Complications and critical incidents arising during anaesthesia due to patient, surgical or anaesthetic factors, may cause harm themselves or progress to more severe events, including cardiac arrest or death. As part of the 7th National Audit Project of the Royal College of Anaesthetists, we studied a prospective national cohort of unselected patients. Anaesthetists recorded anonymous details of all cases undertaken over 4 days at their site through an online survey. Of 416 hospital sites invited to participate, 352 (85%) completed the survey. Among 24,172 cases, 1922 discrete potentially serious complications were reported during 1337 (6%) cases. Obstetric cases had a high reported major haemorrhage rate and were excluded from further analysis. Of 20,996 non-obstetric cases, 1705 complications were reported during 1150 (5%) cases. Circulatory events accounted for most complications (616, 36%), followed by airway (418, 25%), metabolic (264, 15%), breathing (259, 15%), and neurological (41, 2%) events. A single complication was reported in 851 (4%) cases, two complications in 166 (1%) cases and three or more complications in 133 (1%) cases. In non-obstetric elective surgery, all complications were ‘uncommon’ (10–100 per 10,000 cases). Emergency (urgent and immediate priority) surgery accounted for 3454 (16%) of non-obstetric cases but 714 (42%) of complications with severe hypotension, major haemorrhage, severe arrhythmias, septic shock, significant acidosis and electrolyte disturbances all being ‘common’ (100–1000 per 10,000 cases). Based on univariate analysis, complications were associated with: younger age; higher ASA physical status; male sex; increased frailty; urgency and extent of surgery; day of the week; and time of day. These data represent the rates of potentially serious complications during routine anaesthesia care and may be valuable for risk assessment and patient consent.

Introduction

While complications following anaesthesia and surgery are well described, events that occur during anaesthesia are less well documented [1]. Many may be managed effectively without serious or long-term consequences, but some, including serious airway, cardiovascular and drug-related complications, have the potential to cause harm or progress to more serious events, including cardiac arrest or death [2-4]. Some major intra-operative complications have been the subject of previous Royal College of Anaesthetists' (RCoA) National Audit Projects (NAPs), including: cardiac arrest due to central neuraxial block (NAP3) [5]; major complications of airway management (NAP4) [4]; accidental awareness during general anaesthesia (NAP5) [6]; and life-threatening anaphylaxis (NAP6) [7]. For many of these complications, progression may result in a final common pathway of peri-operative cardiac arrest, perhaps the most feared of all complications of anaesthesia and surgery [8].

The 7th National Audit Project (NAP7) of the RCoA is tasked with investigating peri-operative cardiac arrest [8, 9]. This is rare, with recent estimates from outside the UK varying between 2 and 13 per 10,000 anaesthetics [10, 11], but when it does occur it is likely to be associated with one or more antecedent events or complications [8]. Understanding the frequency of complications is essential both for planning safe care and communicating risk to patients. Such risks are often the subject of pre-operative discussions. In patient information resources, the RCoA presents risks for healthy patients having routine surgery in terms of 10-fold differences in risk [12]. These risk bands are anchored in common sense everyday language to aid communication (Table 1). This scale is used commonly, for example, to communicate risk to patients [12] and describe the frequency of adverse effects of drugs [13]; we have used the same terminology to describe the risks of complications in NAP7. Here we report the rates of potentially serious events observed in routine anaesthetic practice through a UK-wide survey.

Table 1. Descriptors of complication frequency.

	Definition	Per 10,000	Range (per 10,000)
Very common	1 in 10	1000 per 10,000	> 1000
Common	1 in 100	100 per 10,000	100–1000
Uncommon	1 in 1000	10 per 10,000	10–100
Rare	1 in 10,000	1 per 10,000	1–10
Very rare	1 in 100,000	0.1 per 10,000	0.1–1
Extremely rare	1 in 1,000,000	0.01 per 10,000	0.01–0.1

Methods

Detailed general methods, regulatory approvals and NAP7 activity survey questionnaire details have been described previously [9, 14]. In brief, all UK NHS hospitals delivering anaesthetic care were invited to participate. Sites were assigned randomly a continuous 4-day data collection period, with an equal chance of starting on any day of the week, between 8 and 24 November 2021. All cases requiring general anaesthesia, regional anaesthesia/analgesia, sedation, local anaesthesia or monitored anaesthesia care were captured. Sedation or anaesthesia solely for critical care or procedures on critical care, newborn resuscitation and patient transfers were not studied. Local co-ordinators, who managed the project in each UK NHS hospital, were provided with a link to the survey via SurveyMonkey^® (Surveymonkey Inc., San Mateo, CA, USA) for distribution at their site and a quick reference (QR) code for direct access. Respondents were advised to complete the survey at the end of each case.

Patient characteristics, anaesthetic techniques, surgical details and intra-operative complications were recorded for every case included in the NAP7 activity survey (online Supporting Information Appendix S2) [9]. The reportable complications were decided by consensus of the NAP7 panel as events that were likely, or had the potential, to be associated with significant patient harm. Complications were categorised broadly into: airway; breathing; circulation; neurological; metabolic; and other. Reporting anaesthetists could record zero, one or more than one complication for each case.

Data were exported to Microsoft Excel (Microsoft Inc., Redmond, WA, USA) for analysis. The rates of complications were calculated as the frequency of the event divided by the number of responses in the survey and presented per 10,000 cases. The appropriate denominator was calculated where rates were calculated for sub-populations (e.g. all cases performed with general anaesthesia). Confidence intervals were calculated using Wilson's method [15]. The frequency of events was described using the following descriptors (per 10,000 cases): very common > 1000; common 100–1000; uncommon 10–100; rare 1–10; very rare 0.1–1; and extremely rare < 0.1 (Table 1). To evaluate the impact of selected variables on the chance of having any complication reported, the Chi-squared value was calculated and statistical significance was accepted when p < 0.05 (GraphPad Prism version 5, www.graphpad.com).

