a b s t r a c t

Background: Rescuers that undergo acute ascent without acclimatization can experience acute mountain sickness. Although performing cardiopulmonary resuscitation (CPR) for a short period requires intensive effort at sea level, performing CPR at high altitude is even more exhausting and can endanger the rescuer. Therefore, we conducted a pilot study to compare the quality of resuscitation in health professionals at high altitude (3100 m) and that at sea level.

Methods: Thirty-eight participants were asked to performed Continuous chest compression CPR (CCC-CPR) for 5 minutes at sea level and at high altitude. Cardiopulmonary resuscitation recording technology was used to objectively quantify the quality of the Chest compressions , including the depth and rate thereof.

Results: At high altitude, rescuers showed a statistically significant decrease in blood oxygen saturation and an increase in systolic blood pressure, diastolic blood pressure, heart rate, and fatigue, as measured with the Borg score, after CCC-CPR compared with resting levels. The analysis of the time-dependent deterioration in the quality of CCC-CPR showed that the Depth of CCs declined from the mean depth of the first 30 seconds after CCC-CPR to that at more than 120 seconds after CCC-CPR at both sea level and high altitude. The average number of effective CCs declined after CCC-CPR was performed for 1 minute at sea level and high altitude. Conclusions: The quality of CC rapidly declined at high altitude. At high altitude, the average number of effective CC decreases; and this decrease became significant after continuous CCs had been performed for 1 minute.

(C) 2014

Introduction

A growing number of people visit mountainous areas worldwide. While ascending to high altitude, a number of acute physiological changes occur [1]. Cardiac arrest is the second most common cause of death in the mountains [2].

If a time-sensitive rescue operation is necessary, usually, no acclimatization time is available for rescuers. Prolonged cardiopul-

? The authors declare that they received no financial support and have no disclosures.

?? Grants: DV101-04 and DV102-02 from the Ministry of National Defense-Medical

Affairs Bureau and Taipei Veterans General Hospital.

??? Conflict of interest statement: There are no conflicts of interest to declare.

* Corresponding author at: Department of Emergency Medicine, Tri-Service General Hospital, National Defense Medical Center, No. 325, Sec. 2, Cheng-Kung Rd, Taipei, Taiwan. Tel.: +886 2 87923311 16877; fax: +886 2 87927034.

E-mail address: [email protected] (Y.-H. Chen).

monary resuscitation (CPR) at high altitude presents a significant physical challenge to rescuers. After continuous single-operator CPR at high altitude for 5 minutes, the rescuer’s arterial blood oxygen saturation (SpO2) decreases; and the rescuer’s Borg scale score, a subjective score of fatigue, becomes higher than that at sea level [3,4]. Although a comprehensive review by Chalkias et al [1] addressed several important issues and proposed reasonable recommendations for CPR and the considerations of rescuers at high altitude, most guidelines for resuscitation do not provide specific recommendations for CPR at high altitude [1,5]. Nonetheless, physiological changes during exercise at high altitude have been studied extensively, which, in conjunction with results indicating quality changes, should able to provide a rationale for modifying current guidelines regarding CPR performed at high altitude.

The Quality of CPR is paramount to advanced cardiac life support. Previous studies have demonstrated that the return of the spontane- ous circulation in patients experiencing an out-of hospital cardiac

http://dx.doi.org/10.1016/j.ajem.2014.07.007

0735-6757/(C) 2014

arrest is dependent on the quality of the CPR they receive [6-8]. Several investigations have also shown that improved outcomes are associated with greater chest compression depth [9,10]. The Quality of chest compressions during CPR has been demonstrated to decline rapidly after a short period [11,12]. A number of simulations have shown that rescuers develop immediate fatigue during CPR and that chest compression depth declines after 1 to 3 minutes of CPR [12-14]. During continuous chest compression CPR (CCC-CPR), chest com- pressions are minimally interrupted; but the depth of compressions decreases more rapidly than in conventional CPR [15]. Data regarding the quality of CPR performed by rescuers and the acute physiological effects of CCC on rescuers at high altitude are still limited. Therefore, this pilot study aimed to compare the time-dependent deterioration of CCC-CPR quality and the acute physiological effects of CPR on rescuers at sea level and high altitude. We provide recommendations on how to best perform CPR at high altitude.

