also frequently used as an adjunct to chest physiotherapy. Some patients received more than one mode of ventilation and continuous NIPPV was weaned to periodic as patient tolerance and clinical findings allowed. This was done to minimise the risk of complications associated with NIPPV. The face mask was the interface most often used. This was because the firm seal required for ventilation was achieved more easily with this, especially in mouth breathing patients and those with lip burns. Some patients used more than one type of interface to achieve maximum comfort with the ventilation.
Fig. 1. PaO2 /FiO2 ratio immediately before institution of NIPPV.
S.T. Smailes / Burns 28 (2002) 795–801 Table 5 The NIPPV modes and interface used
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Table 8 The patient’s outcome after NIPPV use
Ventilation mode and interface
Patients
Outcome
Patients
Percentage
IPPB IPPB + CPAP IPPB + CPAP + BiPAP IPPB + BiPAP BiPAP BiPAP + CPAP CPAP
13 5 4 3 3 1 1
Intubation/reintubation Self-ventilation Died
7 22 1
23 74 3
Face mask Mouthpiece Nasal mask
18 10 5
only and not as part of an established research protocol. Seven patients (23%) required discontinuation of NIPPV and intubation and mechanical ventilation. This was necessary in four cases due to the onset of sepsis with haemodynamic instability and in three cases for elective burns surgery. One patient died after the decision to discontinue active treatment was made.
Table 6 The duration of NIPPV use NIPPV mode
Ventilation days (mean)
Range (days)
IPPB CPAP BiPAP
4.28 4.14 2.36
1–10 1–11 1–9
Tables 6 and 7 show the duration of NIPPV treatment and the ventilation pressures used. There was a large variation in the number of days that NIPPV was required for the group of patients. It can be seen that for each different mode of ventilation the minimum time of treatment was 1 day and this increased to a maximum of 11 days for CPAP ventilation. NIPPV was used for the longest period of time with a patient who developed cavitating lesions secondary to an inhalation injury. NIPPV was generally well tolerated by the patients, this was possibly because low pressures were used initially until the patient was accustomed to breathing on the ventilator. Only at this point was the pressure titrated upwards to patient tolerance and arterial blood gas results. The pressures shown in Table 7 reflect those used for treatment once the patients were established on NIPPV and prior to weaning. A maximum pressure support of 20 cm H2 O was used for BiPAP ventilation. Higher ventilatory pressures were avoided as they are associated with an increased risk of gastric distension. Intubation/reintubation was successfully avoided in 22 out of the 30 patients (74%) as can be seen in Table 8. All of these patients progressed to self-ventilation status following NIPPV. Weaning from NIPPV was done on clinical findings Table 7 NIPPV mode and pressures used (prior to weaning) NIPPV mode
Pressure (mean) (cm H2 O)
Range (cm H2 O)
BiPAP (IPAP − EPAP)/EPAPa
11.18/6
3–20/5–7
CPAP IPPB
6.79 18.58
5–10 10–20
a
(IPAP − EPAP)/EPAP = pressure support/CPAP.
4. Discussion NIPPV is the treatment of choice for patients in hypercapnic acute respiratory failure in many centres. The role of NIPPV in the treatment of hypoxaemic acute respiratory failure is recognised and becoming more widespread [12–16]. The use of NIPPV with burn-injured patients is, as yet, unclear because little work has been documented. We have reported our initial experience of the use of NIPPV with burn-injured patients at the St. Andrew’s Centre for Plastic Surgery and Burns. The results show that most patients who received NIPPV avoided the need for endotracheal intubation and mechanical ventilation. This is regularly cited in the literature as a successful outcome of NIPPV use [12–16]. The most common cause of acute respiratory failure in the patients was pneumonia. This is consistent with current literature regarding the pathophysiology of the burn injury [1–5]. Furthermore, in one case the pulmonary infection progressed to form cavitating lesions. Most patients (26) showed clear signs of respiratory deterioration prior to NIPPV institution as illustrated by a PaO2 /FiO2 ≤40 Kpa. This level of acute hypoxaemia constitutes part of the definition for an acute lung injury [21]. In the other four cases NIPPV was used ‘prophylactically’ to prevent further