Results

Of 416 NHS sites across 182 NHS Trusts or Boards in the UK invited to the study, 352 (85%) participated. The final dataset included 24,172 individual case records from these sites; this population has been described in part previously [14]. Within these, 1922 discrete complications were reported during 1337 (6%) cases.

The obstetric patient population was noted to have a different complication profile to the non-obstetric population (e.g. high reported rates of major haemorrhage) and has therefore been excluded from the main analysis and will be considered separately. This exclusion left 1705 complications reported during 1150 (5%) of the remaining non-obstetric 20,996 cases. Of these, a single complication was recorded in 851 cases (4%, 1 in 26), two complications in 166 cases (1%, 1 in 127), and three or more complications in 133 cases (1%, 1 in 158) (Fig. 1).

Details are in the caption following the image — **Figure 1**
Open in figure viewer PowerPoint

Distribution of the number of serious complications reported during non-obstetric cases in the NAP7 activity survey (n = 1705 complications during 20,996 cases).

Circulatory events accounted for most complications, followed by airway, metabolic, breathing and neurological events (Fig. 2, online Supporting Information Appendix S3). Across all urgencies of surgery, only severe hypotension was common (117 per 10,000 cases). Of the other complications, 17 were categorised as uncommon, 17 as rare, two as very rare and six as extremely rare (Table 2).

Table 2. Rates of complications in all non-obstetric patients in the NAP7 Activity Survey across all levels of urgency. Data are the raw number and rate per 10,000 cases (95%CI) of complications in all cases, general anaesthesia (GA), sedation and awake cases. Complications are ranked within ‘airway’, ‘breathing’ etc., by absolute number of cases. Colour coding shows frequency as per Table 1 (common

, > 100 per 10,000; uncommon

, 10–100 per 10,000; rare

, 1–10 per 10,000; very rare

, 0.1–1 per 10,000; extremely rare

, < 0.1 per 10,000). There were 708 cases where the intended conscious level was not recorded.