Methods

Data collection

Thirty-eight volunteers 18 years of age or older who had completed a basic life support and CPR training course in accordance with the 2010 American Heart Association (AHA) guidelines were recruited for this study. All of the participants were health care providers, including medical staff of a Tertiary medical center and emergency medical technicians. The participants were also enrolled to establish a rescue team. Comprehensive demographic data were collected for all participants. This prospective collection of chest compression data was approved by the Institutional Review Boards of the Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan (2-101-05-037). Informed consent was obtained from every participant. Data were obtained using a commercially available Chest Compression Coach System and manikins. The sensor resolution along the vertical direction when aiming at objects at 60 cm was approximately 0.6 mm. This device allowed for the recording of chest compression rate and depth.

Study protocol

Each participant performed 5 minutes of CCC-CPR on a manikin. Systolic blood pressure (SBP), diastolic blood pressure , heart rate (HR), respiratory rate (RR), and Borg score were measured before and after compressions, as previously described. The symptoms of Acute mountain sickness were measured using the Lake Louise Score [16].

These same Physiological parameters were measured again immediately after the compressions. The Chest Compression Coach System was used to determine the number and depth of the chest compressions continuously for 5 minutes at sea level. Three weeks later, all subjects were transported from sea level to an altitude of 3100 m by car, which took approximately 4 hours. Six hours after ascending to 3100 m, all participants performed another 5 minutes of CCC. The number and depth of chest compressions for 5 minutes were recorded again by the Chest Compression Coach System. Before performing the chest compressions, the participants were instructed to deliver continuous chest compressions for 5 minutes. They were also informed of the ideal rate of chest compression (100 to 120 per minute) and the ideal depth of chest compression (5 cm at least). All of the participants were told that if they were too tired to continue, they could stop the chest compressions and rest. No clock was visible, and the participants were not told how much time remained at any point during the simulation. No Real-time audiovisual feedback was provided to the participants regarding the quality of the chest compressions during the simulation. Any participant who was too tired to complete the 5 minutes of continuous chest

compression or who had severe symptoms of acute mountain sickness (LLS N 6) before performing chest compressions was excluded from the study.

Data analysis

Cardiopulmonary resuscitation performance was analyzed in terms of chest compression rate and depth and the number of effective chest compressions (valid compressions). The measurement was based on hand detection and compression analysis. To determine the validity of each compression, at the beginning of the session, the system acquired the height of the rescuer’s hand in contact with the chest wall at the point of maximum release. The participants wore a glove and attached a hand marker to the surface of the glove. A camera detected the height of the marker at the beginning of the chest compressions. The position of the hand marker was measured throughout the entire 5-minute chest compression period. Each compression depth was calculated as the difference between the minimum and maximum heights of the hand during each compres- sion phase. The period between two consecutive maxima was considered a full compression phase. An effective chest compression was defined as one chest compression with a depth of more than 5 cm.

Statistical analysis

Analyses were performed on an intention-to-treat basis. The data were compared across groups using the ?² test for categorical variables and the 2-tailed paired t test for continuous variables. Nonparametric tests were conducted for the number of effective chest compressions. For the 2-tailed tests, P b .05 was considered statistically significant. The analyses were performed using SPSS (Chicago, IL) version 18.

Results

The baseline characteristics of the study participants are shown in Table 1. Thirty-eight volunteers were enrolled in this study, and 33 participants completed the 5-minute CCC-CPR at high altitude (3100 m). Five participants did not complete the 5-minute CCC-CPR at high altitude because they were tired and asked to cease the test.

Before CPR, the participants’ SBP and DBP were not significantly different between sea level and high altitude (Table 2). The pre-CPR LLS and Borg scores at high altitude were significantly higher than their values at sea level. The values of HR and RR at high altitude were significantly higher than at sea level. The SpO2 value was significantly lower at higher altitude than at sea level. When comparing high altitude to sea level, the post-CPR SpO2 value was significantly lower, the HR value was significantly higher, and the Borg score and RR values were not significantly different. At high altitude, the values of SBP, DBP, HR, RR, and Borg score were significantly higher after CPR compared with resting levels. Performing 5 minutes of CCC-CPR had no significant effect on SpO2 (P = .06) at high altitude.