respiratory complications. In these patients there were a number of factors contributing to them being ‘at risk’ of developing acute respiratory failure. These included ventilatory restriction caused by the pain and tightness of abdominal and chest burns, autografts and donor sites. The presence of injuries to the thoracic cage or within lung tissue compounded this restriction and introduced problems with sputum retention and airway plugging. One other factor which we have found to increase the risk of the patient developing respiratory complications is frequent general anaesthesia. This is associated with reduced lung volumes and is necessary with a major burn-injured patient to enable wound care and surgical procedures. Also, patients who are immobilised in bed for prolonged periods of time have a reduced functional residual capacity and therefore are more
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likely to develop airway atelectasis. By identifying patients ‘at risk’ of developing respiratory failure by a combination of the above factors and by clinical signs, NIPPV can be instituted early or ‘prophylactically’ to reverse airway closure, enable expectoration of secretions and prevent further respiratory deterioration. This is one role that NIPPV has on our burns unit. We have also found that NIPPV has facilitated earlier weaning of mechanical ventilation and extubation. This has been achieved by introducing BiPAP ventilation to the intubated patient. Once the patient is established on the ventilator, they are extubated and commenced on mask ventilation. By doing this, active rehabilitation can begin earlier. However, the patient must fulfil the selection criteria for NIPPV to ensure a smooth transition from invasive mechanical ventilation to NIPPV and ultimately to self-ventilation. Many of the patients (18) required a full face mask to achieve effective ventilation. This was for two reasons: firstly, patients with burns to the lips were unable to form a seal with the mouthpiece; secondly, patient cooperation with the nasal mask and the mouthpiece was sub-optimal in some cases, possibly due to excessive sedation. This raises the question of the need for further selection criteria for NIPPV with major burn-injured patients. This is because cooperation by the patient is necessary for successful ventilation. The use of NIPPV may be more appropriate for a patient in acute respiratory failure and with a largely closed wound. This is because the need for large doses of analgesics and the frequency of general anaesthesia would be diminished thereby optimising patient cooperation and compliance. Also, once the wound is closed, the patient is less likely to develop sepsis or haemodynamic instability [4]. We have found that cooperation by most patients can be gained by the correct approach of the clinician when first introducing NIPPV. To tightly strap a mask on to an already anxious and dyspnoeic patient and to use high ventilatory pressures will undoubtedly increase discomfort and distress. However, by allowing time for the patient to have trials of breathing on the ventilator at low pressures before applying the head straps to the mask and by offering reassurance, there is likely to be a greater chance of acceptance of NIPPV by the patient. The patients did not experience any major complications related to NIPPV. One patient developed a small area of skin breakdown on the bridge of the nose despite regular skin care and dressings. This wound healed spontaneously when NIPPV was discontinued. Five patients had difficulty sleeping whilst on NIPPV and required night sedation. Three patients from the group were electively reintubated for burns surgery and required mechanical ventilation post-operatively. This situation is not uncommon in the major burn-injured patient and, in this instance, NIPPV has not ‘failed’. A tracheostomy would now be considered for this type of patient at the St. Andrew’s Centre to avoid repeated intubations and enhance patient comfort and airway management.
In conclusion, this experience of the use of NIPPV with burns is that most of the patients avoided the need for endotracheal intubation and progressed to self-ventilating status. There is a need for further research and a multi-centre trial would be appropriate to acquire a larger sample size and a prospective study would enable standardisation of monitoring of the patients.