		Events	Rate	Events	Rate	Events	Rate	Events	Rate
		All cases (n = 20,996)		GA (n = 16,604)		Sedation (n = 2255)		Awake (n = 1429)
Airway	Laryngospasm	157	74.8 (64.0–87.4)	154	92.7 (79.3–108.5)	3	13.3 (4.5–39.0)	0	0.0 (0.0–26.8)
	Failed mask ventilation, supraglottic airway placement or intubation	125	59.5 (50.0–70.9)	117	70.5 (58.8–84.4)	8	35.5 (18.0–69.9)	0	0.0 (0.0–26.8)
	Other	93	44.3 (36.2–54.2)	85	51.2 (41.4–63.3)	6	26.6 (12.2–57.9)	2	14.0 (3.8–50.9)
	Aspiration or regurgitation	27	12.9 (8.8–18.7)	25	15.1 (10.2–22.2)	2	8.9 (2.4–32.3)	0	0.0 (0.0–26.8)
	Airway haemorrhage	11	5.2 (2.9–9.4)	11	6.6 (3.7–11.9)	0	0.0 (0.0–17.0)	0	0.0 (0.0–26.8)
	CICO or eFONA situation	3	1.4 (0.5–4.2)	3	1.8 (0.6–5.3)	0	0.0 (0.0–17.0)	0	0.0 (0.0–26.8)
	Unrecognised oesophageal intubation	2	1.0 (0.3–3.5)	2	1.2 (0.3–4.4)	0	0.0 (0.0–17.0)	0	0.0 (0.0–26.8)
	Wrong gas supplied/unintentional connection to air	0	0.0 (0.0–1.8)	0	0.0 (0.0–2.3)	0	0.0 (0.0–17.0)	0	0.0 (0.0–26.8)
Breathing	Severe ventilation difficulties (e.g. bronchospasm/high airway pressure)	97	46.2 (37.9–56.3)	94	56.6 (46.3–69.2)	3	13.3 (4.5–39.0)	0	0.0 (0.0–26.8)
	Severe hypoxaemia	62	29.5 (23.0–37.8)	54	32.5 (24.9–42.4)	5	22.2 (9.5–51.8)	3	21.0 (7.1–61.5)
	Hypercapnia or hypocapnia	61	29.1 (22.6–37.3)	56	33.7 (26.0–43.8)	3	13.3 (4.5–39.0)	2	14.0 (3.8–50.9)
	Ventilator disconnection	19	9.0 (5.8–14.1)	18	10.8 (6.9–17.1)	1	4.4 (0.8–25.1)	0	0.0 (0.0–26.8)
	Endobronchial intubation	16	7.6 (4.7–12.4)	15	9.0 (5.5–14.9)	0	0.0 (0.0–17.0)	1	7.0 (1.2–39.5)
	Pneumothorax (simple or tension)	4	1.9 (0.7–4.9)	2	1.2 (0.3–4.4)	2	8.9 (2.4–32.3)	0	0.0 (0.0–26.8)
Circulatory	Severe hypotension (central vasopressors considered/started)	245	116.7 (103.0–132.1)	228	137.3 (120.7–156.2)	7	31.0 (15.0–63.9)	10	70.0 (38.1–128.3)
	Severe brady- or tachyarrhythmia causing compromise	118	56.2 (47.0–67.3)	99	59.6 (49.0–72.5)	10	44.3 (24.1–81.4)	9	63.0 (33.2–119.3)
	Major haemorrhage	110	52.4 (43.5–63.1)	102	61.4 (50.6–74.5)	7	31.0 (15.0–63.9)	1	7.0 (1.2–39.5)
	Septic shock	41	19.5 (14.4–26.5)	40	24.1 (17.7–32.8)	0	0.0 (0.0–17.0)	1	7.0 (1.2–39.5)
	Cardiac arrest	30	14.3 (10.0–20.4)	20	12.0 (7.8–18.6)	6	26.6 (12.2–57.9)	4	28.0 (10.9–71.8)
	New AF	27	12.9 (8.8–18.7)	22	13.2 (8.8–20.1)	2	8.9 (2.4–32.3)	3	21.0 (7.1–61.5)
	Cardiac ischaemia	16	7.6 (4.7–12.4)	13	7.8 (4.6–13.4)	3	13.3 (4.5–39.0)	0	0.0 (0.0–26.8)
	Emergency DC cardioversion	10	4.8 (2.6–8.8)	8	4.8 (2.4–9.5)	1	4.4 (0.8–25.1)	1	7.0 (1.2–39.5)
	Anaphylaxis	9	4.3 (2.3–8.1)	8	4.8 (2.4–9.5)	0	0.0 (0.0–17.0)	1	7.0 (1.2–39.5)
	Cardiac tamponade	5	2.4 (1.0–5.6)	3	1.8 (0.6–5.3)	1	4.4 (0.8–25.1)	1	7.0 (1.2–39.5)
	Embolic event (PE/fat/bone cement/amniotic fluid/air/CO₂)	4	1.9 (0.7–4.9)	2	1.2 (0.3–4.4)	2	8.9 (2.4–32.3)	0	0.0 (0.0–26.8)
	Suspected Addisonian crisis	1	0.5 (0.1–2.7)	1	0.6 (0.1–3.4)	0	0.0 (0.0–17.0)	0	0.0 (0.0–26.8)
	Incompatible blood transfusion	0	0.0 (0.0–1.8)	0	0.0 (0.0–2.3)	0	0.0 (0.0–17.0)	0	0.0 (0.0–26.8)
Neurological	Stroke, intracranial haemorrhage and/or subarachnoid haemorrhage	16	7.6 (4.7–12.4)	11	6.6 (3.7–11.9)	2	8.9 (2.4–32.3)	3	21.0 (7.1–61.5)
	Intracranial hypertension (e.g. new fixed/dilated pupil or coning)	9	4.3 (2.3–8.1)	8	4.8 (2.4–9.5)	1	4.4 (0.8–25.1)	0	0.0 (0.0–26.8)
	Seizure	7	3.3 (1.6–6.9)	7	4.2 (2.0–8.7)	0	0.0 (0.0–17.0)	0	0.0 (0.0–26.8)
	Vagal outflow (e.g. pneumoperitoneum, oculo-cardiac reflex)	5	2.4 (1.0–5.6)	4	2.4 (0.9–6.2)	0	0.0 (0.0–17.0)	1	7.0 (1.2–39.5)
	Death	4	1.9 (0.7–4.9)	2	1.2 (0.3–4.4)	2	8.9 (2.4–32.3)	0	0.0 (0.0–26.8)
	High neuraxial block	0	0.0 (0.0–1.8)	0	0.0 (0.0–2.3)	0	0.0 (0.0–17.0)	0	0.0 (0.0–26.8)
	Neurogenic shock	0	0.0 (0.0–1.8)	0	0.0 (0.0–2.3)	0	0.0 (0.0–17.0)	0	0.0 (0.0–26.8)
Metabolic	New significant acidosis/acidaemia	126	60.0 (50.4–71.4)	119	71.7 (59.9–85.7)	3	13.3 (4.5–39.0)	4	28.0 (10.9–71.8)
	Significant electrolyte disturbance	97	46.2 (37.9–56.3)	92	55.4 (45.2–67.9)	2	8.9 (2.4–32.3)	3	21.0 (7.1–61.5)
	Hyperthermia or hypothermia	41	19.5 (14.4–26.5)	39	23.5 (17.2–32.1)	2	8.9 (2.4–32.3)	0	0.0 (0.0–26.8)
Other	Emergency call for anaesthesia assistance	43	20.5 (15.2–27.6)	34	20.5 (14.7–28.6)	5	22.2 (9.5–51.8)	4	28.0 (10.9–71.8)
	Intraoperative conversion of anaesthesia (e.g. LA/RA/sedation to GA)	33	15.7 (11.2–22.1)	21	12.6 (8.3–19.3)	7	31.0 (15.0–63.9)	5	35.0 (15.0–81.6)
	Equipment failure	22	10.5 (6.9–15.9)	21	12.6 (8.3–19.3)	1	4.4 (0.8–25.1)	0	0.0 (0.0–26.8)
	Drug error	9	4.3 (2.3–8.1)	7	4.2 (2.0–8.7)	2	8.9 (2.4–32.3)	0	0.0 (0.0–26.8)
	Local anaesthetic toxicity	0	0.0 (0.0–1.8)	0	0.0 (0.0–2.3)	0	0.0 (0.0–17.0)	0	0.0 (0.0–26.8)
	Malignant hyperthermia	0	0.0 (0.0–1.8)	0	0.0 (0.0–2.3)	0	0.0 (0.0–17.0)	0	0.0 (0.0–26.8)
	Total complications	1705		1547		99		59

CICO, cannot intubate cannot oxygenate; eFONA, emergency front-of-neck airway; AF, atrial fibrillation; PE, pulmonary embolus; LA, local anaesthesia; RA, regional anaesthesia.

In patients undergoing elective surgery, the rates of many complications were lower than in the overall population (Table 3). The 14,136 elective cases (67% of non-obstetric activity) accounted for 705 (41%) of all complications, whereas the emergency population (urgent and immediate surgery) accounted for 3454 cases (16% of non-obstetric activity) and 714 (42%) complications respectively (Table 4). Severe hypotension, major haemorrhage, severe arrhythmias causing compromise, septic shock, new significant acidaemia and electrolyte disturbances were all common in the emergency patient population.

Table 3. Rates of complications in elective non-obstetric patients in the NAP7 activity survey (elective day surgery and planned admission). Data are the raw number and rate per 10,000 cases (95%CI) of complications in all cases, general anaesthesia (GA), sedation and awake cases. Complications are ranked within ‘airway’, ‘breathing’ etc., by absolute number of cases. Colour coding shows frequency as per Table 1 (common

, > 100 per 10,000; uncommon

, 10–100 per 10,000; rare

, 1–10 per 10,000; very rare

, 0.1–1 per 10,000; extremely rare

, < 0.1 per 10,000).

