Department of Anaesthesiology and Intensive Care Medicine, Federal Armed Forces Medical Center,D-89070 Ulm, Germany *Corresponding author
Accepted for publication: November 18, 2001
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Abstract |
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Methods. Included in this prospective study were 122 trauma patients with severe head injury (abbreviated injury scale score 3). In all cases, the pre-hospital treatment included endotracheal intubation in the field. Upon hospital admission, and maintaining the same ventilation mode and setting initiated in the pre-hospital setting, arterial blood gas samples were taken.
Results. Optimal oxygenation (PaO2 >100 mm Hg) was achieved in 85.2% and adequate ventilation (PaCO2 3545 mm Hg) in 42.6% of the patients upon hospital admission. Optimal oxygenation as well as adequate ventilation was achieved in 37.7% of the study population. Hypoxaemia (PaO2 <60 mm Hg) was observed in 2.5%, hypercapnia (PaCO2 >45 mm Hg) in 16.4%, and hypocapnia (PaCO2 <35 mm Hg) in 40.9% of the study patients. The incidence of hypocapnia was significantly more frequent in polytraumatized patients. Hypocapnia as well as hypercapnia was significantly more frequent in patients with associated pulmonary contusion.
Conclusions. Endotracheal intubation and controlled ventilation of the lungs initiated in the pre-hospital setting do not guarantee optimal oxygenaton and ventilation in patients with severe head injury.
Br J Anaesth 2002; 88: 3459
Keywords: intubation, tracheal; complications, trauma; ventilation
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Introduction |
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Patients and methods |
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Endotracheal intubation as well as controlled ventilation was conducted according to the current treatment procedure for the Emergency Medical Services of Ulm County, Germany. In this context, immediately after endotracheal intubation the lungs are ventilated using a manually operated ventilation bag (AMBU-Mark III®, Ambu, Friedburg, Germany), connected to an oxygen demand valve (Dräger, Oxydem®, Dräger, Lübeck, Germany), assuring a fraction of inspired oxygen (FIO2) of 1.0. After the correct position of the tracheal tube is confirmed and secured, further pre-hospital artificial ventilation is maintained automatically by a volume constant portable emergency ventilator (Dräger Oxylog®). The ventilator settings used are a tidal volume of 10 ml kg1 of estimated body weight, respiratory weight of 10 min1 and an FIO2 of 1.0. During pre-hospital treatment, all patients were continuously monitored by pulse oximetry. Upon hospital admission and maintaining the ventilator settings initiated in the field, arterial blood gas samples were taken.
Recorded data included physical characteristics, mechanism of injury, AIS, Injury Severity Score (ISS)10, arterial blood gas analysis (pH, base excess, PaO2, and PaCO) upon hospital admission and vital signs upon hospital admission.
All recorded data were collected concurrently and entered into a relational database management system (Microsoft Access, Microsoft Corporation, Redmond, WA, USA) based on the Trauma Registry of the German Society of Trauma Surgery.11
Optimal oxygenation upon hospital admission was defined as a PaO2 greater than 100 mm Hg and adequate ventilation as PaCO2 3545 mm Hg; hypoxaemia was defined as a PaO2 less than 60 mm Hg, hypocapnia as a PaCO2 less than 35 mm Hg, and hypercapnia as a PaCO2 greater than 45 mm Hg.1214 In order to evaluate the potential influence of age, haemodynamic instability, severe chest injury, or a high injury severity on oxygenation and ventilation, we stratified the study population. Old age was defined as greater than 60 yr of age,15 haemodynamic instability as a systolic arterial pressure upon hospital admission of less than 90 mm Hg, and severe chest trauma as the presence of pulmonary contusion. Pulmonary contusion was diagnosed by computer tomography, which was conducted on every study patient during the initial in-hospital phase of resuscitation. High injury severity was defined as the presence of polytrauma.16
Statistical methods
All values in the tables and figures are expressed as mean (SEM) unless otherwise indicated. Each variable was tested for differences between groups by Students t test or chi-squared analysis where appropriate. Statistical significance was set at P<0.05. Statistical analysis was performed using specialized statistical software (Almo© version 5.0; K. Holm, University of Graz, Austria).
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Results |
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The results concerning the incidence of non-optimal oxygenation, hypoxaemia, hypocapnia and hypercapnia within the study population are presented in Table 3.
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Discussion |
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In only 37.7% of the study population, optimal oxygenation as well as adequate ventilation was achieved after pre-hospital-initiated endotracheal intubation and artificial ventilation upon hospital admission. A detailed review of study findings identified that this is not so much connected with oxygenation but primarily results from ventilation problems. Upon hospital admission hypoxaemia was evident in only three (2.5%) cases and these three patients had severe chest trauma with extensive bilateral pulmonary contusions. In a similar study20 conducted in 1989 where none of the patients were monitored by pulse oximetry and only one in three of the patients received an FIO2=1.0, the proportion of patients who upon hospital admission had hypoxaemia was 25%.
An ongoing problem is the pre-hospital control of ventilation. We were only able to meet the desired goal of normoventilation in 42.6% of the cases. In the majority of cases (40.9%), the emergency physician unintentionally hyperventilated the lungs, whereas hypoventilation only occurred in 16.4% of cases. Kehrberger and colleagues20 came to a similar conclusion. Hyperventilation may aggravate cerebral ischaemia20 22 and, therefore, should be avoided during the pre-hospital phase.13 This especially applies to patients with polytrauma, who in our study were more often unintentionally hyperventilated. These patients additionally are at risk of hypotension, a major determinant in the outcome from severe head injury.18
The quality of pre-hospital-initiated ventilation seems to be influenced mainly by the less sophisticated ventilation devices used in the pre-hospital setting in comparison with the in-hospital setting. In the case of manual ventilation using a self-inflating manual resuscitator (i.e. AMBU®-bag) with an additional oxygen supply, it is not possible to measure minute volume; the quality of ventilation depends on the experience and skill of the person squeezing the bag.23 24 Most of the automatic emergency ventilators allow the ventilatory frequency and minute volume to be set but only some of them (i.e. Oxylog 2000®) measure these preset variables. A number of studies23 25 26 have shown, that in nearly all commonly used automatic emergency ventilators, the delivered minute volume differs by up to ±20% from the preset minute volume.
Pulse oximetry has proved useful in the detection of hypoxia in the pre-hospital setting.3 On the other hand there is still no reliable, as well as practical, method for monitoring and controlling ventilation in the pre-hospital setting. Blood gas analysis, the gold standard, seems not to be a practical method for the pre-hospital setting. The use of capnography as a non-invasive as well as continuous monitoring method for controlling ventilation is limited in hypovolaemic patients or patients with severe lung contusion.3 27
Without any doubt, endotracheal intubation and controlled ventilation in the field improves the outcome in patients with severe head injury.47 However, our data document that endotracheal intubation and controlled ventilation in the field do not guarantee optimal oxygenation and adequate ventilation in patients with severe head injury. In order to optimize the pre-hospital respiratory therapy in such trauma victims, additional respiratory monitoring is necessary.
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Acknowledgements |
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References |
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