Oxygen is probably the most commonly used drug in medical emergencies but the extent of use in UK ambulances is largely unknown. There have been few controlled trials of emergency oxygen therapy and its use remains the subject of a debate spanning many specialities. A study of paramedic ambulances in North Ayrshire reported that oxygen use increased from 50% of cases in 1994 to 68% in 1999,1 and a Danish study in 1993 reported oxygen use during 34% of emergency ambulance journeys.2 The authors are not aware of any recent study of the frequency or quality of oxygen use in UK ambulances.

Underuse of oxygen is extremely dangerous as it exposes critically ill patients to the risk of hypoxic organ damage. Overuse of oxygen can also be harmful, especially for patients with chronic obstructive pulmonary disease. (COPD) It was previously believed that high doses of supplemental oxygen were either beneficial or harmless for virtually all other acutely ill patients, but it is now known that hyperoxaemia may have harmful physiological consequences and delay the recognition of physiological deterioration.3^–5 Patients with COPD were thought to constitute a small subgroup uniquely vulnerable to excessive oxygen therapy, but there is now evidence to suggest that many other patients—including stroke patients and patients with ischaemic heart disease—may be at risk.6 7 Because of these concerns, the British Thoracic Society, in cooperation with 21 other Colleges and Societies, has commissioned a new UK emergency oxygen guideline which will be published and implemented in the near future.8

This audit was designed to study the frequency and appropriateness of oxygen use by an inner city ambulance service and a hospital emergency department (ED). Oxygen use was audited against current Joint Royal Colleges Ambulance Liaison Committee (JRCALC) guidance in prehospital care.9 We wished to establish frequency of oxygen use in each setting and the proportion of hypoxaemic patients. We studied the use of oxygen for patients with COPD because they are highlighted in JRCALC guidance as a vulnerable group who should receive controlled oxygen therapy.9

METHODS

A 6-week audit of emergency oxygen use was completed in the “majors” section of the ED between May and June 2007. A proforma was designed to record oxygen therapy in the ambulance and the ED. Data sets were collected from ambulance records of all adult patients brought in by the North West Ambulance Service (NWAS) between 09.00 and 17.00 hours for the first 2 weeks and then for all patients arriving during the remaining 4 weeks of the audit.

Data collection was carried out in the ED to audit patients’ ambulance records as they arrived in the “majors” department. The following data were collected:

• Date and time of arrival in the ED.

• Patient’s main complaint and ambulance staff’s “working diagnosis” (JRCALC category).

• Whether oxygen saturation was recorded (if so, oxygen saturation (Spo₂) measurements were collected).

• Whether the patient was given oxygen in the ambulance (if so, delivery system and flow rate were recorded).

The patient was assessed and treated in the ED, after which a history card was completed as the patient left the ED. From this card the following data were collected:

• Whether the patient was given oxygen in the ED.

• If oxygen was given, which delivery system was used and at what flow rate.

• Any diagnosis documented by the ED.

• The final ED diagnosis was compared with the ambulance diagnosis or JRCALC category.

All data were entered into a master spreadsheet and database for subsequent manual analysis. No statistical analysis was required or attempted in this audit study. The “working diagnosis” was categorised according to current JRCALC guidelines, making it possible to audit oxygen use against an established standard.9 The JRCALC guidance contains advice on oxygen therapy for each category of patient. This includes whether oxygen should be given, by which means and at which flow rate (high, medium or low).

Current NWAS documents do not identify whether oxygen saturation readings are taken before or during oxygen administration in the ambulance. Two oxygen saturation values were recorded in the spreadsheet where possible and patients were categorised as “hypoxaemic” if one or more of the readings was ⩽94%, the level that the JRCALC guidelines categorise as being hypoxaemic.9

RESULTS

Data were collected from the case records of 1022 patients brought by ambulance to the “majors” section of the ED.

Diagnosis

The spread of working diagnoses is shown in table 1. The most frequently encountered JRCALC category was “medical emergency”, which comprised 33% of ambulance cases. 22% of this group had shortness of breath, 16% collapse, 12% chest pain and 10% seizure. The diagnostic categories and the full spread of “medical emergencies” are shown in tables S1 and S2 in the online supplement. For 776 patients (76%) the diagnosis made by ED staff was similar to that made by ambulance staff and only 79 (8%) were significantly different. In patients with significantly different diagnoses, oxygen use was unchanged in 44% (n = 35), increased in 17% (n = 13) and decreased in 39% (n = 31). Further details are shown in table S3 in the online supplement. Although the working diagnosis of ambulance staff differed significantly from the ED diagnosis in 8% of cases, this would have altered the amount of oxygen given in only 3% (n = 33).