		Events	Rate	Events	Rate	Events	Rate	Events	Rate
		All cases (n = 14,136)		GA (n = 11,194)		Sedation (n = 1679)		Awake (n = 1051)
Airway	Laryngospasm	107	75.7 (62.7–91.4)	104	92.9 (76.7–112.4)	3	17.9 (6.1–52.4)	0	0.0 (0.0–36.4)
	Failed mask ventilation, supraglottic airway placement or intubation	70	49.5 (39.2–62.5)	65	58.1 (45.6–73.9)	5	29.8 (12.7–69.5)	0	0.0 (0.0–36.4)
	Other	53	37.5 (28.7–49.0)	48	42.9 (32.4–56.8)	4	23.8 (9.3–61.1)	1	9.5 (1.7–53.7)
	Aspiration or regurgitation	15	10.6 (6.4–17.5)	13	11.6 (6.8–19.9)	2	11.9 (3.3–43.3)	0	0.0 (0.0–36.4)
	Airway haemorrhage	4	2.8 (1.1–7.3)	4	3.6 (1.4–9.2)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	CICO or eFONA situation	1	0.7 (0.1–4.0)	1	0.9 (0.2–5.1)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	Unrecognised oesophageal intubation	1	0.7 (0.1–4.0)	1	0.9 (0.2–5.1)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	Wrong gas supplied/unintentional connection to air	0	0.0 (0.0–2.7)	0	0.0 (0.0–3.4)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
Breathing	Severe ventilation difficulties (e.g. bronchospasm/high airway pressure)	48	34.0 (25.6–45.0)	46	41.1 (30.8–54.8)	2	11.9 (3.3–43.3)	0	0.0 (0.0–36.4)
	Severe hypoxaemia	32	22.6 (16.0–31.9)	30	26.8 (18.8–38.2)	2	11.9 (3.3–43.3)	0	0.0 (0.0–36.4)
	Hypercapnia or hypocapnia	22	15.6 (10.3–23.6)	20	17.9 (11.6–27.6)	2	11.9 (3.3–43.3)	0	0.0 (0.0–36.4)
	Endobronchial intubation	11	7.8 (4.3–13.9)	10	8.9 (4.9–16.4)	0	0.0 (0.0–22.8)	1	9.5 (1.7–53.7)
	Ventilator disconnection	8	5.7 (2.9–11.2)	8	7.1 (3.6–14.1)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	Pneumothorax (simple or tension)	2	1.4 (0.4–5.2)	1	0.9 (0.2–5.1)	1	6.0 (1.1–33.7)	0	0.0 (0.0–36.4)
Circulatory	Severe hypotension (central vasopressors considered/started)	74	52.3 (41.7–65.7)	72	64.3 (51.1–80.9)	1	6.0 (1.1–33.7)	1	9.5 (1.7–53.7)
	Severe brady- or tachyarrhythmia causing compromise	63	44.6 (34.9–57.0)	54	48.2 (37.0–62.9)	6	35.7 (16.4–77.7)	3	28.5 (9.7–83.6)
	Major haemorrhage	31	21.9 (15.5–31.1)	29	25.9 (18.0–37.2)	2	11.9 (3.3–43.3)	0	0.0 (0.0–36.4)
	Cardiac arrest	12	8.5 (4.9–14.8)	10	8.9 (4.9–16.4)	1	6.0 (1.1–33.7)	1	9.5 (1.7–53.7)
	New AF	12	8.5 (4.9–14.8)	10	8.9 (4.9–16.4)	2	11.9 (3.3–43.3)	0	0.0 (0.0–36.4)
	Emergency DC cardioversion	6	4.2 (1.9–9.3)	4	3.6 (1.4–9.2)	1	6.0 (1.1–33.7)	1	9.5 (1.7–53.7)
	Anaphylaxis	6	4.2 (1.9–9.3)	6	5.4 (2.5–11.7)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	Cardiac ischaemia	5	3.5 (1.5–8.3)	4	3.6 (1.4–9.2)	1	6.0 (1.1–33.7)	0	0.0 (0.0–36.4)
	Septic shock	2	1.4 (0.4–5.2)	2	1.8 (0.5–6.5)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	Embolic event (PE/fat/bone cement/amniotic fluid/air/CO₂)	1	0.7 (0.1–4.0)	1	0.9 (0.2–5.1)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	Cardiac tamponade	0	0.0 (0.0–2.7)	0	0.0 (0.0–3.4)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	Suspected Addisonian crisis	0	0.0 (0.0–2.7)	0	0.0 (0.0–3.4)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	Incompatible blood transfusion	0	0.0 (0.0–2.7)	0	0.0 (0.0–3.4)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
Neurological	Seizure	4	2.8 (1.1–7.3)	4	3.6 (1.4–9.2)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	Vagal outflow (e.g. pneumoperitoneum, oculo-cardiac reflex)	2	1.4 (0.4–5.2)	1	0.9 (0.2–5.1)	0	0.0 (0.0–22.8)	1	9.5 (1.7–53.7)
	Intracranial hypertension (e.g. new fixed/dilated pupil or coning)	2	1.4 (0.4–5.2)	1	0.9 (0.2–5.1)	1	6.0 (1.1–33.7)	0	0.0 (0.0–36.4)
	Stroke, intracranial haemorrhage and/or subarachnoid haemorrhage	1	0.7 (0.1–4.0)	0	0.0 (0.0–3.4)	1	6.0 (1.1–33.7)	0	0.0 (0.0–36.4)
	High neuraxial block	0	0.0 (0.0–2.7)	0	0.0 (0.0–3.4)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	Neurogenic shock	0	0.0 (0.0–2.7)	0	0.0 (0.0–3.4)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	Death	0	0.0 (0.0–2.7)	0	0.0 (0.0–3.4)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
Metabolic	New significant acidosis/acidaemia	31	21.9 (15.5–31.1)	30	26.8 (18.8–38.2)	0	0.0 (0.0–22.8)	1	9.5 (1.7–53.7)
	Hyperthermia or hypothermia	15	10.6 (6.4–17.5)	14	12.5 (7.5–21.0)	1	6.0 (1.1–33.7)	0	0.0 (0.0–36.4)
	Significant electrolyte disturbance	10	7.1 (3.8–13.0)	9	8.0 (4.2–15.3)	1	6.0 (1.1–33.7)	0	0.0 (0.0–36.4)
Other	Intraoperative conversion of anaesthesia (e.g. LA/RA/sedation to GA)	23	16.3 (10.8–24.4)	14	12.5 (7.5–21.0)	5	29.8 (12.7–69.5)	4	38.1 (14.8–97.4)
	Emergency call for anaesthesia assistance	18	12.7 (8.1–20.1)	14	12.5 (7.5–21.0)	3	17.9 (6.1–52.4)	1	9.5 (1.7–53.7)
	Equipment failure	10	7.1 (3.8–13.0)	9	8.0 (4.2–15.3)	1	6.0 (1.1–33.7)	0	0.0 (0.0–36.4)
	Drug error	3	2.1 (0.7–6.2)	3	2.7 (0.9–7.9)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	Local anaesthetic toxicity	0	0.0 (0.0–2.7)	0	0.0 (0.0–3.4)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	Malignant hyperthermia	0	0.0 (0.0–2.7)	0	0.0 (0.0–3.4)	0	0.0 (0.0–22.8)	0	0.0 (0.0–36.4)
	Total complications	705		642		48		15