The recorded depths and rates of the compressions are shown in

Fig. 1 and Table 3. At sea level, the mean depth of compression was above 5 cm after performing 120 seconds of CCC. At high altitude, the mean depth of chest compression was significantly lower at 30 seconds after

Table 1

Baseline characteristics of study participants (N = 38)

Age (y), mean +- SD 28.1 +- 7.1

Sex	25 male, 13 female
Weight (kg), mean +- SD	68.5 +- 12.2
Height (cm), mean +- SD	170.6 +- 7.5
BMI, mean +- SD	23.4 +- 3.2

BMI: body mass index.

Table 2

Effect of chest compression on the participants’ physical condition at each altitude

	LLS	SBP, mm Hg	DBP, mm Hg	HR	RR	SpO2, %	Borg score
Sea level Pre-CC	0.03 +- 0.17	121.36 +- 10.15	72.72 +- 10.09	80.82 +- 10.42	17.12 +- 1.39	98.55 +- 1.00	6.73 +- 1.59
	(0-1)	(95-137)	(44-91)	(60-101)	(16-20)	(97-100)	(6-11)
Sea level post-CC		128.15 +- 11.87a	79.64 +- 10.67a	103.36 +- 17.28a	21.27 +- 3.91a	97.52 +- 1.39a	13.76 +- 1.84a
		(107-142)	(45-102)	(77-140)	(18-35)	(94-100)	(11-19)
High altitude pre-CC	0.85 +- 1.64a	119.73 +- 12.17	75.15 +- 9.91	93.79 +- 11.17a	19.52 +- 1.29a	88.45 +- 3.44a	9.61 +- 2.03a
	(0-8)	(96-144)	(51-99)	(75-118)	(18-24)	(84-98)	(6-15)
High altitude post-CC		131.55 +- 14.55c	82.82 +- 10.94c	114.55 +- 15.04b,c	21.58 +- 2.18c	89.82 +- 3.52b	14.39 +- 2.19c
		(98-159)	(64-120)	(93-147)	(18-28)	(80-96)	(9-18)

HR: beats per minute; RR: breaths per minute; CC: chest compression.

^a Significantly different from the sea level pre-CC (P b .05).

^b Significantly different from the sea level post-CC (P b .05).

^c Significantly different from the high altitude pre-CC (P b .05).

the initiation of compression compared with the mean depth at sea level (P = .02) and resulted in a decrease in chest compression depth at high altitude to less than 5 cm at 120 seconds (P = .005). A significant time- dependent deterioration in chest compression depth was observed by comparing the depth at 30 seconds of CCC-CPR to that at more than 120 seconds at both sea level (P = .03) and high altitude (P = .005) (Fig. 1, Table 3). The average rate of chest compressions was not significantly different between sea level and high altitude during the 5 minutes of CCC-CPR. Although the participants could maintain a relatively consistent average chest compression rate throughout the 5-minute CCC-CPR period at high altitude, the difference in the rate at 30 seconds compared with that at sea level approached significance (P b .001).

As shown in Fig. 2 and Table 4, there was a statistically significant difference in the number of effective chest compressions between sea level and high altitude at 30 seconds (P = .005). The number of

effective chest compressions significantly decreased from 30 to 90 seconds at sea level (P = .02) and from 30 to 60 seconds at high altitude (P = .03).

Discussion

Our study showed a difference in the quality of chest compressions performed at sea level and high altitude. The results demonstrated that, at high altitude, the depth of chest compressions declined rapidly, reaching statistical significance at 60 seconds after the initiation of CCC-CPR. At high altitude, the average depth of chest compressions decreased to less than 5 cm and approached statistical significance after CCC-CPR for 2 minutes. Furthermore, prior to the observed decline in depth, after performing CCC-CPR for 1 minute, the participants performed less effective chest compressions. At high

Fig. 1. Recorded depths and rates of the compressions.