Acknowledgements I am grateful to the staff of the Burns Intensive Care Unit at the St. Andrew’s Centre for their encouragement, support and day-to-day work. References [1] Beeley J, Clark R. Respiratory problems in fire victims. In: Settle JAD, editor. Principles and practice of burns management. New York: Churchill Livingstone; 1996. p. 117–28. [2] Fitzpatrick J, Cioffi Jr. WG. Diagnosis and treatment of inhalation injury. In: Herndon D, editor. Total burn care. London: Saunders; 1996. p. 184–92. [3] Judkins KC. Inhalation injury. In: Settle JAD, editor. Principles and practice of burns management. New York: Churchill Livingstone; 1996. p. 321–8. [4] Mlcak R, Manuhbai H, Desai MH, Nichols Jr. R. Respiratory care. In: Herndon D, editor. Total burn care. London: Saunders; 1996. p. 193–206. [5] Traber DL, Pollard V. Pathophysiology of inhalation injury. In: Herndon D, editor. Total burn care. London: Saunders; 1996. p. 175–83. [6] Rashkin MC, Davis T. Acute complications of endotracheal intubation. Chest 1986;89:165–7. [7] Stauffer JL, Olson DE, Petty TL. Complications and consequences of endotracheal intubation and tracheotomy. Am J Med 1981;70:65–75. [8] Hinds CJ. Intensive care. London: Balliere Tindall; 1987. p. 29–32, 240. [9] Hill NS. Noninvasive ventilation. Does it work, for whom and how? Am Rev Respir Dis 1993;147:1050–5. [10] Ellis E, Bye P, Bruderer J, Sullivan C. Treatment of respiratory failure during sleep in patients with neuromuscular disease. Am Rev Respir Dis 1987;135:148–52. [11] Ellis ER, Grunstein RR, Chan S, Bye PTP, Sullivan CE. Noninvasive ventilatory support during sleep improves respiratory failure in kyphoscoliosis. Chest 1988;94:811–5. [12] Andersen JB, Olesen KP, Eikard E, Jansen E, Quist J. Periodic continuous positive airways pressure, CPAP, by mask in the treatment of atelectasis. Eur J Respir Dis 1980;61:20–5. [13] Antonelli M, Conti G, Rocco M, et al. A comparison of noninvasive positive-pressure ventilation and conventional mechanical ventilation in patients with acute respiratory failure. New Engl J Med 1998;339:429–35. [14] Bott J, Carroll MP, Conway JH, et al. Randomised controlled trial of nasal ventilation in acute ventilatory failure due to chronic obstructive airways disease. Lancet 1993;341:1555–7. [15] Kramer N, Meyer TJ, Meharg J, Cece RD, Hill NS. Randomized, prospective trial of noninvasive positive pressure ventilation in acute respiratory failure. Am J Respir Crit Care Med 1995;151:1799–806. [16] Plant PK, Owen JL, Elliott MW. Early use of non-invasive ventilation for acute exacerbations of chronic obstructive pulmonary disease on general respiratory wards: a multicentre randomised controlled trial. Lancet 2000;355:1931–5.
S.T. Smailes / Burns 28 (2002) 795–801 [17] Sheridan RL, Pruitt Jr. BA. Complications of burn injury. In: Settle JAD, editor. Principles and practice of burns management. New York: Churchill Livingstone; 1996. p. 426. [18] Romand JA, Suter PM. Continuous positive airway pressure. In: Webb AR, Shapiro MJ, Singer M, Suter PM, editors. Oxford textbook of critical care. Oxford: Oxford Medical Publications; 1999. p. 1311–13. [19] Meduri GU. Non-invasive positive pressure ventilation. In: Webb AR, Shapiro MJ, Singer M, Suter PM, editors. Oxford textbook of critical care. Oxford: Oxford Medical Publications; 1999. p. 1313. [20] Webber BA, Pryor JA. Physiotherapy techniques. In: Pryor JA, Webber BA, editors. Physiotherapy for respiratory and cardiac
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problems. 2nd ed. Edinburgh: Churchill Livingstone; 1998. p. 169–75. [21] Deby-Dupont G, Lamy M. Pathophysiology of acute respiratory distress syndrome and acute lung injury. In: Webb AR, Shapiro MJ, Singer M, Suter PM, editors. Oxford textbook of critical care. Oxford: Oxford Medical Publications; 1999. p. 54–5. [22] Armstrong RF. Indications for mechanical ventilation. In: Webb AR, Shapiro MJ, Singer M, Suter PM, editors. Oxford textbook of critical care. Oxford: Oxford Medical Publications; 1999. 1316–18. [23] Waldman M. Noninvasive ventilation. In: Hall JB, Schmidt GA, Wood LDH, editors. Principles of critical care. 2nd ed. New York: McGraw-Hill; 1999. p. 168.