CICO, cannot intubate cannot oxygenate; eFONA, emergency front-of-neck airway; AF, atrial fibrillation; PE, pulmonary embolus; LA, local anaesthesia; RA, regional anaesthesia.

Table 4. Rates of complications in patients undergoing emergency (urgent and immediate) non-obstetric surgery in the NAP7 activity survey. Data are the raw number and rate per 10,000 cases (95%CI) of complications in all cases, general anaesthesia (GA), sedation and awake cases. Complications are ranked within ‘airway’, ‘breathing’ etc., by absolute number of cases. Colour coding shows frequency as per Table 1 (common

, > 100 per 10,000; uncommon

, 10–100 per 10,000; rare

, 1–10 per 10,000; very rare

, 0.1–1 per 10,000; extremely rare

, < 0.1 per 10,000).

		Events	Rate	Events	Rate	Events	Rate	Events	Rate
		All cases (n = 3454)		GA (n = 2906)		Sedation (n = 298)		Awake (n = 186)
Airway	Other	23	66.6 (44.4–99.7)	21	72.3 (47.3–110.2)	2	67.1 (18.4–241.4)	0	0.0 (0.0–202.4)
	Failed mask ventilation, supraglottic airway placement or intubation	22	63.7 (42.1–96.3)	19	65.4 (41.9–101.9)	3	100.7 (34.3–291.8)	0	0.0 (0.0–202.4)
	Laryngospasm	20	57.9 (37.5–89.3)	20	68.8 (44.6–106.1)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Airway haemorrhage	6	17.4 (8.0–37.8)	6	20.6 (9.5–45.0)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Aspiration or regurgitation	5	14.5 (6.2–33.8)	5	17.2 (7.4–40.2)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	CICO or eFONA situation	2	5.8 (1.6–21.1)	2	6.9 (1.9–25.1)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Unrecognised oesophageal intubation	1	2.9 (0.5–16.4)	1	3.4 (0.6–19.5)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Wrong gas supplied/unintentional connection to air	0	0.0 (0.0–11.1)	0	0.0 (0.0–13.2)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
Breathing	Severe ventilation difficulties (e.g. bronchospasm/high airway pressure)	30	86.9 (60.9–123.7)	29	99.8 (69.6–143.0)	1	33.6 (5.9–187.6)	0	0.0 (0.0–202.4)
	Severe hypoxaemia	19	55.0 (35.2–85.8)	15	51.6 (31.3–85.0)	2	67.1 (18.4–241.4)	2	107.5 (29.5–383.5)
	Hypercapnia or hypocapnia	17	49.2 (30.8–78.7)	16	55.1 (33.9–89.3)	0	0.0 (0.0–127.3)	1	53.8 (9.5–298.2)
	Ventilator disconnection	5	14.5 (6.2–33.8)	5	17.2 (7.4–40.2)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Endobronchial intubation	3	8.7 (3.0–25.5)	3	10.3 (3.5–30.3)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Pneumothorax (simple or tension)	2	5.8 (1.6–21.1)	1	3.4 (0.6–19.5)	1	33.6 (5.9–187.6)	0	0.0 (0.0–202.4)
Circulatory	Severe hypotension (central vasopressors considered/started)	141	408.2 (347.2–479.5)	128	440.5 (371.7–521.3)	5	167.8 (71.9–386.7)	8	430.1 (219.5–825.6)
	Major haemorrhage	62	179.5 (140.3–229.4)	58	199.6 (154.7–257.1)	3	100.7 (34.3–291.8)	1	53.8 (9.5–298.2)
	Severe brady- or tachyarrhythmia causing compromise	38	110.0 (80.3–150.6)	31	106.7 (75.3–151.0)	4	134.2 (52.3–340.0)	3	161.3 (55.0–463.4)
	Septic shock	38	110.0 (80.3–150.6)	37	127.3 (92.5–175.0)	0	0.0 (0.0–127.3)	1	53.8 (9.5–298.2)
	Cardiac arrest	15	43.4 (26.3–71.5)	9	31.0 (16.3–58.8)	4	134.2 (52.3–340.0)	2	107.5 (29.5–383.5)
	New AF	13	37.6 (22.0–64.3)	11	37.9 (21.1–67.7)	0	0.0 (0.0–127.3)	2	107.5 (29.5–383.5)
	Cardiac ischaemia	9	26.1 (13.7–49.5)	7	24.1 (11.7–49.6)	2	67.1 (18.4–241.4)	0	0.0 (0.0–202.4)
	Cardiac tamponade	5	14.5 (6.2–33.8)	3	10.3 (3.5–30.3)	1	33.6 (5.9–187.6)	1	53.8 (9.5–298.2)
	Emergency DC cardioversion	3	8.7 (3.0–25.5)	3	10.3 (3.5–30.3)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Anaphylaxis	1	2.9 (0.5–16.4)	1	3.4 (0.6–19.5)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Embolic event (PE/fat/bone cement/amniotic fluid/air/CO₂)	1	2.9 (0.5–16.4)	0	0.0 (0.0–13.2)	1	33.6 (5.9–187.6)	0	0.0 (0.0–202.4)
	Suspected Addisonian crisis	0	0.0 (0.0–11.1)	0	0.0 (0.0–13.2)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Incompatible blood transfusion	0	0.0 (0.0–11.1)	0	0.0 (0.0–13.2)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
Neurological	Stroke, intracranial haemorrhage and/or subarachnoid haemorrhage	11	31.8 (17.8–56.9)	8	27.5 (14.0–54.2)	1	33.6 (5.9–187.6)	2	107.5 (29.5–383.5)
	Intracranial hypertension (e.g. new fixed/dilated pupil or coning)	6	17.4 (8.0–37.8)	6	20.6 (9.5–45.0)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Death	4	11.6 (4.5–29.7)	2	6.9 (1.9–25.1)	2	67.1 (18.4–241.4)	0	0.0 (0.0–202.4)
	Seizure	2	5.8 (1.6–21.1)	2	6.9 (1.9–25.1)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Vagal outflow (e.g. pneumoperitoneum, oculo-cardiac reflex)	2	5.8 (1.6–21.1)	2	6.9 (1.9–25.1)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	High neuraxial block	0	0.0 (0.0–11.1)	0	0.0 (0.0–13.2)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Neurogenic shock	0	0.0 (0.0–11.1)	0	0.0 (0.0–13.2)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
Metabolic	New significant acidosis/acidaemia	80	231.6 (186.5–287.3)	75	258.1 (206.4–322.3)	3	100.7 (34.3–291.8)	2	107.5 (29.5–383.5)
Metabolic	Significant electrolyte disturbance	77	222.9 (178.7–277.7)	73	251.2 (200.3–314.7)	1	33.6 (5.9–187.6)	3	161.3 (55.0–463.4)
Other	Hyperthermia or hypothermia	20	57.9 (37.5–89.3)	19	65.4 (41.9–101.9)	1	33.6 (5.9–187.6)	0	0.0 (0.0–202.4)
	Emergency call for anaesthesia assistance	19	55.0 (35.2–85.8)	16	55.1 (33.9–89.3)	2	67.1 (18.4–241.4)	1	53.8 (9.5–298.2)
	Intraoperative conversion of anaesthesia (e.g. LA/RA/sedation to GA)	5	14.5 (6.2–33.8)	2	6.9 (1.9–25.1)	2	67.1 (18.4–241.4)	1	53.8 (9.5–298.2)
	Equipment failure	4	11.6 (4.5–29.7)	4	13.8 (5.4–35.3)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Drug error	3	8.7 (3.0–25.5)	2	6.9 (1.9–25.1)	1	33.6 (5.9–187.6)	0	0.0 (0.0–202.4)
	Local anaesthetic toxicity	0	0.0 (0.0–11.1)	0	0.0 (0.0–13.2)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Malignant hyperthermia	0	0.0 (0.0–11.1)	0	0.0 (0.0–13.2)	0	0.0 (0.0–127.3)	0	0.0 (0.0–202.4)
	Total complications	714		642		42		30