Table 3

Comparison of the time-dependent deterioration of chest compression at sea level and high altitude

		Sea level			High altitude
	Segment (s)	Depth (cm), mean +- SD	P value		Depth (cm), mean +- SD	P value
	0-30	5.50 +- 0.68	–		5.17 +- 0.88	–
	31-60	5.57 +- 0.84	.35		5.08 +- 0.94	.13
	61-90	5.46 +- 0.90	.68		5.08 +- 1.13	.41
	91-120	5.37 +- 0.93	.20		5.02 +- 1.19	.22
	121-150	5.26 +- 0.95	.03		4.87 +- 1.05	.005
	151-180	5.22 +- 0.97	.02		4.87 +- 1.08	.01
	181-210	5.14 +- 0.96	.003		4.87 +- 1.11	.02
	211-240	5.06 +- 1.07	.001		4.86 +- 1.09	.01
	241-270	5.06 +- 1.06	.002		4.83 +- 1.08	.01
	271-300	5.14 +- 1.22	.03		4.83 +- 1.15	.01
	Segment (s)	Rate (/min), mean +- SD	P value		Rate (/min), mean +- SD	P value
	0-30	116.08 +- 13.81	–		111.89 +- 9.21	–
	31-60	113.68 +- 14.30	b.001		111.37 +- 10.26	.36
	61-90	112.44 +- 14.49	b.001		110.36 +- 10.83	.04
	91-120	111.93 +- 14.36	b.001		110.85 +- 12.44	.429
	121-150	111.92 +- 15.75	.001		109.53 +- 11.42	.03
	151-180	111.59 +- 15.46	.001		110.77 +- 12.39	.38
	181-210	111.93 +- 16.84	.004		111.16 +- 12.42	.57
	211-240	110.84 +- 17.28	.002		111.35 +- 12.28	.68
	241-270	110.47 +- 17.25	.002		111.46 +- 12.92	.77
	271-300	110.51 +- 17.39	.002		112.79 +- 14.23	.62

altitude, the rescuers developed desaturation and tachycardia after performing CCC-CPR; and fatigue was more easily observed.

The 2010 AHA guidelines for CPR recommend that the chest compression depth should be at least 51 mm and rescuers should perform chest compressions and switch roles every 2 minutes [17]. Adequate chest compression depth is one of the critical character- istics of high-quality CPR, and it is clear that high-quality CPR is the primary factor in the survival of cardiac arrest patients. Although the benefit of high-quality CPR is well known, CPR quality varies widely between systems and locations [18]. In line with the 2010 AHA guidelines for CPR, many studies have suggested that deeper chest compressions are associated with improved survival and functional outcome following out-of-hospital cardiac arrest [19,20]. The results of our study support the recommendation to “switch about every 1 minute to prevent a decrease in Compression quality” made by Chalkias et al [1] in addition to the use of mechanical CPR devices and oxygen supplement to sustain the quality of CPR at high altitude. Although these recommendations are based on physiological changes, an ideal CPR strategy cannot be established because of a lack of data regarding quality of CPR Our study demonstrated that the overall quality of the rescuers’ CPR performance decreased over time.

Although the average depth of compression began to decline significantly at 30 seconds after beginning CCC-CPR at high altitude compared with that measured at sea level, the average compression depth did not drop below 5 cm until 2 minutes after initiating CCC- CPR. Prior to the decline in depth, the participants performed a lower number of effective chest compressions at high altitude after performing 1 minute of CCC-CPR. At high altitude, the number of adequate chest compressions was lower than that at sea level throughout the entire 5-minute CCC-CPR period. Although mechan- ical CPR devices can be used to provide high-quality CPR, they are usually not available at high altitude. Capnography is generally recommended to confirm the quality of CPR, but the malfunction of capnography equipment is common at high altitude [21]. Significant hyperventilation and low PaCO2 levels also make colorimetric PCO2 detectors unreliable [22]. In conclusion, we recommend that a modified CPR strategy should be determined for the high-altitude setting.

Vigorous exercise clearly increases the risk of AMS, and people are advised to avoid Strenuous exercise when first arriving at a high-altitude location. With increasing altitude and decreasing barometric pressure, arterial blood oxygen saturation decreases.