Noninvasive Positive Pressure Ventilation in burns S.T. Smailes St. Andrew’s Centre for Plastic Surgery and Burns, Broomfield Hospital, Broomfield, Chelmsford CM1 7ET, UK Accepted 2 August 2002
Abstract Objective: Acute respiratory failure is a common complication of the severely burn-injured patient. Endotracheal intubation and mechanical ventilation is associated with a high rate of complications. Noninvasive Positive Pressure Ventilation (NIPPV) has been shown to be as effective as conventional ventilation in improving gas exchange and is associated with fewer complications with patients in acute hypercapnic and hypoxaemic respiratory failure. We report our experience with NIPPV in 30 burn patients. Method: The records of all burn patients from 1998 to 2000, where NIPPV was used as part of their management at the St. Andrew’s Centre for Plastic Surgery and Burns, were reviewed. Results: Mean age was 47.56 years (range 12–81). Nine patients were female. Mean burn size was 24.4% total body surface area (TBSA) (range 3–54). Inhalation injury was confirmed in eight cases. A positive diagnosis of pneumonia was made in 29 patients. The mean PaO2 /FiO2 ratio prior to institution of NIPPV was 28.98 Kpa (range 8.75–52). Intermittent Positive Pressure Breathing (IPPB) was the most common ventilatory mode employed (25 patients) and the face mask was the most used interface (18 cases). Twenty-two patients (74%) avoided endotracheal intubation and their respiratory function continued to improve after NIPPV was discontinued. One patient (3%) died and seven patients (23%) were reintubated. Three out of the seven were electively reintubated for burns surgery. Conclusion: In burn-injured patients with acute respiratory failure, NIPPV appears to be effective in supporting respiratory function such that endotracheal intubation can be avoided in most cases. © 2002 Elsevier Science Ltd and ISBI. All rights reserved. Keywords: Acute respiratory failure; Burns; Endotracheal intubation; Complications; Noninvasive Positive Pressure Ventilation
1. Introduction Pulmonary dysfunction is common following a burn injury and the aetiology is multi-faceted. Respiratory complications may result from smoke inhalation, direct airway burn from superheated smoke particles, the effect of the systemic inflammatory response to a burn or a combination of these factors. Airway obstruction is produced by the presence of mucosal casts, oedema and tenacious secretions. Ventilatory restriction and an increased work of breathing may result from the associated pain and wound tightness of the cutaneous chest burn. Furthermore, the patient may present with inflammatory changes within the lung parenchyma resembling the Acute Respiratory Distress Syndrome (ARDS). This results in capillary leak, widespread atelectasis, consolidation and ventilator dependence. Further respiratory complications arise from the onset of pneumonia, immobility and anaesthesia-induced atelectasis [1–5]. Endotracheal intubation and positive pressure ventilation are commonly used to prevent or treat hypoxia and to secure a patent airway in the burn-injured patient [2,4]. However, the presence of the endotracheal tube introduces
problems by bypassing the protective mechanisms of the upper airway, increasing the incidence of nosocomial pneumonia, damage to the airway resulting in tracheal stenosis [6,7] and secondary complications associated with invasive monitoring and sedation [8]. Noninvasive Positive Pressure Ventilation (NIPPV) refers to techniques of augmenting alveolar ventilation without an endotracheal airway [9]. NIPPV has been used with success in the treatment of chronic respiratory failure in patients with neuromuscular diseases and chest wall disorders [10,11]. There is also a large body of literature including five randomised studies that support the efficacy and advantages of NIPPV with patients in hypercapnic acute respiratory failure and hypoxaemic acute respiratory failure [12–16]. However, the outcome of NIPPV with burn patients is less well documented. The purpose of this article is to report on our initial experience with NIPPV in a series of burn-injured patients. NIPPV was used in patients who showed signs of deteriorating respiratory function in an attempt to avoid endotracheal intubation or reintubation. To our knowledge, this is the first report of the use of NIPPV with this group of patients.
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2. Materials and methods The medical records of all patients treated with NIPPV as part of their burns management at the St. Andrew’s Centre between 1 April 1998 and 30 April 2000 were reviewed. In each case the patient’s age, sex, total body surface area (TBSA) burn size and whether burns surgery was performed were recorded. Inhalation injury was documented based on history, physical findings and serial fibre-optic bronchoscopy in all cases. The requirement for endotracheal intubation and ventilation as part of the burns management and the ratio of the PaO2 to the FiO2 (PaO2 /FiO2 ) for each patient immediately prior to the institution of NIPPV was noted. The cause of respiratory failure, NIPPV interface, ventilator mode and pressures and whether intubation/reintubation was avoided was also recorded. The diagnosis of pneumonia was made on the basis of the presence of hyperthermia (>38.2 ◦ C), leukocytosis (WCC >15×109 /l), positive sputum cultures and radiographic identification of infiltrates [17]. NIPPV was delivered using three different ventilators. The Drager CF800 ventilator (Drager Medical, Drager Limited) was used to provide Continuous Positive Airways Pressure (CPAP). CPAP prevents or helps to reopen collapsed alveoli and atelectatic lung zones and it is often used to facilitate weaning from mechanical ventilation [18]. The Bilevel Positive Airways Pressure (BiPAP) Vision ventilator (Respironics) was used to deliver CPAP and Bilevel Positive Airways Pressure ventilation. The spontaneous/timed mode on the BiPAP Vision ventilator provides two ventilatory pressures: the Inspiratory Positive Airways Pressure (IPAP) and the Expiratory Positive Airways Pressure (EPAP). The IPAP minus the EPAP corresponds to pressure support ventilation and the EPAP is equal to Positive End Expiratory Pressure (PEEP) on a mechanical ventilator. Pressure support ventilation has been shown to improve tidal volume, gas exchange, respiratory rate and diaphragmatic activity in proportion to the amount of pressure supplied [19]. The Bird 7A Respirator was used to deliver Intermittent Positive Pressure Breathing (IPPB). IPPB is the maintenance of a positive airway pressure throughout inspiration, with airway pressure returning to atmospheric during expiration. This mode of ventilation provides pressure support to the spontaneously breathing patient and is a useful adjunct to chest physiotherapy treatment. Its effects are as those for pressure support and it is administered intermittently to the patient [20].