CICO, cannot intubate cannot oxygenate; eFONA, emergency front-of-neck airway; AF, atrial fibrillation; PE, pulmonary embolus; LA, local anaesthesia; RA, regional anaesthesia.

Complications were more likely to occur in cases performed at weekends; at night; during more urgent or longer complex cases; in neonates and infants; in patients with higher ASA physical status; or in patients living with frailty (p < 0.0001 for all, Fig. 3).

In the non-obstetric population, 30 cases included cardiac arrest as a complication (14 per 10,000), of which five would not have reached the threshold for inclusion as a NAP7 case (≥ 5 chest compressions and/or defibrillation). The overall rate for cardiac arrest as per the NAP7 definition in this population was 12 per 10,000 (see online Supporting Information Appendix S4). Of the 30 patients where cardiac arrest was noted as a complication, seven (23%) reported either ‘no return of spontaneous circulation’ or ‘initial return of spontaneous circulation but not surviving to the postoperative area’. For elective patients, the rate of cardiac arrest was 8.4 per 10,000 cases, but this reduced to 7.7 per 10,000 when a case reporting < 5 chest compressions was excluded. There were no deaths reported in 14,136 elective patients in the activity survey.

Discussion

Whilst many studies have evaluated postoperative complications associated with anaesthesia and surgery, there are limited data about complications that occur intra-operatively. We present contemporary data showing that in non-obstetric patients, potentially serious complications occurred in 1 in 18 (6%) cases. Whilst 6% of cases reported a complication, each individual complication was reported with lower frequency.

Circulatory issues were the most common cause of complications, accounting for more than 1 in 3 reported complications. Of these complications, severe hypotension was common (100–1000 per 10,000 cases), whilst arrhythmias causing compromise and major haemorrhage were uncommon (10–100 per 10,000). Airway complications accounted for 24% of all reported complications, with laryngospasm and failure to successfully manage the airway being the most frequent, albeit both uncommon. The most frequent breathing complications were problems with lung ventilation and severe hypoxaemia (both uncommon), as were the metabolic complications of new acidaemia and electrolyte disturbance. Rates of complications were lower in elective cases than in emergency cases (in some cases up to 10-fold). In emergency cases, profound hypotension, bradycardia, major haemorrhage and septic shock were the four most frequent complications and were all common. Complications were notably more frequent during general anaesthesia than in sedated or awake patients. However, it is likely at least some of this is a matter of case mix, and in emergency patients, complications became frequent across these domains. The relationships between these complications and peri-operative cardiac arrest will be explored in the report of the registry phase of NAP7.