Fig. 2. Number of effective chest compressions between sea level and high altitude.

Table 4

Comparison of the number of effective chest compressions at sea level and high altitude

	Sea level			High altitude
Segment (s)	Number	P value		Number	P value
0-30	44.57	–		30.93	–
31-60	42.90	.82		28.18	.24
61-90	39.09	.14		24.09	.03
91-120	36.42	.02		22.96	.007
121-150	33.48	.005		21.48	.006
151-180	32.72	.002		21.30	.006
181-210	29.57	.001		22.09	.005
211-240	27.00	b.001		22.18	.01
241-270	24.51	b.001		22.06	.005
271-300	26.66	.001		22.51	.01

physical exercise, including CPR, at high altitude further decreases arterial blood oxygen saturation [3,4]. Acute mountain sickness scores and the perception of fatigue have been shown to be significantly higher in people performing hypoxic exercise than in those performing normoxic exercise [3]. Hypoxia at high altitude may predispose people to sympathetic stimulation, ventricular dysfunction, and acute coronary syndrome. These physiological changes can induce arrhythmia and cardiac ischemia [23-26]. We intended to test the quality of chest compressions 6 hours after ascent to high altitude because the symptoms and signs of high- altitude illness are easier to perceive at that time. In our study, CPR at high altitude had no effect on SpO2; but HR, SBP, and subjective Borg score values were significantly different from those at sea level. The SpO2values before CPR were significantly lower at higher altitude than at sea level, compatible with the reduce quality of CPR. Therefore, using supplemental oxygen may be a reasonable strategy for preventing rescuers’ fatigue [1]. However, the role of oxygen in protecting rescuers requires further research. Consistent with previous research, our study further demonstrated a signif- icant decline in CPR performance accompanying physiological distress when performing CPR for 5 minutes at high altitude [4]. The safety of rescuers should be considered when they are experiencing subjective fatigue and an objective decline in performance. Our study demonstrated that performing CCC at high altitude is a significant physical challenge to rescuers and might endanger the rescuers in the context of prolonged resusci- tation. The recruitment of rescue personnel suitable for high- altitude operations, the arrangement of field duty shifts, and the establishment of a retrieval plan for rescuers at high altitude should be incorporated into the working manual of rescue planning to achieve the goals of successful rescues and rescuer safety.

An audiovisual Feedback device is able to improve chest compression performance and also effectively evaluate a rescuer’s fatigability [6,27]. As previously mentioned, our results have shown that an objective real-time monitoring device can more effectively detect a decline in CPR quality prior to a change in physiological parameters or the subjective fatigue of rescuers and thus help achieve constant, high-quality CPR at high altitude. This study had several limitations. First, this is a manikin study.

A manikin is an imperfect representation of the human body. Rescuers may exhibit different attitudes toward a simulated versus an actual cardiac arrest situation. Cardiopulmonary resuscitation on a manikin model does not perfectly resemble clinical CPR and does not take into account certain issues, such as chest-wall molding and physiological differences among human bodies [15]. The second limitation of this study was that trained CPR providers could reasonably adhere to the basic life support standard more effectively than lay rescuers. In our study, the participants performed CPR with an average depth of more than 5 cm within the first 2 minutes; but it is doubtful that lay rescuers would be able to maintain a depth of chest compression of more than 5 cm for as long as health care providers do.

Conclusion

This is the first study to assess the quality of CPR performed by health care providers at high altitude using a real-time monitoring device. The quality of chest compressions rapidly declined at high altitude. In addition, the average number of effective chest compres- sions decreased after CCC-CPR was performed for 1 minute; and the average depth of chest compressions decreased to less than 5 cm after CCC-CPR was performed for 2 minutes. More research is needed to evaluate the appropriate guidelines for CPR and the best time interval for switching roles at high altitude.

Acknowledgments

We gratefully acknowledge Kaz Hanamura and all members of KISSEI COMTEC CO, LTD, for their instruction in the operation of the Chest Compression Coach System. We also thank all of the ED staff at Tri-Service General Hospital for volunteering to participate in the study.

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