bronchial secretions. Patients with extensive and deep burns to the face or facial trauma were excluded for mask ventilation. Evidence of acute respiratory failure had to be exhibited by the patient and this was defined as acute hypoxaemia where the PaO2 /FiO2 ratio was ≤40 Kpa. A PaO2 /FiO2 of ≤40 Kpa forms part of the definition for an acute lung injury (ALI) [21]. NIPPV was used “prophylactically” in four patients (PaO2 /FiO2 >40 Kpa) in an attempt to prevent further respiratory deterioration and endotracheal intubation. Three of these patients showed restrictive ventilatory problems due to the pain caused by abdominal and chest wounds, donor sites and autografts. One patient received NIPPV because he was identified as being at risk of developing respiratory complications after sustaining fractured ribs, a haemopneumothorax and lung contusions. The PaO2 /FiO2 ratio at which mechanical ventilation is indicated is 27.5 Kpa (PaO2 below 11 Kpa on FiO2 0.4) [22]. NIPPV was instituted in all patients fulfilling the selection criteria in an attempt to avoid endotracheal intubation or reintubation. Eight patients, who received NIPPV, had sustained inhalation injuries. In these cases endotracheal intubation was not necessary to protect the airway, i.e. airway oedema had resolved and NIPPV was used to prevent reintubation, or there was little or no evidence of oedema post-injury. Six patients had burns to the face, in these cases mask ventilation could not be used unless the wounds were largely healed. This was because of the ineffective seal produced by applying the mask over dressings and the discomfort for the patient as a firm fitting is essential for ventilation. A mouthpiece was used where mask ventilation was contraindicated. The complications with using NIPPV include skin pressure lesions, facial pain, dry nose, eye irritation, discomfort, poor sleep, mask leakage and gastric distension. The risk of many of these problems occurring was minimised by using the correct mask size, silicone gel masks and by paying close attention to the fitting of the headgear. Significant mask leakage was tolerated by the BiPAP Vision ventilator which continued to deliver ventilation even in patients who did not achieve an optimal mask fit. All patients had a small pressure dressing applied to the bridge of the nose to reduce the risk of pressure sores. Gastric distension was successfully avoided by the placement of nasogastric tubes prior to the institution of NIPPV and by regular decompression of the stomach. Nosocomial pneumonia, thromboembolic disorders and gastrointestinal disorders also occur in patients treated with NIPPV but with a lower incidence than that with invasive ventilation [23].
2.1. Institution of NIPPV 2.2. Training of personnel The criteria for selecting patients for NIPPV included a combination of all of the following factors. The patient was haemodynamically stable and their level of consciousness was such that they were alert and cooperative with their treatment. There had to be no need for endotracheal intubation to protect the airway or to remove excessive tracheo-
Before introducing this new technique of ventilatory support to the burns intensive care unit, all nursing and medical staff received a formal 1 h training session in which explanations were given about the use of the ventilators. The initial setting up of ventilation on the patients was done by
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the consultant anaesthetist and clinical specialist physiotherapist with the nursing staff on duty in attendance. Informal teaching sessions at the bedside with all intensive care nurses were provided on a daily basis until all staff had been trained.
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Weaning was based on clinical findings and not as part of an established research protocol. On discontinuation of NIPPV, supplemental humidified oxygen was provided and physiotherapy to encourage patient mobilisation and expectoration continued.