Oxygen therapy

Thirty-four percent of all patients were given oxygen in the ambulances and a further 3% were given entonox (mixture of 50:50 oxygen with nitrous oxide). Oxygen use was nearly 1.5 times more frequent in ambulances (n = 351) than in the ED (n = 239), as shown in table 2. In approximately 45% of patients (n = 171) treated with oxygen in the ambulance, this treatment was discontinued in the ED. For 5% of patients (n = 34) not given oxygen in the ambulance, oxygen was started de novo in the ED. Incompletely documented oxygen use occurred twice as often in the ED as in ambulances.

Measurement of oxygen saturation

Although it is recommended in the JRCALC guidelines that a pulse oximeter should be used whenever oxygen is being administered,9 19/351 patients (5%) did not have such a reading. Other cases in which JRCALC guidelines recommend the use of pulse oximetry are patients with respiratory symptoms or impaired level of consciousness and cardiac or significantly injured patients. Using Spo₂ ⩽94%, the figure suggested by JRCALC guidelines as indicating hypoxaemia, a quarter of patients with documented Spo₂ (218/921) were hypoxaemic but only 17% (n = 159) fell below 94% at any time. Sixty-two patients (7%) were significantly hypoxaemic with Spo₂ <90%, the more widely accepted figure for hypoxaemia.10 11 Fourteen patients (33%) with COPD had at least one saturation measurement <90% and 48/878 patients without COPD (5.5%) had Spo₂ <90%.

Diagnosis and management of COPD

Thirty patients were recorded as having COPD by ambulance personnel with a working diagnosis of breathlessness or exacerbated COPD. Of these, 25 were confirmed as suffering from an acute exacerbation of COPD by ED staff and the remaining 5 had a different diagnosis (table S4 in online supplement). Eighteen further patients were admitted without ambulance staff being aware that they had COPD, which was later diagnosed in the ED (table S5 in online supplement). Thus, 58% of the 43 patients with COPD were correctly identified during prehospital care.

Twenty-six patients (87%) believed to have COPD were treated with oxygen in the ambulance, three (10%) received no oxygen and one (3%) was undocumented (table 3). The mean delivery rate was >5 l/min, equivalent to >40% oxygen therapy.12 13 Thirty patients with COPD (70%) received oxygen in the ED, seven (16%) received no oxygen and six (14%) were undocumented.

Adherence to JRCALC guideline

Oxygen administration by ambulance staff was assessed in terms of high, medium or low flow for each diagnostic category (table 4). This was cross-referenced with the suggested flow rate given in the JRCALC guidelines.9 A total of 135 patients were treated in accordance with JRCALC guidance and 100 patients were treated outside the JRCALC recommendations. Most were normoxaemic patients given medium-flow oxygen in situations where current JRCALC guidance specifies high-flow oxygen. Many patients could not be classified because they did not clearly fit into the JRCALC categories. For patients with “medical emergency”, “trauma emergency”, “cardiac chest pain” and “cardiac arrest”, the predominant use of high-flow oxygen was as advised in the JRCALC guideline. Patients with “pulmonary disease” did not receive any high-flow oxygen, in accordance with JRCALC guidance, although most patients with COPD received medium-flow oxygen and none received controlled oxygen therapy from a Venturi mask (these were not carried by NWAS ambulances at the time of the audit).

DISCUSSION

This audit found that 34% of patients brought by ambulance to the “majors” area of the ED were given oxygen therapy by ambulance staff. This is identical to the reported oxygen use in emergency ambulances in Denmark in 1993 but substantially lower than the reported use (50–68%) by Scottish paramedics in the 1990s.1 2 The NWAS serves a population of nearly seven million, transporting approximately 677 000 patients to the ED per year. Assuming the emergency oxygen use by NWAS is typical of that nationwide, it would equate to 2.2 million instances of oxygen use.

Ambulance crews and ED staff made the same or similar diagnosis for 776 patients (76%). However, there is a wide spread of ambulance guideline categories into which some patients do not clearly fit. Oxygen use and adherence to guidelines may improve with simpler guidelines based on target oxygen saturations rather than specific devices and flow rates. For this reason, the new UK emergency oxygen guideline will specify target ranges rather than delivery systems.8

Ambulance staff used oxygen about 1.5 times more frequently than ED staff. It is possible that they were more cautious because they were treating in the community. Furthermore, oxygen may be stopped in the ED because of improvement in the patient’s condition or oxygen saturation. However, the use of oxygen in the ED was often poorly documented and may have been underestimated, because ED records—unlike ambulance records—do not have a dedicated space to record oxygen therapy. It is also possible that the focus on oxygen during the audit period may have affected both its use and the recording of its use. Ambulance records lacked a designated area to indicate which oxygen delivery system was used. This suggests a role for more formal documentation of oxygen therapy in prehospital care and in the ED. It is also important to document whether oximetry measurements are made while breathing air or oxygen.