According to the current Guidelines for the Provision of Anaesthesia Services (GPAS) [16] “risks associated with anaesthesia should be discussed during consent for anaesthesia”. The Association of Anaesthetists [17] and General Medical Council [18] also emphasise the need to provide precise information to patients about risks before procedures. Such a requirement is enshrined in law as part of the consent process [19]. The RCoA provides patient information leaflets for the most frequent events and risks to aid this consent process, and also publishes a single-page document enumerating the risks of anaesthesia [12]. While many anaesthetics occur without serious incidents, given the high number of cases performed annually in the UK, complications with a low likelihood of occurrence do occur. The current data add to our understanding and will help refine the processes of information provision, shared decision making and consent [20].

A key strength of this study was capturing data from all anaesthetists during all cases in the majority of UK hospitals, giving the data generalisability to the ‘real world’. The survey was performed using an electronic survey link, and anaesthetists completed the survey after the end of a case. To balance the burden of the study on reporting anaesthetists' time and improve the completion rate, we did not provide strict definitions of the criteria for each complication, leaving this to the discretion of the reporting anaesthetist. Whilst some events are easy to recognise (e.g. new atrial fibrillation or ‘emergency call for assistance’), others are more subjective and there is likely to be variation in thresholds for reporting some events. That said, many of the event rates are comparable to contemporary reported literature. For example, in the study by the AeroComp group (which was also conducted in November 2021) the pulmonary aspiration rate was 0.1% in adult patients [21], very similar to the 0.13% rate in our survey. The same study also reports difficult facemask or supraglottic airway device insertion in 4.3% of cases [21]. In our survey, the more extreme endpoint of a failed airway management with facemask, supraglottic airway device or tracheal tube occurred in 0.7% of general anaesthesia cases and, again, this has face validity.

The reported rate of anaphylaxis was 4.3 per 10,000 cases which is higher than the value in NAP6 (approximately 1 per 10,000) [2]. Confirming the diagnosis of anaphylaxis requires further investigation, and this was not possible in the NAP7 activity survey reporting time window, which may have led to an overestimation as suspected, rather than confirmed, cases of anaphylaxis were reported. Further, NAP6 only included life-threatening cases (i.e. associated severe hypotension, bronchospasm or airway compromise) or fatal cases, whereas the NAP7 activity survey likely included non-life-threatening cases. This issue will be explored further in the registry phase of the NAP7 project [9].

Two potential complications are on the current ‘Never Events’ list for England: unintended connection to air/wrong gas supplied; and administration of an incompatible blood transfusion [22]. Reassuringly, there were no cases reported in the NAP7 activity survey. From 1 April 2021 to 31 March 2022, which includes the period when the activity survey was undertaken, there were 13 cases of unintentional connection to air for a patient requiring oxygen and seven ABO-incompatible blood transfusions across all NHS settings [23]. It is not possible to determine if these events occurred in peri-operative settings.

Unrecognised oesophageal intubation is currently suspended from the never-event list [22]. Yet it remains of considerable interest to anaesthetists due to the potentially severe consequences, and international consensus guidelines for its avoidance have been published recently [24]. Two cases of unrecognised oesophageal intubation were reported in the activity survey. Neither case was associated with cardiac arrest or death, and no further details are available but this must have been detected before there was significant patient harm. Our interpretation is that these cases are likely to represent delayed, rather than unrecognised. Instances of unrecognised, recognition of oesophageal intubation oesophageal intubation were identified among NAP7 case reports, and this remains an area of significant concern.

We assessed the frequency of complications by various patient, surgical and anaesthetic factors. Using univariate analysis, age, ASA physical status, sex and frailty score were statistically significant patient factors, whereas BMI and ethnicity were not. Very young age was associated with higher rates of complications, more so than advancing age. Whilst most neonates and infants are healthy, those requiring anaesthesia for surgery in this age range are more likely to have comorbidities, and the distribution of ASA physical status is shifted towards higher scores compared with older children [14].

Many studies have shown the association between ASA physical status and postoperative morbidity and mortality, but the link with intra-operative complications has been comparatively understudied. In this study, increasing ASA physical status grade was associated strongly with the risk of any complication; patients who had ASA physical status 3 and 4 were twice and five times as likely to have an intra-operative complication, respectively. Within the 24-hour peri-operative window, Tiret et al. assessed reported rates of “any fatal or life-threatening accident, or any accident producing severe sequela” [25]. Compared with patients who were ASA physical status 1, patients who were ASA physical status 3 and 4 were 14 and 88 times more likely to have an event, respectively. Over the 35 years since this study was published, whilst the relationship is still evident, these extreme odds for patients who are ASA physical status 3 and 4 appear to have been reduced substantially.

We found that the day of the week and time of day impacted the chance of an intra-operative complication. At their peak effect (i.e. a weekend night-time), these effects were moderate compared with ASA physical status, NCEPOD category and anaesthetic and surgical time. They are likely to be confounded by the relative proportion of emergency and complex cases occurring during these periods compared with daytime on a typical working day and should be viewed with caution. We are planning to perform a multivariate analysis of our dataset to control and adjust for these factors.

It was not the prime purpose of the NAP7 activity survey to determine rates of intra-operative cardiac arrest or death. The sample size (approximately 20,000) is arguably too small to enable that, as small case numbers would lead to wide confidence intervals. Furthermore, small numbers in the denominator and the possibility of misclicks or erroneous reports mean the results would be fragile [14]. The registry phase of NAP7, which involves an in-depth review of all peri-operative cardiac arrests reported to the project over a year, combined with the activity survey data (providing a denominator of around 2.7 million cases [14]), is better calibrated for that purpose.

Within the full activity survey dataset, we observed a high rate of major haemorrhage in awake patients. Of the 106 major haemorrhages reported in patients who were awake, 105 were in obstetric cases. There were also eight cases of combined high neuraxial block and neurogenic shock in obstetrics, with none reported in non-obstetric cases. We, therefore, judged that the obstetric complication profile was not representative of the rest of the anaesthetic activity and chose to describe this separately.