2.3. Application of NIPPV The patient was positioned sitting up in bed with the head inclined to approximately 45◦ . A small pressure dressing was applied to the bridge of the nose and the patient was measured so that the correct size mask was selected. The ventilator was switched on, the circuit was attached and the alarms were set and silenced. As the patient was acclimatising to the sounds produced by the ventilator, a full explanation about the modality was given and reassurance was provided. The mask was then offered to the patient and, where possible, the patient assisted with the putting on of the mask to achieve maximum comfort. The pressures set on the ventilator were low initially (CPAP = 2 cm H2 O, pressure support = 5 cm H2 O). When the patient was comfortable with the ventilator the headgear was applied to ensure a firm but not tight fitting, to check this two fingers could be placed beneath the straps. The pressures were titrated upwards according to the patient’s tolerance and arterial blood gas results (the maximum pressures used were CPAP = 10 cm H2 O, pressure support = 20 cm H2 O). A member of staff stayed with the patient all of the time initially. Some patients, once established on NIPPV, could be nursed less intensively (these patients were given a call button). Most patients were able to remove their masks for a few minutes for talking and in some cases to drink small amounts of water. All patients received chest physiotherapy whilst on NIPPV, to assist with expectoration of secretions and reversal of atelectasis, twice daily and on call treatment was required in some cases. IPPB was administered periodically to the patients, in contrast to CPAP and BiPAP ventilation. It was used every 2 h for 15-min periods and also for chest physiotherapy sessions for most patients. A saline nebuliser was included in the circuit and, if prescribed, a bronchodilator was given during these periods. The patients were positioned in the same way as for CPAP and BiPAP ventilation or, if indicated, in a postural drainage position for chest physiotherapy. 2.4. Weaning and discontinuation of NIPPV NIPPV was to be discontinued in those patients who showed signs of haemodynamic instability, poor mask tolerance, persistent poor gas exchange and in those who required endotracheal intubation to remove excessive secretions or protect the airways. Weaning was commenced following improvements in gaseous exchange such that the PaO2 /FiO2 ratio no longer fulfilled the selection criteria for NIPPV. The amount of presssure support was lowered or the patient was allowed “NIPPV free” periods which were gradually lengthened.
3. Results Between 1 April 1998 and 30 April 2000, 30 patients were treated with NIPPV as part of their burn management at the St. Andrew’s Centre for Plastic Surgery and Burns. They all received routine burn management according to the unit’s protocols prior to the institution of NIPPV. Table 1 shows the baseline characteristics of the patients. There was a wide age range (12–81 years) and also a large variation in the TBSA burn size (%). The aetiologies of the injuries were thermal (scalds, flames), electrical and frictional in nature; four of the cases were self-inflicted. Inhalation injury, diagnosed at fibre-optic bronchoscopy, was present in eight patients and six patients sustained burns to the face. Most of the group (24 patients) underwent early excision of deep partial thickness and full thickness burns. Wound closure was achieved either temporarily with human cryopreserved cadaveric allograft or permanently with split thickness autografts. Twenty-one of the patients required endotracheal intubation and mechanical ventilation prior to NIPPV use as part of their burn management for a period of between 1 and 22 days. Table 2 shows the pre-morbid conditions of the patients. Three patients were known to local psychiatric services before their burn injury. Two patients who had been diagnosed with chronic obstructive pulmonary disease were receiving ongoing inhaled medication and the two patients who had been treated for asthma did not require regular inhalers. The additional injuries sustained by the patients at the time of the burn injury are shown in Table 3. Treatment for these injuries was on site at Broomfield Hospital. As Table 4 illustrates, the diagnosis of pneumonia was made in 29 cases, this being the most common cause of Table 1 Demographics and clinical course before NIPPV institution Variable
Data
Number of episodes Age (mean year) Female/male Extent of burn (mean %TBSA) Facial burns Inhalation injury Burns surgery Conservative wound therapy Intubated and ventilateda Ventilation days (mean)
30 47.56 (range 12–81) 9/21 24.4 (range 3–54) 6 8 24 6 21 5.6 (range 1–22)
a
Not including elective intubation for surgical procedures.