Oxygen saturation measured by pulse oximetry was well documented by ambulance staff, with 920 (90%) of all patients having at least one reading recorded, and it is possible that some of the 5% of patients who should have had their saturation measured according to JRCALC guidelines did not have such a measurement because of faulty probes or because ambulances were not equipped with pulse oximeters. In such instances it is important that pulse oximetry is not relied on solely but that it is used in conjunction with assessment of clinical signs of hypoxia. Approximately one-quarter of patients whose Spo₂ was measured had at least one reading that showed the patient was hypoxaemic according to JRCALC guidelines for levels of hypoxia (Spo₂ ⩽94%).9 However, the normal range for oxygen saturation varies according to the patient’s age, and a saturation of 92% may be normal for patients aged >70 years.14 Although JRCALC defines hypoxaemia as a saturation ⩽94%, they acknowledge that the lower limit of the normal range could be 91% for some patients and many authors use 90% as a cut-off figure to define clinically significant hypoxia.10 Bowton and colleagues reported an increased risk of death if the oxygen saturation fell below 90%, but this could also be a marker of disease severity.11 Sixty-two of 920 patients (7%) for whom saturation was recorded had a saturation of <90%, including 14 patients (33%) with COPD and 48/878 patients (5.5%) without COPD.

During this audit, ambulance staff correctly identified only 58% of patients with an acute exacerbation of COPD. If this figure can be improved upon—possibly with the implementation of an alert system such as alert cards carried by patients—early and appropriate treatment can be started during this crucial transfer time.15 16

The description of the delivery system used for oxygen administration was poorly documented. Ambulance staff indicated that the only oxygen delivery systems available to them were non-rebreathing reservoir masks and medium concentration masks. For patients thought by ambulance staff to have an acute exacerbation of COPD, the mean oxygen flow was >5 l/min delivering an oxygen concentration of >40%, which is higher than that recommended and can lead to harmful outcomes.12 13 17^–20 With the provision of only reservoir masks and medium concentration masks, ambulance staff were unable to provide patients with COPD with the correct controlled oxygen dose. Ambulances need to be supplied with nasal cannulae and Venturi masks in order to treat patients with COPD and other at-risk patients in accordance with forthcoming UK emergency oxygen guidelines, and high-risk patients should ideally have alert cards specifying oxygen saturations.8

Of those patients who fitted into a specific JRCALC category requiring oxygen therapy, 162 (62%) were treated by ambulance staff according to JRCALC guidance and 99 (38%) were treated outside this advice. However, some patients did not fit “neatly” into a guideline category and this led to difficulties in auditing the appropriateness of their treatment. Of 40 patients brought to the ED by ambulance with a “working diagnosis” of “cardiac chest pain”, 32 had received oxygen, 84% at high flow and 16% at medium flow. Those given high-flow oxygen were in accordance with guidelines. However, no study has demonstrated benefit from supraphysiological oxygen levels for patients with cardiac ischaemia, and some studies have found that high concentrations of supplemental oxygen may cause reduced myocardial blood flow.7 The only controlled trial of oxygen in myocardial infarction (published in 1976) suggested that the use of oxygen for non-hypoxaemic patients with myocardial infarction may be associated with adverse outcomes.21 The new UK emergency oxygen guideline will suggest aiming at normal oxygen saturation in most disease states.8

CONCLUSIONS

This audit found that oxygen was given to about one-third of patients transported to a UK hospital in an emergency ambulance and the oxygen saturation was documented for 90% of patients. One-third of patients with COPD and 5.5% of other patients had oxygen saturation levels <90% during their journey to hospital. Only 58% of patients with COPD were recognised as having this condition in prehospital care and, while the JRCALC guidelines were followed for all of these patients, none received controlled oxygen therapy. For patients who may have worsening of chronic hypoxia as part of their acute presentation, target oxygen saturation is more important than flow rate. It is hoped that the British Thoracic Society emergency oxygen guideline (due for publication in 2008) will be of value to ambulance services and EDs by standardising and enhancing oxygen therapy in medical emergencies, including the introduction of target saturation ranges for all common medical emergencies.8