In line with the other reported outcomes from the activity survey [14], these data have limitations, and our findings should be interpreted carefully. We were conscious of the possibility of ‘careless data’ that may have entered the database [14, 26, 27]. As discussed above, a few erroneous case reports could significantly alter the reporting rate for low-prevalence complications. We inspected the individual records to ensure they were internally consistent and plausible: five cases were removed and 12 likely single-click errors were edited [14]. To ensure absolute confidentiality, the study team did not collect data on which hospital or anaesthetist reported each case. We hope this will have enabled anaesthetists to report complications freely, but it also prevented us from querying cases where the reported clinical events were not plausible or where there were missing fields. The ability to report complications with complete confidentiality is a strength of our data and may have led to higher reporting rates.

The data that may not have been captured are also worthy of consideration. This study phase was designed only to collect complications during a case, and events occurring after the patient left recovery were not captured. It is also important to note that, just because a complication occurred, this does not mean care was deficient. The Poisson distribution means that in a given population, event frequency will often differ from its true incidence [25], particularly affecting low-incidence occurrences. Therefore, uncommon events in our sample may have over- or underestimated frequency. For example, in our survey of 24,000 patients, there is an approximately 2.5% chance that an event with an incidence of 1 in 7000 will not occur [28] and that events with a true incidence of 1 in 4000 or 1 in 3000 will occur only once and twice, respectively [29].

In summary, these data from the NAP7 activity survey complement the literature and add contemporary estimates for the rates of potentially serious complications and critical incidents observed during anaesthetic practice. These data confirm that during elective non-obstetric practice, individual complications are uncommon, and this is reassuring for patients, surgeons and anaesthetists. However, the higher rate of complications in non-elective settings and patient risk factors associated with an increased incidence of complications will be of value to clinicians in improving patient care pathways.

Acknowledgements

The project infrastructure is supported financially and with staffing from the Royal College of Anaesthetists. The NAP7 fellows' salaries are generously supported by: South Tees Hospitals NHS Foundation Trust (AK); Royal United Hospitals Bath NHS Foundation Trust (EK); and NIHR Academic Clinical Fellowship (RA). Panel members receive travel expenses and no remuneration. JS and TC's employers receive backfill for their time on the project (4 hours per week). IM and SA are Editors of Anaesthesia. We thank E. Wain, K. Samuel, S. Kendall and C. Bouch for their contribution to this work. We wish to thank all anaesthetists who entered data into this study. No competing interests declared.

Appendix 1 Full author affiliations

A. D. Kane^{1, 2}, T. M. Cook³*, R. A. Armstrong^{1, 4}, E. Kursumovic^{1, 3}, M. T. Davies⁵, S. Agarwal⁶, J. P. Nolan⁷, J. H. Smith⁸, I. K. Moppett^{9, 10}, F. C. Oglesby¹¹, L. Cortes¹², C. Taylor¹², J. Cordingley¹³, J. Dorey¹⁴, S. J. Finney¹³, G. Kunst¹⁵, D. N. Lucas¹⁶, G. Nickols¹⁷, R. Mouton¹⁷, B. Patel¹⁴, V. J. Pappachan¹⁸, F. Plaat¹⁹, B. R. Scholefield²⁰, L. Varney²¹, J. Soar²²

1 Research Fellow, 10 Director, 12 Research Team, Health Services Research Centre, 14 Lay Committee, Royal College of Anaesthetists, Red Lion Square, UK

2 Consultant, Department of Anaesthesia, James Cook University Hospital, South Tees NHS Foundation Trust, Middlesbrough, UK

3 Consultant, Department of Anaesthesia and Intensive Care Medicine, Royal United Hospitals Bath NHS Foundation Trust

4 Academic Clinical Fellow, Department of Anaesthesia, Severn Deanery, Bristol, UK

5 Consultant, Department of Critical Care and Anaesthesia, North West Anglia NHS Trust, UK

6 Consultant, Department of Anaesthesia, Manchester University Hospitals Foundation Trust

7 Professor, Resuscitation Medicine, Warwick Clinical Trials Unit, University of Warwick

8 Consultant, Department of Anaesthesia, Great Ormond Street Hospital

9 Professor of Anaesthesia and Peri-operative Medicine, University of Nottingham, UK

11 Specialty Registrar, University Hospitals Bristol and Weston NHS Foundation Trust, UK

13 Consultant, Department of Critical Care and Anaesthesia, Barts Health NHS Trust, UK

15 Professor, Department of Cardiovascular Anaesthesia, Kings College London, UK

16 Consultant, Department of Anaesthesia, London North West University Healthcare NHS Trust, UK

17 Consultant, Department of Anaesthesia, North Bristol NHS Trust

18 Associate Professor, Southampton Children's Hospital, NIHR Biomedical Research Centre and Consultant, Department of Paediatric Anaesthesia and Intensive Care Medicine, University Hospital Southampton NHS Foundation Trust, Southampton, UK

19 Consultant, Department of Anaesthesia, Imperial College Healthcare NHS Trust

20 NIHR Clinician Scientist, Institute of Inflammation and Ageing, University of Birmingham, UK

21 Anaesthesia Associate, Department of Anaesthesia, University College London Hospitals, London, UK

22 Consultant, Department of Anaesthesia and Intensive Care Medicine, Southmead Hospital, Bristol, UK

Supporting Information

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Volume79, Issue1

January 2024

Pages 43-53

The incidence of potentially serious complications during non-obstetric anaesthetic practice in the United Kingdom: an analysis from the 7th National Audit Project (NAP7) activity survey

Summary

Introduction

Methods

Results

Discussion

Acknowledgements

Appendix 1

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Supporting Information

References

Citing Literature

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The incidence of potentially serious complications during non-obstetric anaesthetic practice in the United Kingdom: an analysis from the 7th National Audit Project (NAP7) activity survey

Summary

Introduction

Methods

Results

Discussion

Acknowledgements

Appendix 1

Full author affiliations

Supporting Information

References

Citing Literature

Figures

References

Related

Information