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Table 2 Pre-morbid conditions of the patients
Table 4 The cause of acute respiratory failure
Medical condition/surgery
Patients
Cause
Patients
Angina Asthma Carcinoma of the prostate Chronic obstructive pulmonary disease Confusion CVA Dementia Epilepsy Glaucoma Hypertension Kyphoscoliosis Left-ventricular failure Meningitis Nocturia Schizophrenia Oophorectomy
2 2 1 2 1 1 1 1 1 3 1 1 1 1 2 1
Upper airway oedema Pneumonia Bronchospasm Pulmonary contusions Pulmonary abscesses
1 29 4 1 1
Table 3 Additional injuries sustained by the group Nature of injury
Patients
Cervical spine injury Head injury Haemopneumothorax Rib fractures Extensor tendon rupture Limb fractures
1 1 1 1 1 1
respiratory deterioration. In some cases, although pneumonia was the primary diagnosis, another respiratory pathology was deemed to be contributing to the acute respiratory failure exhibited by the patient.
The PaO2 /FiO2 ratio of the patients immediately prior to NIPPV institution can be seen in Fig. 1. The mean PaO2 / FiO2 ratio was 28.98 Kpa (range 8.75–52 Kpa). Twenty-six patients had a PaO2 /FiO2 ≤40 Kpa which satisfied part of our selection criteria for NIPPV use and forms part of the definition for an acute lung injury. Table 5 indicates that IPPB was the most commonly used mode of ventilation (25 patients). IPPB was used every 2 h and the patients were always supervised during their treatment. This may have enhanced the patients’ acceptance of ventilation because the nursing staff were present to offer reassurance and to increase motivation. IPPB was also frequently used as an adjunct to chest physiotherapy. Some patients received more than one mode of ventilation and continuous NIPPV was weaned to periodic as patient tolerance and clinical findings allowed. This was done to minimise the risk of complications associated with NIPPV. The face mask was the interface most often used. This was because the firm seal required for ventilation was achieved more easily with this, especially in mouth breathing patients and those with lip burns. Some patients used more than one type of interface to achieve maximum comfort with the ventilation.
Fig. 1. PaO2 /FiO2 ratio immediately before institution of NIPPV.
S.T. Smailes / Burns 28 (2002) 795–801 Table 5 The NIPPV modes and interface used
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Table 8 The patient’s outcome after NIPPV use
Ventilation mode and interface
Patients
Outcome
Patients
Percentage
IPPB IPPB + CPAP IPPB + CPAP + BiPAP IPPB + BiPAP BiPAP BiPAP + CPAP CPAP
13 5 4 3 3 1 1
Intubation/reintubation Self-ventilation Died
7 22 1
23 74 3
Face mask Mouthpiece Nasal mask
18 10 5
only and not as part of an established research protocol. Seven patients (23%) required discontinuation of NIPPV and intubation and mechanical ventilation. This was necessary in four cases due to the onset of sepsis with haemodynamic instability and in three cases for elective burns surgery. One patient died after the decision to discontinue active treatment was made.
Table 6 The duration of NIPPV use NIPPV mode
Ventilation days (mean)
Range (days)
IPPB CPAP BiPAP
4.28 4.14 2.36
1–10 1–11 1–9
Tables 6 and 7 show the duration of NIPPV treatment and the ventilation pressures used. There was a large variation in the number of days that NIPPV was required for the group of patients. It can be seen that for each different mode of ventilation the minimum time of treatment was 1 day and this increased to a maximum of 11 days for CPAP ventilation. NIPPV was used for the longest period of time with a patient who developed cavitating lesions secondary to an inhalation injury. NIPPV was generally well tolerated by the patients, this was possibly because low pressures were used initially until the patient was accustomed to breathing on the ventilator. Only at this point was the pressure titrated upwards to patient tolerance and arterial blood gas results. The pressures shown in Table 7 reflect those used for treatment once the patients were established on NIPPV and prior to weaning. A maximum pressure support of 20 cm H2 O was used for BiPAP ventilation. Higher ventilatory pressures were avoided as they are associated with an increased risk of gastric distension. Intubation/reintubation was successfully avoided in 22 out of the 30 patients (74%) as can be seen in Table 8. All of these patients progressed to self-ventilation status following NIPPV. Weaning from NIPPV was done on clinical findings Table 7 NIPPV mode and pressures used (prior to weaning) NIPPV mode
Pressure (mean) (cm H2 O)
Range (cm H2 O)
BiPAP (IPAP − EPAP)/EPAPa
11.18/6
3–20/5–7
CPAP IPPB
6.79 18.58
5–10 10–20
a
(IPAP − EPAP)/EPAP = pressure support/CPAP.
4. Discussion NIPPV is the treatment of choice for patients in hypercapnic acute respiratory failure in many centres. The role of NIPPV in the treatment of hypoxaemic acute respiratory failure is recognised and becoming more widespread [12–16]. The use of NIPPV with burn-injured patients is, as yet, unclear because little work has been documented. We have reported our initial experience of the use of NIPPV with burn-injured patients at the St. Andrew’s Centre for Plastic Surgery and Burns. The results show that most patients who received NIPPV avoided the need for endotracheal intubation and mechanical ventilation. This is regularly cited in the literature as a successful outcome of NIPPV use [12–16]. The most common cause of acute respiratory failure in the patients was pneumonia. This is consistent with current literature regarding the pathophysiology of the burn injury [1–5]. Furthermore, in one case the pulmonary infection progressed to form cavitating lesions. Most patients (26) showed clear signs of respiratory deterioration prior to NIPPV institution as illustrated by a PaO2 /FiO2 ≤40 Kpa. This level of acute hypoxaemia constitutes part of the definition for an acute lung injury [21]. In the other four cases NIPPV was used ‘prophylactically’ to prevent further respiratory complications. In these patients there were a number of factors contributing to them being ‘at risk’ of developing acute respiratory failure. These included ventilatory restriction caused by the pain and tightness of abdominal and chest burns, autografts and donor sites. The presence of injuries to the thoracic cage or within lung tissue compounded this restriction and introduced problems with sputum retention and airway plugging. One other factor which we have found to increase the risk of the patient developing respiratory complications is frequent general anaesthesia. This is associated with reduced lung volumes and is necessary with a major burn-injured patient to enable wound care and surgical procedures. Also, patients who are immobilised in bed for prolonged periods of time have a reduced functional residual capacity and therefore are more
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likely to develop airway atelectasis. By identifying patients ‘at risk’ of developing respiratory failure by a combination of the above factors and by clinical signs, NIPPV can be instituted early or ‘prophylactically’ to reverse airway closure, enable expectoration of secretions and prevent further respiratory deterioration. This is one role that NIPPV has on our burns unit. We have also found that NIPPV has facilitated earlier weaning of mechanical ventilation and extubation. This has been achieved by introducing BiPAP ventilation to the intubated patient. Once the patient is established on the ventilator, they are extubated and commenced on mask ventilation. By doing this, active rehabilitation can begin earlier. However, the patient must fulfil the selection criteria for NIPPV to ensure a smooth transition from invasive mechanical ventilation to NIPPV and ultimately to self-ventilation. Many of the patients (18) required a full face mask to achieve effective ventilation. This was for two reasons: firstly, patients with burns to the lips were unable to form a seal with the mouthpiece; secondly, patient cooperation with the nasal mask and the mouthpiece was sub-optimal in some cases, possibly due to excessive sedation. This raises the question of the need for further selection criteria for NIPPV with major burn-injured patients. This is because cooperation by the patient is necessary for successful ventilation. The use of NIPPV may be more appropriate for a patient in acute respiratory failure and with a largely closed wound. This is because the need for large doses of analgesics and the frequency of general anaesthesia would be diminished thereby optimising patient cooperation and compliance. Also, once the wound is closed, the patient is less likely to develop sepsis or haemodynamic instability [4]. We have found that cooperation by most patients can be gained by the correct approach of the clinician when first introducing NIPPV. To tightly strap a mask on to an already anxious and dyspnoeic patient and to use high ventilatory pressures will undoubtedly increase discomfort and distress. However, by allowing time for the patient to have trials of breathing on the ventilator at low pressures before applying the head straps to the mask and by offering reassurance, there is likely to be a greater chance of acceptance of NIPPV by the patient. The patients did not experience any major complications related to NIPPV. One patient developed a small area of skin breakdown on the bridge of the nose despite regular skin care and dressings. This wound healed spontaneously when NIPPV was discontinued. Five patients had difficulty sleeping whilst on NIPPV and required night sedation. Three patients from the group were electively reintubated for burns surgery and required mechanical ventilation post-operatively. This situation is not uncommon in the major burn-injured patient and, in this instance, NIPPV has not ‘failed’. A tracheostomy would now be considered for this type of patient at the St. Andrew’s Centre to avoid repeated intubations and enhance patient comfort and airway management.
In conclusion, this experience of the use of NIPPV with burns is that most of the patients avoided the need for endotracheal intubation and progressed to self-ventilating status. There is a need for further research and a multi-centre trial would be appropriate to acquire a larger sample size and a prospective study would enable standardisation of monitoring of the patients.
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